90stang5speed Rear Mounted Turbo Project Thread

90stang5speed said:

I agree but, the more I look at that twin set up, the more it makes me want to flip my turbo around & route it in a similar way. I can see a few benefits to doing it their way and only 1 disadvantage. That is a pure track car I'm sure. Mine will see street time & maybe some 500 mile trips to KY. I need to be able to run an air filter when not at the track. my setup leaves more room for a filter box. They have two 90* bends for the air intake where my single setup will be more of a straight shot. I doubt that will make much difference though. I Really like their setup. I will most likely finish what I have started but, if I ever go twin, I might have to copy that.

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I would keep it inside. Yah most guys don't run a 800rwhp car in the rain, but hey @ least you could.
I do know of one application where the air filter would suck in water, and kill the MAF , and car would die. It was from direct tire/water spray. Remember thier is a lot of sucky-sucky going on with the turbo. Our tracks here are hideously dusty and dirty and I wouldn't trade a few tenth's for a toasted/motor/turbo.

90stang5speed said:

Yeah I think the filter box is going to be a good thing even if it looks like something that that shoulod be under the hood of an International semi truck. I was talking to my import buddy with the VR4 about reversion & he sent me this link.
Tuning the LET - Exhaust
Its a pretty good write up I think. I wonder how hard it would be to make a peak hold gauge to measure exhaust back pressure. It would be interesting to compare peak back pressure to peak boost pressure. It seems that it would give some insight to if I need a bigger AR housing on the exhaust side.

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I like the article but it needs to be read carefully, most only applying to a front mount set up. Some of the info does apply.
2 to 1 was what we would shoot for on boost vs. back pressure.
I can simplify the a/r thing.
I look @ the a/r like a camshaft in an engine, you are picking the range of operation. If you want boost sooner a smaller a/r , and larger a/r for more top end. You will scarafise so top end power with the smaller a/r.
I looked @ the LS1 forum yesterday. What a mistake. There were guys that wanted to take the SAME turbo and run it in a front mount, then a rear mount set up and compare.
No correct rear mount unit would work well in a front mount, and the front mount would be to big the back. The farther back you go, the smaller the compressor and a/r you need. Move it forward and you need to get bigger.
You will win this battle because you are increasing the efficiency and making more with less.
All rear mount turbo’s I used were custom, hybrid units best suited for the rear mount. The key is making more power with less boost.
If you need to ram 30-50 psi in the motor, most of the time that will be out of the compressor maps of your unit, it will add heat by working the turbo to hard and hurt efficiency. I have seen more boost with little or no HP improvement when outside the map.
Buy a bigger turbo and run lower boost.
Rear mount is way different than front mount set up.

The key thing on the 90stang5spd build is the hedders and pipe are wrapped. Thermal expansion is what spools the turbo. If you were to run stock manfolds, you would see boost quicker when the engine is cold . The hedders un wrapped would allow gobs of heat out of them and kill the thermal expansion on you set up. Your engine combination may benefit from the hedders but not so much on the rear mount turbo.
Most guys buy the hedders first so we would not make a big deal if you had them, but would not recommend the either. I sure pissed of many aftermarket companies we talked to.
Nope, we don’t need hedders, custom cams, stock works great, no special intakes, and so on.
Even the new SVO has the turbo's away from the motor. It is starting to happen.

Sorry guys no fox

not sure

90stang5speed said:

Loftus,
If 2 to 1 back pressure to boost is the optimum setup, how & where do you measure the back pressure? I was thinking that I could use a cylinder compression tester & adapt it to be a peak hold back pressure gauge. I was thinking that if I drilled & welded a bung into the exhaust right before the turbo, it would give an idea of if I need to do anything with the AR of the exhaust housing.

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Anywhere between the manfold/hedder and turbo,the pressure will be equal.


Run it first, and like the rocker arms , cam , manifolds ,cryo bar on intercooler only mess with it IF there is a problem or poor performance.

The 2 to 1 thing was used to determine the correct combinations for the bolt on kit where hundreds of kits would be massed produced, and had a "stock"
motor and combinations of parts.

Agent 47

90stang5speed said:

Thanks for the info. The pic you posted last wont open for some reason. Also, what is this Cryo Bar?

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It was these neat side window/scoop deals from agent 47.
Yours are done so it was for the other kids to see.
@ the end I noticed they are sn95 and 05 and newer.

Well, this is pretty interesting.