Crank Referance ?

[Z9's]

Crank Reference ?

I had my car on a Mustang Dyno and am experincing a problem with high rpm under boost. This is an IPU set up. I have the distributor set at 50 before . The problem is that under big (boost 20+lbs) It seems to hit a wall it will not pull past 5000 rpm . At 20 lbs my timing is 25-26 degrees could it be that it does not have enough lead time at 50 before. With an old program that had 27-28 degrees it would pull thru to redline 7200 rpm. The car still made 740 rwhp with this problem but I have a race in B.G next weekend and really neeed some advice. TIA Chris

 

[CSJTA]

Chris, that sounds like a timing issue. You still run the LT1 motor in that car? Why I'm asking, see if you can get a timing light on it to see what the timing is doing, but I know with the Lt1, they don't have a pointer.

 

[Z9's]

Yes it is still an LT1 that I have modified for a Distributor.I have a timing pointer on the motor with a ATI Super dampner so I can verify timing. I am in the process of changing cap/rotor/ wires, Then will recheck timing.With the cap I did notice that I had corrision buildup on each terminal off the dist. on the trailing edge.Which to me indicated the lead time prob. The car ran fine with the old program at a race in Lousisanna in the fall with a start up program. With more timing Just made some very minor tweaks to the program.Something else that bothered me was the load of the dyno they set it to 3750lbs. On each pull bringing the car up to speed when I would pull 2nd and third gear I would have to really give it alot of throttle to keep the R's up ! way more than at the track.

 

[Craig Smith]

It sounds like a rotor phasing problem to me.

The pickup in the distributor is phased with the rotor. Meaning if you have the pickup set to trigger at 50 degrees, your rotor is also phased at 50 degrees. This is a common problem when triggering from a distributor with an aftermarket ECM.

Solution #1: Modify the distributor so that there is 20-25 degrees of offset between the rotor tip and the pickup in the distributor. If you can have the reluctor tab centered in the pickup at 50 degrees, and then rotate the engine to about 30 degrees and have the rotor properly phased, I bet this will cure the problem.

Solution #2: Put a crank trigger on it. This, in our opinion, is always the best way to do it. I realize it isn't always practical to go this route, especially with blower setups. But there isn't a more stable, accurate way of triggering than directly off the nose of the crank.