i need more speed/mileage

[spankrz]

i'm not sure what my gears are now, but i know it was a quarry truck for the allen company new, and it was bought with the lowest gears it could be bought with. its a heavy duty truck- it's a 72 CHEVY 2wd with rear leaf springs. the only other 72's i have seen with leaves where GMC's.

[Longhorn Man]

is this a c/10...C/20... C/30...?
Leafs were avalible on any GM pick up 67 - 72, and standard on any longhorn or one ton regardless of chevy/GMC.

[69GMCLonghorn]

Something that needs to be said about converting to an overdrive vs. changing the rear end gears: First of all, in other forums, it was touched upon that the heavier duty rear ends (Corporates?) came with 2 gears; low and lower. It doesn't sound like this is a 1/2 ton, so getting higher gears is probably not an option. Plus, it's a freakin' truck. You don't want to up the gear ratio and lose your low end. Get an O/D tranny, whatever it might be. The 700's and 200's have a LOWER 1st gear than a Turbo 350 or 400, AND the O/D 4th gear. It is a win/win.

And about lowering the RPM's too much? Be serious! If you went nuts and did an O/D tranny AND a Gear Vendors, you'd be just under 2000 at 70. Quite doable even with a inline 6. So FORGET the concern about "too low" of a highway RPM. It ain't gonna happen. If it does, let's get a discussion started. I'd be interested to hear how it was accomplished.

[Longhorn Man]

if it is a truck to be used as a truck, I would not advise the 700 R4 nor the 200 4R... unless a lotta money was spent on the internals. They are fairly weak in stock form, and since you shouldn't haul heavy loads in overdrive on either of those trannys, you are right back to 'screaming' when loaded on the highway. This is why GM never installed either of those in anything over a 1/2 ton truck. They stayed with the TH400 untill the 4L80E came out.
As for going too low in RPMs... it can be done, and has been done, over and over, even in stock aplications in later years. There's quite a few on here who ignored the recomendations of some of us, and did a 3.07 gear with an overdrive, and DROPPED in MPG. Some ppl have gotten away with it, but more often than not, in an old school motor, with the aerodynamics of a barn door, your MPG will drop if you lower the RPMs too much. 2200 is about as low as you'd want your cruise RPM to be in an old school small block, BBC, I'd be willing to bet it may tug as low as 2000 with improved MPG. (these numbers are for stock built engines)

[Longhorn Man]

otherwise, we could just do a 1:1 rear gear and have real low RPMs... even overdrive it and have RPMs at idle when doing 75 MPH.

[maddog1331]

Spankrz, if it turns out that you want to go the 200R4 route, I just saw this on ebay up in Louisville:

http://cgi.ebay.com/ebaymotors/200R4...Q5fAccessories

I am going to study some of these coversions myself, I would like to eke out a few more mpgs out of my truck, but don't want to spend a ton. As far as I know right now I have a 350 turbo (not 100%sure honestly) and no idea what the gearing is on the rear end. I'll have to check into all this and maybe decide if it is worth my time to convert a bit.

[spankrz]

Originally Posted by Longhorn Man

is this a c/10...C/20... C/30...?
Leafs were avalible on any GM pick up 67 - 72, and standard on any longhorn or one ton regardless of chevy/GMC.

yeah, i know they where available, they're just rare on the chevy 2wd's. whenever someone looks at the truck (no bed right now) that is the first thing they ask about lol. it's just a custom/10.

[spankrz]

Originally Posted by maddog1331

Spankrz, if it turns out that you want to go the 200R4 route, I just saw this on ebay up in Louisville:

http://cgi.ebay.com/ebaymotors/200R4...Q5fAccessories

I am going to study some of these coversions myself, I would like to eke out a few more mpgs out of my truck, but don't want to spend a ton. As far as I know right now I have a 350 turbo (not 100%sure honestly) and no idea what the gearing is on the rear end. I'll have to check into all this and maybe decide if it is worth my time to convert a bit.

thanks for the link, that's a nice find. i might throw a few bids on it, it's only a 2 hour drive. brother's girlfriend's family lives up there, they could pick it up and store till i need it. you guys think i should plan on a rebuild if i get it?

