Got a Small Block Chevy 350 (1974) with some nice gen 1 trickflow twisted wedge heads, currently with Edelbrock Carb.
Thinking of Upgrading to the GM/Chevy TPI-Tuned Port Injection system. My trickflow heads are supposed to accept stock intakes, so the TPI setup should work for me.
Which one would be best to use for power? I know there's the MAF vs MAP version.
Also read and seen that the stock GM/Chevy TPI Intake Manifolds are very restrictive.
I've seen these type of Corvette TPI Intake Manfiolds that feature the 2 rectangular runners on ea side vs the GM/Chevy TPI Intakes with the 4 little pipe runners.
I've built many versions of "TPI" engines over the years using stock-cast iron L98 heads, Aluminum Corvette L98 heads, the aforementioned TFS Twisted Wedge Heads, and Vortec L31 iron heads. I've used stock & ported (long tube runner) TPI intakes, the LT1-like Miniram intake, and the Accel Superram intake.
Any 350 build using the long tube runner TPI intake is going to be a torque monster. It will produce excellent low and mid-range torque but will run out of breath quickly above 5000 rpm. Siamese runners, aftermarket / ported lower intakes help a little, but they don't change the characteristics of this being a long tube runner intake which will always favor lower RPM power production at the cost of upper RPM HP. A 350 engine producing massive amounts of low-RPM torque can be very harsh on a FWD-type transmission, especially manuals.
The Miniram intake performed poorly in my heavy G-body car (it had an automatic trans). It has very short runners (like the LT1 intake) which means it produces great upper RPM HP, but at the cost of low end torque. In a lighter Fiero I suppose it would work fine (it would work even better with a manual trans). Its low profile design would probably fit under the Fiero’s decklid better than any other intake discussed here.
The Accel SuperRam intake is a huge looking box that replaces the upper plenum and runners used on the TPI engines. While it reuses the TPI lower intake manifold, the SuperRam has 1/2 length (of stock TPI) runners and a huge open area upper plenum. This intake produces awesome mid-range torque without giving up much in the low-end and still allows a 350 cube engine to produce great upper RPM HP (to about 6000 rpm or so). It is a complicated intake (lots of fasteners), it is large, and I don't know if it will fit well under the stock Fiero decklid.
Anyway, of all the 350 EFI builds I've done, I found the GM LT4 HOTCAM works well with both the stock TPI intake and also the SuperRam intake. If you are going to use either of these intakes, I suggest you either heavily port the lower baseplate intake manifold or you get a "high-flow" aftermarket unit. As far as throttle bodies are concerned, you don't need anything more than a 52mm throttle body (TB) with airfoil. Save your money and don't waste it on the 58mm TB - your 350 cube engine will never need it. (As a matter of fact, a stock 48mm TB with airfoil might work fine - depending on your build). If you end up going with the Miniram intake, you may want to use a cam that produces power earlier in the RPM band than what the HOTLT4 cam does, unless you built your engine to turn some very high revs.
Concerning ECMs: I would stay away from the 86-89 (1227165) MAF sensor based systems. They used a troublesome BOSCH MAF sensor that you really don't want to mess with. Instead, use something newer like the 90-92 speed density (1227727/1227730) ECM which uses a MAP sensor. Note that both of these systems are batch-fire type injection systems (meaning all 8 injectors fire at the same time).
Recently, it has become popular to get a retrofit kit so you can use an LS1 OBD2 PCM and coil-per-plug ignition systems with these older engines (I believe you might have one of these systems pictured above). However, these setups can be pricey because a lot of custom/aftermarket parts are needed to make it work.
