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leadfoot · Posted: Thu Jan 04, 2007 11:04 am Post subject: vw flatops

5mm from top of bore... these are 88mm vw pistons

Progress on the rebuild is getting there...
turbo head is at the machine shop, should have it in on the weekend... if it doesn't rain...
As a question of interferance or not i'm waiting to get the cam back to see how far out the valves protrude from the head then I'll know for sure...
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

flosho · Posted: Thu Jan 04, 2007 11:53 am Post subject:

Crank pulley and water pump pulley.... info on those?
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leadfoot · Posted: Thu Jan 04, 2007 12:28 pm Post subject:

24 carat gold plating... just kidding...
Crank pulley is steel, and because it was starting to rust I had it cleaned and then Cadnium coated (you can get either silver or gold colour) I then sprayed it with gold enamel paint and clear coated it as well.
The water pump pulley is aluminium so I just cleaned it and sprayed it gold and clear coated it.
The block was black, my hoses will be red so gold seemed fitting in the color scheme for a german car... something a little different too.
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

flosho · Posted: Thu Jan 04, 2007 1:46 pm Post subject:

Lol.. I thought they were some crazy aftermarket ones..

That'll really dress up the engine bay, they look brand new! Gives me something more to do this spring.
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Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

Leadfoot, I'm sorry, I've either not been paying attention or totally missed something. Are you doing a high compression normally aspirated engine with a 931 head? The holy grail of 924 engines - the D-Production variant? Do tell, what enhancements to the 931 head? What compression ratio overall? Cam specs? EFI I assume?
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1987 951 - M193 Version for Japan

leadfoot · Posted: Thu Jan 04, 2007 3:04 pm Post subject:

Overbore 88mm vw flatop pistons - compression should be 8.9 : 1 using the turbo head which has also been port matched to match the new intake manifold (pictures posted earlier) and to the stock N/A manifold which I must say took me days to do, port match and match stud holes.
Supercharged EFI as before but I remade the SC's inlet and oulet manifolds as they were restrictive. I'm looking at 10psi with the restrictions gone and the length of piping and bends reduced.
Cam is the same...
274 advertised duration
233 intake and exhaust duration
.459 lift
something like that at any rate, it's been posted earlier as well...
So more bore more psi and more fun hopefully...
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Joes924Racer · Posted: Thu Jan 04, 2007 4:09 pm Post subject:

fun is fun. Looking good.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

arx · Joined: 16 Dec 2005 Posts: 129 Location: Estonia, Tallinn

Leadfoot, what manufacture VW flattops you used, where did you bought and how much they were? I was searching to buy ones last year but it appeared that that the original Mahle forged pistons are disappeared from market.

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

Wow, that will be a nice setup, I expect you will have lots of fun with that!
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1987 951 - M193 Version for Japan

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

OOoooo! I envy your progress!! Looking very nice. Can't wait to see how well it runs.

Will you be running the same SC pulley setup before the head swap? If so, I'll wager the boost pressure actually goes down but your fuel demand and performance go up. Boost is just a measure of restriction, not air flow.

Todd
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'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

leadfoot · Posted: Fri Jan 05, 2007 8:35 pm Post subject:

pistons are mahle forged (questionable) most people say they are hyperutetic cast... they sent me the wrong size rings though so be aware.
https://www.actionimport.com/vw/empi_products.htm
Same pulley and SC, I had different boost levels measured at the sc outlet and manifold hence me making a new sc outlet manifold. I'm curious to see what the outcome is too.
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Looking good! FWIW, I measured almost dead on 1/4" (6.3mm) from the top of the bore with mine. I have another block that's been decked probably almost 1mm. I think there is a spec on the height of the block from the oil pan gasket surface to the deck. I think these pistons will push over 9:1 if you don't do any headwork. My static compression puts me at the same ~150/155psi as folks with 8.5:1 engines. That's after I pulled about 1.5-2cc out of the head.

I had heard that Mahle "forged" pistons are "press-forged" which is supposed to differ greatly from a JE "forged" piston. The huge jump in price attests to something obviously very different about the two types!

Were your rings on the pistons when they were sent? My set of pistons/barrels had the pistons already in the barrels with rings on. How did find out the rings were wrong? Diameter? Thickness? Just curious!
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

sequential · Joined: 18 Nov 2005 Posts: 500 Location: BANNED

Pressed forged for the most part is a better technique and gives you a harder more consistent piston with great coefficient. The JE are dropped forged and i'm not sure they are doing pressed forged pistons as ,i do not use them .... hence no technical data on that.

Just curious why all you SC guys can't seem to get by that 10-11 PSi barrier , try 1 bar , ( i should rephrase that for the aussie's me thinks) i would love to see the TQ numbers .

ARX nice avatar !

leadfoot · Posted: Sat Jan 06, 2007 1:38 pm Post subject:

I hade the piston set sent without the barrels to save on shipping costs, the rings came a package with the set and they went on by hand, so I knew they were the wrong size.
The new rings are 2 x 2 x 5 STD (RS 1553) if that code makes any sense, and the pistons are setup with .002 clearance.
In regards to your measurement of 6.3mm are you measuring from the deck or the bevel at the top of the bore??
5mm was measure by my machinist and noted on my spec sheet, if it turns out to be 6.3mm the my comp would drop to 8:1 no great loss as i can then increase the boost and run a non cluctched pully on the sc.
The crank pulley is as big as i can go due to the oil pump bolt already being ground somewhat for clearance, so depending on final CR and boost at the manifold I will make a judgment call on increasing the sc pulley when I know more definately.
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

arx · Joined: 16 Dec 2005 Posts: 129 Location: Estonia, Tallinn