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PostPosted: Wed Nov 14, 2018 6:51 pm 
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Joined: Sat Dec 12, 2009 8:08 am
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Location: Atlanta, Ga
Figured I'd post this while everyone has plenty of down time.

I'd like to remind everyone that races prod in a limited prep class and has a limit on compression ratio that they need to carefully check their motor's compression ratio. We manually checked a number of cars at Sonoma and found some things of concern. No fingers pointed.

One interesting thing did surface and that was it appears a motor that has a piston that protrudes above the deck will not whistle correctly. Not sure why but I believe it maybe an interference by the head gasket. So, if you have been whistled and have a piston above the deck, I recommend you cc the engine by hand. Basically and I've been telling the SM guys this for years, do not build your motor using only the whistler. There maybe some other variables on some of these small motors that cause a low reading. We did not have time/man power at Sonoma to whistle and cc but I think that will not be the case at VIR. I know we will be cc'ing.

I can assure all that we will continue manually checking motors along with the use of the whistler. I urge you to have your engine builder closely check your compression ratio. Not saying which but we had a class at Sonoma where two of the top cars cc'ed less than a tenth from maximum allowed. Good job, engine builder. It would be bad to throw away an entire season because you did not check the compression ratio.

And finally, I'd like to publicly thank my tech crew at Sonoma. They were short in numbers but did a heck of a job checking the cars. Yes, I may not have communicated well and I apologize for keeping some of you for what seemed a long time. But, if a car had a fuel problem, weight problem or on track problem, everyone had to stay in post qualifying impound until all was resolved. From our standpoint, we only had two actions. All in all, I was pleased with the production field at Sonoma. Lot's a of good looking cars. The only concern I left with is there seems to be a lot of strange interpretations about spoilers and front fender flares. Everyone needs to read the fender flare section closely keeping in mind the sentence concerning the stock appearance of the opening. I had to remind several competitors that these are not GT cars. Enough said.

See everyone at VIR.

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PostPosted: Thu Nov 15, 2018 9:46 am 
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Jim, I am pulling apart the engine that I ran in GTL this year. It whistled well below what it was measured at before assembly.

follow up on the bodywork issue, I think GT is also required to follow the factory wheel house shape.
it just tends to get over looked.

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PostPosted: Thu Nov 15, 2018 1:07 pm 
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What exactly were the problems you were seeing with the flares?

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PostPosted: Thu Nov 15, 2018 1:53 pm 
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Location: Spring Hill, FL.
Jim, please share your CC equation .
Thanks. MM

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PostPosted: Thu Nov 15, 2018 10:33 pm 
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We used several different equations. One was done manually and another was done using two on line calculators. We were always within several hundreds doing it this way. And two of us did calculations independent of the other. All cc'ing numbers were run a minimum of twice.
Here's link to one of the on line calculators.
https://www.rbracing-rsr.com/compstaticcalc.html

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PostPosted: Fri Nov 16, 2018 5:48 am 
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Joined: Sun Jan 30, 2011 5:15 pm
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"They were short in numbers but did a heck of a job checking the cars."

These people have my complete respect and gratitude.

I think tech is the most challenging job in scca. to stay on top of rules that in breadth must account for cars from the 1960's all the way thru the ever-changing and very sophisticated modern cars is basically impossible. I saw this while i was on the board and it was discussed but there is no easy fix for this. the task is just simply impossible for a full time professional much less part time volunteers! Unfortunately (but necessarily..) this is causing a continual shift to competitor enforcement of the rules. i dont see a way around this trend with such a diverse set of cars and rule sets.

my 13 yr old son is fascinated by all thing mechanical and is going to 'assist' tech in the west next year, running errands and helping out. He's braver than I!!! :D


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PostPosted: Fri Nov 16, 2018 7:52 am 
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Location: Atlanta, Ga
Mike is correct. The Runoffs's is the exception when we normally have people who are experts in specific classes. On a normal race weekend, I'm overwhelmed by some classes and their specific rules. I always defer to someone who has more experience or go find someone who does.

One of the best weekends I ever had in tech was at a Road Atlanta race where we had the Boy and Girl Scouts there on a camp out weekend. Part of their badge requirements for the weekend was to help out in various areas. Well, when they came to tech, we couldn't get them to leave. They've loved pushing the cars on and off the scales. And we explained things we were checking and let them assist. Of the 30 at the track, we had 20 working tech on Sunday. And guess what? None of them had had much exposure to cars prior to the weekend. All it took was some time to explain what and why we were doing and they were hooked. If you have a teenager who is bored at the track, send him or her to tech. They won't get bored there.

You too can help at tech. Come to the track on a weekend you're not racing and volunteer. You may also get hooked. Or if your race is over early on a day, go to tech and ask to help. If nothing else, help with the scales. The final tally for the Runoffs this year was 2,580,749 pounds
of cars pushed on and off the scales by tech. A normal weekend has far less.

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PostPosted: Fri Nov 16, 2018 7:16 pm 
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Let me make a suggestion to all with limited prep motors. When you cc your motor, keep a record of each reading you get or calculate. Place it in your logbook. And if we end up cc'ing your motor at the Runoffs, we can compare your results with ours. It would certainly be helpful in case there's a problem.

Let me also clarify that we did clean out the sealer at the piston/cylinder gap so as to not skew that volume reading. By putting the sealer on the cylinder wall and bringing the piston up to TDC and then back down to a predetermined setting, we were able to seal the ring gap and then remove the sealer from the gap between the piston and cylinder wall. If not, this would have given us less volume and an incorrect CR.

And we did use volumes and actual measurements for calculations. And when asked, we did share our calculations with each competitor or engine builder. No secrets from them. Of course, no other team was privy to the info. We did our best to keep it private.

Hope this helps you get ready for VIR.

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PostPosted: Sat Nov 17, 2018 8:50 am 
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Don’t have the rule book handy. What does it say about removing carbon when checking

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PostPosted: Sat Nov 17, 2018 11:17 am 
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Jim, thanks for explaining your methods and taking your time to keep us all legal.

My pistons are drilled for gas porting , stick out the top .029. and have a dish turned in the face. They are very hard to get a solid CC value by themselves. I did he first few sets ( as all of these mods I do my self) and finally gave up and now simply CC the entire chamber as assembled .
The tolerance stack of the methods you describe is easily .3 to .5 pts. Just by the piston crown and head gasket thickness IMHO.
You could save your techs a lot of work by whistling all of the cars, and actually CCing the engines in the cars that whistle within .2 pts over or under . The assembled CC Value should trump any other values.
All thats required to get a valid in car CC is to get the plug high . Some are high as they sit, some need to be rolled up on the tail or side a bit.
You still need to pull the head and check bore/stroke and stock chamber/ports of course.
The pan has to come off to verify stockish crank. You dont need to pull rods anymore or pistons

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