"Factory" oversized replacement Pistons...

Stephen,

You are right, from a strictly "rules nerd" reading of the rule... It does say "Factory oversize" or their "exact equivalent"...

BUT, I think it's pretty clear that, if you are allowed to overbore your engine .040", you are allowed to put .040" pistons in it...

I think it could be strongly argued that a non-stressed reading of the rules would allow you to make a piston that meets the listed requirements but would be .040" over...

I can't think of anyone who would protest an engine that is .040" over, using pistons that have the "same dome/dish/valve relief configuration, ring thickness and spacing, pin height relationship, weight, and compression ratio as factory replacement oversize pistons", even if the factory doesn't make that particular size. Your compression is limited by the spec line and the .5 allowance, the rest is pretty much spelled out.

You provide a stock piston, and your .040" piston to tech, and if everything else matches, I seriously doubt you're going to get so much as a raised eyebrow if one is std bore and the other is .040" larger in diameter...

Just my opinion...

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Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
http://home.comcast.net/~djjordan/Web/DJ_AV1.jpg

[This message has been edited by Banzai240 (edited October 12, 2004).]

I suspect this was in response to:

"No .40 over pistons are available so to have them made would be illegal."

From:

http://forum.improvedtouring.com/it/Forum1...TML/000803.html

Otherwise, Darin, you forgot to take your medicine today... http://Forum.ImprovedTouring.com/it/wink.gif

How did a thread about RX-7's devolve into a discussion about replacement pistons ?

Has this piston thing come up again ? Over a decade ago, I had a discussion with the 'then' Technical Director of Club Racing about piston replacements. I got tired of scattering Volvo engine internals all over race tracks, and I had Mahle's cracked at the wristpins as proof that it was the pistons causing that particular problem (one of many...). He laughed out loud when I told him that a Reg'l Tech Chief had suggested that non-factory pistons weren't legal. His comment ? "I want to know who it is, because they don't know what they're talking about..." The story then is still the story now, unless I've missed something HUGE in FasTrack since then.

Replacement pistons, of alternate manufacture, are permissible. They must be the same 'configuration', including deck height, ring # and pack, dome shape, weight, etc. Forged are OK, if you're replacing cast (although you have to be careful about the weight thing). Doesn't matter whether it's a stock size or the max. allowed 40 over...identical replacements from an alternate manufacturer are OK.

John--They are dreaming about .040 forged rotors...

You are right. Actually the rule was changed last year to clarify that a forged replacement was cool in IT, no doubt in response to the miles of posts here about the issue.

Left unchecked, this "unavailable .040" theme could also run on for miles...

Cheers.

Quote:

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Originally posted by grega:
Otherwise, Darin, you forgot to take your medicine today... http://Forum.ImprovedTouring.com/it/wink.gif

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Well... actually, my perscrition hasn't been filled as of late... http://Forum.ImprovedTouring.com/it/biggrin.gif

I just didn't want to muddle up the other thread with this topic, so, as Stephen suggested, I started a new thread...



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Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
http://home.comcast.net/~djjordan/Web/DJ_AV1.jpg

Quote:

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Originally posted by JohnRW:
How did a thread about RX-7's devolve into a discussion about replacement pistons?

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Well... You get RX drivers together with Audi drivers and throw in a Nissan driver and you just never know what might happen... http://Forum.ImprovedTouring.com/it/wink.gif

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Originally posted by joeg:
John--They are dreaming about .040 forged rotors...

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The only 'bigger' thing the Mazda rotary guys need are BIGGER MUFFLERS. Nothing I hate more than the early a.m. "Mazda wake-up call" in the paddock. Yeesh. It's Club Racing's equivalent of a dentist's drill.

Were you around before the SCCA instituted sound restrictions?

The old CP RX7s actually used MEGAPHONE exhausts. When they would go by, I would literally get sick to my stomach from the noise - with earplugs in.

K

Kirk, don't forget the IMSA Radial Sedan RX3's. Those were LOUD as well as the RX7's in GTU.

Compare that to the SWEET sound of a Porsche 935 twin turbo, that just "wooshes" by you.

I miss that "turbo chrip" sound.



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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit
http://linerud.myvnc.com/racing/index.html

Quote:

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Originally posted by racer_tim:


I miss that "turbo chirp" sound.

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You forgot to mention the 6 to 8 foot flames shooting out the back whenever the cars shifted or braked.....Cool stuff!

