03-15-2011, 08:38 PM | #26 |
Registered User
Join Date: Aug 2009
Location: Newberry,FL
Posts: 277
|
Re: 3.73 to 2.73?
BTW 1700-2000rpm sounds way to low for 3.73s, at least above 3200 at 65mph depending on tire size and torque converter.
__________________
1970 Chevrolet C-10 w/355sbc 2010 Silverado Daily Driver 1971 Mercedes 280sl project car |
03-15-2011, 08:58 PM | #27 | |
1965 Chevy C10, 2005 4.8L/4l60
Join Date: Aug 2004
Location: DFW Texas
Posts: 8,539
|
Re: 3.73 to 2.73?
Quote:
__________________
Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 support our troops! |
|
03-15-2011, 09:18 PM | #28 | |
Registered User
Join Date: Jan 2007
Location: Midwest
Posts: 262
|
Re: 3.73 to 2.73?
Quote:
You obviously don't comprehend what I'm building and I'm not going to try to explain it. I've done a similar build before and I'm building it not having it built. It works, there's no "maybe" to it and it suits my purposes just fine. |
|
03-15-2011, 10:11 PM | #29 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
|
Re: 3.73 to 2.73?
a couple things stand out to me here...
your tach is wrong, WAY wrong. You are probably in the 2500 to 2800 RPM range. NOTHING with give you a 100% MPG increase short of a late model eng/trans swap. Your ambulance is tall enough that aerodynamics is your main problem here. I suspect, if you put a 2.73 rear in there, your MPH will be the same, possibly even worse. You'll have the RPMs too low unless you wind it up to 70 or 75, and by that time, you are trying to punch a huge hole through too much air to be able to do it with good MPG. You want 2200 to 2600 RPM with an old school engine, and with the height of your rig, I would shoot for the upper end of that. With all this being said, if you install it yourself and need no other mods, or minimal mods, you can stab it in there and swap it back out if you feel the need. Another point, is that it is cheap enough that you may be able to get all your money back if you decide to unload it later. |
03-15-2011, 11:02 PM | #30 | |
Active Member
Join Date: Dec 2004
Location: Marysville, OH
Posts: 667
|
Re: 3.73 to 2.73?
Quote:
Yeah, probably. I need to get that figured out. The only reason I know it off the top of my head is because my speedo doesn't work, so I measured speed with my GPS and made a note of where the RPM's were at 65, since they seemed to be repeatable, and they were showing between 4000-4500 on the tach. Like I said, that seems high, but if I get the tach there in final gear it always works out to the same speed range. Some other good points you made there about the wind resistance and size of the vehicle. I may just have to live with 10 MPG.
__________________
1957 GMC Ambulance 1962 Belair Wagon 1963 C80 Truck Cab *FOR SALE* 1969 Chevy C10 Short Bed 1972 Chevy C10 Long Bed *SOLD* 1996 C3500 Dually *SOLD* |
|
03-16-2011, 11:33 PM | #31 |
Registered User
Join Date: Feb 2009
Location: Southern Oregon
Posts: 1,352
|
Re: 3.73 to 2.73?
Heck for 50 bucks give it a shot! Worst case your out 50 bucks but still have a spare diff. You may want to confirm that the other rearend accepts the same size U-joint before you commit or you may be modifying your driveline.$$ Keep us posted if you decide to go for it I'd love to hear the outcome.
|
03-17-2011, 09:26 AM | #32 | |
Registered User
Join Date: Aug 2010
Location: Charleston, SC
Posts: 311
|
Re: 3.73 to 2.73?
Quote:
if you have a GPS you know your true speed. measure how tall your tires are. you know your rear gear ratio and your transmission ratio... so you can work backward to calculate your RPM.... and see how far your tach is off. |
|
03-17-2011, 11:11 AM | #33 |
Registered User
Join Date: Mar 2011
Location: Fort St John, BC
Posts: 85
|
Re: 3.73 to 2.73?
