Okay time for another question..... (HELP!!) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CHEVY & GMC FOREVER · 03-19-2005, 01:31 AM

Okay tommorow I am bringing my rebuilt 355 (bored .30 over) motor home....it has all that good stuff on and in it (I'll have details with pic's later hopefully) so I was wondering I want to change my rear end ratio a little bit from a 3.07, to get a lot more GO!!!!, so I was thinking of maybe a 3.73 or 4.10 what would be better I still want to be able to drive this truck around at 50 MPH and not having the engine turning 10,000 RPM's

, you understand right??

CHEVY & GMC FOREVER · 03-19-2005, 02:05 AM

no one???

bjohn3x · 03-19-2005, 02:08 AM

it depends on your tranny. Do you have overdrive?

jhow66 · 03-19-2005, 02:09 AM

For street you will find that the 3.73 is the better option. Depending on your tire size you will turning about 3000 + or - rpm at 65 mph.
Use this formula for figuring your rpm with each gear ratio:
rpm = mph X rear ratio X 336 divided by tire diameter

CHEVY & GMC FOREVER · 03-19-2005, 02:18 AM

Quote:

Originally Posted by bjohn3x

it depends on your tranny. Do you have overdrive?

TH400 no overdrive, being rebuilt with shift kit by yours truly..

bjohn3x · 03-19-2005, 02:22 AM

Yeah, I would stay definitely higher than a 3.73. Anything lower and it won't be very nice to drive on the freeway. Even with 3.73's you will still be turning some high RPMs. That's why you need a 6 speed like me

**pjmoreland** · 03-19-2005, 03:32 AM

I had 4:11 gears originally. It was great for driving around town, but on the freeway it was miserable. I got a job that required commuting about 1 hour each way, so I switched to 3.07 gears. I could cruise at 75-85 MPH with the engine purring. It wasn't very fun around town though. I then switched to 3.73 gears. That's what I have now. It's decent for driving around town, and tolerable but not so great for short highway trips. If you plan on doing a decent amount of highway driving, 3.42 gears might be a good choice.

I'm in the process of putting a 700R4 in my truck so I can have the best of both worlds.

CHEVY & GMC FOREVER · 03-19-2005, 02:51 PM

I think I'll go with 3.43 gears... Thanks for all your help..

70 shorty · 03-19-2005, 09:54 PM

I would also stay away from the 4:11's for around town. I know my inline 6 with 3:73's is turning about 3200 at 70, well the speedo says 70, but I think I'm going faster than that.

WRMZ71 · 03-19-2005, 11:38 PM

3:40's are nice. I had 3:73's in my 71 before and I was driving from Nebraska to North Carolina usually at least once a year with it that way. Just going 60 was about 3200 RPM let alone getting out into interstate traffic doing about 80-90 MPH. Had to unplug the tach cause i was tired of looking at it, and cranked up the radio cause after 26 hrs that drone makes you start to hear things which makes a guy nervous. With the 3:40's I dropped the RPm by about 500 doing 60. I can still burn the tires on occasion but not nearly like they did on demand with the 3:73's.

CHEVY & GMC FOREVER · 03-20-2005, 01:07 AM

Well I just got the motor back today and I'll try to list all the stuff later, so I guess I'll just keep the 3.07, would that still be able to burn the tires at least a little bit????, I think that there should be no problem cause the motor is very low end oriented cause there are still stock chevy heads on it, but what do I know I'm a diesel truck mechanic, so any help is welcomed.

03-19-2005, 01:31 AM	#1
CHEVY & GMC FOREVER Registered User Join Date: Nov 2004 Location: New Lenox,IL Posts: 306	Okay time for another question..... (HELP!!) Okay tommorow I am bringing my rebuilt 355 (bored .30 over) motor home....it has all that good stuff on and in it (I'll have details with pic's later hopefully) so I was wondering I want to change my rear end ratio a little bit from a 3.07, to get a lot more GO!!!!, so I was thinking of maybe a 3.73 or 4.10 what would be better I still want to be able to drive this truck around at 50 MPH and not having the engine turning 10,000 RPM's , you understand right?? __________________ 1985 Chevrolet C-30 454 1-TON Dooley 1969 CHEVROLET CST-10 PICK-UP Good memories 1999 Chevrolet Z71 Ext. cab 5.7L Good Memories With a quart of oil, and a gallon of gas, she won't let no other car pass!!!. & FOREVER Last edited by CHEVY & GMC FOREVER; 03-19-2005 at 01:39 AM.

