G head

[csteffee]

I've been thinking of picking up a "G'" head that's been mildly ported and polished then shaved to the same cc's as a fast-burn combustion chamber. Is this a good idea?

[BadAssPerformance]

depends what you're going to put it on.

[csteffee]

Common Block T-II with swirl head pistons.

[BadAssPerformance]

I meant how big of turbo, how much boost, how big of injectors, poted manifolds, etc...

[turbovanman²]

What kind of car/van?

[csteffee]

Planning on running stock turbo, ported exhaust manifold, 3" exhaust, stock 1-piece intake, TB, & IC regular T-II inj with Adj. FPR, GLHS Stage II Comp graigered to 18psi. Road racing an Omni and figure I need to keep the horsepower below 300.

[GLHSKEN]

If you are road racing, you will need throttle response. Basically you are looking at a stock +fuel, boost and exhaust car.

#1 That's on the edge for stock injectors. #2 you will max out that combo at about 260-270 whp. That combo is better off with a swirl. G head is great for high boost 2.5L

[csteffee]

Why would I get better response with the swirl head? If the G chambers are cc'd to match would there be that much difference? Not saying your wrong, just trying to understand how your right. Are the flow characteristics that different? (BTW the valves are also backcut).

Also what injectors would you suggest for this set-up? (with the swirl)

[turbovanman²]

Why would I get better response with the swirl head? If the G chambers are cc'd to match would there be that much difference? Not saying your wrong, just trying to understand how your right. Are the flow characteristics that different? (BTW the valves are also backcut).

Also what injectors would you suggest for this set-up? (with the swirl)


The chamber is larger on the G-head so to match the Swirl head, you would need to weld up the chamber or mill the crap out of it. The design of the Swirl is to build better throttle response, the chamber design is the reason.

Based on what your doing, +20's should cover it.

[The S is Silent]

The chamber is larger on the G-head so to match the Swirl head, you would need to weld up the chamber or mill the crap out of it. The design of the Swirl is to build better throttle response, the chamber design is the reason.

Based on what your doing, +20's should cover it.

That's what he is asking about. Use a G-head on a block with swirl head pistons to get the better flow properties, and then mill the crap out of the head so the compression doesn't drop.

I'm curious to know if this will work as well.

[BadAssPerformance]

It should work out... how much does the compression drop? Is it worth it?

[puppet]

He'd be looking at taking .063" off the "G" to equal up the chamber volumes.

[GLHSKEN]

Then you have MAJOR timing belt issues. If the car is a 2.2L... run the swirl.

[puppet]

They still make that shorter belt? ... and he'd be 5-6*retarded.

[GLHSKEN]

They still make that shorter belt? ... and he'd be 5-6*retarded.

WAY too much. You would need an adj sprocket.

[puppet]

Yep ... that's another $120 bucks or so.

[GLHSKEN]

Yep^%^^ for a 2.2, the swirl is the way to go. with stock pistons and a 2.5L... chrysler compromised (imho)

[csteffee]

In response to all the responses.
1. Yes the G head has been milled approx .62 ( head had been surfaced couple of times before)

2. I have the larger tensioner pulley (brand new)

3. I also have the full set of offset cam keys

4. Don't you advance cam timing with a round tooth sprocket on a square tooth sprocket cam? (Roller cam out of a Shelby Lancer)

+20% injectors it is

[tryingbe]

Where can I found a larger tensioner?

[turbovanman²]

Where can I found a larger tensioner?


88 2.5L TBI non common block.





3. I also have the full set of offset cam keys

4. Don't you advance cam timing with a round tooth sprocket on a square tooth sprocket cam? (Roller cam out of a Shelby Lancer)


I would get the adjustable sprocket, so much easier. I have used both and will never use the keys again, I can adjust my cam timing in sec's.

Roller cam using square tooth is 4 deg retarded-so yes, you advance it. You now you would be aprox 10 deg retarded. If the above math is correct.

[MiniMopar]

If the camber has the same volume, then the only difference is the flow characteristics. The swirl will provide faster and more complete combustion, which should help things like torque and probably spool-up. The delta may be neglidgable at high output level, though.

The downside of the swirl is it has more hot spots, which make it more prone to detonation than a G-head. The chambers can be reworked a bit on a swirl to supprerss this, though.

So all things being equal, if you take a milled G head like this one and a swirl head with a reworked chamber, I don't think anyone really knows which one will be better. There are so many other factors, like cam, turbo, etc. Since you already got it, may as well run with it.

[csteffee]

Isn't one tooth off on a sprocket approx. 10 degrees?

[turbovanman²]

Isn't one tooth off on a sprocket approx. 10 degrees?


I seem to remember 18 deg for one tooth.

[csteffee]

Are adjustable sprockets easy to use? How do you find your base static time?

[turbovanman²]

Are adjustable sprockets easy to use? How do you find your base static time?


It has a large mark for TDC, then on either side, you have little marks that are 2 degs each. Mine has 4 allen screws that you loosen for adjustment. I marked all mine with Black pen to see the marks easier. I simply set the gear facing down so I can see my marks, loosen screws, turn the cam with my 18mm wrench, move it whereever I want and tighten. Probably takes a whopping 1-2 minutes start to finish.

[The S is Silent]

You are both pretty much correct. There are 40 teeth on the gear, so that means 9 degrees of cam timing per tooth. BUT, the cam turns once for every 2 rotations of the crank, making it 18 degrees of crank timing per tooth. I don't remember which, but this was covered in a different thread recently.

edit: search and ye shall recieve.

http://www.turbo-mopar.com/forums/showpost.php?p=50417&postcount=5 :thumb:

[csteffee]

Thanx Matt. Don't know why I didn't put that together on my own. Simon, where did you get your adj cam procket?

er, sprocket

[turbovanman²]

I got mine thru the for sale section, its a Gary D unit but if you can't find one, then www.fwdperformance.com sells them, there around $125