What does it take to use a G-head

[1983Rampage]

Well, I am looking at possibly removing the 782 head on my car due to a possible blown head gasket But I was wondering what it would take to swap the head over to a 287 or 445 head? I have one of each laying in the shop and am kicking around the concept of putting one on the car. The engine is a 2.5l Turbo engine with a stock bottom end. I know swapping the heads with the stock bottom end would change the compression ratio, which I didn't know if that would be bad, or be alright to run. But I have a 60 trim turbo with FFV injectors. But I was looking at using those on the head as well. But any help would be appreciated. Thanks.

[Tbone]

The piston dish on the swirl head pistons was 14.5 cc vs. 9cc, therefore you will lower your compression. It will go down to about 7.66 CR with the G head. Stock compression is around 8.1:1. Also, your spark timing will be way to retarded for the G-head. You will need a G-head calibration. The timing is more aggresive to make up for the lack of swirl/homogeneos mixture. If you have the right calibration, you could make it work well.

[1983Rampage]

Yah, I called Cindy from FWDPerformance.com and we talked about getting a custom cal for the car. But she also said something about changing the timing on the cam by 14 degrees (but I forgot it that is ahead or back), so I would need to know about that a little more. And she told me about the reduction in compression (which I expected) down to 7.5 or so, which the 7.66 would be a little more exact.

[puppet]

Expect higher EGT's due to the lower compression as well.

[1983Rampage]

would it be anything that would run the risk of detonation?

[puppet]

Higher EGT's don't automatically mean detonation. ... melting things, yes.
Parts downstream ... like the turbo will be hotter, exhaust valves, pistons. Depends a bunch on your tune though.

The lower compression allows you to run more boost but it isn't a free lunch.

[1983Rampage]

Hmm, that may be something that is doable then. Do you know what kind of timing I need to do then? AKA, can I just set the cam forward or back a tooth or 2 to work better?

[4Daytonas]

Quote:

Originally Posted by 1983Rampage Hmm, that may be something that is doable then. Do you know what kind of timing I need to do then? AKA, can I just set the cam forward or back a tooth or 2 to work better?

Retarding or advancing the cam one tooth is 9 degrees.If you retard it one tooth you will kill your low end .you;ll be winding to 3500 before you get any boost and you will hate it.I just put a2.5 together and it didn't have any low end .I was real dissappointed in it-hell my 84 would out run it.Well I thought I'd advance the cam a little and when I pulled the cover off my cam was fully 12 degrees retarded.The bolts were not tight from the factory on the Adj gear!.I advanced the cam to actual 3 degrees and now it flies!One tooth advance will make it run out of breath about 4800.I'm using a ported G head and a 85slider cam.just run the cam straight up and you'll be ok

[1983Rampage]

Well, I am looking at possibly swapping over to either a roller TBI cam or something a little more aggressive.

[4Daytonas]

The stock turbo slider IS a little more agressive than the tbi roller.

[1983Rampage]

I thought it was more aggressive then the roller turbo cam, but the roller 88 TBI cam was the best stock cam from the factory. It was kinda of the strange year from the factory.

[detobias]

Quote:

Originally Posted by 1983Rampage she also said something about changing the timing on the cam by 14 degrees (but I forgot it that is ahead or back), so I would need to know about that a little more.

I think she said "4 degrees" since that is the offset you get when switching from round <-> square tooth cam gears

BUT that is debateable topic with some claiming there is a Zero offset

WRT cam choice, various cam grinds, etc - topic has been covered MANY times ; search forums, there are websites with actual cam specs, etc; your choice depends a lot on your usage & goals & engine/body/trans etc...

I have a 'GLHS-style' TII 2.2 A413 in a *light* street/strip car ; I like the softer hit and big Hp that my 89+ TBI gives as it is (sposedly) retarded 4 degrees on my 86 motor

[puppet]

The turbo slider has more duration than the TBI cams and more overlap.

FWIW all the TBI roller cams are the basically the same. One isn't better than another from any year.

[puppet]

Quote:

Originally Posted by detobias I think she said "4 degrees" since that is the offset you get when switching from round <-> square tooth cam gears BUT that is debateable topic with some claiming there is a Zero offset

Want to make a believer out of you.
Take a spare head w/cam installed and put a sqth sprocket on it. Line up the cam gear with the arrows aligned with the #1 bearing cap base. Take off the sprocket and install a #557 rdth in it's place. Look at where the arrows are aligned. Same place ... end of the BS stories.

If you replace the sqth sprocket with a #690 rdth you'll see 4* retard from the marks. <---- easy way for a guy to retard a cam without an adjustable gear. Pretty sure this cam sprocket came to be because of the later 2.5 engines (after '89 when Mopar stopped grinding 9* RET into cams special for the 2.5) They could use the same cam grind w/5* RET and just swap in the other sprocket, now the cam has 9* RET for the 2.5 .... done.

'88 on up 2.2l TBI cams might like this. They are all ground w/5* RET (factory) ... and they are all the same.
'88 and '89 2.5 TBI cams are ground w/9* RET (factory). <--- only two years. Otherwise, the timing events as they relate to each other, duration, lift, etc are the same as all other TBI cams.

So, pick a cam and dial it in. No need to search out a specific year. Best TBI roller cam is one that isn't worn out.

[Juggy]

G head likes timing, youll get the most out of the head with a custom calibration meant for the head.

I had ran my head on the 2.5L b4, it worked out pretty good but expect high EGT's on the 2.5 G head combo (1600-1700)....switched to 2.2 now and dropped 2-300 degrees on the temps