SCCA Street Prepared engine rules

Figured some of you guys will know this...

Okay, some of these rules are hard to understand for us not so experienced folks. I want to build this car dead nuts legal, no iffy stuff. I'm getting ready to do the engine. This is going to cost plenty as it is, so I don't want to end up having to do it again. Here's what I'm worried about:

"15.10 S. Cylinders may be rebored to no more than 0.0472 in. over standard bore and the appropriate standard oversize piston may be substituted. This overbore dimension is an absolute limit; no additional tolerance is permitted to accommodate wear. Cast or forged, non-stock pistons of the same dimensions and confi guration as original equipment pistons may be used. Additionally the replacement pistons must be of the same weight or greater as the original equipment pistons. Replacement pistons must match OE piston configuration exactly including quench area. The allowance for the use of aftermarket forgings vs. OE castings does not permit alternate piston dome designs. This allowance does not permit alternative ring confi gurations."

Okay, how do you know when you buy pistons if they are the same dimensions, configuration including quench area and same weight or greater? It seems like they are making an allowance to use after market pistons, but then making rules that make it almost impossible to do it. I'm just not sure what to do here. I'd rather use after market pistons just because they're a lot less expensive. But if I can't figure this out, I'm probably going to inspect what I have and reuse them if they're okay. That would be legal, but sure would be giving up some power on the max overbore. I'd really hate to do that just 'cause I'm too stupid to figure out the rules.

And then this:

"T. Rotating and reciprocating parts may be balanced but not lightened."

Well, I assume what that means is you can remove material on all but the lightest piston? But that's kind of weird too, isn't it. I mean, how do you balance without lightening?

This car may not really work at all and I'll be a back packer in national events. But if by some weird chance I should trophy, I sure want to be 100% that everything is totally legal.

Anyone familiar with this stuff and have any advice?

Thanks,

Ed

You want a piston manufacturer who has made a duplicate replacement piston for the OE one. One that has been scanned/cast/molded from the OE. Quench area should then be the same.

Don't forgt you can balance by ADDING weight and making them all weigh the same. Heavier than stock, but all the same weight.

That's how I interepret the rules.

Edit: I'd contact the SCCA and ask them how they define "quench area". It's not always the total top surface are of the piston. Also, they should have the allowable piston weight on record--or as supplied to them by the manufacturer of the auto in question. And, you could always pose the same questions you posted here to them.

What I get out of reading the rules is they are saying stock or standard size bores oem design only. No dished/domed super dooper complicated designs allowed.

As far as the balance question, I read it as saying "no knife edging of the crank".

Looks like you need NHRA Stock/Super Stock design piston.

Basically on balance and lightening, you can't buy a domed piston, even if they came stock, and then take all the material away from under the dome. You also can not cut down the skirt or pin width. Altho, you could run a bigger, fatter pin albeit MUCH shorter.

To balance your rotating assembly without lightening it, weigh all your pistons, rods, wrist pins, etc. individually. Then combine them in a manner that produces the most consistent weight across all of them. Example: if you have piston weights of (dramatic differences for the sake of making my point) 100g, 125g, and 150g and rod weights of 75g, 50g, and 25, combine the lightest piston with the heaviest rod and vice versa.

Will wrote: To balance your rotating assembly without lightening it, weigh all your pistons, rods, wrist pins, etc. individually. Then combine them in a manner that produces the most consistent weight across all of them. Example: if you have piston weights of (dramatic differences for the sake of making my point) 100g, 125g, and 150g and rod weights of 75g, 50g, and 25, combine the lightest piston with the heaviest rod and vice versa.

Thanks- this is pretty much what I had in mind. I've only put one engine together, and it isn't running right (but has run, so I think I'll be okay). I'm not sure I want to grind or try to weld crap on anything right now.

will paring the lightest piston with the heaviest rod so that all 4 piston/rod combos weigh roughly the same throw off the balance of the motor, since some pistons are lighter than others and some conrods are slinging more weight side-to-side than others? I would have figured that buying up a bunch of old pistons and conrods and picking the 4 most consistently light examples of each would be a better solution, if not more expensive

In reply to Slyp_Dawg:

Yes, that is a better option, but sometimes it's outside people's budgets. If you can afford it, go for it.

In reply to Slyp_Dawg:

That's how the shops that build spec motors do it. Buy all the parts in bulk and start matching weights. Not very feasable for the garage mechanic.

I doubt shaving a couple of grams here and there to balance isn't considered "lightening". At least that was my take when I built my motor under Street Prepared rules. Of course I am not a top runner locally, let alone nationally, to even worry about such little things. I've also sinced moved to SM, so even less of an issue.

Hey, with all the people building street prepared 22REs, I'm sure I could buy a whole mess of pistons from Toyota and weight match a bunch of sets and sell them to the other builders.

Let's see, there's me... and.

Well, I'm sure somone else is building one.

I heard from a friend who did build one that the pistons he got from Toyota were remarkablly well balanced out of the box. Dunno.

Well, I should have checked more sources before I bothered posting this. You can get the Toyota pistons for a pretty reasonable price in the max oversize. So rather than worry about it, I'll just do that. Easy peasy, legal shmegal.

I know someone who weighed every damn connecting rod that came thru his shop. When he would find a new light one, he would save it. He then balanced all of the rods in his motor to this weight. He kept the factory lightest rod ever in his protest kit. It's purpose was to be the untouched one against which the others were measured.

DILYSI Dave wrote: I know someone who weighed every damn connecting rod that came thru his shop. When he would find a new light one, he would save it. He then balanced all of the rods in his motor to this weight. He kept the factory lightest rod ever in his protest kit. It's purpose was to be the untouched one against which the others were measured.

Nice. My "protest kit" won't be as good as that, but I will keep all the recipts. Be nice to have that Toyota part number handy on a recipt if anyone questions. Just one less thing to worry about. I'm planning to take a lot of pictures too.

DILYSI Dave wrote: I know someone who weighed every damn connecting rod that came thru his shop. When he would find a new light one, he would save it. He then balanced all of the rods in his motor to this weight. He kept the factory lightest rod ever in his protest kit. It's purpose was to be the untouched one against which the others were measured.

I was about to say, I bet talking to a shop who sees a ton of internal parts would be a good place to start to "build" a factory stock "lightened" rotating assembly. But yeah, receipts from Toyota would be hard to argue with!