Okay, I may have missed it through all that reading, but how exactly do you make this intake? I'm talking only about the physical manifold, not the computer adjustments and what not. Is it just replacing the upper intake with the two tubes? Or cutting and modding the middle intake?
I am very much interested in making one of these.
I guess everyone has a way of doing it some cut the middle intake flange off and weld tubes to them. Mine was made by welding a 2-2.5" wide x about 12" long strip on top of each side. Then port match the strip of metal to the intake ports. You can then bend a sheet of metal into a Ushape and match that up to the sides of the strip. Weld on end caps. I had the shop cut off the stock flange off of 2 intakes so i knew that my gasket would seal right and my TB mounting screws were the stock ones. The intake is slightly offset so you should make sure the TBs are even with one another and the linkage should be alot easier.
[This message has been edited by goatnipples2002 (edited 10-09-2006).]
well, good to see some more info on this. I think the IAC system does a good job of acting as a balance tube between the two sides, being it is on its own path thru the intake manifold - bypassing the plenums. and, yes, I have NO idea what the ECM does with the TPS signal. I assume problems with WOT airflow at 1/2 throttle. if not, my main concern with this setup is moot - except the sensitve throttle - and thats a preferance thing - not a real issue. my next concern with this setup is intake velocity. since each TB is on either the Odd side, or Even side, and the firing order is 1-2-3-4-5-6, the intake velocity on each "nacell" of the "enterprise" will be really sloooow, especially with big "logs". but - again - kinda moot - being its such an improvement from stock with its overall airflow.
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11:00 AM
Xanth Member
Posts: 6886 From: Massachusetts Registered: May 2006
Has anyone made versions that bolt directly on? And do they really need to be quite so large? If velocity is an issue wouldn't having slightly smaller tubes help with that? Or would some benefit be lost by making them smaller than the TB? Or using smaller tubes with smaller TB's from another car?
[This message has been edited by Xanth (edited 10-09-2006).]
Originally posted by Pyrthian: my next concern with this setup is intake velocity. since each TB is on either the Odd side, or Even side, and the firing order is 1-2-3-4-5-6, the intake velocity on each "nacell" of the "enterprise" will be really sloooow, especially with big "logs". but - again - kinda moot - being its such an improvement from stock with its overall airflow.
Intake velocity is not an issue in EFI.
I think you're confusing it with a carb, or the intake velocity once it passes the valve.
Has anyone made versions that bolt directly on? And do they really need to be quite so large? If velocity is an issue wouldn't having slightly smaller tubes help with that? Or would some benefit be lost by making them smaller than the TB? Or using smaller tubes with smaller TB's from another car?
If you look at TT Slick's his seems to be bolted on. Mine is welded. I don't think mine is large, but that is a personal thing. The tubes need to be atleast big enough for the TB to fit or for the throttle plate to open. I used stock TBs for ease of installation and they seem to be doing fine as far as flow.
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11:37 PM
Oct 10th, 2006
TT Slick Member
Posts: 135 From: Columbus, Georgia Registered: Dec 2004
My tubes are 2" ID x 3" OD extruded aluminum, one side is milled flat just wide enough to bolt to the middle intake. These are then bolted in place, mounted to a milling machine bed and the fronts are milled square and parallel. The flanges are 3/4" thick and weleded to the front of the tubes. The cam in my engine is indeed a H260, CompCams roller rockers, bored .030 over. All intake flow paths gasket matched, bottom end balanced, 110lb. valve springs. Double roller timing chain, high volume/high flow oil pump. Stock injectors, chip has been modified but before I installed the twin throttle bodies. The full displacement is a little over 3.1L. The previous intake was a bored over Darrell Morse unit, and allthough he does a great job, the engine never quite feels as though its pulling as hard as it could. With twin throttle bodies it never stops pulling, I don't think I've had it to max RPM yet.
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12:34 AM
tjm4fun Member
Posts: 3781 From: Long Island, NY USA Registered: Feb 2006
Originally posted by tjm4fun: 2. that the motor is capable of drawing in 300cfm per bank. the motor will draw what it can based on the volumetric efficiency of the intake, heads and exhaust system. the biggest possible issue is bog from reducing velocity by having the throttle wide open before the velocity of air is sufficient to support it. Bogging is the only real issue, same as over sizing a carb on a carbed motor.
