Mid-ohio gearing?

Joe Harlan

Joe Harlan

Well-known member
I have a car going to Mid-Ohio for a vintage race, 7500 rpm 1:1 4th 21.7 diameter tire. What rear gear for the back straight?

Thanks for any info.
 
I ran 4.22 gears at Mid-Ohio with 20" Goodyear tires in GP. My redline was around 8,000 rpm but I don't think I ever hit redline in high gear (1:1) on the back straight.
 
We ran a 4.55 on the 948 configuration with 20 inch Hoosiers at 8500 . We run the 3.9 with the 1275 at 7200 like Dayle.
 
Thanks Guys! I am going to send the car with 3.90 and a 21.7 inch tire. The engine is good to 7800 so that sounds perfect.
 
Gearing also depends on the horsepower of the engine.
Full-prep 948 Sprite, 20" tires, use 4.55:1
Full prep 1098, 20" tires, use 4.22:1
Etc.
Your selected combination of 21.7" tires and a 3.90 diff gear, will require considerable horsepower to reach 7800 rpms (129 mph).

Charlie T.
 
Thanks Charlie. this is a 1500 non crossflow engine that makes pretty good HP. I was really just wanting to make sure he did not run out of gear down the back straight and it sounds like from everyone's advice we are pretty good.
 
I agree with Charlie. Running 21.7" tires with 3.9 gears will probably result in considerably lower rpm than 7800 down the back straight. Maybe that works for you though.
 
Joe,

I returned on Monday after a five day invitational vintage sports car event (VSCDA) at the Indianapolis Motor Speedway, as part of the crew for my friend and his 1963 Turner roadster (1200 pounds), which has a non-crossflow 1500 cc Ford engine. This engine might be similar to yours? ( 700 cars were at this event. )

The front straight section was used for both the road course events and also for the full 2.5 mile oval "exhibition".

With 22" tires, 4.22 gearing, top speed was at 7500 rpm, which calculates to 116 mph. Dyno sheets show about 140 hp.

Charlie T.
 
Thanks Charlie, The Sabra that was there is the e car I am working on. he is running the 185x13 hoosier and indicated he was pulling 7800 on that track.
 
Joe, if you can get 7800rpm out of a Ford 204E, which is the engine that came in all the Sabras, my hat is off to you. Six port cylinder head with one of the worst intake runner system I have ever seen. Yes, it is over square, but the tractor like three main crank would not be up to the task. The stock ZF gear box is sweet though. Can't say the same for the differential.
 
Not the factory engine, It has been replaced with a 1500 pre-crossflow ford and a lotus 3rail gearbox, Engine done by Tony Ingram and I did some set up and prep work. Good customer and friend so just trying to make sure he has a great time his first trip to Ohio.
 
The C/R 2000e trans has the same ratios as the ZF. Must have changed the rear axle housing as well. The only ratio that came in the Sabra is 3.55. And it is a very weak piece.
 
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