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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Thu May 07, 2020 3:31 pm 
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Joined: Sun Jan 21, 2018 11:22 pm
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Model: 924 turbo S1
Omega are somewhat acting like they haven’t done this before or perhaps aren’t that interested. I’ve just sent them back the photos that Kingzetts posted as reminder. They are also estimating 14-16 weeks or longer delivery. I’m not sure I want to wait that long now my garage is actually working on the car.

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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Thu May 07, 2020 5:21 pm 
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Model: TheOnly Way Is Turbo
Up to 12wks wait for bespoke pistons is what I was being quoted some while ago with JE etc. Unless you have an off the shelf option like Mittelmotor the wait is normal, maybe worse now with virus issues? As I mentioned, my engine too nearly 2ys. Partly because the shop was busy, partly we had to wait for parts before the next stage could progress, partly due to the shop not being in a hurry as they probably had bigger spenders than me to keep happy.

Group buys are always tricky getting everyone aligned in a timeframe that suits all. But if you are looking to a quicker solution then you need to drive it through. Fix the offer, the time frame and message everyone who have offered to join you. or go it alone.

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Steve - Joined: Sat Jan 30, 2010 10:13 pm......think I have lost far too much time in this forum.........
1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 239.5 rwhp @ 1.05bar, Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
2017 VW Passat Variant GTE Advance
2015 Nissan Leaf Tekna


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Thu May 07, 2020 8:49 pm 
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Joined: Tue Dec 29, 2009 11:16 am
Posts: 4238
Location: Stoke On Trent
Model: Supercharged 924
Carrera RSR wrote:
Up to 12wks wait for bespoke pistons is what I was being quoted some while ago with JE etc. Unless you have an off the shelf option like Mittelmotor the wait is normal, maybe worse now with virus issues? As I mentioned, my engine too nearly 2ys. Partly because the shop was busy, partly we had to wait for parts before the next stage could progress, partly due to the shop not being in a hurry as they probably had bigger spenders than me to keep happy.

Group buys are always tricky getting everyone aligned in a timeframe that suits all. But if you are looking to a quicker solution then you need to drive it through. Fix the offer, the time frame and message everyone who have offered to join you. or go it alone.


Couldn't agree more. I've arranged 2 or 3 group buys for things now and it's always a bit of a headache and each time I've had to fund the bulk purchase, then slowly recoup my expenditure as the items sell. I proposed some club involvement for bigger cost items as single people often can't take the risk of a £££ order, but the club wasn't keen on shouldering that responsibility either and storage and ownership etc were hurdles.

If you have 4 people interested that sounds like a good position to be in, and bare in mind if you get into a serious conversation with a supplier they might meet you part way in reducing the minimum order a little.

Just my 2p, I bought my forged set for my 'ultimate engine' about 8 years ago! One day I'll build the engine with them in!!

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924T engine with Eaton M90 Supercharger (DB7), 565cc injectors, coil pack ignition, Adaptronic ECU, Custom Air/water charge cooler, Wideband O2 + 4x EGT. 4pot Brembos, Spax adjustable dampers. 951 G'box with LSD & cooler, 944T style bumper. HID Lo-Pro headlights. 968 mirrors, handles + spoiler. Zender rear valance. Custom side skirts, Forged 17" wheels (8J front, 9J rear). Custom hubs (5x114.3 PCD), Twin circuit coolant re-route (2 pumps, 2 'stats, 2 radiators), 6 gauge centre console.


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 7:49 am 
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Joined: Wed Dec 24, 2014 1:14 pm
Posts: 25
Model: 924 Carrera GT
Sorry, I've been distracted and only just picked up this thread - which I'd found it earlier! Following my original thread discussions, I ordered 87mm 8.2:1 pistons from Mittelmotor, which they said they had on the shelf, and they eventually arrived last week. They're JE with coated skirts and some sort of ceramic coating on the crown.

They weigh 368gm without rings and pin v 508gm for the cast Mahle S2 we used in the race engine. JE pin is 118gm v 139gm standard. Look very well made, skimpy and eye watering price of €1900. BUT the wrong pistons - they have a small combustion chamber (ca 22cc ) and 4mm reduced compression height so I calculate them out as 7.5:1. Currently in discussion with Mittelmotor on what's gone wrong and have they really got 8.2:1 on the shelf or this need to be a custom order. Presumably that'll take a long time if they actually come from JE.

Does anyone know if this is the piston configuration for the race 7.5:1's? I know the S1 piston is a big wide bowl but you still get some squish from the outer ring's close approach to the flat head face outside the combustion chamber. And the 8.5:1 piston configuration for S2 & GT has more squish piston land. I'm a diesel development engineer by trade, so I don't really understand petrol combustion systems, but I thought squish was important on these turbo engines? So having a 4mm deep by 87mm wide pancake as a combustion chamber ( holding ca 24cc ) with no squish seems strange to me. For info, I measured the head combustion chamber as 19.7cc ( head skimmed nearly to limit ) and the head gasket volume as 11.4cc.

Anyway, if Mittelmotor can't sort this soon, I'm certainly interested in participating in a group buy. My goal is 8.2:1 sized for 87.02mm bore ie 2nd oversize with group II hone. As far as I can tell, the standard aftermarket pistons were all sized for the group II hones.

