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I want to run a rear mount on a TPI and had a few question needed to clarify.
I have a 91 formula 350 L98 with 140,xxx on car and motor, it has a header back exhaust and is in great running condition mechanically. I am looking for the basics that I need to do for the car electronically speaking. The mounting and piping seems pretty straightforward and just time and labor consuming, but exactly what must I do to the ECM for it to work, get a 2 bar map sensor and a 749, and is the 749 a direct fit?
I just want a simple but thorough list of what will need to be changed on the car, I have a good idea of most but when it comes to the computer there is still some confusion. Thanks for any and all help,
Before you start, I have to give my 2c about rear mounts. Why do you want that? Yes, it simplifies the exhaust plumbing, and clears out the engine compartment, but what about efficiency? You're mounting the turbo as far from the energy that drives it as you can get. Then you have to pipe the air that you compressed about 10 feet to the front of the car. It makes little sense to me. The only advantage IMO is a short exhaust after the turbo.
Before you start, I have to give my 2c about rear mounts. Why do you want that? Yes, it simplifies the exhaust plumbing, and clears out the engine compartment, but what about efficiency? You're mounting the turbo as far from the energy that drives it as you can get. Then you have to pipe the air that you compressed about 10 feet to the front of the car. It makes little sense to me. The only advantage IMO is a short exhaust after the turbo.
coolctk, if you plan on keeping low boost (6or less psig) then your computer should be fine the way it is, maybe just bump up FP if you keep the stock inj.
I am not going to argue about engine vs. rear mount because I simply don’t know enough. But I am putting a rear mount in because its cheaper, passes CA smog, and I see it as easier to deal with/modify. I don’t know how much you know about the actual physics and how much energy is actually lost for the ten feet instead compared to one foot, but I know its not enough to discourage anyone who has a streetcar for doing it because it can still put up as much power as you want.
I have a been watching some of 89jyturbo install, but your saying if I only want to run 6LB then it would just need a prom tune with a bump in fuel pressure and no FMU? But I will eventually want to up the boost once I build a forged long block, so then what exactly will I need ECM wise to do this on LTR TPI?
I am not going to argue about engine vs. rear mount because I simply don’t know enough. But I am putting a rear mount in because its cheaper, passes CA smog, and I see it as easier to deal with/modify. I don’t know how much you know about the actual physics and how much energy is actually lost for the ten feet instead compared to one foot, but I know its not enough to discourage anyone who has a streetcar for doing it because it can still put up as much power as you want.
I have a been watching some of 89jyturbo install, but your saying if I only want to run 6LB then it would just need a prom tune with a bump in fuel pressure and no FMU? But I will eventually want to up the boost once I build a forged long block, so then what exactly will I need ECM wise to do this on LTR TPI?
You should be fine with 6psig and nothing else done to your fuel delivery. You have to remember that normal atmosphere is 14.7psi (1 bar) and probably have a 2 bar sensor (MAF should be ok too if placed before the turbo). Your car will run fine at the top of a mountain or at sea level, right? Adding another 6psi shouldn't be a problem. I am using large injectors with lower base FP and it works. Of course it won't be as good as fine tuning with the ECM, but people have been using boost at moderate levels on a stock tune for years without problems.
Last edited by firstfirebird; 06-01-2007 at 08:24 PM.
The bird has SD and not MAF. At no more than 6 psi would I be fine with no re-tune on a MAF ECM, but on SD with a 1-bar I dont know how it would react with no tuning and boost.
But the point is that I want to set it up electronically early (as in using 749) so that way later on I can drop in a long block and turn up the boost. so again is it as simple as plugging int he 749 EMC to stock harness, and what is needed to do so if not? do I need to buy a new SD sensor to read 2-bar?
for anyone who has done the rear mount or has studied up on it im kind of interested in it. it would be very helpful if the originator of the mod would have given a detailed explaination or a walk through of what he did. does anyone know what you would have to do to run this on a carb'd motor.?
You need, the turbo, Piping and an oil return pump and lines. Then you need to add more fuel. A 749 ecm will work, as will another non stock ECM. A boost referenced fuel pressure regulator is the easiest and least expensive way to add more fuel per pound of boost.
Then you need a bonnet with a boost safe carb or a carb box.
And with some carb fuel pumps you can plug a boost line into the atmosphere port and have a boost referenced fuel pump. With a carb setup you will definitely need a boost referenced fuel regulator /pump.
been searchin and yes a bost sensitive regulator will be a for sure buy. im thinking about going with a air tight box fab'd up. i figure i'll buy the parts and match it to bolt to my intake, then the carb ontop of that. plumb the intake pipe to the box, tap in some fittings for the fuel lines, and find a marine type throttle linkage to make sure everything is sealed up. thats about all i would need to do. now i gotta finda turbo. i hope someone can explain to me the step through for plumbing oil
Great site, with great results. Read the FAQ section on remote mount turbo's and you'll believe in them too. Plus the video's and dyno sheets speak for themselves. You gain so much efficiency from dropping all of that heat that it makes more power being in the rear. Think of it as an air compressor with the air line being the piping from front to back. When it's full it's pressurized so you won't lose any power.
