Another poll! Should've put it in the other one, and would have edited it to add it, but only moderators can edit polls Anyways, here it is, 3.73's again, and wait till I can afford a T-56 transmission to replace my 700R4 and get that nice double overdrive gear? Or drop down the gears to I think the next step down is 3.23? I really like having accelleration, I hate having bad gas milage...I'm leaning towards keeping the 3.73's.

 

I don't see your car making it to 200 mph. It takes a lot of HP to push you along, not too mention how much space you need. I think you'll get better acceleration w/ 3:42s considering your set up. So I say none of the above. If you can afford the T-56 go for it, but your gears right now keep you slightly out of your power band as far as your 3:73s go.

 

I agree, 3.42's would be a good bet. Besides, Unless your at the salt flats you'll never get a chance to go 200 mph. Aim for a top speed between 130 and 150 (unless you race as much as I do you'll probably never see those speeds either) and you'll have a pretty good compromise between mileage and acceleration.
John

 

3.42s are only a 10 MPH difference in top theoretical speed, at 136.2 MPH with the 700r4so probably like 150 with the T56. I guess I'll make price my deciding factor....

 

One more thing I forgot. If you're worried about gas mileage do the calculation to check the difference in rpm at your cruising speed. The diff between 3.73's and 3.23's at 70mph with a 700r4 is only like 300 rpm, so you'll see only a little improvement in gas mileage. Basically at this time I wouldn't waste your money on changing your gearset, do some more mods on the engine, as you move the rpm band up the 3.73's will become more and more appropriate.
John

 

Exactly, having lower gears (numerically higher) won't decrease milage if your powerband is pushed up.

 

Oy, guys, I can't agree with that!

More rpm means more fuel consumed. It is a law of physics that can't be refuted by "powerband" ruminations. With the same displacement motor, 3.73s are gonna need more gas at highway speeds, no matter how you build that engine.

If you want better mileage you are going to have to drop down to 3.42s or 3.23s. Even better would be 2.73s, if mileage is your overriding concern.

 

I'm not arguing that more rpms mean more gas used on the same engine, I just said that the rpm difference between the gears he was considering was minimal and he might be better off to pursue other avenues.
John

 

My main concern is fun My friends and I drive drom Denton TX to Dallas, Fort Worth, Grapevine Mills, etc. Usually since my car doesn't have it's back seats, and its poor fuel economy, we just use one of their 4 cyl 5 seater cars. Basically My plan was to keep with the 3.73's and down the line pick up a T-56. Someone said "if you have the money" which I laugh at, no I don't currently, but prices I have seen on used T-56s have been like $300-$500 the cost of a rebuilt 700R4 is like $1700 minus the core return for like $250 making an auto much more expensive. Of course install prices are going to suck unless I find a place to do it myself with a friend or two... I didn't see there being much difference there btw 3.73's and 3.43's and probably not a huge difference to 3.23's. I know right now, I can hit my car's top speed though, Last year at the SWMG our fearless leader took off racing some supra's down the road, and noone else really knew where they were going...so we all took off, and for about 5 minutes or so I was running my car in 4th gear (auto) at 52-5400RPM which put me near 125 MPH the top speed of the car.
The other concern I have is durability, I know 4.10s suck for durability...2 sets 2 years, and I heard of someone else with a similar experience. (on this board) So I am at 3.73's. I am sure that $#&*%$ magnet $#!@*& up my gears this time, so 3.73's seem ok. I was just looking for other peoples experience, and I think whoever said I might see 300 rpm difference, is probably right. Right now, to cruise at normal texas speed of 75-80 MPH I have to be up at about 3500 RPM which kills the gas milage, 3200 or even 3000 would still suck! The wonderful T-56 with a .5 6th gear ratio would help a lot more than 3.43 gears I think. I just wonder what kind of ET change I might see in the 1/4th with 3.43's or 3.23s' compared to the 3.73's if anyone knows off the top of their heads. I will probably jsut stick with the 3.73's since I really need to get the order in tonight or early tomorrow morning (oh wait it's 3:20 AM its already early tomorrow morning!) I'd still like to know for future mods....now just to try and remember, was it a series 2 or series 3 carrier....hmmmm.....

 

Corry,

3.73s have often times not been helpful to people in the quarter mile. I know of one guy running his Camaro with 3.27 gears in the 11s here in Calgary.

If you just love that off the line rush that comes with 3.73s, even though it uses more gas and doesn't go thru the quarter any faster, then that's what you want.