And yes those uncorked Mazda's were loud.

only thing worse in the paddock than rx7's are the those glorified chain saw engines in the f500's...;-)

Quote:

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Originally posted by racer_tim:
Kirk, don't forget the IMSA Radial Sedan RX3's. Those were LOUD as well as the RX7's in GTU.

Compare that to the SWEET sound of a Porsche 935 twin turbo, that just "wooshes" by you.

I miss that "turbo chrip" sound.

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Tim,

I remember going to the Camel GT at Pocono, and the Camel Continental at The Glen. You could always tell when a rotary powered car was comming! And yeah, I miss those days. Cool cars, cool racing. I still want another Firehawk 24Hr race at the Glen!

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

Mazda's upcoming return to full factory racing was brought up by the announcers during the telecast of one of the ALMS races. One of the announcers said that his ears were still ringing from the rotary engines of the 80s. http://Forum.ImprovedTouring.com/it/biggrin.gif

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Chris Ludwig
08 ITS RX7 CenDiv

.040 over pistons are legal if they'll fit in an .040 overbore motor. If one overbores by more than .040 to give the extra clearance necessary for racing IT motors and especially forged pistons, then I would argue that this is illegal according to a strict reading of the rules. It all depends on the factory specification and allowances for a stock bore + .040 to it.

For example, what if I put .040 pistons but the cylinder's have worn to .045 or even .050 overbore. Rings are unrestricted so I get same thickness but wider rings made to fill the cylinder. Yes, I'll have excessive piston slap but there is some limit where I can get a wee bit more displacement and more power.

.040 overbore may not give enough clearance for .040 forged pistons which need about .005 minimum clearance.

Now, what if I build a legal .040 motor. After a long season, the tops of the cylinders have worn so I now have up to .043 overbore. Am I legal or ?

Quote:

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Originally posted by Joe Craven:
....040 overbore may not give enough clearance for .040 forged pistons which need about .005 minimum clearance.

Now, what if I build a legal .040 motor. After a long season, the tops of the cylinders have worn so I now have up to .043 overbore. Am I legal or ?

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Ummmm.... Oh, nevermind... http://www.coloradoscca.org/prodcar/...frustrated.gif

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Originally posted by Banzai240:

Ummmm.... Oh, nevermind... http://www.coloradoscca.org/prodcar/...frustrated.gif

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Darin, the rule seems very clear to me and I would suspect that there are quite a few non-RX7 cars out there that might have been overbored more than .040 beyond the manufacturers standard bore + service limit. Is trying to understand the rule the same as beating one's head against a wall? Do you know something that I don't? Please share.

W

Joe, the way I see it, the FSM will spec a max standard bore (with whatever tolerances). Add 0.040" to that for your max bore. The FSM will likewise spec a max standard piston diameter. Add 0.040" to the for your max bore.

If you bore your cylinders to the limit of the rules and they wear to an illegal size you're SOL. I don't see any way around this.


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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

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Originally posted by Banzai240:
Stephen,

You are right, from a strictly "rules nerd" reading of the rule... It does say "Factory oversize" or their "exact equivalent"...

BUT, I think it's pretty clear that, if you are allowed to overbore your engine .040", you are allowed to put .040" pistons in it...

I think it could be strongly argued that a non-stressed reading of the rules would allow you to make a piston that meets the listed requirements but would be .040" over...

I can't think of anyone who would protest an engine that is .040" over, using pistons that have the "same dome/dish/valve relief configuration, ring thickness and spacing, pin height relationship, weight, and compression ratio as factory replacement oversize pistons", even if the factory doesn't make that particular size. Your compression is limited by the spec line and the .5 allowance, the rest is pretty much spelled out.

You provide a stock piston, and your .040" piston to tech, and if everything else matches, I seriously doubt you're going to get so much as a raised eyebrow if one is std bore and the other is .040" larger in diameter...

Just my opinion...

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See I see it completly different.....

I see...... "Factory oversize" or their "exact equivalent"... so to me I would say that is preventing me from using something that is not a Factory oversize piston or exact replacement.

It doesn't matter what it says you can bore the engine to. I would agree that my Factory .020 pistons are legal with ton's of blow by because I bored my block to the maximum .040

Both rules limit you and in my opinion you need to follow whichever one limits you the most. In my case I can't go more than .020 because that is all that is listed as Factory replacements in my manual. That is what the rule says I can do. No rules nerd thing here... this is what the rule says pretty clearly.

