Gear recommendation

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DRVDuster

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Hey guys,

What will be the best gear ratio for my build

318, 0.030 over
360 intake, port matched
600 cfm carb
Headers
.441 cam
Heads were milled 0.020 and have 360 valves.
A833 NO OD

I´m running 3.09 gear ration now, but it feels a little slow.
Not sure if I should get 3.23 or 3.55, tire diameter is 25.7".

Thanks in advance.
 
I run 3.23 in my dart. It's doing 2600 rpm's at 60 mph. Son in law has 3.55's. Both seem like okay gears for cruising.
 
What rpm are trying to stay under/at while cruising? That will pretty much tell you what gear you want/need.
 
DRVDuster said:
Hey guys,

What will be the best gear ratio for my build

318, 0.030 over
360 intake, port matched
600 cfm carb
Headers
.441 cam
Heads were milled 0.020 and have 360 valves.
A833 NO OD

I´m running 3.09 gear ration now, but it feels a little slow.
Not sure if I should get 3.23 or 3.55, tire diameter is 25.7".

Thanks in advance.
Click to expand...


If you have a 2.66 1st gear a 3.55 will do (9.443 over all). If you have a 2.44 1st you need a 3.73 (9.1012 over all). Either live with the cruise RPM of use a little taller tire if you don't like the cruise RPM.
 
I don't think going to a 3.23 is going to be much change. I would go 3.55 or 3.73 depending on what kind of highway rpm you can live with.
 
The cams duration @.050 would help.
 
Here is some math to help.

Tire size 25.7 X 3.14.28 = 80.8 inches traveled per RPM at axle.
80.8 / 12 = 6.73 Ft travelled per RPM at axle.
5280 / 6.73 = 784.5 RPM at axle for 60 MPH
784.5 X 3.23 = 2533 Engine RPM in 1.00 Drive final gear.
784.5 X 3.55 = 2784 Engine RPM in 1.00 Drive final gear.

Depends on where one lives, but here in CA trucks will run you over at 60 MPH.

So here are numbers based on 72 MPH

3.23 2533 X 1.2 = 3039
3.55 2784 X 1.2 = 3340
 
Mad,

What does first gear have to do with it,

My 340 is touching 7000 RPM in first with 727 LOL !!

Rear gears 3.23
 
It has to do with the math of torque multiplication and the way it feels on take off. This ratio varies with tranny's and years. Though the final drive ratio is allways the same on standard 3spd's.

Going with a 999 for example with it's deeper first gear can make the car feel and actually be faster. This is a good thing to consider when deciding on a gear ratio & how the car will feel when driven.
 
You will not see a difference with a 3.23 gear.
3.55 maybe
I would look at around 4.11 if you don't alot of highway driving.
 
Rob,

Got it! He is not looking for cruise but offline. So first gear ratio is a factor.
 
I´m not sure what is the 1st ratio.

My driving is 90% city, here in MX there is a lot of stop lights, but from time to time I take the car cruising, but I´d like to stay in the 3000-3500 range when cruising.

Thank you all for your input.
 
Nice street cam. I have run a Crane with similar duration before. Good to 5500.
3.21 or 3.55's are good with that duration.
(I think you'll like 3.55's)
I have run nearly that exact combo before with a 4spd car.

Tips on a performance edge with that combo would be;

For auto trans, 2000/2200 stall
Low first gear trans (3.09)
Wider tires, you'll smoke the stock width Bologna tires.
Good rear springs.
Street light brat can go to 3.91's and I suggest a 26 inch tire x 9 wide. You should still be in your cruise range with the 3.91's. I was with the 4.10's and a 27-1/2 tire.
I don't know what intake you have but a dual plane should be employed.
IMO, a AVS style carb would be nicer. Ether a stock small AVS which are rated @ 630 cfm or the new Edelbrock AVS Thunder series carb.
2-1/2 exhaust pipe.

Enjoy, I did with my combo. Just like yours. Fun ride.
LMAO
 
I'd say 3.55's if mostly citing driving vs 3.23's.
 
...as I'm just learning about all of this stuff, I had no idea that changing the rear gears would lower the RPMs at highway speeds.

I have a stock 318 with a 7.25 rear and 2.76 gears and always have white knuckles when I have to drive it at anything over 60mph. It sounds like it's revving way to high.

I'd like to be at about 2000-3000 @ 60-70mph.
 
Hi, With a 225 60 15 tire (or other tire that's about 25.6" tall) and those 2.76:1 rear gears you should only be turning about 2500 RPM at 70 MPH. If it's an auto that might be 2600, but it sounds more like it's either not shifting into high gear or it's slipping pretty badly. It's also possible the tag on the rear is wrong, or your speed-o is under reporting and you're really going 80 at an indicated 70 if the OEM rear was a 3.55:1 or so

Dave

Saverio said:
...as I'm just learning about all of this stuff, I had no idea that changing the rear gears would lower the RPMs at highway speeds.

I have a stock 318 with a 7.25 rear and 2.76 gears and always have white knuckles when I have to drive it at anything over 60mph. It sounds like it's revving way to high.

I'd like to be at about 2000-3000 @ 60-70mph.
Click to expand...
 
Saverio said:
...as I'm just learning about all of this stuff, I had no idea that changing the rear gears would lower the RPMs at highway speeds.

I have a stock 318 with a 7.25 rear and 2.76 gears and always have white knuckles when I have to drive it at anything over 60mph. It sounds like it's revving way to high.

I'd like to be at about 2000-3000 @ 60-70mph.
Click to expand...

There's another issue there. Your car should be at a low rpm when cruising with 2:76 gears!
 
thanks for the info guys.
I think my tire size may be contributing to this (i spoke with a rear end guy who said the same thing you all did).

The tires on there now are 195 75R 14 (I think, have to verify when I get home)

I was advised to consider looking for a taller tire.
 
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