3.25 Gear Experience ?

hotrodalley

hotrodalley

Senior Member
I am considering a 3.25 rear gear for my hi-boy roadster. I am running a mildly hopped up "A" engine, and Mitchell's Synchro Transmission with 15% higher 2nd gear. With an engine that develops horsepower at about 2500 rpm, an overdrive would drop rpm's below the hp curve. That is the objective of the high rear gear. I would appreciate any validation or experiences. thanks
 
You might also try posting this question on the HAMB, they have a "banger" group over there. Some one here will probably chime in also, many run the mitchell but don't remember mentioning of a 3.25, 3.54 yes.
Paul in CT
 
You may want to consider a 4:11 rear with an overdrive to get the best of both worlds.

The price of 3:27 gears are pretty pricy and you can probably find 4:11 gears in the swap section pretty reasonable

Richard
Anaheim CA
 
Yep, it works well IF the proper cam is selected. The key is you are not going to 'get it done' with a typical reground camshaft as it takes torque to pull that gear. BTW, a fully restored '30 Tudor is the heaviest car I have ever tried that ratio with.

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I am running 4:11 gears with a Mitchel OD and Syncro on a car similar to your car. Generally there is no problems running in OD (about 3.1) with no problems.

I don't think it would work as well with a fully weighted Model A.
 
I have 31 stock body tudor. running gear is updated inserted engine, web carb, cam, elct ign, 5.9 brum head, 3.27 gear, 26% mitchell, stock trans, 65 hp @ 2900 rpm and on hiway runs 93 mph. no,headers there stock . This has also been on dyno. rpm at 60 mph in overdrive 1810 on road. Has been all over also in great race runs very good have fun modelAtony, lafayette,la
 
hotrodalley said:
I am considering a 3.25 rear gear for my hi-boy roadster. I am running a mildly hopped up "A" engine, and Mitchell's Synchro Transmission with 15% higher 2nd gear. With an engine that develops horsepower at about 2500 rpm, an overdrive would drop rpm's below the hp curve. That is the objective of the high rear gear. I would appreciate any validation or experiences. thanks
Click to expand...

It looks to me that yiou have enough torque so I think a 3.25 would work well. What size rear tires are you running?

My opinion,

Chris
 
Re: 3.27 Gear Experience ?

When I bought my '31 roadster in '76 it had a Model B engine and trans with a big B police head. It also had large intake valves with a factory B cam. Coming out of an estate, all that I knew was the B engine. My '31 town sedan was my drive at the time and was pretty much used to the feel of driving an A and didn't notice anything unusual about the roadster's road manners, expecting some performance from the much lighter car. I did a complete tear down of the roadster and foung the rear gears to be 3.27s and was not familiar with that ratio. Completely unexpected but seemingly normal because of the weight difference. Years later i put a sedan body on the roadster chassis to sell as a car. That combination was still OK but not as natural a match as with a roadster body. For my own use and budget, a 3.78 and a Mitchell would get the vote. Too much high gearing will lug a banger and shorten its life. Many non believers out there with some pretty wild numbers but that is for their car and will impress the rookies when they have worn out the clutches and pounded the center main, offering for sale.. Good Luck: Fred A
 
Jus' curious, ...."what" pounds out the center main in lugging?


I am of the opinion that it is detonation however that generally affects the rods more than a main bearing. Therefore I believe pounding out a center main is caused by incorrectly ground crankshafts (whipping) ...and too many shims under a cap allowing the cap to walk.

Since this individual is already using a Mitchell syncromesh transmission, I am of the opinion he already has the capability of shifting with more frequency (ease of downshifts), AND already has 1st & 2nd gear ratios more suited to downshifting to avoid any lugging. The only thing he has not chimed in on is the camshaft he is using. It may be that he either needs to advance the camshaft a few degrees to bring in the torque band a little earlier, or switch to a camshaft that already has a torque band in lower RPMs.

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I ran a set of 3.27's in my speedster for awhile, there were fine on the highway but didn't like getting away from a stop light with them. I replaced them with a quick change but 4.11's and an overdrive give you the best of all.
 
Hey Jim, which one of your cams were you using at the time?

Do you think if you would have used another one of your different profiles you would have liked the performance better??


(Something about using the words Hillclimber and 3.27 gear ratio together just doesn't sound right!!
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I have a B diamond, Lion Head, T5 and running 3:54s in the rear end with 600X16 radials. While in florida, she was a real runner and many times the speedo was as far as it could read, on insterstate 75 and still was not lacking for power. Then I brought her to St.Thomas, and the mountains killed her, ALMOST. The rods were noisy and upon inspection, I found the rod caps beautiful while the rods had lost most of the babbit from climming the hills in 1st and 2nd. The crank has since been drilled for pressure, but not running yet. If I had left the ratio at 3:78 she would probably still be running, cause the engine was really strong but definatly miss matched for our hills. (My 3 cents) Iceman
 
Hey guys thanks for the great input. More specs on my engine
.060 Over Bore
.010 Over Mains
.020Over Rods
High Volume Oil Pump
3/4 Winfield Grind Cam
Aluminum Timing Gear
Thomas Finned Aluminum Head 7:1 Compression
v-8 Clutch and Pressure Plate
Lightened Flywheel
Dual Stromberg 81's
 
IMHO, a "¾ cam" will not get the job done for this application without some real effort such as removing some timing, using premium gas, and making sure you stay in the power band. Bill Stipe's IB 340 would be the proper choice in my opinion you will see the same amount of power yet an increase in torque.

Iceman, I am pretty sure what you found in the rods was a prime case of severe detonation, --which the Lion head's combustion chamber is a strong promoter of that.

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Brent, too much cam, 280 degrees/.350" lift. A milder cam might help but it is still a tall gear to pull away from a stop with. That same cam, with 3.04's in the QC gets 24 or better on the highway!
 
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