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I have the 3.55 gears, and would never go with a higher gear. Heck, I would go lower than 3.55 if I was doing a swap, prob 3.73.
I dont like running at such high highway RPMs either, but I am going to address that with a 700r4. And this is a fun car, not a road trip car too.
This is the only way to do it. I removed my Th-400 and 3:08 gears and put in a 700-R4 and 3:73 gears. WOW!!! what a Sweet change Bear in mind that I do have around 400H.P.
If I had to the option to do it all over, I would do the Exact same Change-Over
I blew up that TH350 on the first day of my 383/525 HP Stroker breakin.. Thought it would hold under moderate bursts til my new trans was ready. ... It didn't!! I yanked it and converted to a Built-Up 700r4... You should consider it.. High HP., a 700r4 and 3.73 gears is a match made in heaven.. Blazing acceleration, and yet I can cruise at 80 MPH at 2500 rpm... 19mpg last time I checked and I can do 6800RPM shifts all day.. ahhh Life is good!
Without an overdrive you will be miserable after 5 minutes on any highway. When I had a 4 speed and a small block, I would use 3:08 . Very cheap plentiful axle ratio that gives you the best of all worlds. 3:23 if I'm running a small displacement with a hot cam. I went 3:42 with 28 inch tall tires, I had to take back streets everywhere and it took forever. You can run it down the highway, just remember the ware and tear that motor goes thru on a 85 degree day. Any weak link, any oil leak and just the amount of revolutions the motor now has to turn will shorten it's time greatly.
It's a blast when you're 17-18 , it sucks when your 30+ Trying to cruise to the show 30 miles away.
Yeah 3.73 gear you can't hardly go wrong with around town driving, and still prob won't run out of gear at the track. But for highway driving the OP sounded like he wanted to not compromise his highway driving as much as possible. 3.55 is a great compromise, particularly with OD. But I like 3.73's too.
This is the only way to do it. I removed my Th-400 and 3:08 gears and put in a 700-R4 and 3:73 gears. WOW!!! what a Sweet change Bear in mind that I do have around 400H.P.
If I had to the option to do it all over, I would do the Exact same Change-Over
Its the absolute best of both worlds.. I did mine 7-8 years ago ...w/525HP .. THE Best choice in my opinion
Last edited by fishslayer143; 02-04-2016 at 10:03 PM.
Seems like there was a thread around here in the past that talked about this. And finding the "sweet spot" for the cam where the motor just likes to effortlessly hum along. Every motor is different I suppose, but in general your looking around 2,000-2,200 rpm at highway speeds, maybe less. But you can find that sweet spot then back out through calculations what the ideal highway gear is.
I blew up that TH350 on the first day of my 383/525 HP Stroker breakin.. Thought it would hold under moderate bursts til my new trans was ready. ... It didn't!! I yanked it and converted to a Built-Up 700r4... You should consider it.. High HP., a 700r4 and 3.73 gears is a match made in heaven.. Blazing acceleration, and yet I can cruise at 80 MPH at 2500 rpm... 19mpg last time I checked and I can do 6800RPM shifts all day.. ahhh Life is good!
Man, I'm sold. If my C3 wasn't already a manual car, that's absolutely what I would do. I used to have a '94 LT1 Z28 with the 4L60E trans and a 3.23 rear gear. I put a 3,200 stall converter in it and it was VERY fun. That same setup with a 3.73 would be an absolute blast.
Originally Posted by htown81vette
Seems like there was a thread around here in the past that talked about this. And finding the "sweet spot" for the cam where the motor just likes to effortlessly hum along. Every motor is different I suppose, but in general your looking around 2,000-2,200 rpm at highway speeds, maybe less. But you can find that sweet spot then back out through calculations what the ideal highway gear is.
How do you find the sweet spot? Monitor for high vacuum at different RPMs and then gear to use that RPM during typical cruise speeds?
Without an overdrive you will be miserable after 5 minutes on any highway. When I had a 4 speed and a small block, I would use 3:08 . Very cheap plentiful axle ratio that gives you the best of all worlds. 3:23 if I'm running a small displacement with a hot cam. I went 3:42 with 28 inch tall tires, I had to take back streets everywhere and it took forever. You can run it down the highway, just remember the ware and tear that motor goes thru on a 85 degree day. Any weak link, any oil leak and just the amount of revolutions the motor now has to turn will shorten it's time greatly.
It's a blast when you're 17-18 , it sucks when your 30+ Trying to cruise to the show 30 miles away.
You seriously took back roads with a 3:42 ratio? I ran 5:38 gears and stayed off the interstate. "Man's got to know his limitations " Clint eastwood.
Jim, make absolutely sure you won't have a problem seeing the tach at 3200 going down the highway. This is the decision that matters the most. Everything else makes the 3.54 gear the better choice. Engine wear, gas mileage, etc do not have any bearing on this decision. Upgrade to OD, larger wheels and tires, and performance will all benefit going to 3.54.
Mike
Mike, why do you say engine wear and gas mileage have no bearing on this? I'm not worried about gas mileage but are you saying the engine will run better at that rpm? And for now, I'm not planning on any future trans or gear changes for a long time. Thanks, Jim
For one, I am not concerned with getting 100k+ miles out of my engine, so engine wear isn't much of a factor.
