Re: A question about Compression
[Re: bobs69]
#1713803
12/22/14 12:46 AM
12/22/14 12:46 AM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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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?
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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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Anonymous
Unregistered
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Anonymous
Unregistered
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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!
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Re: A question about Compression
[Re: ]
#1713807
12/28/14 01:01 PM
12/28/14 01:01 PM
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Joined: Nov 2003
Posts: 10,384 Upstate NY
Bigcube
I Live Here
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I Live Here
Joined: Nov 2003
Posts: 10,384
Upstate NY
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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
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Re: A question about Compression
[Re: bobs69]
#1713809
12/28/14 02:28 PM
12/28/14 02:28 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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Re: A question about Compression
[Re: bobs69]
#1713811
12/28/14 04:49 PM
12/28/14 04:49 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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Re: A question about Compression
[Re: bobs69]
#1713813
12/28/14 05:34 PM
12/28/14 05:34 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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