Increase CR with head gasket?

modusmortis

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Aug 3, 2006

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Nov 21, 2006

#1

• Nov 21, 2006

• #1

So i'm looking at getting some afr 165's with the 58cc combustion chambers in the future, and was looking at other ways to safely increase the Compression ratio, since im going NA. Plus I live at 5200ft above sea level so I'm trying to get back some lost hp.

Basically I've seen some head gaskets that offer a smaller compressed thickness as compared to a stock style head gasket. Is there any disadvantage to using these? Do they seal as well? I've seen the cometic sets but they require me to smoothe the deck surface beyond what I can do by myself with my basic hand tools. Is there any thin gasket that I can just do some normal deck cleaning and bolt on?

All in all, I figure a thin headgasket should be worth about a point and a half increase in CR, but every bit helps right? (I mean .15 not 1.5 here)

btw, before anyone gets all bent out of shape I've been spending the last two days using the search button.

Thank you in advance for any and all help.

 

8

86bluecobra

Advanced Member

Dec 20, 2004

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B.C. Canada

Nov 21, 2006

#2

• Nov 21, 2006

• #2

I'm not sure on specific head gaskets but you are correct that you will increase your compression ratio. look through the summit catalog there are head gaskets with lower thicknesses that should work. Any chance you can have the 58cc heads decked further?

 

352Ford2

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Oct 12, 2005

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Nov 22, 2006

#3

• Nov 22, 2006

• #3

Yes, but it is far more important to nail down your quench clearance. If too tight piston hits cyln head, if too loose engine doesn't make any power, and runs like crap. I always pick my head gaskets to get the the quench clearance I am after

 

modusmortis

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Aug 3, 2006

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Nov 22, 2006

#4

• Nov 22, 2006

• #4

you're talking about ptv clearance right? I'll have that figured out when I get my custom cam decided. Right now I'm just trying to figure out ways to get my CR up.

I've thought about shaving the heads but I'm a little leary of doing that with some $1300 heads. Plus I don't know any good machine shops around here anyways. I've heard that when you do that you have to shave the lower intake too.

 

65ShelbyClone

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Sep 9, 2000

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Antelope Valley, SoCal

Nov 22, 2006

#5

• Nov 22, 2006

• #5

modusmortis said:

you're talking about ptv clearance right? I'll have that figured out when I get my custom cam decided. Right now I'm just trying to figure out ways to get my CR up.

I've thought about shaving the heads but I'm a little leary of doing that with some $1300 heads. Plus I don't know any good machine shops around here anyways. I've heard that when you do that you have to shave the lower intake too.

Click to expand...

The quench clearance is the distance between the piston crown and that flat spot of the head next to the chamber. If the quench is too tight, the piston can slap the head and cause big problems. If the clearance is too wide, it can reduce ping resistance.

I personally wouldn't mill a set of brand-new heads unless it was for a maximum-effort race engine and was necessary to so things right. If you're going to build the whole engine, maybe look at some mildly domed pistons or maybe even a stroker kit. I suspect you want to put the heads on a stock shortblock, though. In that case the options are limited. I put Edelbrock Performers(60cc) on my roller 302 with flat tops and only landed about 9.5:1. Now that the engine is out of my '89GT daily driver and in my '68 non-smog toy, I wish I had gone more agressive.

 

mstngjoe

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Jul 26, 2002

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Nov 23, 2006

#6

• Nov 23, 2006

• #6

modusmortis said:

All in all, I figure a thin headgasket should be worth about a point and a half increase in CR, but every bit helps right?

Click to expand...

Just as an example: All other things being equal if you went from a .045 compressed head gasket to a .040, your static c/r would increase approximately 0.13.

As you see, getting an increase of "a point and a half" ain't gonna happen with just a skinny head gasket in most cases.

The most important question is: What is your piston to deck clearance going to be?

 

thumper460

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Jul 24, 2000

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Orange Park , Fl

Nov 23, 2006

#7

• Nov 23, 2006

• #7

the thinner gaskets will allow maybe two or three TENTHS!! not points!! cool??

Heads.. mill the suckers!! ruff rule is .005 off is 1 CC, you dont have to mill much to get 54 CCs and then you should be around 10:1 ( 58 CCs mill off .020 = 54 CCs)

OR .. when you have the cam made ( custom ) have then make the ICL at 104 or 106 ICL to increase the compression thru the intake valve closing sooner!!

Only really two ways !! Oh yeah Pistons also!! that makes 3 ways!! the easyest is the cam advance!!

Just me..............................

Thumper

(Ps: Millinf a new set of alum heads is pretty common!!)

 

W

wicked84gt350

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Aug 20, 2006

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West palm bech florida

Nov 23, 2006

#8

• Nov 23, 2006

• #8

Dont mill the heads big mistake unless warped, mill the block much better choice. You can have the block parrell decked and you will get the compression you want not to mention the compression will be exactly the same across all cylinders. You can usally get away with milling .015 and not have to cut the intake. But every casting is different. A parrell deck will go for 160~200 not to mention it is better for the heads, scealing, and resist warping the heads better. And the motor will be much smoother.

 

modusmortis

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Aug 3, 2006

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Nov 26, 2006

#9

• Nov 26, 2006

• #9

Thanks for all the replies!

yeah that's what I meant was just a .15 increase in comp. Not 1.5.

I figure I'll get around 9.6:1 comp with the 58cc combustion chambers and a .040 headgasket. Which will be quite an increase from the 8.8-9.0 stock CR.

Does anyone know a good headgasket that I could use, that I wouldn't have to have the block deck professionally surfaced?

Piston to deck clearance is going to be calculated with a completely stock bottom end. So essentially I'll be flush with the deck at TDC if not a little below.

 

S

SmockDoiley

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Jun 14, 2003

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San Diego, CA

Nov 26, 2006

#10

• Nov 26, 2006

• #10

To be honest, I think you are puting way too much stock in squeezing out more power from CR. You run into too many issues, and too much money just to get a few extra horses if that. Dont waste your time milling anything for several reasons. Milling brand new heads on a street motor means you have one less chance of fixing anything if you ever warp them. You can also run into clearance issues with the piston and valve train geometry. If you only take a little off, you shouldnt have to worry about milling the intake though. If you mill the engine, then you need to dissamble it and take it to a machine shop. Is it really worth it?? Just be happy with 9.5 and get your power somewhere else. I mean do you really want to push it and be forced to run premium all the time with these prices. You wont even notice a difference in your pants or the track, except in your wallet.