hey everyone name is montie.I drive a 1993 3000gt sl engine blew up need help im buying a jdm engine for it,but while its out i want to do a twin turbo conversion what do i have to change to bring my compression from a 10.1 to 8.1 never done a project this big.... also trying to stay away from messing around with the pistons so maybe just a thicker head gasket and vr4 head??? help please thanks guys.

 

You CANNOT change the compression ration without replacing pistons. The pistons are the ONLY thing that will give THAT much of a compression ratio change period. Unless you plan on buying custom designed and built rods that are shorter than stock, but at that point you'd be better to just do the pistons.

Also you might want to look into exactly what work you're going to need to do to perform this conversion. It's not nearly as simple as slapping in 2 turbos and replacing the exhaust. You'll have intake issues to worry about, internals to worry about, an inadequate fuel system to reconfigure, an ECU that isn't built for turbo applications to replace, ect.

Since we're on the topic of turbo charging an (I'm assuming) N/A engine and the pistons, you'll want to replace both the pistons AND the rods anyways. Rods made for turbo applications are MUCH tougher than regular rods. Pistons will give you the 8.1 ratio you need. And let's also consider the crank. Most turbo cars have nitrided cranks to assist in withstanding the extra abuse they will receive. So think long and hard about how much you want to put into this project and what you REALLY want to do before jumping on the TT bandwagon. It's ALOT of work and will cost a good amount. I rebuilt my engine to withstand higher pressures and more abuse and my car was already a turbo to start with. I now have close to $4k into the engine and exhaust alone and I haven't even gone MPI yet.

Anyways if you DO decide to continue on this project, I'm sure we'll all be glad to help but PLEASE pay attention to which section you're posting in. You have a 3k GT post in that section not the Outlander section. You'll get ALOT more answers that way. Thanks.
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Buy a Vr4 engine. You will need:

Engine, Intercoolers and intercooler piping, ECU, Injectors, Turbo wiring harness (corresponds to the year engine, and ECU year), turbos, turbo fuel pump, etc, etc.


You're looking at around $3500 or so for just the parts.

You're better off just swapping in a stock 10:1 N/A engine, selling your car, and buying a vr4.

 

He's a 93, so, he already has a forged crank. There is no difference in the crankshafts from the turbo to N/A models. they are the exact same part/part number.

 

the heads would be the way to go, you will also need the vr4 cams. the lobe profile of the cam and the heads will be enough to lower your compression. the best turbo set up would be to get the stock turbos out of a vr4. 1st gen or 2nd gen it doesnt matter. same turbo different psi. also it will bolt up to your heads all you will need is the other pipes and turbos

 

Uh.... no. Please don't give information on a subject you are not knowledgeable about.

Cylinder heads, and cams will not change the compression. Compression is determined by the piston/rod and crank assemblies.

And the stock turbos will NOT bolt up to N/A heads, unless you install turbo manifolds.

 

Exactly. I'd love to see where the information you're getting tells you that you can lower compression with heads futhey. There's not a vehicle out there that you can lower the compression via heads. You MIGHT be able to get .1 or .2 lower with a head IF you go extreme which is NOWHERE near what he needs to drop it. You're going to need to either change the stroke length or the pistons themselves to give you THAT much of a change.

And Girly, thanks for clearing up the crank thing. I know some vehicles don't have forged or nitrided cranks for N/A applications. I.E. the Dodge Caravan uses the EXACT same crnk as my Chrysler Conquest BUT the block is different and my Conquest crank is nitride treated whereas the Caravan crank is not. So I was running off prior experience with turbo vehicles not much in the way of this models specific specs. Yeah yeah I know keep my mouth shut about things I don't know about... But at least I wasn't telling him heads will give the compression change he wanted...