If you have to run a cat, then I wouldn't run that thing you have in the pictures if you have room to run something bigger. That one you have in the picture is restrictive. Thrasher did a "study" some time ago about different converters and such and it was worth noting they found the factory converter that came on the W-bodies was one the least restrictive units available: http://www.thrashercharged....ech_htm/exhaust.shtm .
If you have room to run something bigger in size, I would recommend using one from a mid 90's GM fullsize truck. Some have inlets and outlets that measure just over 3.0" in diameter and they flow pretty well. But the general rule of thumb when it comes to catalytic converters is this: the larger the cross-sectional surface area of the catalyst substraight, the better the flow. And truck converters tend to have very large cross-sectional areas.
Concerning torque converters, stall speeds, and turbo spool; it takes airflow to spool a turbo. An engine is an air pump, and most engines flow more air with more RPMs (depending on design, cam profile, etc). So a higher torque converter stall speed can help a turbo make more boost, on the line - assuming your brakes can hold it. If your brakes can't hold the car on the line, then this is all moot.
I had ceramic pads on all 4 corners of my Fiero at one point and found they had very little HOLDING power. I couldn't build more than a few PSI of boost on the line before the car was pushed off the brakes. I switched back to semi-metallic pads on the rear and that fixed the problem. As far as torque converters are concerned, I'm running a stock 245mm converter from a 95 3100 which was rated at 2095 RPM stall with that engine. With my 3800, I can say it stalls at around 2300 rpm without boost and as high as 2800 rpm with boost.
IMHO, the "antilag" setup is a bad idea. Retarding ignition timing increases exhaust gas temps to a level that can damage valves and other exhaust system components. I suppose if it were only used for a very short period of time and not very often, it might not hurt anything. But I certainly wouldn't want to be sitting there on the line with this "anti-lag" thing operating for a long period of time (ie: more than just a few seconds). But then again, I've never needed it. In the Buick Grand National builds I've worked on that had big turbos, we've used higher stall converters and line-lock's to allow for us to build the amount of boost on the line we've wanted. Other guys have installed trans brakes, but I don't recommend that either.
-ryan
------------------ OVERKILL IS UNDERRATED Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com
Porting a cylinder head is a delicate task combining craftsmanship, artwork, and science. It is possible to hog out the ports and make then too large, and as a result, lower the flow velocity. Lower velocity means less inertia, less inertia means less potential energy. Some symptoms to over porting are sluggish response and poor bottom end performance along with a rough idle.
Incomplete cylinder filling at low rpm causes an engine to have poor bottom-end power and throttle response. Symptoms of over-porting are an engine with a soggy bottom-end or an engine that only makes horsepower in a narrow, few-hundred rpm band at the top-end, accompanied by a rough, lumpy idle.
There are a few reasons I didn't get a 1.3 60 this year... but the only one that really held me up was a broken timing chain last month as I never got a chance to use my un natural asperation.
The Neil chance converter concept is dumb.... I have the fastest setup with a Zzp.. fierox went slower with his as well as Canada... seems like a pretty dumb statement.
I'm not stating it's a general rule of thumb on Converters picking up power or helping ET's, but I'm just stating my fact and what happened with "MY" particular setup. It may vary like LFiero67 said, and it "DID" work with mine. Most of the time, you don't need a bigger converter with all the torque the supercharged motor will provide, but it changed the way my car operated going from a ZZP 2500 stall to something custom Neil Chance put together based on my dyno runs and graph and what my setup had and what my transmission and rpms looked like going through the traps, etc. My best time at the track with my ZZP setup was 12.1 @ 113 on ET Streets, busting off a 1.71. Now from last year with the same tune and tires, similar temperature, I ran a 11.99 @ 113mph. I didn't pick up any mph but I picked up 2 tenths. I had only made one or two passes, so I knew I could improve my launch. A few months later, same setup, adding only a bigger IC reservoir and that was it, same timing of 16 degrees which is weak honestly, but I was on 91, I went 11.86 @ 115mph basically (114.65). That was on Nitto 555R drag radials pulling off a 1.66 60ft. The conditions may have been different, I don't know, my car feels better with this converter, isn't as violent on a downshift and feels in my powerband so much better. This car will never ever pull like a Turbo car, it's not possible, but for what I was aiming for on the car and what I achieved, the converter helped somewhat. I don't think an IC reservoir being bigger and a bigger IC pump is going to pick up 3 tenths and 2 mph on the same 2.8" pulley and timing and virtually the same tires. Just my 2 cents and not trying to prove anyone right or wrong here. I still think with 22 degrees of timing and race gas with the right conditions the car could go 11.6's maybe even 11.5's if I got lucky. It's at the peak of what the M90 will achieve and that's fine, the car is exactly what I wanted, a solid street car.
-Amir
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[This message has been edited by Rare87GT (edited 11-06-2012).]
