Rear end swap? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

primerib · 08-06-2004, 04:30 PM

My truck is a daily driver. It has a 250 and a 4.11 rear end. The mileage is pretty lousy (about 13 mpg). I'm looking at accepting a job that would require me to drive 230 miles of highway a couple of times a week. The old girl is wound-up awful tight at anything above 50 mph, and this stretch of road is a 70mph zone.

If i were to swap to a better ratio (like a 3.08) would my mileage be significantly better or would it not make much difference.

Thanks

Longhorn Man · 08-06-2004, 04:35 PM

A 3.07 gear would make it much more bearable on the road...like 2500 RPM at 60 MPH (or close to that) but IMO. you'll be lucky to do much better...maybe one or two MPG.

dennis111 · 08-06-2004, 04:38 PM

Mileage would improve but one thing you must consider is that you will have increased wear on your clutch. With a 3:08 ratio, it will take alot more rpm and clutch slippage in order to get rolling from a standing start. You could almost forget about starting on a hill.

A 3:42 ratio would be far more friendly.

stelth2002 · 08-06-2004, 05:24 PM

If he has a 4 gear granny i dont think he will have any problems with a 3.08 rear. I mean it will be sorta powerless at the top, but what does one expect. I would be surprised if your mileage improves at all, your pushing a small stock inline pretty hard at 70mph which is definatly doable.

dennis111 · 08-06-2004, 05:47 PM

Quote:

Originally Posted by stelth2002

If he has a 4 gear granny i dont think he will have any problems with a 3.08 rear.

His sig shows he has 3 on the tree which is what I based my experience on.

Inspector722 · 08-06-2004, 06:17 PM

I am puting a 350 trubo on my 250.It has a 3.73 posi in it now. Would a 3.08 be to much for it?

dennis111 · 08-06-2004, 07:18 PM

Quote:

Originally Posted by Inspector722

I am puting a 350 trubo on my 250.It has a 3.73 posi in it now. Would a 3.08 be to much for it?

I doubt if you would have too much trouble running a 3.08 with this combo because the torque converter will do all the work from a standing start.

You might miss the bottom end spunk though. I don't think I would do it if most of my driving was in town. If you are building a highway cruiser, I'd go for it.

Tx Firefighter · 08-06-2004, 07:37 PM

I'd do it. I believe the relief of going from a 4:11 to a 3:07 will be very profound. It will drive like a different truck.

A 6 cylinder has inherent torque over a V8 anyway. I bet if you said you had a 283 V8, no one would say a thing bad about the swap. The 250 is not that much smaller, but it's an inline and they are torquier.

I think you'll be pleasantly surprised.

The Tx Firefighter Super Secret Project (TM) that's going to be debuted soon has a 250 inline 6 with a 2.73 rear gear.

Inspector722 · 08-06-2004, 07:45 PM

There needs to be a Firefighter group here too.

08-06-2004, 04:30 PM	#1
primerib Registered User Join Date: Nov 2001 Location: Ft.Worth, TX Posts: 35	Rear end swap? My truck is a daily driver. It has a 250 and a 4.11 rear end. The mileage is pretty lousy (about 13 mpg). I'm looking at accepting a job that would require me to drive 230 miles of highway a couple of times a week. The old girl is wound-up awful tight at anything above 50 mph, and this stretch of road is a 70mph zone. If i were to swap to a better ratio (like a 3.08) would my mileage be significantly better or would it not make much difference. Thanks __________________ 72 Stepside 250 w/ 3 on the column DFW area

08-06-2004, 04:38 PM	#3
dennis111 Registered User Join Date: Jul 2004 Location: Amish Wonderland of Central PA. Posts: 31	Mileage would improve but one thing you must consider is that you will have increased wear on your clutch. With a 3:08 ratio, it will take alot more rpm and clutch slippage in order to get rolling from a standing start. You could almost forget about starting on a hill. A 3:42 ratio would be far more friendly. __________________ Dennis 68 GMC SWB Custom 1/2 ton, 2WD, 350 V8, PS, PB, 3-Speed, 3:08 12 bolt rear, tilt, tach, vac, cruise and more. . . . Last edited by dennis111; 08-06-2004 at 07:20 PM.

08-06-2004, 05:24 PM	#4
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	If he has a 4 gear granny i dont think he will have any problems with a 3.08 rear. I mean it will be sorta powerless at the top, but what does one expect. I would be surprised if your mileage improves at all, your pushing a small stock inline pretty hard at 70mph which is definatly doable. __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

08-06-2004, 07:37 PM	#8
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	I'd do it. I believe the relief of going from a 4:11 to a 3:07 will be very profound. It will drive like a different truck. A 6 cylinder has inherent torque over a V8 anyway. I bet if you said you had a 283 V8, no one would say a thing bad about the swap. The 250 is not that much smaller, but it's an inline and they are torquier. I think you'll be pleasantly surprised. The Tx Firefighter Super Secret Project (TM) that's going to be debuted soon has a 250 inline 6 with a 2.73 rear gear. __________________ I'm on the Instagram- @Gearhead_Kevin

08-06-2004, 04:35 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	A 3.07 gear would make it much more bearable on the road...like 2500 RPM at 60 MPH (or close to that) but IMO. you'll be lucky to do much better...maybe one or two MPG.

08-06-2004, 06:17 PM	#6
Inspector722 Fixing my 67, & loving it Join Date: Jun 2004 Location: Bridge City, Texas Posts: 524	I am puting a 350 trubo on my 250.It has a 3.73 posi in it now. Would a 3.08 be to much for it?

08-06-2004, 07:45 PM	#9
Inspector722 Fixing my 67, & loving it Join Date: Jun 2004 Location: Bridge City, Texas Posts: 524	There needs to be a Firefighter group here too.



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