77MM Pistons?

77MM Pistons?

Postby Veefan » January 25th, 2011, 2:16 pm

I'm selling some spare parts on e-bay, one item I have listed is a set of 77mm .020 over pistons.

Providing all the below rules are met, shouldn't they be legal?

The GCR says

"The engine shall be a standard VW power plant, as normally fitted
to VW sedans as defined herein. Any engine part(s), listed by the
manufacturer (VW) as a current, superseding, replacement part for
the standard VW 1200 series, Type 1, U.S. model sedan and interchangeable
with the original part(s), may be used."

4. Pistons and wrist pins minimum combined weight without clips
or piston rings = 330.0 grams

a. Maximum bore: 3.040 inches
b. Stroke: 2.520 inches +/ 0.005 inch.
c. Minimum capacity of combustion chamber in head: 43.0cc
(Polishing and/or tooling is prohibited.)
d. Minimum depth, top of cylinder barrel to top of piston:
0.039 inch


http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270696652986
Image
Veefan
 
Posts: 247
Joined: August 14th, 2007, 9:22 pm

Re: 77MM Pistons?

Postby FV80 » January 25th, 2011, 2:32 pm

John,
No - they are not legal. VW has never defined the 0.020 over pistons as "replacement parts". I sent you an email a few minutes ago. VW HAS, however, just notified SCCA that the newer aluminum cases are now official replacement parts for the mag cases (see Feb FasTrack). The pistons do not define "the bore" - the cylinders do that.

Steve, FV80
The Racer's Wedge, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please send me an email or PM with your name, location (city/state), make/model of car, phone # and any other appropriate info.
User avatar
FV80
 
Posts: 1146
Joined: June 27th, 2006, 9:07 am
Location: Near Athens, GA

Re: 77MM Pistons?

Postby SR Racing » January 25th, 2011, 7:14 pm

FV80 wrote:vw just notified SCCA that the newer aluminum cases are now official replacement parts for the mag cases (see Feb FasTrack). Steve, FV80


And a good idea if you need another 14 lbs of ballast. :lol: We have built some of the hyper Bug engines with them, but they are pretty heavy for FV.
User avatar
SR Racing
 
Posts: 1213
Joined: June 24th, 2006, 1:58 pm
Location: Lexington, KY

Re: 77MM Pistons?

Postby tiagosantos » January 26th, 2011, 1:32 am

Are they cheap though? I could use the ballast! :D
tiagosantos
 
Posts: 391
Joined: June 20th, 2010, 12:10 am

Re: 77MM Pistons?

Postby SR Racing » January 26th, 2011, 6:29 pm

About $100 more than a stock case. You can probably find 15lbs of ballast cheaper than that. :)
User avatar
SR Racing
 
Posts: 1213
Joined: June 24th, 2006, 1:58 pm
Location: Lexington, KY

Re: 77MM Pistons?

Postby tiagosantos » January 26th, 2011, 6:33 pm

Gee.. For that much money, I can probably EAT 15lbs of ballast! :D
tiagosantos
 
Posts: 391
Joined: June 20th, 2010, 12:10 am

Re: 77MM Pistons?

Postby hardingfv32-1 » January 26th, 2011, 7:42 pm

Is this new case extra strong, a rhino case?

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby brian » January 27th, 2011, 3:12 pm

I know there are some heavy duty after market aluminum cases but aren't the new cases simply made of different material?
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: 77MM Pistons?

Postby hardingfv32-1 » January 27th, 2011, 5:02 pm

So the 15 lb. might come from the loss of magnesium?

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby DanRemmers » January 28th, 2011, 1:34 pm

The density of magnesium is about 1.74, and aluminum is about 2.8. So if the magnesium case saves 15 lbs, then it weighs about 25 lbs and the aluminum case weighs about 40 lbs.
User avatar
DanRemmers
 
Posts: 293
Joined: June 24th, 2006, 7:21 pm
Location: Springfield, VA

Re: 77MM Pistons?

Postby hardingfv32-1 » January 28th, 2011, 4:41 pm

I did not appreciate that the case was pure magnesium.

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby brian » January 28th, 2011, 4:52 pm

They weren't. The cases were a blend of materials. AS41 casted on the cases described the mix of materials. Cant remember the exact combination but the AS41 included zinc.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: 77MM Pistons?

Postby smsazzy » January 28th, 2011, 6:11 pm

AS41 composition is 4.3% Al , .35% Mn , 1.0% Si , remainder MAGNESIUM
Stephen Saslow
FV 09 NWR
User avatar
smsazzy
 
Posts: 701
Joined: June 24th, 2006, 5:56 pm
Location: Seattle, Wa

Re: 77MM Pistons?

Postby FV80 » January 28th, 2011, 7:38 pm

smsazzy wrote:AS41 composition is 4.3% Al , .35% Mn , 1.0% Si , remainder MAGNESIUM

Hmmmm... 94% Mag - I think we can call that pretty much a Magnesium case :-).