I will agree with you that it is common practice and would probably not hold up in the tech shed.... just like the use of wheel spacers before they clarified the rules about a year or so ago. A year or so ago those where only allowed to be used to allow for tire clearance not to widen track. It was updated in a fast track later to allow for the use to widen track. Just because something is common practice doesn't make it correct.

I appreciate your response and what I always thought wasn't allowed seems to be OK so in the future I may think about having some made.... I'll have to get a bunch richer though since I have to buy 5 of them http://Forum.ImprovedTouring.com/it/smile.gif Thanks for the explanation of your view and your reasoning behind it.

stephen

[This message has been edited by RSTPerformance (edited October 13, 2004).]

Aren't most pistons made in a factory?
So if they are made in a factory, and they are oversize, they meet the letter of the rule (agreed, maybe not the intent of your interpretation).

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"Bad" Al Bell
ITC #3 Datsun 510
DC Region MARRS Series

Quote:

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Originally posted by badal:
Aren't most pistons made in a factory?
So if they are made in a factory, and they are oversize, they meet the letter of the rule (agreed, maybe not the intent of your interpretation).

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That's pretty tortured.


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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

I was going to stay out of this one, because it seemed pretty obvious and straightforward, but Stephen brings up a valid point (although I disagree with it).

Here is exactly what the rule says:

"Engines may be bored to a maximum of .040 inch over standard bore size. Factory oversize replacement pistons or their exact equivalent shall be used. Cast or forged equivalent pistons shall provide the same dome/dish/valve relief configuration, ring thickness and spacing, pin height relationship, weight, and compression ratio as factory replacement oversize pistons. Piston rings are unrestricted.

Stephen, your point appears to be that if there never was a factory oversize piston, then there can never be an "exact equivalent" within the aftermarket (how can you be "equal" to something that doesn't exist?). Read that way, you are absolutely correct. However, you cannot take that one sentence in a vacuum. For example, how can that one sentence be applicable if the car came with cast pistons and you decided to install forged? That's because the rules allow the mod of forged pistons, even though they are not the "exact equaivalent".

When a modification is allowed, there are always implied modifications that go along with it. If you are allowed to overbore the engine, and balancing and blueprinting is allowed, there is no plausible and safe way to properly build an engine without appropriate oversize pistons. Since aftermarket pistons are allowed, I contend that aftermarket oversize pistons are also allowed, as long as the remaining features match the factory pistons.

As an aside, if you guys are running .020" oversize pistons in a .040" overbore, you're giving up a crapload of power and longevity. You're much better off using a .020" overbore block and making those rings seal better. Beside, you're running a large risk of cracking pistons and rings and/or damaging the block.

As to running longer (not wider) rings to make up a high piston-to-bore clearance, that's a horrible practice. By allowing that kind of p-t-b clearance your rings are not stabilized, will not seal to the piston properly, will not be adequately pressed into the bore, and will break much more easily. Any 'increased displacement' you get from doing this is more than overcome by decreased combustion chamber sealing and increased drag from chattering rings and pistons. If you're doing this you're much better off just not bothering to overbore the engine; you're simply pissing away time and money.

As to the clearance/service limit question, when an engine is properly built, the desired piston-to-bore clearance is maintained. Pistons (overbore or not) are designed and built based on the nominal bore diameter, not the service limits. Thus, when you buy/build overbore pistons, they will be .040" larger than stock nominal value, and you'll hone the bore to each piston and grind the rings to the desired end gap. These resulting bore values will be well within the +/- service limits of the original, plus the allowable .040". Unless you're driving this car to work every day, and/or you're running crappy oil in the thing, it is unlikely you will ever wear the cylinder bores to the point that the value is greater than the outside limits. My NX2000 had 11,000 total miles on it after nearly a decade of Showroom Stock racing. With the noted exception of the hole on the front of the block, the cylinder bores were nearly factory value.



[This message has been edited by grega (edited October 13, 2004).]

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Originally posted by grega:
...With the noted exception of the hole on the front of the block...

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Hey...that's not legal in Showroom Stock.

Cheater.

hey john
i have a double whammy for you! i am a dentist and i race an rx7!! http://Forum.ImprovedTouring.com/it/biggrin.gif
john costello
its rx7#87

And if your motor is metric, you can't use .40 overbore because it's all done in millimeters.

Load of crap.

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<font face=\"Verdana, Arial\" size=\"2\">Cheater.</font>

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Drats, foiled again!!