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Originally posted by ryan.hess:
No. It is NOT the same thing as over sizing a carb on a carbed motor. In fact, a car with a larger throttle body will have more acceleration off the line than a car with a smaller throttle body. With a carb, if you lose air velocity, metering and gas vaporization suffer. You get a sh*tty idle, and bogging, like you said. With a throttle body, you don't have to deal with any of that. The fuel injectors take care of idle fuel, and they don't care if you have a 10" throttle body.
However - if you just swap that 10" throttle body on, and do nothing else, you WILL get a hesitation/bog off the line. This is because the second you snap the throttle open, air inside the plenum is *instantly* pressurized to ambient pressure (14.7psia). Whereas before, it took 0.5 seconds to pressurize. This creates a lean spot, which means you need to adjust the chip to provide more Acceleration Enrichment (like a pump shot on a carb). Once that is fixed you will be faster than the car with the smaller TB.
ummm, where did you learn that engine theory? intake air velocity has every bit as much a factor. it;s about getting the air into the cylinders, and has just as much to do with efi as a carb. if intake velocity didn't matter, then the stock manifold would be fine as is. the injectors don;t care about anything except gas. that is only part of the combustion process. you need o2 in the air in order to create the fire. in partial throttle conditions, the air movement is limited by the plate and the efficiency of the intake/heads, flooring the car relies on the continued flow of air into the intake, and ambient air pressure does not magically flood the cylinder with 14 psi air. the challenge of making proper manifolds is to create air velocity that forces more air into the cylinder than it would normally receive just trying to suck it in thru the manifold and valves, etc. Why would they have long or short tube intake manifolds? it is for the proper management of the air velocity, and that goes for efi and carbs. you may be confusing the velocity thru the carb and carb efficiencies, while I am trying to point out that your intake has to maintain a level of air velocity. by your statement you are inferring that long/short runner intakes are a complete waste of money. proper sizing does matter. yes a smaller (read very undersized) tb will be outperformed by a larger tb(oversized), but the performance between idle and when motor will grenade will suffer more with the oversize especially at low rpm and hitting it to the floor. the proper size tb is what is required. if you spec that you will draw 180cfm per bank, then the tb should be sized to flow that, not 300 cfm. now without running numbers , the differrence in size may not be enough, as the stock tb may not truly flow the full 300cfm.
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Originally posted by tjm4fun: one thing I think that should be addressed is the tps would need recalibrating, either thru the chip or running 2 in parallel.
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Originally posted by ryan.hess: Don't do that.
don;t do what? run 2 tps's or recalibrate? the tps is used for the fuel mixture along with the map. the map is only going to be able to work with the range the fuelmap allows for a specific tps value range. these aren;t the brightest most advanced ecm;s out there but you are right in one respect, 2 tps's would not work, they would need some circuitry to adjust the output to reflect the recalibrated flow rates for the intake system. I expect that since they are simply a variable resisitor, and I think linear taper, one with a log taper would match the effects of the 2 tb's.
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12:54 AM
Raydar Member
Posts: 40912 From: Carrollton GA. Out in the... country. Registered: Oct 1999
My tubes are 2" ID x 3" OD extruded aluminum, one side is milled flat just wide enough to bolt to the middle intake. These are then bolted in place, mounted to a milling machine bed and the fronts are milled square and parallel. The flanges are 3/4" thick and weleded to the front of the tubes. The cam in my engine is indeed a H260, CompCams roller rockers, bored .030 over. All intake flow paths gasket matched, bottom end balanced, 110lb. valve springs. Double roller timing chain, high volume/high flow oil pump. Stock injectors, chip has been modified but before I installed the twin throttle bodies. The full displacement is a little over 3.1L. The previous intake was a bored over Darrell Morse unit, and allthough he does a great job, the engine never quite feels as though its pulling as hard as it could. With twin throttle bodies it never stops pulling, I don't think I've had it to max RPM yet.
I've told you this before, but I still think you should consider building these for sale if you've got the time and the inclination. I've seen the quality of your work. The picture just doesn't do it justice.
------------------ Raydar 88 4.9 Formula IMSA Fasback..........................88 3.4 coupe................................................ Read Nealz Nuze!Praise the Lowered!
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05:58 AM
PFF
System Bot
1MohrFiero Member
Posts: 4363 From: Paducah, Ky Registered: Apr 2003
I think that is my picture of TT Slicks set up and I agree with Raydar that is doesn't show the true quality of the unit. I also agree with him that I would love to buy one if you produced it.
