Register or Log In To remove these advertisements. |
|
|
|
Thread Tools | Display Modes |
|
11-10-2010, 02:19 AM | #1 |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
|
sm465+rear gear ratio=what rpms???
I have a 69 c20 and have looked up rpm calculators for figuring out what rpms ill be running at driving speeds and theres a buch of different out comes for each rpm calculator so i figured id ask the people that actually run these trucks. I have a sm465 and have decided to switch it out to 5 lug and am wondering what rpms ill be running for different gear ratios and what kind of mpg ill get also. I usually cruse around town and dont hit highway speeds much but i do at least once a week go for about a 30 mile trip id like to take my truck on in the summer. Any information on this would be great.
Thanks |
11-10-2010, 07:52 AM | #2 |
Registered User
Join Date: Mar 2003
Location: San Francisco, CA USA
Posts: 2,454
|
Re: sm465+rear gear ratio=what rpms???
I can't understand why different online calculators should give you different answers, but I always do mine with a hand-held calculator.
The magic number is 20168. Divide your tire diameter into that to get tire revolutions per mile, and then multiply the result by your axle ratio. The number you get will be driveshaft revs per mile, which is the same as engine revs/mi if you don't have overdrive or torque comverter slip. As an example, let's say you have 31" tires and a 4.10 rear end, so: 20168/31 = 650.6 tire revs/mi 650.6 x 4.10 = 2667 2667 engine revs/mi. That is also your engine rpm at 60 mph. Other speeds are proportional, so if you want the engine speed at 70 mph: 2667 x 70/60 = 3111 rpm at 70 mph. Ray
__________________
Live more responsibly. Eat lower on the food chain. Eat vegetarians. Last edited by raycow; 11-10-2010 at 07:53 AM. |
11-10-2010, 08:57 AM | #3 |
Registered User
Join Date: Dec 2008
Location: Holbrook Nebraska
Posts: 6
|
Re: sm465+rear gear ratio=what rpms???
I have a 72 Chevy C10 that still has the 4 speed and 3.07 gears in the rear end. It also has 30-9.5x15 tires on the back. Running down the highway at 65 it usually runs around 2300 to 2400 rpms.
|
11-10-2010, 06:50 PM | #4 |
Simple? What's simple?
Join Date: Apr 2007
Location: Southeast CT
Posts: 1,472
|
Re: sm465+rear gear ratio=what rpms???
I had a 3.73 behind my SM465/307 and got between 10 and 13 mpg, best cruising in town around 35mph.
If you shoot me your email address I can send you an excel spreadsheet that will give you all the information you're looking for - I have it on my laptop from when I was considering the NV4500 swap. **EDIT** I figured out how to attach it directly. The spreadsheet is set up with two sheets, for NV4500 and SM465, as I was comparing the two. You can change tire height and rear end ratios (highlighted in yellow) to see what the speeds look like for different ratios and tire heights. Gives you MPH in each gear in 100RPM increments.
__________________
CURRENT '50 GMC 100 shortbed Gen IV 4.8 LS - 4L65E (Secret truck, Shhh!!!) Build '63 Buick Wildcat Coupe 401ci Nailhead (Very much in pieces) Photos '66 Impala SS convertible 327-QJet-glide (4 speed swap one of these days...) Photos '69 CST/10 4x4 SWB Stepper 350 2bbl - NV4500/NP241C (Broken Truck!) '72 Sierra Grande 2WD LWB fleetside 350-TH350 Refresh '99 K2500 Silverado RCLB 5.7 Vortec - NV4500/NP241C (Daily) '99 K2500 Suburban 7.4 Vortec - NV4500/NP246 (still working out the bugs) SOLD '71 Custom/10 2WD LWB fleetside - '72 GMC K/3500 Dually (Sold to redryder) Last edited by JJorgensen52; 11-11-2010 at 12:21 AM. |
11-12-2010, 03:29 PM | #5 |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
|
Re: sm465+rear gear ratio=what rpms???
Raycow thank you very much, im going to print this out tonight so i can keep it for further reference.
JJorgensen52 That is awsome thank you, im deffenitally saving that lol. Farm Built-72 With the 3.07 rear end does it take a lot to take off? I would think not if you used 1st gear. Thanks |
11-17-2010, 01:15 AM | #6 |
Registered User
Join Date: Dec 2008
Location: Holbrook Nebraska
Posts: 6
|
Re: sm465+rear gear ratio=what rpms???
With the 4 speed it doesn't take a lot for it to take off. I originally had a 250 inline six with a bad clutch so you had to baby it in 3rd and 4th or the clutch would start slipping. Recenty just put in a 350 with a new clutch and it seems to have plenty of power with this set up. Haven't driven it much with the new motor as I am still working out a few bugs, but will let you know more when its all finished.
|
01-11-2011, 02:55 AM | #7 | |
But Found Her 25yrs Later!
Join Date: Oct 2010
Location: Oregon City, Oregon
Posts: 10,510
|
Re: sm465+rear gear ratio=what rpms???
Quote:
Had it do towing with that combo?
__________________
I lost my 65 - Found it 25 years later: http://67-72chevytrucks.com/vboard/s...d.php?t=426650 66 C20 Service Truck: http://67-72chevytrucks.com/vboard/s...d.php?t=428035 Last edited by LostMy65; 01-11-2011 at 02:58 AM. |
|
11-17-2010, 06:51 AM | #8 |
Special Order
Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,862
|
Re: sm465+rear gear ratio=what rpms???
What does the SM465 have to do with the cruising RPM?All transmissions are 1:1 final drive ratio,then add overdrive if that's what the trans is.It looks to me like you are calling the rear you swapped out an SM465?What ratio is the 5-lug rear you swapped in?What diameter tire?Give us that info for a baseline.
__________________
"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
11-18-2010, 12:51 AM | #9 | |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
|
Re: sm465+rear gear ratio=what rpms???
Quote:
|
|
06-24-2016, 10:57 AM | #10 |
Senior Member
Join Date: Mar 2012
Location: ripley ny
Posts: 2,894
|
Re: sm465+rear gear ratio=what rpms???
20168, where did this number come from? old post lol
|
06-24-2016, 11:15 AM | #11 |
Restoring it $200 at a time...
Join Date: Aug 2008
Location: NE Kansas
Posts: 886
|
Re: sm465+rear gear ratio=what rpms???
Tire diameter * pi = Circumference, which is going to translate to distance traveled.
You're looking for tire rotations per mile. 5280 * 12 = 63,360 inches in a mile 63,360 / pi = 63.360 / 3.14159 = 20,168
__________________
Charter member of the 'Put the dimmer switch back on the damn floor where it belongs' Society '68 5.3L-4 speed LWB C20; grandpa bought it for the farm in '71. Now LS 5.3, rather than 327. DD '09 Pilot Weekender '65 Skylark 300-4V-4 speed Wife's '07 Lexus ES350; 117 actuator motors and I can't see the engine. Son's '04 F250 SuperCab 6.0 |
06-24-2016, 11:22 AM | #12 |
Senior Member
Join Date: Mar 2012
Location: ripley ny
Posts: 2,894
|
Re: sm465+rear gear ratio=what rpms???
i have a post up looking for the answer on going from 456 to 354 gears, what ratio adapter i would need with out changing speedo drive gears
|
06-24-2016, 11:42 AM | #13 |
Senior Member
Join Date: Mar 2012
Location: ripley ny
Posts: 2,894
|
Re: sm465+rear gear ratio=what rpms???
i found my answer at PATC Tranmission
|
Bookmarks |
|
|