Stupid rod bolt question...

[Rick Lee]

I've just recently learned of the potential for disaster in over-reving 3.2 Carreras. Since I have an aftermarket chip and assume my rev limiter is gone, I try real hard to not top 6200 rpms. As I know absolutely nothing about engine internals, is upgrading to 10mm rod bolts something I can do without a total engine teardown? If it's just a matter of dropping the engine or getting inside the valve covers, then no problem. But if it's only done during a rebuild, then I guess (and hope) I have a while to go. Thanks.

[pete911]

As a minimum the cylinders have to come off, so I think it is too big of a job. My track car has a 3.2 with stock rod bolts and regularly sees 6900 rpm. I know a guy that put almost 40000 miles (all track) on a 3.2 before the engine failed due to the rod bolt issue. He is a club racer and used all of the rpm's available

Pete

[Randy W]

Engine failure is not to be taken lightly. A 3.2 case, rods, pistons, valves and crank are not cheap. If you are keeping revs to 6200, no problem. If you are going to 6900 and the oil is getting hot, the odds are you will have a problem. The 9mm rod bolts in the 3.2 cannot be replaced with 10mm ones. It is advisable to upgrade to Raceware or ARP 9mm rod bolts on a 3.2 that is tracked alot above 6700. Otherwise, keep your ears open for a "knocking" noise - you might be able to get away with just valves, one rod, the engine oil cooler and alot of machine work like I did ($$$).

[Wayne 962]

Hmm, I'm sure that's not reassuring... No one really knows what will stress the bolts to their limit, but over-revving is one thing that will hasten the failure.

If the engine failed at 40,000 with racing 'abuse,' will it fail at 80,000 with normal abuse?

The best bet is to just keep your eye on your tach and not rev your car up to the rev limiter. I predict that the bolts have a 'limited number' of 'over-revs' in them before they fail. Over-rev it many times, and you're probably in for trouble. Over-rev once or twice, and you're probably fine. Of course, I've heard of exceptions to both of these circumstances...

You need to remove the top end to replace the rod bolts and rod bearings. As of this moment, I don't recommend tearing down your engine just to fix this problem...

-Wayne

[Jim Richards]

Are there aftermarket chips available that don't disable the rev limiter? The NoVA Pelican gang needs a solution that'll push Richard's next engine drop out a few more months. All in good fun.

[Rick Lee]

I wouldn't mind dropping it once a year or so. But I don't want to get clipped for the cost of engine parts. I just need to upgrade to a 993.

[Joeaksa]

Jim,

Most modifed chips do not eliminate the rev limiter. They usually just move the limit up from 6200 to 6800 or so to give the motor more power. What is important is finding out and confirming that the rpm limit is not too high. Here is where you have to trust the person or company who programs the chip...

If someone is good with electronics, you can pull the chip out of the DME and read the code there. Better people can program the puppy and duplicate the results given by some of the aftermarket chips for $15 and a few hours work. The bare chip costs under $10... its the reader and knowledge that counts.

Joe

[APKhaos]

Hi Richard - feeling nervous??

Replacing rod bolts with ARP or Racewear is the best insurance, but the time to do this is when you are doing a top end refresh.

The rev limiter is still active in after market chips, just set at a higher threshold. The rev limit settings for the stock chip is 6520; Weltmeister is 6840, Autothority is 7040.
More details - Check It Out! OEM, Autothority, Weltmeister chip maps!

Shift point over-rev is something you can control. The risk of stretching the rev band on the track is real, but its hard to imagine doing this on the street - unless the red mist has gotcha.

Bigger risk is mechanical over-rev due to a missed downshift - 5th to 2nd when trying for 5th to 4th is the most common. The rev limiter won't help in this situation. Avoid it at all costs.

[targa911man]

Richard--

You consider a 993 an "upgrade"? I hope you're just kidding.

[Rick Lee]

Careful there, Dan. You may end up getting another "I'm saddended by what I read" thread started.

[Early_S_Man]

The 'stock' rev limit for a 3.2 is 6520 rpm ... per the '84-'87 spec book. If I remember correctly ... the Club Sport special edition had a limit set 200 rpm higher, on an otherwise stock engine!

[304065]

Richard,

I drove my '88 carrera actively in two seasons of PCA DE and hit the rev limiter of my Weltmeister chip a couple of times, not a big deal as long as you don't do it at the end of every straight.

A far bigger concern but probably not material considering your G50 has much better defined shifting is the risk of an over-rev on downshift. I've heard that you can "zing" the motor to 8000 rpm like this about a half-dozen times before the bolts let go. I keep an eye on the tach needle when I downshift- if I hear the motor begin to whine and see the needle accelerate toward 5:00 it's time to immediately shove the clutch in and get the right gear. But that's with a 901 box in the heat of battle.

Unless you are door-to-door with somebody and are trying to put a pass on them, there's no reason to over-rev the motor. In the PCA stock classes changing the DME or KLR chip ist verboten anyhow.

Does anybody know what the "safe limit" of something like a 911R-style 2.0 screamer motor is? With TI rods and low reciprocating mass, and low-inertia valve train with TI keepers, what's the practical limit?

[ChrisBennet]

Originally posted by Early_S_Man
The 'stock' rev limit for a 3.2 is 6520 rpm ... per the '84-'87 spec book. If I remember correctly ... the Club Sport special edition had a limit set 200 rpm higher, on an otherwise stock engine!

The CS had hollow intake valves but there was nothing special about the rod bolts.
-Chris