I really want the overdrive because the high rpm just makes me uncomfortable and seems to run a higher risk of overheating when everything isn't in tip-top shape.
Sorry I know this gets beat to death but... I am on the fence and looking for general input. I will be swapping out my 2.87 rear to a 3.31 or 3.54 soon and I am looking for some input to sway my decision. Off the line, the 3.54 would be better but on the highway (at 70 mph) it would be turning 3084 rpms versus 2883 for the 3.31 gears. I don't do a ton of highway driving but I don't want it to be a pain and sound like it's screaming.
My tranny is a Super T10 with 2.88 first (very low) so I will have overall ratio of 10.2 with the 3.54 gears, and 9.5 with the 3.31's. I've never swapped gears before so I don't know how much different these will feel. I am leaning towards the 3.31 just because of the highway rpm's unless someone can convince me that's not a big deal. Price is the same for both, so that's not a consideration. This is a job that I only want to do once, so I will live with it. And I just did the tranny, so that's not changing.
Engine is a warmed over crate 350 with vortec heads and XE268 comp cam.
Thanks
Go 3.70 and be done with it. If you don't do that then atleast go 3.55, the 3.7 are only .066% lower and will give a noticable increase above the 3.55, 3.36, 2.78 for sure. Most of us end up going with an overdrive of some kind, but even with out, I'd go 3.7. with the engine being slightly modified you are apparently after the driving experience and You'll get the best with 3.7 or lower. Good Luck on your project.
Leave the 2.87 gear alone and put a Richmond 4+1 street 5-speed in instead of the 2.88 ST-10... 3.27 1st gear with 1-1 5th gear, great off the line, low cruising rpm...
Leave the 2.87 gear alone and put a Richmond 4+1 street 5-speed in instead of the 2.88 ST-10... 3.27 1st gear with 1-1 5th gear, great off the line, low cruising rpm...
Hope this helps... Crash
that would be the cheapest way to go and get the best of both word
I bought an '82 rather than an earlier year for exactly the reason mentioned above - I wanted the 700R4. Also, I bought this car with the intention of installing a shorter ratio in a few months. That combination should make for excellent acceleration around town, even with the stock motor.
Back when I was still just thinking about all this, I built an Excel spreadsheet so I could make comparisons. I especially wanted to compare the difference in 1st gear leverage with the '82 to the various ratios I've used in the past with standard 3-sp autos. I have a pretty good idea how earlier C3s run with different motors and ratios, so it's not too difficult to look at the numbers and determine what's required for what I'm hoping to accomplish.
Just one example of how I'm using this...
My '72 454 had a TH400 and 3.70 rear. Looking at the spreadsheet, it's immediately apparent that 1st gear would have provided an overall "launch" ratio of 9.18. There's no close duplicate for that in the new ratios, but that's OK, I'm no longer running that motor. Now, the motor is much smaller and more anemic. So, I know if I want to get close to the 1st gear acceleration of the 454, I'll need a much shorter ratio, probably something close to a 4.56. That gearing would have provided an overall 1st gear ratio of 11.31 in the old days, and based on the sheet, I can duplicate it using the 700R4 and 3.70/3.73 rear end.
On the other end of the scale - highway cruising - the old 454 with a 3.70 would have been turning at almost 3,200 RPM at 70 MPH. The 700R4 will reduce that to roughly 2,200, even after I make the gear change. In fact, hwy cruising RPM is reasonable with virtually any ratio. Nice!
The spreadsheet lets me enter any tire diameter, and it recalculates globally using that number. Also, the right side of the sheet lets me enter a fixed RPM as a shift point, and it calculates vehicle speed at that RPM for the 700R4 with various rear ratios.
If anyone would like a copy of this sheet, just send a PM.
Leave the 2.87 gear alone and put a Richmond 4+1 street 5-speed in instead of the 2.88 ST-10... 3.27 1st gear with 1-1 5th gear, great off the line, low cruising rpm...
Hope this helps... Crash
I though that with the 3.08's and the 700r4 first gear of 3.06, but there is a pretty good drop that is somewhat taken up be the converter, but for most racing the acceleration if second and third are almost as importantl. I want to change the 700r4 first out with the 2.87 and lower the rear gear even more so that the torque multiplucation is strong as the bottom of the gears plus the ability to pull through a corner and come out at the bottom of a gear pulling like a freight train with out having to shift. and pull through it.
If you have a carb avoid tall gear ratios and look for 3.36 and deeper so you do not end up with a car that can only use over drive and lock up at 75 mph LOL..
I know the 82 had a 700 and a 2.87 but most importantly it had fuel injection and that was the key to that combo. Even though it was not ideal had they put a carb on it the car would have never been able to utilize that over drive and lock up. It would have stumbled kicked and bucked like ya had egg shaped tires lol
02-04-2016, 04:41 PM
Bear in mind that I do have around 400H.P.
Its the absolute best of both worlds.. I did mine 7-8 years ago ...w/525HP .. THE Best choice in my opinion 
