LaughaC

My rebuilt 2.7 has a tach redline of 6500, so I'm currently running rev-limiting rotor for that RPM.

The MSD I plan to install only includes rev-limiter buttons for 6000, 7000, or 8000 RPMs. Has anyone seen dyno results for these CIS motors? I wonder how much power I stand to miss out on by limiting it to 6000 RPMs.

Loaded

I think it is but throw it on a dyno and take a look at your power band. SOme of the fellas here should be able to say what the 2.7 is capable of in your config.

theiceman

I never push it to cut off anyway . I usually shift before 6000. Your owners manual will show rpm of peak torque.

LaughaC

I wish I had an owner's manual. My 928 S4 owner's manual was full of good info.

My 2.7 CIS has ported heads, SSI "headers", a sport 2 into 1 muffler, and 8.5 compression. I have read this combo will put it somewhere near 190-200 peak hp, but the real question is where the power peaks.

Adding the Pertronix smoothed everthing out, and I'm hoping the MSD will add a little more torque and better gas mileage.

Have looked for a trailer dyno each time I go to the track, but the line has always been too long. Next time I'll invest in waiting my turn.

psalt

Chris,

The stock engine hp peaks at 5800 rpm , so technically you would not be losing any power. However, maximun performance (acceleration) usually occurs when shifting at or near the redline due to the drop in rpm between shifts. Limiting the rpm to 6000 will reduce performance, and it is generally not a good idea to use mulitple rev limiters. Personally, I would use a plain rotor and the 7000 rpm pill. That is all the protection you need, as most engine damage from overreving comes from downshifts, where rev limitors provide no protection.

Paul

LaughaC

Good info, Paul.

If the wheels are spinning, do you feel relatively safe that my engine won't grenade if accidentally hit the 7000 RPM limiter?

psalt

Yes, my opinion is it would be silly to limit below the factory redline, unless you intend to lend the car to an idiot. A rev limitor is intended to offer a little protection in certain circumstances when you "over rev" the engine. The next 911 (SC) used a fuel pump cutoff at +/- 6840 rpm, Porsche is usually conservative and it is generally accepted that the stock valve train is OK up to 7 K occasional. The shorting rotor is old tech and I would check with MSD warranty before I would mate them. None of them...5k, 6k, 7k will protect from the money shift.

LaughaC

The MSD is now installed, but it's too late at night to start the engine for a test run. Wish me luck.

Autozone had a 6400 RPM limit button in a kit that I picked up today. This seems to be where the red zone starts on my tach, so I'll stay conservative until I hear these 2.7 motors can safely go higher.

Steve Weiner-Rennsport Systems

Chris:

Your 2.7 has cast pistons so you should limit maximum RPM to 6500. Further, there is no reason to pull beyond that as you are well beyond peak torque & HP.

LaughaC

Thanks, Steve. I set the MSD box to limit at 6400 RPMs and my rotor is set to crap out at 6500. Should I switch to a standard rotor?

Steve Weiner-Rennsport Systems

You're quite welcome..

I would install the Turbo rotor without the rev-limiter when using the 6AL.

GrantG

You can buy extra MSD kits that have rev limit resistors spread in 100rpm increments...