Can't stop the detonation
Thread Starter
Teching In
Joined: Jul 2013
Posts: 4
Likes: 0
Can't stop the detonation 355, vortec heads, rpm air gap intake, longtubes, 212/218@.050" cam, 9.39:1 SCR, 7.80:1 DCR, and 5000 miles on the motor. 3.08 gears and 700r4.
I have not been able to get rid of detonation with this motor. It pings every time I accelerate heavily. Cruising is fine but any time I try to have some fun I get spark knock. The strangest thing is that the spark knock does not respond to retarding timing.
Things I have tried:
-Running 93 octane (I always do)
-Retarding timing to 5* initial advance (26* total)
-Reading the plugs after a WOT run
-Unhooking vacuum advance
-Verifying my timing marks and timing light are correct
-Compression test gives 150psi=DCR not too high/cam correctly timed
-Installing wideband AFR gauge to make sure im not lean
-All sorts of carb enrichening including pump shot, secondaries and primaries
-Trying two stages cooler plugs (RS9YC)
-Motor only has 5000 miles on it so carbon build up is unlikely
-160* thermostat so I run at a consistent 170*
-Checking for oil getting in chambers=all clean
There is one last thing I can think of--I used sealed power H345DCP pistons which have a compression distance of 1.540" which gives me 0.084" quench because I didn't deck the block. I wouldn't have used these pistons had I known at the time the importance of quench. HOWEVER, I don't know if that would really cause the trouble I'm having.
If I haven't figured something out by this summer I'll be tearing it down and replacing the pistons. Any other ideas?
I have not been able to get rid of detonation with this motor. It pings every time I accelerate heavily. Cruising is fine but any time I try to have some fun I get spark knock. The strangest thing is that the spark knock does not respond to retarding timing.
Things I have tried:
-Running 93 octane (I always do)
-Retarding timing to 5* initial advance (26* total)
-Reading the plugs after a WOT run
-Unhooking vacuum advance
-Verifying my timing marks and timing light are correct
-Compression test gives 150psi=DCR not too high/cam correctly timed
-Installing wideband AFR gauge to make sure im not lean
-All sorts of carb enrichening including pump shot, secondaries and primaries
-Trying two stages cooler plugs (RS9YC)
-Motor only has 5000 miles on it so carbon build up is unlikely
-160* thermostat so I run at a consistent 170*
-Checking for oil getting in chambers=all clean
There is one last thing I can think of--I used sealed power H345DCP pistons which have a compression distance of 1.540" which gives me 0.084" quench because I didn't deck the block. I wouldn't have used these pistons had I known at the time the importance of quench. HOWEVER, I don't know if that would really cause the trouble I'm having.
If I haven't figured something out by this summer I'll be tearing it down and replacing the pistons. Any other ideas?
Last edited by SBCWes; Feb 25, 2014 at 01:23 PM.
This may sound stupid but ive seen worse so im gunna ask. What plug wire are you putting the timing light sensor on. Dont tell me #1 tell me location of the cylinder in relation to the car.
On The Tree
Joined: Feb 2014
Posts: 157
Likes: 3
Check nthe timing curve of your distributer, by that I mean how fast is your mechanical timing coming in?
Sounds to me like your springs are weak or too light or weights too heavy.
These springs can and do wear out. a dist curve kit is very inexpensive.
Sounds to me like your springs are weak or too light or weights too heavy.
These springs can and do wear out. a dist curve kit is very inexpensive.
