19 replies to this topic

[Brandon]

Call me crazy, but if you have a problem making weight (like me - I'm a chunk I guess ) there is nothing stopping you from rebuilding your engine w/the requisite allowable overbore, right? Of course, ensuring you have the proper weight marked on the vehicle is not only necessary but makes it legal too.

So, does anyone feel this is a 'gray area' or well within the allowances.
And yes, I'm stirring here but trying to plan for 2013 (anticipating an off-season rebuild and not losing the weight ) but was curious everyone else's opinions/thoughts.

Oh, and what is the maximum legal overbore and considerations thereof? Meaning if it's .0015 (FSM specified) we should have an allowance for wear so going to .0010 would be best, right?

Have a good night!
Brandon

[Rob Burgoon]

I know I've already been told this, but what was the long term plan with the overbore? Is the weight penalty going away in 3 years or so or is it intended to stay?

Should new engines be built with the overbore?

[Tom Sager]

.010 overbore is allowed with a 15 pound weight penalty. If you're willing to strap a bowling ball in the cockpit, you can have about 1 extra horsepower. It probably comes down to the condition of your bores and your willingness to source another block if your bores are not in hone-able shape.

[dstevens]

The overbore penalty is a reaction from rule makers that are out of touch with reality. Most other sanctions allow a 30 thou over along with a 30 thou crank under with no penalty. When you increase the bore but do nothing to the combustion chamber volume, you decrease the static compression ratio. In talking to my machinist, they don't even do 10 thou on a street car. They go to 20 thou right out the gate on a 4 banger. Look at the after market parts guys. 20 thou is a standard. It's not like a a regular regional race you'll get a bore check anyway. You'll be lucky if tech knows the weight of the class or even has the scale calibrated. Unless you cheat the head and cam, your over bore is a performance decrease. I don't know what the agenda is for those that made the rule but it's clearly not in the best interest of the hobby racer.

[Rob Burgoon]

The overbore penalty is a reaction from rule makers that are out of touch with reality. Most other sanctions allow a 30 thou over along with a 30 thou crank under with no penalty. When you increase the bore but do nothing to the combustion chamber volume, you decrease the static compression ratio. In talking to my machinist, they don't even do 10 thou on a street car. They go to 20 thou right out the gate on a 4 banger. Look at the after market parts guys. 20 thou is a standard. It's not like a a regular regional race you'll get a bore check anyway. You'll be lucky if tech knows the weight of the class or even has the scale calibrated. Unless you cheat the head and cam, your over bore is a performance decrease. I don't know what the agenda is for those that made the rule but it's clearly not in the best interest of the hobby racer.

Mr Creosote, I believe we are allowed to shave the head to increase compression ratio to the ragged edge of the spec.

[DrDomm]

Brandon, I'd bet anyone under 250lbs. should be able to get to 2350...2360 to have some tech cushion.

I think you're going to Lime Rock next weekend, right? See ya there.

[Rob Burgoon]

Brandon, I'd bet anyone under 250lbs. should be able to get to 2350...2360 to have some tech cushion.

I think you're going to Lime Rock next weekend, right? See ya there.

I'm at 180lbs and my 1.8 is right about 2345 with a smallish aluminum bottle fire system. Not sure where I could legally pull more weight aside from the fire system, wideband, and temp sender and gauge. The tie down hooks are gone. Cage is a miatacage. With my driver cooler is right about 2355.

[Jim Drago]

Brandon, I'd bet anyone under 250lbs. should be able to get to 2350...2360 to have some tech cushion.

I think you're going to Lime Rock next weekend, right? See ya there.

You probably own one of the lightest cars in the country.. I wouldn't base your opinion on your car as I always had to strip cars to the bone tryng to make weight.

Jim

[Keith Novak]

I'm at 180lbs and my 1.8 is right about 2345 with a smallish aluminum bottle fire system. Not sure where I could legally pull more weight aside from the fire system, wideband, and temp sender and gauge. The tie down hooks are gone. Cage is a miatacage. With my driver cooler is right about 2355.

