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 Post subject: LP motor testing
PostPosted: Thu Jun 21, 2018 8:19 pm 
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Some of the things that determine the exhaust note of a race car are, type of exhaust, cam design, carb size and at the top of the list is compression ratio. And I have taken note that more and more LP cars have exhaust notes that, let's just say are a lot crisper than I would have
guessed, given the rules

I have never built a Limited prep motor so I don't know any of the 'Tuning tricks' that people that do built them might have discovered over the years.
But I was talking to a racer earlier this year about his personal experiences with building one and the way SCCA checks the compression ratio for compliance with the 11 to 1 rule. He said he built his motor to a calculated 11 to 1 and when it was checked last year it tested well below the 11 to 1 number. He speculated others know that too and have begun to " adjust" the Calculated CR to pass the inadequate testing procedure. I have always thought the CR testing was a weak link in the LP rule compliance efforts but I have never been close enough to the problem to form an opinion about it.
Anybody know anything about that?


Last edited by rick haynes on Thu Jun 21, 2018 10:24 pm, edited 1 time in total.

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 Post subject: Re: LP motor testing
PostPosted: Thu Jun 21, 2018 8:52 pm 
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Location: Oregon City, Or.
rick haynes wrote:
Some of the things that determine the exhaust note of a race car are, type of exhaust, cam design, carb size and at the top of the list is compression ratio. And I have taken note that more and more LP cars have exhaust notes that, let's just say are a lot crisper than I would have
guessed, given the rules

I have never built a Limited prep motor so I don't know any of the 'Tuning tricks' that people that do built them might have discovered over the years.
But I was talking to a racer earlier this year about his personal experiences with building one and the way SCCA checks the compression ratio for compliance with the 11 to 1 rule. He said he built his motor to a calculated 11 to 1 and when it was checked last year it tested well below the 11 to 1 number. He speculated others know that too and have begun to " adjust the Calculated CR to pass the inadequate testing procedure. I have always thought the CR testing was a weak link in the LP rule compliance efforts but I have never been close enough to the problem to form an opinion about it.
Anybody know anything about that?


What is the testing method? I would think the are cc'ing them just like you or I would..

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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 5:46 am 
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Many Regions use a "Whisler" for expediency.

I know of an IT car that was somewhat over the maximum CR, and it tested just fine with a "Whistler".

The fuel debacle of the 21st century.

R. J. Sorensen


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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 5:51 am 
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What happens when you get to runoffs? Testing via Whistler at a local race is one thing.. but what happens if/when you wind up top 5 at Runoffs and the expectation is to take your engine home in a box? how is compression tested there?

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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 6:05 am 
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At Run-Offs, believe CR is checked by measuring the cc.

For decades, there have been cars that dominated their division only to show poorly at the Run-Offs. Became predictable. Coincidental?

With today's qualifying requirements, less obvious. No need to beat a competitor or even finish.

RJS


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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 7:58 am 
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... and then there's the ones that run just hard enough during the year to qualify, then clean out all those bags of sand for the big race...

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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 8:09 am 
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Location: Wauwatosa, WI
Comment only on the Whistler, from the SCCA Whistler procedure. Within a certain un-named class a couple engine builders figure a way to have a bit more CR without the Whistler knowing using the process as was normally completed with the valve/cam cover on. Take the valve/cam cover off and whala over spec CR. Occurred in FL and became known as WhistleGate.

7. Determine correct spark plug adapter and install it in place of the spark plug (minimal
torque is required). In some cars, especially overhead cam vehicles with spark plugs well
down in the engine, it may be necessary to remove the valve cover to get an accurate
reading
.

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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 12:25 pm 
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I’m sure it’s a reasonable way to test CR within certain parameters and assuming that the operator has been thoroughly trained. That said, at the 2005 Runoffs, Matt Brannon, John Salisbury, Tom Feller, me and a couple of other LP engined cars were whistled. None of us were measured anywhere near 11:1......including the defending champion. Do you think they got accurate numbers? Hell no!

Lesson learned.......train the folk using it so they know how to properly measure CR when it matters.

Dayle

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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 12:54 pm 
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Even better... write it into the GCR that a complete CC test will be used at the Runoffs for top 5. No whistler. But, make it official and state the method upon which it will be tested.

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 Post subject: Re: LP motor testing
PostPosted: Fri Jun 22, 2018 2:16 pm 
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The Whistler is only as accurate as the person who's operating it, which is the exact same situation as the "old" method of a graduated pipette and a glass plate. I've thoroughly been through both methods, and know exactly how a person could cheat either one. That's part of being an informed racer and a competent engine builder. Several times I've had my engine "Whistled" and had it come back way under, due to operator error. At The Runoffs though, if you chose to gamble on that stage (or really any stage, IMO) that you're going to have an inept tech worker who doesn't know how to take a proper reading, so you're going to build your engine high, that's a hell of a gamble. Especially if I'm standing near by paying attention to what they're doing, and how wrong their readings are.

A well done Whistler reading will be within +/- 0.1, and from my experience with "the old method", it isn't any more repeatable or accurate than that.

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