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06:18 AM
fierochild Member
Posts: 346 From: Woodstock, Ga. USA Registered: Mar 2001
Goatnipples, you have a great looking intake which I'm sure performs better that the stock Fiero intake. What I see in the pictures is basically a modified 3.4 intake which uses two throttle bodies. I would be very interesdted in seeing dyno results for this mod. As far as TPS and IAC you would only need one of each. TPS simply tells the ECM how far open the throttle plate is. The ECM then uses that data along with MAP (mainfold absolute pressure IE vaccuum) to look up in the tables to find the correct pulse width to obatin the correct fuel flow. MAP pickup point may come into play since you have multiple entry point for air. I should think that the lower manifold would be best. Single IAC is pretty much a non-issue since it feeds directly into the lower intake. Multiple IAC and TPS would cause the ECM to set many fault codes and go into limp mode. Keep up the good work. The Fiero community continues to learn from these types of expieremnts.
Chuck
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09:35 AM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Originally posted by tjm4fun: ummm, where did you learn that engine theory? intake air velocity has every bit as much a factor. it;s about getting the air into the cylinders, and has just as much to do with efi as a carb. if intake velocity didn't matter, then the stock manifold would be fine as is. the injectors don;t care about anything except gas. that is only part of the combustion process. you need o2 in the air in order to create the fire. in partial throttle conditions, the air movement is limited by the plate and the efficiency of the intake/heads, flooring the car relies on the continued flow of air into the intake, and ambient air pressure does not magically flood the cylinder with 14 psi air. the challenge of making proper manifolds is to create air velocity that forces more air into the cylinder than it would normally receive just trying to suck it in thru the manifold and valves, etc. Why would they have long or short tube intake manifolds?
Jesus told me. And yes, when you floor a car, air magically floods the cylinders with 14psia. But everything is about air velocity, so I have an experiment you can try. I'll give you a recipe for an intake that will give you the highest air velocity you can get.
Behind the throttle body, place a 1/2" thick piece of aluminum with a 1/2" hole in the middle. There's your incredibly high velocity. The air might even go so fast, it will break mach 1 (you'll recognize this by the whistling it makes).
Somehow I don't think you're try this, because you know in engines, flow is king.
In regards to "long and short runner intakes"... Yes, that's a case where you are trying to force more air into the cylinders than it would normally take in. But only at certain RPMs. It works on resonance - the valve opening or closing event causes air to bounce around in the intake runner until it ends up as a high pressure area just as the valve opens again. Nothing to do with velocity, everything to do with flow.
quote
Originally posted by tjm4fun: don;t do what? run 2 tps's or recalibrate? the tps is used for the fuel mixture along with the map. the map is only going to be able to work with the range the fuelmap allows for a specific tps value range.
Don't run 2 TPS's. Like I said, the TPS is used for AE and PE. Creating some kludge job will only make things worse. You can change the necessary parameters in the chip in about 5 minutes.
[This message has been edited by ryan.hess (edited 10-10-2006).]
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09:59 AM
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
maybe intake velocity may not be the right term, but, what I am talking about is the flow of air moving thru the system. the air has forward momentum. with this 2 t/b setup, the forward momentum is not only way slow, but it is also pulsed alot more, due to being on either 1-3-5, or 2-4-6. now, whether this means anything or not, I dunno. in a way, I think the pulsing may actually be better. now, independant throttle bodies - everything I am thinking is out the window. and they work great. so, I maybe thinking backwards. maybe the fact that forward momentum is created is a bad thing?
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10:42 AM
5.0Vert Member
Posts: 287 From: Hurst, Tx, USA Registered: Mar 2005
Jesus told me. And yes, when you floor a car, air magically floods the cylinders with 14psia. But everything is about air velocity, so I have an experiment you can try. I'll give you a recipe for an intake that will give you the highest air velocity you can get.
Behind the throttle body, place a 1/2" thick piece of aluminum with a 1/2" hole in the middle. There's your incredibly high velocity. The air might even go so fast, it will break mach 1 (you'll recognize this by the whistling it makes).
Somehow I don't think you're try this, because you know in engines, flow is king.
In regards to "long and short runner intakes"... Yes, that's a case where you are trying to force more air into the cylinders than it would normally take in. But only at certain RPMs. It works on resonance - the valve opening or closing event causes air to bounce around in the intake runner until it ends up as a high pressure area just as the valve opens again. Nothing to do with velocity, everything to do with flow.
