Re: New Engine Update (archive)

Tim,
If you are interested in dicussing this further, please email me. I only get to check the board once a day, but check my email all the time.
The cam is a custom grind. The engine runs rich in the low end because the AFM dictates the mixture, and this doesn't seem to work well. At a certain point in the powerband, the AFM and the TPS max out giving a programmed mixture. If this happens a 5000rpm the mixture continues to lean out as the engine sucks in more air and accelerate. By 5800rpm the engine sounds strained and has lost significant power long before the rev-limiter.

Autothority charges the following:
$125 an hour for the dyno
$100 for custom chip configuration(on top of the $450 I paid for the chip)
$40 Computer connection fee.

--Justin

Please let us know how it the split second unit works out, you must be pretty busy preparing for the race and we appreciate your updates. I'm stumped as far as rich at low rpms and lean at high. How about cam timing? If your cam is retarded, the exhaust valves will open late, you miss the high pressure blow down, and you might not have time to fully purge at high rpms. Are you gradually running out of steam as you approach 6000, or hitting the rev limiter? You will also back pump charge into the intake manifold at low rpms due to the late closing of the intake valve, but I don't see how that would make it run rich, the AFM should still measure net air flow.

I got the 90 mm crank from racing dynamics along with a set of 143.5mm H-beam rods (stock is 135mm, the longer rods keep the rod ratio closer to stock). If I force feed it, I probably won't go to the 95mm bore, I'm not sure if the head gasket can take it, there won't be much space left between the cylinders. I'd also have to machine a bowl in the piston crown to lower the compression ratio back down to 9:1 or less.

I downloaded a demo copy of Conforti's DME editor program from Bonneville Motor Works that lets you program and burn your own chips, but a shop with a dyno would be much better. What does Autothority charge for the custom chip work?

Thanks again for the info,

Tim

Thanks for the advice. I have replaced the fuel pressure regulator. The split second system allows for adjustment of the fuel mixture along with a fuel mixture gauge that mounts in the car. I have checked all the sensors and everything is within spec. But the mixture is definitely to rich on the low end and to lean on the high end. The mileage did not drop during track use. It stayed at 11mpg, while street driving yeilds 12mpg. Plus the engine will not spin up to 6000rpm. This could be the factory chip that I am using.
The Split Second system arrives on Weds and on Thursday the car goes on Autothority's dyno for the custom chip :-)

I am not very comfortable tweaking engines, I am much better at tweaking the chassis/brakes/suspension. All of the other systems on the car are working great. The car handles so well, my last driving instructor thought that we were running on race tires when I was using street tires. Few cars can turn and stop as well as mine. I just need somework with the go.

Where did you get a stroker crank for the 3.5? It sounds like your engine might be better set up for forced induction than mine.

--Justin

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