We’ve got the answers when the Summit Racing tech department tackles your automotive-related conundrums. This week, we help eliminate an engine knock problem.
L.P. Roseburg, OR
Q: I just put a new 9.7:1 compression 383 small block engine in my 1978 Chevy 4 x 4 pickup. It has less than 100 miles on in it and runs great until engine speed drops while under load. At this point, the engine also begins to knock/ping (usually while the truck is in fourth gear). The engine was built to give me more torque and power for pulling a trailer. It uses the same Edelbrock Performer intake, Quadrajet carburetor, and exhaust (tri-Y headers, 2.25-inch dual pipes) as the 350 that used to be in the truck. The ignition system is a new HEI distributor with an ACCEL Supercoil.
Retarding the timing eliminates the knock. Am I just running too much ignition advance, or do I need to re-curve the distributor? A water injection system was suggested to me, as was an MSD ignition with an advance control. Is there something else I should do to fix this problem?
A: You may have to do a number of things to eliminate the knock. Retarding the timing obviously worked. You can also add octane booster to the fuel; your 9.7:1 compression ratio is too high even for 92 octane premium. Re-curving the distributor is a good idea, as is an MSD Timing Control to let you adjust the timing from the driver’s seat. You might also consider a gear swap to help take some of the load off of your engine. For example, if you have 31-inch tall tires, a 4.10 gear front and rear would work very well.