Check out this calculator. It will be very helpfull showing your speed and rpm/ shift points for a wide range of trans and you can input any geer/tire hieght you want.
http://www.americantorque.com/graph-rpm-vs-speed/ I currently have a 350/TH400 and 3.08 geers in a 69 chevy. stock motor with intake and headers and at highway speeds the 3.08 is perfect. Drove 600miles got about 16-18 mpg not great but i was cruzing at about 75mph on a fairly hilly twisty road in through british columbia. For $50 I say do it and see how you like it, if it doesn't work you can sell it or swap geers. I am looking to drop the 3.08 open rear for a 3.73 posi to get better stop light to stop light fun, just need to find one here in western canada. Last edited by Jay W; 03-17-2011 at 11:16 AM. |
03-18-2011, 02:24 AM | #34 |
Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
|
Re: 3.73 to 2.73?
I guess I have a "freewayflya"....3.40 gear, on a 29" tire,with 6 gears of Richmond on the "row". At 65mph, there is no point to shift into OD....that pulls 1800 on the tach, but my 383 is not into the sweet spot till about 22- 2400 (about 85mph). @ 3150 on the tach in OD my old longhorn is cruisin @ 105 mph(a little too fast for a "brick in the wind',as far as mileage. My old B ville(03), that car gets better mileage running 82 mph ,than it does @72mph....the engine is in the "sweet spot" IMHO, if you get that baby into the sweet spot, tween 70-75 mph, You will see good things. A mid 3's gear will give the best of both worlds....still fun to play with, but not too "tight" on to hyway.....just depends on what you want. best of fun,crazyL
__________________
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.... |
03-21-2011, 09:00 PM | #35 |
Registered User
Join Date: Jun 2005
Location: Midlothian, VA
Posts: 148
|
Re: 3.73 to 2.73?
I've got the 2.73 rear gears, the overdrive tranny, and a torque monster 383. With my 255/70/15's 70 mph is 1400 and change. I haven't twisted her hard coming off the line or banged on the gears, but rolling on hard after I get her moving, when the engine gets to about 2300 rpm she'll break the non-posi loose.
As far as top end goes, at about 90 my testicles disconnect! Around town driving civil I get 10 to 12, and I have broke 16 mpg on the highway. I put together an Excel spreadsheet that pretty much calculates anything you want to know about RPM / tire sizes / tranny info, and I'm working on speedo-gears. PM me if you'd like to see it. . .
__________________
72 Chevy C-10 Custom LWB 383 Stroker - Edlebrock Air Gap intake and 670 CFM Holley Street Avenger carb. Hooker Comp Headers w/ X-Pipe and 2.25 duals TKO-500 & 3.08:1 rear I Love HEMI's, they're soft & chewy! |
03-22-2011, 10:34 AM | #36 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
|
Re: 3.73 to 2.73?
a low end torque monster can pull that off. Any 455 or caddy big block could do it to, but not your typical stock/stock-ish small block
|
03-22-2011, 11:43 AM | #37 | |
Account Suspended
Join Date: Sep 2010
Location: hingham ma
Posts: 1,721
|
Re: 3.73 to 2.73?
Quote:
my '86 monty SS 3.73 and 200r4 locked up is 2200rpm at 65 same tire size |
|
03-22-2011, 11:48 AM | #38 |
Account Suspended
Join Date: Sep 2010
Location: hingham ma
Posts: 1,721
|
Re: 3.73 to 2.73?
to the o/p
I'd install that 2.73 rear end.. with a 400 cid it pull those gears just fine.. then down the road, you can install a 700r4 with it's 3.00 first gear.. and all that talk about bog'n and lag'n gears will be all but history.. you might be happy with the th400 and 273's alot of 400cid trans am's had 2.43 rear gears and are almost as heavy as these trucks.. you said the rear is cheap.. if you don't like it, your out short money and a days work.. I say go for it.. |
03-22-2011, 10:08 PM | #39 | |
Who's got steelies?
Join Date: Feb 2006
Location: Morrison, Oklahoma
Posts: 1,023
|
Re: 3.73 to 2.73?
Quote:
__________________
1969 C10 LWB W/ 250 I6 & 3spd 1970 C10 with '67 small window cab, 68 front end, blue; 305/TH350, 3.08 limited slip rear end, manual brakes, power steering; & 4-wheel drums-My daily driver. 1975 Chevelle Malibu Classic Coupe 350/th350 mint green 1970 C20 Suburban 350/700R4 4.10 gearing green & white 1978 Big 10 Silverado 350/th350, working ac, 2 tone blue-My summer daily driver 1983 GMC 1500 Sierra 305/SM465 2.73 rear end How to add a trip odometer to your 67-72 stock speedometer How to rebuild your Q-Jet My Truck Page My Youtube Channel |
|
03-23-2011, 09:31 AM | #40 |
Active Member
Join Date: Dec 2004
Location: Marysville, OH
Posts: 667
|
Re: 3.73 to 2.73?
