Twin turbo's

[dieseldummy]

Ok, here it is. Me and a friend had have his pickup tore down to rebuild the motor. We kept thinkin' about it and decided we are going to try to build a twin turbo setup for his pickup. We were thinking that two GM-4 turbos would spool up quick enough and have enough top end to do what we want them to. We figured this using a turbo calculator. We are milling the pistons for a goal of 18:1 compression. Has anyone else tried this? If ya have any better suggestions for turbos let me know, we were going with the GM ones because that's what we have to work with.

On Edit: I forgot to ad that this is on a early 96 with elctronic injection, do ya think that a good reflash will provide enough fuel for that much air?
Justin

[Jim P]

I have no idea how the twin turbos will work but if it does, I would like to do it to mine too.

Just a few words of caution. The pistons have a ceramic coating on the top of them to help prevent damage from the heat. If you mill them, this coating will be gone. Also I think the 96s are the blocks that are known for cracking so it may not take the added stress of two turbos.

[Peter J. Bierman]

I suppose you have read my article on the Twin Turbo Diesel engine here in the diesel page.
There is a discription off what you are looking at
As for milling down the pistons, I think to get to 18:1 you have to take off too much to be sure of the strength of the piston and the cappacity to withstand heat, unless you have piston cooling.
I would go with the 18:1 pistons sold by many suppliers, or take off 1.5 MM and see where that gets you.
The GM4 turbo's seems kinda big for a twin setup but hey, they told me it can't be done :D .

One thing I know for sure, the electronic pump is not ever gona deliver enough fuel for this setup!
You have to go to at least a 4911 or bigger DB2.

Any way, you have to do what you have to do ;)

I had great fun and took pride in my project and can recoment to do a simmilar thing.

I can only advise to try to calculate things before you get started, so you more or less know what you are doing.

Goodluck and have fun

Peter

[grape]

.020" is enough to add 2cc's to the chamber which takes a 21.5-1 engine down to 19.5-1 at 400 cubic inches. I cut a stock piston in half on the band saw at the thinnest point the piston was over .480" thick. So yes it's doable, however taking two turbos designed for 400 cubic inches per turbo will drastiacally increase the lag. If you do twins you have to theoretically cut each exhaust a/r in half from the single set up.

[dieseldummy]

The reason we thought that we might be able to get away with to GM turbos is because we aren't to worried about quick spool. The primary concern is higher rpm's and lowering the egt's at those higher levels. The pickup doesn't need to be a race car off the line, but does need to have some good pulling power in the upper end. We are looking into ceramic coating the exhaust passageways, and thermal wrapping the outsides to provide maximum thermal efficiency of the motor.

[Peter J. Bierman]

I did some rough calculations on CR.
You have to take 1.5 MM off the poston deck to get to 19.5
Going to 18:1 needs 2.8 MM :eek:
If not going for high boost I'd go to 19.5 and still have stong pistons.

One other piont of consern is that you have not enough exhaust gas flow to spool up those two big turbos to the level were they make some boost.

Just a thought, good luck on your project.

Peter

[dieseldummy]

Peter,
Your project was kind of the inspiration for our try at this. Ours will be a low budget version however. :( We probably wont be able to obtain the desired 18:1 ratio, but we will be able to lower it. In the grand scheme of things the GM turbos will be replaced, if they are even used at all. We will probably give them a try, it's just a matter of switching them out if they don't work. Thanks for all the advice. I'll keep you all posted on progress.
Justin

[Peter J. Bierman]

I did start as a low budget project too.
In the end I did stay within budget couse of all the cheap or free Volvo parts.
But with everything working out so well, I expanded budget to whatever I can miss.
The marine pump was the most expensive till now.
I have late 6.5 heads, a 599 6.5 block, Humvee intake and 4L80e comming in. :D :D
I truely believe thats not the end of it :eek:

But if you do not go to 15 psi off boost or more you will be allright. smile.gif

Goodluck, Peter