I'm not sure what you didn't legally remove but I'm about 190# after I have a good sit in the can and with 25# bolted to the floor I'm at 1 1/4 gallons to get to weight. 4 tie down hooks. Insulation on the firewall. Windshield washer fluid filled to the brim from last year to make weight. Large extinguisher but no push button fire system. I could easily (and legally) take another 10-15 lbs out of the car without much difficulty at all.

[Rob Burgoon]

Oh duh, it's probably my abs. I always forget about that.

[Ron Alan]

At 2350 we have 60lbs on the floor...used to be 110lbs...yikes!

[DrDomm]

You probably own one of the lightest cars in the country.. I wouldn't base your opinion on your car as I always had to strip cars to the bone tryng to make weight.

Jim

I see that now...oops. Thanks. And it's a good thing...

[davew]

The overbore penalty is a reaction from rule makers that are out of touch with reality. Most other sanctions allow a 30 thou over along with a 30 thou crank under with no penalty. When you increase the bore but do nothing to the combustion chamber volume, you decrease the static compression ratio. In talking to my machinist, they don't even do 10 thou on a street car. They go to 20 thou right out the gate on a 4 banger. Look at the after market parts guys. 20 thou is a standard. It's not like a a regular regional race you'll get a bore check anyway. You'll be lucky if tech knows the weight of the class or even has the scale calibrated. Unless you cheat the head and cam, your over bore is a performance decrease. I don't know what the agenda is for those that made the rule but it's clearly not in the best interest of the hobby racer.

It always amazes me how someone with no knowledge of how or why a rule was written will make such a condisending statement about the rules makers. The rules makers are much more in touch with reality than some guy who has not completed his first SM build.

First, the rules have nothing to do with what you or your local street car shop want to do to street cars.

Second, we can not use aftermarket pistons, so what is available aftermarket is of no concern. Mazda DOES make a +10 piston.

Third, you do not have to "cheat the head or cam" to get the correct compression ratio. You can legally deck the head and cam more than enough to get maximum legal compression.

Forth, what difference does it make what "other sanctions" put in their rules.

Fifth, Unless you are standing in the tech shed from 7am to 6pm at a regional race, for the glory of being there, DO NOT belittle our volunteers. I would love to see more tech, I would love to see more people in tech. Tech makes mistakes. But untill you stand in their shoes, do not insult their abilities.

Due to SM's reliance on Showroom stock rules as the overlying regs, we where never allowed to use anything except a standard piston. About 5 years ago, an allowance was made to sleeve the blocks to standard size. This allowed saving of worn blocks. Low and behold, racers starting doing some pretty wild things with those "legal" sleeves. So for this year the sleeves where disallowed effective Sept 1, 2012. But a 0.010" overbore was allowed. This still allows a worn block to be reused, without the expense of sleeving.

The 15 pounds is basicly to keep every front runner from going +10. As the power improvement (after resetting compression ratio) would be negatively offset by the added weight.

The rules makers ONLY have the best interest of the hobby racer on their mind. I know these guys, I was these guys. If the masses even knew 20% of what is discussed at these meeting, you would know this.

Facts and knowledge will get you much farther than spouting off your incorrect opinions.

Dave
Former Chairman of the SMAC

[dstevens]

I appreciate your response and perhaps I was a bit harsh in my tone and words and for that I apologize for the way it came out. However, I stand by my assertion that a weight penalty for such a small adjustment is not called for . From what I understand from private conversations with a person with first hand experience with the rule the compromise was made for the penalty to get consensus to pass the rule for the reasons you stated.

The comparison to aftermarket and street car is valid. FWIW, my machinist is a race builder as well and has many engines in many different classes. The comparison shows that the operation isn't that standard and offers no appreciable performance increase. In a class with several other mods that do enhance performance this rule to me is arbitrary and perhaps punitive. As an opposite example, when it was determined that they couldn't tech the adjustable timing they went ahead and let it in. No penalty.

