Don Terrill’s Speed-Talk

JodyB wrote: ↑Fri Oct 04, 2019 1:00 am Saw the idea years ago. A corvair land speed racer was injecting water into the cooling fan to help keep head temps under control. Why isn't this captain obvious idea more widespread with aircooled guys?

RCJ wrote: ↑Fri Oct 04, 2019 8:06 am Besides coating, how are other ways to pull the heat out of pistons.

hoffman900 wrote: ↑Fri Oct 04, 2019 8:41 am

RCJ wrote: ↑Fri Oct 04, 2019 8:06 am Besides coating, how are other ways to pull the heat out of pistons.

Piston oil squirters. Porsche adopted them in the early 1970s. They’re pretty much a requirement on any high output engine that has to live for more than a quarter mile at a time.

Truckedup wrote: ↑Thu Oct 03, 2019 9:16 am Smokey Yunick claimed that on the dyno,a SBC continued to make more power up to about 230F if detonation was under control...

HiPer Express wrote: ↑Sun Oct 06, 2019 5:44 am

Truckedup wrote: ↑Thu Oct 03, 2019 9:16 am Smokey Yunick claimed that on the dyno,a SBC continued to make more power up to about 230F if detonation was under control...

It was Grumpy , guy who actually knew something.

Kevin Johnson wrote: ↑Sun Oct 06, 2019 2:13 amProper windage control is needed to remove the oil droplets from the cloud at high rpm. The impacts with the rotating assembly heat the oil and are a parasitic drag as well as adding volume to trapped pooled oil under sustained lateral acceleration which could then be churned by the rotating assembly; i.e. the collected oil could not drain back to the sump proper. The areas where the oil temporarily collected became defacto sumps. Porsche had to withdraw the use of oil squirters in the 928 because of this. Other manufacturers designed pumping systems to transport oil away from these collection areas in the style of scavenge stages for dry sumps. Often something like this that works is illegal to retrofit in various racing classes.

ptuomov wrote: ↑Mon Oct 07, 2019 9:44 am

Kevin Johnson wrote: ↑Sun Oct 06, 2019 2:13 amProper windage control is needed to remove the oil droplets from the cloud at high rpm. The impacts with the rotating assembly heat the oil and are a parasitic drag as well as adding volume to trapped pooled oil under sustained lateral acceleration which could then be churned by the rotating assembly; i.e. the collected oil could not drain back to the sump proper. The areas where the oil temporarily collected became defacto sumps. Porsche had to withdraw the use of oil squirters in the 928 because of this. Other manufacturers designed pumping systems to transport oil away from these collection areas in the style of scavenge stages for dry sumps. Often something like this that works is illegal to retrofit in various racing classes.

Having now run 928 S4 engines both with piston oil cooling jets and without them, I would dispute both the fact about what they do and don't do inside the engine and also the reason for their discontinuation by the factory. I believe that the most likely reason why the piston oil cooling jets were removed from the 928 S4 was that a multi-car track testing program showed very low piston temperatures and that they were therefore unnecessary. Expensive and unnecessary things are not added to car engines by car factories. The existing blocks with piston oil cooling jets were used, though. The crankcase breathing and oiling behavior of engines with and without the piston oil cooling jets appear close to identical in our use.

If you have evidence on either (the piston oil cooling jets actually causing problems or the factory discontinuing their use for any other reason other than cost), I'd like to hear it. I recall Porsche communication on the discontinuation being: "Bores for piston crown cooling have been omitted in the upper crankcase section since January of 1987 because of positive endurance testing results."

This has been of interest to us recently, because in order to run higher rpms, we need lighter pistons and thinner piston rings which will by our calculations require piston oil cooling jets.