How bad is this tire/gear combo killing me??

It’s interesting to read about so many of you being interested in the best E.T you can get by going for the lowest ratio you can then complaining/commenting!! about open road revs. Aussie Street machine magazine ran a test day with a strip based Holden ute. Numerous passes with 4.11:1 diff were made then changed to 2.95:1 and several passes more were made on the same day. The difference with only a ratio change, .25 of a second. If outright racing is what you are doing it’s worth it, but if dial your own street type racing is what you are doing is the open road revs worth a super low ratio? Most street cars don’t make enough HP in the upper end of the rev range to make 3.9 or lower viable. Slightly taller gears and changing at peak toque suits a milder compo better than wringing the neck out of an engine that only makes power to a moderate maximum RPM!
I would be looking at other things before ratio, with a moderately light car 340 V8 4 speed and lowish gearing; this thing should go as is. A lower ratio will get you off the line quicker, but is it a street car that sometimes races or a race car that sometimes sees the street? Like someone said earlier what is your yard stick? Your slow maybe my fast and visa versa!!
Good luck with it

I ran 410's with 29 inch tires and loved it..Great off the line and didn't scream at 65 mph

In Your case...tires won't help much...Tou need to go to 391's or 355's with that tire size

i used to have an open diff with 2.44 gears with a 255/60/R15 tire and rim combo behind my 360 with the worlds worst intake ever (torker 340) LOL and even that would spin the tires on take off.

No one has mentioned timing yet. Sounds to me like there is something not working right in your combo, especially with your 4 speed that car shouldn't feel like a slug unless the timing is out or the cam is not installed (degreed) properly.

Go through the timing numbers, doesn't cost anything to check and a retarded timing will make any performance car feel like your grandmas groceries getter LOL.

Hope you'll find your culprit.

It's a 4sp... w/a/c on it. What rpm do you shift at? Does the car feel any snappier if you drive around in 3rd rather than 4th? If the engine has some mods and the cam is the "484" (it won't be a "424", check the writing there...) it will be sluggish until at least 3K rpm, and you should be shifting around 6K at full throttle. If you're leaving at 1800 (just off idle) and shifting at 4500, it will be a pig.

I just measured my 275 60 15 cooper tires on 8" rims and they are 26.5 inches tall...something else is wrong. That car should be in the mid 14's.

SleeperScamp said:

I have a set of 4.10 gears. If I went with a 255/60 15 How " streetable" would that be?

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When I had the 340 (11:1, huge-*** cam, 780 Holley) in my Duster, I ran 14" 245/60s with the 4.10s, and thought the streetability of it was fine. Top speed was about 110, but it got there in a damn hurry.
Highway cruising was good, I could even cruise at 85 comfortably (not so much with the 360 that's in there now-feel like I shouldn't even take it up to 60).
And around town nothing could keep up off a light
(that's all with a built 727)

4 speeds rule. sounds to me like your engine is not making the hp it should for whatever reason. my 35 plymouth 340 x head 40 over comp cam 4 speed 323 posi with 255 /60r15 's will shredd the tires and lift the wheels at any given time. i have a bears ladder bar with coil over setup in the rear. mustang 2 in the front and the car launches like jack the bear. try dumping the clutch at a higher rpm and if it bogs down than chances are its all in the engine. just my thoughts.

The 1st thing I'd try is the gears. I think you'd notice a big difference by going to 3:55s and still have the streetability you'd want. It would be nice to know someone with a spare rear end with this setup or a junkyard. It's trial and error, but I think this would deliver the results you're looking for.

67cuda360 said:

i used to have an open diff with 2.44 gears with a 255/60/R15 tire and rim combo behind my 360 with the worlds worst intake ever (torker 340) LOL and even that would spin the tires on take off.

No one has mentioned timing yet. Sounds to me like there is something not working right in your combo, especially with your 4 speed that car shouldn't feel like a slug unless the timing is out or the cam is not installed (degreed) properly.

Go through the timing numbers, doesn't cost anything to check and a retarded timing will make any performance car feel like your grandmas groceries getter LOL.

Hope you'll find your culprit.

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I,m leaning toward cam timing or timing chain off a tooth. Also check the free stuff first. Are you sure the throttle cable hasnt slipped and is not fully opening the carb. You wouldnt be the first to have this happen to them.