Hey guys. Hoping for some help and education. I have a mild built 455 and th400 with a little bit higher than stock converter. I have a 12 bolt posi with 2:73 gears. I did it on purpose as I like driving and cruising and thought with the mild 455 that it would feel quicker than it does. But even with the 455 it is not much fun from a stop and will not break the tires loose. I am running 20x10 wheels and 275 35 tires. My questions are 1should it still get up an go or are the gears that much of a problem? It sounds like spacers are not ideal in the rear end but I will never race the car but maybe a little stop light action on a car that gets maybe 2000 miles a year. Or if I get a 3:73 gear to fit the 2 series carrier how will freeway life be? Like I said I like driving and cruising and freeways are a must.

 

just to give you an idea, my car with 355, th350 and 3.42 gears spins about 3000rpm at 70mph. It's not that bad once you get used to it. I think 3.73 is too much gear for a street car. I would go with 3.42 or maybe even 3.23. JMO

 

I agree.
I changed mine from a 2.56 to a 3.42 to get more power and it's to much. I plan on going down to a 3.08 as soon as it gets back from paint.

 

Thanks for the input. So would a 3.08 be that big of an improvement over 2.73? Should it be that much of a dog and not break the tires free with the 2:73 gears?

 

http://tire-size-conversion.com/tire-height-calculator/

http://www.angelfire.com/fl/procrastination/rear.html

Here's what I suggest.

play with calculators above so you know where your rpm's will be and where you want it.

someone here shared them with me and it was a big help. I was looking for the same thing you are but also wanted to make long trips on the interstate.

wish I would have had this knowledge first before I went all the way to a 3.42.

having a 455 you should be able to rip the tires off with a 2.73 you may want to check all the other stuff first like your timing.

 

275-35-20 tires are 27.6" tall, which is similar in height to the 245-60-15s that I have on my car, and 2" taller than the 245-60-14s that were on the car for over 20 years before that. I drive ~4500 miles per year and I have no issues with ~3000 RPM on the highway.

If your 455 will not break the tires loose from a stop, then I think there is more going on that the gearing. Lots of folks with 455 cars and any rear gear ratio(even 2.56) will obliterate 275-60-15s that are ~.5" taller than your tires.

 

Thank you guys. With a cam only a little bigger than stock and a 750cc carb stock c heads and wz exhaust what should timing be set at? It fires right up and does not diesel. Idles around 800 on the tic to tach...

 

I have a 350 sbo so I can't answer that but be careful with the tic toc tac some of them are not accurate and need to be calibrated.

Do a search for both timing and tac calibration.

The search function can be your best friend here. As Joe has pointed out to me several times. LOL

 

https://classicoldsmobile.com/forums...djustment.html

tach adjustment

 

If your going to fine tune your timing I'm going to suggest doing it on the dyno. Your not going to advance your timing much more than where you have it now without detonation on pump gas. The general rule of thumb is 36-38 total and 50-52 with vacuum. I've seen engines that can tolerate a bit more and a lot of engines that could not. I will also add that setting an engine for wot peak power may not be able to run on the street with fluctuations in fuel quality and changes in atmospheric conditions.

this is a quote from Eric that knows is olds *%$@

 

Guys,
Thinking about this. Can it be that the kick down switch at the pedal is not adjusted correctly? I did not have the correct brake so I modified one...thoughts?

 

I would not suggest the dyno at this point, but do suggest you verify your tune up specs. However I do agree with the others, you should be able to spin the tires from a standstill. Make sure your switch is engaged at full throttle (pedal floored). I'm not going to deny that gears would not make it easier, just think about what you want out of your car before jumping in there and changing them.