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A question about Compression #1713797
12/21/14 10:07 PM
12/21/14 10:07 PM
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bobs69 Offline OP
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I have a friend with a Chevrolet that runs 5:97 My barracuda runs 6:03 I have came up from 13 to 1 compression to just over 14 to 1 also I have changed my 4:56 rear gears to 5:13 both cars have power glide transmission both cars weigh with in 50 pounds of each other. He is not changing anything. Have I done enough to get around him? I have already lost two cases of beer to him.

Re: A question about Compression [Re: bobs69] #1713798
12/21/14 10:25 PM
12/21/14 10:25 PM
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Sport440 Offline
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The compression change alone should get him. I wouldnt of changed the gears at all. That jump to the 5.13,s may cost you ET Get ready to shell out another case. IMO

Re: A question about Compression [Re: Sport440] #1713799
12/21/14 10:33 PM
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bobs69 Offline OP
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I was shifting at 6500 and crossing at 6200 I felt I was not using all of my motor.

Re: A question about Compression [Re: bobs69] #1713800
12/21/14 10:42 PM
12/21/14 10:42 PM
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Quote:

I was shifting at 6500 and crossing at 6200 I felt I was not using all of my motor.




What engine? Don`t have 100% faith the one point will get you that much goin from 13 to 14 and have personally seen smaller gains than people thought. Now from 10 to 11 or less I`ve seen bigger gains....... I like beer so either way..............


72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
Re: A question about Compression [Re: Thumperdart] #1713801
12/21/14 10:49 PM
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bobs69 Offline OP
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Both cars have a big block My car is a 514 with Indy EZ Heads mega block solid roller really wants to run at higher rpm's

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Re: A question about Compression [Re: bobs69] #1713802
12/21/14 11:00 PM
12/21/14 11:00 PM
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Not familiar w/those BIG motors............. But hear less rpm`s are the ticket generally so hard to say. I spin mt 470 past 7000 on most occasions and it`s faster/quicker that way so have you tred shifting higher and did it help? Ask sixpack gut how to get .2+.................


72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
Re: A question about Compression [Re: bobs69] #1713803
12/22/14 12:46 AM
12/22/14 12:46 AM
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Quote:

I was shifting at 6500 and crossing at 6200 I felt I was not using all of my motor.




At the same Et and MPH that your running now, the 5.13,s should put you close to 7000 RPM,s in the 1/8th. With a faster MPH, that you want to run to beat your buddy, even more RPM,s I just think the 5.13,s were to big of a jump for what your trying to do.

At your level of performance, I agree you wont see a Whole lot of performance gain from the Comp increase, but I think it may be just enough.

As asked, have you tried different shift points then 6500? Or has that been the best for your combo?

Re: A question about Compression [Re: Sport440] #1713804
12/27/14 01:43 AM
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bobs69 Offline OP
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I have not tryed different shift points. The powerglide is new to me and my car. I think my converter is tight but it is loaned to me from another racer. Next race i will have my converter and hope to pickup some.

Re: A question about Compression [Re: bobs69] #1713805
12/27/14 10:44 PM
12/27/14 10:44 PM
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Quote:

I have not tryed different shift points. The powerglide is new to me and my car. I think my converter is tight but it is loaned to me from another racer. Next race i will have my converter and hope to pickup some.


You should reaaly try 500 RPM lower at first and look real closely at all the times in the 1/8 mile, if it slows down go the other way and try shifting it at 7000 RPM. Make sure and do at least one run at 6500 before testing These dang gum Mopar race cars don't all respond to the same changes like everyone elses cars do Do you have a copy of his time slips? if so where is he faster? As far as the gear rato I would have gone the other way, 4.30 or 4.10s Let it spend more time in low gear instead of high gear


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: A question about Compression [Re: Cab_Burge] #1713806
12/27/14 10:58 PM
12/27/14 10:58 PM

