.040 pistons

S

Scirocco#28

New member
Just wondering who would supply these for our cars (1.8 8.5:1 that is). I know you can get the .020 at the dealer but I want to price compare. BSI's website says that they only have the .020 as well. Are these the type of thing that you have to contact a custom company (wiseco,schmidt,etc) or are these already readily available?

Thanks
Steve

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88 ITB Scirocco
www.geocities.com/highspeedconnectionracing
 
Steve,

The .040 over (82mm) are somewhat hard to find. I believe that you can get them from Wiesco, J-E, or Mahle, but they won't be cheap. The .060 over (82.5mm) are easier to find.

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MARRS #25 ITB Rabbit GTI
 
Steve,

I know that Stu is working on a supply of 40 over pistons from Europe that he promised would be "reasonable". I don't know if he will have them for 8.5:1 as well-those are the ones you're looking for aren't they?
rolleyes.gif


I'll ask him this week-end and let you know.

We're off to fly the Canadian flag at ARRC tonight. Talk to you when we get back.

Cheers!



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Colin Harmer
ITB #2 Red Golf
Halifax, NS
http://users.andara.com/~mountain
[email protected]
 
Colin,

Yep those would be the ones. And there was nothing wrong with my motor last year if thats what you are implying
biggrin.gif
I'd like to build a fully developed motor this year and 82mm pistons is a good place to start.

Good luck down south, see you at the ARMS banquet

Steve

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88 ITB Scirocco
www.geocities.com/highspeedconnectionracing
 
Steve,

I have a brand new set of .040 over (82mm) pistons with rings. Let me know if you're interested.
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Glenn
MARRS ITB #07

[This message has been edited by GTI Cup (edited November 06, 2001).]
 
I've found a healthy bottom end, so i was thinking of just getting new rings for the bottome end, and just do a proper IT head.

Might as well get some money for the pistons, since I gotta get new tires as well!

It sucks to have this hobby and have no money!



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Glenn
MARRS ITB #07
 
I can get 81.5mm and 82mm 8.5:1 piston set. The brand is Mahle of Germany and I'm sell the set for $150.00 with rings, and pins. I also have 81.5mm 10:1 for $160.00 a set.

Thank you
Jose Rotger
 
I'm very close to giving the tectonics 9:1 82mm pistons a try. I've been assured that you can still take a cut off the head and block while maintaining IT specs. Anyone else run these pistons. They come with pins & goetz rings and go for about $250 a set.

Jose,
give me an email at [email protected] about those pistons. I would be interested in hearing more.

Thanks
Steve

ps
I've got a set of 82mm Wiseco flat tops, for a VW 1.8L. Were used in a Scirocco GT car. I'd love to chuck them in my IT car but Colin might tell on me
smile.gif
They're good for about 13:1 Don't have a clue what they're worth, but I'm open to offers.

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88 ITB Scirocco
www.geocities.com/highspeedconnectionracing
 
How much compression do you gain by putting in 40 over pistons. Since the rule allows 40 over and your allowed to shave the head you could probably get more than that half a point in compresion. For those that are knowledgable and willing to give up some speed secrets!! How much more compresion does 40 over get you and how much does that change if you plain the head or shave it 10, 20, or 30 thousanths???? What is a better more efficint way to get the extra horsepower... I would think shaving the head since with the 40 over pistons you have more friction and mass to move inside the engine, however I really have no idea what the best method is. What do you guys think?? I could probably post this on any thread (except those crazy rotary fans!! JK) but since I race an Audi it's most like the VW so I figured this spot would be a good start.

Stephen

PS I wish this site had spell check, don't make to much fun of me!!! I guess you need to consider me part of the new generation... the calculator spell check/grammer check generation!!!

[This message has been edited by RSTPerformance (edited December 04, 2001).]
 
Stephen,

Larger diameter pistons in and of themselves will do nothing to change the compression ratio. They will increase the displacement, but that's all. This is, given that there is no change to the stock configuration (you maintain the stock ratio of 'unswept' volume to total volume). However, if you change things like the dish profile, you've changed that volumetric ratio.

For example, w/ VW's, they made an 8.5:1 1.8 and a 10:1 1.8. Both are the same bore/stroke, It's just that the 8.5:1 pistons had a much larger 'dish' in the top.

So, what you get out of going 0.040" over is more displacemnt, which lets you move more air/fuel mixture through the car on a given stroke, thereby making more power. All else being equal, a motor that is 0.040" over-bored should make more hp than an engine w/ stock bore.

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MARRS #25 ITB Rabbit GTI
 
I have to disagree a bit here. Although the gains are small, an increase in bore size does increase the compression ratio. Here goes:

Compression ratio (Cr) is defined as the ratio of the combustion volume plus the displacement over the combustion volume. (Cv + D)/Cv.

For a VW/Audi 1.8/2.2 liter motor, the displacement of one cylinder is 445.21 cc. (bore radius squared X pi X stroke) or ((81mm/2)**2)* pi*86.4mm. Assuming 8.5 compression ratio, it is possible to iterate the combustion volume, which equals 59.4 cc. Therefore (Cv + D)/Cv = (445.21 + 59.4)/59.4 = 8.49 (close enough to 8.5)

Boring the motor increases to bore size, and therefore the displacement. So we'll do +.020" (1/2 mm) and +.040" (1 mm) oversizes.

The bore size goes up to 81.5 mm and 82 mm respectively. The resultant displacements go up from 445.21 cc to 450.73 cc and 456.28 cc.

The combustion volume is in the piston top and the cylinder head, so for the most part, the combustion volume stays the same at 59.4 cc. So you can calculate the new compresion ratios:

For +.020" (1/2mm) overbore, Cr = Cv + D)/Cv = (450.73 + 59.4)/59.4 = 8.59

For +.040" (1mm) overbore, Cr = Cv + D)/Cv = (456.28 + 59.4)/59.4 = 8.68

So the answer is that compression ratio goes up a tenth of a point for .+.020" overbore and bout two tenths of a point for .+040" overbore. That's if I did the math right, anyway.
 
Originally posted by SteveMc:
So the answer is that compression ratio goes up a tenth of a point for .+.020" overbore and bout two tenths of a point for .+040" overbore. That's if I did the math right, anyway.
Click to expand...

You're right, and that is one of the reasons there is a 1/2 point allowance in compression in IT - the other reason is that if you must have the head resurfaced as a part of a normal rebuild, you will gain a slight amount of compression. They figured .5 would be enough to handle rebuilds.

Anyone who takes an IT engine out to a deliberate .5 increase without allowing for future rebuilds must have deep pockets - they have to start with a new block and head at every freshening.

Don
 
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