Switching from a 4.10 to 3.55

Hey guys - Since my racing opportunities are few and far between, I decided to pull the 4.10 out and just purchased a new 3.55 3rd member from Dr Diff. I still want to race every now and then and prepared for the 60fts to suffer. For those of you who have made a similar change in favor of better street manners, what was your real world drop off in ET? Havnt raced it with the new engine, so I wont know the difference...I actually gave some thought to 3.23's. I think I'm getting old.

My 67 dodge coronet went 11:40 with a 4.10 28" tall radials, went to the 3.55 went out with the same tires, ran a best of 11:58. The 60 ft dropped almost a tenth. But for street driving it was a god send.. I did later switch to a 26 in tire and got some of it back. IIRC it went 11:47. I would have to dig out my log book to be sure though. Good luck.. Have fun

"But for street driving it was a god send." This is what im hoping for!

Thanks for sharing your ets. I figured there would be a drop off. Not horrible

Tony I run a 3.23 in my Duster, it's the steepest gear I can handle on the highway. I run a 28" radial street tire on the street and I'm gonna try a 26" slick if I ever get it to a track. With a stroker motor and fairly loose converter the car feels like it has a 4.10 in it.

There's some good info here.....

https://board.moparts.org/ubbthreads/ubbt...-3-55-gear.html

The 505 in my '63 loves the 3.54 gear!

No way I'd run a deeper gear...

Try a low first gear in the tranny ?

I suppose it depends on how hot the combo is. Years ago there was a thread about 4.10 to 3.23's I thought for 'warm' 440's, and I even thought GY3 was one of the people who replied and said not much difference in ET. Theory being a 'warm' cam and still stock(ish) heads on a 440 don't change the torque curve enough that the 4.10's were ever really needed.

Good memory!

I did test a very mild smallblock powered '71 Cuda back in the late 90's going from 3.23's to 4.56's. Car e.t.'d virtually the same.

I've never done it with a 440, though, as I never felt a torquey street motor needed anything deeper than 3.55's.

I agree that there will definitely be some combos that need more gear than others. My engine is a 520 with good torque all the way around. Cam is a pretty mild 252@.050 hydraulic roller, and I have a 9 1/2" converter and 28" tire. It is a heavy car though at just over 4000 w me in it.

FWIW, back in the 12s (ETs, not years), the difference I saw between 3.55 and 4.10 was .2 in ET with no change in MPH.

Based on the details, the memory was actually incredibly foggy! Seems like a 520 should have plenty of pull to not feel it and/or move to 26" tires for the track like others mention.

If you have a non race suspension to begin with and running a street tire, the tire is your limiting factor, so I would guess you would give up .1 to .2. If you have a street suspension and you are going to throw on some sticky tires, probably .2 to .3. That's my guess.

I'm thinking along similar lines with my 512" Duster; the 3.91s are pretty busy on the highway, and I need to run 65-70 for almost an hour to the nearest track. All the while, I'm thinking about how long the stroke is and a 505" Challenger I know that runs 11.50s with 3.23s and the same 28" diameter street tire. That's good enough for this car, as I already have a high-strung 10-sec SB car...

Hopefully in a couple months I can report back with some results with my 3.23's in my Duster. I didn't care for the 3.55's on the highway but the 3.23's are livable. I'm around 2600 on the highway with a 27.5" tall tire.

At over 4000 pounds the 3.55's will probably be the best choice for you Tony.

That's what I'm hoping for, Bob. Thanks

I am curious to see what it does. I have heard of guys with 500 strokers dropping from 4.10's to like 3.55's and going just as fast. I honestly think my 63 may go faster if I drop a little gear. I think I am above my peak torque at the traps and have been thinking of dropping my 4.30's to about 3.91's. But I do run a 30" tall tire. You may not loose much if any Tony. Keep us posted on how it goes because I want to know. Ron

I run a 3.55 now, but I am looking to swap in a 4.10 to be able to run on a 11.50 index. From what I recall it was 0.1-0.2 quicker with the 4.10. 493" with 9.5" converter, 28" tire

What axle? I've got a 8.75" with a 489 case, SG 4.10 that I'd like to go back to 3.55. You open to the idea of trading?

Sorry Mark, not looking to trade at the moment. I have a 4.10 spool pumpkin ready to go with aftermarket axles. I'm sure I'll get tired of the 4.10's and go back to the 3.55's anyway. I drive on the street too much

I'll keep you posted, Ron. Like I said, I wont have a comparison because I havnt raced the new engine yet. I do plan on racing at some point this year, and I'll be sure to post times. I know the 3.55's will certainly make my drive to and from the track more enjoyable

Not apples to apples but, I made the switch from 4.10's to 3.73's and went from 12.38 to 12.25; at the same time, I re-curved the distributor though. No other changes were made.

I have a 470. I really think with the torque, it doesn't matter that much.

Here is the 3.55 third member as received from Dr Diff. It used to be fun locating all the parts and then getting it set up...or I can just call Dr Diff and get this. I like option 2 now!

Pic two

Is this the nodular case?

Yes