03-19-2005, 02:05 AM	#2
CHEVY & GMC FOREVER Registered User Join Date: Nov 2004 Location: New Lenox,IL Posts: 306	no one??? __________________ 1985 Chevrolet C-30 454 1-TON Dooley 1969 CHEVROLET CST-10 PICK-UP Good memories 1999 Chevrolet Z71 Ext. cab 5.7L Good Memories With a quart of oil, and a gallon of gas, she won't let no other car pass!!!. & FOREVER

03-19-2005, 02:09 AM	#4
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	For street you will find that the 3.73 is the better option. Depending on your tire size you will turning about 3000 + or - rpm at 65 mph. Use this formula for figuring your rpm with each gear ratio: rpm = mph X rear ratio X 336 divided by tire diameter __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

03-19-2005, 02:51 PM	#8
CHEVY & GMC FOREVER Registered User Join Date: Nov 2004 Location: New Lenox,IL Posts: 306	I think I'll go with 3.43 gears... Thanks for all your help.. __________________ 1985 Chevrolet C-30 454 1-TON Dooley 1969 CHEVROLET CST-10 PICK-UP Good memories 1999 Chevrolet Z71 Ext. cab 5.7L Good Memories With a quart of oil, and a gallon of gas, she won't let no other car pass!!!. & FOREVER

03-19-2005, 09:54 PM	#9
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,768	I would also stay away from the 4:11's for around town. I know my inline 6 with 3:73's is turning about 3200 at 70, well the speedo says 70, but I think I'm going faster than that. __________________ 70 C10, shortstep, .30 over 250,Hurst shifted 3 spd parts hauler. Holley 390, Clifford Intake, Header, ported cylinder head, unknown bigger cam. 79 Corvette L82, 4 spd, black, red interior, headers, flowmasters, and unkown bigger cam. '03 Grand Cherokee Laredo, 4.0 4x4 daily driver. 165K miles, and runs great '08 Tahoe LTZ 4x4 155K

03-19-2005, 02:08 AM	#3
bjohn3x Registered User Join Date: Dec 2003 Location: Beaverton, OR Posts: 49	it depends on your tranny. Do you have overdrive?

03-19-2005, 02:22 AM	#6
bjohn3x Registered User Join Date: Dec 2003 Location: Beaverton, OR Posts: 49	Yeah, I would stay definitely higher than a 3.73. Anything lower and it won't be very nice to drive on the freeway. Even with 3.73's you will still be turning some high RPMs. That's why you need a 6 speed like me

03-19-2005, 03:32 AM	#7
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,413	I had 4:11 gears originally. It was great for driving around town, but on the freeway it was miserable. I got a job that required commuting about 1 hour each way, so I switched to 3.07 gears. I could cruise at 75-85 MPH with the engine purring. It wasn't very fun around town though. I then switched to 3.73 gears. That's what I have now. It's decent for driving around town, and tolerable but not so great for short highway trips. If you plan on doing a decent amount of highway driving, 3.42 gears might be a good choice. I'm in the process of putting a 700R4 in my truck so I can have the best of both worlds.

03-19-2005, 11:38 PM	#10
WRMZ71 Cause the Chicks DIG IT!! Join Date: Nov 2003 Location: Beaufort SC Posts: 509	3:40's are nice. I had 3:73's in my 71 before and I was driving from Nebraska to North Carolina usually at least once a year with it that way. Just going 60 was about 3200 RPM let alone getting out into interstate traffic doing about 80-90 MPH. Had to unplug the tach cause i was tired of looking at it, and cranked up the radio cause after 26 hrs that drone makes you start to hear things which makes a guy nervous. With the 3:40's I dropped the RPm by about 500 doing 60. I can still burn the tires on occasion but not nearly like they did on demand with the 3:73's.

03-20-2005, 01:07 AM	#11
CHEVY & GMC FOREVER Registered User Join Date: Nov 2004 Location: New Lenox,IL Posts: 306	Well I just got the motor back today and I'll try to list all the stuff later, so I guess I'll just keep the 3.07, would that still be able to burn the tires at least a little bit????, I think that there should be no problem cause the motor is very low end oriented cause there are still stock chevy heads on it, but what do I know I'm a diesel truck mechanic, so any help is welcomed. __________________ 1985 Chevrolet C-30 454 1-TON Dooley 1969 CHEVROLET CST-10 PICK-UP Good memories 1999 Chevrolet Z71 Ext. cab 5.7L Good Memories With a quart of oil, and a gallon of gas, she won't let no other car pass!!!. & FOREVER Last edited by CHEVY & GMC FOREVER; 03-20-2005 at 01:10 AM.



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