Which afr heads
Team Owner
Joined: Jul 2004
Posts: 28,353
Likes: 3,253
From: Hartford WI
Thread Starter
Racer
Joined: May 2009
Posts: 364
Likes: 3
From: merced ca
Well doing some what of better research on my specs and stock specs. Apparently I'm running 11.13:1 compression. Stock is 9.5:1. If I had 65cc heads I get 10.23:1. 75cc heads would give me 9.19:1. I do want to run the stock temp. So maybe just doing the head swap would ideal. If I have time I'll hook up my dads autoxray again and see where my temps are at.
Safety Car
Joined: Sep 2001
Posts: 4,137
Likes: 531
From: Glenbeulah Wi
Well doing some what of better research on my specs and stock specs. Apparently I'm running 11.13:1 compression. Stock is 9.5:1. If I had 65cc heads I get 10.23:1. 75cc heads would give me 9.19:1. I do want to run the stock temp. So maybe just doing the head swap would ideal. If I have time I'll hook up my dads autoxray again and see where my temps are at.
Thread Starter
Racer
Joined: May 2009
Posts: 364
Likes: 3
From: merced ca
I was thinking of getting a set of thicker head gaskets also. A .051 thick head gasket with the 65 cc head will put me around 9.99:1 compression. It's the felpro 1044 which is used for clearance issues.
Safety Car
Joined: Sep 2001
Posts: 4,137
Likes: 531
From: Glenbeulah Wi
You should be able to run 10.5 to 1 compression with the proper squish clearance and water temps at 200 or under, assuming you have the correct timing and air fuel ratio.
Last edited by bjankuski; Jan 18, 2016 at 10:05 AM.
Racer
Joined: May 2008
Posts: 312
Likes: 19
My 91 would knock bad when hot, I checked the knock sensor with a analog vom against a used lt1 ks that I had. Both worked however the lt1 sensor was much more sensative, installed the lt1 sensor no more knock! Vom setting is mv and tap sensor on block side of sensor. I would try your sensor against a new gm l98 sensor. Good luck!
Team Owner
Joined: Jul 2004
Posts: 28,353
Likes: 3,253
From: Hartford WI
My 91 would knock bad when hot, I checked the knock sensor with a analog vom against a used lt1 ks that I had. Both worked however the lt1 sensor was much more sensative, installed the lt1 sensor no more knock! Vom setting is mv and tap sensor on block side of sensor. I would try your sensor against a new gm l98 sensor. Good luck!
Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 195
From: folsom california
I don't know about swapping heads just yet; I've run naturally aspirated small blocks with similar compression without any pinging or knocking.
your knocking sounds like it could be timing related; if that's the original harmonic balancer on your engine, there's a good chance the outer ring (along with the timing marks) may have slipped or the elastomer between the outer ring and the center hub may have deteriorated; in either case the timing marks would now be retarded in relation to the crank and piston, so any attempt to time the engine using these marks would result in the engine firing in a much more advanced position.
classic symptom of over advanced ignition ? pinging or knock
personally I'd find TDC on the number 1 piston (admittedly easier with the head off) and then verify that the timing mark is at 0 degrees.
your knocking sounds like it could be timing related; if that's the original harmonic balancer on your engine, there's a good chance the outer ring (along with the timing marks) may have slipped or the elastomer between the outer ring and the center hub may have deteriorated; in either case the timing marks would now be retarded in relation to the crank and piston, so any attempt to time the engine using these marks would result in the engine firing in a much more advanced position.
classic symptom of over advanced ignition ? pinging or knock
personally I'd find TDC on the number 1 piston (admittedly easier with the head off) and then verify that the timing mark is at 0 degrees.
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Thread Starter
Racer
Joined: May 2009
Posts: 364
Likes: 3
From: merced ca
I don't know about swapping heads just yet; I've run naturally aspirated small blocks with similar compression without any pinging or knocking.
your knocking sounds like it could be timing related; if that's the original harmonic balancer on your engine, there's a good chance the outer ring (along with the timing marks) may have slipped or the elastomer between the outer ring and the center hub may have deteriorated; in either case the timing marks would now be retarded in relation to the crank and piston, so any attempt to time the engine using these marks would result in the engine firing in a much more advanced position.
classic symptom of over advanced ignition ? pinging or knock
personally I'd find TDC on the number 1 piston (admittedly easier with the head off) and then verify that the timing mark is at 0 degrees.
your knocking sounds like it could be timing related; if that's the original harmonic balancer on your engine, there's a good chance the outer ring (along with the timing marks) may have slipped or the elastomer between the outer ring and the center hub may have deteriorated; in either case the timing marks would now be retarded in relation to the crank and piston, so any attempt to time the engine using these marks would result in the engine firing in a much more advanced position.
classic symptom of over advanced ignition ? pinging or knock
personally I'd find TDC on the number 1 piston (admittedly easier with the head off) and then verify that the timing mark is at 0 degrees.