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Post Info TOPIC: The right rear end ratio?


ONTARIO

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The right rear end ratio?
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What rear end ratio would be the best? The car weighs 3400 LBS. loaded, engine is a low horse 240 Hp. stock 327, trany is a TH 350, rear end is a 10 bolt posi., rear tires are 28" dia.               Looking for the best all round ratio to use for cruzing not racing.



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COURTICE, ONT

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There's some good calculators here.
www.csgnetwork.com/multirpmcalc.html


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3.08


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LONDON, ONT

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3.08 or

3.31 



-- Edited by el toro on Thursday 11th of February 2016 02:09:54 PM

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65'elCamino,350 4sp 3.73s



PORTLAND, ONT

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I'm running a 3:42 behind a 250 Cu . inch Inline six / T-5 and love it . It pulls strong , cruises great , super mileage and don't need the 5th gear ( .72 ) until 50 MPH-- Hope this helps -- LATER -- DON / Fleet 51

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MINDEN, ONT

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3:38 good performance and not bad mileage with 28" tires

 



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WEST PERTH, ONT

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Not enough info for me to suggest ratio.

Firstly, it's a 10 bolt so I'm thinking your 28's are there to already alter the ratio.

2ndly, it boils down to gas mileage or GO.

I'd totally agree with chips at a 3:08, but if you're looking for the best of both worlds, I'd fly with the old tried/tested and true 4:11.

Just my opinion.

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COURTICE, ONT

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I have 27.5" Tires, 350/350 and gm 10 bolt (7.5) and I think it's 2.73's. It's def good for cruising on the highway but feels like a slug getting going.
I'm working on switching over to a 700r4 and 3.73's though.

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I stated "3.08's" in my earlier post.

As others have suggested, you might want to expand on your interpretation of the word "cruzing" (meaning is this car going to see 80kmh at the most just putzing around the village or going from town to town, with the odd BLAST down an empty stretch, or is it going to be hitting a steady 115kmh on the 401 twice a week?).


3.08's (in my opinion) are a good "do everything well enough" gear. Enough gear to get the car up and moving but also a good ratio to have when you aren't running an overdrive trans and you're going to be doing some highway driving.

I tossed a 3.73 rear end in one of my cars (with a TH350) and a much shorter tire than you have and I wouldn't want to put too many highway miles on that setup (due to the higher revs at decent 401 speeds). I think my tires are around 25-26 dia.

Lots of 70's and 80's Trans Ams and Z28's (with shorter tires) had 3.08's and more than a few had 3.73's.

In my opinion, anything in the 2's just won't make the car "fun" to drive.



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BLACKSTOCK, ONT

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I have to agree with Don for his set up & mine too!!! I'm running the 3:42's with a tremec 5spd. & have the best of both worlds!! Got 25 MPG on trip to W.Virginia last fall, & car launches like a scalded dog!!! With no OD I'd go with 3:08 or 3:31 good all round gear. Have 3:71's in my Avanti & it only gets around 15 MPG on highway which "ain't bad" but sure like the Torpedo backs mileage pushing 400HP

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ONTARIO

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It's a 327 . It wants the revs . Don't go any lower than 3.42:1






-- Edited by Petebil on Thursday 11th of February 2016 10:37:27 PM

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CLINTON, ONT

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Petebil wrote:

It's a 327 . It wants the revs . Don't go any lower than 3.42:1








          I agree     if it was a BB  then 3:08's 



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LONDON, ONT

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My 57 runs a 355/700r4 with a 3:55 rear end. Launches really well and runs the 401 at 70mph at 2200 rpm. As far as I'm concerned the best of both worlds

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BUCKHORN, ONT

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your car's power, weight, tires and driveline sound similar to my 76 vette. the rear gear in it is 3.08 and is good ratio in it for overall driveability.



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FOXBORO, ONT

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studeshaker wrote:

your car's power, weight, tires and driveline sound similar to my 76 vette. the rear gear in it is 3.08 and is good ratio in it for overall driveability.


 X2, my 78 4 spd vette had 4:10's in it and at hwy speeds it was up there with the revs.



-- Edited by shag766 on Wednesday 17th of February 2016 03:49:59 AM

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FOXBORO, ONT

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dualquadpete wrote:

I have to agree with Don for his set up & mine too!!! I'm running the 3:42's with a tremec 5spd. & have the best of both worlds!! Got 25 MPG on trip to W.Virginia last fall, & car launches like a scalded dog!!! With no OD I'd go with 3:08 or 3:31 good all round gear. Have 3:71's in my Avanti & it only gets around 15 MPG on highway which "ain't bad" but sure like the Torpedo backs mileage pushing 400HP


 dang pete, you can't be much more than idling with the 5 spd with those gears on the hwy. good for you on the 25 mpg.



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CORNWALL, ONT

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low power + 28" tires = 3.55 to 3.73

4.11 won't help much more and just eat gas.



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BRADFORD, ONT

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3:42 or 3:55. Fun to drive and low enough rpm at Highway speed. IF you go to 700R4 or 200-4R then 3:73, 3:91 or 4:11. More Fun and excellent highway rpm/fuel economy.

the Kid.


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OAKVILLE, ONT

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I have to agree with Rochie,what car do you have? Are you comfortable driving at 110-120? What ratio is in the diff now? You can still find a 200r4 out there and they will fit where your t350 is now just a little messing with the tv cable bracket or buy one from gm. That will give you the all round best cruising and hwy without bothering with the diff. Or stay with the t350 and 3.55 ratio. My 2 cents.

 

Randy



-- Edited by v8deuce on Friday 10th of June 2016 11:03:01 AM

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FOXBORO, ONT

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close to kid's thinking

3:42's or 3:55's for a gear change but on the o/d route i wouldn't go below the low 4: range or it will be close to lugging in o/d with the 327. i have one with a tremec 5spd and 15" rears that rev's in the 19 to 2100 range depending on the grade but it is a big block. those rpm numbers wouldn't be much more than idling for a low hp small block i wouldn't think, maybe.

well 1/2 donkey close, lol.        rick



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Although I think you already have enough info to make the correct decision, I will chime in because I did this last year. A gear change that is. My perspective is the manufacturers made a bad decision using these short ratios in an attempt to get their mileage numbers up.

So what I did and why. Why first, I wanted the car to work better in town and still be able to cruise highway speed on expressways. By work better in town, get into power band sooner to ensure fuel consumption was best balanced for driveabilty.

What I did, swapped out the 2.80 gear for the 3.50. The result mostly met my expectations perfectly. In town, this car is quite a bit of fun to drive and gets decent mileage if I practice the measure of restraint needed when it is so much fun to launch the car that weighs 4400 pounds. Last year, the 429 C6 3 speed got 14mpg driving to Detroit for Woodward Cruise doing 70mph. I will say that the rpm levels felt somewhat high and I would likely be happier overall with a 3:30.

The thing is, we are so tuned into our new cars that have computer controlled transmissions that cruise at 2k rpm or less, we expect that from our oldies. This unfair to them as their optimal rpm is often much higher and often produces more engine noise that might give you the impression the engine is working harder when it is really in its' sweet spot.

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