Steves07GTCS

I've found a lot of info about various gears by reading through this forum but am yet to be able to make a concrete decision. I think a lot of people are wondering the same thing: how hard will (X) set of gears push my engine and effect MPG?

I've got a manual trans and 235/50/18's. What RPM is anyone with similar tire size seeing with 3.73's and 4.10 at 70mph and 80mph in 5th gear?

I've read some posts that some are running 2600rpm at 80mph in 5th with 4.10's; I can't imagine that's right, I'm at 2200 at 80 with 3.31's. I really want to step up my gears and would love the acceleration of 4.10's but don't want to cringe the entire time I'm on the highway. Hopefully truth can be found from the masses. If anyone is wondering the same thing, please say so, I hope I'm not the only one, but seriously doubt it. Thanks for your help, headers are coming and once I can get some solid numbers, gears are next. Thanks again!

jahudso2

With 3.73s in 5th gear at 70 mph, you will be at ~2200 rpms and at 80 mph you will be around 2500 rpms.

With 4.10s in 5th gear you would be at 2400 rpms at 70 mph and 2750 rpms at 80.

Steves07GTCS

Awesome. Now I'm not questioning you, but out of curiosity where did you get those numbers? I see you have 3.73's on your stang, have you run 4.10's before?

Fullsayl

Steve,

I run 4.10's and can verify that the above statement is correct, +/- 50RPM. I take her 60 miles a day to and from work and still get 23+ on the highway (depending on how heavy my foot is).

~Matty

Steves07GTCS

Matty,

In your opinion do you feel you're pushing the car too hard? I don't know if I'd want to cruise at 2700 RPM for any extended period of time... Thanks for the verification though, that's exactly what I'm looking for.

Steve

jahudso2

Someone on the forums created a spreadsheet that lets you put in whether you are an automatic or manual tranny, your rear end ratio, and your tire size and it tells you your speed every 1000 rpms. I opened that spreadsheet, plugged your data in, and linearly interpolated to find the engine speed at a certain vehicle speed. If you PM me your email address, I will email the spreadsheet to you so you can play around with it. What I did before I installed my gears, is I took my average cruising speed on the highway and found out what rpm that would correspond to if i had 3.73 gears instead of 3.31s. Then I drove on the highway for 20-30 minutes at that rpm. 4th worked for me, but if you are doing 4.10s, you may have to use 3rd. That will let you see how your car will sound like on long highway trips.

grampa_stang

Here you go: rename the attachment to a .xls. (it's not really a .zip..I just renamed it a .zip because of the size limitations) There are 2 sheets. One is a gear calculator and the other is a tire size chart. In the gear calc, you can input tire width, profile, diameter and gear ratio for manual and auto's.

Fullsayl

Steve,

Not at all, my commute to and from work is about 45min (30 miles) one way and she purrs right along, and you are welcome.

~Matty

jahudso2

Thanks grandpa, i was unaware we could attach files other than photos.

Nuke

Just be aware that where we begin to gulp fuel is just past 1800-2000 RPM. I often take 410 mile trips or longer one way and gas station-to-gas station mileage cruising at ~1800 RPM/60 MPH is ~25 MPG (27 if I go by the on-board) but it drops to ~20 MPG (22 per the on-board) cruising at ~2300 RPM/75 MPH with my 3.55's.