Max RPM for stock 993 bottom end?

[Jeff Alton]

What sort of RPM can a stock 993 bottom end take? Are the rods that much better then the 3.2/3.3/964 ones and are the only upgrade required rod bolts? I would want to run this too around 7500 or so redline.....

Cheers

[Steve@Rennsport]

Jeff,

Max RPM for the 993 is around 6800 RPM.

Beyond that, those motors need EVERYTHING done to them.

[Jeff Alton]

Hmmm, great, I guess I need to open the wallet a little more.......

Thanks for the info Steve!

Cheers

[Jeff Alton]

What are we talking here? Rods? Any oiling mods that need to be done?

Cheers

[shbop]

signing-up. Headed down a similar path.

[304065]

Interestingly, the PCNA engines used for Daytona prototypes had a rev LIMIT of 9200 RPM imposed, implying that the safe limit is beyond that. But that's a different breed of cat. . .

[aws]

I have seen a twin turbo 993 being spun 7200 for 75 race hours making 500 HP to the rear wheels with no major problems. This engine had a stock bottom end with only Carrillo rods. Stock pistons and heads, no center main oiling mods, stock oil pump. Porsche narrowed the rods in order to thicken the throws when they redesigned the 993 engine much like they narrowed the 3.0 rods from the 2.7. The problem with this is that there is not enough bearing area to support the forces generated by the longer stroke and higher RPM'S. The 993 crank is torsionally more rigid, but this does not outweigh the reduced bearing area. Part of this opinion was caused by Porsche going back to the 964 based crank with the earlier 3.2-3.3 rods and more rod bearing area when they developed the 4 valve water cooled GT-3 RSR engines. ( that are spinning 9200 in the Daytona Prototypes). I think 7200 with a stock engine with aftermarket rods will work because I have seen it, anything more than that and you will have to talk with someone with a lot more experience with these engines than I have.

[Bill Verburg]

Originally Posted by aws

I have seen a twin turbo 993 being spun 7200 for 75 race hours making 500 HP to the rear wheels with no major problems. This engine had a stock bottom end with only Carrillo rods.

That's not exactly a stock bottom end. I'm curious too, mine is stock except for Raceware rod hardware. I've spun it to 7200 a few times but don't make a habit of it.

Originally Posted by aws

Porsche narrowed the rods in order to thicken the throws when they redesigned the 993 engine much like they narrowed the 3.0 rods from the 2.7. The problem with this is that there is not enough bearing area to support the forces generated by the longer stroke and higher RPM'S. The 993 crank is torsionally more rigid, but this does not outweigh the reduced bearing area. Part of this opinion was caused by Porsche going back to the 964 based crank with the earlier 3.2-3.3 rods and more rod bearing area when they developed the 4 valve water cooled GT-3 RSR engines. ( that are spinning 9200 in the Daytona Prototypes). I think 7200 with a stock engine with aftermarket rods will work because I have seen it, anything more than that and you will have to talk with someone with a lot more experience with these engines than I have.

I've heard that same opinion from a # of different reputable sources. The M001 993 Cups, used the 964 crank/rod setup.

The guys that are spinning their 964/993 to big rpms seem to be using the GT3 crank and a custom set of rods, last one I saw was a beautiful set of Ti Pankles(they are like feathers when you pick them up), along w/ the GT3 oil pump.

[aws]

[QUOTE=Bill Verburg;3870805]That's not exactly a stock bottom end. I'm curious too, mine is stock except for Raceware rod hardware. I've spun it to 7200 a few times but don't make a habit of it.

I didn't know raceware made hardware for 993 rods. Are the rods forged? I've always felt all the early stock rods (except the early 2.0 rods) were up to the task as long as no mistakes were made. (ie: over-rev) A 2.9 I freshened up several years ago had gone through a serious over-rev ( well over 9000) and survived with the only problem being all the big ends were .0015 out of round (stretched). I think the weight of the rod versus a Carrillo is what makes a difference in an over-rev. I don't think the Carrillo is any stronger, just lighter.

Great article on brakes on your Home page


aws

[Bill Verburg]

From the 3.2 up the rod bolts have been the first potential failure point. You are right the rods are plenty strong, same rods were used on the GT2.

Don't remember all the weights, here's one on a scale

[aws]

No offense Bill but those don't look like half the rod of the earlier engines. I should qualify my statement about the earlier rods being strong enough--- provided they have aftermarket hardware like ARP or Raceware. One thing I will say about yours, they sure are light, 497 grams for a stock steel rod is pretty good. I have a set of Jet titanium 3.2-3.6 rods that weigh 377 grams, so 497 for steel is really good.

aws

[Steve@Rennsport]

Based on what I've seen to date on 993 engines used for racing, I would not spin one of these beyond 6800 with stock rods, no matter what bolts they have.

Porsche was very wise retaining a 6700 RPM rev limit on these things.

[Bill Verburg]

stock rev limit is 6840

looks like i'll be buying that GT3 crank and Ti rods sooner than expected.

[Steve@Rennsport]

Originally Posted by Bill Verburg

stock rev limit is 6840

looks like i'll be buying that GT3 crank and Ti rods sooner than expected.

Don't use factory rod bearings, either.

[Bill Verburg]

Originally Posted by Steve@Rennsport

Don't use factory rod bearings, either.

yes, i read about that. and the asymmetric Mahles

Hopefully you guys will figure out a bullet(and fool) proof config before i need it.

[Steve@Rennsport]

Originally Posted by Bill Verburg

yes, i read about that. and the asymmetric Mahles

Hopefully you guys will figure out a bullet(and fool) proof config before i need it.

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