I have the .68AR on mine. While I haven't been able to drive it properly, I can tell you the low end will be much improved and way more responsive. Leave the .81AR's to the roll racers. Nothing wrong with going big, but don't expect the low-mid hit of a "mid sized" hot side. However, if you are only concerned about 1/4 times, the .81 is much better for that application.
I have the .68AR on mine. While I haven't been able to drive it properly, I can tell you the low end will be much improved and way more responsive. Leave the .81AR's to the roll racers. Nothing wrong with going big, but don't expect the low-mid hit of a "mid sized" hot side. However, if you are only concerned about 1/4 times, the .81 is much better for that application.
I agree 100% for roll racing , twin charged, or a v8 application . However, to make a good 1/4 mile in a 3800 and a big hotside. You need anti-lag, high stall converter, two step, etc, etc. As it won't spool fast enough without aid. Think of a typical modded supra. Great from a roll an on the dyno. Not so great in the 1/4 mile.
I agree 100% for roll racing , twin charged, or a v8 application . However, to make a good 1/4 mile in a 3800 and a big hotside. You need anti-lag, high stall converter, two step, etc, etc. As it won't spool fast enough without aid. Think of a typical modded supra. Great from a roll an on the dyno. Not so great in the 1/4 mile.
Supras work great from a stop... the MK4 world is easily my second largest area of expertise and i can tell you they run faster on the same turbo than I have with roughly the same weight through a manual transmission.
Just because you are too afraid to use antilag does not really lend well to offering advice all the time... I have used many converters in my days as well... you havent...
The simple fact is a 3800 will want a big exhaust side to make good power... I know mine is still the limiting factor of my car, I would never suggest anything smaller to someone looking at power levels similar to mine. There is also MANY MANY more factors in turbo spool/lag than exhaust housings... Most of which are bigger factors in reality.
I really think people make too big a deal on the turbine housing. On factory internal gate turbos I think it makes a difference, that's where you see boost creep because the wastegate can't flow enough, and the housing ends up becoming restrictive because the exhaust is being forced through it. On a well designed external gate setup, large amounts of exhaust are diverted around the turbine housing, only what is needed to power the turbo is actually flowing through the turbo. I have a open exhaust dump and can tell you the exhaust note is changed by a huge amount when the 46mm gate opens. There is no boost creep, because it can flow properly. I have seen the difference in airflow and traction between my 19lb runs and when I accidentally ran 23lbs on the street, I don't think my turbine housing is holding anything back. Unfortunately my transmission didn't allow me to run what I wanted to this year, but I have seen enough to know I'm not going any bigger on my exhaust housing.
I really think people make too big a deal on the turbine housing. On factory internal gate turbos I think it makes a difference, that's where you see boost creep because the wastegate can't flow enough, and the housing ends up becoming restrictive because the exhaust is being forced through it. On a well designed external gate setup, large amounts of exhaust are diverted around the turbine housing, only what is needed to power the turbo is actually flowing through the turbo. I have a open exhaust dump and can tell you the exhaust note is changed by a huge amount when the 46mm gate opens. There is no boost creep, because it can flow properly. I have seen the difference in airflow and traction between my 19lb runs and when I accidentally ran 23lbs on the street, I don't think my turbine housing is holding anything back. Unfortunately my transmission didn't allow me to run what I wanted to this year, but I have seen enough to know I'm not going any bigger on my exhaust housing.
Well this got me thinking. Last fall when I trapped 132.7 I had an open dump on the WG. I figured I would do a lot better recently with some changes I made. But this time my WG is recirculated. Even throwing more boost at it didn't improve my trap speed. I wonder if my exhaust is holding me back now? Sad thing is, I wouldn't go back because it sounds so much better now.
Recirculating causes two issues, one your allowing pressurized exhaust into an area that you want as little pressure as possible, post turbine pressure causes an increased pre turbine pressure. The turbine requires a pressure drop across it to work, if you increase post turbine 2 psi, you need 2 psi more pre turbine to do the same amount of work. This will reduce power. Secondly you are merging two exhaust flows, this will cause turbulence, reducing flow, again increasing back pressure, again reducing power.
4 degrees will kill power too lol.
The best turbo exhaust system is no exhaust, that's pretty hard to do on a street car though.
Supras work great from a stop... the MK4 world is easily my second largest area of expertise and i can tell you they run faster on the same turbo than I have with roughly the same weight through a manual transmission.
Just because you are too afraid to use antilag does not really lend well to offering advice all the time... I have used many converters in my days as well... you havent...
The simple fact is a 3800 will want a big exhaust side to make good power... I know mine is still the limiting factor of my car, I would never suggest anything smaller to someone looking at power levels similar to mine. There is also MANY MANY more factors in turbo spool/lag than exhaust housings... Most of which are bigger factors in reality.
I keep using term spool incorrectly. I am actually referring to boost threshold rpm.
The bigger the .AR the higher up in the rpm band is the Boost threshold.
Offering advise and sharing personal experience is exactly what you do...LOL
And how BIG is your exhaust side?