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<font face=\"Verdana, Arial\" size=\"2\">And if your motor is metric, you can't use .40 (sic) overbore because it's all done in millimeters.</font>

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1 millimeter is .0394 inches. Since metric pistons are typically sold as either 1/2 or 1mm overbore, I'd call it "close enough"; how about you?

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Originally posted by apr67:
And if your motor is metric, you can't use .40 overbore because it's all done in millimeters.

Load of crap.

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Again... http://www.coloradoscca.org/prodcar/...frustrated.gif

Doesn't common sense come into play anymore??? http://Forum.ImprovedTouring.com/it/rolleyes.gif

First of all I am going to thank all of you for saying this is legal, maybe someday I will get up the money to build an engine with these custom made pistons that I am sure someone will build for me but I will continue to tell you my reasoning why I still think it is illegal if you don't mind. Once this thread turns into ripping me apart I will be out of it. so far so good http://Forum.ImprovedTouring.com/it/smile.gif

Quote:

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Originally posted by grega:
Cast or forged equivalent pistons shall provide the same dome/dish/valve relief configuration, ring thickness and spacing, pin height relationship, weight, and compression ratio as factory replacement oversize pistons. Piston rings are unrestricted.

If you purchase an aftermarket .040 piston what weight are you compairing to? If no factory piston of this diameter exists can I just make the piston the same weight as the stock diameter or do I make it weigh more because it is larger? (This is one reason the rule in my opinion is flawed)


Stephen, your point appears to be that if there never was a factory oversize piston, then there can never be an "exact equivalent" within the aftermarket (how can you be "equal" to something that doesn't exist?). Read that way, you are absolutely correct.

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Isn't that what it says? I thought that is what I read as well http://Forum.ImprovedTouring.com/it/wink.gif (Not trying to be a jerk just telling you what I see in the rule)


For example, how can that one sentence be applicable if the car came with cast pistons and you decided to install forged? That's because the rules allow the mod of forged pistons, even though they are not the "exact equaivalent".[/QUOTE]

Exactly in IT it says you can do certain things..... If it doesn't sya youcan than you can't. If the rule said you can make any piston you want as ong as it will fit in you .040 bore and it meets the following requirments: Cast or forged equivalent pistons shall provide the same dome/dish/valve relief configuration, ring thickness and spacing, pin height relationship, weight, and compression ratio as factory replacement oversize pistons. Piston rings are unrestricted. then I would say .040 is allowed even if not a factory replacement.


When a modification is allowed, there are always implied modifications that go along with it. If you are allowed to overbore the engine, and balancing and blueprinting is allowed, there is no plausible and safe way to properly build an engine without appropriate oversize pistons.

Since aftermarket pistons are allowed, I contend that aftermarket oversize pistons are also allowed, as long as the remaining features match the factory pistons.

see I read the rule that factory replacement pistons are allowed and aftermarket pistons are allowed as long as they are the same only to keep costs down. I see nothing that says I can go have JE build me .040 pistons that never existed before.


As an aside, if you guys are running .020" oversize pistons in a .040" overbore, you're giving up a crapload of power and longevity.


Oh no beleive me we are not doing this! we have factory 20+ year old pistons with newer rings on them and factory bore. I did hone them with a craftsman hone and a makita drill though http://Forum.ImprovedTouring.com/it/smile.gif my speed secrets are now getting out! (Actually this is what I did to the engine before I seized it up when I tried to vacume up the pond at LRP outside the left hander http://Forum.ImprovedTouring.com/it/frown.gif


thanks for listening to my reasoning and my point of view. sorry if I don't respond as quickly as the rest of you. I don't have time to do this at work so it's every few days when I check my e-mail as well.
Stephen

PS I have a conversion chart somewhere that can convert the .040 to milimeters. I used to know exactly what is was but I forget. It is simple math I just don't rember the answer for you.

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Originally posted by RSTPerformance:
PS I have a conversion chart somewhere that can convert the .040 to milimeters. I used to know exactly what is was but I forget. It is simple math I just don't rember the answer for you.

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They got it for you. I know it was easy and I thought it was 1mm but I couldn't remember.

Stephen

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Originally posted by Banzai240:

Doesn't common sense come into play anymore???

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Sarcasm (sär-kaz-em), n. 1. ironical taunt; a sneering or cutting remark.

IT.com has, apparently, lost its sense of humor.

I thought the metric thing was pretty funny.