I was going to do it, but I waited too long and the seller scrapped the rear end. Didn't occur to me at the time, but I would have been going from a 10 bolt to a 12 bolt, so I probably would have had to change the yoke as well.
Sounds like a 3.08 is what I should be looking for. I might just swap gears. I've been reading up on it, and while it is a pretty precise procedure it doesn't seem too complicated if I take my time.
__________________
1957 GMC Ambulance 1962 Belair Wagon 1963 C80 Truck Cab *FOR SALE* 1969 Chevy C10 Short Bed 1972 Chevy C10 Long Bed *SOLD* 1996 C3500 Dually *SOLD* |
03-23-2011, 01:31 PM | #41 | |
Registered User
Join Date: Nov 2007
Location: Bay Area, Ca
Posts: 2,841
|
Re: 3.73 to 2.73?
Quote:
What tire do you run? Some simple math: Tire ------- Gear -- 3rd -- verter slip 275/60/15 + 3.73 + 1:1 + 15% = 65mph @ 3,500rpm 275/50/15 + 3.73 + 1:1 + 15% = 65mph @ 3,800rpm (Roughly same as 275/40/17) 225/50/15 + 3.73 + 1:1 + 15% = 65mph @ 4,100rpm 275/60/15 + 3.73 + 1:1 + 20% = 65mph @ 3,700rpm 275/50/15 + 3.73 + 1:1 + 20% = 65mph @ 4,000rpm (Roughly same as 275/40/17) 225/50/15 + 3.73 + 1:1 + 20% = 65mph @ 4,300rpm So either you have a very inificiant verter, a short tire, different than 3.73 gear or you are doing more than 65mph.
__________________
------Motor---------------Bottle 60'---1.53---------------1.41 1/8---6.58 @ 105.92----5.87 @ 118.41 1/4---10.38 @ 126.97----9.24 @ 142.49 |
|
03-23-2011, 08:13 PM | #42 | |
Chris
Join Date: Nov 2004
Location: Monaville, WV
Posts: 3,737
|
Re: 3.73 to 2.73?
Quote:
As for building a highway gear rear end, on anything, I personally hate it, if you like it and it works for you good. It sure as heck doesn't work for me and I hate it.
__________________
Chris GIT R DONE!!!!!! Check out all our rides, http://www.cardomain.com/id/benwa454 |
|
03-23-2011, 10:53 PM | #43 |
Active Member
Join Date: Dec 2004
Location: Marysville, OH
Posts: 667
|
Re: 3.73 to 2.73?
I don't remember off the top of my head, but the wheel/tire combo is 29" tall. I think I am running 255/45/20's in the rear.
__________________
1957 GMC Ambulance 1962 Belair Wagon 1963 C80 Truck Cab *FOR SALE* 1969 Chevy C10 Short Bed 1972 Chevy C10 Long Bed *SOLD* 1996 C3500 Dually *SOLD* |
03-24-2011, 12:43 AM | #44 |
Registered User
Join Date: Nov 2007
Location: Bay Area, Ca
Posts: 2,841
|
Re: 3.73 to 2.73?
29" tire + 3.73 + 4,00rpm@65mph = 30% converter slip. If that number is accurate, it is horrible!!!
Is it a stock converter? If not, who makes it and what is the stall rating? You sure that you have 3.73's in the rear? Jack up the rear, mark the tire and driveshaft. Rotate the driveshaft and count the turns it takes to make the tires go one full revolution. If it's 3 3/4 turns of the drive shaft then you have 3.73's. If it's 4 1/8 it's a 4.10. If it's 4 1/4 turns a 4.30 and 4 1/2 a 4.56.. Do you have a trans temp guage? If so what is your freeway cruise temp? It is possible your tach is off like you have been suspect of. Who makes the tach? Is there a 4cyl/6cyl/8cyl mode? If so is it in the correct mode?
