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Thread: Sniper loses acceleration power.

  1. #21

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    Thanks for the reply Matt. It currently it has 3.42 rear gear on a 275 tire. I may try to hop up to a 3.73 gear then and see if it helps.

  2. #22

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    If it were me, I'd probably have the converter loosened up some first. That RPM drop on the shift is hurting you a bunch. Definitely takes the engine out of power by about 25%. Rear gearing will help it accelerate through, but a converter that drops closer to 800 RPM on the shift would help tremendously to keep the engine happy.

  3. #23
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    Just for comparison, I have a 3550 lb car with a 383 SBC, TH350 transmission, 3.42 gears, 26" tall street TAs and a 3000 Coan torque converter. On the 1/2 shift I loose 1800 RPM. I did a pass on the street with a lot of spinning and on & off the throttle once, and from about 2200 RPM at launch to 6000 it took me 3.9 sec. It was 1.4 sec before I even got the tires to stop spinning. The best I have gotten was 380 HP at the wheels. And that was with a bigger cam than I have now, so my numbers now would be less than that.

  4. #24

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    I see there. I run an MT PBR slick didn't notice any wheel spin. It was hooking good in first. Just felt like I was driving a manual transmission skipping 2nd gear going from 1st to 3rd. I think next year I'll come down a little in cam size, 601/611 I think might be overkill for the Snipers street/strip setup. Going to get converter checked out for now and go from there.

  5. #25
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    I also looked at after the 1/2 shift. From 4300 to 5000 RPM, it takes you 6 seconds. From 4200 to 5000 RPM, it takes me 1.7 sec. That is a big difference. I think I would start with the basics. Pull all the plugs do a compression test on all cylinders, check all wiring. Check spark plug firing order and so on. Your torque peak is at 5200, but you're still making over 400 lbs at 4300 RPM. So I don't think it should be that much of a dog in second gear.
    Last edited by 81 TransAm; 09-05-2017 at 02:24 PM.

  6. #26

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    I swapped out plugs yesterday and found two not firing. Put all new ones in. I'm getting ready to go out and take for a ride & datalog. I did a compression check as well, all cylinders were between 130 & 155. I think the lower numbers just haven't seated yet; engine maybe has 45 miles on it.

  7. #27

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    With two spark plugs not firing, you also would see very lazy engine acceleration as well. My statements about converter & gearing were with the understanding the engine was new and the ignition system was up to the task of the engine.

  8. #28
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    You could go here: http://www.wallaceracing.com/dynamic-cr.php and find out what you dynamic compression ratio should be.

  9. #29

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    OK, here's a fresh datalog. Still same issue was hoping it was plugs: https://www.dropbox.com/s/49vp1z63ti...%3D17.dlz?dl=0

    Matt everything is new. Engine has less that 50 miles on it, transmission maybe 30. All electronics are new.

  10. #30
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    This thing is losing RPM in third gear. Your RPM trace still doesn't look good to me. A lot of noise in it. Where are you getting your RPM signal from?
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