Thread: Detonated Dreams

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At first, I though NAAAA, this fellow has figured the SCR and DCR incorrectly. I refigured it and he's right on the money, so the cam and cylinder pressure match up, the squish looks ok at 0.051"/0.052" depending on whether he's using a 0.039" or 0.040" gasket and the motor absolutely should not be detonating on 91 octane fuel. I have a Crane catalog right in front of me that has the Cam Facts for this cam....."Good low end and mid range torque and horsepower. Daily useage and off-road, towing, performance and fuel efficiency. 8.75 to 10.75 static compression ratio advised."

OP, I'm gonna take you at your word when you say better fuel makes it a little better and go out on a limb here. I'm betting the inertia ring on the damper has slipped circumferentially in relation to the hub and you are getting incorrect ignition timing figures when you put a light on the motor. Here's a tutorial I wrote for the Crankshaft Coalition Wiki a couple of years ago. It explains how to correct the condition.
http://www.crankshaftcoalition.com/w...op_dead_center

The other long shot I was thinking about is that the noise is not spark related at all and is a mechanical interference noise. What made me think of that is the 1.6 rockers. Did you check for piston to valve clearance, spring coil bind clearance, retainer to guide/seal clearance and rocker slot to stud clearance at full lift? I know with the other things you said, it is unlikely, but just asking if you checked this stuff.

I run a lot of DynoSim combinations and the usual improvement I have seen going from 1.5 to 1.6 rockers is a single digit improvement in hp and torque. When you consider the extreme additional pressure that is generated at the lifter/lobe interface with these higher lift rockers, it hardly seems worth it. You want more lift, use more cam that is designed for more lift from the gitgo. That's just my opinion.

Glenn offered a reasonable explanation also, with hot spots in the chamber/piston crown, so clean all that up and round off everything while you have the motor apart. As Pat said, use a head gasket with a large enough I.D. so that it doesn't overhang the bore and glow red hot. The bore of the gasket should just exactly match the counterbore at the top of the cylinder. Using a bore that is too large is just as bad as one that is too small in my opinion. A very large bore gasket leaves a crevice where unburned gases can hide.

OP posted:
"In no way is this engine fast enough to warrant the need for race gas."
If the ignition timing is advanced as far as I think it is, that would explain the general lack of performance. Peak cylinder pressure could be occurring at the wrong piston position.

OP posted:
"I've heard that some things can happen to make your engine "see cylinder pressure" that rivals that of 11:1 even though you are only at 9.5:1. Not sure i understand how that would happen or what to do about it but i am VERY open minded at this point."
I think what you're alluding to is the DCR, which you already understand, apparently.