which gears? 3.40? 3.73?.....

[mean_maverick]

if you cant tell, im kinda new to the I6 thing. im used to SBF powerplants so im learning along the ways of the I6 setups. im planning on buying another car next week that has a 250/C4 in it and for the time being im going to leave it stock and then slowly do some work to it.

eventually ill end up cutting the head down, a crane cam, a 2v swap, and maybe even a stall converter.

now with everything said, i guess my biggest question is what gear would work best with a 250 and a 250 with the stated mods done to it. and btw, fuel economy is always in interest as well. im not trying to build a power house or anything, just something that runs good and is completely drive-able no matter if it's to the store or to work (over 100 miles round trip) so just drop your opinions and such because i'd like to see what the experienced I6 crowd has to offer

 

[BENJENBROOKS]

Well, Mav,

Without really going into the tech specs of your engine, given the lack of detail in your combo description, it is hard to tell what the best gears will be. I can only give you an idea of the speed at which your engine will be turning with an arbitrary tire size, say 215-75-14 for instance...

only you will really be able to decide, however some quick mental math gives me approximate rpm @ 60mph based on 215-75-14 or similar height tires.

3.73 gears ~2950 rpm

3.40 gears ~2700 rpm

If you are going to race the car, by all means go for a steep set of gears, however if you are going to try to pull mileage out of the car, you might consider a gear of 3.20 or close. These engines don't like to run past 4500 without some serious work to make the head flow better. The good news is that they do like to run at low rpm, torque is pretty good down low, so they can take a tall set of gears where a bent-8 won't like it so much...

I feel that with a relatively light car, these gears give you the highway legs that are desired with ample performance for those times when you gotta get on the go pedal...

It doesn't sound like the goal is to race, but have decent performance with good highway mileage, so I would suggest 3.20 or 3.00 gears, they may give up some flat out acceleration, but a relatively stock motor such as yours(current and planned) will be pretty happy turning these types of RPM all day.

Be Blessed,

Ben

 

[mean_maverick]

Thanks Ben. even with my very broad ideas, which are somewhat incomplete (lol), it sounds like you hit the nail on the head as for what im after with this. it's my goal just to make a decent driver out of it w/o dropping a pocketful of money into it.

that's another reason i had previously mentioned something about dropping in a 170-200 transplant with a stick shift behind it but since the 250 is already a strong runner ill just leave it be for now and see what it goes :roll:

 

[BENJENBROOKS]

I'll tell you this, My 6 cyl has a H/W5200 carb, a Pertronix ignitor kit, backed by a 3.03 manual transmission. Internals are all 40yr old, stock parts.

I currently have 2.79 gears and are too tall, when I get the money, I'll be going back to a 3.25 type rear gear as was stock before upgrade to the 8"...

Stock gearing for my 68 stang was 3.20 and had plenty of power to pull the passes, got 24mpg and could spin the tires if I had to...

I could also run up to 90mph if I were feeling frisky on a back road (what am I talking about, all roads here are back roads)

hope this helps,

Ben

 

[MustangSix]

250's have a ton or torque but don't rev well. 3.00 or 3.20 gears work pretty good, but a better option is an AOD with 3.73 or even 4.11 gearing.

With a .67 OD, 4.11 gears have the same effect as a C4 with a 2.75 gearset, but with much better effect in first thru third.

 

[mean_maverick]

yeah, that's another possibility as i have an extra AOD laying around from a running car. i also have a couple of SROD trannies laying around as well that sparked my interest.

so far, thanks for the input. this is giving me more of a direction to go with the car

 

[Eric Rose]

I have a 200 with mods similar to those you listed. I have a C4, a stock 3.10 rear end, and I run 185-75-14 tires (I will check to be sure).

The mods you have posted are pretty mild and probably won't shift the powerband of the engine up far enough to need taller gears than stock. Even the higher revving 200's will run out of breath pretty low on the tach.

My car cruises comfortably at 70mph turning 3000 RPM. I have made a few 200 mile round-trips with it and its done fine.

I second the vote for an AOD. I'd be running one now if it weren't for my 200 having the wrong bellhousing pattern

 

[Cool23]

Have a look here

http://www.currieenterprises.com/cestor ... ators.aspx

See if this helps you.

 

[mean_maverick]

thanks for the link. according to the calculator, i would really benefit from an AOD swap....

 

[xctasy]

Gearing is interesting with our big sixes.

I've tended to stay with the 3-speed auto and 2.77 ish area on my 250 sixes.

For fuel economy, based on road load at 65 miles and hour, open road fuel economy is hurt by about 9% with 29% drop in gearing. That's a 3.6:1 diff ratio verses a set of 2.79's.

Performance wise, a 29% drop in gearing is only about 0.3 seconds over the standing quarter mile. If your 2.79:1 250 Maverick did a 19 second quarter mile before, it'll do an 18.7 sec quarter with a 3.6:1 (3.40 or 3.73 diff). 0.3 secs is like adding another 5 hp. Basically, if a loss of 9%, or about 1.7 miles per gallon turns you on, go for it.

Without an overdrive, 3.4's and 3.73's are definately out. With an AOD, wide ratio RUC or SROD4 or T5, you can use a 3.40 or 3.73 ratio without an economy loss.

For fuel economy gains, the T5 is the ticket. Going from a C4 auto to a T5 makes your engine perform like it has another 10 hp extra. Most tests confirm about 26% of the power is lost with a manual, and about 36% with a C4. Add that lopeing 0.79 or 0.72 overdrive, and you have another 2 miles per gallon at 65 mph.