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Old 08-29-2015, 10:36 AM   #10 (permalink)
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Excuse the tardiness in reporting back. In the interim I have been struggling with unexpected detonation issues, both at light throttle and at WOT, preventing the engine from realizing its full potential. The time that has passed represents trying to correct different things that might exacerbate detonation with little or no success.

1) Carburetion: Removed my modified Q-Jet. Changed to an E85-specific modified Holley 800 Spreadbore from because of detonation and power "falling down".

2) Fuel delivery: Added in-tank E85 Walbro fuel pump, using a Tanks Inc. fuel tank. Changed all fuel hose to Aeroquip -8 AN lines inlet and return. This assured a constant supply of fuel to the carb, around 6 lbs. I suspected fuel leaning out and causing power to fall down, as well as detonation.

3) Torque convertor and transmission repair: O'Reilly Auto Parts sold me a defective radiator that leaked water into the transmission. I suspected transmission slipping as a contributing cause to detonation. Incidentally, O'Reilly's never made good to reimburse me and stopped returning my calls. Still detonation.

4) Ignition: Upgraded ignition to locked-out MSD distributor with MSD 6AL-2 programmable to use a laptop to change the shape of the timing curve. No matter what curve was tested, nothing helped. Radically cutting back timing, killed power and still detonated.

5) Engine temperature: Removed excellent factory cast iron intake for aluminum Edelbrock Performer to cool intake temperatures. I also changed the thermostat to cool the engine down. Temperature gauge read lower, still spark knocking at WOT.

6) Carburetion: Now doubting the efficacy of the Holley Spreadbore, purchased brand new Quick Fuel Q-Series E85 carburetor. Seems to be more responsive and powerful, but still detonates at WOT.

My conclusion: Total fail. The compression is simply too high for the octane available in E85 using vintage iron 1969 Pontiac D-port heads, which by design, have poor anti-detonation qualities. I used an Innovate Motorsports wide-band O2 sensor gauge for tuning and was able to have excellent drivability, but no matter how rich I ran it, it still knocked, verified aurally and visually with a knock light. The compression calculated out to 13.13:1, dynamic compression with the Crower 60919 cam 11.92:1.

While other racers are running 14:1 and higher, they are most likely using modern heads with a fast-burn combustion chamber design and perhaps more radical cams to reduce dynamic compression. The result was totally unexpected given the extensive research I had done on E85 and ended up costing me a lot of money and time and aggravation, but sometimes that happens when you push the limits on the road less travelled. Call it a learning experience.

As I write this, the old heads are off. I am waiting for a brand new set of CNC-ported KRE D-ports, aluminum with a modern combustion chamber design, port-matched to an Edelbrock RPM intake. The compression ratio with 74 cc heads will be 11.75:1, conservative for E85, but allowing me to run outside my E85 availability range on 93 octane if necessary.

One last bit of advice: Make sure you dyno-test a new engine before tuning in-car. No one wanted to run this motor because they weren't the ones that built it. If I had dyno-tested it from day-one as planned, much of this could have been avoided.

Sorry, again, for not following up sooner, but it's been a long aggravating and disappointing journey, that at least taught me some important lessons, which stand as a warning to others.

Last edited by Aguila1; 08-29-2015 at 10:42 AM..
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