Well, after literally 5 years of dinking around part time on my 396, I finally got it to the track.

A little history...

My old setup was the bone-stock LT1 plus a stock-pulley S-Trim, which inexplicably made 11psi after installing my own intake tube. It ran a best of 11.9 while hitting the rev limiter due to the ODB1 shift problem. I shortly thereafter switched to a FAST ecu, hit their "cursor key corrupts table data" bug which gave me 63 degress of advance at 11psi. My ringlands immediately went on a wildcat strike, and I had to build a new motor.

My new motor is a 396 LT4 w/AFR 210cc heads, LT4 intake, 236/236 cam. I changed the blower pulley over to a 2.75 so that I'm still seeing 11-12psi of boost (and on my puny Vette 6-rib setup, no less!). I also added a Vigilante 2800 stall converter at the same time as well as the FAST (nee TCI) trans controller.

I finally got to the track, and the first thing I learned is that the 2800 Vigilante flash-stalls out to about 5900rpm. Since the FAST trans controller shifts based on RPM, it immediately upshifts when you have the shift points set at 5500 :-), but I sorted that out pretty quickly.

The best run was an 11.9@119, which is of course the same ET I started out with many thousands of dollars ago. I did drop my 60-foot from 2.1 to 1.6, though.

The motor has a very noticeable random misfire under WOT that is clearly costing me a lot of HP. When I first put the motor in I had some major arcing to the #5 header pipe that I've since solved, but along the way I replaced coil and Opti, so I know they're good. I also gapped my plugs down to .035 rather than the stock 0.60 as extra insurance. So I of course have to triple-check all my other plug wires, but beyond that I'm looking for some guidlance as to what else could cause a WOT misire and how to track it down. Once I cure this problem I will start tuning with my alky injection to get the timing back up from the 20 I can only run it at now, and I think there's a lot of power in those 15 degrees of advance as well...

Are irridium plugs worth it?
Will an incorrect mixture cause this?
Can too much retard cause it (being at only 20 degrees total)?

Any other sage-like advice on how to methodically trouble shoot this is very, very welcome. I really want to hit the 10s so I've got a full second of troubleshooting to do :-)

Thanks!
- Dave

 

11psi on a stock LT-1







any how are they hiring where you work...cause I could use a TT 12Cyl Mercedes.

 

Yes, and surprisingly it held up really well for quite a long time at 11psi, though of course there was a lot of timing taken out of it to work with the stock compression ratio.

And yes, they are hiring if you're a hardcore ASP.NET/C# developer :-)

 

Just because you replaced the opti, doesn't mean it is good. Plenty of people have replaced a bad opti with bad new opti.

As far as the iridium, I don't know. I thought you were not supposed to use plugs with any special metals on them.

If the mix was bad enough to cause a misfire, it seems you would have more major problems on your hands than a misfire. Have you dyno tuned it?

The 20 degrees advance won't cause any problems like that.

 

I spoke with a guy at NGK about a year ago. He said the metal that the plug electrodes are made with doesn't matter, and that the heat range of the plug is what does matter. He said even platinum plugs are great for a supercharged motor, as long as you select the correct heat range.

I've been running some cold NGK Iridiums (heat range 7) for over a year, and haven't had any detonation problems.

Raymond

 

So you went 11.9 at 119 with a 1.6x 60ft? That doesn't really add up, whats the rest of the slip look like? 1.6x 60ft and 119mph should be good for about 11.40's in an stalled auto.

 

I am just going on what ATI said. According to the instruction manual, you are supposed to remove platinum plugs before running with boost.

 

I know. The timeslips are in the car, which is at the shop, so I can't see them right now.

I'm not sure where and how it would have to lie down to do that, though it was definately in the high RPM range that it was having trouble.