Don't run 2 TPS's. Like I said, the TPS is used for AE and PE. Creating some kludge job will only make things worse. You can change the necessary parameters in the chip in about 5 minutes.
You're correct about the 14.7 part....naturally aspirated motors pull in ambient air which is at atmospheric pressure. Atmospheric pressure is 14.7.
Flow and velocity are equally important, if anyone doesn't understand this, they need to do some research.
If you wanted to see the best results out of this setup, I'd recommend connecting the two plenums at the back, there are a couple of reasons for this. I'll try and find the article on building this setup with regards to physics, hopefully I'll be able to find it tonight....its not the same car but the concept is universal.
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11:00 AM
5.0Vert Member
Posts: 287 From: Hurst, Tx, USA Registered: Mar 2005
As with any aluminum cylinder head casting, the key is to maximize airflow improvements while minimizing material removal. Contrary to popular opinion, the flow rate of a head port will not continue to increase with material removal. In this case, bigger does not always mean better. There is a limit to the airflow gains that can be achieved through portin, and after maximizing the flow rate( READ: VELOCITY), a bigger port will simply decrease air speed. The key to a successful port is not maximizing the size but rather maximizing the flow through proper shaping. CNC porting is an easy way to do this successfully. The end result is a cylinder head that offers exceptional airflow with minimal stock removal(to maximize air speed) with little (if any) port to port flow variance. " I decided to build this custom tubular monstrosity that not only provided that George Jetson/rocketter look, but also impressive performance. Agreat deal of testing went into the design, including extensive calculations regarding the optimum engine speed for effective induction inertial ram charging, induction wave ram charging, and even Helmholtz resonance charging. The three distinct forms of improving the cylinder filling must be calculated and the intake designed accordingly. This is not as easy task as the three forms often overlap and care must be taken to eliminate the cancellation of effective charge filling.
A properly designed intake takes a great deal more than simply connecting eight runners(the intake he built was for a 4.6L SOHC v8) to a common plenum and calling it good. In most of my testing, the factory PI(that means performance improved) intake has proven itself tough to beat, especially up to 6,000 rpm. Intake runner length determines the effective rpm range of the motor (effecting inertial, reflected wave, and Helmholtz resonance tuning). The presence of boost pressure (from a turbo or blower) does not magically change the tuning effect and allow the short-runner intake to produce low-speed torque comparable to a long-runner intake. This custom intake is no exception, as it was designed for a specific rpm range."
"To illustrate the effectiveness of the intake design, I took the liberty of putting my money where my mouth is, and testing it against the stock PI intake.." The motor with the stock PI intake produced 426 hp at 5,800 rpm and 427 lb-ft of torque at 4,700 rpm. After swapping on the new intake, the peak power soared to 490 hp at 6,300 rpm, while the peak torque was up to 441 lb-ft at 5,400 rpm.
I wish I could show you a picture of the intake, it uses factory flanges to mount to the heads, has long runners, and 2 huge plenums, each runner has its own full radius air horn in the plenum. " One of the keys to the impressive airflow supplied by the custom intake was the use of full-radius air horns. The positioning of the horn in relation to the plenum floor, sides, and ceiling was critical to the overall tuning offered by the intake." Since it was a dual plenum design, the use of twin throttle bodies was necessary. They used a pair of 75mm throttle bodies. The plenums are also connected around back. One of you guys mentioned putting on end caps, whereas they made two 90* bends(almost the same size as the plenums), and used a clamp to connect them.
You guys had a great idea, but there's still some room to improve.
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11:40 AM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
two 75mm throttles is huuuge... That's like 600hp worth of throttle. For the record, you can get nice velocity stacks from Ross Machine Racing... they've got great prices. $142 for 4 stacks-
With that link posted, I'd just like to say that you can't read their back issues online, which really sucks. Its the June 06 issue. The title of the article is Au Naturel. Its on page 266. I'm not at home right now, and I don't have a scanner. I suppose when I get home tonight I can try to take some pictures of the article, but I need to work on my car now, hopefully I'll have it finished today.
EDIT: Just wanted to add that you're right, those throttle bodies are overkill, there is a chance that they could pick up some power by going to two 70mm units just with the increase in air speed.
[This message has been edited by 5.0Vert (edited 10-10-2006).]
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12:56 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Lets not confuse air velocity directly before/after the intake valve, with air velocity in the plenum.
Air velocity after the intake valve is important for intercylinder swirl and tumble and low rpm torque.