The next best thing would be to use a 12200411 OBD2 PCM with 2001-02 Vortec L30/L31 GM Van based programming. All you need to run this on your engine are these parts which you can get from any 1996-02 L30 (5.0L) or L31 (5.7L) Vortec engine:
-distributor which contains the cam sensor -coil/ignition module -crank sensor -NEW Vortec timing cover (with provisions for crank sensor) -reluctor (for the crank sensor) that installs over the timing gear on the crank -OE style timing chain or single roller timing chain – since that is all that will fit behind the stock Vortec timing cover (there might be an aftermarket vortec compatible timing cover available that allows you to use a double roller timing chain)
Both the LS1 and Vortec systems are SFI, which means the injectors are fired sequentially. There is also the ability of these PCMs to control a modern electronic auto trans such as the 4T60-E and possibly the 4T65-E.
-ryan
------------------ OVERKILL IS UNDERRATED Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com
[This message has been edited by Darth Fiero (edited 03-09-2013).]
Excellent reply Darth Fiero. I too agree that the earlier MAF system adds unnecessary complexity to the installation (space and electrical requirements). I converted my TPI engine from MAF to Speed Density (using the 1227730 ECM) primarily because of the poor reliability of the MAF sensor, which isn't cheap.
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08:00 AM
woodyhere Member
Posts: 399 From: prior lake, MN USA Registered: Aug 2011
I have been running an 800 Edelbrock carb on my 421. I have found out some intersting things about tuning these carbs when they have to sit sideways in a Fiero. I was going to chuck it in favor of some sort of FI. Had a terrible time getting a consistant F/A ratio. Darn thing would go rich but not consistantly enough to make a jet or metering rod change. Not that I didn't try that route. Little stumble on turns and a feeling the motor just didn't feel right. I made some vent tube extensions on a hunch the fuel was splashing around. I also raised the float level to 3/8 inch. Next test drive with no other changes, the car ran way lean but was consistant. Now a secondary jet change and primary metering rod change worked like it should have in the first place. The little stumble on turns was gone. I did some fine tuning, by drilling the primary air bleeds, to get the cruise A/F to 15.5. On power at a nice consistant 12.5. I know this isn't what you asked and you did get some very good answers on the FI switch. Sometimes simple is fun.
------------------ woodys 427
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08:29 AM
FFIEROFRED Member
Posts: 751 From: GULFPORT, MS Registered: May 2008
I was using a 86 tpi on my V8 fiero. TQ monster. lost that engine ( katrina ) than a 305 crossfire. both ran out of air to soon. next i built a 357, drat headed, com cam roller. Holley 950 pro mpi FI. with a victor-E intake. Never could get it to run very well. stuck a 600 cfm carb on it with a normal old HEI. Now it pulls to 6000+ rpm. Will still spin the tires (4t60-E/3.29 ) if you want, from rest. If i was going to do it all over again ( FI ) I would get one of the NEW, complete set ups. I don't care if it fits under the deck lid. The victor-E intake works just fine with a carb if you plug the injecter holes.
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08:41 AM
fieroguru Member
Posts: 12448 From: Champaign, IL Registered: Aug 2003
In my opinion, if you are going to run an automatic, then the TPI intake would be a good fit. The 4 speed autos have better gearing for a higher torque engine and the excess low rpm torque will easily overcome the increased driveline loss through the auto.
If you are going to run a manual transmission, then I would stay away from the TPI and stick with carb, LT1 intake, TPIS MiniRam, RamJet, HSR, Edelbrock Pro-Flow XT as all these will make power up to 6500 rpm with the right cam and heads and you will like the extended RPM range with the gearing in the manual transmissions. Here is a pic of my Ramjet setup:
Here is a miniram setup (not mine):
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01:27 PM
Will Member
Posts: 14272 From: Where you least expect me Registered: Jun 2000
Originally posted by Darth Fiero: I've built many versions of "TPI" engines over the years using stock-cast iron L98 heads, Aluminum Corvette L98 heads, the aforementioned TFS Twisted Wedge Heads, and Vortec L31 iron heads. I've used stock & ported (long tube runner) TPI intakes, the LT1-like Miniram intake, and the Accel Superram intake.
quote
Originally posted by fieroguru: If you are going to run a manual transmission, then I would stay away from the TPI and stick with carb, LT1 intake, TPIS MiniRam, RamJet, HSR, Edelbrock Pro-Flow XT as all these will make power up to 6500 rpm with the right cam and heads and you will like the extended RPM range with the gearing in the manual transmissions.
