Help! Is a 4.57 rear gear tolerable?

[padresag]

Originally Posted by Insideline

Actually the height of the 8R 17.5 tires is right at 31". What makes almost all the difference in this equation is Chev's 327 V8 engine architecture is designed to rev much more freely and has a much more free breathing crank case vent system along with a peak torque that is quite a bit higher. Whereas the 250 6 is a low revving engine with a 'tight' crank case vent system, and peak torque is much lower, so add all these things up and a 327 revving at 3200rpm is miles happier than a 250-6 at the same revs.
As a change up to this, I had Mike Sissell build me a custom lump port 292-6 with fully programable fuel injection built with light slipper pistons, lighter crank and rods, a full roller cam valve train with all of the reciprocating mass significantly reduced and that engine made 325 ft lbs of torque at 2200 rpm. I mated it to a GM factory close ratio 5 speed box, and that engine/trans is more efficient, more responsive and way more fun than a 327/350-700R combination. The only downside is it cost more than twice the V8 set up.
This stock GM 327/turbo 400/4:56 locker truly is a decent compromise between power, noise, torque and being quite drivable. As mentioned, putting the 4:11 gears into the locker assembly could make this set up ideal.

these must be a lower profile type tire I have 17 and 18" wheels here and they are both between 33 and 34". no 17.5 though
ron

[factorystock]

Originally Posted by Insideline

As mentioned, putting the 4:11 gears into the locker assembly could make this set up ideal.

I agree with you! Add one more thing, 19.5" wheels with 34" tall and skinny tires. This stock combo will improve top end and still retain your reliability and pulling power of a 3/4 ton truck. Adding anytype of overdrive or changing the complete rear axle will require plenty of fabrication work and won't be period correct. Here is a link to what these wheels look like. http://67-72chevytrucks.com/vboard/s...d.php?t=550144 I would love to see a photo of this truck, I know oem4me has a taste for high calibur original vehicles.

[jocko]

rpm is rpm is rpm. Absolutely, one engine (v8) may be more comfortable at 3200 rpm than another (i6) - but that doesn't mean the passengers are... This is all about perspective: if the buyer, not the seller, is comfortable at 3200 rpm at 65 mph, then, it's a good deal for the buyer. Have had several that cruised on the highway on the low-3000s and, for me, it was miserable. Again, that's just one's perspective. All that matters are the numbers and what the prospective buyer is comfortable with for a cruising rpm. This setup is 3200-ish at 65 mph, 3700-ish at 75 mph, and we all know what 3200/3700 rpm on the highway feels like. Some folks aren't bothered by it, others can't stand it. As padresag stated, a lot depends on what you grew up with and what your tolerances are. If oem4me has had a 4.56 and didn't exactly enjoy it, then I'm guessing this one wont be much more fun since it all comes down to the numbers. Having said that - if you're gonna be towing a trailer and maybe plan to keep it at 55 on the highway, then might be doable as is. Adding to the herd?

[jocko]

concur capev86 - either o/d puts you at about 2200-ish at 65 mph, a very nice cruising rpm. The 2004R would perhaps be a better option to keep 1st gear from being so deep. 700R4 + 4.57 would be a 14:1 1st gear final drive and become somewhat useless except for pulling tree stumps, which might be nice occasionally. But unlike a manual trans, you don't really have the convenient option of starting off in 2nd gear. Having said that, since the truck comes with a TH400, a great trans, especially if oem4me plans to do some trailering, seems the rear gear might be the best option for a change. Could get expensive swappin the trans first only to find that one misses one's nice old original 1st gear final drive ratio. But, if I read the original post correctly, the idear is to buy the truck as is and he's asking what it'd be like to cruise on the highway like that. I'm a huge o/d trans fan personally, and plan to stick one on my 71 eventually. Fortunately, I only have a 4.10 dana.

[RANDY COX]

That's the reason I'm changing from 3/4 ton running gear 456's to 1/2 ton with 373's,I'm not going to be pulling or hauling alot,I want to be able to drive this truck,without it screaming down the road.I'll prolly be running 750x16's so that will help some also....

[brokenspoke]

I'm with Jocko on all points

[clemdaddy]

i had similar questions about a 3/4 ton that i'm working on. same 4:57 eaton rear but with a granny 4-speed and 327 engine. i think i will do one thing at a time and work my way towards the solution. i located an eaton with the 4:10 gears from a camper special and thats where i'll start.

that may well be all you would need to do especially with an rpm motor and turbo 400. good luck, hope you get that truck... its a beauty.