Air velocity in the plenum is mostly meaningless. I can guarantee if they swapped on two 90mm throttle bodies, they would not see any statistically significant change in horsepower one way or the other.
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01:42 PM
5.0Vert Member
Posts: 287 From: Hurst, Tx, USA Registered: Mar 2005
Lets not confuse air velocity directly before/after the intake valve, with air velocity in the plenum.
Air velocity after the intake valve is important for intercylinder swirl and tumble and low rpm torque.
Air velocity in the plenum is mostly meaningless. I can guarantee if they swapped on two 90mm throttle bodies, they would not see any statistically significant change in horsepower one way or the other.
I think they most certainly would lose some, although probably not much. I'lla gree that its much more important the closer to the valve you get.
Lets not confuse air velocity directly before/after the intake valve, with air velocity in the plenum.
Air velocity after the intake valve is important for intercylinder swirl and tumble and low rpm torque.
Air velocity in the plenum is mostly meaningless. I can guarantee if they swapped on two 90mm throttle bodies, they would not see any statistically significant change in horsepower one way or the other.
concur - what you will see is more power with less throttle response and then it will just gain nothing more with more throttle input.
air volume (CFM) at the TB is important but not velocity inless you are getting high velocities due to restriction from being too small. velocity does matter at the valve bowl but that has nothing to do with that intake
Originally posted by 5.0Vert: I think they most certainly would lose some, although probably not much. I'lla gree that its much more important the closer to the valve you get.
reducing velocity in the plenum after the TB should actually improve throttle response - but the power output will not go down.. increasing velocity int he plenum will not change the power output untill it starts restricting airflow
intake trumpets aren't for velocity - they are for smooth airflow - shark corners create a lot of flow resistance
[This message has been edited by Kohburn (edited 10-10-2006).]
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02:09 PM
5.0Vert Member
Posts: 287 From: Hurst, Tx, USA Registered: Mar 2005
reducing velocity in the plenum after the TB should actually improve throttle response - but the power output will not go down.. increasing velocity int he plenum will not change the power output untill it starts restricting airflow
intake trumpets aren't for velocity - they are for smooth airflow - shark corners create a lot of flow resistance
The TB helps to maintain velocity in the intake tract.
If the TB is too big, you will have a problem.
Think about this. The cylinders have to be able to pull air into them to let the combustion event take place. If the TB is too small, they are going to be fighting to get air in, like if you try sucking air through a straw while running. If the TB is too big, the vacuum created as the piston falls is not sufficient to get the cylinder full of air before the intake valve closes.
Ever had a bog? That's where you stand on the gas pedal and the car doesn't go anywhere because all of a sudden the engine has access to too much air and not enough engine speed to suck it in and process it. That's what a too-big TB will do.
Fuel injected cars are a lot less sensitive to oversized TBs than carbs are to big venturi, that's because the fuel is injected into the engine no matter what in EFI - with a carb, you are relying on the pressure differential outside and inside the engine to control fuel flow.
Question posed: Let's assume that you had a 347 with 450 fwhp, and that the compression was at a low 8.5:1, and the heads were only capable of 250 cfm. How would swapping out your 75mm for a 90mm TB affect power output? Then yes it would cause a power loss due to the intake velocity being reduced. It is like this in my mind, the 75 mm tb is like holding your thumb on the water hose to squirt water the 90 mm tb is like letting your thumb off the hose. Heck if the heads are only moving 250 cfm say at 7000 rpm and the compression is 8.5:1 then I would think given my past experiences a 65mm tb or 70mm tb would best work.
Ever had a bog? That's where you stand on the gas pedal and the car doesn't go anywhere because all of a sudden the engine has access to too much air and not enough engine speed to suck it in and process it. That's what a too-big TB will do.
Question posed: Let's assume that you had a 347 with 450 fwhp, and that the compression was at a low 8.5:1, and the heads were only capable of 250 cfm. How would swapping out your 75mm for a 90mm TB affect power output? Then yes it would cause a power loss due to the intake velocity being reduced. It is like this in my mind, the 75 mm tb is like holding your thumb on the water hose to squirt water the 90 mm tb is like letting your thumb off the hose. Heck if the heads are only moving 250 cfm say at 7000 rpm and the compression is 8.5:1 then I would think given my past experiences a 65mm tb or 70mm tb would best work.
actually that bog would be from an impropper tune causing an poor a/f mixture - the RPM, valve size and lift, control the air velocity as it enters the chamber.
why would you want 450 front wheel horse power?
a 75mm throttle body should support that power level but an 80 or 90 will be less of a restriction. its not due to changing the velocity in the runners because is doesn't its not about velocity its about flow (volume) CFM is not velocity BTW
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07:31 PM
tjm4fun Member
Posts: 3781 From: Long Island, NY USA Registered: Feb 2006
Lets not confuse air velocity directly before/after the intake valve, with air velocity in the plenum.
