GT Block conversion

[CLDFRZE]

So, I have read all I can read about how peeps have done the top swap on their GT's. On my end, I already have the GTP Supercharged, but am looking into converting to a GT motor with my top end. Reason being, well, my car has 216k on it, and I am gonna need new/rebuilt, or fairly used, so now is the time to decide.

Now, the GT peeps state to have the PCM tuned or leave it be, and allow it to adjust, if it can. My question is:

With me changing the motor, will I need to change the PCM to a GT? Will my GTP PCM auto adjust the timming, if need be, due to the difference in compression ratio?

The deciding factor is: Is it worth the work, for roughly only 5% more hp increase? If I decide to start to mod with smaller pulley, or better intercooler, will the higher compression ratio be a problem?

[Bio248]

no, leave your GTP PCM in the car. youll need it for your transmission, the injectors, and the fueling/timing it has.

the compression ratio is always going to force you to having more done than a normal GTP to run the same amount of boost. however, you should be able to make similar power numbers on less boost than a GTP modded in the exact same way.

either way, youre going to need some breathing mods (headers) and a good tune to make it work right. i would not just swap the block and expect it to run right.

[blueguy]

I'd swap the block...get a set of headers and have it tuned. Done...should run pretty good with a 3.8" and a good amount of timing tossed at it.

[CLDFRZE]

Sounds good. Headers aren't to hard to get, and it seems that is one of the first aftermarket parts everyone puts on anyways, so it will be easier to mount them with it out of car.

On the PCM, what's an average to expect for price to pay, when having this done? Will I need to have the car there, or just take the PCM to the peeps? Forgive my newbness on this, never had to retune a car. I usually deal with old school carberation. With the ability to just turn the distributor to adjust.

[Bio248]

you cant put headers on the motor outside of the car and still put the motor back in. headers need to be installed with the motor in the car.

youll need the car there. they will have to scan it, tweak it, scan it, tweak it, etc. until its right. it takes a while but it is well worth it when finished. a good tune makes or breaks these cars. in your case, without a tune your car will not run for very long since the boost on the high compression block is a cause for some serious detonation.

[blueguy]

Maybe read my Safely Modding your 3800 thread too? It has a lot of good modding information also. As for the PCM...I'd have it custom tuned. And since your in Wisconson, I know there are plenty of people up there.

[Sandman]

I'm thinking of doing the same thing to my car since I have a chipped piston. You will need flow mods, at least a plog and DP.

[blueguy]

Headers can be had for about the price of a DP and PLOG...so why skimp? Especially on a high comp build it HAS to breathe.

[matt5112]

Headers can be had for about the price of a DP and PLOG...so why skimp? Especially on a high comp build it HAS to breathe.

I was once told theres "other" ways to mod a car so skipping headers was a good idea and just running PEM's or stockers and an I/C with the smallest pulley possible.

Its odd those with money for an I/C can't afford headers which play a vital role in the quest for power.

[gtpinsc]

you cant put headers on the motor outside of the car and still put the motor back in. headers need to be installed with the motor in the car..

i did, during first motor swap.... SSAC knock offs.

[98GTPCALGARY]

I was thinking along the same lines, My gtp has 319,500 km on it, and my car needs paint, and full exhaust, and door hinges, and a rear side window.... (get the idea?) I was looking at some gt's and thinkin I could send my s/c and intake in to zzp, and getting "fresh" ones with porting. any advice?

[blueguy]

Save your money and get Reptile to do them...saves you tons of money for just as good of work if not better.

[98GTPCALGARY]

Save your money and get Reptile to do them...saves you tons of money for just as good of work if not better.

ok, thanks. but how hard would the whole job be?

[CLDFRZE]

@98GTPCAL, about a week ago I was on ZZP's site looking at stuff, and came across some read, where they talked on how some company's don't rebuild the S/C very well, because of the pressed bearings and what not. They mentioned of certain things are needed in order to do the procedure, and that's what sets them apart from others. Don't get me wrong here. I am, by any way, saying Reptile can't do it, all I'm saying, is that it seems to be quite the job, without the right tools.

I find it hard to believe, that I couldn't do the headers while the motor was out of the car, since I'm just going to drop everything out from underneath? It be easier that way. I hate messin with lining up the spline on the tranny and only having limited space. I'll have to look over the engine compartment alittle, and see what are my choices.

[matt5112]

ZZP says that about a lot of things... they ARE a buisness you know?

[98GTPCALGARY]

lol @ Matt.
And yes, with a bit of grunting, you should be able to install the motor with header from underneath, at least the rear header, might be easyer to slip the front one in after.

[minichopper6hp]

Spline on the tranny? This is an auto...

[Bio248]

why in the hell would you take the motor out the bottom? that is so much more work.

[CLDFRZE]

@minichopper: yeah, I forgot that you can just leave the torque converter atached tp the tranny. Been awhile since I have removed just a motor. I also deal more with RWD.

Anyways,I'm sure it is aleast alittle more work dropping all from underneath, than just pulling the motor, but not too much. I've looked it all over, and it isn't going to be like I will have to do the swap in one day, so I can drive my car the next. I'm going to take my time, and look at everything as it comes out. The car does have alot of miles on it, and I have no idea of what the condition is on all the other parts, except the fact that the tranny has been rebuilt recently. Got me some papers to prove that. Who knows when the struts have been done? It needs new front hubs, that has already been established. Sounds as though that the power steering pump is shot, or the rack and pinion is going bad, since I get a wine when I turn and it can be tough to turn from time to time. This is going to be quite the project, since the motor isn't the only thing I need to look at, so I am aproaching it that way, and deciding on what is easier all around for the job.

I do agree, the front header does look like an easy in and out, even with the motor in the car.