RPM & Gear Ratio

[tekatlarge]

Ok here is a question for all of you V8 drivers.

First off what RPM are you turning at freeway speed? What is your Gear ratio? Is your gear ratio satisfactory? And lastly, what size of rear tire are you running.


I am trying to decide if my 3.5's in my T roadster along with 30 inch tall rear tires. 285/70/15 will make it sluggish out of the hole.. I don't want a 180 MPH top end. I do want to snap necks with the acceleration!!!!

Whadyathink? 4:10's 3:7's or stay with the 3:50's

[ranger5.0]

My 66 chevy ran 3200 at 60 with 245/60- 15's. The truck had 4:10's in it. It would get out of the hole and I could bury the tach in 4th gear about 90-100 mph. My BII had 34 inch tires with 4:11's . The motor ran about 2500 at 60 mph. Since it had a v-6 the launch was not nearly as good. The hotrod guys that I know like the 3:73's unless they can get an overdrive, then they go for the 4:10's . There is also the 3:90's, though I have no experience with them.

[mccutcheon4]

Tek,

I run 3.70s with a 265-70-15 tire, that measures 28 inches in a 79 short box F100. Its powered by a slightly warmed up 302 & C6. I used it to pull the family 24 foot camp trailer. I still use it to pull a car trailer.

The 3.70s are very street friendly, 2800-3300 RPMs at roughly 65-75 mph. I also installed a 2.78 low gear set in the C6 which helped the bottom end.
I know 2800-3300-seems like a lot of rpms but, SB Fords will do that all day and be happy about it. I still get 15-16 MPG.


With a 30" tire, 3:70s or even 3:89s may work fine if your not planning a lot of freeway driving.

Years ago, I had a set of 4:57s in a 66 fastback with 26 inch tires,
It was just plain unbearable over 50 mph, at least more than a 1/4 mile
at a time

[tekatlarge]

I had a sneeky hunch that 3.7's were what I should be running.

I will be doing a lot of around town and some limited freeway driving. 3.7's were my gears of choice back when I built a lot of street cars. Although I usually had lower profile tires on them, I found 3.7's to be quite exciting on the street when needed!

When I finally rolled my rear tires over to the T and set them in the wheel well I was surprized they were so BIG!! They are the same height as a stock model T tire!

At any rate I guess I will save my pennies up for a set of 3.7's. I picked up a 9 this last weekend and although it is a 31 spline rear and a ford "Equa Lock" carrier but unfortunately it has the 3.5's. I guess we can't win em all. Next step is to clean up the housing and send it to scribners for centering and narrowing.. Damn this thing is costing a fortune to build and I am pushin the envelope in the budget dept now as it is!

At any rate I appreciate all the info. This rpm's and tire size thing is going to be a try and see thing I guess. More to come.