Gears 3:55 vs. 3:73

[HYRDGOON]

Hi Everyone,

I did a search and found some good info but wanted to re-open the discussion and hear some real world experience as I have recently been looking at a lot of cam options for my 383 and thought I might want to change the gears first.... see if it's more what I'm looking for then cam appropriately with those gears... essentially looking at the 3:55 or the 3:73 (not a stock mopar option I know but available)

The car sees some highway so may see cruising speeds of 75mph (120kph) but most driving is done around town or short trips on country roads.

current set up 69 Roadrunner

383 (9:06 heads, headers, Holley Street Avenger 670cfm, edelbrock performer intake going on this week)
4 spd
3:23 gears
tires are 26" tall (nitto NT555 - 285's out back)


I would definitely like a bit more low end grunt and once gears are done cam selection will begin again

On a complete side note looking forward to seeing how it behaves with the new intake and carb actually set up... the guy I purchased the car off of told me he took the holley out of the box and onto the car and it's run great for the 4 years I've had it so it's never been played with.... will be interesting to see if I can squeeze a bit more out and get rid of some flat spots

Thanks in advance for your help and opinions!

 

[62 Dart Convertible]

Subscribed. I have a 3.23 SG and have been considering the same options....

 

[eric383]

Here is a link to a calculator.
http://www.ringpinion.com/calculators/calc_rpm.aspx

 

[Seax440Dodge]

whichever you do, make sure you do your homework.. I went from 3.23's to 4.10's and HATE IT would MUCH rather have 3.55's

 

[451Mopar]

With the 26" tall tires, I would choose the 3.55:1 gears.
I have had two street avenger carbs, and the idle restrictions in the metering block were a bit small for my engines. Making them slightly larger really helped the off-idle transition. The power valve restrictions are also on the small side.
I experimented with a Quick Fuel metering block that has the screw-in restrictions, then just used a pin drill to open the stock metering block restrictions to the same size.

 

[ilm65]

When I assembled my Satellite, I specifically went with a Dana just so I could run 3:73 gears--was sure this was the right move. But on the freeway, I was cruising at 65 mph at about 3300 RPM. It was just too much and I switched to 3:54's. WOW--what a great difference. I'm now able to cruise at 70 mph at 2800 to 2900 RPM. I still have huge grunt out of the chute!

 

[Meep-Meep]

It all hinges on the cam. Whatever cam you chose will have a particular RPM range that will require the rest of the car to follow suit. I tend to tune for optimum 1/4 mile performance or close to it only because that is a bench mark to shoot for and easy to check results at the local track. If road racing then test on a road course, etc..

I have tried 4.30, 4.10 and 3.55 in my 66 Bel with a mild 440 and seems to like 3.55's the best. But for more street driving I would have 3.23's or even 2.94's at the expense of a 60' time. This does not mean that a high overlap cam with a 9" converter will be happy with 2.94's. You need to plan the entire build properly then fine tune for optimum performance within your desired driving style.

 

[Cranky]

You'll be making about a 7% change in gear ratio. Why not try a set of rear tires that have about 7% less roll out to get an idea if you'll like the 3.73's or not? I had a pair of 24" tall tires for my Dakota to see if I'd like a set of 4.30's and with OD, it's great and with the 10.50-31's I normally run on it, the 4.30's would be just the ticket!

 

[Ghosty]

It all hinges on the cam. Whatever cam you chose will have a particular RPM range that will require the rest of the car to follow suit. I tend to tune for optimum 1/4 mile performance or close to it only because that is a bench mark to shoot for and easy to check results at the local track. If road racing then test on a road course, etc..

I have tried 4.30, 4.10 and 3.55 in my 66 Bel with a mild 440 and seems to like 3.55's the best. But for more street driving I would have 3.23's or even 2.94's at the expense of a 60' time. This does not mean that a high overlap cam with a 9" converter will be happy with 2.94's. You need to plan the entire build properly then fine tune for optimum performance within your desired driving style.

Sounds like great advice, thanks & noted.

 

[UKPlymouth]

All other things being equal, I enjoyed my 3.55 gears best out of 3.91, 3.23. 2.76
Good compromise gear. You can race and have fun but still not get driven mad on the highway. Some of the Chevy guys get tired of 3.73 pretty quick due to fuel consumption and noise levels in the car., remember that from when I had a Camaro.
Guess it depends on what you want from the car.

 

[HYRDGOON]

It all hinges on the cam. Whatever cam you chose will have a particular RPM range that will require the rest of the car to follow suit. I tend to tune for optimum 1/4 mile performance or close to it only because that is a bench mark to shoot for and easy to check results at the local track. If road racing then test on a road course, etc..

I have tried 4.30, 4.10 and 3.55 in my 66 Bel with a mild 440 and seems to like 3.55's the best. But for more street driving I would have 3.23's or even 2.94's at the expense of a 60' time. This does not mean that a high overlap cam with a 9" converter will be happy with 2.94's. You need to plan the entire build properly then fine tune for optimum performance within your desired driving style.

Thanks to everyone so far for their replies and interest... looks like a few people debating the same switch out.

Meep I'm trying to work backwards from what you suggested here... I figured change the gears and see if it performs closer to what I'm looking for then select a cam to make up where I feel that drivability may be lacking... I know cam selection involves the drivetrain choices so why not select my gears which (essentially) should be an easier choice (there's sure as hell less options!!) then match the cam up to my final decision?