Air velocity after the intake valve is important for intercylinder swirl and tumble and low rpm torque.
Air velocity in the plenum is mostly meaningless. I can guarantee if they swapped on two 90mm throttle bodies, they would not see any statistically significant change in horsepower one way or the other.
here is where we have the point of confusion. velocity and flow are closely related. youre analogy about the 1/2" hole was cute. that is when I realized why we are arguing. different pictures of the same thing. I don;t consider velocity like the hose analogy of pinching it off. in engine intakes, I consider velocity directly tied to flow. you cannot create one without the other. yes velocity at the port and valve are higher, due to the restrictions there versus the volume of the plenum and runner tubes. BUT if you have no velocity on the air to the port, you will not fill the cylinder efficiently. there are ample restrictions in the existing manifold to create some low end torque, but highly restictive to the flow requirements of high rpm. hence my statement that just slamming open the tb will not magically fill the cylinder with 14 psi air, as it has restrictions along the way. the air will rush to fill the forming vacuum, but if not enhanced will not fill the cylinder to that pressure before the valve closes. if there is correct velocity for the given rpm, then the air is assisted into the cylinder by the velocity. that is why intakes tend to be either or, it;s hard to have low rpm and high rpm torque on one set of runners, you have to pick your sweet spot. or do the long runner/short runner with valving thing they did on that one 'vette motor for I think only one year cause it was a mechanical nightmare. (or did they fix that? I was not following car tech changes that much around that time, so I never followed it's history)
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07:50 PM
5.0Vert Member
Posts: 287 From: Hurst, Tx, USA Registered: Mar 2005
actually that bog would be from an impropper tune causing an poor a/f mixture - the RPM, valve size and lift, control the air velocity as it enters the chamber.
why would you want 450 front wheel horse power?
a 75mm throttle body should support that power level but an 80 or 90 will be less of a restriction. its not due to changing the velocity in the runners because is doesn't its not about velocity its about flow (volume) CFM is not velocity BTW
FLYWHEEL Horse Power(Not a difficult concept there . I don't see how that bog could possibly be from an improper tune, considering the fact that that hypothetical 347 still utilizes the stock system with 02 sensors and a MAF. The system is pretty adept and keeps the AF ratio pretty close to stoich, as long as it has the right size injectors, and the motor isn't too radical. There's nothing radical about this hypothetical 347.
A 75mm TB should easily support that kind of power, however the TB is a necessary restriction. There is a reason why people always go smaller in size from the MAF to the TB . My friend will be utilizing a single 90mm Accufab TB on his car, its been put on hold but will be forcefed, with over 1000 rwhp(racecar only). Velocity and flow are related. Without one, you don't have the other. CFM is not velocity, its Cubic feet per minute, which is flow, I don't know why you bothered to add that bit?
Read TJ's post, yet another explanation of how velocity and flow are related.
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08:06 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Originally posted by 5.0Vert: If the TB is too small, they are going to be fighting to get air in, like if you try sucking air through a straw while running. If the TB is too big, the vacuum created as the piston falls is not sufficient to get the cylinder full of air before the intake valve closes.
Whaa?
Think about that for a minute. Go to your straw analogy. Your lungs are exactly like a piston/cylinder. Your diaphragm moves down (like a piston) so you suck in air. Compare a runner with a straw in his mouth, to a runner without. Which one gets the "cylinder full of air"?
quote
Originally posted by 5.0Vert: Ever had a bog? That's where you stand on the gas pedal and the car doesn't go anywhere because all of a sudden the engine has access to too much air and not enough engine speed to suck it in and process it. That's what a too-big TB will do.
No, that's what a too-bad of a tune will do. A larger throttle body will be faster off the line than a smaller throttle body. Simply because it allows more air in faster. Any cars that bogged after a throttle body swap NEEDED to be adjusted to have more acceleration enrichment to account for all that extra air it's letting in when you stab the throttle.
quote
Originally posted by 5.0Vert: Fuel injected cars are a lot less sensitive to oversized TBs than carbs are to big venturi, that's because the fuel is injected into the engine no matter what in EFI - with a carb, you are relying on the pressure differential outside and inside the engine to control fuel flow.
