3.54 vs 3.25

flathead 39

flathead 39

Member
Currently constantly looking for another gear when driving my 3.78. I'm sure I have enough power for the 3.25, but will have to use 1st & 2nd gear a bit more.?? Any advice appreciated.
 
What top speed are you wanting?

4:11 in my '36 Phaeton, the engine screamed at me over 55. Switch to 3:78 and the same configuration is ok to 70.

So where is the 3:78 letting you down?
 
VeryTangled said:
What top speed are you wanting?
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I can't answer that for him, but his speedo does go to 140 mph! DD


458714
 
VeryTangled said:
What top speed are you wanting?

4:11 in my '36 Phaeton, the engine screamed at me over 55. Switch to 3:78 and the same configuration is ok to 70.

So where is the 3:78 letting you down?
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Gas mileage, noise, & the feeling that there needs to be another gear. I drive her a lot.
 
The 3.25 will lower your RPMs at 55mph to 2145. I think it will take it to make a significant difference. Then you might have difficulty getting rolling. That can be helped with pick-up transmission gearing. One thing leads to another.
 
I shoul have made it more clear. I don't like the 378. Some have gone to the 354 and are quite happy. I'm wondering what' wrong with the 325.?
 
JM35Sedan posts about his car with 3.54’s. He does a lot of long trips. I don’t know what he runs for tires. Maybe try a PM. Real good guy and if he has info to help, I’m sure he’ll share it....... Mark
 
I run 3.54s with 7.50:16s on my roadster. I think with the 235-70-15s you'd be ok with the 3.25s.
If you found it difficult to pull away you could always pair the 3.25s with a 15/29 gearset to lower the first gear.

Edit: You could try some taller tyres. I ran L78s on my 40 with 3.78s and it was ok.
 
40cpe said:
The 3.25 will lower your RPMs at 55mph to 2145. I think it will take it to make a significant difference. Then you might have difficulty getting rolling. That can be helped with pick-up transmission gearing. One thing leads to another.
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I shouldn't have any trouble getting rolling in 1st gear, It's almost worthless now.. with the 378 it' like a very close ratio xmission. I like using the gear shift & will like it even more when I get more proficient at double clutching.
 
How much motor do you have and any towing or major hills to deal with ? Ive got a 41 tudor with 378 and have been working on a 354 dif this week . I too have been thinking about changing . 378s down here in Florida are decent but always looking for more also .
 
Here's a link to a calculator that I used a lot to figure out my gearing/speed/rpm. You'll need your tire diameter as one of the factors. My 40 Fordor came with a 4.11, talk about screaming at 55, that lead me to buy a Mitchell OD, ends up an equivalent of a 3.10 +/-
I don’t think the 3.54 would make enough difference for you but the 3.25 would. Others with a 3.25 will know.
http://www.advanced-ev.com/Calculators/TireSize/
 
Ggmac said:
How much motor do you have and any towing or major hills to deal with ? Ive got a 41 tudor with 378 and have been working on a 354 dif this week . I too have been thinking about changing . 378s down here in Florida are decent but always looking for more also .
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Got enough motor, built 8ba, 284 cu in, cam, 2 94s properly tuned, offy heads.etc. I do live in the mountains & the 3.78s Has no problem pulling 6% grades with little effort, so the 3.54s would be fine. might have to downshift occasionally with a 3.25.
 
HDowse said:
Here's a link to a calculator that I used a lot to figure out my gearing/speed/rpm. You'll need your tire diameter as one of the factors. My 40 Fordor came with a 4.11, talk about screaming at 55, that lead me to buy a Mitchell OD, ends up an equivalent of a 3.10 +/-
I don’t think the 3.54 would make enough difference for you but the 3.25 would. Others with a 3.25 will know.
http://www.advanced-ev.com/Calculators/TireSize/
Click to expand...


Thanks, I used that & charted all 3 ratios from 25mph to 70mph. Yea I was hoping to hear from a 3.25 user two.
 
39,
When you mentioned 1st gear for you is almost worthless made me wonder if you already had the 15/29 first gear in the trans now. Obviously third is still one to one
so high gear on the road won't change. The motors in my '32 and '41 pickups are near
what you are running and first gear for me is very worth while ,both trans have the 16/28 gear set.
The cam in my '32 makes power above 3000 rpm and the drivability went to hell when I changed to 3:78's from 4:11. Something to keep in mind as the rear gets taller.
I do have a Columbia with 3:78's in the '41 and in OD I think the ratio drops to 3:22
or somewhere close. The Max 1 cam has no problem motivating in OD.
Charlie ny
 
Charlie ny said:
39,
When you mentioned 1st gear for you is almost worthless made me wonder if you already had the 15/29 first gear in the trans now. Obviously third is still one to one
so high gear on the road won't change. The motors in my '32 and '41 pickups are near
what you are running and first gear for me is very worth while ,both trans have the 16/28 gear set.
The cam in my '32 makes power above 3000 rpm and the drivability went to hell when I changed to 3:78's from 4:11. Something to keep in mind as the rear gets taller.
I do have a Columbia with 3:78's in the '41 and in OD I think the ratio drops to 3:22
or somewhere close. The Max 1 cam has no problem motivating in OD.
Charlie ny
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I have a Schneider cam but don't know the #. It seems to have lots torque from very low rpm until I shut it down, probably around 3000 rpm (abt 70 mph). I'm pretty sure my trans will be ok with a 3.25.
 
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