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hayeslewis · Joined: 21 Aug 2011 Posts: 74 Location: Alexandria, VA

We're about to finally purchase our custom pistons for SCCA H-production. Price is around $700 for a set and you may need to also buy custom rods from Pauter for about $1100 a set.

11:1 compression
.040" over
Weight TBA but expected to be at least 35% lighter than stock
balanced within a gram

The o pistons will have partial valve reliefs of .220-enough so that you won't bend valves on a mechanical over-rev, but not so much as to compromise the combustion chamber shape, which is a simple 42cc bowl with a "quench ring" of about 5cm width at the top. Compression ratio is 11:1 with a .051 head gasket, a 231.2mm block (standard) and a true 0cc head. You could reduce the CR and increase the pocket depth 1.2 points with a Cometic .120 head gasket. Rings, wirelox, wristpins, etc included.

Sound expensive? Want to have a go at making it happen? Good luck. It has taken a year for me to get to this point. Some suppliers never returned calls. An "expert" I worked with for a while didn't properly do the original order. Ask 924RCR or Fifty50plus how much work I've had to put in to get to this point.

Expected delivery mid-march

If you want to build an engine in the next year I highly suggest you get in on this buy. It aint cheap, but is it worth all the effort of building a engine without putting good stuff inside.

What kind of performance gain?

I expect about a 5-7HP improvement over my current race motor. The rod/piston combo will be lighter than my current setup, better balanced, have a much better combustion chamber shape (42cc bowl vs the cylindrical combustion chamber from my current flat-top pistons) some quench area, and top rings about half as thick, It's just a guess, but there are only two types of HP numbers, guesses and dynos, everything else is BS.

My current H-prod motor has factory lightened rods and one of the last sets of those VW 1641 forged malhe pistons left in America. The weight of the rod and piston is around 300g lighter than stock. I have the light weight lifters from ACM in Sweden installed with 9mm Alfa shims and Manley lash caps ont the lifters. Cam is a custom grind from Elgin cams (You can ask me about that too) 244 at .050", 267 seat-to-seat but only .425 lift (.047 less than stock due to H Prod rules) Headers and CIS, but the WUR is replaced with a fuel pressure regulator that allows me to tune the AFR to a window of about .5 points from 4700-6300. I have over 120 HP at the rear wheels on a fresh dyno, and there's a bit left on the table. Torque was flat as a pancake from 2500 to 6K. Fuel was a mix of 93 and 110 leaded, but frankly 11:1 compression would probably be just fine with 93.

I can't see any reason this combo wouldn't work great on a street engine too.

Call-don't write me-if you have interest or questions. I'm too busy to go back and forth with tons of questions, but I'm happy to talk to you about the whole project and answer any questions I can. You can reach me at seven 000h tree-too six nine-7even tree five 7even

_________________
Hayes Lewis
1979 924 HP
1979 924 ITB/HP???
2007 Armada
2013 Hyundai Elantra
1972 MG Midget Vintage project
Unstable electrified three wheeled Bicycle truck

924RACR · Posted: Sat Feb 05, 2022 10:22 pm Post subject:

For reference - just got a quote from EBS for a new set of IT-spec level pistons (lower compression, based on stock design). When I first built an IT motor with these, they were about $600; this time around they're $925 (also with rings, pins etc).

This crap ain't getting cheaper - this is DEFINITELY a buy at $700, which is why I'm signed up for a set even though I don't know when we'd be jumping to HP...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

MikeJinCO · Posted: Sun Feb 06, 2022 4:38 am Post subject:

I decided to go with the more expensive JE for my 931 head motor. Different deck height, 87mm bore, different cam lift of .500, different valve size, different head gasket .040. That is too much to ask.
_________________
Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

dial67 · Joined: 07 Apr 2013 Posts: 20 Location: DeRidder, LA

Any update? I am interested in pistons for a rebuild. Any info?

Fifty50Plus · Posted: Thu May 26, 2022 6:50 am Post subject:

We received the H-Prod race pistons (Traum) over a month ago. Rods coming shortly.
Are you looking for 924 street pistons? Or 11 to 1 high compression?
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

dial67 · Joined: 07 Apr 2013 Posts: 20 Location: DeRidder, LA

This build is for a street car. I do not need con rods. Can these pistons be used with stock rods?

Fifty50Plus · Posted: Thu May 26, 2022 8:26 am Post subject:

Once again, it's an 11 to 1 compression ratio piston. Too high for pump gas.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

dial67 · Joined: 07 Apr 2013 Posts: 20 Location: DeRidder, LA

At 11:1 pump gas is not an option without some method of increasing octane. I have had no luck so far finding any replacement pistons for less than $1200. Any suggestions?

Karlio · Joined: 17 Nov 2019 Posts: 119 Location: UK

dial67 · Joined: 07 Apr 2013 Posts: 20 Location: DeRidder, LA

Karlio, thanks for the reply. I will keep you in mind. It is a better deal than $1200. This was a euro spec car. I have three std pistons that I can reuse. I am also looking to buy just one standard piston in good shape. If I can not source a single piston I will buy yours for $925. Do you accept PayPal?

924RACR · Posted: Thu May 26, 2022 10:21 pm Post subject:

I got a set of JE pistons (including new wristpins and Total Seal rings) made up for just under $900... so $1200 seems high.

But it took about 3 months. So Karlio's option might be your best, quickest bet...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

daniel · Joined: 18 Jun 2009 Posts: 686 Location: Sydney, Australia

FWIW:
My 11:1 race car uses 98 octane pump gas no problems.
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

Karlio · Joined: 17 Nov 2019 Posts: 119 Location: UK

gegge · Joined: 27 Jul 2007 Posts: 1124 Location: Sweden

IIRC my CR is 11,3:1 and 95 octan works, but with a wild cam. The duration effect is significant on actual CR.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

924RACR · Posted: Sat May 28, 2022 8:09 pm Post subject:

Also keep in mind in North America octane is reported differently at the pump - (R+M)/2 method, so lower numbers.

...and on the west coast, Cali particularly, it's hard to get better than 91, from what I remember.

Here in the Motor City, 93 at the pump is normal...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype