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Where is everyone getting Pistons from for their 931's
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Sharky  



Joined: 29 Jun 2012
Posts: 14
Location: Australia

PostPosted: Wed Nov 18, 2020 6:33 pm    Post subject: Where is everyone getting Pistons from for their 931's Reply with quote

So... for a turbocharged '81 924, and with ideola's garage no longer operating (Super Sad about that...) where is everybody getting pistons from?
I am trying to get a set ordered, have been for a while now.
I understand they need to be forged, but honestly...
Last time I spoke to Diamond, they sent me a form that wanted specific dimensions that I just don't understand... and at around AU$1200 for a set, I'd really like to get it exactly right so I don't end up with something that I cant use, and probably couldn't even sell considering the specifics involved in the dimensions.
I really like the coating Diamond offers for their products, and I was really interested in getting that done as part of the purchase.

If you guys could offer any help on where to go and how to get the ball rolling on a new set of pistons & rings I would be very grateful.


Thanks for your time
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CÚdric  



Joined: 27 Aug 2004
Posts: 2073
Location: Sweden

PostPosted: Wed Nov 18, 2020 7:32 pm    Post subject: Reply with quote

Aren't there any local campany which makes custom pistons? Maybe some place where you could send in an old piston for them to measure?

I bought a set of omega pistons from a guy in the uk, but i think they have a minimum order of 3 sets or something like that.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2100
Location: Somerset, UK

PostPosted: Wed Nov 18, 2020 7:39 pm    Post subject: Reply with quote

Off the shelf...... Mittelmotor have JE

Special order...... JE, Diamond and most will want a properly filled in spec form regardless of them making them previously. You may need the help of your engine builder to measure your block and existing pistons

Omega in UK want 4 sets minimum order

Expect to pay USD 1000 to 1500 per set.

You must have piston maker in Aus?
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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safe  



Joined: 18 Mar 2017
Posts: 210
Location: Sweden

PostPosted: Wed Nov 18, 2020 9:20 pm    Post subject: Reply with quote

There must be tones of "speed shops" in 'stralia that can help you custom order a set of pistons from JE or somewhere else.
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jazz guy  



Joined: 26 Nov 2002
Posts: 425
Location: Colorado

PostPosted: Thu Nov 19, 2020 5:41 am    Post subject: Reply with quote

I agree with the suggestions to find a local piston maker. With their help and maybe a donor piston you should be able to get something done.

I've been looking for pistons too. Omega looked like a good option but when I talked with them this past Summer, they had a minimum order quantity of 20 pistons per design.

There are some builds out there using the Mittelmotor JE's. Not a cheap option but other than Omega, maybe the more proven option?

I'm down the path a ways on a custom JE set. The cool thing is I get to spec whatever dimensions I want! The scary thing is that I get to spec whatever dimensions I want...

I'm not moving very fast but if I run into any other options, I'll certainly pass them along.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1132
Location: Washington DC area

PostPosted: Thu Nov 19, 2020 8:03 am    Post subject: Reply with quote

Diamond has the specs for a turbo piston as well as the specs for an NA piston having made both types. I don't know if the turbo specs are under Dan/Ideola or Chris's (friend of Vaughan Scott) name, but the NA specs are under my name (Chuck Allard). As I recall, eight pistons were about $1200 while four pistons were close to $800.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2100
Location: Somerset, UK

PostPosted: Thu Nov 19, 2020 7:58 pm    Post subject: Reply with quote

Fifty50Plus wrote:
Diamond has the specs for a turbo piston as well as the specs for an NA piston having made both types. I don't know if the turbo specs are under Dan/Ideola or Chris's (friend of Vaughan Scott) name, but the NA specs are under my name (Chuck Allard). As I recall, eight pistons were about $1200 while four pistons were close to $800.


JE also have the specs as they have built many dozens of sets, but they still want you to complete a spec form to avoid any issues of making the wrong piston.

I blind bought some JE for series 1. The CR will/should be lower......I guess these are 7.5:1 CR (I wish Dan's piston/CR tool was still online.....) and ideally you would want a touch more, CR for series 2 is 8.5:1. This image might help with a discussion with a piston shop / JE. There appears to be a mix of imperial and metric measurements in the spec


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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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924RACR  



Joined: 29 Jul 2001
Posts: 8372
Location: Royal Oak, MI, USA

PostPosted: Thu Nov 19, 2020 11:10 pm    Post subject: EBS knows the 924 Reply with quote

Just a reiteration, EBS knows well how to spec out JEs for the 924s. Been very happy with these in our 924NA racecar.

