944JM

What is the mechanical limitations on rpms for the 88 N/A? By this I mean at what point do the valves start to 'float' and such. What is the highest rpm I can expect without a total rebuild? What can be done to the valve train to safely raise this limit? Do the balance shafts come into play when raising the limit (do they need attention)? Are the stock injectors up to feeding more rpms? Any DME problems? Looking into whatever is possible and cheapest without rebuilding the entire engine.

MHT

how do you plan to get around the rev limiter in the control unit? That is where the limit is set. Without major modifications, all you are doing beyond about 6500 rpm is making a lot of noise, by that time you are well past peak HP. The stock cams in these cars are very soft, not agressive,. If you put in a more radical cam there might be some benefit to raising the rev limit, but even then you trade low end torque for high end power.

944JM

I figured the max rpm is limited by the DME. I was more concerned with the mechanical end. Is the stock valve train and related parts capable of say 7000? As for the cam. I don't consider it too big a deal to change as well as different valve springs, retainers and such if needed. I just didn't want to get into the bottom end. Not that I don't know how, but just didn't want to get that extreme.

dave120

Most aftermarket chips raise the rev limit up to 7k or so. The one I have in my car did anyways. For the most part the stock parts can handle that rpm, the only issue being possible rod bearing failure due to lubrication issues when you're pulling a g or two in a corner and holding it at 7k rpms. If you're just hitting it in a straight line, assuming the car is in good mechanical shape to begin with, it should be fine.

That said, without modifying something in an 8v car, the extra rpms won't get you much besides worse mileage and more wear on your parts. The 16v cars take much better advantage of the higher rev limit.

ian

Due to the rod bearings I wouldn't spin the motor past 7k on a regular basis, our cars have problems with spinning rod bearings at the stock rev limit, and pushing it much further would just magnify the risk.

Stock your cars peak hp is at 5500 rpms, if you wanted a cam with a longer duration to maybe move it to a peak hp at 6000 or around there I don't think that would be a problem, but trying to make these motors into high rpm screamers would be a ton of work and you would have more luck swapping a honda S2000 motor into the car......

Geo

The max rpm limit is usually dictated by the valvetrain. More specifically it has to do with harmonics. That is why lower mass components will raise the limit. Usually springs are changed to increase the rev limit. Usually heavier springs are substituted. This works, but it can be like using a Howitzer to plink cans. A friend went through an exhausting cam development program with a consultant and found that spring material can affect the rev limit a great deal. However, unless a vendor has already done this homework, we're usually just limited to heavier springs which increases internal drag on the engine.

I don't think bearings are so much as issue as oiling. There are ways around this as well, including cross-drilling the crank and running an Accusump (what I'm doing for the race car).

944JM

I'm really not looking into making it a high winding machine. Just looking into every possible nook and cranny to eek out a few HP here and there. Mine dynoed in stock trim except for headers and cone filter at 127 peak at 5800 rpm. According to the dyno tech it just 'ran out of gas' at the top. I know, I know, want hp get a turbo. Just that my N/A is a sunroof delete and in too good a shape to part with. Still new at the 4 cyl. EFI engines and learning.

Geo

Without performing a bunch of breathing modifications, raising the rev limit will just make it weeze more a the top (relatively speaking).