On the street, if feels like a misfire. The same hesitation you get from detonation.

 

For the record the springs are Crane 10308 anfd they are about 3 years old. I do not know what the lifters are.

Ellis: Actually I'm not sure I would agree that I have had this problem before. About 2 months ago I went to a dyno running NA. I did NOT get this same problem. I did suffer from a slight miss and found that my number 6 boot had burnt up on the header and thus attributed it to that. However, the car still pulled with a 'normal' curve all the way to 6200

 

Can someone tell me what they would estimate my timing should be with the following.

At WOT, 13# of boost, air temp 90 degrees. During this dyno I was at 22 degrees and I'm beginning to think that is too low. Would that timing level account for the stumble?

 

Same issue noted here. Now, it pulls hard to 7,000 rpm!!!

 

Well It MAY be a timing issue. I added some timing in above 5000 RPM and although I have only had one opportunity to to test it on the street, I did not have the stumble from before. That being said, I would like to test that result a few more times.

I then called the FAST folks and discussed my situation and they also suggested I had the timing excessively retarded. - I had 22 degrees at WOT and they say 24, even 26 degrees would be fine. Although he also recommended I add more fuel.

Unfortunately, the dyno operator did not think to mention that it might be excessive retard.

We shall see and I'll update when I know the solution.

 

Are you running race fuel?? If so I currenlty have my timing set at 27 degrees. I am running 110 octane fuel though. My car was tuned with C-16 (116 octane) and I probably could have put another 2-3 degrees of timing in it but I did not want to run the car to the extreme.

 

So 24-25 is about as much as I will want to go on 94 Octane. DO you know your intake temperatures? Mine are about 90 and I see you have a similar set up to mine - bigger blower of course

 

My inlet temperature were pretty high. I believe they were around 140 or so. I would think you could get away with running 24 degrees of timing safely.

 

Another question. You high boost blower and turbo guys. What spark gap are you at?

I'm at 35 thou and it has been suggested that a narrower gap might help, that the drop off in power is from the spark being blown out.

Any thoughts? Any negative to going to 25 thou for example?

 

I am running my plugs gapped at .032.

 

One more suggestion, I would move your corection factors back up. You say you have them at 5 percent, so that means the FAST can only correct 5 percent either way. I would move them back up to 25 percent to see what happens. Just a thought.

 

Actualy I have that the FAST can remove up to 5% but can ADD up to 25%. I heard that was a cautious way of tuning things.

 

I don't know if I alrerady mentioned this but the rimgs did not seat in the new motor and it burns oil. I pulled the plugs and they are are fouled. I put new plugs in and FOR THE MOMENT, that appears to have solved the issue. However, it has only been a few days and I'll see if the problem returns quickly.

 

Heh, I’m a bunch behind in my ‘reading’ but was going to suggest that you play with more timing advance or smaller plug gaps. FWIW, I’ve had to run as small as .022” gaps on a few boosted applications (lots of rpm + lots of boost = hard to prevent misfires without really small gaps) and never saw any real problems. I have seen tests that indicate that as your plug gaps get smaller the plugs run slightly hotter, but we’re not even talking the same difference as if you went with a one step hotter plug.

 

Thanks Mark

Actually, making the gap smaller was also on my "plan of attack". For the moment the new plugs at 35 thou seem OK.