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Compression change

  
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Compression change

 
rick539 rick539
I love my Chevy Chevette! | Posts: 2 | Joined: 11/13
Posted: 11/02/13
06:39 PM

I am wanting to increase the compression and flow in  my 383 stroker. I thought I would do it by changing my heads that flow 185 with a 70 cc chamber to a 215 with a 64cc chamber.  If the deck thickness and gasket thickness is the same, it should not change my valve to piston clearance, right?  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 11/02/13
08:41 PM

You didn't state what you want to do with your 383.

1.Do you want to race it and keep it as a race engine only?

2.Is it going to be used for street/strip combination?

You can increase the compression by using.....

3.Steel shim head gasket

4.Get a higher compression type head

5.Mill your head as far as you can. (Doing that causes so many problems)
A. You will need to mill your intake manifold
B. You may have to mill the top of your piston even if they are not high
compression pistons, it will be the angle the piston sits in the bore.
C. I would not go this route because it is time consuming and the parts you may need are only special order. You can wind up with water leaks between the intake and the heads.  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 11/02/13
08:41 PM

You didn't state what you want to do with your 383.

1.Do you want to race it and keep it as a race engine only?

2.Is it going to be used for street/strip combination?

You can increase the compression by using.....

3.Steel shim head gasket

4.Get a higher compression type head

5.Mill your head as far as you can. (Doing that causes so many problems)
A. You will need to mill your intake manifold
B. You may have to mill the top of your piston even if they are not high
compression pistons, it will be the angle the piston sits in the bore.
C. I would not go this route because it is time consuming and the parts you may need are only special order. You can wind up with water leaks between the intake and the heads.

The logical and easiest way to build compression is to determine what compression ratio you want. Then order new pistons and work with them. I know they are expensive, but the only way to do it right.

If your looking to increase the flow of your heads. Again not knowing what heads you have?
D. Have you heads professionally ported and flowed. It's also expensive as it is very time consuming.
E. Again I would purchase better heads with a higher flow rate. Stay around 200 to 220 CFM. Intake and exhaust valves play a part in how your head moves air. Cool  
F. Just a little FYI. Don't get heads so big your cam will need changing also.
G. Just another FYI. I don't care what mods you make, just make sure you have at least
H. .100 Exhaust .080 Intake if you are using Steel Rods. Grin   Cool

I. .120 Exhaust .100 Intake if you are using  Aluminum Rods. Grin   Cool
J. Now your carburetor may need changing or re-jetting.
K. Have a good ignition system. MSD, Mallory et cetera.
POST THE HEAD PART NUMBER. I'm sure someone can help you.

Good Luck

Bob

"NO RICE BURNERS ALLOWED"  

rick539 rick539
I love my Chevy Chevette! | Posts: 2 | Joined: 11/13
Posted: 11/03/13
04:04 PM

This a pro et bracket car. As u can see below I am way down on compression and way over cammed. The engine has less than half a season it and really don't  want to go thru the engine yet. I was wanting to go with E85 next year and I know this likes compression. I thought if I go with some smaller chambers, a better flowing head and moving up from 2.02 to 2.055 valves that it might wake up a bit

388 compression 10.49:1
Edelbrock performer rpm heads with some port and chamber(70cc) work
Valves 2.02/1.6 on 1.5 rockers
Schnieder solid roller cam - lift .645/.630, 278 duration @ .050, lobe separation 106
Super Victor intake with a mighty demon 750
PG with 5500 chance convertor (2 step set at 5000)
Gears 4.56
Tires 28-10.5/15  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 11/03/13
06:14 PM

Yeah that is a big stick. Not to have any compression the overlap cycle is going to kill compression also. If you go to a bigger valve you will loose more compression. Because you have to un shroud the valves. You will probably be down in the 9:?? then.
  Look for a smaller cam at swap meets. Something in the .610-.630 lift and .272-.274 @ .050. I would purchase a set of 12.5 or 13.0 pistons. I know they are expensive. Check you valve to piston clearance. rebalance the assembly if you need to. Run the heads you have.  
  I ran a similar combination in my Chevy II. I had a 331 Cu. In. engine. Tunnel Ram with 2 660 Holley's. TH400 with a brake and a 6500 convertor. Home brewed 461 heads 2.02/1.65 valves. A 5:67 rear gear with a 28/12.5/15. With a solid roller Crane .630/.630 1.5. If I was on a good pass the engine was 9000RPM. That engine had heart. Not much else you can do.

Bob