I appreciate what you've done for the sport and how you've personally helped me. However, I'm still going to have an opinion and while you're certainly free to agree or disagree, please don't take it personally.

[Jim Drago]

Dave
In a weekend like this last one, I may have sold my soul for one extra HP. I was basically #3 in power to my team mates, at the front of a race like the sprints or the Runoffs, IT matters! I agree in any other walk of life and in 95% of Sm races, it doesn't mean much.

As one who basically passed the rule.. The 15 lbs represented what gain we calculated by displacement ( mathematically) +about 5 lbs.. Then a discussion took place between us.. Would you run a .010 with no weight penalty, 100% unanimous on SMAC, yes absolutely! Would you run a .010 at a 25 lb weight penalty ( I think it was mostly probably nots) At 15 lbs, we were all split, so that became the number. It is slightly higher than the calculated gain of the overbore.

If no penalty was imposed I absolutely would run one as I am about 7-10 lbs over now. If that became the rule with no penalty, I think we would lose more people who will refuse to build another motor. I agree they wouldn't need to, but perception becomes reality in these situations, I have seen it time and time again.

I think the decision was a very good one. It allows people to save some money and not force them to buy a new crate, still be competitive and does not force the class into chaos and feel the need to build new engines. If no weight penalty were the rule, I can assure you I would have sold twice as many engines this year, but it would be terrible for the class IMO

[wheel]

What Jim said.
wheel

[davew]

I feel that these 2 lines from Jim Drago sum up what happens on most SMAc conversations;

As one who basically passed the rule.. ...If no weight penalty were the rule, I can assure you I would have sold twice as many engines this year, but it would be terrible for the class IMO

Dave
ex SMAC

[Brandon]

Due to SM's reliance on Showroom stock rules as the overlying regs, we where never allowed to use anything except a standard piston. About 5 years ago, an allowance was made to sleeve the blocks to standard size. This allowed saving of worn blocks. Low and behold, racers starting doing some pretty wild things with those "legal" sleeves. So for this year the sleeves where disallowed effective Sept 1, 2012. But a 0.010" overbore was allowed. This still allows a worn block to be reused, without the expense of sleeving.


Dave
Former Chairman of the SMAC

As part of the 'showroom stock' rules that our class is based off of, those hearken back to what the factory has indicated/allowed within the service manual.
Should a customer arrive at a Mazda dealership with a fried #4 cylinder (entirely possible considering the cooling system compromises ), that service needs to have specifications laid out that not only repair the issue but facilitate ongoing warranty work after this service visit.

Of course, what this means is you get a ten-thousand overbore specification, which, as DS notes, any good engine builder would say is a waste of time; but they're not responsible for warrantying that repair or vehicle for X-number of future miles afterward either. I'm sure you'd find most auto techs employed by said dealership would also feel that small of an overbore to not be worth much (if anything) but they're following their employer's rules in this case.

So, between the SS-based ruleset & a need to eliminate a (seriously large?**) gray area thus was born the allowed overbore with weight. This had a secondary effect of offering a potentially cheaper way to "fresh power" without resorting to a new crate purchase.

And not to fan any potential smoke into flames, I too appreciate the time DW & others has spent on the respective committees and both welcome & enjoy their perspectives on various subjects important to us.

So what's the verdict then? I don't have the FSM handy at the moment but if it allows upwards of a 15-thousand maximum bore diameter does that make the 10-thou the largest (durable) bore possible or is there a higher number that would still result in a decent 2 or 3 season motor?

[dstevens]

Thanks guys. I appreciate the responses.

[davew]

If you do the math, as based off of the SCCA GCR, a standard size engine is allowed 0.005" in wear. From 0.006 to 0.015 you are considered overbore and +15 pounds. Anything above 0.016" over stock bore will be considered non compliant.

I did the math.

Dave