Redline for 2.4 S

[Edwin Ek]

What all does everyone use for a max. rpm for the 72-73 cars? Do you stick to the recommendation of 7300 or ...?

Since you can remove the rev limiter or modify it, what is a safe engine speed? Among other things, the connecting rods are 60 grams lighter than those in the 2.2 S's. When does valve / piston interference become a problem?

I think I remember reading somewhere that a piston speed of 2500 feet per minute is a max?

[simonozrs]

I stick to 7,300 on my MFI 2.4S. The rotor button limiter works very well. Of course the tacho may well be out somewhat.......... Must check that one day. My mechanic tells me it wont pop at those revs so I am happy to leave well enough alone.
Rgds
Simon

[pwd72s]

[QUOTE=Edwin Ek]

Since you can remove the rev limiter or modify it, what is a safe engine speed? Among other things, the connecting rods are 60 grams lighter than those in the 2.2 S's. When does valve / piston interference become a problem?


Hey, try 8, then 8,500, then 9. Let us know what you find out, okay?

[Chuck Miller]

Ed,

I use my stock 7300-S rotor for my new 2.7 rebuild...

You say modify the rotor... how so?
I understand the concept, just put in a 'slightly' stronger spring...

However, who does the trail and error? ... I would imagine it could be done on a distributor machine.

I have not heard of anyone routinely doing this...

What I have heard is... Changing to a contemporary CD-Box with a infinitely controlled cutout.

If you do know of someone who does modify the stock 7300 S rotor please let me know... I think the old blue car would be just fine at about 7800...

Cheers,

[911pcars]

Using a distributor machine would be handy, but you'd have to rig a working ignition system to output enough secondary voltage via a coil and through the rotor and spark plug to observe the cutout speed.

As a project in school, I once made a copy of a SnapOn ignition system simulator. With an electric motor and rheostat, I could spin the distributor (Chevy V8) to any speed and watch the spark plugs fire. At 6000 rpm, the spark at each plug pretty much looks continuous - mesmorizing as well.

A spring in the rotor, it being a mechanical component, may not be all that consistent from unit to unit (don't know), whereas an electronic ignition box may be more accurate in limiting spark. The Crane boxes are supposedly variable with a rotary wheel while the MSD units use preset "rpm pills" to set the ignition cutout limit.

Sherwood

[ttweed]

Personally, I would not spin it past 7,300 without racing valve springs and retainers and Carillo, Pauter or factory titanium rods. Why would you want to anyway, since without a race cam, you are already past your peak power and torque at that point??? Just shift it and you'll be back in the sweet part of the curve. Maybe with a 906 cam you would benefit from revving to 8K+.

I use an MSD 6AL in my 2.0S with a 7,000 limit "pill" and I rarely miss having that extra 300 RPMs. I figure it provides a little safety margin anyway and helps with engine longevity. Most of the high RPM racing engines are "40-hour motors."

My '73 has a 3.4l with Carillo rods and Aase springs, but the cam peaks at 6800 RPM so I rarely run it above 7K either.

TT

[Chuck Miller]

Very good info and practical advice Tom...

Cheers,

[69911T]

Right Tom and Chuck,

On the 2.7 engine that Tom Woodford built for me I set the Crane 800 rpm below what Tom said the engine could safely turn. There were a few spots on differant tracks where I'd have been happier if I had just a bit more head room but I learned to change the line or the shift point and got along fine and I was always comfortable running the motor to the rev limiter either on purpose or accidentially.

[pwd72s]

Tom's advice is sound. I figure that Porsche installed the rev limiters for a reason.

[Chuck Miller]

... And as before the rebuild, I'm again run'n my car in the 'Short Track Series' on 'the Streets of Willow' ... AND touching the 7300 limiter at lest twice a lap, every lap, with the confidence that 'everything will stay happy'

So there-ya-go