how high should - The 1947 - Present Chevrolet & GMC Truck Message Board Network

3r!c84 · 06-29-2009, 12:31 AM

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

Prong · 06-29-2009, 02:47 AM

What's the height of the tires? That affects the outcome.

3r!c84 · 06-29-2009, 08:28 PM

stock umm 235/75 R15

Pyrotechnic · 06-30-2009, 01:08 AM

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

3r!c84 · 06-30-2009, 05:24 PM

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

Pyrotechnic · 07-01-2009, 12:59 AM

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.

glock35ipsc · 07-01-2009, 09:27 AM

Here are my gearing calculators, they say 63 mph @ 2500rpm with that combo:

http://www.mediafire.com/?nzztmwwbmjj

3r!c84 · 07-01-2009, 02:06 PM

thanks is that 4500 when shifting or at a constant speed

Pyrotechnic · 07-02-2009, 01:22 AM

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.

3r!c84 · 07-02-2009, 01:31 PM

thanks im just used to driving cars with overdrive

larrystone · 07-02-2009, 04:30 PM

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.

06-29-2009, 12:31 AM	#1
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	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 __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

06-29-2009, 02:47 AM	#2
Prong Registered User Join Date: May 2007 Location: CO Posts: 474	Re: how high should What's the height of the tires? That affects the outcome.

06-29-2009, 08:28 PM	#3
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	Re: how high should stock umm 235/75 R15 __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

06-30-2009, 01:08 AM	#4
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	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 __________________ 1977 GMC Sierra Grande

06-30-2009, 05:24 PM	#5
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	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 __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

07-01-2009, 12:59 AM	#6
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	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. __________________ 1977 GMC Sierra Grande

07-01-2009, 09:27 AM	#7
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Re: how high should Here are my gearing calculators, they say 63 mph @ 2500rpm with that combo: http://www.mediafire.com/?nzztmwwbmjj __________________ *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

07-01-2009, 02:06 PM	#8
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	Re: how high should thanks is that 4500 when shifting or at a constant speed __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

07-02-2009, 01:22 AM	#9
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	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. __________________ 1977 GMC Sierra Grande Last edited by Pyrotechnic; 07-02-2009 at 01:23 AM.

07-02-2009, 01:31 PM	#10
3r!c84 Badass Join Date: Jan 2009 Location: lox. fl Posts: 4,586	Re: how high should thanks im just used to driving cars with overdrive __________________ Think outside the box? -84c10 (1stcar)→My Build← -00 Saturn 5spd drop a gear and disappear! 1/4:13:90

07-02-2009, 04:30 PM	#11
larrystone Registered User Join Date: Jan 2008 Location: White Haven PA Posts: 59	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. __________________ 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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