MSD rev limit tech question., Bill Pickering? Options

[Trekkor]

Got the odd increment pack.
The mechanical rev limiting rotor was a 7300 unit.
I replaced it with a standard Bosch rotor.
I've been running on the provided 7k MSD pill.

I guess my question is, how high can I safely rev my SIX at the a/x for short blasts?


KT

[nine14cats]

Hey Trekkor,

With my 2.7 I used the 7500 RPM pill the first season then ended up buying the 100 RPM selector switch for it. I would run 7200 RPM as a safe zone then dial it up to 7400 or 7500 depending upon the course if I wanted extra revs.

As us know my 2.7 wasn't stock (IMG:http://www.914world.com/bbs2/html/emoticons/rolleyes.gif) so the goodies inside let it rev to 7500 pretty safely. I ended up moving it down to 7200 the second year for engine life. I wanted to get 3 total years out of the motor before a tear down and everything was going to plan until I missed that shift at Buttonwillow... (IMG:http://www.914world.com/bbs2/html/emoticons/ar15.gif)

I believe your 2.2 is not stock and will rev to the moon like mine did. I'm looking at my Porsche engine book and I see peak HP is:

125HP @ 5800 RPM
155HP @ 6200 RPM
180HP @ 6500 RPM

Peak torque is somewhere between 4200 to 5200 RPM. These are all stock numbers.

If memory serves the 2.2's and 2.4's had redlines at 7200 or 7300 RPM.... (IMG:http://www.914world.com/bbs2/html/emoticons/blink.gif)

I think....

Hey JP, weren't you runnin' your 2.7 with a 7300 pill?

I hope that helps you get started....

Bill P.

[J P Stein]

Yeah, but I had brand new valve springs. I've since dialed it back to 7100 for longevity.

[nine14cats]

I guess you and I had the same idea about trying to make the motor live longer....but wait...they are so cheap to fix...these german masterpieces of engineering....

Can't wait to see the $$$ carnage when I blow the 3.6....

Bill P.

[Trekkor]

Thanks, Bill.

Are you coming to Marina?

I don't want to blow this motor. I just want to eek out the max speed before the shift. At Infineon I got stuck using second gear the whole course, because if I went for third, I'd have to go right back to second and thus, lose speed.

I'd love to run that course again in SIX trim. (IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif)

KT

[nine14cats]

Hi Trekkor,

We won't be at Marina. No 914 racing until the "beast" is done. I'm not kidding about 2006...very sad.

One trick for your car as you go forward is to re-gear your 901. I know that your car is slowly becoming a race car, so I feel okay telling you to do it! (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

Cheap way is to flip 5th, put it into 3rd, get a "Q" gear for 4th and move the 4th "V" gear to 5th. You're only buying one new gear that way. My tranny had that gearing and with a 7200 RPM rev limit I could get into 3rd at Candlestick, Alameda, and Golden Gate Fields. With that gearing I normally could only get into 2nd at Marina (unless Randal had designed one of his wicked long sweepers down the middle!).

Oh...and while you're in there, put an 80% limited slip in there as well...really feels nice on the big tracks and you can adjust your driving style to get around the added understeer at auto-x's. And....and...and....and...and....and...

Welcome to the dark side....... (IMG:http://www.914world.com/bbs2/html/emoticons/happy11.gif)

Bill P.

[Trekkor]

Quick, somebody get the lights!

Right now my second is good to about 50-60 mph and at the RR/PCA a/x, my video showed the speedo creeping up on 80mph as I approached the top of third. (IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif)

Video to follow...

KT

[ArtechnikA]

if you have the counterweighted crank and new valve springs you should be good through 7300, like the other guys say. i've run a 2,0T 914.6 engine to 7100 a couple of times.

a while back i posted the rpm/resistance curve for the MSD tach limiter - the 'pill' is just a resistor and it's just a matter of finding the resistance that gives you what you want; the 'curve' is very linear.

(and the HI-6 sets the rev limit with digital-select switches that i have set to '71'.''')

[nein14]

If anyone is interested I have a MSD 6 AL with the MSD Rev Limiter w/manuals for $180.00 + shipping. Get it before it go's to herschey

[brant]

Trekkor,

I've always been instructed by my motor builder that life will be directly related to redline...
food for thought.


Bill,

hang in there. It will be worth it. I know how hard, and what a committment it is to take a year or two off in order to build up a new car. Hang in there!

b

[nine14cats]

Thanks Brant!

I appreciate the encouragement. Actually, it will get easier this summer to deal with once the car starts being re-assmembled....at least it won't look like a carcass... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Trekkor,

I agree with Brant, the motor life is all about the redline. Jerry Woods and I settled on the stock redline for my 3.6 that they are working on. The motor itself has been warmed over and there is more room to push the limits, but when we talked about what I wanted (reliable power) he said the quickest path to death is revving it's little neck. So we stayed conservative.

As I mentioned in my previous post, we have reworked our WEVO 915 to have a close ration box, with a much taller first gear. Basically we matched the gearing to the Torque range of the motor from it's dyno runs. We have 75 MPH available in the first 2 gears. Auto-x in first and second, use all gears on the track....

Re-gearing if you can do it helps keep the motor in the sweet spot. It allows you to make the most of the available power without stressing the motor to all heck...

Bill P.

[Trekkor]

I understand the need to avoid blowing up the motor. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

At the a/x you know its mostly 4500-5500 rpm's and steady acceleration to redline in the straights.

A usual course, say 60 secs, may only contain a few portions of the track where you rev it all the way up *maybe* 10-15 secs total on redline, spread out over 3-7 seperate occurances.

KT

[TimT]

AFKQV

MSX

7300 is the stock rev limit.. unless you have improved your engine stick with that

I built an engine years ago based on a 2.2T crank that I revved to 7500, but that had fully balanced internals to less than a gram

in some circles T cranks are desirable because they have less rotating mass....and they are plenty strong..