I think my goal for 8.2:1 is a 38cc piston bowl which can be achieved with the following bowl design:-
Frustrum shape ie cone with top cut off. 64mm diameter bowl at the top with 44mm diameter on the bowl bottom. Bowl bottom is 17mm deep. Bowl bottom blends to sloping bowl side with a 15mm radius. Bowl side blends to piston top with 1mm radius. This feature maybe 1.5mm radius.

This design is basically the 8.5:1 Mahle tweaked wider to get the volume but with the same compression height and bowl depth to the piston under crown and gudgeon pin supports can stay the same as std Mahle. I presume the weight of this piston will be similar to the Mahle ie 508gm.

Comments/advice always appreciated!


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 9:02 am 
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Joined: Sat Jan 30, 2010 11:13 pm
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Hi Colin

Theres posts on this forum with images and comments regarding piston bowl shapes, cc's and squish etc. Mostly from Wes who was a mine of information when I was looking to buy pistons some years ago. I'll type from memory, but I stand corrected.

Bowl cc of 7.5:1 pistons is 45cc. Bowl of 8.5:1 pistons is 35cc. Of course head (deck) skims and/or thickness of the HG will manipulate the ultimate CR achieved.

I used a 35cc S2 Omega piston and had to use circa 0.080'' thick Cometic to bring the compression down on my motor. So getting a higher CR piston isn't a huge problem and can be compensated/adjusted with the right HG

Yes, squish is a consideration and circa 0.050'' is desirable. If Iirc stock HG is 0.042'' compressed.

S1 pistons have offset bowl but a reasonable sized squish pad. S2 pistons have centralised bowl and good sized squish pad to head face.

From memory the JE pistons have a limited squish surface around the perimeter of the bowl. As do the pistons that used to be sold on Ideolas Garage, which were made by Diamond Pistons in the US.

Omegas by contrast are hefty pistons. Huge face around the perimeter of the bowl. Quite deep bowls. Ceramic coated skirts. Wes' view these pistons would take some abuse on the crown and with sizeable ring lands

ImageUntitled by stevenmcooper, on Flickr

Next to an S1 piston

ImageUntitled by stevenmcooper, on Flickr

ImageUntitled by stevenmcooper, on Flickr

ImageUntitled by stevenmcooper, on Flickr

Last time my head was off due to head failure, machine shop f3ck'ed up somehow, ARP studs lost clamping force, stock HG failed and I had pressurised coolant. All fixed with a fresh head on + ARP studs + Cometic.

ImageUntitled by stevenmcooper, on Flickr


Note to moderators. Once we have discussed this piston situation, please can we sticky this from Wanted to the 924 turbo tech area. I suspect this conversation will come up again in the future.

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Steve - Joined: Sat Jan 30, 2010 10:13 pm......think I have lost far too much time in this forum.........
1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 239.5 rwhp @ 1.05bar, Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
2017 VW Passat Variant GTE Advance
2015 Nissan Leaf Tekna


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 9:09 am 
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Piston thread...... http://www.924board.org/viewtopic.php?p ... 93784349e5

JE piston with no ceramic coating on crown or skirt
Image

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Steve - Joined: Sat Jan 30, 2010 10:13 pm......think I have lost far too much time in this forum.........
1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 239.5 rwhp @ 1.05bar, Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
2017 VW Passat Variant GTE Advance
2015 Nissan Leaf Tekna


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 9:10 am 
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Another piston discussion thread ..... http://www.tipec.net/_forums/viewtopic. ... 6&start=30

Diamond piston with ceramic coated crown and skirt next to stock S2

Image

OEM S2 and Diamond are the middle two

Image

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Steve - Joined: Sat Jan 30, 2010 10:13 pm......think I have lost far too much time in this forum.........
1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 239.5 rwhp @ 1.05bar, Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
2017 VW Passat Variant GTE Advance
2015 Nissan Leaf Tekna


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 9:30 am 
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Model: TheOnly Way Is Turbo
Rawiz wrote:
Anyone selling a set of 924 turbo series 1 forged pistons?


Stock cast Mahle Series 1 pistons are available from Porsche in 3 sizes circa £425each. Great for a stock engine build.

Series 2 cast Mahle and forged CGT Kobelschmitt versions appear not to be currently available.

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Steve - Joined: Sat Jan 30, 2010 10:13 pm......think I have lost far too much time in this forum.........
1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 239.5 rwhp @ 1.05bar, Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
2017 VW Passat Variant GTE Advance
2015 Nissan Leaf Tekna


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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 10:45 am 
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Just to throw another hat in the ring you could give Troy a bell at EBS, Reno nevada, as they can get any piston to any cr made, with around a 6 week turn around.

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 Post subject: Re: 924 turbo series 1 forged pistons
PostPosted: Sat May 09, 2020 11:19 am 
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Joined: Wed Dec 24, 2014 1:14 pm
Posts: 25
Model: 924 Carrera GT
Thanks, guys - loads of info to absorb!

Seems, from the examples, everyone signed up to a bowl with a squish land around the perimeter, not a flat top with the combustion chamber going out to the cylinder bore like these pistons MM sent me.

Do you need a specific surface finish on the metal surfaces for a Cometic style MLS head gasket or just need clean and flat surfaces?


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