Rear end gear ratio and OHV

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Model T Ford Forum: Forum 2017: Rear end gear ratio and OHV
Top of pagePrevious messageNext messageBottom of page Link to this message  By Alex Dragone on Wednesday, February 15, 2017 - 08:06 pm:

I know this has been a topic that has been talked about quite a bit in the past, but I would like to revisit the topic since I am currently rebuilding my rearend. The car is a roadster and has a rebuilt stock engine with a roof 8 valve head. Should I put the 3:1 gears or the stock gears in the rear. Any advise or experience would really be appreciated. Thanks!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould, Folsom, CA on Wednesday, February 15, 2017 - 08:42 pm:

My vote is definitely for going with the 3.63 to 1 gears. Enhanced HP (if the Roof head actually gives you an increase) does not equate with a higher RE ratio. You MIGHT get away with 3 to 1
if you have a very light speedster, but not a roadster. That's my two cents.


Top of pagePrevious messageNext messageBottom of page Link to this message  By tim moore, "Island City" MI on Wednesday, February 15, 2017 - 08:46 pm:

I did a 3:1 in a 2 speed rear end with a Fronty and regret it. Yes the Ruxtell is great but with the additional power and speed of the overhead the top speed of the car is too much in 3:1. It isn't so much as how fast you can go but how soon you can get there (and then stop).

Your Roof head will allow fast acceleration and you will like it but in 3:1 you will just go way too fast to be safe. In my opinion the only time to use 3:1 is in flat country with a stock motor with lots of room ahead.

I will never put in a 3:1 again in anything and with overheads will actually go with smaller pinion gears. Getting out of the way is more important than going fast slowly.

Tim Moore


Top of pagePrevious messageNext messageBottom of page Link to this message  By Walt Berdan, Bellevue, WA on Wednesday, February 15, 2017 - 08:58 pm:

Do you have a Ruckstell or aux transmission? Either of these greatly expand the rear axle ratio options. Warmed up motor folks often like a 12 tooth or possibly even 13 tooth pinion with a Ruckstell. 10, 11, 12, or even 13 tooth pinions with a Warford or similar are options depending on the engine options and terrain you drive. I happen to like a 10 tooth pinion married with my Chicago trans on my Fronty powered speedster. Then again I like mountains too. In flatter country I'd probably run stock rear gears with my aux trans.

The overall engine package for cam, carb, exhaust . . . Matters too of course.

Without a Ruckstell or aux transmission I'd consider the following.
How fast do you want to cruise? If you like to cruise at 30 to maybe 45 or so, stay with stock gears and be happy that you won't be slowing down much if at all on the hills. Want to cruise 40 to 50+? Pick the 12 tooth pinion and be happy in most cases. The 13 tooth pinion would be OK for mostly flat areas but probably disappointing in hilly areas without a Ruckstell.

Naturally, more variables and expectations so YMMV.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alex Dragone on Wednesday, February 15, 2017 - 09:19 pm:

The car has the roof 8 valve which has it's own exhaust manifold which connects to the stock Ford exhaust pipe. The carb is much a much larger than stock sidedraft. No auxiliary trans or Ruckstell. It has a stock cam, stock crankshaft with aluminum Pistons. Has a high tension mag (Bosch DU4). Engine is all freshly rebuilt. With just the stock transmission and these upgrades do the 3:1 gears really give speed? It seems like almost everyone regrets the 3:1 gears no matter what they do. I just don't want to be pushing the engine to the point where it sounds like it's going to explode. It seems like even with upgrades people really dislike the 3:1's. After all the point of OHV and speed equipment is to go faster. Thanks for the great comments so far. Anyone else have any experience with these 3:1 gears?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alex Dragone on Wednesday, February 15, 2017 - 09:28 pm:

This is the setup I have on my car:

http://www.nwvs.org/Technical/Engines/RoofE131.shtml


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett in Auburn Ca. on Wednesday, February 15, 2017 - 09:34 pm:

Overheads live for higher RPMs because they flow better. Use the stock ratio to take advantage of this. Without a Ruckstell you really don't want 3:1 gears in any model T.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Wednesday, February 15, 2017 - 10:21 pm:

Perhaps consider a 12 tooth pinion. With a 39 tooth crown you get 3.25-1. But definitely I would have a Ruckstell as well


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Wednesday, February 15, 2017 - 10:22 pm:

Without the Ruckstell stay with the stock gears


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alex Dragone on Wednesday, February 15, 2017 - 10:31 pm:

Ok looks like the consensus is to stay with stock gears, so that's what I'm doing, staying with stock gears. Thanks everyone for the help. I should have the car on the road in the next week or so so I will let everyone know how it goes eight the stock gears.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chadwick Azevedo on Thursday, February 16, 2017 - 12:46 am:

Why hasn't anybody asked what type of roads he is planning on driving on? To me where you are driving plays a big part.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth in Alabama on Thursday, February 16, 2017 - 01:10 am:

I have 3:1s in a Ruckstell with a Chicago auxiliary. I have a Rajo 4 valve with domed pistons and dual carbs and dual exhaust. I love it. It plenty hilly here. I can do anything from pull stumps to crawl or sprint up a hill to happily cruise at 65 mph.

Edit to add: probably the only negative I can come up with for the setup is that the engine braking isn't quite as good as it used to be with 3.64s. If you know the road you're on and shift ahead of time it's easy. But sometimes it can be awkward when you start going downhill and really need to downshift but you're already picking up speed. I always try to do as little regular braking as possible do 95% of my speed control with the engine.

I can definitely say that having driven my speedster this way I wouldn't change it back.

(Message edited by Wreckrod9 on February 16, 2017)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Bennett - Australia on Thursday, February 16, 2017 - 05:32 am:

Seth has a very good point.I would go a little further than "engine braking isn't quite as good". I found the engine braking to be severely compromised on my speedster with the 3:1 gearset.

When I built my roadster I fitted the 39 tooth crown wheel and a 12 tooth pinion to get a 3.25:1 ratio. It gives me longer legs, the Ruckstel still lets me climb well, and the brakes are almost adequate.

Allan from down under.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Barker - Dayton, OH on Thursday, February 16, 2017 - 09:15 am:

Alex - The set-up on my Speedster isn't very different from yours. I have a Rajo 8-valve head (model 30) and a Stromberg RF carb. Stock cam and crank, aluminum pistons, no aux tranny, and a Texas T parts distributor. Stock brakes as well (lined rear shoes and cotton lined transmission bands). Rear-end is stock 3.63 ratio. Weight (empty) is about 1,300 pounds.

I live in southwestern Ohio, and have some hills to drive on. Driving alone, I've had her on the highway driving at 65 a few times, with plenty of throttle left (had to back-off due to some wheel wobble). She runs great at 35 - 50 on most normal roads around here, and I have plenty of engine braking available, and I've found no significant need for auxiliary brakes (yet). I rarely use the handbrake for regular stopping.

It's a bit of a different story when on tours with other Model Ts; I've often found I've had to hold her back a bit when driving curvy backroads, as cars in front of me have to slow down so much. When approaching hills, many cars I tour with will need to engage low, whereas I could easily take them in high, but get slowed down to low by the other cars. I'm typically the only Speedster on our tours, so I drive along with the rest of the group, though I could easily leave them in the dust if I wanted to.

I've also considered 3:1 gears in the past, but I suspect (as others have commented) that without the aux tranny, the 3:1 would be more limiting, and not be as pleasant a driving experience for me and the roads I drive on. If I were to want to drive primarily on highways (which I don't), 3:1 gears may make more sense.

For me, at this point, the stock gears make the most sense. I can get my high-speed jones satisfied when needed, but can also tour along with others at their pace without any significant drawbacks.

Hope this helps a bit. Good luck.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alex Dragone on Thursday, February 16, 2017 - 12:06 pm:

Dave, That post is the best one yet. Thanks very much for that. It definitely does help me stick with the stock gear ratio.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chadwick Azevedo on Thursday, February 16, 2017 - 12:10 pm:

As mentioned, where you want to drive/how you drive may have everything to do with it. I would think very hard about 3:1 with no aux tranny. With some form of underdrive to me its almost a no brainer due to the pace modern traffic moves at.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Thursday, February 16, 2017 - 01:27 pm:

As others have written, it has everything to do with the kind of roads you're going to drive it - and with whom you're driving.
I haven't got any other T'ers close by, so no need to adjust speed to others than the moderns, though they'll pass regardless how fast I dare to drive.. But still, I love the 3:1 without accessory transmission in my primitive pickup. It's rather strong in the mid rpm register due to a 7.5 degree advanced cam shaft and a Prus head.

My runabout has std gears with an accessory Jumbo Giant transmission, thus I have an overdrive that results in about 2.77:1 final drive in third and regular 3.64:1 in second. Should work just fine with a '28 Chevy head and accessory outside brakes - when everything finally comes together :-)


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