But I can't provide any specs for Turbo pistons, mine are still original...
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2100
Location: Somerset, UK

PostPosted: Fri Nov 20, 2020 11:06 pm    Post subject: Reply with quote

PS most piston companies can offer crown and skirt treatments if required. Not just a Diamond thing
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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TJC  



Joined: 04 Apr 2010
Posts: 777
Location: Central-ish Arizona, USA

PostPosted: Sat Nov 21, 2020 2:30 am    Post subject: Reply with quote

Fifty50Plus wrote:
Diamond has the specs for a turbo piston as well as the specs for an NA piston having made both types. I don't know if the turbo specs are under Dan/Ideola or Chris's (friend of Vaughan Scott) name, but the NA specs are under my name (Chuck Allard). As I recall, eight pistons were about $1200 while four pistons were close to $800.

Say Chuck, regarding the NA piston for a moment...wasn't there an off the shelf VW piston, possibly a flat top, that could be used with a slight overbore for an NA application?
And with the proliferation of small bore turbocharged engines in the last decade or so wouldn't there be a possibility that there are other "stock" pistons, from various auto manufacturers, available with specifications similar enough to the 924 Turbo that may be used? Seems to me custom pistons at $200.00 per is a bit pricey...but then again given the "beat down the door" demand for such a thing, perhaps not.
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'95 BMW 318i/5 ..."Pearl"
'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

Still on the Prowl!

www.ttrs1.com
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1132
Location: Washington DC area

PostPosted: Sat Nov 21, 2020 4:54 am    Post subject: Reply with quote

I didn't shop for stock pistons since my application was SCCA's IT-B class. We are allowed one half point increase in compression over stock. I chose to have that encompassed in the piston top rather than milling the block (head is flat on the NA). The fact that they are forged, lighter and all weigh exactly the same out of the box. All bonuses in my opinion. I've also seen the turbo version of the Diamond pistons and they are also works of art. Dan/Ideola was a great help when I was starting this build.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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safe  



Joined: 18 Mar 2017
Posts: 210
Location: Sweden

PostPosted: Sat Nov 21, 2020 5:20 am    Post subject: Reply with quote

TJC wrote:

Say Chuck, regarding the NA piston for a moment...wasn't there an off the shelf VW piston, possibly a flat top, that could be used with a slight overbore for an NA application?


Yes, 87mm VW flat top (Google it). They are completely flat but with 1.5 mm lower compression height.
The volume of the NA dish is 19,8 ml and 1 mm across 86.5mm would equate to 5,87 ml. So it would be like decking the block 3.37 mm which is a bit much I would say, maybe 1.37-1.87 mm too much. A bit thicker head gasket might fix it, or maybe E85....
They are also a bunch lighter than stock.

Don't hold me to my math on this!! Recheck yourself if trying it. I would try it for an NA build, I have a set somewhere...

Also the calculations is for a ROW spec engine.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1132
Location: Washington DC area

PostPosted: Sat Nov 21, 2020 8:16 am    Post subject: Reply with quote

Flat top piston...any cut out for the valves? Or does it become an interference engine? Sounds like a great way to really bump the compression ratio. Similar to putting turbo pistons in an NA engine.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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safe  



Joined: 18 Mar 2017
Posts: 210
Location: Sweden

PostPosted: Sat Nov 21, 2020 8:43 am    Post subject: Reply with quote

Fifty50Plus wrote:
Flat top piston...any cut out for the valves? Or does it become an interference engine? Sounds like a great way to really bump the compression ratio. Similar to putting turbo pistons in an NA engine.


No valve relieves. Not sure the vales will clear at all, trial and error
If its interference or not, who cares, never understood that "selling point". Never had a cam belt snap on any car I've had despite being old and high mileage.
On my 911 I think I have 0.8 mm of minimal clearance of the valve chasing the piston, when the timing is good.
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TJC  



Joined: 04 Apr 2010
Posts: 777
Location: Central-ish Arizona, USA

PostPosted: Sat Nov 21, 2020 9:24 am    Post subject: Reply with quote

Thanks Chuck and Safe!
I'm at some decision making crossroads and this info will help a ton.
I should probably start a new post with my questions so as not to muck up this one, sorry Sharky!!! It's just that this came to mind as my daughter and I were just discussing if we should do anything with "Pogo" in the near future and the thought of forsaking the factory turbo setup for a hot NA appeals to me if we keep it.
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'95 BMW 318i/5 ..."Pearl"
'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

Still on the Prowl!

www.ttrs1.com
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