6000 RPM limit too low?
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Burning Brakes
Joined: Jul 2005
Posts: 955
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From: Nashville x-burbs
6400 RPM limit too low for 2.7 engine?
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.
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.
Last edited by LaughaC; May 18, 2007 at 03:14 AM.
Thread Starter
Burning Brakes
Joined: Jul 2005
Posts: 955
Likes: 2
From: Nashville x-burbs
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.
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.
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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
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
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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.
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Thread Starter
Burning Brakes
Joined: Jul 2005
Posts: 955
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From: Nashville x-burbs
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.
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.
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From: Portland Oregon
Originally Posted by 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?
I would install the Turbo rotor without the rev-limiter when using the 6AL.
