373 gear ratio - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**N2TRUX** · 11-26-2004, 02:30 AM

Don't change gears, get an OD trnasmission. I have found that with an OD transmission the difference between 3.08, 3.42, and 3.73 is only about 1.5 mpg but the difference in torque is huge....

68LSS1 · 11-26-2004, 02:48 AM

My problem is I've got the 3.73's and I am planning to up it to 4.11's. And I still think 20 mpg is feasible. Gotta love 6 gears. Sorta wish 2 of them weren't overdrives but I'm sure my wallet will.

68CST327 · 11-26-2004, 06:33 AM

I had to get on the freeway the other day, and I was spinning 4000 at 70 mph.

70 shorty · 11-26-2004, 11:37 AM

Hey Longhorn, 2 things. You got some balls to take a picture at 90 and also, you better get some gas soon, or you'll be walking!

GreyHoundSteve · 11-26-2004, 11:57 AM

To those who posted about wanting to go to 4:11's...... talk to me before you buy because i have a brand new set of 4:11's and i want to go down because i soend most of my time on the highway and dont really haul anything so if your looking to swap up to 4:11's pm me and we can work something out.

red71cheyenne · 11-26-2004, 12:12 PM

Can someone tell me what is meant by a new "carrier"? Do you mean an entire new axle with different pumpkin? I still don't get the whole rear end thing. My 700R4 with 3.73 still only gets about 14 on the highway and 8-10 in town. Thats with fuel injection as well. Have thought about going to 3.07, but don't know if it will make any difference. Did see a drop of about 300 rpm though at highway speed when I dropped the TH350. Jeff.

**N2TRUX** · 11-26-2004, 12:27 PM

Quote:

Originally Posted by red71cheyenne

Can someone tell me what is meant by a new "carrier"?

Jeff the "carrier" is what you ring gear is bolted to. What they are reffering to is there were different series or sizes of carriers made. They were designed for higher ring gears (3.08 to 3.73) and lower ring gears (3.73 to 4.56) because of the "physical" size of the ring gear....

red71cheyenne · 11-26-2004, 12:30 PM

Ok, so just buying a new ring and pinion would not do it for you. You'd have to get the carrier as well right? Because 3.07 won't fit in the 3.73. Is that right?

**N2TRUX** · 11-26-2004, 01:00 PM

I'm not 100% sure. I know that there is a cross over point on the gear sets fitting the carriers. I think it's at 3.73 but won't swear my memory is correct.

I "think" you can order 3.73's for a small or large carrier, just have to know which one you have.

Can someone with a better memory help here....

67ChevyRedneck · 11-26-2004, 01:14 PM

I've always had gear questions too and no one has ever really been able to answer them. My truck is a '67 Chevy with a 350 mated to a 700R4 which spins a 3.73 rear. The carb is an edelbrock 650. My truck gets 15.5 mpg on the highway going about 75mph. At about 65 the tach reads 2000 and at about 75 it reads between 2300 and 2400. I have recently converted my truck to power disk brakes off a 71 GMC...and yes, GMC did put coil suspensions on trucks, which gave me awesome braking power and gave me the 5 lug pattern. Out back, she still has 6 lugs. I have access to a 5 lug 3.07 and a 5 lug 3.73. I think the 3.07 would be too high for the 700R4 but I would like to improve my mpg, her "around town" average is only around 13. The only other route would be to spend some big bucks on something in the 3.40's...is this even worth it? Is 15mpg the best these can do? I've seen a couple of magazine articles where these trucks could get 18 highway...are these people liars?? I like the way the 3.73 and the low first and second gears of the 700R4 combine to kick ass at stoplights!

Should I just swap my 3.73 for another 3.73? I need to convert to a 5 lug rear anyway. Also, I DID NOT "hit" the gas at all on the tanks I was trying to figure out my mpg's.

chickenwing · 11-26-2004, 01:43 PM

If you plug in the numbers on one of the calculators I think you can proove this one yourself. http://www.quiknet.com/~ke6vut/rpmcalc.html I don't have your tire size or I'd plug in the #'s.

Longhorn Man · 11-26-2004, 08:20 PM

I say stay away from 3.07 gears with overdrive trannys. it'll be too much of a load on the engine.
As far as taking pics at 90 MPH, do you really drive with 2 hands on the wheel? I never do. So that leaves a hand free to do what ever. I took about 5 or 6 pics and that was the only one that came out. I started takin pics at 100 MPH. Just point and click...never looked through teh camera nor used the LCD screen. I have pics of a few of my vehicles pegged.

