I just bought a 67' RS a few weeks ago . Drive line was swapped out a long time ago for a 396, 325hp (454 heads), th350 and a 12" posi with 4:10 gears. At 100 kph (60 mph) I'm running at 3400 rpms and would like to make it more suitable for hwy driving and bring it down to 2100 rpm or so without loosing performance. What gears would you recommend I switch to??

Cheers!
Marc

i have 373 in my 70 .i was thinking about going to a 343 .if i could find a good 308 posi i would put that in it.i have a 396 in mine also .should still have good power with a 308 .

To go from 4:10s running 3400rpms at 60 to 2100 rpms at 60 with just changing your rear end gear and not losing any performance is basically going to be impossible. A gear thats gonna give you that type of rpm at 60 is gonna be a dog off the line. The only real way to get the best of both worlds would be to go to a 5 speed tranny. Something like a tremec. Then you could get the low end power and that 5th gear for low rpm highway cruising.

First off, welcome Marc!

Do you have any idea what the specifics of the engine combo are, like the cam and compression? Normally, big blocks are a lot more forgiving of a taller (numerically lower) gear, because they generally make more torque lower. It sounds like you have a lot of different things put together, a 396 with open chamber (possibly peanut port) heads etc. Kinda hard to guess where you are making power and how a gear change might affect things without knowing more. Also the size of the rear tires (diameter) affects things too.

4.10s are a lot in a street car, for sure. The next step down is 3.73, then 3.55, 3.42, 3.31 (if you can find them) and so on. All may (again, depending on how the engine is setup and where it makes power) reduce performance. In some cases dropping gears can actually help off the line. With 4.10s on street tires that fit in a 1st gen Camaro wheel well, a decent big block is going to be severely traction limited.

There are a number of gear/speed/RPM calculators available (I think they have one on the CC5S site ( www.classicchevy5speed.com ), so that's simple enough to figure out. It's the "without reducing performance" part that's tougher. As Craig mentioned, reducing cruising speed without greatly reducing off-the-line performance almost always points you to a trans with overdrive, whether it's an auto (200R4, 700R4), manual (TKO, T56), or an add on OD like a GearVendors unit.

My wife would kill me if I tried to purchase an new tranny after buying this car. Basicly where I live there is alot of hwy driving to get from point A to point B. What I'm looking for is the best of both worlds and I know it's not the 4.10 that I presently have. I'm looking to you guys because I'm clueless (I'm a newbie, but you got to start sometime eh!!)
Marc

396 325 hp
dome pistons
ported heads
10.5:1 compression
performance cam 520 inch lift
roller rockers
edelbroke performer RPM dual plane intake manifold
edelbroke 1411 750 cfm
GM HEI with MSD
hooker headers
Heads are from a 454 , I think they're 116ccm

Marc

I would guess from what you have listed that 325hp is somewhat conservative..i may be wrong and someone who knows a lot more about engines than me will probably chime in. Either way the torque of that big block will still allow you great performance with a more street friendly gear. If you are looking for a middle of the road gear to have a nice compromise between low end performance and highway cruising i would say something in the 3.42 or 3.55 range.

Thanks Guys for the help. I'll call the local (2 1/2 hrs away) performance dealer and price out some new gears.

Cheers!!
Marc

I'm with Craig. I don't have Desktop Dyno or any program like that, but looking down your list I'm guessing at least low 400s for the HP, and there's really nothing there to say the torque isn't in the same range. The lift of the cam and the Performer RPM intake suggest the best power range may start at a higher RPM than stock, maybe around 1,800 RPM or so, but if the engine has had that much work I suspect you may have a higher stall speed torque converter to deal with the shift in power production.

3.42 is a pretty nice street gear with a BB. That's what I am running with my 396/350 HP, and a 27" tall tire. Of course I also have the TKO, so I can come of the line at whatever RPM the tires and drivetrain can handle.

There's only two things I'd do before I order gears.

- Run the gear/tire/RPM calculator and see if the change gets you down to the cruise RPM you want.

- Pull the rear cover off to see what your carrier is. If your 4.10s are on a 3-series carrier (either with a spacer ring or a thicker ring gear) then you're set to add new 3-series gears. If you actually have a 4-series carrier, then you'd have to buy a new carrier too. Yes it's messy to open the rear cover, but short of having a receipt with a model number for the rear carrier, it's the only way to know and avoid a surprise later.

i love my 3.55 in my car at 80 on the interstate i still feel like i have some top end left at say 110 its getting on up there..it has great street manners and i drive it everyday