Head Gaskets and Compression Ratio
Thread Starter
Pro
Joined: Jun 2002
Posts: 544
Likes: 0
From: La Jolla California
Head Gaskets and Compression Ratio
I'm trying to lower my compression ratio without rebuilding the bottom end. I'm currently running nearly 11.7:1 and am having problems with tuning/timing/etc. I want to get it down around 10.5:1 so it'll run OK off of street gas. Does anyone know if there are extra thick head gaskets made somewhere for this purpose? If not, can I double up gaskets or would this lead to trouble? If this would work, would you just double the compressed thickness of each gasket to arrive at the new total gasket height? Or am I just going to have to cut the chambers? If it matters it's an LT1 engine out of a late model camaro with the specs below. Thanks for any response.
Jason Langhoff
'79 Vette
'79 vette (~3600 lbs)
383 LT1 w/ aluminum heads (w/ porting and valve job)
GM Carb Intake w/ Holley 750 DP
11.7:1 compression
TH-350 w/ 2500 stall
3.55:1 rear end
Cam Specs:
Intake Exhaust
Gross valve lift at 1.5 - .51 .54 (I run 1.6 rocker arms)
duration at .050 230 244
lobe seperation 112
valve timing OPEN 37 BTDC 90 BBDC
CLOSE 73 ABDC 37 ATDC
I rev the engine to 6000 RPM.
Jason Langhoff
'79 Vette
'79 vette (~3600 lbs)
383 LT1 w/ aluminum heads (w/ porting and valve job)
GM Carb Intake w/ Holley 750 DP
11.7:1 compression
TH-350 w/ 2500 stall
3.55:1 rear end
Cam Specs:
Intake Exhaust
Gross valve lift at 1.5 - .51 .54 (I run 1.6 rocker arms)
duration at .050 230 244
lobe seperation 112
valve timing OPEN 37 BTDC 90 BBDC
CLOSE 73 ABDC 37 ATDC
I rev the engine to 6000 RPM.
Safety Car
Joined: Mar 2000
Posts: 3,620
Likes: 2
From: Hillsboro OR
Re: Head Gaskets and Compression Ratio (Langadorf)
I have heard of people using two head gaskets to reduce compression but that will increase the space between the piston and the head which reduces the effect of the quench area and not help at all.
You probably need to put in dished pistons or use a computer controlled timing setup with a knock sensor. I have heard that 12:1 is possible with late model LT1 engines but never tried it myself.
You probably need to put in dished pistons or use a computer controlled timing setup with a knock sensor. I have heard that 12:1 is possible with late model LT1 engines but never tried it myself.
Drifting
Joined: Mar 1999
Posts: 1,931
Likes: 1
From: Norcross GA
Re: Head Gaskets and Compression Ratio (ralph)
Look around, there are thick head gaskets out there. A doubled up head gasket is asking for trouble. Yes, some have gotten away w/ it, but why ask to do the job twice.
Check out dead soft copper gaskets. Mfg's might list them a spacers.
Check out dead soft copper gaskets. Mfg's might list them a spacers.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Head Gaskets and Compression Ratio (Langadorf)
Actually you might benefit from reworking the heads and a thinner head gasket to reduce the quench area and so reduce octane sensitivity.
Examine the head chambers for any roughness or burs around the cylinder opening and gasket match. Trim the spark plug boss and do some valve unshrouding as well as removing a little material from the chambers. Finish up with a golf ball "divit" finish in the chambers to promte swirl.
Examine the head chambers for any roughness or burs around the cylinder opening and gasket match. Trim the spark plug boss and do some valve unshrouding as well as removing a little material from the chambers. Finish up with a golf ball "divit" finish in the chambers to promte swirl.
Team Owner
Joined: Apr 2001
Posts: 22,267
Likes: 3
From: Dallas TX
Re: Head Gaskets and Compression Ratio (ZylaRace)
I have 11.55:1 compression.. when i have some more head work done, i'll have a bigger dish put in which will reduce that to around 11.2 or so hopefully. :cheers:
Instructor
Joined: Apr 2002
Posts: 126
Likes: 0
From: port saint lucie florida
Re: Head Gaskets and Compression Ratio (Glock'94)
depending on your induction carb/fuel inj you can use a restrictor plate. it will make the climb up in rpms a little slower but it will help. we have ran a static 14:1 cr with a restrictor and pump gas. there is a difference between static compression(what you figure when you build) and dynamic compression(actual squish during operation) if you restrict the air volume and the proper ratio of fuel actual static compression becomes less of a problem. i know several will chime in and have other views but it works for us . like i said . i dont know what you are trying to accomplish but before you tear into a good engine give it a look....best of luck
[Modified by old salt, 10:06 AM 6/22/2002]
[Modified by old salt, 10:06 AM 6/22/2002]