Great site, with great results. Read the FAQ section on remote mount turbo's and you'll believe in them too. Plus the video's and dyno sheets speak for themselves. You gain so much efficiency from dropping all of that heat that it makes more power being in the rear. Think of it as an air compressor with the air line being the piping from front to back. When it's full it's pressurized so you won't lose any power.
What part of the STS FAQs do you believe? I do not believe half of what STS says in their FAQs. In each FAQ they state something and twist the rear-mount to sound superior. Although, it goes against what they said in earlier FAQs. Get a physics book and compare it to what STS says about how rear mounts work. A lot of what they say is fabricated truth. They are great at marketing & advertising though.
You NEVER gain efficiency by mounting the turbo further away from the engine. The reason STS focuses on "compressor efficiency" is to get away from the large "turbine inefficiency" problem. It is the old move the hands and distract magic trick act. A good shop air compressor has an aftercooler on it (some call it an intercooler). The don't run a bunch of pipe. The surface area of pipe compared to an aftercooler is like pennies compared to thousands of dollars. Do the surface area calc. STS' claim is all fools gold about comp. pipe temp. drop. You talk about not losing PSI drop on the comp. pipe........well you ain't gonna have an IAT drop either at the air speeds under boost. So there goes the STS "good comp. efficiency" claim.
Not that rear mounts are bad. It goes like this: no_turbo < rear_mount < front_mount
To start with, Junkcltr is right about the FAQs at the STS site, that info should not be used as support in an argument for rear mounts. STS is the only mass produced rear mount turbo kit company that I know of, and it goes without saying that all of there information is extremely biased.
And it is possible that rear mount kits are less efficient than that of one mounted in the engine bay on paper (looking at it from a strictly scientific standpoint). But in practicality are very good kits to use, especially for street cars. The facts are that rear mounts can produce plenty of power in a nice RPM range, with the car engine still being inefficient. The best broad test for efficiency in a car would be the gas mileage and how fast parts wear out, and rear mounts do good on both of these test compared to header mounted kits. So the engine stays efficient (relatively speaking) even though there seems to be a “turbine inefficiency”. And the air that’s traveling past the rear mount intake piping has a higher velocity than the air traveling through an aftercooler.
And the reason why there are no pro mod cars doing it is because there is no advantage to doing a rear mount over an engine bay mounted kit. If you can easily have turbo in the engine bay because your running a pro mod car than there would be absolutely no reason to run a rear mount unless you were sponsored by STS and had something to prove (to help your rear mount business).
In conclusion, rear mount kits are good for street cars and have the power and efficiency to show for it. They are so much easier to install, maintain (IMO), and pass CA smog with it than an engine mount kit.
Rear mounts are a good setup. Pro Mods don't run them because it is all about max. HP. A front mount makes max. HP. Heat/Energy drives a turbo so any loss in heat is wasted HP.
The rear mounts shine in emission setups as stated above. If you do a rear mount......size the turbine accordingly, make a sump for the oil outlet, run the pump after shut-down a little bit, and use the correct oil pump.
Just came across this thread and thought I'd post my opinion since I just got my rear mount project going. I got a lot of information from the thread mentioned above. My car is a 1994 Infiniti Q45. I'm a believer in the rear mount when it's the best option which it was for me and sounds like for this person for emissions reasons. I believe you can get very similar response and power from a rear mount when sized properly. When sizing you need to choose a smaller turbine a/r than you would for the same turbo mounted in the front. The exhaust gasses are cooler so the volume is less. The velocity is the same but as it cools it takes up less space so the smaller a/r will give you pretty much the same response as you'd get with a larger one up front.
I have less lag than just about all the turbo'd vehicles I've been in and I have a long 4 door sedan with the turbo all the way in the rear. The long compressor pipe doesn't create lag. The pipe doesn't have to fill up before making boost, it's already got air in it and it's moving so fast it only takes a second or less to pressurize. The cooler intake temps you should get with a rear mount don't have much to do with the long pipe but are mostly because the turbo and plumbing are cooler to start with. To keep the exhaust gasses as hot as possible I wrapped most of the rear section of my exhaust pipe with fiberglass heat wrap.