 

Well you're wrong. It's not common but it happens. Think about it, say your engine creates no power at 1500 rpms, and you cruise at that rpm, well you're putting a strain on the motor. Now if your motor creates upper rpm HP and you have lower gears it is possible that mpg won't suffer. Ask 82camaro he explained it some time ago.

 

$1700? For a rebuilt 700? your getting rippppppped off Hell a highpo unit from summit will only run you 1500. I've seen 'em as low as 500 if you shop around though the going rate seems to be about 975 ( with a new stock converter even). When I got my last one rebuilt it cost me 1500 and they actually took the old one out, rebuilt it with all the upgrades, put in a 2100 stall converter, and reinstalled it. I'd shop around a bit more.
Johh

 

Oh no, somebody mentioned me. Changing gear ratio won't hurt mileage unless it's a huge change under certain circumstances. If you have a killer engine with a nice HP cam and rough idle, you won't want a cruise rpm very low. Efficiency is the key to mileage--if you engine doesn't run efficient until 1800 rpm, you won't want a cruise rpm of 1400. What you have to look at is how much energy it takes to keep the car moving at a specific rate(say 60mph). Then figure out how much fuel is required to create that energy. Of course part of that energy required is frictional losses in the engine--this is how a 4cyl gets better mileage. The difference it frictional losses in a car from a few hundred rpms is very minimal. I went from 3.08 gears/th350 tranny to a 3.73 gears and th350 tranny without a change in mileage(cruise rpm was 3000rpm at 60 w/'3.73's). Then installed a 700r4 tranny and still get the same mileage(cruise rpm adding the overdrive ended up being 2150).

 

Well still higher RPM's make more fuel used, but power and effiecency play in there too...I don't know if it ever shoed the sig for the mods or not, but I will this time....
I did put my order to summit on hold....I am considering doing the "Building a better 10 Bolt" tech artlcle....the thing that has me stuck is the axles....I don't know if I can swing new axles....I am pretty sure I have the series 2 carrier, with 26 spline axles...but I am sick of rebuilding this rearend! Even if I don't cinsider this to be my fault....
Right now the order to summit, SLP, and Drivetrain direct includes Series 2 3.73s' the crushless crush collar to properly hold the pinion gear in place, the shockproof gear oil, and the SLP diff cover which claims to keep rear end temp 80º cooler. Considering the OEM carrier replacement, 28 spline axles, and series 3 3.73 gears, or maybe a numerically lower ratio still...Money is going to be the deciding factor here...unfortunatly...

 

go to www.f-body.org/gears it is a gear calculator, it probably isn't SUPER precise, but itll give you an idea.

 

There's a gear calculator on this home page.

 

oh sorry I haven't seen that. :-)

 

Hi Mark,

Yes, efficiency is king. But at highway speeds, which is what we are talking about, even my 700r4 with 2.73 gears turns above 2000 rpm. My 305 produces more than enough hp at that rpm not to strain the engine.

I can agree that under certain circumstances what you say is true. It's just that it is quite uncommon, as you said.

Sheesh! Why did I even post this? We are agreeing anyway

 

Well, 80 is about the speed I want to go.
3.73 3500 rpm or so
3.43 3200 rpm or so
3.23 3000 rpm or so
2.77 2600 rpm or so
(all figures calulated by me, I don't need a gear calcluator :P lol)
anyways, 500 RPM isn't much difference, and I ain't goin down to 2.73's! The 3.73s were good to me (except on gas milage, and the others don't seem to be willing to help there!) so I will probably stick w/ 'em
now....
80MPH with a T-56
3.73 2500 rpm or so
3.43 2300 rpm or so
3.23 2150 rpm or so
2.73 1850 rpm or so
All rounded off
80mph/60min/sec*5280 ft/mi=7040 feet per second
50mm/25.4mm/in*2+16*pi=5.2194964559 ft/revolution of the tire
7040ft/s / 5.2194964559 =1348.78911 heel rpm at 80MPH
1348.78911 * intended gear ratio = riveshaft RPM
driveshaft rpm * .7 for 700R4 *.5 for T-56 =engine rpm
Still the 3.43's tempt me......

 

I find that the thing that bothers me most at 70 or 80 mph is the pitch of the exhaust. It can get to be such a drone, depending on your mufflers and rpm, that it drives me crazy.

Just something else to keep in mind.

 

Heh, the drone gets to me above 2000 rpm lol, but I kinda like the sound of the SLP 1 3/4" headers, into the SLP 3" catback