I have a "pinging" problem due to a to high compression. The engine is a 351W w/ GT40 cast iron polished and cleaned up bowls, port-matched heads, GT40 intake, SVO 70mm mass air, SVO 65mm throttle body, SVO EGR high flow spacer, SVO EEC-1V processor, 30lb SVO flow matched injectors, SVO ceramic coated short tube headers, 3" single exhaust w/ 2 chamber flow master and high flow cat, Crane 1.6 rollar rockers, Crane roller cam #444112, .530 valve lift, 208-216 degree at .05 lift.

This engine pryor to 70mm and 30lbs injectors had 65mm and 19lbs inj. ran on a dynajet produceing 202 hp at 4500 rpm, 349 torque at 2750 rpm. Horsepower was flat +-5 hp from 3000 to 5200 rpm. On all pump gas (91 octane). But it pinged so changed to 70mm & 30lbs hopeing to help but it didn't.

This is in an early Bronco so low end responsiveness is important. I believe my CR is 10.5 baised on best info I have. Cranking pressure is 185lbs. I want to run 91 octane premium. I'm getting tired of using 100 octane at $4.69 a gallon to keep it from "pinging". It runs great except for lack of top end pull 4000 up which probably is the cam.

I think my options are : 1) go to aluminum heads (as I've been told 10.5 CR is okay w/ 91 octane), 2) machine the GT40 heads to 68-70cc (can this be done? and what drawbacks?).

If I go with #1, head choices are: GT40X, Brodix 5.0R 68cc, World Winsor lite, Canfield 65cc or ???

Sorry for the long post but want to give all info in the hopes of getting some good responses.

Thanks very much, Cary

 

I posted a reply to this in your other thread.