Steve
The Racer's Wedge, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please send me an email or PM with your name, location (city/state), make/model of car, phone # and any other appropriate info.
User avatar
FV80
 
Posts: 1146
Joined: June 27th, 2006, 9:07 am
Location: Near Athens, GA

Re: 77MM Pistons?

Postby SR Racing » January 29th, 2011, 12:34 am

The aftermarket AL cases also have larger webbing etc. They are quite a bit beefier.
User avatar
SR Racing
 
Posts: 1213
Joined: June 24th, 2006, 1:58 pm
Location: Lexington, KY

Re: 77MM Pistons?

Postby hardingfv32-1 » January 29th, 2011, 4:35 pm

I'm looking for a more stable case to develop a zero clearance engine. This could be the answer.

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby SR Racing » January 29th, 2011, 10:32 pm

Zero clearance? You mean like interference fit rods and main? We have acouple laying around if you want one. :lol:
User avatar
SR Racing
 
Posts: 1213
Joined: June 24th, 2006, 1:58 pm
Location: Lexington, KY

Re: 77MM Pistons?

Postby hardingfv32-1 » January 30th, 2011, 1:51 pm

To be honest I'm not sure what it means. I have seen it used in a couple of places to indicate an engine that has very little clearance when cold. When the engine is at operation temperature the clearances are more like the numbers we normally use. I have cut my cold clearances in half so far. Working my way down until I get a failure. Very few crank grinders willing to or capable of holding the tolerances required.

Why? Thinner oil, less friction. Can now use 15W @ 240 deg with no problem.

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby brian » January 30th, 2011, 6:55 pm

The tighter clearances also means higher oil pressure, doesn't it? Recent thinking seem to contend that higher oil pressure means more drag and less flow.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: 77MM Pistons?

Postby hardingfv32-1 » January 31st, 2011, 1:46 pm

No, the requirement for tight clearances is strictly to keep the oil from leaking out of the bearings and causing oil pressure losses. They are required to maintain normal oil pressure.

There is no drag penalty for tight clearances until you get metal to metal contact. Scientific studies have shown it is a complete myth about extra clearances being needed for a race engine. A free spinning cold crank assembly means nothing. How it spins when at operating temperature is what counts. Of coarse we are talking about a high maintenance race engine, not common idiot proof FV dune buggy examples.

More power the thinner the oil gets. Don't need the power extra power, then stick to the simpler dune buggy engines.

I have not studied the effects of high oil pressure because that in never an issue.

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby brian » January 31st, 2011, 4:02 pm

Crank clearances for our motors is designed to prevent metal to metal events. It' s nice to think of our cranks as stable units but the truth is that they are really moving around in the case and if you don't have at least .002.5 on the mains you'll get contact.

I agree with you Brian that on our motors there's a ton of oil escaping the rod bearings and flooding the engine which should be reduced. But current thinking combined with recent developments in synthetic oils have shown that by reducing oil pressure, which is resistance to flow, increases life and hp. Flooding the bearings maintains film strength and will help prevent failures. All bets are off when one talks about dry sumps, evacuated crankcases and more modern engine designs.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: 77MM Pistons?

Postby hardingfv32-1 » January 31st, 2011, 10:47 pm

I'm not sure that our cranks move around. Regardless, thinner oil films handle heavier loads than thicker films.

Is your stated .0025 clearance cold? What does that become when the engine is at operating temps?

Our engines do not leak oil from the bearings any more than other engines of that period. This is not an issue of synthetic oil or reduced oil pressure either. I'm using 30-35 psi for normal at speed oil pressure. I use the smallest oil pumps with two cover gaskets to insure the pump does not get into the pressure relief valve when hot. No wasted pump energy. The oil pressure trace looks just like the RPM trace. You do have to be careful during hot idle situations. The driver is busy until he shuts the engine off in his pit.

There is no flooding to maintain film strength. You maintain your oil pressure, you have no bearing failures.

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby brian » February 1st, 2011, 1:38 am

You know Brian, Ive never been able to mike a hot engine.:lol: Honestly, I don't know what the clearances are hot. A common failure in vw's is a frozen rear main. The quickest way I know of locking up a rear bearing is to have an oval bore in the case. A .001 out of round rear main bore is a 40% reduction in clearance. Another issues in insufficient end play. While I have never been able to measure it, at high rpm, the crank is flexing in the middle and moving back and forth. On virtually every motor i have taken apart has had some contact in the center main. I have seen high speed films from a spintron test on small block chevys and the cranks are really moving around there.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: 77MM Pistons?

Postby hardingfv32-1 » February 1st, 2011, 1:57 pm

The load a bearing can support increases to infinity as the oil film thickness decreases. Smaller clearances would reduce crankshaft flexing in that case.

What would cause the crankshaft to move fore and aft? It is under load from the camshaft drive gears.

Brian
hardingfv32-1
 
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: 77MM Pistons?

Postby brian » February 1st, 2011, 4:12 pm

Our beveled cam gear is one and thrusting from the clutch assy is another.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
 
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Next

Return to Tech Tips, Rules, and Safety

Who is online

Users browsing this forum: No registered users and 5 guests

cron