Dude you ran a 10.0 and you are telling me that your exhaust .AR is the limiting factor of your car, really? Lemmie, go look at your 60' time again.
I WILL use an antilag setup if I really need one. I just don't like the thought of NOT being able to disable it. An open circuit or stuck switch and my engine is toast.
I keep using term spool incorrectly. I am actually referring to boost threshold rpm.
The bigger the .AR the higher up in the rpm band is the Boost threshold.
Offering advise and sharing personal experience is exactly what you do...LOL
And how BIG is your exhaust side?
Dude you ran a 10.0 and you are telling me that your exhaust .AR is the limiting factor of your car, really? Lemmie, go look at your 60' time again.
I WILL use an antilag setup if I really need one. I just don't like the thought of NOT being able to disable it. An open circuit or stuck switch and my engine is toast.
Wrong wrong wrong.
First off. Setup antilag so a broken switch enables normal timing if you are concerned... otherwise it is far from an instant death as I have driven a few miles with antilag on full.
I have never worried about 60fts because I know what I can do with mine with the proper setup... this same turbo in my fwd stuff has went 1.4 60 and faster more than a few times in more than a few different cars... some even with smaller converters. The time I ran a 10 this year was just another shakedown style run as I did not have the brake prop valve or nitrous I have planned on from the start.
First off. Setup antilag so a broken switch enables normal timing if you are concerned... otherwise it is far from an instant death as I have driven a few miles with antilag on full.
I have never worried about 60fts because I know what I can do with mine with the proper setup... this same turbo in my fwd stuff has went 1.4 60 and faster more than a few times in more than a few different cars... some even with smaller converters. The time I ran a 10 this year was just another shakedown style run as I did not have the brake prop valve or nitrous I have planned on from the start.
Again, what are you running for a .AR hotside?
I'm NOT doubting you know your stuff, as I have copied/followed most of your setup and suggestions.
Hell, if it makes sense and works then I am probably going to do it.
I want Fast and Reliable and not necessarily concerned about Cheap.
If A/R doesn't matter why don't you run a T6 1.32? It should be plent big so you aren't held back by your housing, and since you state that the housing AR doesn't affect spool you should be able to run the same as you do now.
The turbine housing dictates when the engine can spin the turbo fast enough to create a positive pressure. If its too big you can't make any boost on the line, if you want to 60' without using nitrous, you need positive pressure on the line. You need a combination of things to get that. Brakes, tires, rpm, anti-lag all help, but if you can't get the turbo to spin up enough because your AR is too big, the rest doesn't matter.
If A/R doesn't matter why don't you run a T6 1.32? It should be plent big so you aren't held back by your housing, and since you state that the housing AR doesn't affect spool you should be able to run the same as you do now.
The turbine housing dictates when the engine can spin the turbo fast enough to create a positive pressure. If its too big you can't make any boost on the line, if you want to 60' without using nitrous, you need positive pressure on the line. You need a combination of things to get that. Brakes, tires, rpm, anti-lag all help, but if you can't get the turbo to spin up enough because your AR is too big, the rest doesn't matter.
LoL, I had a huge response to the .AR size but then I said....WTF
I'm too worn out over Bronco Bama and Mitt Omney to say what DH already knows.
If A/R doesn't matter why don't you run a T6 1.32? It should be plent big so you aren't held back by your housing, and since you state that the housing AR doesn't affect spool you should be able to run the same as you do now.
The turbine housing dictates when the engine can spin the turbo fast enough to create a positive pressure. If its too big you can't make any boost on the line, if you want to 60' without using nitrous, you need positive pressure on the line. You need a combination of things to get that. Brakes, tires, rpm, anti-lag all help, but if you can't get the turbo to spin up enough because your AR is too big, the rest doesn't matter.
Plenty of reasons why I won't upgrade the housing size... mostly because i have a very high flowing exhaust wheel that doeant need much a big exhaust housing to flow well. If I ever switched to a bigger Turbo I would get a ****** wheel that would be tighter and I can then run a 1.0 sized t4 housing. I will spool slower but I would be able to make more boost on the line.
HOT DAMN you guys have spent some money on your fieros. Wow, and to think I felt guilty spending an extra $200 to upgrade my injectors to 42.5# with a larger fuel pump and another $200 on a used AEM Progressive water/meth kit.
O_O
Crazy crazy crazy, well done though. Kudos on the artistic touch.
So is this one a race only car or a street car? Come on, we MUST know. Will the 3800 gods bless us wih their knowledge? It's not like anyone will troll your build, unless you troll yourself too.
So is this one a race only car or a street car? Come on, we MUST know. Will the 3800 gods bless us wih their knowledge? It's not like anyone will troll your build, unless you troll yourself too.
Nothing wrong with going big, but don't expect the low-mid hit of a "mid sized" hot side. However, if you are only concerned about 1/4 times, the .81 is much better for that application.
