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Rear end ratios

Rear end ratios

2004-02-02 by Don Lattimer

Maybe I'm missing something here but I have a 3.77:1 ratio and also the
4-speed with overdrive behind an Essex V6.  At 65MPH I'm turning approx
33-3500RPM.  No trouble getting up and over 100MPH+.  My tires are 24.1 inch
in diameter.  Gas mileage in the mid 20s'.

I'm assuming those who are going to a taller gear don't have overdrive??
It makes a big difference.

Will the more knowledgeable folks please enlighten me ?   Thanks.

Don Lattimer
#3m5759

RE: [MarcosManiacs] Rear end ratios

2004-02-03 by McLeod, Ronald

Don . . .
 
As a data point for comparison - my Mantis has a very low rear end ratio,
around 3.08:1 I think, but I can find out exactly. Engine is the Triumph
2.5PI, with the Triumph 4-speed box, and overdrive on 2nd, 3rd, and 4th.  In
top overdrive, I am turning 3100 RPM at 100 MPH - just loafing along,
really.  The downside, I guess, is that I don't do as well on the 0-60 time
as I could with a numerically higher ratio.  The upside is that I get over
35 miles/USGallon in highway driving.
 

Regards . . . Ron McLeod 
1970 Marcos Mantis P8/5858
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-----Original Message-----
From: Don Lattimer [mailto:donlattimer@...] 
Sent: Monday, February 02, 2004 5:59 PM
To: MarcosManiacs@yahoogroups.com
Subject: [MarcosManiacs] Rear end ratios


Maybe I'm missing something here but I have a 3.77:1 ratio and also the
4-speed with overdrive behind an Essex V6.  At 65MPH I'm turning approx
33-3500RPM.  No trouble getting up and over 100MPH+.  My tires are 24.1 inch
in diameter.  Gas mileage in the mid 20s'.

I'm assuming those who are going to a taller gear don't have overdrive??
It makes a big difference.

Will the more knowledgeable folks please enlighten me ?   Thanks.

Don Lattimer
#3m5759




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Re: [MarcosManiacs] Rear end ratios

2004-02-03 by patemery@sympatico.ca

Dear Don! My Marcos 3L V6 has the Salisbury rear axle with 3.58:1 gear ratio. The transmission is a four (4) speed unit with overdrive in third and fourth. The

Re: [MarcosManiacs] Rear end ratios

2004-02-04 by Don Lattimer

Pat,
Thank you! Makes it easy to grasp. My gearbox ratios are the same as yours although I have a Corsair rear end which is of the "banjo" type and is 3.77:1. I don't use first gear much myself but it's fun at stoplights for the first 100ft.! My travel is mostly on two lane hiways up here in the redwoods. If I do get on the freeways, I usually keep it around 70MPH. California speed limit is 55 but on most freeways it's 65MPH. I draw enuf attention without going faster. Of course I'm getting older too...........might have somrthing to do with it!
Reading an old review of the V6 Marcos they mention that the max power of the Essex V6 is at 4750RPM and top speeds were 1st:31mph, 2nd:44, 3rd:68, 3rdOD:83, 4th:107, and 4thOD:125
Again, thanks for the info. Someday I'll need to get the rear end done and maybe I'll change the ratio then. Your info is invaluable.
Don Lattimer
#3m5759
Willits, CA, USA
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----- Original Message -----
Sent: Tuesday, February 03, 2004 3:22 PM
Subject: Re: [MarcosManiacs] Rear end ratios

Dear Don!

My Marcos 3L V6 has the Salisbury rear axle with 3.58:1 gear ratio. The transmission is a four (4) speed unit with overdrive in third and fourth. The ratios are: first 3.163:1; second 2.214:1; third 1.412:1; fourth 1:1; overdrive is 0.8205:1. Tire diameter is theorically 24.10" (P235R60-13). The first gear is useless, unless you want to use the car for farm work! I can take off in second gear with no hesitation. First gear, with it's combined gear ratio of 11.323:1 gets me to 34.838 MPH at 5500 RPM. And I can easily loose the tach needle if I don't watch it. Could be costly! If I leave in second gear, with a combined ratio of 7.926:1, I am good to 49.77 MPH at 5500 RPM. In my view, the best ratio in somewhere in between. Half way between 11.323:1 and 7.926:1 is 9.624:1. If I divide this proposed combine gear ratio by the ratio of my first gear, 3.163:1, I get 3.04:1 as the rear end gear ratio. Now, with 3.04:1, I could get 41 MPH in first; 58.61 MPH in second; 91.9 MPH ! in third and theorically 129.76 MPH in fourth, all at 5500 RPM. One hundred and twenty (120) kilometer per hour, 74.56 MPH in overdrive mode would show 2593 RPM. With the present arrangement, it reads 3053 RPM at the same speed in overdrive mode. With 2.88:1 gears, it would read 2456 RPM. So, 3.0:1 seems about right fot better use of low first gear ratio and as a mean to improve cruising effort on the express-way. As a comparaison, to do 40 MPH at 5500 RPM with 3.77:1 rear end gears and 24.10" diameter tires, you would need a transmission first gear ratio of 2.616:1. This is quite tall but would pull you off the line the same way it would with 3.163:1 first gear, like mine, and 3.11:1 rear gears. The difference would only be at cruising speed, where 3.77:1 gears would show higher RPM. I do not worry about fuel consumption as I hardly ever use this car. What bugs me is that I know that it is not geared right. So I guess Don that it all boils down to what is your cruisin! g speed. Up here, they walk all over me if I drive 65 MPH.
In closing, I have read that Reliant Scimitar equipped with Ford Essex 3L V6 have a second gear ratio of 1.950:1 and overdrive ratio is 0.778:1. That is a much better set up. Here are some helpful formulas:
Miles Per Hour= tire radius x RPM / 168 x gear ratio ;
RPM= MPH x 168 x gear ratio / tire radius ;
Gear ratio= tire radius x RPM / 168 x MPH .

Thanks to Donny for the tip on TR8 rear axle.
And Garry, I will get back to you concerning your deal on wheels.

Best Regards to all,

Pat Emery

> From: "Don Lattimer"
> Date: 2004/02/02 Mon PM 05:58:36 EST
> To:
> Subject: [MarcosManiacs] Rear end ratios
>
>


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Maybe I'm missing something here but I have a 3.77:1 ratio and also the
4-speed with overdrive behind an Essex V6. At 65MPH I'm turning approx
33-3500RPM. No trouble getting up and over 100MPH+. My tires are 24.1 inch
in diameter. Gas mileage in the mid 20s'.

I'm assuming those who are going to a taller gear don't have overdrive??
It makes a big difference.

Will the more knowledgeable folks please enlighten me ? Thanks.

Don Lattimer
#3m5759




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