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It is typical with Indy heads to see folks turning less than the combo can do or likes--I mean--I see on the dyno all the time when ports are borderline big or just plain too big to make peak power at a reasonable rpm like 6500--we see combos with dash ones all the time that keep making HP way past 7500-7800 range --that is out of the comfortt zone for most racers and really they should build combos for lower power bands as bracket racers just so it ain't so darn hard on everything--hard to get folks to size the port to the unit correctly and not over cam but that is the way the world is so....
I am saying that lots of guys can turn that big cube engine another 1500--1800 RPM and really see what they got! Too scared to--and rightly so. I hate the myth about big cube loves low ROM yadda yadda--Na--they LOVE to have the crap turned out of them usually to make impressive peak numbers--just like ANY good race engine
Jr Johnson said it best--Give me an engine that never quits going upstairs and let me do the driving. He was right.
The old Shift Loop is long forgotton but PLENTY useful tool --use it to discover what your combo Really likes--Many times just buzzing an engine another 1000 RPM is the key--
Go get him!! Good Luck!

Re: A question about Compression [Re: ] #1713807
12/28/14 01:01 PM
12/28/14 01:01 PM
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To add to what was said above, compression helps to carry a motor past it's peak. I went from 15:1 compression to 11:1. Heads were unchanged. The cam was slightly smaller. What I noticed is the low compression motor made 50 hp less than high compression (800 -vs- 850) but also fell off much quicker after peak. With the high compression the motor basically flat lined from 6500-7500 rpm. With lower compression it was more like 6400-7000.


Jim

Re: A question about Compression [Re: bobs69] #1713808
12/28/14 02:11 PM
12/28/14 02:11 PM
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What does your car sixty foot? Much easier to pick it up there for the ET gain you are looking for. I would expect you can find the best benefit from leaving the gears 4.56 and getting the correct converter for you application.

Re: A question about Compression [Re: bobs69] #1713809
12/28/14 02:28 PM
12/28/14 02:28 PM
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Quote:

I have not tryed different shift points. The powerglide is new to me and my car. I think my converter is tight but it is loaned to me from another racer. Next race i will have my converter and hope to pickup some.




Your using a loaned to you conv.. if you have one
built for your set up it will help you... whats the
stall now and where is your peak torque on the engine
and where is the max power rpms... you have found
that it likes to turn rpm... use it... most guys
are afraid to turn up the rpms but there can be power
up there if your built for it.. big ports and big
duration cams want to rpm

Re: A question about Compression [Re: MR_P_BODY] #1713810
12/28/14 04:03 PM
12/28/14 04:03 PM
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bobs69 Offline OP
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Next race i will have my converter in the car. Right now i can beat the big block Chevy for the first 100 ft. After that he takes off. But he runs a 557 gear with a 33 rear tire and a loose converter and he winds his motor up to around 7300. But we have a lot of fun.

Re: A question about Compression [Re: bobs69] #1713811
12/28/14 04:49 PM
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Quote:

Next race i will have my converter in the car. Right now i can beat the big block Chevy for the first 100 ft. After that he takes off. But he runs a 557 gear with a 33 rear tire and a loose converter and he winds his motor up to around 7300. But we have a lot of fun.




If you get him off the line the conv and gear wont
help unless your conv now has a lot of slippage..
you need more power

Re: A question about Compression [Re: MR_P_BODY] #1713812
12/28/14 05:22 PM
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bobs69 Offline OP
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I'm not sure about that. I beat him until he changed gears and converter.

Re: A question about Compression [Re: bobs69] #1713813
12/28/14 05:34 PM
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Quote:

I'm not sure about that. I beat him until he changed gears and converter.




I was thinking that you were beating him off the line
NOW... you set the gear ratio for the RPM you want
to cross the line at.. ..I use 10% above the peak
HP rpm for the gear..conv for the start.. if you
know the peak torque rpm of your engine you will have
a better chance of getting the right conv... a glide
likes a higher stall point over the peak torque

Re: A question about Compression [Re: MR_P_BODY] #1713814
12/30/14 05:19 PM
12/30/14 05:19 PM
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The gear will probably make more than enough. Your present 1st gear is probably 1.80 with a 4.56 you total 1st gear is 8.20, if you go to a 5.13 your total 1st gear will be 9.28. I think you will pick up the .06 you are looking for in the 60 ft times.

Re: A question about Compression [Re: hustlin hoosier] #1713815
12/30/14 05:49 PM
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I picked up over a tenth going from hooker fender well headers to home built big tube's

Re: A question about Compression [Re: FastmOp] #1713816
12/31/14 03:59 AM
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Are you both running the same mph? Did you give your Mph?







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