Thread: Opinions..

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Whats a acceptable 65 mph rpm on a chevy small block?
This is for performance and a 60 mile one way trip is going to be considered a massive journey.Mostly in town and maybe 10 to 15 mins max highway mixed in.
From what I have read ,it seems the best performane rpm at cruise {or 65 mph for me} is going to be a rear gear that puts it right at max torque rpm.For me thats 3500 rpm at 65 mph .In order to achieve this rpm at 65,current 3.73 gear would require a 24 inch tall tire or a 30 inch tire with a 4.88.I was thinking about 26 to 30 inch tires for the back and 26 to 28 for the front.
I am flexable on tire size for the rear and front.
http://www.wallaceracing.com/calcrgr.php
This is a continuation of my other thread sorta...I am into the rear end and going to go ahead and change the ring and pinion while I am in there.The specs on the motor are 3500 rpm max torque 356 and 5500 rpm max hp 290.....I am also running a 3 speed manual trans and this is for my 66 chevy truck at approx 3500lbs.

Heres my opinion on it ,This will be for fun as I have other transportation to use every day,no actuall truck duties will be performed with it and I built it to have fun.....My idea of fun is to be able to quickly accelerate and I like feel of the pull of a motor.Gas is no concern as I will drive as I can afford it ,economy is no concern and being able to go 300 miles away is of no concern........4.11 seems to be a happy medium...but it is a compromise of gas mileage and performance which tells me it does neither of those well.They would be a compromise ,well I am willing to compromise biased to the performance side,I just do not want to get too crazy with it where top speed is 90 mph at 5500. 100 mph in the 1/4 is all this would probably do on a good day soo that would be plenty,considering its going to see the track one time in its life at the most. I also notice the ratio determins price.....theres a set of 4.56s alot cheaper than the lower or higher sets.. possible upgrades in the future are a 5 or 6 speed trans or a 700r4...engine will remain the same untill it blows.Ohh and if makes any difference there will be no launches and its a open differential for now..

At 5,500 with a 88" tire (circumference) and 4.56 gears, you'd be at 100.5 mph. I've had some stiff geared rigs in the past and they are a hoot to drive, ear to ear grins.

A change later to a stock T5 with a .63 (final drive 2.87) or .68 (final drive 3.10) 5th gear would allow you to "freeway" with the rest of the guys, although 1st gear would be so low as to be almost unusable except for climbing trees.

Here's a link to g-force and their remanufactured T5's. A guy would want to choose helical gears over the straight cut ones unless he drove with ear protection.
http://www.gforcetransmissions.com/tran_gt-5.asp

I set mine up so I can cruise at the speed limit (70 mph) at highway speeds with the converter operating at minimal slip. In my case at 2800 rpm and 3.50 rear gear with 30" tires.

Of course the 502 will make ~500 lb-ft from there to 5,000 rpm. I want to be able to cruise it for a tank of gas without it whining too bad.

Kitz

WEll ,I guess common sense has gotten a hold of me and I will use 4.10:1 4.56:1 sounded fun for a while ....I did see a 4.30 set that was tempting me I guess I can switch tire sizes from 26 to 31 to adjust the 4.11s and then when there is finally a 5 speed or 700r4..I think that will give me enuff of the low gears to get it out of the system ,then the od will be a welcome thing!!
I do know one thing it sure seems tempting to over gear ...alot more so than over camming,atleast on the cam you have the engine parts to tell you it aint gunna work too good.The rear gear has nothing telling you its a bad idea The rear gear talks to you saying a little lower and get more response,a little lower and you may lift the front left ...a little more you may pull the wheels ....a little more.....and ?

I would suggest that if you can get a 430 gear then go with that.
I have 411 gears in my Model A with 350/350 combo and 30" x 18.5" Mickey's.
I'm turning about 2600 rpm's at 60 mph. It's not quite enough and I would prefer 456 gears if I ever decide to change.

Let's simplify things,
3 speed 1:1 output trans, 3:73 rears equals about 3200 RPM's @ 60 MPH.
3 speed 1:1 output trans, 3:42 rears equals about 2100 RPM's @ 70 MPH.
4 speed overdrive trans, 3:73 rears is about the same as 3 speed 3:42 rears.

I had to get rid of my 4:11 rears...I shifted twice before I hit the end of the driveway.

Originally Posted by dans30

I would suggest that if you can get a 430 gear then go with that.
I have 411 gears in my Model A with 350/350 combo and 30" x 18.5" Mickey's.
I'm turning about 2600 rpm's at 60 mph. It's not quite enough and I would prefer 456 gears if I ever decide to change.

IMO 430's or even 411's are too deep for the street without overdrive. Look at Lakotas chart, which is pretty accurate. I was running 390's in my 3 speed with 30 inch tires and went to 370's and was much happier. (so was my valvetrain)

Don