__________________
------Motor---------------Bottle 60'---1.53---------------1.41 1/8---6.58 @ 105.92----5.87 @ 118.41 1/4---10.38 @ 126.97----9.24 @ 142.49 Last edited by Super73; 03-24-2011 at 12:45 AM. |
03-26-2011, 02:32 PM | #45 |
Registered User
Join Date: Mar 2011
Location: Richland, WA
Posts: 13
|
Re: 3.73 to 2.73?
I'm trying to decide the same thing. I was told a big block 400 with over 300hp should still have the get up and go I would like as well as good highway cruising. I was going to put in 2.73.
|
03-27-2011, 08:06 PM | #46 |
Active Member
Join Date: Dec 2004
Location: Marysville, OH
Posts: 667
|
Re: 3.73 to 2.73?
Ok, put another tach on it today and ran her up the road and back - new tach is showing 3100 rpm @ 65 mph, old one is still showing 4500 rpm @ 65 mph. 3100 is a little more sane I think. I'm guessing if I get some 3.08's in there I'll be a happy boy.
FYI, gunning the engine with the old tach showed an approximate redline of 7500-8000 rpm! Hello NASCAR, watch out for the big blue-green ambulance...
__________________
1957 GMC Ambulance 1962 Belair Wagon 1963 C80 Truck Cab *FOR SALE* 1969 Chevy C10 Short Bed 1972 Chevy C10 Long Bed *SOLD* 1996 C3500 Dually *SOLD* |
03-28-2011, 12:54 AM | #47 |
Registered User
Join Date: Nov 2007
Location: Bay Area, Ca
Posts: 2,841
|
Re: 3.73 to 2.73?
Current.. 3,100 rpm + 65mph + 3.73 + 29" tire = 10% verter slip
With your new gears.. 10% slip + 65mph + 3.08 + 29" = 2,575 rpm
__________________
------Motor---------------Bottle 60'---1.53---------------1.41 1/8---6.58 @ 105.92----5.87 @ 118.41 1/4---10.38 @ 126.97----9.24 @ 142.49 Last edited by Super73; 03-28-2011 at 12:55 AM. |
11-20-2017, 01:18 PM | #48 |
Registered User
Join Date: Mar 2010
Location: thomastown mississippi
Posts: 1,261
|
Re: 3.73 to 2.73?
I would add this to every ones already good advice. I have installed lots of gears in Chevys, and TWICE in my lifetime I found going from 3.73s to a faster gear, one was 2.73 & another was 2.56 the pinion was physically too large to fit into the rear axle housing. Only saw this happen twice. On one truck we got another axle housing & gears dropped right in. On the other the chosen ratio was ditched for another.
In hindsight I think it had to do with the year of the housing. It was prolly one that was made before 2.73s were available & so no provision was made for them. Never had a problem with 3.08s. Just something else to keep in mind, it COULD happen! |
11-22-2017, 05:56 PM | #49 |
Registered User
Join Date: Sep 2011
Location: Ark City, Kansas
Posts: 3,284
|
Re: 3.73 to 2.73?
I would not touch what you've got!!!
Sound like your speedo and tach could both be a touch off., maybe. Not trying to sound like a Beavis here, just help... I had a 67 Bel Air (my first car, Had from 1975-1997) was a heavy car, a;though not quite as heavy as a pickup. Had a 2.73 gear in it, MPG was 18-20 with a 283. Power was OK, but I will never do that again. My life learned lesson is to compromise on the side of power, not MPG. These old pickups are very heavy. The $$ spent to make one get better MPG is not worth it, my opinion...Just drive it 55-60 MPH on the highway, since you don't do that very often... |
11-29-2017, 03:59 PM | #50 |
driving is in my blood
Join Date: Dec 1999
Location: Mesa AZ
Posts: 5,694
|
Re: 3.73 to 2.73?
I ran 3.07's with overdrive. No overdrive with 2.73's is no problem what so ever. I had a stock vortec 350 in the truck [a 79]. 3.07's with no overdrive was 3k at 80mph, which to me still isen't a freeway gear. 2.73's will still be howling at that speed but more reasonable. Do it.
So far right lane with hazard flashers on everywhere? That doesn't make any sense. Most people want to at least drive the speed limit.
__________________
-78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me. |
Bookmarks |
|
|