Question posed: Let's assume that you had a 347 with 450 fwhp, and that the compression was at a low 8.5:1, and the heads were only capable of 250 cfm. How would swapping out your 75mm for a 90mm TB affect power output? Then yes it would cause a power loss due to the intake velocity being reduced. It is like this in my mind, the 75 mm tb is like holding your thumb on the water hose to squirt water the 90 mm tb is like letting your thumb off the hose. Heck if the heads are only moving 250 cfm say at 7000 rpm and the compression is 8.5:1 then I would think given my past experiences a 65mm tb or 70mm tb would best work.
Agreed on the carb, but not on the power loss when using a larger TB.
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08:37 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Originally posted by tjm4fun: BUT if you have no velocity on the air to the port, you will not fill the cylinder efficiently. there are ample restrictions in the existing manifold to create some low end torque, but highly restictive to the flow requirements of high rpm. hence my statement that just slamming open the tb will not magically fill the cylinder with 14 psi air, as it has restrictions along the way. the air will rush to fill the forming vacuum, but if not enhanced will not fill the cylinder to that pressure before the valve closes. if there is correct velocity for the given rpm, then the air is assisted into the cylinder by the velocity. that is why intakes tend to be either or, it;s hard to have low rpm and high rpm torque on one set of runners,
You can have a 5" throttle body on a fiero 2.8, and create a low rpm torque monster. You do this by tuning the intake runner lengths, usually by making them long to take advantage of low order harmonics.
The throttle body only restricts flow through the engine. You gain NOTHING (but a linear throttle feel-something important in a street car) by going to a smaller throttle body. You will not gain torque, you will not gain hp.
FLYWHEEL Horse Power(Not a difficult concept there . I don't see how that bog could possibly be from an improper tune, considering the fact that that hypothetical 347 still utilizes the stock system with 02 sensors and a MAF. The system is pretty adept and keeps the AF ratio pretty close to stoich, as long as it has the right size injectors, and the motor isn't too radical. There's nothing radical about this hypothetical 347.
A 75mm TB should easily support that kind of power, however the TB is a necessary restriction. There is a reason why people always go smaller in size from the MAF to the TB . My friend will be utilizing a single 90mm Accufab TB on his car, its been put on hold but will be forcefed, with over 1000 rwhp(racecar only). Velocity and flow are related. Without one, you don't have the other. CFM is not velocity, its Cubic feet per minute, which is flow, I don't know why you bothered to add that bit?
Read TJ's post, yet another explanation of how velocity and flow are related.
if you know much about EFI then you'll know that the A/F is measured after the fact, the amount of fuel injected on the fiero 2.8 is estimated based on the TPS, RPM, MAP, and IAT readings. when you change the size of the throttle body it causes the settings based on TPS to be innacurate - port the heads and it messes up the settings for air flow based on the MAP reading. A car with a MAF sensor will not be so sensative to air flow changes because it actually is measuring air flow into the engine not estimating based on pressure
you don't have to believe me - but don't bother trying to argue the point with me because I understand the inner workings of propulsion systems fairly well - you can read some books like fluid dynamics textbooks, car tuning guides, etc if you don't want to take my and others word for it
[This message has been edited by Kohburn (edited 10-10-2006).]
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09:13 PM
5.0Vert Member
Posts: 287 From: Hurst, Tx, USA Registered: Mar 2005
if you know much about EFI then you'll know that the A/F is measured after the fact, the amount of fuel injected on the fiero 2.8 is estimated based on the TPS, RPM, MAP, and IAT readings. when you change the size of the throttle body it causes the settings based on TPS to be innacurate - port the heads and it messes up the settings for air flow based on the MAP reading. A car with a MAF sensor will not be so sensative to air flow changes because it actually is measuring air flow into the engine not estimating based on pressure you don't have to believe me - but don't bother trying to argue the point with me because I understand the inner workings of propulsion systems fairly well - you can read some books like fluid dynamics textbooks, car tuning guides, etc if you don't want to take my and others word for it
You're right, AF is measured after the fact, and the stock PCM used with the hypothetical 347(read, not fiero 2.8, actually a SBF) uses a MAF system in which air flow is actually measured, unlike the speed density system. When you change the size of the throttle body using the stock PCM in this situation(read, not fiero), it will not change the settings based on TPS. The TPS only tells the computer if its at 'closed throttle', 'part throttle', or 'wide open throttle'.
