Ignition Coils to run in IT7 / Engine dead spot?

[mackguy]

At RRR last weekend I was having an issue with my IT7 car hitting a dead spot right around 7krpm. It would pull strong up to about 7k, then almost stall, then come back to life and pull fine up to 8500.

Only did this in the straight, did not notice any problems running this engine speed when cornering or just sitting static in the paddock. Sounds bizarre but it almost seemed like an electronic interference (it happened right at the finish line, and nowhere else).

Seems like it's somehow ignition related and a quick look at our ignition system revealed a cap and rotor that were a little bit corroded (though replaced less than a year ago), and coils that are very old. Figured it might be a good time to replace the coils whether they are the root cause of this problem or not, but I'm not finding much info on what to look for. Does everyone just use stock replacement coils, or are there better ones to use? MSD and Mallory both sell a variety of "universal" coils but I'm not sure how to select between them.

Car is a 79 with a newer electronic distributor. No MSD box or anything, just stock 80+ ignition.

Any suggestion on coils, and anything else that could cause this type of problem would be appreciated!

Thanks!

[dickita15]

I have had good luck with MSD Blaster coils.

[RX555]

Did it do it every lap?
Not sure where RRR is, but at Gateway I have had a similar issue in my IT7 with low fuel levels combined with the banking. It would fuel starve for just a 100 yards or so right after the banking at start line.
Just throwing it out there.

[team-gpracing]

Yeah, I'm with RX555, that sounds like it could be a fuel starvation issue.

But to answer your question I use stock coils. They're pretty old too.

[TomL]

I think RX555 may be onto the answer. If your fuel pickup is toward the right side of the cell/tank, the long run through Turn 7 may be uncovering the pickup and emptying the float bowl enough that the engine dies just after you get onto the straight (which would occur somewhere near start/finish). Then, once you're going straight for a bit, the fuel pump catches up and the engine runs normal again.

By the way, you mention running up to 8500 rpm. Where are you doing that, and what gear and final drive? I don't quite hit 8000 in 5th, even with a 5.12 rear, and I was going faster on the front straight than you last weekend.

On the coils question, I've used both MSD Blaster2 and stock coils, and I've never had a problem with either.

[mackguy]

I think RX555 may be onto the answer. If your fuel pickup is toward the right side of the cell/tank, the long run through Turn 7 may be uncovering the pickup and emptying the float bowl enough that the engine dies just after you get onto the straight (which would occur somewhere near start/finish). Then, once you're going straight for a bit, the fuel pump catches up and the engine runs normal again.

By the way, you mention running up to 8500 rpm. Where are you doing that, and what gear and final drive? I don't quite hit 8000 in 5th, even with a 5.12 rear, and I was going faster on the front straight than you last weekend.

On the coils question, I've used both MSD Blaster2 and stock coils, and I've never had a problem with either.

Will try to get a better look at the fuel pickup. Stuff in the fuel cell did get moved around during the "incedent" on Saturday. But it seemed like it was happening about midway down the straight, though I had not considered there being a lag.

Yes, you were faster than me on the straight. Every IT7 car there was faster than me on the straight, and I was routinely at 8k+ in 5th on the straight. We counted 2.5 driveshaft revs for one wheel rev (open differential). I know I was slow all the way around the track but when you get passed when you're already at "top speed" (I know I was passed by you, Steve Rose, and the Hines car when I was in 5th and feathering the throttle around 8500).

Part of the answer there I think is tires... we are running 45profile R888's. I know Steve was running a taller profile (60 maybe?) RA1.

[team-gpracing]

We counted 2.5 driveshaft revs for one wheel rev (open differential).

I know this isn't a response to your question and maybe open diffs are different, but doesn't that mean that you have a crazy low rear gear? 2.5:1 ???

[mackguy]

I know this isn't a response to your question and maybe open diffs are different, but doesn't that mean that you have a crazy low rear gear? 2.5:1 ???

We went around in circles about that but apparently for an open diff you x2, so it's about a 5:1.

If we had 2.5:1 I'd have been going about 190mph in the straight!

[joeracerx95]

We went around in circles about that but apparently for an open diff you x2, so it's about a 5:1.

If we had 2.5:1 I'd have been going about 190mph in the straight!

"I'd have been going about 190mph in the straight!"

Yeah, I'm pretty sure you wouldn't. But you probably would get better gas mileage.

Anyway, put in a fuel pressure gauge and look at it as you come out of the last turn before your problematic straight. You'll probably see little or no fuel pressure. It then takes from there to your hesitation spot for the fuel lines and float to run out of fuel and then the engine goes dead. Meanwhile the gas sloshes back because you are now going straight and the pressure rebuilds and refills the float, and then you have your engine back. Happens to me on left hand turns if I run less than five gallons in the stock tank.

I've always used stock coils and never had one go bad. I've been told by people that know more than me that the stock 12a ignition is more than adequate for stock engines. Now a turbo motor at 9000+ is a different story.

[mackguy]

well Yes, I'm sure you are right but if I was turning 8krpm with a 2.5 rear and a .83 overdrive... that would be quite fast.

Good observation. The cell did get jostled around so that could be part of the issue. What is strange is that it didn't exhibit that issue anywhere else on the track except on the straight, thus I didn't think about it being a fuel issue.