[AlienYouth]

ur only spinnin 3 grand at 75? man, u've already got pretty tall gears... 5 grand'll take u around 125...

[maddog1331]

Originally Posted by spankrz

thanks for the link, that's a nice find. i might throw a few bids on it, it's only a 2 hour drive. brother's girlfriend's family lives up there, they could pick it up and store till i need it. you guys think i should plan on a rebuild if i get it?

Yeah Louisville from there is all interstate too, should be an easy drive!

If it were me, I would install it as is and try it out. If it ran decent and everything I would just leave it in. But that is just me, definitely take into consideration the folks on here who have a lot of experience with this kind of stuff. I don't, so I am reading these posts trying to glean any bit of knowledge I can.

[spankrz]

Originally Posted by AlienYouth

ur only spinnin 3 grand at 75? man, u've already got pretty tall gears... 5 grand'll take u around 125...

not quite 3 grand about 60 lol. dont have a tac, just guessin.

[spankrz]

Originally Posted by maddog1331

Yeah Louisville from there is all interstate too, should be an easy drive!

If it were me, I would install it as is and try it out. If it ran decent and everything I would just leave it in. But that is just me, definitely take into consideration the folks on here who have a lot of experience with this kind of stuff. I don't, so I am reading these posts trying to glean any bit of knowledge I can.

hey i see you're in somorset. come time for the cruise might see ya down there. truck aint ready yet, but might be down there in the 86 monte ss.

[maddog1331]

Sounds good man, They will definitely be starting up soon. My old clunker isn't a show truck, but I'll definitely run it down the road a few times during the cruises this summer. Shoot me a PM when you are coming down and I'll show you the best BBQ place in town (Beefy King, south 27....MUCH better than Sonny's, IMO).

[spankrz]

aight man i would drive my truck down there but thats part of the problem with my setup on this post, i would be pullin 3.5 grand the whole way down and back lol.

[Longhorn Man]

since you don't have a tach, and are "just guessing"... you need to find out what gears you have before you do anything at all.

[mrein3]

In my opinion you need to figure out a lot of things before you go install anything.

FIRST. Figure out your mileage. Don't just guess. Fill your tank. Write down the odometer. Drive like you normally do. Run it down to about 1/4 and fill it up again. Write down your odometer again. 2nd reading minus first reading = miles driven. Miles driven divided by gallons on 2nd tank = miles per gallon. In my opinion you should write down every tank so you always know what is going on but that is a post for another thread.

SECOND. How many R's are you turning on the freeway? If you're aiming to reduce freeway R's, you MUST have a tach.

THIRD - Figure out your rear end gears. Take the code off the axel tube and hop on the google. Turn the tires on jack stands counting drive shaft revs. Pull the rear cover and count teeth. Whatever is your perferred method, figure out your final ratio.

Once you got those numbers, current MPG, rpms at 70, 65, 60, or 55 or whatever you usually drive, and rear end gear ratio, people here can help.

Longhorn Man is right. We've seen many folks here who installed a 700r4 in front of their 3.07 rear end gear and REDUCED their gas mileage. If you turn that small block too slow you'll "lug" the engine and reduce gas mileage.

When I was in college I had a 1971 Monte Carlo. It had a 350 small block, 2bbl carb, th350 with no lock-up, 15" tires, and 2.73 rear end gears. On the freeway I got 23 mpg all day long. My '72 Chevelle with a 307, th350, 2bbl carb, same rear end, and 14 inch tires got 18 on its best day. Except for the sheet metal on the nose they were the same car. Other than 43 cubic inches the only difference was the tires. The taller tires put that Monte into its sweet spot on the highway. I wish Detroit and/or Japan still made cars that road like that, moved that much metal at the mpg, and looked that good. The point is the Monte probably had a lower highway RPM (neither car had a tach and I was just a kid). The smaller tires on the Chevelle made the engine spin more thus wasting more gas. Each configuration has a sweet spot. You can google a tool that will help you figure out your final engine RPM based on tire diameter, tranny, and rear end. You can also google what RPM works best for a stockish small block.

You need data.