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Author Topic: Trap RPM Question  (Read 4975 times)
68mustang
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« on: August 20, 2013, 10:12:25 pm »


Hello,

I am spinning thru the traps @ 7,100 with  33x15x15 Hoosiers and 4.56 gears I shift @ 6,400 any advice on this I don't think I'm making power @ this rpm. The motor is a 408 stroker w/ a solid lifter cam that is 264, 268 @ .050. and 12:5 to I1 comp. The converter is 4,800.. Any advice would be helpful been out of racing for a while.

Thanks
68mustang
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289nate
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« Reply #1 on: August 20, 2013, 10:21:32 pm »

It depends on how well your particular engine holds on to power after peak.  Most say to cross the traps a few hundred rpm beyond their shift point.
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\'65 fastback pump gas 289, 4.56 gears, and faceplated T5.  11.123 at 122.4
Bam54
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« Reply #2 on: August 20, 2013, 10:35:15 pm »

What mph are you running in the 1/4? Is this a 9 sec car? 7100 for a 408 is not bad if it was falling on it face you would be able to tell. I turn my 454W 7800 out the back and shift at 6800 to 7000. Give us a example of your time slip and we can figure out if a gear change might help.

Bam
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"Take the horse out of the barn and let her run baby run"

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CHI headed 454 Clevor
9.24@142 1.30 60ft N/A
5.84@117 1.28 60ft N/A
3040lbs race weight
68mustang
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« Reply #3 on: August 20, 2013, 10:44:25 pm »


Bam, attached is a time slip

60....1.343
330..4.043
1/8...6.367
mph..105.34
1000..8.403
ET.....10.149
mph..128.18

Thanks
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Bam54
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« Reply #4 on: August 20, 2013, 11:28:30 pm »

Something is wrong you are turning to many rpms for that mph with that gear and tire size. Are you sure you don't have more gear in it. Because if you don't your converter or your trans is bad. We turn 7500 at 126 with a 28" tire and 4.56 gears. Im thinking you have more like a 5.30 gear or some were around there.


Bam
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"Take the horse out of the barn and let her run baby run"

www.ponyexpressracing.com

CHI headed 454 Clevor
9.24@142 1.30 60ft N/A
5.84@117 1.28 60ft N/A
3040lbs race weight
68mustang
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« Reply #5 on: August 21, 2013, 07:58:33 am »


I am positive it's a 4.56 gear. The converter is about 12 yrs. old, but in a race car it hasn't seen street duty so age in this case doesn't matter I guess. I use a C-4 possibly it needs band adjustment. My shifts are crisp though.

I don't get out much at the end of last yr. it went 10.05 @ 130. I don't know why I didn't mph that this time. I did pull the dist to spin up some oil maybe my timing isn't quite right. Let me know what you think. Where do you think I should be mph wise.

thanks for the help
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Ammosteve
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« Reply #6 on: August 21, 2013, 10:57:40 am »

7100 with 33 inch tires and 4.56 gear should be over 150 mph...

Your mph is showing about 6000 rpms to go 128.

Your convertor isn't very efficient out the back.  Try shifting at 66-6700 and see what she does.
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Bam54
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« Reply #7 on: August 21, 2013, 06:25:47 pm »

The car is running pretty good to the 1/8 the 60ft is real good for the ET. But it is starting to fall off from there out. So it seems like it has to much gear but something else isn't right. With a 33", 4.56 gear and 128mph you should only be turning 6100 to 6200 rpm not 7100rpm. So you either have more gear in it than you think or you are blowing thru the converter (that would be my guess). How many rpm does it drop when you shift? Do you happen to have a video of it going down track with sound?

Bam
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"Take the horse out of the barn and let her run baby run"

www.ponyexpressracing.com

CHI headed 454 Clevor
9.24@142 1.30 60ft N/A
5.84@117 1.28 60ft N/A
3040lbs race weight
68mustang
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« Reply #8 on: August 21, 2013, 07:14:49 pm »


I appreciate you digging into this to help me Bam. I don't have a video , but the rpm's drop about 300 it recovers quickly. The cam is on a 108 lsa so maybe that's why. I agree with the interval times it 60 ft's good and up to half track, but dissinagrates after that. I can feel there is no more pull past 3/4 track for sure..it's out. I'm going to jack it up and count the turns to get the ratio for sure. I gave a call to a friend that races regularly and he thinks there isn't a problem..I don't agree. I'm probably one of the few that runs 10.14's and mph's 128 lol.

thanks,
T
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Bam54
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« Reply #9 on: August 21, 2013, 09:02:07 pm »

That converter is really loose to only be dropping 300 rpm on the shift that is more than likley were the rpm is coming from but definatley check the rear gear ratio.

Bam
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"Take the horse out of the barn and let her run baby run"

www.ponyexpressracing.com

CHI headed 454 Clevor
9.24@142 1.30 60ft N/A
5.84@117 1.28 60ft N/A
3040lbs race weight
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