"Factory" oversized replacement Pistons...

Banzai240

Banzai240

New member
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...

------------------
Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
DJ_AV1.jpg


[This message has been edited by Banzai240 (edited October 12, 2004).]
 
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.
 
Originally posted by grega:
Otherwise, Darin, you forgot to take your medicine today...
wink.gif
Click to expand...

Well... actually, my perscrition hasn't been filled as of late...
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...



------------------
Darin E. Jordan
SCCA #273080, OR/NW Regions
Renton, WA
ITS '97 240SX
DJ_AV1.jpg
 
Originally posted by JohnRW:
How did a thread about RX-7's devolve into a discussion about replacement pistons?
Click to expand...

Well... You get RX drivers together with Audi drivers and throw in a Nissan driver and you just never know what might happen...
wink.gif
 
Originally posted by joeg:
John--They are dreaming about .040 forged rotors...
Click to expand...

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.



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


I miss that "turbo chirp" sound.
Click to expand...

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...;-)
 
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.
Click to expand...

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!

------------------
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.
biggrin.gif


------------------
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 ?
 
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 ?
Click to expand...


Ummmm.... Oh, nevermind...
icon_frustrated.gif
 
Originally posted by Banzai240:

Ummmm.... Oh, nevermind...
icon_frustrated.gif


Click to expand...

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.


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

Click to expand...

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
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).

------------------
"Bad" Al Bell
ITC #3 Datsun 510
DC Region MARRS Series
 
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).
Click to expand...

That's pretty tortured.


------------------
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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