why did my car slow down?
 

I raced the Super Chevy show at Texas motorplex last weekend. Went a couple of rounds on Saturday, and then made it to the finals on Sunday. Lost about .12 in final.
67 Firebird convertible, zz4 IHRA crate motor stocker legal motor. 3400 lbs. Set up soft, shifting about 6800, big bias tires, leaving at 2500 footbreak. 5-30 full syn oil. Turbo350, deep pan, syn fluid, no cooler. Was about 85 degrees and sunny out.
5 round race, and car had been in the 11.58-11.60 all weekend. They were hot lapping us late Sunday. Had been running about every hour, 4th round was a 40 minute run to run per the time slips, and 5th round was at 20 minutes, per time slips.
Car lost .05 in 60' then about .02 every break rest of way down track... 60' had been within one # all weekend. Did not feel it spin. Had .023 light in finals... playback tach of run shows that converter flashed same (5200) as earler runs, shifts were on the mark and did not flash between. Lost about 3/4 mph at 8th mile mark and about same at finish I am guessing, as I tapped brakes since I was behind.
I have ran valves, and did not find any issues. Changed oil and cut filter, all looks good. Trans fluid is clean. Car does not have any miss or any noise. Everything ran fine and felt fine on the run, just slow. Everything sounds fine now. Good oil pressure, etc.
Water temperature was back within 5 degrees of other runs when I staged, and pump and fan were on and working. Staged at 155.
Was motor and trans just hot?
I cant find anything wrong with it... ?

Sorry so long, but wanted to give all data.
thanks,
Ken

Stock 412

Re: why did my car slow down?
 

Weather/Wind ?

Re: why did my car slow down?
 

wind and weather was same...

Ken

Re: why did my car slow down?
 

Losing .05 in 60' is a lot! Watch the playback again. My Autometer playback has been a huge help even without using it's driveshaft or download features.
You have a PM.

Re: why did my car slow down?
 

Do you have a trans temp gauge? My car would really slow down with to much trans temp.

Re: why did my car slow down?
 

I do not currently, but thinking about a gauge and cooler.

Re: why did my car slow down?
 

I had a customer that had a similar issue in late rounds and it turned out to be the sprag in the converter liked a certain temp to be consistent. he found it by changing his warm up procedure.

Re: why did my car slow down?
 

Ken,

A deeper tranny pan will also help , do you use a fan or sprayer to cool motor & trans between rounds ??? Good Luck..

Re: why did my car slow down?
 

Put a stick in it.

Re: why did my car slow down?
 

Dwight, I want to, along with a Pontiac 400... Just time and money:-)
Dave, have deep pan, adding a temp gauge.
Thanks everyone. I am planning to run it tomorrow and see what happens. Will let you all know.
Unless I got the sprag in the ATI, I can't find anything wrong but heat.

Ken
Stock 412
67 Firebird