67ChevyRedneck · 11-29-2004, 02:13 PM

According to that calculator, which was cool...thanks chickenwing, I'd have about a 400 rpm drop going from a 3.73 to a 3.07...something in the 3.40's was only about a 150 rpm drop....soooo, if I want to keep some power, I guess just keep the 3.73. Doesn't seem to me that 400 rpm would be much more than an extra mile per gallon..... Also, newer Chevy trucks that have the 5.3L...is this a modern 327??... tend to come with a 3.73 gears....ALL Z-71's come with it. I think the only other gear is in the 3.40's and it's typically in the V-6's and in some regular car v-8's. Not 100% on this. So if Chevy is still goin with a 3.73 after all these years....why not keep it in the older trucks??

67ChevyRedneck · 11-29-2004, 02:14 PM

I meant regual "cab" V-8's, not "reguar car"

67ChevyRedneck · 11-29-2004, 02:16 PM

holy crap I can't spell today.....REGULAR CAB not REGULAR CAR!!!

Tx Firefighter · 11-29-2004, 02:54 PM

Quote:

Originally Posted by 67ChevyRedneck

So if Chevy is still goin with a 3.73 after all these years....why not keep it in the older trucks??

Because all of the newer trucks have overdrive transmissions and the older ones didn't.

By the way, the 3.42 gear ratio was the most common from 88 through 98 trucks, whether with V6 or V8 engines. A 3.42 with an overdrive transmission is a pretty good combination.

86 Red_Bowtie · 11-29-2004, 06:23 PM

I have 3.73 gears in my truck and TH700 transmission and i am getting better gas mileage than i was with 3.08

Super Duck · 11-29-2004, 06:51 PM

the newer overdrives are (bigger) a 700r4 is a .62 if i am not mistaken and a 4l65e is a .68 or something close, the other thing to think of is tire size. I have 3.07s with a th350 and 255 60s out back. a taller tire will make it seem as if I had a 2.73 gear. so lots of factors

Tx Firefighter · 11-29-2004, 07:40 PM

I believe the OD ratio in a 700R4 is 0.70.

Super Duck · 11-29-2004, 07:44 PM

thanks. I couldn't remember off the top of my head but I know there is a difrence in final ratio infavor of the newer trans

chickenwing · 11-29-2004, 07:53 PM

I thought it was .74? Just splittin hairs.

bowtieman4life · 11-29-2004, 11:36 PM

Quote:

Originally Posted by KEH

I have my differential apart and determined I have 3.73 gears. What would I need to do to switch to 3.07? Just a new ring gear and pinion? Thanks for the help.

Trade gears and carriers with me

RON WOODGEARD · 11-30-2004, 04:36 AM

Gears are one of the most important facters in what you want to do with your truck..

If you don't haul or pull and do a LOT of highway driving, then 307's are the way to go.. But you're going to suck at "off the line performance" Just remember tire size also has a lot to do with the final gearing to the street. Taller tires are going to give you a Higher ( lower numerically) Ratio, and short tires are going to do the opposite..

373's are a great performance gear for a Small Block.. 350's would be fine for a big block.. But basically, you have to tune the gears to your usage.. In Drag Racing, you want you Ideal RPM ( red line) to be just as you hit the traps ( end of the Quarter mile)

I have 4:10's in mine now, I put them in when my Truck was Raised 8" and I had 32" tires all the way around. Now I have 27" tires and it's lowered ( which the lowering doesn't have anything to do with Final Ratio) I live in a rural area, 35 miles from the closest little town, I'm sure I will be changing them out in the Future when I get it back on the road. But I like that Off the line snap, so I won't be putting in 307's.

One additional thing !!
You need to keep the motor you have in the working RPM that it's designed for.. And here's where some work can come in... figuring what RPM at what speed you'll get the best gas Mileage at.. I've always done this with a Vaccuum guage..

67ChevyRedneck · 11-30-2004, 09:11 AM

That's the second or third time someone has mentioned figuring mileage with a vacuum gage. I know what its for and I believe, can't remember exactly, but I think a 350 should pull between 12-16" at idle speeds. SO, what are good and bad readings going down the road??? If this really helps I might add a vacuum gage to my cluster....

stickshift_or_walk · 11-30-2004, 12:29 PM

Redneck,

In most carbs, the power circuit kicks in at around 7". That's when your mileage really goes south. If you can cruise above 9", you're in good shape.
And below 7", just enjoy the ride...