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09:39 PM
PFF
System Bot
Xanth Member
Posts: 6886 From: Massachusetts Registered: May 2006
This may be stupid, but when running these dual TB's, what does the size really even matter anymore? Surely two TB's can flow more air than the engine can possibly use. The lower part of the intake is still stock correct? So all that amount of air still has to flow through the stock openings. How can it go any faster or slower than normal? To be going faster you would then have to force it more air, but the engine wouldn't naturally draw that much more. I understand it would be a bit more, because you eliminated the restrictions of the upper manifold, but you still must get through the lower. So if you use small TB's, the air would be going faster through the TB because of it, but no difference once you hit the lower manifold, since you are going back down to a stock size opening, drawing in relatively the same amount of air...
I am not speaking from actual experience, only trying to understand the concept. Feel free to correct me.
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10:34 PM
Reise Member
Posts: 69 From: Berrien Springs, MI, USA Registered: Aug 2006
when did we forget that engines are in fact air pumps and that the engine will only take in what it can draw? like xnath said the lower plenum would need to be changed also, or modified, with a good porting...I am surprised that no one has come up with an x type dual tb setup for thier 2.8,3.1,or 3.4L where you have two tb's and the left one feeds the right side and vice versa, should be a pretty easy deal as you could matchport the runner to the head. i am strictly talking hypothetical as the engine would be able to suck in all it could then slam the valve shut. if you would add in more fuel to this then maybe the engine would FINALLY be able to breath a lot better. but this is just my opinion and if I am wrong then I am sorry for interupting.
edit: where did you find that six tb intake on page one??? that thing is sick!
[This message has been edited by Reise (edited 10-10-2006).]
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11:15 PM
Oct 11th, 2006
Blacktree Member
Posts: 20770 From: Central Florida Registered: Dec 2001
Your cylinder heads will only flow so much. If your throttle body flows noticeably more than the heads, then your engine will simply reach the "WOT state" at a lower throttle level. The larger the difference, the more the throttle will resemble an on/off switch. And the more difficult it will be to modulate the throttle. Not only can this make the car undriveable on the street, but it can make the car difficult to manage on the track.
My advice would be to find out how much your heads can flow, and size the throttle body(s) accordingly.
5.0Vert POST THAT DAMN PIC OF THE INTAKE..................................please...I must see.
In all actuallity what does it matter...flow vs velocity. The intake is way better than stock. The acceleration is way better than stock. The looks are way better than stock. Making power all the way to 5.5k is awesome.
I understand that I need to run a balance tube so I can run my vacuum port for the map, but how big should the tube be to connect both plenums. Is 1/2 or 3/4 big enough?
quote
Originally posted by Reise:
edit: where did you find that six tb intake on page one??? that thing is sick!
I found it on here or RFL or 60V6. It is ryan falconer's design. They have website and you can buy it for $1500.00.
[This message has been edited by goatnipples2002 (edited 10-11-2006).]
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03:42 AM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Originally posted by Kohburn: reducing velocity in the plenum after the TB should actually improve throttle response - but the power output will not go down.. increasing velocity int he plenum will not change the power output untill it starts restricting airflow
intake trumpets aren't for velocity - they are for smooth airflow - shark corners create a lot of flow resistance
what was the idea behind that custom plenum you made? by the looks of it, it was to create maximum intake velocity before the runners and of course, look really cool
what was the idea behind that custom plenum you made? by the looks of it, it was to create maximum intake velocity before the runners and of course, look really cool
the first one or second one? - the first was maximum flow volume and smooth transitions into the runners -- the second one was a compromise between having to use the stock intake runners while removing every possible restriction in the intake and adding a larger TB
basicly smooth unrestricted flow with shorter runners and increased plenum volume.
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09:40 AM
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
Originally posted by Kohburn: the first one or second one? - the first was maximum flow volume and smooth transitions into the runners -- the second one was a compromise between having to use the stock intake runners while removing every possible restriction in the intake and adding a larger TB
basicly smooth unrestricted flow with shorter runners and increased plenum volume.
not sure - the one where it had a torpedo shape, that narrowed as it passed the runners. that narrowing is to maintain & use intake velocity as much as possible. where did the idea of this plenum come from?
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10:06 AM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
