Case and crank mods: are they worth it?

[snowman]

Race engines do not count because they only have to live a few hours. If its air cooled and 600HP it will have a silver lining.

[350HP930]

Its all about heat soak. Short spurts of 600 HP will not hurt a properly built, cooled and tuned 930 motor.

When you have that much power in a small car you are not likely to use it for long unless you are trying to go 200 MPH.

One also needs to keep in mind that 911/930 engines are air AND oil cooled.

One of my mods to help deal with the extra heat is increasing the size of the orifices in my cam tower spray bars.

When it comes to keeping pistons from melting, both water and air cooled motors use piston squirters for that purpose.

Beyond the greater risk of detonation the main downside to air cooled motors is keeping the exhaust valves from melting since their heat sink is a lot hotter than a water cooled head's. Thats the reason 930s have sodium filled valves.

[snowman]

The guys I was running against at MIS were going full power for 1/2 hour to 0ne hour continuous. Mostly full throttle. I can tell you for sure they can't take that. But my M635 is speced to run continuous at 6500 RPM in high gear. Did thoroughly smoke and I do mean smoke the brakes though.

That 300HP at the rear wheels means what, about 420 HP at the crank? 600 is a lot higher.

BMW must spec very conservatively, my 286HP engine ends up putting 275 at the rear wheels as measured on dyno and backed up by the 13.4 sec 1/4 mile for a 3700 lb car with driver.

[snowman]

1996-1999 993 Carrera 4 & 2
3600 cc
285 bhp @ 6100 rpm
340 NM @ 5250 rpm
compression: 11,3:1

This is the highest spec I can find for a stock Porsche, am I missing something?

The Turbo 993 rated at 400 plus HP in 1996 was probably done against all advise from Porsche engineers, one of those marketing kind of things. Porsche engineers KNOW that this is NOT a relaible engine, yet they made it anyway. At least thats what the Porsche engineer I know says.
And being an engineer for over 30 years I know how marketing works, in any company, thats why I think Detroit blew it, they listened to the dope, air heads in marketing, you know the ones that actually smoke crack.

In any case they were doing water cooled heads soon after. Which means they were doing them at the factory at least 5 years before this.

[blue72s]

Some recommend scrapping anything that has 0.002" or higher clearence in the rod journals. The NASCAR guys use 0.0015" for the rods and they run a constant 9000 RPM.

Thanks snowman. I'll forget about 906/910 crankshafts and buy a 901 one instead.

[Tim Walsh]

snowman,
Just to clarify. The car that you quoted was not a turbo. Looked at the compression ratio (11.1:1).

second assuming 15% drivetrain losses, 300 HP at the wheels is 352 HP, not 420.

[snowman]

I think the turbo had much less than 11:1 compression. I always use 25% for drive train loss. Unless its a Chevy, then I use 33% to 50% depending on the year.

[snowman]

Originally posted by blue72s
Thanks snowman. I'll forget about 906/910 crankshafts and buy a 901 one instead.

what that got to do with anything?

[blue72s]

what that got to do with anything?

A while back I asked a question about 906/910 vs 901 crankshafts but did not get answers I wanted.

906/910 crankshafts are identical to 901 except that the journals are about 1 thou smaller for higher clearances.

[snowman]

I could see making a crank with guarenteed clearences. Could it be more a guarenteed, consistant number rather than just more clearence?

[Henry Schmidt]

We are cross drilling all our cranks. Proper oil flow to all the rods is a good idea at any rpm.
It's cheap and well worth the piece of mind.
The new chrome moly billet cranks that we are building will oil the rods from every main journal. This will allow us to reduce the flow through the number 1 and 8 mains to guarantee even oil flow to all 6 rods.
Is this new /modern oiling schematic necessary ? no, but with a clean sheet of paper why not improve on an old design if you can.
These new cranks are coming soon and will offer a 66 mm 9 bolt crank for very high rpm engine using 3.0, 3.2, 3.3 and 3.6 base engines.
Snowman talks about 8 and 9000 rpm Porsches like that's easy to do. They are easy to build but hard to keep alive. Short stroke engines with proper rod length to stroke ratios are the best way to achieve this goal. Pankl Titanium rods won't hurt either.

When it comes to main bearing movement, the addition of high strength LocTite 568 (574 if that's all you have) between the main webs will greatly reduce main bearing moment on lower out put engines. Shuffle pinning as stated here is advised for all higher out put engines. The amount of time spent near redline rather than the total hp out put is probably a better indicator of shuffle pins as a required modification. What I mean by that is a 220 hp mag cased 2.0 that spins 8000 rpm 80% of the time needs shuffle pins. A 3.3 turbo that make 400 ph 5% of the time (short freeway blasts) would be less likely to need shuffle pinning but would benefit greatly from LocTite between the main webs.

As for clearance on the rod bearings as a general rule slightly larger clearances with higher oil pressure/ volume in high rpm Porsches is a good idea. That is why Porsche GT3s run hugh oil pumps and the bearings come color coded for the crank. It is not uncommon to see a GT3 crank that requires three different color code bearings.
That right, with a GT3 you might need 3 bearing sets to build it with the correct tolerances.