SSOW

11-26-2004, 02:30 AM	#26
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	Don't change gears, get an OD trnasmission. I have found that with an OD transmission the difference between 3.08, 3.42, and 3.73 is only about 1.5 mpg but the difference in torque is huge.... __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

11-26-2004, 02:48 AM	#27
68LSS1 Registered User Join Date: Dec 2002 Location: Tampa Posts: 1,191	My problem is I've got the 3.73's and I am planning to up it to 4.11's. And I still think 20 mpg is feasible. Gotta love 6 gears. Sorta wish 2 of them weren't overdrives but I'm sure my wallet will. __________________ '68 Short Step LS1/T56, Hydratech, Fatman Fabrications Stage III, Baer, Hot Rods to Hell, US Body, S&W, etc

11-26-2004, 12:12 PM	#31
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Can someone tell me what is meant by a new "carrier"? Do you mean an entire new axle with different pumpkin? I still don't get the whole rear end thing. My 700R4 with 3.73 still only gets about 14 on the highway and 8-10 in town. Thats with fuel injection as well. Have thought about going to 3.07, but don't know if it will make any difference. Did see a drop of about 300 rpm though at highway speed when I dropped the TH350. Jeff. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty

11-26-2004, 12:30 PM	#33
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Ok, so just buying a new ring and pinion would not do it for you. You'd have to get the carrier as well right? Because 3.07 won't fit in the 3.73. Is that right? __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty

11-26-2004, 01:43 PM	#36
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	If you plug in the numbers on one of the calculators I think you can proove this one yourself. http://www.quiknet.com/~ke6vut/rpmcalc.html I don't have your tire size or I'd plug in the #'s. __________________ The truck... you hear that? No really, you did hear that?!!!

11-26-2004, 06:33 AM	#28
68CST327 Registered User Join Date: Aug 2002 Location: USA Posts: 443	I had to get on the freeway the other day, and I was spinning 4000 at 70 mph.

11-26-2004, 11:37 AM	#29
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,772	Hey Longhorn, 2 things. You got some balls to take a picture at 90 and also, you better get some gas soon, or you'll be walking!

11-26-2004, 11:57 AM	#30
GreyHoundSteve Registered User Join Date: Oct 2004 Location: DFW TX Posts: 769	To those who posted about wanting to go to 4:11's...... talk to me before you buy because i have a brand new set of 4:11's and i want to go down because i soend most of my time on the highway and dont really haul anything so if your looking to swap up to 4:11's pm me and we can work something out.

11-26-2004, 01:00 PM	#34
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	I'm not 100% sure. I know that there is a cross over point on the gear sets fitting the carriers. I think it's at 3.73 but won't swear my memory is correct. I "think" you can order 3.73's for a small or large carrier, just have to know which one you have. Can someone with a better memory help here....

11-26-2004, 01:14 PM	#35
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	I've always had gear questions too and no one has ever really been able to answer them. My truck is a '67 Chevy with a 350 mated to a 700R4 which spins a 3.73 rear. The carb is an edelbrock 650. My truck gets 15.5 mpg on the highway going about 75mph. At about 65 the tach reads 2000 and at about 75 it reads between 2300 and 2400. I have recently converted my truck to power disk brakes off a 71 GMC...and yes, GMC did put coil suspensions on trucks, which gave me awesome braking power and gave me the 5 lug pattern. Out back, she still has 6 lugs. I have access to a 5 lug 3.07 and a 5 lug 3.73. I think the 3.07 would be too high for the 700R4 but I would like to improve my mpg, her "around town" average is only around 13. The only other route would be to spend some big bucks on something in the 3.40's...is this even worth it? Is 15mpg the best these can do? I've seen a couple of magazine articles where these trucks could get 18 highway...are these people liars?? I like the way the 3.73 and the low first and second gears of the 700R4 combine to kick ass at stoplights! Should I just swap my 3.73 for another 3.73? I need to convert to a 5 lug rear anyway. Also, I DID NOT "hit" the gas at all on the tanks I was trying to figure out my mpg's.

11-26-2004, 08:20 PM	#37
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I say stay away from 3.07 gears with overdrive trannys. it'll be too much of a load on the engine. As far as taking pics at 90 MPH, do you really drive with 2 hands on the wheel? I never do. So that leaves a hand free to do what ever. I took about 5 or 6 pics and that was the only one that came out. I started takin pics at 100 MPH. Just point and click...never looked through teh camera nor used the LCD screen. I have pics of a few of my vehicles pegged.

