Mayf,
Since I'm the guy doing most of the certifying I'll try to answer these
questions.
1) We use vernier calipers or an air pump to verify the displacement of
record engines. The NBS is not involved at any level. Remember this is
sportsman racing, in over 50 years a more accurate method or higher standard
has not been required.
2) The calipers and mics are to .001 resolution.
3) A dial or digital caliper can read to .001 so a guess to .00025, .0005,
etc. is not required. Most, if not all, engines are not built at exactly the
bottom or top cubic inch limit for a given class.
4) The calipers or mics are as accurate as you would usually find in
anyone's tool box. These things are transported, dropped and salt rusted.
5) Temps are not taken into consideration unless the air pump is used. A
temp factor is added to the displacement shown on the pump cylinder. If an
engine is so close to the displacement limit that temp would become a go/no
go issue accommodations can be made in order to insure the fairest treatment
for the competitor.
I usually measure only one cylinder for a displacement check. If a given
cylinder does not pump well we will use another. Ring blowby, valve seating,
cracked piston, etc. can cause a cylinder to read excessively large. You may
have noticed that there is approximently 1 cubic inch gap between the upper
and lower limits of each engine class and the one preceding or following.
This .999999999999 cubic inch usually is sufficient to allow for an engine
built at the class limit.
I hope this helps your understanding of the process. I know these tolerances
are not what you are use to but, they work for us.
The measurements you outline figure to 306.1 cubic inches. This displacement
is well above the D class limit. Bores and strokes will usually measure a
little on the large size. We can measure all cylinders and average the
displacement if needed to arrive at the actual displacement for your engine.
The FIA requires each cylinder to be measured on their tech form. When we
had an FIA steward at the '99 World Finals he accepted our methods and
signed off on the records set under his standards.
Dan
PS - I'm going to forward this email to the list. I think this may be good
info to be passed on to the others. It will probably open another "can 'o
worms", but that's the cross I bear.
DW
----- Original Message -----
From: "DrMayf" <drmayf@teknett.com>
To: "Dan Warner" <dwarner@electrorent.com>
Sent: Thursday, June 21, 2001 4:29 PM
Subject: Motor Class Question
> Dan, you may not be the one to ask these rather dumb questions of, but
here
> goes. When a racer breaks a record, is the engine always checked? I
suspect
> yes. What happens in the case where the engine is very close to the size
> limit for that calss? Is one head taken off and the bore checked? I
suspect
> yes. Now here are the real questions..
> 1) Do the measuring instruments trace back to the NBS?
> 2) What are the resolutions of the instruments? Micrometers typically have
> 0.001 graduations.
> 3) Is the measurements between the thousandths guestimated? Or What?
> 4) What is the accuracy of the instruments? IE. typical accuracy is +
or -
> 0.001
> 5) Are the instruments and motor temperature normalized before
measurement?
> (at the same temp)
>
> The reason is that I have been doing a little thinking out of the box for
> me. My short block is a DSS block, 4.030 bore x 3.00 stroke, that is
> supposed to be a nominal 4.030 bore. But, a bore difference as small as
> 0.0015 on the small side puts my motor into class D, not C. I am having it
> measured in four places for each bore next week, so this may all be of
> academnic interest only.
>
> As an aside, my car in the current configuration will never be a contender
> for a class record. But am curious about measurement controls, resolutions
> and accuracies with temp thrown in...
>
> mayf, the ignorant desert rat....
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