I'm still chasing the Mystery Rev Limiter. This morning's data says that the engine will rev beyond 6800 with the blower belt removed:

http://para.noid.org/~lj/NA-NoRevLimiter.gif

My first test run this morning, which resulted in the engine refusing to rev beyond 6800, was with the blower hooked up. I thought I heard a noise like a pop-off valve when the engine stopped gaining revs. This makes me wonder if the Vortech Mondo bypass is misbehaving.

But I cannot understand how that would create a rev limiter!

Can anyone think of a way that the intake tract from K&N, through the blower, bypass, intercooler, and elbow, could fail in a way that prevents the engine from gaining revs?

To rule out valve float I swapped in these springs:

Manley p/n 22440 H11 tool steel
seat: 250lb @ 1.850"
nose: 680lb @ 1.150"

I guess it could still be ignition, but this seems like a solid system:
MSD Digital 7
MSD 8251 coil
MSD Opti cap and rotor (less than 100 miles)
MSD 8.5mm Super Conductor wires, inspected and heat shielded
NGK iridium plugs, BKR9EIX gapped at .030

 

I gap my plugs at .025 with 7AL3 .Might want to try that You are running 20+ lbs of boost correct? Good luck .......gremlins suck

 

Well, you swapped in some hefty springs, so I dont think you're floating the valves... The only thing that could be left is you're blowing out the spark.. Drop the gap on the plugs and see where that gets you..

If you suspect the intake tract, pull it off and take it for a quick ride, or dyno pull....

When you hit this limit, does it just hang there, like a soft rev limiter, or does it come back down? How's your fuel pressure looking?

With the blower belt on, w/o putting the car underload, can you free rev it to 7000?? i.e. in neutral?


--Sean

 

What do you have for plumbing on the inlet side of the blower? I didn't see anything in the sig to tell. Just wondering if you might have something collapsing on the inlet side. It's a long shot. I'd be leaning more toward a misfire under high boost though.

 

I'll try dropping the plug gap today. The fuel pressure stays solid as does the AFR on both sides, although the AFR oscillates more than usual when the rev limiter hits:

http://www.acceleronics.com/images/AFR-RPMgraph.gif

It's very much a soft limiter. The engine runs fine if I upshift or back out of the throttle.

The blower intake is a big K&N hanging on the end of this:

http://para.noid.org/~lj/1000hp/images/inlet1.jpg

The filter shows no signs of collapsing.

With all due respect, I could not bring myself to free rev the engine to 7k.

 

Yea, I would say your intake tract is fine.

A quick rev in park or neutral to 7k won't hurt anything, might annoy the neighbors though...

I'm just asking because i have a friend with a big turbo mustang who is having very similar problems. With the turbo not spooling (not under load) the car will free rev up to 7k w/o a problem. With it under load, it just hangs at 6200.. We've done everything you've done and actually tracked it down to the converter.

With the turbo on, the car is blowing through the converter. We had to take it on a dyno to figure it out, it would rev up to 6200, and he just stayed in it, after like 2 seconds, it went past (the converter locked) and then it pulled to 7000.

He's sending the converter out now to get tightened..

Let us know how you make out with the plug gaps ..

 

I had a simmilar problem on the engine dyno. Basically under load/boost the optispark was no longer a reliable source for timing signal. After conversion of the FAST to a crank trigger it will rev to the moon. Perhaps this does not directly relate but then again maybe something to look at.

 

Just a suggestion or something else to check. I have had coil paks act in the same manner. Under load they don't like putting out high voltage. I even had a set of plug wires give me some greaf one time after changing everything else. As for the spark plug gap that may be something to look at.

One other thing is to check the voltage of the alt. I ran into a problem like your talking about once and ended up finding out the alt was loosing voltage as the boost and rpm went up. I found this out while looking at graphs on the F.A.S.T system. The voltage would start at about 14v and at high boost and RPM drop to about 13.6 and the ecm and stuff did not like it.

Good Luck