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Faster you get to OD = less rpm = better mileage. Which results in a happier performing baby cam car.
4.10's are almost "mandatory" on even lightly modded M6 F-body's. These cars have been out for 24 model years now. You're not going to discover some magic recipe at this point, especially on the LT1.
I am going to be stubborn. Driving my car around town, I am only using the 1500-2000 RPM band and it is utterly ridiculous that I am shifting from first to second to third and finally fourth gear maintaining the 1500-2000 RPM groove in a matter of around 5 seconds, to go 30 MPH! The motor isn't crying about it, she is not complaining about being in too low of an RPM range, she hums along just fine as I shift. I still have the option to open the throttle up all the way when it is safe to do so.
Now, I am torn between the 2.73 and 3.23 gears. The 3.23 would be a safe bet, but the 2.73 is what seems to be better suited for my driving style. Once I am working again, I think I should just pay for a used Firebird 2.73 rear axle and have it thrown on my car and try it! I won't get rid of the 3.42 axle, just in-case I am proven wrong. I will say this, I will not be able to tolerate the 4.11 gear on my car! I don't get my thrills trying to drive my car like I am at the track! I would rather have the 2.73, or 3.23, and just stay in one gear when I do open up the throttle when it's safe to do so. Yeah, it's corny, but again I don't take her to the track and she is basically my good looking daily cruiser instead of a full-fledged race car.
Originally Posted by fbody_brian
Find yourself some 2.56 gears, then you will only ever have to shift from 1st to 2nd, you'll never need 3-6!
think of the mpgs!!!!
I am only going as high as the 2.73, but nice joke.
going to 2:73 or even 3:23 is not what anyone else would do...but again its your car
Assuming you have 3:42 (IIRC M6 came with that gear) and you want a "long" gear and keep rpm under 2k in your normal street driving (read holly F lets lug the motor and load it up)...just leave in 2nd gear and shift into 4th under normal driving. Your clutch will take more wear doing so...just like with 2:73 gears
This way there is no cost to "have someone throw in a 2:73 rear end", reprogramming so speedo is accurate
Also you would still have a low enough gear (1st) for up hill take off....or God forbid in cases when you actually need to get the car moving faster....a need that can occur in "traffic".
Assuming you have 3:42 (IIRC M6 came with that gear) and you want a "long" gear and keep rpm under 2k in your normal street driving (read holly F lets lug the motor and load it up)...just leave in 2nd gear and shift into 4th under normal driving. Your clutch will take more wear doing so...just like with 2:73 gears
The speed at the RPM ranges from gear-to-gear is consistent with a 3.42, but again I prefer to have my tachometer slowly reach 2,000 or even 3,000 before I have to shift. Now, I tried driving from second gear and my car really did not like it! It sounded like something was bad with my transmission as the engine certainly sounded bogged down until enough engine torque kicked in at 2,000 RPM and I was shooting off into 30mph. This certainly felt like "lugging", my engine sounded like it was grinding so I will refrain from doing this again! As I see it, driving in second with a 3.42 is not going to be the same as driving in first with a 2.73 rear, or better with a 3.23 rear!
I am a little fearful of the 2.73 from all the negative comments I am reading, but there are a few who have survived with these rear axles as temporary fixes for replacement racing axles and they claim it is not as hard on the engine as is claimed, but you certainly won't shoot up to the stars as fast with your tachometer, but again, my car spends more time in the low to mid RPM range and for my "launches", she will need more power in the low to mid-range. This is why I am trying to make her a "torque-monster" in this spectrum and why I am choosing higher rear axle gears to apply this power to.
The speed at the RPM ranges from gear-to-gear is consistent with a 3.42, but again I prefer to have my tachometer slowly reach 2,000 or even 3,000 before I have to shift. Now, I tried driving from second gear and my car really did not like it! It sounded like something was bad with my transmission as the engine certainly sounded bogged down until enough engine torque kicked in at 2,000 RPM and I was shooting off into 30mph. This certainly felt like "lugging", my engine sounded like it was grinding so I will refrain from doing this again! As I see it, driving in second with a 3.42 is not going to be the same as driving in first with a 2.73 rear, or better with a 3.23 rear!
I am a little fearful of the 2.73 from all the negative comments I am reading, but there are a few who have survived with these rear axles as temporary fixes for replacement racing axles and they claim it is not as hard on the engine as is claimed, but you certainly won't shoot up to the stars as fast with your tachometer, but again, my car spends more time in the low to mid RPM range and for my "launches", she will need more power in the low to mid-range. This is why I am trying to make her a "torque-monster" in this spectrum and why I am choosing higher rear axle gears to apply this power to.
Running a 2.73 gear is not hard at all on the engine. It's hard on the clutch. Good luck with your "launches", you'll get smoked by just about everything. There's no way to leave a stoplight hard without seriously slipping the clutch.
Running a 2.73 gear is not hard at all on the engine. It's hard on the clutch. Good luck with your "launches", you'll get smoked by just about everything. There's no way to leave a stoplight hard without seriously slipping the clutch.
I have morons in Chevy Malibus and imports blowing by my car on the expressway each day doing at least 90mph with no state troopers around to nail them hardcore! I have accepted that my car can't compete against the newer Camaro and Corvette. My intentions behind modifying my LT1 motor are to increase it's lower-end and mid-range power production while maintaining emissions compliance and if possible, to maintain or improve my fuel efficiency.
