gearing and ratios - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SnowNeck · 08-27-2014, 08:27 PM

1985 chevy, 350 crate motor, carbed, 700r4 trans, 35 inch tires, axle gears 3.08s, transfer case is np 208, good or bad idea?

Dunenutt · 08-27-2014, 08:29 PM

Probably want to go 3.73 with the OD.

**kwmech** · 08-27-2014, 10:53 PM

35'' tires and a 700................4.56 gears

crazy longhorn · 08-27-2014, 11:46 PM

35" tire, I would also go 4.56 on the gear

longhorn

**Captainfab** · 08-28-2014, 12:03 AM

I agree with a 4.56 gear with those 35" tires. The 3.08 gears with 35" tires would just be absurd.

SnowNeck · 08-28-2014, 01:01 AM

Quote:

Originally Posted by Captainfab

I agree with a 4.56 gear with those 35" tires. The 3.08 gears with 35" tires would just be absurd.

Alright sounds pretty conclusive, 4.56s it is. Haha and just curious if i switch the gears, how would it run with 33s? Mpg? performance? over all? Cause most likely it'd be a lil while b4 35s.

tjsblazer · 08-28-2014, 01:14 AM

Check out this website. Great driveline / gear / tire calculator. Use the drop downs to input your tranny and transfer, then input your tires and change up the gearing till you get the rpms where you want them at specific speeds. Can also do a side by side comparison.
http://www.grimmjeeper.com/gears.html

crazy longhorn · 08-28-2014, 03:12 AM

Quote:

Originally Posted by SnowNeck

Alright sounds pretty conclusive, 4.56s it is. Haha and just curious if i switch the gears, how would it run with 33s? Mpg? performance? over all? Cause most likely it'd be a lil while b4 35s.

If you are running 33" tire now,IMHO, they will need a 4.10-4.33 gear to work out properly. I will step back, & let Capt chime in....I respect his opinion also

Longhorn

SnowNeck · 08-28-2014, 08:05 AM

Quote:

Originally Posted by crazy longhorn

If you are running 33" tire now,IMHO, they will need a 4.10-4.33 gear to work out properly. I will step back, & let Capt chime in....I respect his opinion also

Longhorn

Which sounds good, but if I'm going over to the 35s sometime this winter there's no use putting gears that match up with 33s, see what I'm saying? Might as wel gear for 35s, an run 33s for a while

**kwmech** · 08-28-2014, 01:02 PM

Even 33s with a 4.56 will be fine. I had a 1990 suburban years ago that I had put in 4.56 gearing with 31'' tires, and the 700 ... best change I ever made. You got to remember when the trans shifts into 4th and locks up the convertor you are reducing the effective ratio by almost a third. So your 4.56 becomes just around a 3.2 ratio final drive. Stick with the 4.56

95 S_Trucker · 08-28-2014, 02:32 PM

I had 3.08 and 35 on my 85, I don't think it ever shifted into overdrive until 60+

Another option would be a 3/4 ton rear or swap to 1 tone axles, if you still have 2 10 bolts.

crazy longhorn · 08-28-2014, 10:55 PM

Quote:

Originally Posted by SnowNeck

Which sounds good, but if I'm going over to the 35s sometime this winter there's no use putting gears that match up with 33s, see what I'm saying? Might as wel gear for 35s, an run 33s for a while

It sound to me that you have it figured....no point in doing it 2 times

longhorn

08-27-2014, 08:27 PM	#1
SnowNeck Registered User Join Date: May 2012 Location: Pennsylvania Posts: 132	gearing and ratios 1985 chevy, 350 crate motor, carbed, 700r4 trans, 35 inch tires, axle gears 3.08s, transfer case is np 208, good or bad idea? __________________ 1985 High Sierra step side 4x4

08-27-2014, 08:29 PM	#2
Dunenutt Newbee Join Date: Jan 2010 Location: Phoenix, Arizona Posts: 1,406	Re: gearing and ratios Probably want to go 3.73 with the OD. __________________ My Build, http://67-72chevytrucks.com/vboard/s...58#post4464158

08-27-2014, 10:53 PM	#3
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,608	Re: gearing and ratios 35'' tires and a 700................4.56 gears

08-27-2014, 11:46 PM	#4
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	Re: gearing and ratios 35" tire, I would also go 4.56 on the gear longhorn __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

08-28-2014, 12:03 AM	#5
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,251	Re: gearing and ratios I agree with a 4.56 gear with those 35" tires. The 3.08 gears with 35" tires would just be absurd. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

08-28-2014, 01:14 AM	#7
tjsblazer Registered User Join Date: Oct 2009 Location: Great White North Posts: 1,520	Re: gearing and ratios Check out this website. Great driveline / gear / tire calculator. Use the drop downs to input your tranny and transfer, then input your tires and change up the gearing till you get the rpms where you want them at specific speeds. Can also do a side by side comparison. http://www.grimmjeeper.com/gears.html __________________ Jeff. '72 Blazer K5 "Camshaft opinions are like belly buttons; everyone has one and no two are alike" My Blazer Build: http://67-72chevytrucks.com/vboard/s...d.php?t=626752 My Engine Build: http://67-72chevytrucks.com/vboard/s...d.php?t=637336

08-28-2014, 01:02 PM	#10
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,608	Re: gearing and ratios Even 33s with a 4.56 will be fine. I had a 1990 suburban years ago that I had put in 4.56 gearing with 31'' tires, and the 700 ... best change I ever made. You got to remember when the trans shifts into 4th and locks up the convertor you are reducing the effective ratio by almost a third. So your 4.56 becomes just around a 3.2 ratio final drive. Stick with the 4.56

08-28-2014, 02:32 PM	#11
95 S_Trucker Registered User Join Date: Oct 2009 Location: . Posts: 2,187	Re: gearing and ratios I had 3.08 and 35 on my 85, I don't think it ever shifted into overdrive until 60+ Another option would be a 3/4 ton rear or swap to 1 tone axles, if you still have 2 10 bolts.



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