lowering reciprocating weight/drag

[Porschekid962]

It was either in Excellence or another porsche mag but someone advertises lightweight cam gears and tensioner gears. What about straight cut intermediate shaft gears or is this nonsense strictly for over the top spenders and factory use? I just thought it was a logical idea. Anyone have some real world input?

[911pcars]

In terms of pure rotating weight like a gear, that would be considered sprung weight; same as any part bolted onto the chassis. IMHO, the weight saved (grams) is negligible unless you're multiplying this effort many, many times.... or into cycling.

And then there's reciprocating weight; engine parts that slide back and forth at a high rate (e.g. usually pistons and connecting rods). Lower bearing loads and higher revs for more HP with an increased safety margin are the benefits. However, reducing this weight can get expensive. You can judiciously remove some grams off the piston bosses and con rod ends. That helps a little. The next step is to replace with lighter reciprocating parts. Mahle pistons are pretty light already and there aren't many options in this area. If you remove too much material in the wrong area, then you chance piston failure.

Titanium rods are available. They have a significantly better strength-to-weight ratio than steel rods, but you pay for that privilege.

Reducing sprung weight is easier achieved by removing the A/C system, replacing with a lightweight battery or losing a few personal pounds. It's cheaper to do also.

Hope this helps,
Sherwood

[jluetjen]

You also need to consider how fast it is spinning. So the if the oil-pump jack-shaft is spinning 1/3 as fast as the crank, then the savings from reduction in inertia will be significantly less then a reduction in inertia of the crank-shaft itself.

[Tyson Schmidt]

Great replies above. I'll just add that those lightweight sprockets have a very short service life.

Do you really want to replace them every 25 engine hours?

[Porschekid962]

25 hours? no way man! It was just one of many thoughts that I have had and wondered what the benefits/pitfalls are of some of the cool racing parts porsche has put in cars over the years. I will probably just end up with a high comp 3.something or other with a 70mm crank and some crazy induction and high CR.

Came up with an idea that I thought would be pretty slick for and ITB setup and relatively easy to make, I am thinking about mating that to an MFI pump and crankfired twin plugs...

[Walt Fricke]

I like steel straight cut intermediate shaft gears, but not because they reduce the moment of inertia. They are stronger than the steel/aluminum setup, and I see Porsche has switched to steel helical cut gears. The straight cut gears don't put a side load on either the crank or the IS shaft. Whether this will let the axial load sides of the #1 main last longer or not I don't really know. I think straight cut gears have less friction. They make more noise, but on a race motor that is often not a concern. Probably not a good idea on a street engine.

Walt Fricke