turbo setup, help needed.

[ryanelco]

ok, im going to be enrolled in an automotive engineering program at a local state university in the fall, and i am looking to get a little experience, and have a little fun. im looking into building a turbo setup for my 400. i have the front mount and a t3 garret turbo. i know the basic function of the turbo and how it works, but can i do it to my car? i was thinking if i modify the headers by running four seperate pipes off of each exhaust port into one pipe, which will lead to the turbo, then from the turbo to the fmi and then duct that pipe into a blow through carb. sounds simple enough, and thats why im nervous, i know the fabrication and tuning will be the most difficult, but other than a wastegate am i missing anything? can i run it off of only one header, i only want a single turbo, they are more efficient anyway. any suggestions are greatly appreciated. this looks like it might be my next winter project. im not looking for major boost nor am i looking for 4 digit horsepower (yet). i want to get the functionality issue sorted and then unleash the crazy!!!

 

[85 Cutlass Brougham]

Well for one, the turbo will be too small. That turbo isn't much good when you go past say 3 liters of displacement. Now, you could run twin T3's and maybe it would work, but one T3 on an engine that big is just a flow restriction. (IIRC, the T3 was factory on the 280ZX, and Ford 2.3 turbo 4's) You also want the headers to be stainless steel, and you would want to have the exhaust pulses of all 8 cylinders spooling it. Then you will need a blow off valve, something to cut timing as boost increases, etc. It is a plumbing nightmare. Yes, people make ghetto turbo setups at home all the time. It's not too hard if you have the technical knowledge and fabrication skills. However, you need to keep a lot of things in mind when you design the system, or all you will have done is waste time and money making the car run like crap. Research the compressor maps of the turbos you are thinking about before going any further. I have seen turbo mods that made less power because of poor design, like the FMIC that some friend's of mine installed on a DSM using pre-bent exhaust elbows and a MIG welder to replace the small stock SMIC. The changes added too much volume to the system and the small stock turbo took too long to pressurize it leading to excessive lag.

As for the fuel system, you need to decide if you want the carb to be pressurized after the turbo, or placed before the turbo. Before the turbo is not a great idea since fuel will puddle in the compressor housing and cause poor driveability and an unstable fuel curve. Blow through (after turbo) systems are better, but they do require a specially modified carburetor set up to run at greater than atmospheric pressure. Remember that a carburetor normally operates on a pressure drop based upon sea level atmospheric pressure of 14.7psi. Pressurize the carburetor, and now the fuel is being forced back into the carb, and the boost pressure works against the fuel pump too. This is why you need to boost reference the fuel pressure. There are too many details to get into here, but it is not something you do on a small budget.


BTW, I am an Engineering student too.

 

[midwestls]

I say, get it to work good. Then give it to me for testing purposes!!! 😀 Good luck keep us updated on what you do and how it works, very interested.

 

[ryanelco]

hmm interesting about the stainless steel headers, is that because of temperature? what size turbo do you think i should run? i really dont want crazy horsepower just yet, im really just looking for a functional setup thats different. will running it off of one header only severly compromise the functionality of it?

 

[midwestls]

I wouldn't necessarily say compromise it, remember the GN, Supra and some other cars only ran a single turbo, if you do it right, you do it right. But 2 turbos, thats what I'd shoot for. BOOST!!!!!!! 8)

 

[85 Cutlass Brougham]

Mild steel will crack due to heat. Stainless is very hard to work with though. As for a turbo, something like a T-78 would be more appropriate, but pretty expensive. The T-3 is nothing more than a flow restriction on an engine that size as it really can't feed more than maybe 300hp. A mild 400 should easily make that number N/A with a cam so mild it would almost idle down to 400rpm. You need to do A LOT more research before you begin this project. I had about a month or two into planning a ghetto turbo setup for a 1995 Sentra before deciding it was too much work and too much money. I was planning on using either a 1g DSM turbo or a T-25, T-28, or T-3 turbo for it as they were closest to the needs of the 1.6 liter 4 banger (but the GT28RS would have been sexier!). Remember that the popular turbo for the Honda VTEC crowd was a T-3/TO4 hybrid, and their engines were 1.6 or 1.8 liters mostly, with the wild ones having a CRVTEC with 2 liters. (One liter=61.023 ci) Oh, and don't get a Chinese knockoff turbo unless you like sending shrapnel through your engine. Get a genuine Garrett, Mitsubishi, etc. turbo.

 

[megaladon6]

you don't have to use stainless steel headers, but you do need good steel. matter of fact there have been alot of problems with stainless headers cracking due to poor quality and alloy mix.
you can run a single turbo, but it must be fed off of both engine banks.
is the 400 already built? if so what's the compression? remember that forced induction requires you to lower the compression ratio. IIRC with approx. 9.5:1 you can run 8psi and 12 with an intercooler. if you drop to 8:1 you can more than double those numbers. those are approximate numbers, good for a guideline only.
considering the cost and the tuning difficulties of a carb, it may be cheaper to go EFI, it's definately easier.

 

[85 Cutlass Brougham]

The issue a lot of stainless headers have is that they are made from very thin material to keep costs down. Plus, if it is not built to hold the weight of the turbo, the weight will crack it too. This tends to happen with the cheap Ebay turbo headers that are sold for $100 to ricers who don't know any better, usually made by companies like OBX.

 

[ryanelco]

the compression ratio is 8.5:1 right now and the motor made about 375 horsepower. i know this isnt gonna be an over night project, but one im looking forward to working with, i hope nobody minds ill be asking a lot more questions and for many more opinions, any information is greatly appreciated. iirc twin turbos use two different sized turbos, the smaller one spools the larger one. is that in fact better for my setup or am i better off with a single? im also looking at theturboforums.com and one guy used e bay f-body headers so im looking into that as well, im curious if that obx company supplied them or not, but his malibu set up looks pretty legit. thanks, ryan.

 

[megaladon6]

i don't know if this is exactly correct but a dual or twin turbo setup uses one turbo on each bank, sometimes they only feed the one intake bank and sometimes they combine at the intake but they are fed by seperate exhaust banks. a bi-turbo uses 2 staged turbos, one small one to spool quickly and feed the low end and one large one to feed the high end. this is more complicated as you need to bypass the smaller one at the right time to keep it from being a restriction.
another way to do it, but the turbos are VERY expensive, is a VGT turbo. it has variable pitch vanes to spool quickly and then move to a higher boost/speed position for the high end. this is what most companies are going to for OEM applications.
i've actually seen a story on a home built setup that used turbo's from a john deere diesel tractor!! it took awhile to figure out what he had and where to get the right flanges, but damn if that car didn't move