I really need to have a 2.73 rear axle thrown on my car to see how bad you all claim it is. I don't drive my car shifting in the high RPM range, I shift it very low in the city and when entering the expressway I will ride the tachometer to near red line. So, how bad will my clutch hurt with the 2.73 the way I drive my car when I often have to ride it for traffic idling slower than my car idles on first gear?
This decision is not set in stone and I could end up going for the 3.23 rear axle. Either way, I am not happy with the 3.42 and I want something higher! The 3.23 may be it to save some acceleration and to marginally improve 6th gear high way mileage. Fair enough?
It would not be so bad if you had a 93 6 speed it is geared differently but the 94 up T56s are geared to match 3.42s from the factory. You will overwork any clutch you choose using 2.73s
It would not be so bad if you had a 93 6 speed it is geared differently but the 94 up T56s are geared to match 3.42s from the factory. You will overwork any clutch you choose using 2.73s
Well, I suppose my rear axle swap in the next few years should be a used 3.23 axle then. I don't have my heart set on an axle swap to a higher gear for mileage sake. I am modifying my car to suit the kind of driving I am doing and the low range shifting I make. So, I will settle with the 3.23 rear axle. Hopefully with my transmission gearing, it should produce the effects that I think the 2.73 would have produced without prematurely wearing down my clutch or accelerating too slow.
Now, I have read all the opinions of M6s using higher gear ratios and yes, for highway it will bump up your mileage, if you keep the RPM down! From driving around town in lower RPM, the 2.73 gear ratio should better help me keep my RPM below 2,000. In playing around with a gear ratio/transmission speed calculator, I should be able to get away with using the 2.73 without problems of lugging my motor, I have mastered the feather foot technique.
How's this going for you? Just to give you a little more info I just got back from a trip where 99.999999999∞ of it was driven on freeways where the speed limit was 80mph. It was four hours each way. My car has a 396 and around town gets on average about 12mpg. This is the first long distance trip the car has taken in years and it recorded 20mpg both to my destination and back. The trip there was in 95* heat running the A/C. The trip back was in the morning so the windows were down for the entire way since temps were around 80*. MPG stayed the same. According to a gear/mph calculator at 80mph the engine is spinning at 2400rpm in 6th gear.
My question is, why would my mpg be so shitty in town when the car is just lugging along compared to the open freeway where the car is running a consistent 2400rpm for four hours?
City MPG is always lower than FWY as you are constantly "accelerating" in city/stop & go driving. Fwy you usually just have a lower steady gas pedal to maintain speed so you get a higher MPG on FWY
You need to keep the stock 3.42 gears given your current goals. They provide a good balance of gas mileage, rpm, and gearing for "spirited driving" when needed.
At this point, you really need to listen to what these guys are telling you unless you like wasting your time and money.
However, given your mentality so far, you may need to get one of these to go with the mods you are considering.
Have another question Phoenix'97. Perhaps you can clear it up? Today I was driving one of those fancy cars that has instant MPG readings. Was on a road with a crosswind. Once I happened upon a large vehicle like a semi it would block the crosswind and MPG would improve by 20% or more all the while remaining at the same RPM. Why?
For a mild cam it is perfect. I only have experience with it with ported heads. Ran it in my car for over 80,000 miles with no problems. It peaked at 5800rpm, put down 370rwhp and 350rwtq with accommodating mods. Ran 12.09 @ 115.5 for a best with a 1.70 60' in a 3750lb car. Got 27ish/22ish MPG. I think you'll be real happy with it for what you're looking for.
It's quite possible these days. There's a sticky dyno thread at the top of this forum which may be worth looking at as a reference. As far as gears, I forgot about a 3.23 ratio. Not sure how that would suffice with the two cams which are pretty much referred to as RV cams. Meaning they produce Nebraska Oak pulling torque at low rpm and have a short power curve. If it were me with an auto I'd live a little and go with a 3.42. Your acceleration with the torque produced at low rpm will be outstanding.
You know what, after doing some research and considering the things I want to do with my car which include giving it wide and tall tires in the rear with skinnies in the front, I am going to have to go with a lower rear gear ratio to compensate for taller and wider rear wheels. I may actually need 4.10s after all is said, researched, and done. So, you were right!
I would like some more acceleration versus what I am getting out of my car, and I would really love to get as much power out of my LT1 that I can using a mild custom grind camshaft modeled after the crane 227. I will also consider what you said about mild ported heads for my application, and I may even revisit the notion of using a cross ram EFI throttle body intake on my motor since the goal is maximized lower to mid range power since the car will spend most of it's time in this range. Then, to have a custom true dual exhaust using an H-pipe to finish off and complete the magnaflow sound.
Of course, I need to weigh my options! If all of the above modifications will cost me MORE than the cost to swap in a 2014 LT1, then I seriously need to consider it. I love my car, I enjoy driving her daily, and I am realizing how to improve upon my joy when driving her.
You need to keep the stock 3.42 gears given your current goals. They provide a good balance of gas mileage, rpm, and gearing for "spirited driving" when needed.
At this point, you really need to listen to what these guys are telling you unless you like wasting your time and money.
However, given your mentality so far, you may need to get one of these to go with the mods you are considering.
You really need to trust me and have some faith in what I am considering for a future restoration-modification project for my car.
05-30-2017, 10:23 PM
