Detonation???
 

I have a 67 Fastback with a 302 in it. Around town, everything sounds nice, but on the highway some sounds start to occur. Hitting speeds such as 70,80,90...nice rattling sound is heard from the engine, ride becomes rough. The engine itself is bored .30 over. Has a Lunati cam, .512 lift, 230 duration. Comp. Ratio is 10.5 to 1, Roller rockers, open chamber heads,Keith Black Pistons, Holley 650.I put mids in for my gas, rear is a 2.73 and i have a c4. I had read somehwhere that it could be detonation, caused by improper timing? Any suggestions?

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67 Mustang
302 bored 30 over
Roller Rockers
Lunati Cam
TCI Street Fighter

You need to see what your total timing advance is. Sounds like it's too much. Also, with that much compression, you need the best pump gas you can buy (93 octane)and possibly even octane booster.

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

what is your timing set at and also what gas are you using?? what octane?

with the cam you have you need more gear ratio too 2.73 might be good for running 80-90 but under 60-70 must not run too smooth especial with an automatic

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93-LX: 5 Speed, Flow's with H-Pipe, 3.73's Sub's and K&N.

I think that your system isn't balanced out. You have too little cam for the stall your carrying and too much cam and stall for the rear end gears. I would have gotten the tci break away one and at least a 3.25 traction lock rear. Now if you wish to keep the cam I think the carb is a little small I'd suggest a 750 cfm with a high rise manifold but still the stall is a little high about 500 rpms. Yup its detonation! Check what they have told you up above.

I ahd the same problem with my clevlend. Once I got the timing dialed in and started using octane boost it clear up my problem. I also found the plugs last twice as long now.

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1970 Mach 1 351C