I've heard that the Holley Stealth Ram (HSR) is a good all-around choice for a street car.
quote
Originally posted by Darth Fiero: The Miniram [...] has very short runners (like the LT1 intake) which means it produces great upper RPM HP, but at the cost of low end torque.
A whole lot of people say that, but the LT1 actually produces an almost flat torque curve from idle to ~4000 RPM. The runners are so short that they operate as dumps rather than as pulsed-flow systems.
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03:31 PM
Mar 10th, 2013
Darth Fiero Member
Posts: 5921 From: Waterloo, Indiana Registered: Oct 2002
A whole lot of people say that, but the LT1 actually produces an almost flat torque curve from idle to ~4000 RPM. The runners are so short that they operate as dumps rather than as pulsed-flow systems.
As far as I remember, the Miniram intake had larger cross-sectional area runners which was supposed to increase flow. However, on smaller cubed engines, this hurts low RPM torque production. The LT1 intake has smaller runners, so that helps it perform all-around better on a small cube engine like a 350. I think the Miniram shines well on 383-400 cube engines. But I didn't have good luck with it on my 350; of course, it was in a 3500+lb car with an automatic transmission. In a ~3000lb Fiero, it might do fine.
I've heard the Holley Stealth Ram (HSR) performs better than the Miniram. From what I've read, the HSR is pretty close in performance to that of the Accel SuperRam but favors upper RPM HP production a bit more (while giving up a little on the lower end). But the HSR is a tall intake and I'm not sure if it will fit under the decklid of a Fiero.
But not much looks as cool as a polished factory-type TPI setup with the individual tube runners.
[This message has been edited by Darth Fiero (edited 03-10-2013).]
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06:45 PM
ericjon262 Member
Posts: 3130 From: everywhere. Registered: Jan 2010
But not much looks as cool as a polished factory-type TPI setup with the individual tube runners.
Meh. I think they're ugly. need to change injectors? Lol, talk about a PITA. I still vote stealthram, or ramjet, but decklid clearance may be an issue with the HSR as darth pointed out.
------------------ we're in desperate need of a little more religion to nurse your god-like point of view...
It's been a while and I might be wrong but if I remember correctly there is a difference between the older SBC intakes and the newer. So a TPI intake might not fit your older heads.
[This message has been edited by 85 GT (edited 03-11-2013).]
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10:22 AM
ericjon262 Member
Posts: 3130 From: everywhere. Registered: Jan 2010
keep in mind, if TPI was so magical, GM would still be making it.
I will say this: the TPI intake was an intake GM should have put into their trucks. But they didn't because it was complicated and expensive. Certainly more expensive to manufacture than a 1-piece cast aluminum manifold (LT1) or something made out of plastic like they are using nowadays.
I do agree that a TPI intake probably wouldn't be good to use in a Fiero because of the large amount of low-RPM torque it makes which can be detrimental to FWD-type transmissions.
Originally posted by n_tensetuning: Is it just me or does the LT1 TPI Intake look pretty damn close to the TPIS MiniRam Intake? even the fuel rails look identical. Does anyone know IF the LT1 intake off the 92-96 Corvette C4 can fit the old SBC heads (pre-86)?
Yes, the two are similar. There used to be a kit to use the LT1 manifold on Gen I engines, but the website that sold it has been taken down.
I too agree that the earlier MAF system adds unnecessary complexity to the installation (space and electrical requirements). I converted my TPI engine from MAF to Speed Density (using the 1227730 ECM) primarily because of the poor reliability of the MAF sensor, which isn't cheap.
