3.73 gears in 700R4 ?

[TomsResto]

So I know the whole "what RPM" will I be turning question is a complicated one with several contributing factors ... I now have a 275/40ZR19 rear tire behind a Ramjet 350 (350HP, 390TQ) and 700R4 with 3.41's in a GM 10 bolt.

RPM's are really low at cruising speeds (1750RPM at 60mph) and she'll bark a quick patch on dead stop before hooking up (nearly 11" strip of contact patch on each wheel now on Michelin Pilot Super Sport 300 treadwear) but I'm considering going to 3.73's to have a little more "throw you back in your seat fun" when I get on it ... but dealing with the age old "but how much more R's will I turn when I get out on 2 lane highways, etc." issue as this car is a cruiser before racer (and this time of year with fall colors intend to be doing quite a bit of road trip cruising)

I know the 700R4 has a tall "overdrive" 4th gear but I haven't yet come across an online "calculator" where I can throw my current setup in and see the result that matches what I see on my tach to have confidence if I leave everything the same and change the rear end ratio to see my new 60mph rpm. Does such a calculator exist and I'm just missing it? ... is it affected by GVWR?

Does anyone out here by strange chance have almost same/comparable config with 3.73's that can share what they are turning at highway RPM's?

Thanks,
Tom

[williecutlass]

I use to run a 383 with a 700r4 and 4:11 gears and it ran about 2500 rpm @ 55. That was with a 275 60 15 . I had switched over to a 3:73 for awhile but I don't remember the R's it was running. I ended up switching back to the 4:11's.

[silo84]

3.73 with 700R with 27.7" rear tire will net you 69.4 MPH @ 2200 rpm (60 MPH = 1900RPM)

[kevvingib]

I believe the calc at the bottom of this page will provide what you are looking for as long as you know the final drive in the 700R4

http://www.csgnetwork.com/multirpmcalc.html

[TomsResto]

3.73 with 700R with 27.7" rear tire will net you 69.4 MPH @ 2200 rpm (60 MPH = 1900RPM)

Holy cow, down to the tenth of a mph... did you run that through a calculator somewhere or people call you Rain Man ;) ?

[TomsResto]

Holy cow, down to the tenth of a mph... did you run that through a calculator somewhere or people call you Rain Man ;) ?

But seriously... thank you ... that sounds likely given where I'm at with current config

[TomsResto]

I believe the calc at the bottom of this page will provide what you are looking for as long as you know the final drive in the 700R4

http://www.csgnetwork.com/multirpmcalc.html

It looks like final drive on the 700r4 is 0.70 , when I punch in that with 27.7" rear tire it comes up a little under 1600rpm, which seems a little low for what I see running 55mph

However, that does help... if I punch in 3.73 then it calcs 1742 , so only an increase of ~250rpm at 55mph ... 2217rpm at 70mph

I'll find a flat stretch of 2 lane this weekend and jot down what rpm's I'm reading at 55mph and 70 today, and pay attention to exhaust note at the different RPM levels to give myself an idea of what it would be like

Thanks for the link!

[Kenova]

Here is the calculator that I like to use: https://weddleindustries.com/gear-calculator
It has a brain fart if you only put ratios in for a three speed so I just put in 1:1 for third and fourth.
I have spent wayyyy too much time playing with it.LOL

Ken

[Motown 454]

Nice calculator. Thanks.

[TomsResto]

For what it's worth, at the same time I was asking out here I also came across a vendor that had specific references to 700R4's on their website and so I used the "contact us" form asking the question. They replied with the same values that silo84 identified and that the online calculators ... with that much consistency I feel pretty confident that's my answer.

===============================================

Hi Tom;

60 mph = 1903 rpm
70 mph = 2200 rpm

Thank You;

Rich Weller
Bowtie Overdrives
760-947-5240

[1BADBET]

Are you running a lock up converter?

[silo84]

Looks like I was pretty close, I have an excel file that I made in college for calculating CVT and final drive ratios for SAE Mini Baja, I have since converted it to have most GM transmissions loaded and ready.

[TomsResto]

Are you running a lock up converter?

Not as separate lock up switch or anything ... do have a B&M hammer shifter though that doesn't control launch/engagement but can hold it in lower gear/out of overdrive 4th

Why do you ask?

- - - Updated - - -

Looks like I was pretty close, I have an excel file that I made in college for calculating CVT and final drive ratios for SAE Mini Baja, I have since converted it to have most GM transmissions loaded and ready.

nice work

[1BADBET]

I was just trying to figure out if the gear/ rpm calculators account for converter slippage or if they assume full lock up. From the looks of your real world data, assuming the 1750rpm @ 60 figure is in 4th with the converter locked, the calculators don't account for slippage. I'm running a 700R with a gear vendors and a 5.14, I know the rpm drops when the converter locks up I just wasn't sure if it would drop below the calculated RPM or to it.



Ps changing the rear gear is going to drop converter stall speed a little, if that matters to ya.