Henry Frye wrote:
>Hi gang,
>
>I need to work out a few issues that cropped up at the Jeff 500 before
>Mosport. I need to run the car, and I guess either a chassis dyno or a
>track day will suffice.
>
>I can get 4 hours of track time or 1 hour of dyno time for about the same
>$$$. I think the track time is the better way to go, as I plan on changing
>out some parts for testing purposes, and I do not think I can get much
>value out of one hour at the dyno.
>
>The problem is the TR is really, really loud. The tracks that I can get to
>for testing have noise restrictions, looks like I need to be at or below 99
>dB. At the Jeff 500 I had a guy tell me my car was the loudest in the
>session. Doesn't surprise me.
>
>I am thinking I want to have a very low restriction muffler for track days,
>and a bypass pipe for race days. I am concerned about how the different
>backpressure will effect the engine.
>
>So how do you guys handle this?
>
>.
>
>
>
Years ago on the TR6 we found 12 hp at the rear wheels by removing
the flowmaster and cutting the tailpipe shorter. We went to the chassis
dyno with the tailpipe cut into sections so we could quickly change
lengths. Ended up with as short as legally allowed (past the halfway
point of the wheelbase). We put a turndown on the end to point the noise
at the track and were never again over 100db. Made sure to wear earplugs
though because the cockpit got way noisier.
If you use a chassis dyno for tuning make sure it is an absorption
type and not an inertia type. You have to be able to load and stabilize
the engine at the test rpm (we used 500 rpm increments from 4000 to 7000
rpm) to get valid HC and CO numbers. From this you can tell a lot about
the jetting, cam, and optimum throttle plate position. If you have never
been to a dyno it would be worth a try but it usually takes 5-6 hours
for a good test session. Be forwarned, it is torture standing there
watching and listening to your prized creation pulling it's guts out.
If you have to choose between dyno or track time though, pick the
track time.
Greg Lund
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