How much compression can you drop from porting heads?
Thread Starter
Joined: Nov 2001
Posts: 8,259
Likes: 4
From: Valrico, Florida
How much compression can you drop from porting heads? I have some 5.7L's in the garage. I was planning on going with the 6.0L heads, but after a few post that have verified that these heads do not drop compression as much as we thought. I figured I could save the 450 bucks and try to get the 5.7L heads down to below 9.5:1. I am not changing my forged pistons now. My shortblock is already together. I am trying to achieve 600rwhp on a 346ci forged shortblock. What are your suggestions? If anyone even knows...
Re: How much compression can you drop from porting heads? Vince,I dont think there would be an advantage with the 6.0l heads over the 5.7l heads.The 5.7 heads actuatly have a better exhaust port,and can achieve 9.2-9.5 comp. once unshrouded and reworked,and just a surface deck.And you already have the 5.7 heads <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
With the right heads\cam\turbo setup and tuning,your goal will be easily surpassed <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> <img border="0" alt="[hail]" title="" src="graemlins/gr_hail.gif" /> <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />
With the right heads\cam\turbo setup and tuning,your goal will be easily surpassed <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> <img border="0" alt="[hail]" title="" src="graemlins/gr_hail.gif" /> <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />
Thread Starter
Joined: Nov 2001
Posts: 8,259
Likes: 4
From: Valrico, Florida
Re: How much compression can you drop from porting heads? Thats what I wanted to hear.. Thanks Allan.. Now I do not have to purchase the 6.0L heads.. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> One thing down..
Re: How much compression can you drop from porting heads? i belive the 6.0 heads flow better then the 5.7's since there modeled after the ls6 ports.
its easier to get the 6.0 heads to have larger chambers, but you can work the 5.7 to have the same chaber sizes, maybe.
its easier to get the 6.0 heads to have larger chambers, but you can work the 5.7 to have the same chaber sizes, maybe.
Re: How much compression can you drop from porting heads? 600 rwh on stock bottom end, thats pushing it, how long do you plan for your engine to stay in one place.
that would be sweet though, good luck, whats your set up gonna be.
Im hoping for 450-500 rwh on pump gas. I plan on droping the compression to about 9.1:1. geting cometic gaskets and apr head bolts, if im going broke, might as well go broke. <img border="0" alt="[Fluffy]" title="" src="graemlins/fluffy.gif" />
that would be sweet though, good luck, whats your set up gonna be.
Im hoping for 450-500 rwh on pump gas. I plan on droping the compression to about 9.1:1. geting cometic gaskets and apr head bolts, if im going broke, might as well go broke. <img border="0" alt="[Fluffy]" title="" src="graemlins/fluffy.gif" />
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Re: How much compression can you drop from porting heads? well, through the use of head thicker gaskets and porting your heads you could get down to 8.5:1, but you'll be using a real thick head gasket, not sure i would.
My set up is about to consist of 6.0 heads, chambers increased to 72cc fron 69cc, .078 cometic mls headgasket, APR 12 point head studs. stock bottom end.
This combo will put me at 9.11:1 CR.
hope to run 7-9#'s on pump gas. at about 450-500rwh.
My set up is about to consist of 6.0 heads, chambers increased to 72cc fron 69cc, .078 cometic mls headgasket, APR 12 point head studs. stock bottom end.
This combo will put me at 9.11:1 CR.
hope to run 7-9#'s on pump gas. at about 450-500rwh.
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Verdad Gallardo Re: How much compression can you drop from porting heads? just checked a 73cc chamber will get you 9.5:1 CR
that should be achevable.
http://www.rosspistons.com/CR%20Calculator.htm
that should be achevable.
http://www.rosspistons.com/CR%20Calculator.htm
TECH Regular
Joined: Feb 2002
Posts: 414
Likes: 0
From: the moon
Re: How much compression can you drop from porting heads? If you can handle some die grinder and carbide cutting work it's quite easy to get 73cc chambers-
https://ls1tech.com/ubb/cgi-bin/ulti...;f=20;t=000626
Just use an old set of valves to protect the seats and clamp an old gasket on the deck to protect the head surface.
Scribe the heads to match a stock set of graphite gaskets which is a 4" bore.
You then remove that material and maybe recontour the plug boss and you can remove a quick 3.5cc or so and fully deshroud the valves.
Don't take anything off from the quench side.
You will need some equipment to cc the chambers though as eye balling it won't be accurate.
After using any large bore head on a stock bore 346 you should radius the block nicley along the edge of the cylinders or you will leave a sharp ledge.
Steve
https://ls1tech.com/ubb/cgi-bin/ulti...;f=20;t=000626
Just use an old set of valves to protect the seats and clamp an old gasket on the deck to protect the head surface.
Scribe the heads to match a stock set of graphite gaskets which is a 4" bore.
You then remove that material and maybe recontour the plug boss and you can remove a quick 3.5cc or so and fully deshroud the valves.
Don't take anything off from the quench side.
You will need some equipment to cc the chambers though as eye balling it won't be accurate.
After using any large bore head on a stock bore 346 you should radius the block nicley along the edge of the cylinders or you will leave a sharp ledge.
Steve
Re: How much compression can you drop from porting heads? If you go 6.0, you'll be putting heads made for a 4.000 bore onto a 3.900 bore shortblock. Not sure how I like that.
TECH Regular
Joined: Feb 2002
Posts: 414
Likes: 0
From: the moon
Re: How much compression can you drop from porting heads? I don't think it's a big deal John especially if you radius the bores a little where needed.
The small block chevy typically used a 4" bore and a 4.125" chamber head.
The small block chevy typically used a 4" bore and a 4.125" chamber head.
