Just Curious, In the 944 Spec racing, do they allow you to run the higher compression motors?

 

IIRC from reading the rules, as long as it was delivered in a 944 from the factory you can run it... meaning it should be alowable to run an 83 chasis (lighter) with an 88 motor (few more hp)...

 

I'd like to see those pictures for flat top 2.5na's. Here is what 10.6 euro pistons look like:
http://www.ebay.de/itm/Porsche-944-Kolben-Pleul-Bolzen-4-Zylinder-Motor-ohne-Lager-Sport-Getriebe-/160654056332?pt=DE_Autoteile&hash=item2567ba5b8c#ht_1350wt_179

 

944-spec rules allow 9.5:1 pistons and 10.2:1 pistons only. Head may be shaved (rules call out actual limits for each piston type) and compression ratio is limited to 10.5:1 on all cars.

So the euro pistons are illeagal both because they were never sold on a USA legal car and also they are clearly over 10.5:1 as is.

 

Yes that is true, but to a point.

All cars must come in no less than 2600lbs with driver. So the 83 weight savings is muted to an extent, but if you are big guy it will be easlier to get to min weight in a 924S or 83-84 944 chassis as compared to an 88 chassis.

Any car may run a motor from any year and you may run either piston and/or shave heads. At nationals the this year the winning car used 88 10.2:1 pistons and the second place car use 9.5:1 pistons. Both heads shaved near the limits. Both cars made with in 1-2 hp of each other when tested on the dyno at the event. Now when it comes to actual hp there are many nuances that we in class are a looking at to ensure all cars have similar hp with either piston. We are not yet ready to share everything we have learned yet as we need to make sure we understand it first.

 

Ok
Thanks I was mistaken.

 

Correct, it looks good on paper but not a net 20hp. Euros were also designed to run on 98RON gas and no CAT. Still it's a nice bump in hp & torque and cost/hp is quite cheap compared to other methods of extracting power from these motors.

 

good pistons are hard to find at reasonable prices. I think factory is the way to go with the iron coating, but there are differences from K-S to Mahle and their weights/shape. I would be curious to know what pistons are being run in spec and why.

 

Porsche OEM stock only. 9.5:1 or 10.2:1. I don't believe anyone has bought new pistons. Too expensive. Best place to find pistons is in a motor attached to a car. Those will be the best value. 9.5:1 pistons are pretty common. 10.2:1 are more rare and we are always wacthing to limit any performance gain on track from using these. So for nearly 10 years we have been sucessfull in that.

 

This is theoretical as I have no measurements but it seems to me you can fly-cut the valve reliefs further on the 10.6 pistons, bring them to 10.2 or 9.5 spec and create a non-interference engine. I've asked before but no definitive answer.

 

I am sure you could try. However you starting to get into things like the shape of the squish area and deep valve reliefs can have big issues. Personally I think the who '"interference engine" deal is way over blown. That and the "fear of t-belt". All the "solutions" are 10x the work of just maintaining the car as is.

 

IIRC, 9.5 was 84-85. The 44/7 motor went to 9.7. and the 88 to 10.2. I've wondered where the difference is in the 9.5/9.7 pistons.

 

Yes that's were the last post on non-interference went, I guess I'll just have to try and see. Maintenance is fine, but I had a belt break after 12k due to a bad batch of belts issued a while back. It's just extra insurance and i think a valuable one. Fly cutting is regularly done on other engines, deeper valve inserts don't seem to cause an issue and ours have a variety of combustion chamber designs that I cannot see squish or hotspots causing a big difference with larger valve reliefs. Other thing we are not talking a great deal of cutting here, plenty of meat still left on the piston.

 

That is NOT correct. There are only 3 compression ratios. 9.5:1, 10.2:1, and 10.6:1

The 9.7:1 was a mistake in a FAQ from many years ago.

 

Thanks for all the input guys!

I love this forum.

So if the euro is only 10 hp more, why is it so much faster?

137mph vs what like 125?

That sounds like more than 10 hp.