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Discussion Starter #1
Last September my first run at Irwindale (1/8th mi) was 7.25, about what I had been running since making some minor changes. Over the next 4 runs the car slowed to 7.66 without any changes whatsoever. The next time out, times were about the same and I have been chasing my tail ever since.:confused: Some of the things I have tried to get my ETs back include changing the power valve, rejetting both primay and secondary, changing the advance curve, installing a brand new distributor with melonized gear, checking compression, readjusting the valves, etc. The motor is still running strong, but ET has not improved and thinking the problem may be in the trans and/or converter, I went back to 2012 when the trans was built, and also took a closer look at my data logger from last September. This is what I found:

  • I have made 443 passes at the track since September 2012
  • Trans fluid was changed once since then and all looked good
  • The converter has flashed to 4000 rpm on all 443 runs
  • On the first run of 9/29/18 it was in first gear for 1.6 sec
  • On the last run of 9/29/18 it was in first gear for 2.0 sec
  • In second gear it also was slower by 0.4 seconds, a total of 0.8 seconds
  • 60 ft slowed from 1.60 to 1.67
  • ET slowed from 7.25 to 7.66
  • MPH slowed from 93.8 to 89.3
  • The loss in ET and MPH appears to be in the trans
  • My data logger showed similar A/F readings during both runs

Am I on the right track here? Thanks for any suggestions you have.:yes:
 

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Tough one. 4 MPH slower and the drop in 60' is a lot. If your motor still seems to be dialed and running good I'd probably look at the trans also. A lot of other variables could be the cause but if you covered those not sure where else to look but the transmission/converter.
 

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I am going to say its a good idea to have both the converter and trans checked. But I would lean to the converter as being hurt. The fact that you were in first gear LONGER to me shows down on power and engine speed acceleration. If the trans was slipping I would expect the rpm to increase faster and be in first gear LESS. That's not to say something in the trans isn't binding up as well.
 

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This statement makes sense to me:
"The fact that you were in first gear LONGER to me shows down on power"
The loss of MPH also indicates power loss. Have you checked the valve springs?
The converter flashes to the same RPM as it always has. Seems like the loss of power is at higher engine speed.
 

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This statement makes sense to me:
"The fact that you were in first gear LONGER to me shows down on power"
The loss of MPH also indicates power loss. Have you checked the valve springs?
The converter flashes to the same RPM as it always has. Seems like the loss of power is at higher engine speed.
But it lost .07 in 60' as well. So not necessarily down at only high engine speed.
 

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Have you confirmed that the car is not spinning off the line now? Are you also factoring in weather? Density Altitude can account for some of your losses too? With that many runs on the engine and trans... there are likely some issues in both engine and transmission. Have you done a leak down test on the engine?
 

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Discussion Starter #7
Have you confirmed that the car is not spinning off the line now? Are you also factoring in weather? Density Altitude can account for some of your losses too? With that many runs on the engine and trans... there are likely some issues in both engine and transmission. Have you done a leak down test on the engine?

Sorry for the delay in replying, but I had to reset my password and response from the site was very slow.

As for density altitude, I check it every run and there was no significant change. A leak down test showed all cylinders are good. Plugs are new, plug wires are good, A/F is good with no change between runs. I have checked and rechecked everything on the engine, and remember: this drop in ET occurred on the same day over a span of 2-3 hours without any changes made to the engine, staging, shift point, etc.
 

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Discussion Starter #8
I talked to my trans guy yesterday, and he thinks the problem is in the converter. He will have the converter redone and do a visual inspection of the trans next week. Stay tuned...:yes:
 

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Discussion Starter #10
Update: It was the converter

Had DMC in Ventura check the trans and and converter. Donnie said the trans looked good, but converter was was definitely tweeked. After I put 300 miles on it, took it to Fontana, ran a best of 11.66 in the 1/4, 7.38 in the 1/8, with 60 ft of 1.61. At the same track in May with the same DA (about 3200 ft), ran a 7.80 in the 1/8. So finally got some resolution after chasing my tail for a year. :rolleyes: Lesson learned.:yes:

Looking to get it down another 0.2 seconds so I can run the 11.50 index class.
 

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Very good!

Or instead of waiting to run a 11.50 index class go out next weekend for the summit series bracket races. Sounds like the car would run in pro, or slow it down to 12.0 or slower and run in sportsman.

Glad you found the issue.
 

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Discussion Starter #12
I have run Summit many times and will continue to do so. :yes: But I like index racing because it is heads up.
 
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