Gear Ratio Swaps?

[blkcorvair]

My 69 is finally done and I notice this thing is revving on the highway. To the point where I feel uncomfortable at 65 mph. I generally toot along at 55-60 but everyone is passing me up.

I have the 250 3OTT with a posi rear. Im gonna chack my ratio tonight but I suspect it to be 4:11.

I was looking at swaping in a lower ratio like 3:42 or even 3:08. Its strictly for show and I wont be trailering or hauling anything, but would like to be able to go down the highway and maybe even pick up some mpgs.

I notice the aftermarket gears reference two different carriers. Gears to fit a 3:73 and up and those to fit a 3:42 and down. Do I need a different carrier to swap in some 3:42 or 3:08's? Any other pros/ cons?

Thanks!

[blkcorvair]

Okay. So turns out it has 3:73. Thinking 3:08 would be the better swap to make a noticable difference

[68gmsee]

Originally Posted by blkcorvair

Okay. So turns out it has 3:73. Thinking 3:08 would be the better swap to make a noticable difference

3.08 might be little high for you 250. You will lose a lot of low end power. I have 3.54 on my 68 GMC 250 three speed and it does real good on the highway at 60 to 65 and even 70.

Personally, I would stay with the 3.42.

[leddzepp]

Even if you go to a 3.42 you will need a series 3 carrier. 3.73 and numerically higher gears use a series 4 carrier.

[soxplayer]

I think you are being misled by fan noise. The cooling fan tends to mask the motor sound at high rpm. My wife's truck has a 250 with 5.13 gear and tall 16 inch tires. The tach reads 4200 at 72 and it will run there all day if you can buy the gas .http://67-72chevytrucks.com/vboard/i...ilies/wink.gif

I think you could easily run 80 at about 3600 rpm without any harm assuming you are running regular 15 inch tires.

[GASoline71]

The lower gears that came stock in that truck are to get the thing moving with the I-6 when hauling stuff. So as stated before... the engine will labor more with higher gears in there.

The '67 C10 I had originally came with a 292 and a granny low 4 speed. It also had a posi-traction rear with 4.11's. It was great when I tossed a street/strip 355 and a TH400 in it. It barked rubber in every gear... but sucked on the highway.

Gary