Hot Rod Forum banner
1 - 8 of 8 Posts

·
cutouts and 7k shifts = cops
Joined
·
60 Posts
Discussion Starter · #1 ·
Hi,

I was wondering what it would take to knock back my compression to about 8.5:1 so I could screw on a procharger and run it at about 5-6 psi.

heads I am running now are Dart iron eagles w/ 215 cfm intake ports, and 72 cc chambers. pistons are speedpro H616p's, yeah, I know their hypereutectic's, but I'm not going to run big boost for now. I will change the pistons when I rebuild the motor later on. engine is .030 over, and I would run a much milder solid flat lifter cam than the .630 in. roller in it now.

Is there a head reccomendation that would knock the compression down to reach my goal, or do my pistons have me stuck here?
 

·
Registered
Joined
·
96 Posts
what compression do you have now?

i don't know those heads but the only way would be to open up the chambers on the heads and wack the tops off the pistons. if you've got 10to1 you'll need to lose 13cc some where to go down to 8.5to1.

best bet is to wait until you get new pistons.

edit sorry i did see where you asked for different heads. if you post what your compression is know i'll tell you what size chamber you need to look for.
 

·
Registered
Joined
·
17,613 Posts
According to a chart on flatlander's, your c.r. is 9.99 with 72 cc heads. It also shows a c.r. of 9.62 with 76 cc heads, the largest that I know of for a small block. Looks like maybe there's a piston change in your future. Using the calculator on KB, with a bore of 4.155", stroke of 3.750", 72 cc heads, Chevrolet 10185054 head gaskets (4.166" X 0.041"), zero deck and 30 cc dish in the piston, you'd be at 8.498....that's about as close to 8.5 as I can figure for you.
 

·
Save a horse, Ride a Cowboy.
Joined
·
5,122 Posts
Some people (Steve Dulcich) have had success with thick copper head gaskets. This usually necessitate a thicker or even 2 intake gaskets on each head.

It works. Since deep dish pistons don't have quench anyway,

the combustion effects seem to be ok by using a thick head gasket on a quench head.

That's what I would do. :thumbup:

Usually 5 psi is acceptable on 9/1 compression, especially with a centrifugal blower that is rpm dependent and does not build as much boost at lower rpms.

You might ask the blower companies for recommendations.
 

·
cutouts and 7k shifts = cops
Joined
·
60 Posts
Discussion Starter · #5 ·
thanks guys.

the engine builder claims I am at 10.2:1, and the deck is .020, fyi. I think the head gasket is at .030 or .037.

Run 2 head gaskets?? really? I am curious if that would hold together for a couple of blasts down the track. hmm.

looking into building a bullet proof short block, but all I can find are 350's around here. I love the 400 cube SBC. it's got the torque down low to push my sled.
 

·
Save a horse, Ride a Cowboy.
Joined
·
5,122 Posts
mad55chevy said:
thanks guys.

the engine builder claims I am at 10.2:1, and the deck is .020, fyi. I think the head gasket is at .030 or .037.

Run 2 head gaskets?? really? I am curious if that would hold together for a couple of blasts down the track. hmm.

looking into building a bullet proof short block, but all I can find are 350's around here. I love the 400 cube SBC. it's got the torque down low to push my sled.
:nono: NO, NO, NO, I did NOT say that. :rolleyes: :rolleyes:

I said, thick copper headgaskets, which raise the head up off the block farther,

which also makes the heads farther apart,

which will necessitate thicker intake gaskets...... often 2 intake gaskets on each side. It is a put-it-on and measure the intake gap.


This has been done for years and gaskets are made for this purpose.
 

·
Banned
Joined
·
1,680 Posts
mad55chevy said:
thanks guys.

the engine builder claims I am at 10.2:1, and the deck is .020, fyi. I think the head gasket is at .030 or .037.

Run 2 head gaskets?? really? I am curious if that would hold together for a couple of blasts down the track. hmm.

looking into building a bullet proof short block, but all I can find are 350's around here. I love the 400 cube SBC. it's got the torque down low to push my sled.
If your looking to build a bullet proof short block you may want to start with a Dart Or Bowtie block as we have seen over the years some 400 blocks that have not stood up very well and we have NOT seen the same problems with the Dart or the Bowtie blocks as those are Bullet proof compared to a stock GM block.
 

·
Registered
Joined
·
10 Posts
I've built a few 383 with the help of a compression simulator found on this site http://cochise.uia.net/pkelley2/index.html
A blower motor will need to be designed from the crank up with attention to CR. Steel crank, forged dish pistons, stage 2 rods or better, blower friendly cam with less overlap, and a good flowing head with the right size CC.
I prefer to shorten the deck to minimize quench area that will help on pre-detonation that lets you run lower octain on higher compressions. I keep a minimum of .040 clearance for head to piston interference without any problems so far.
WORLD makes a good block that can go up to 427+ with the right parts.
Lots of $$$$$$ and lots of luck.
Arlo
 
1 - 8 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top