 

[67 coronet]

when starting with an assembled running vehicle you need to begin with fine tuning you motor for power before you tackle gearing and such.start by making sure you are getting all the power you want from the motor before you touch the gearing.swapping gears is like tricking your motor to feel more powerful by doing it first.if you build enough power to begin with,you may not need to change gears.by doing the gears first,you are working backwards.

 

[HYRDGOON]

when starting with an assembled running vehicle you need to begin with fine tuning you motor for power before you tackle gearing and such.start by making sure you are getting all the power you want from the motor before you touch the gearing.swapping gears is like tricking your motor to feel more powerful by doing it first.if you build enough power to begin with,you may not need to change gears.by doing the gears first,you are working backwards.

Thanks! I guess I got ahead of myself by thinking that if gears are necessary for the equation in cam selection then why not select a set of gears that would work better for how I drive the car first.

 

[Cranky]

Thanks! I guess I got ahead of myself by thinking that if gears are necessary for the equation in cam selection then why not select a set of gears that would work better for how I drive the car first.

Imo, a 3.73 will make a difference in just about any car with a mild engine. Heck, it'll even make an engine with a stock cam wake up. I've run lots of engines that were stock long block but had headers, intake and a better carb with everything from 3.55's to 4.56's! Yeah, a wilder engine will make better use of the 4.56's but it still hauled *** in the 1/8 mile. Anyways, that's why I mentioned a tire change. Shorter tires will affect gearing just like a gear change does only it's a lot easier to do and if you don't like it, all you have to do is take them off and for the test, you might can borrow a pair....

 

[Bee383]

i just changed my 69 bee from 3:23 to 3:73.383 mild build,auto.not sure on cam.28 inch tires.i also had a hard time making up my mind between 3:55 or 3:73.really happy so far.good feel from the throttle response.about 3000 rpm at 70.used the yukon gears and a truetrac unit.a little noisier on the highway but not too bad

 

[Kern Dog]

I have a 3.91 set in the Charger. 27" tall 295-45-18 tire. I've tried several ratios. Here is my take.
4.10: A blast out of the hole. Great ratio if you never plan to go on road trips.
3.91: Pretty much the same as above.
3.23: Not too bad for the combination, but this gearset was an open carrier, so I avoided any full throttle starts due to inadequate traction.
2.76: Woefully inadequate. Made my 3000 stall converter feel like a 5000.
Here is where things differ...USE a Gear Vendors overdrive unit. I currently have the 3.91 gears in the car with the GV. One of the features mine has is the ability to keep it in OD all the time. The .78 OD ratio turns the 3.91 into a 3.05. It feels pretty soft leaving the line in OD though! Freeway RPMs are nice in OD. It is expensive, but I bought mine used from a Mopar guy that switched to a 5 speed manual.

 

[HYRDGOON]

I have a 3.91 set in the Charger. 27" tall 295-45-18 tire. I've tried several ratios. Here is my take.
4.10: A blast out of the hole. Great ratio if you never plan to go on road trips.
3.91: Pretty much the same as above.
3.23: Not too bad for the combination, but this gearset was an open carrier, so I avoided any full throttle starts due to inadequate traction.
2.76: Woefully inadequate. Made my 3000 stall converter feel like a 5000.
Here is where things differ...USE a Gear Vendors overdrive unit. I currently have the 3.91 gears in the car with the GV. One of the features mine has is the ability to keep it in OD all the time. The .78 OD ratio turns the 3.91 into a 3.05. It feels pretty soft leaving the line in OD though! Freeway RPMs are nice in OD. It is expensive, but I bought mine used from a Mopar guy that switched to a 5 speed manual.

Thanks Gregory,

I'm a 4spd so the GV isn't really an option for me.

 

[747mopar]

Glad to see you are looking at the whole package, smart move. First performance car I built had a 3,500 converter and 3.89's "I hated it" it was an absolute blast in town but that was it. This time around I went with more cubes, tamer motor, 2,500 stall and 3.55's. Overdrive is the answer, I believe Passon offers a 5 speed that uses the same case as the 4 speeds, I'm sure someone will chime in and correct me if wrong. I will be upgrading to a T56 6 speed once the finances allow, then I'll be switching to 4.11's and still be around 2,000 on the freeway.

 

[HYRDGOON]

Glad to see you are looking at the whole package, smart move. First performance car I built had a 3,500 converter and 3.89's "I hated it" it was an absolute blast in town but that was it. This time around I went with more cubes, tamer motor, 2,500 stall and 3.55's. Overdrive is the answer, I believe Passon offers a 5 speed that uses the same case as the 4 speeds, I'm sure someone will chime in and correct me if wrong. I will be upgrading to a T56 6 speed once the finances allow, then I'll be switching to 4.11's and still be around 2,000 on the freeway.

Thanks for pointing me in the direction... might be very useful in the future. They have a 5 speed that's a direct swap in available soon

https://www.passonperformance.com/i...documents/Passon_5-Speed_Flyer_2010-11-18.pdf

 

[Mebsuta]

I have 3.91 with 4 spd and 383 RR, factory pattern cam. I use 275 60 15 tires (28 inch) in back to slow the motor down enough to drive on the interstate. 26 and 27 inch tires with 3.91 are good for going up and down the blvd but it sux on the freeway. All that noise and not really going anywhere is not very much fun.

If things were easy to change, I would try a 3.55 with a mild single pattern cam for low-mid performance. Factory motor is not going to turn much over 5000 rpm anyway so why make all your power up there?