11-29-2004, 02:13 PM	#38
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	According to that calculator, which was cool...thanks chickenwing, I'd have about a 400 rpm drop going from a 3.73 to a 3.07...something in the 3.40's was only about a 150 rpm drop....soooo, if I want to keep some power, I guess just keep the 3.73. Doesn't seem to me that 400 rpm would be much more than an extra mile per gallon..... Also, newer Chevy trucks that have the 5.3L...is this a modern 327??... tend to come with a 3.73 gears....ALL Z-71's come with it. I think the only other gear is in the 3.40's and it's typically in the V-6's and in some regular car v-8's. Not 100% on this. So if Chevy is still goin with a 3.73 after all these years....why not keep it in the older trucks??

11-29-2004, 02:14 PM	#39
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	I meant regual "cab" V-8's, not "reguar car"

11-29-2004, 02:16 PM	#40
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	holy crap I can't spell today.....REGULAR CAB not REGULAR CAR!!!

11-29-2004, 06:23 PM	#42
86 Red_Bowtie Registered User Join Date: Nov 2003 Location: South Wichita,KS Posts: 698	I have 3.73 gears in my truck and TH700 transmission and i am getting better gas mileage than i was with 3.08 __________________ Sean Midwest All Truck Nationals, Riverside, MO - 2008 - 2015



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11-29-2004, 06:51 PM	#43
Super Duck Chevy Nuttttt Join Date: Sep 2004 Location: Santa Maria Ca. Posts: 568	the newer overdrives are (bigger) a 700r4 is a .62 if i am not mistaken and a 4l65e is a .68 or something close, the other thing to think of is tire size. I have 3.07s with a th350 and 255 60s out back. a taller tire will make it seem as if I had a 2.73 gear. so lots of factors __________________ 67' Chev swb step side 69' SS elky 03' Chev ext cab 4X4 hey who lernt me to spell is there anything else?

11-29-2004, 07:40 PM	#44
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	I believe the OD ratio in a 700R4 is 0.70. __________________ I'm on the Instagram- @Gearhead_Kevin

11-29-2004, 07:44 PM	#45
Super Duck Chevy Nuttttt Join Date: Sep 2004 Location: Santa Maria Ca. Posts: 568	thanks. I couldn't remember off the top of my head but I know there is a difrence in final ratio infavor of the newer trans __________________ 67' Chev swb step side 69' SS elky 03' Chev ext cab 4X4 hey who lernt me to spell is there anything else?

11-29-2004, 07:53 PM	#46
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	I thought it was .74? Just splittin hairs. __________________ The truck... you hear that? No really, you did hear that?!!!

11-30-2004, 04:36 AM	#48
RON WOODGEARD Resident Young Old Dude ! Join Date: Jul 2001 Location: Nevada Posts: 1,948	Gears are one of the most important facters in what you want to do with your truck.. If you don't haul or pull and do a LOT of highway driving, then 307's are the way to go.. But you're going to suck at "off the line performance" Just remember tire size also has a lot to do with the final gearing to the street. Taller tires are going to give you a Higher ( lower numerically) Ratio, and short tires are going to do the opposite.. 373's are a great performance gear for a Small Block.. 350's would be fine for a big block.. But basically, you have to tune the gears to your usage.. In Drag Racing, you want you Ideal RPM ( red line) to be just as you hit the traps ( end of the Quarter mile) I have 4:10's in mine now, I put them in when my Truck was Raised 8" and I had 32" tires all the way around. Now I have 27" tires and it's lowered ( which the lowering doesn't have anything to do with Final Ratio) I live in a rural area, 35 miles from the closest little town, I'm sure I will be changing them out in the Future when I get it back on the road. But I like that Off the line snap, so I won't be putting in 307's. One additional thing !! You need to keep the motor you have in the working RPM that it's designed for.. And here's where some work can come in... figuring what RPM at what speed you'll get the best gas Mileage at.. I've always done this with a Vaccuum guage.. Last edited by RON WOODGEARD; 11-30-2004 at 04:40 AM.

11-30-2004, 09:11 AM	#49
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	That's the second or third time someone has mentioned figuring mileage with a vacuum gage. I know what its for and I believe, can't remember exactly, but I think a 350 should pull between 12-16" at idle speeds. SO, what are good and bad readings going down the road??? If this really helps I might add a vacuum gage to my cluster....

11-30-2004, 12:29 PM	#50
stickshift_or_walk Left Foot Functioning Join Date: May 2004 Location: Duncan, OK Posts: 351	Redneck, In most carbs, the power circuit kicks in at around 7". That's when your mileage really goes south. If you can cruise above 9", you're in good shape. And below 7", just enjoy the ride... SSOW __________________ 69 C10 (#1 son's ride) 72 C20 (Dad's farm truck) 82 K30 (Ex - brush pumper project)

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