3.73's and highway speeds

[ninety15.0]

With the stock tire size and 3.73's im turnin about 2400 @ 70 mph. how fast do you guys normally cruise on the highway. It seems like doing 85 is almost out of the question because your at like 2900 rpm. I feel like i shouldn't be going faster than 75 or maybe 80 for extended periods of time just because of the horrible gas milage and there must be much greater engine wear maintaining that rpm for a long time on the highway? Maybe i just baby my car way too much so i was wondering what other people think about cruising speeds with short gears. I can only imagine 3.90's or 4.10.....it seems like you could only cruise at like 65????

 

[87MustangGT5.0]

well my cousin has a c4 and 3.73 gears and since the c4 is a 3 speed he puts out like 2500-2900 at like 65 mph I think.

 

[CManT1914]

I'm at about 2300 rpms with 3.73's, but I have a little taller tires (315/35/17's). I have NO problems running 80+mph, and maintaining 3000+rpms. My car seems to like the higher rpms now with the new heads/cam anyway. I still got 16mpg in town and on highway mixed with no tuning. Now I have a big exhaust leak, so it's gone down quite a bit, but it should be a lot better once I get that fixed.

 

[ninety15.0]

My new motor seems to like higher rpm's too...it just seems like 3k on a pushrod V8 is a lot of RPM to maintain for a three hour sprint down the highway? maybe its just me?

 

[CManT1914]

My new motor seems to like higher rpm's too...it just seems like 3k on a pushrod V8 is a lot of RPM to maintain for a three hour sprint down the highway? maybe its just me?

Well............ I don't know where you're from..... but I'm from Texas. The distance between Austin and San Antonio usually takes an hour and a half to drive.

*Gets into flame suit* My buddy (2000 GT) and I made it in 45 minutes when we met up with an 03 Cobra along the interstate. That was 100mph+ sustained for that 45 minutes. I had no problems.

And yes that is incredibly dumb to drive 100mph+ for 45 minutes, but that was a while ago and I have wisened up a LOT since then. Luckily for me, it didn't take anybody getting hurt for to to wise up.

 

[Michael Yount]

My wife's Bimmer turns over about 3700-3800 rpm cruising up around 75-80. Been doing it for 80K miles now - car runs even better now than it did new.

If your car is in shape, the highway revs won't hurt it. It's actually putting out only a fraction of the HP it's capable of at that rpm - so it's really loafing. Yes, you'll consume some gas, but you don't have to worry about hurting anything if the motor/car are in good running order.

 

[Michael Yount]

By the way, you should take a trip to Germany. That will expose you to high revs for extended periods of time while cruising at high speed. When you come back here, you'll realize how modest 2900 rpm at 85 mph actually is!

 

[ninety15.0]

i have no problems ringing the car out at 145 at almost 5k for a few minutes. My mother owns a 328i that does 80 at 3500 too, so its not like i've never seen that kind of RPM....but the differences in technology from a OHV ford v8 to a DOHC bimmer or even a SOHC 2000 gt are astounding. Those motors were designed to cruise at an RPM where the motor makes peak torque. Five-oh's were never designed that way. a stock geared stang cruises at 2500 rpm at 100 mph. i dont know....i guess i just wanted to see what the general concensus was for cruising speeds with geared five oh's.

 

[txstang84]

Well............ I don't know where you're from..... but I'm from Texas. The distance between Austin and San Antonio usually takes an hour and a half to drive.

*Gets into flame suit* My buddy (2000 GT) and I made it in 45 minutes when we met up with an 03 Cobra along the interstate. That was 100mph+ sustained for that 45 minutes. I had no problems.

And yes that is incredibly dumb to drive 100mph+ for 45 minutes, but that was a while ago and I have wisened up a LOT since then. Luckily for me, it didn't take anybody getting hurt for to to wise up.

dude, how the hell did you get away with driving down I-35 in excess of 100 without getting tagged by DPS...?!?!?

 

[txstang84]

also take into consideration, the gears were put into the car for good economy, the 5.0, if in good running order will take extended periods of high rpm just fine...

 

[Grn92LX]

I do about 75 at 2500 rpm with 3.73's. Though I rarely cruise that fast on the highway. I want to do 4.10's in my car which would increase my highway rpm's by around 250 rpm which is neglegible.

 

[Michael Yount]

ninety15.0 - the gearing on the stock Stang wasn't done that way to save the engine from revving - it was geared the way it was to make a certain gas mileage target so Ford could hit its CAFE targets. There's nothing fundamental about OHV vs. OHC that makes one any better able to withstand cruising at 2000 rpm vs. cruising at 3500 rpm. They are ABSOLUTELY loafing in terms of taxing the engine under cruise. It takes very little HP (compared to what the engine can make) to keep the car under cruise at those speeds.

I understand if you don't want to do it due to poor fuel mileage or perhaps decibel level. But the engine could care less -- 3500 rpm for extended cruises is nothing - for your 5.0 or your mom's/my wife's Bimmer.

 

[Michael Yount]

....by the way, mine has 3.73's with a slightly shorter tire than the Stangs --- like a Stang with a 3.90 gear. Also I have the T5Z tranny which has a bit longer 5th gear - .625 instead of .675 in the Stangs. So I see about 23-2400 rpm at 70. Mine consistently gets 25-26 mpg on the highway - best tank of 26.8 mpg. The revs don't appear to be impacting the fuel mileage too badly. And mine isn't exactly a paragon of aerodynamic efficiency. Flying brick is more like it.

 

[Modular2v]

all that higher rpm= more wear is a bunch of crap it all depends on how well the vehicle is maintained

 

[ninety15.0]

HAHA yea...i guess im just a little girl when it comes to that sh1t. I got 24.5 mpg on the way out the college this year and that was cruisin at 2400-2500 almost the entire way up here, with a few quick blasts up to 100. Im not dissapointed by any means i just wanted to get an idea of how the rest of you guys deal with that much rpm and also all that noise!!! 2500 is a particularly loud speed with my setup. cheers!

 

[wht93gtEd]

Well...with the 3.08's I see about 1800-1900 around 65 and just about 2k for 70.

 

[CManT1914]

dude, how the hell did you get away with driving down I-35 in excess of 100 without getting tagged by DPS...?!?!?

I was freaking lucky is how. I won't do it again I guarantee it.

 

[Dbeck002]

2400 RPM @ 75 mph odd..

When im doing 70 im at around 2100 with 3.73s (not sure how tall the tire is, its not that tall i know for sure)

 

[Michael Yount]

Dbeck - what kind of tach? And did you adjust the speedo correctly after the gear change?

 

[5spd GT]

I have 373's (2,400 rpm at 70mph). I don't like just real extended cruises either. I usually will cruise a bit above that. I still good gas mileage but don't like the faster up and down motion of the pistons for that long of a time. More up and down for longer period of time equals more friction/wear on the engine.