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06-29-2009, 12:31 AM
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#1 |
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Badass
Join Date: Jan 2009
Location: lox. fl
Posts: 4,586
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how high should
how high should my motor be reving at highway speeds?
it has a 305.th350 with 3.42 gears at like 45 its buzzing at 2.5k
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Think outside the box? -84c10 (1stcar)→My Build←  -00 Saturn 5spd drop a gear and disappear! 1/4:13:90 
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06-29-2009, 02:47 AM
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#2 |
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Registered User
Join Date: May 2007
Location: CO
Posts: 475
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Re: how high should
What's the height of the tires? That affects the outcome.
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06-30-2009, 01:08 AM
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#4 |
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Registered User
Join Date: Feb 2007
Location: Austin, TX
Posts: 3,930
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Re: how high should
2500 RPM should be 60 MPH with that combo. Either your speedometer isn't reading right or you have a higher gear than you think. Also if your tach is aftermarket make sure it is in 8 cyl mode.
This is good to calculate speeds with. http://www.public.asu.edu/~grover/willys/speed.html
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1977 GMC Sierra Grande |
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06-30-2009, 05:24 PM
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#5 |
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Badass
Join Date: Jan 2009
Location: lox. fl
Posts: 4,586
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Re: how high should
my tach is after market and and we did check the speed with a gps.
so how high is over reving your motor? like at shifting and at highway speeds
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Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90
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07-01-2009, 12:59 AM
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#6 |
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Registered User
Join Date: Feb 2007
Location: Austin, TX
Posts: 3,930
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Re: how high should
Maximum safe RPM depends on the motor, but a good safe limit for stock engines is 4500 RPM. That is where most stock cams stop making power so it's really pointless to rev higher than this if it's all stock.
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1977 GMC Sierra Grande |
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07-01-2009, 09:27 AM
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#7 |
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Next project: 1970 K10
Join Date: Feb 2004
Location: Fort Collins, Colo 80524
Posts: 6,684
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Re: how high should
Here are my gearing calculators, they say 63 mph @ 2500rpm with that combo:
http://www.mediafire.com/?nzztmwwbmjj
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Bob 1970 Chevy K10 LWB "Goldie" 350/TH350 next project!! 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE |
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07-02-2009, 01:22 AM
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#9 |
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Registered User
Join Date: Feb 2007
Location: Austin, TX
Posts: 3,930
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Re: how high should
You should shift at around 4500 under full throttle, or rather the transmission should. Constant RPM depends on some things. Anywhere from 2000 to 3500 RPM constant is probably fine. Even for hours on end. Of course the higher the RPM, the more wear is happening, but the wear won't be drastic at these speeds. It also depends how fast the vehicle is moving. 3500 RPM at 70 MPH is a much lighter load on the motor than 3500 RPM at 120 MPH.
Chances are as long as your in 3rd gear and going at a legal speed, you shouldn't have to worry about a high sustained RPM.
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1977 GMC Sierra Grande Last edited by Pyrotechnic; 07-02-2009 at 01:23 AM. |
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07-02-2009, 04:30 PM
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#11 |
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Registered User
Join Date: Jan 2008
Location: White Haven PA
Posts: 59
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Re: how high should
I don't think 2500 at 60 mph is all that bad.
For instance my 1986 has 2.73 gears with 27.4" high tires so my rpm at 60 is close to 2100.
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1992 C1500 WT LWB 4.3TBI 700r4 4.10 limited slip= Work Truck 1986 C10 Custom Deluxe LWB 4.3-4V TH350C 2.73 ac cruise tilt= Cowboy Cadillac |
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