As for the tuning question originally asked, I have the equipment to reprogram any part of my ECU but I'm not sure how your ECU's work. I can burn a new EPROM and drop it in mine and have a new tune in minutes (not including the time it takes to actually modify the program). Like others have said, it should work at low boost completely stock. My car runs find w/o detonation with the stock ECU up to around 4 psi. Over that and it starts to lean. If you use a boost referenced FMU you could get a few more PSI from the stock ECU program. If you add methanol/water injection you could probably get few more PSI. I'd guess 7-8 would be about the max you'd every want to go on a stock motor anyway. Higher and you'll need to lower the compression ratio of the motor.
Anyone with these STS turbos on this site have any actual results other then the 14.97 second cavaliar?
I am skeptical about the STS turbos just because every car I have run into personally with that setup has been pathetically slow for a turbocharged motor (usually LS1 around where I am from).
I want to run a rear mount on a TPI and had a few question needed to clarify.
I have a 91 formula 350 L98 with 140,xxx on car and motor, it has a header back exhaust and is in great running condition mechanically. I am looking for the basics that I need to do for the car electronically speaking. The mounting and piping seems pretty straightforward and just time and labor consuming, but exactly what must I do to the ECM for it to work, get a 2 bar map sensor and a 749, and is the 749 a direct fit?
I just want a simple but thorough list of what will need to be changed on the car, I have a good idea of most but when it comes to the computer there is still some confusion. Thanks for any and all help,
Cameron
yep thats right im bringing it back from the dead. did you ever get around to this build? i would love to see how it looks and what all you did. and any input on the size turbo would be great.
i have mounted and used the sts turbo's on a few vehicles that have worked very well. i dont know about the facts on the sts site but they do work and work well. most people dont believe that they will work since the piping is so long but they do work.
Had an STS setup on my IROC for bout 3 years. Worked for the most part. Just hacked it all off to build a front mount setup cause i got tired of it and all the little problems I had with it.
Had an STS setup on my IROC for bout 3 years. Worked for the most part. Just hacked it all off to build a front mount setup cause i got tired of it and all the little problems I had with it.
care to go into more detail on the problems so people know more about it.
Ive personally seen a few cars a guy I know built put down over 600+ with twin rear mounts
Im not here to argue about the better of the to turbo setups. But i will say the 749 swap is great. You do have to move a few of the wires in the ecm plug, buts its easy. Then it plugs right in. I did all the tuning to my car and it runs very well. I am NOT a tuning expert either. Good luck with your build.
__________________ Boosted and intercooled L98 with 749 ecm
10.72@129-1.5 60ft(new best time Nov/2010)-570rwhp@13lbs on pump gas. Est. 600+rwhp@16lbs on 100 octane. Capable of 18lbs, but havent done it, ok maybe once.
Featured in GMHTP mag July 07
Im not here to argue about the better of the to turbo setups. But i will say the 749 swap is great. You do have to move a few of the wires in the ecm plug, buts its easy. Then it plugs right in. I did all the tuning to my car and it runs very well. I am NOT a tuning expert either. Good luck with your build.
why did you choose 749 ecm vs the 7730 with the $59code
The rear mount setup like i said is great for a (rather) quick install and go on a mild motor with a smallish turbo (T-60/67). Now for my 407ci motor i need to run say a 80 trim turbo and then you run into feeding the turbo with enough and then having big enough charge pipe. Plus once you get a boost leak somewhere its a PITA cause you have so much charge pipe. Now that I have all the STS stuff off there was like 10 feet of charge pipe and about 20 ruber couplings... thats just way to much. Plus oil issues either to much or not enough, crank pressure the list goes on and i decided to just **** can it and go a diffrent route.
Wow... I really don't get why people try to make this sound like the way to go or better than anything else.
It's simple, the only thing that is better about a rear mount setup is packaging issues: if you don't have room closer to the engine, if you can't mess with the exhaust before the converter (emissions requirement...), or if you want to avoid messing with that plumbing. Period.
It doesn't work better in any way. It will never spool as well, it will never be as efficient in any way. You will always have a shorter power band than a similarly well matched front mount turbo, and even though it's easier to get past emissions testing if it's strictly enforced (because it doesn't mess with any of the emissions equipment as certified by the manufacturer), I can guarantee that emissions are not actually lower. On top of all this, there are tons more places for things to go wrong, just by virtue of 2x or more more plumbing (intake, exhaust, oil...) and worse, that plumbing is in a location that is more likely to get damaged/exposed to road crap. Heck, just the potential for catastrophic failure that you're creating by adding 20-30' of engine oil fed oil line under the car should make anyone think twice about doing this.
Obviously, it does work, but I would only choose it in the place of a more conventional setup if you can't make a more conventional setup work, or if you just want to screw around with a rear mount setup to mess with a rear mount setup.
