9.8 or 10.1?

[pete917]

Thanks Ralph, Interestingly I was told the same thing: that it would produce 10.3:1 when I bought my piston and barrel set.
Regards
Peter

[pete917]

Hey Ralph,

I just asked Mahle Motorsport via EBS Racing who I opurchaded my 3.5 ltr Mahle set from to confirm the deigned volume for the piston dome. The answer Mahle gave was 35.14cc. This would mean a cylinder head volume of approx 90cc would be needed to give 10.3:1.

I wonder why Mahle would say the cc is 10cc more than yoour measurement.

Pete

[Carrera3.5L]

Originally posted by pete917
Hey Ralph,

I just asked Mahle Motorsport via EBS Racing who I opurchaded my 3.5 ltr Mahle set from to confirm the deigned volume for the piston dome. The answer Mahle gave was 35.14cc. This would mean a cylinder head volume of approx 90cc would be needed to give 10.3:1.

I wonder why Mahle would say the cc is 10cc more than yoour measurement.

Pete

Hi Pete,

Well, perhaps I measured wrong but I don't think so...

Don't lose any sleep over it at this point, do the calculations and see where you are at and we can go from there...

The couple of times that I spoke with Mahle Motorsport in North Carolina, nobody there knew anything about Porsche pistons/cylinders...they were letting SSF (whom EBS probably bought the set from to sell to you) and a couple of other parts warehouses dealing with European car models handle all of the tech/distributing. Mahle opened up a US branch simply to build in-roads into Nascar and penetrate the good old boy network...

Andial (being the exclusive Mahle importer/distributor for many years prior) and developing many of their own piston/cylinder conversions in conjunction with Mahle still buys direct from Mahle in Germany and bypasses Mahle Motorsport in NC. Andial also builds engines using these pistons & cylinders rather than simply slapping a new UPS label on them and sending them to the end user.

Whether you end up at 9.5:1, 10:1 or 10.5:1, it really won't matter all that much in the grand scheme of things. Still a street motor needing pump gas and a "normal" lifespan, right? Is an extra 5-10 horsepower really going to kill you? Some of your UK mates are claiming huge hp gains on their bone stock 3.2L's simply by swapping a chip and muffler, your motor should make 400 hp on these optimistic dynos based on some of the claims I've seen from UK enthusiasts on this board...

Since it seems that we are the only ones still participating, perhaps we should take this to private message and let this thread die?

Ralph

[Jeff Alton]

For what it is worth, my twin plugged 3.2 heads had a 90cc volume. With pretty good sized reliefs for the second plug and a chamfer. That is in the ball park of what Ralph measured originally before having some more taken off the heads.

Cheers

[911 tweaks]

You cant take this to Private Message...I for one appreciate all that you guys are discussing in an open and forthright manner. I am learning a lot and getting tons of ideas just for openers!!

You are doing the porsche community a great service by openly discussing a matter that I am sure others will and do find very usefull. Others will chime in...maybe not as readily as you would think.

Keep up the great work and I for one MUST see the final outcome of this project,,,even a few sound bites when she's fired-up would be awesome??

Best of Luck!!

Bob

[pete917]

OK so lets keep it open....

Ralph. I agree there have been some big boasts in the UK and I for one dont believe most of them. I am being realistic in what to expect from my motor when she's done. But you're right, what 5-10bhp for a predominantly street application.

However, I am the sort of person that likes to get to the bottom of things. If Mahle claim 10.3:1, then it makes want to find out where the differences are comming from.

Im certainly not going to take Mahle's word for it on the dome volume and will measure it myself. Im in the middle of measuring so will report back soon.

I do wonder though, what volume Porsche changed between the US and Euro spec cars the make the CR different. Im guessin it would be the heads, so as soon as I measure mine we'll have some real data for a comparason. From you post and jeffs it seem US heads are about 89-90cc.

Speak again soon

[Jeff Alton]

The pistons were different between ROW and US cars.

Cheers

[Carrera3.5L]

Originally posted by pete917
From you post and jeffs it seem US heads are about 89-90cc.

The heads have many variables that can affect their volume. Single/twin-plugging, 12mm or 14mm plug being used for the 2nd plug, have the seats been sunk by the machine shop, etc all can play a part in the outcome.

I don't know for sure what the difference is, but I would agree with Jeff and say it is probably the piston itself that is different. To me that would be the most logical at least...

It sounds like you will have a great motor when it is all done though, just like with Jeff's I am envious of your induction...

Ralph

[CruiseControl]

Ralph

Just to add a few more figures....
I measured the JE 10.5 pistons (98mm dia., 3.2 to 3.4L) with a dome capacity of 38.89cc.
With a deck height of 1.25mm, 98mm bore, and a head capacity of 88.8cc this results in a 10.457 comp ratio.
Interested to get a few more readings of 3.2L head capacities if any one has them available.

Paul

[pete917]

Ill have my head reading soon and will post here straight away. I just need to buy a Burette!

[Jeff Alton]

I don't have my notes in front of me, but I had 90cc head volume and 1mm deck height and the 10.5 JE and when I measured it all out I have 10.50xxx CR as well. I also double checked Paul's math for kicks, and it is bang on!!

Cheers

[ChrisBennet]

My 3.4 (from 3.2) twin plug head volume was 90.5cc.
My 98mm "10.5:1" JE's dome measured around 40cc (I had trouble getting consistent readings).
My deck height was 1.12mm (avg of 4 sides).
-Chris

[Scott Clarke]

Well, my pistons are installed. Here are the promised before and after photos:

I measured the dome volume after the surgery, and found that I should end up at 9.7:1 with 1mm deck height. Cam carriers to be installed this weekend.

[Grady Clay]

Scott,

How thick is the piston crown after the machine work?

Best,
Grady

[Scott Clarke]

Grady-
The underside of the piston is basically flat, so the thickness in the middle is still significantly more than the thickness at the edges. 7.5mm of material was removed.
-Scott

[pete917]

Has anyone experienced any fuelling problems on the capacity upgrades. Has the standard 3.2 fuel pump been adequate?

[pete917]

i finally finished my build and ended up with a deck height of 0.75mm and a CR of 10.5:1

It seems to running fine, although its early days as Im still running the engine in.