Cascade Crew

DBL_TKE · Posted: Sun Mar 25, 2012 8:19 pm Post subject: high RPM's

Exactly how high can you safely rev a stock 136k miles LB9? I ask this because I've found that 3.73's seem to be a bit steep on some autocross courses and I've ended up having to rev out 2nd gear a little further than I'd like. To the tune of 6k RPM's a couple times. I know that's way past the optimal RPM band for power but on a 35-50 second course, shifting to 3rd gear momentarily and back down to second will kill your run times and really upsets the balance of the car under heavy braking. I'm pretty sure I don't have much to worry about the bottom end as that really isn't that high of an RPM, I guess I'm just worried about the valvetrain. I can already tell that my P.S. Pump doesn't like it much either, but at least I have a low miles spare. I really wish these cars had rev limiters.

Twilightoptics · Posted: Mon Mar 26, 2012 10:47 am Post subject:

Oil pressure good, valve adjust good, no reason it can't touch 6k a few times. Wouldn't want to go over or hang out there for long.

aaron_sK · Posted: Mon Mar 26, 2012 4:55 pm Post subject: Re: high RPM's

Quasi-Traction · Posted: Mon Mar 26, 2012 6:03 pm Post subject:

why not just put in a MSD 6AL box, Gives him the option to change the limit with a single fuse and gives him better spark delivery. Just my $.02.

Alphius · Posted: Mon Mar 26, 2012 6:56 pm Post subject:

Wouldn't burning chips move him up too many classes in Auto-X? It's been a while since I looked at the classing guide but ECU modifications generally put you pretty high up I thought. Wink

aaron_sK · Posted: Mon Mar 26, 2012 7:32 pm Post subject:

Alphius · Posted: Tue Mar 27, 2012 8:09 am Post subject:

Nice, I thought they didn't allow that in STX or STU. I was probably thinking of tunes on Subarus since they do disallow changing boost tables. Wink

DBL_TKE · Posted: Tue Mar 27, 2012 12:53 pm Post subject:

I actually think they allowed tuning starting in the 2011 season for the street touring classes. I think I may do that. I'll have too see if I can borrow Dereks cable and burner, then I'd just need an adapter and chips. How does the stock rev limited work? Does is cut spark, fuel, timing?

Twilightoptics · Posted: Tue Mar 27, 2012 2:11 pm Post subject:

I was unaware of a thirdgen stock rev limiter.

Speed limiter yes....

aaron_sK · Posted: Tue Mar 27, 2012 5:04 pm Post subject:

Nothing to see here, Paul. Very Happy

Skyler, the stock limiter just cuts the injectors off hard till a given low RPM is reached. I ran one on my IROC and hit it many times. However, I never tried bouncing off of it for any length of time so I can't advise you on that.

Twilightoptics · Posted: Tue Mar 27, 2012 5:06 pm Post subject:

Right on. The earlier software (pre Mangus) didn't have that cut into the definition files.

Alphius · Posted: Tue Mar 27, 2012 5:28 pm Post subject:

Most (never make a blanket statement!) factory EFI systems up until the last few years have done only fuel cut, as it's much nicer on cats and oxygen sensors than a spark cut or even a combination cut. Wink

Unburned fuel is hard on those things, and even worse if it happens to ignite in the exhaust stream. Of course, fuel cut is much harder on the engine itself (super lean as it burns on the fuel pooled and atomized in the intake!), but the manufacturers have much less worry about that aspect of it.

I believe nowadays they simply all have drive-by-wire and limit RPM that way.

See my Youtube video in the Youtube thread for an example of why the factory prefers to not use spark cut... Twisted Evil