turbo's and gears.......the big debate.

[4.8t]

ok i have questions about turbo's and gears. here is what i know.... people say high(ratio) gears load the turbo better and help it spool. but gears like that are hard to get around on in heavy trucks with big wheels/tires. fom what i have found is most people seem to say 3.73's are a great gear for trucks and turbo's. here is where my question comes in. most guys htat say this have short tires. the may have big rims but the short tire makes the gears seem lower (ratio). i did some math and a 30" tire with 3.73's is almost the same as 4.10's with 32 almost 33" tall tires.

so it seems to me that in my heavy AWD tahoe with 275/60r20's i should run a 4.10 gear to get the same performance as a lowered truck with short tires on a 3.73 gear. am i correct in this?

i have to rebuild my front end and put a new trutrac in my rear. i broke the detroit locker with the last axle i broke.

[George C]

that logic with gearing works well for a light vehicle. once you start tossing in the weight factor normal thoughts are thrown out. Youre tahoe is easily over 5k in weight might even be close to 6k. youre standard height tire is about 31.5 and running a 373 might not be enought to help you get off the line. Ppl forget the fact that gearing as always helped a heavy vehicle make up for some lack of power. I went from 488s to 410s with a calculated 30" tire and i actually lost mph in the 1/8th. I gained more on the topend but lost it where i needed it the most. If i had a 32" tire i probably wouldnt hesitate on running a 430 gear combo to be honest if i was 6k in weight. The weight of the overall package also helps load the turbo so keeping a gear that will help you accelerate i think is more important then a lower [numeric] gearing.

also another way to look at is gear the vehicle for the mph you intend on running. Its better to be in the middle to peak of youre power band then the lower part crossign the traps. So figure on your mph and desired rpm then select gearing to go along with these based on your tire size.

your weight and rotating weight will help spool the turbo

[4.8t]

this is what i have been trying to explain to people myself. you worded it better for sure. my calculated tire hieght it 32.99 according to this Gear Ratio Calculator so i should go for the 4.10's for sure then? my biggest fear is that i loose gas mileage. but then again it might get a touch better due to wieght and tire size. 2000rpm at 70 and 1700 at 60 with 4.10's

[George C]

this is what i have been trying to explain to people myself. you worded it better for sure. my calculated tire hieght it 32.99 according to this Gear Ratio Calculator so i should go for the 4.10's for sure then? my biggest fear is that i loose gas mileage. but then again it might get a touch better due to wieght and tire size. 2000rpm at 70 and 1700 at 60 with 4.10's

heres the thing about trying to explain something to ppl. The majority of ppl cant grasp things along with normal things that occure in daily life, so they follow what others say and so on. then you get to a point where the info they are speaking is so watered down it holds no infomational value. This is a downfall to the internet.

Only you can have the true answer to this by experimenting. Once you get the info then you can souly speak with actual real world experience a facts instead of most where they just write a check to have someone do their work and research

so you upgrading to 410s with youre 33" tire will help you out, youre 60 and 1/8mile times should improve

[George C]

as for gas mileage, the steeper gear should actually help you since its making the motor work less by not straining trying to move yorue heavy ass truck.


ex..... my truck stock with me in was 4400lbs with 5.3 and 373 rear buddy had his truck weighed in at 4300lbs with 4.8 and 342. my truck got better highway and city with the fact i had a bigger motor but it was in direct result of gearing


the happy point of mpg ive found to be aroune 17-2100 rpms for most applications, anything lower and you lug youre setup and anything above that you start winding it to much

[4.8t]

i agree totally. my own little experiment was with the 4.3l turbo silverado project i finished not long ago. it had 3.42 gears and was a extcab 2wd with nv3500 trans. it ran real good but the gears were so high that it took for ever to get into a good powerband. once boost came on it would move real nice. but when he shifted the rpm dropped so low, that it took forever again to get to the rpm it needed to be at. we put a set of 3.90's in it and oh man did it wake up!! boost came on real fast and when he shifted gears boost would come right back on. it ran 103 in the 1/4 mile. 4.3l v6 with a mpt70 turbo.

i agree with the fuel mileage thing too. funny thing is it took my wife to prove it to me. we went on a trip and i was driving 70 in my silverado trying to keep mileage good. i was getting 19mpg so i was happy. i told her to keep it around 70mph to keep the mileage. she said ok and i fell asleep. i woke up to her hauling ass. i ask her what she was doing and she tells me the truck felt "better" at the faster speed. she got 21-22 mpg doing this. and i got the told ya so look on top of it. lmao

[George C]

i agree totally. my own little experiment was with the 4.3l turbo silverado project i finished not long ago. it had 3.42 gears and was a extcab 2wd with nv3500 trans. it ran real good but the gears were so high that it took for ever to get into a good powerband. once boost came on it would move real nice. but when he shifted the rpm dropped so low, that it took forever again to get to the rpm it needed to be at. we put a set of 3.90's in it and oh man did it wake up!! boost came on real fast and when he shifted gears boost would come right back on. it ran 103 in the 1/4 mile. 4.3l v6 with a mpt70 turbo.

thats another thing a manual boosted setup needs different gearing aspect and turbo sizing then a stalled auto. A good stall will make up for spool time where as a manual still has to go thru the rpms to reach the same point unless you slip it as you drive which will do nothing more then eat the clutch's life.

i noticed the same thing going from 488s to 410s. it made it nicer crusing on highways, it made it nicer roll racing but made it horrible for getting off the line and shift rpms

[4.8t]

i think the 4.10's will give me the best of both worlds. as much as i can get anyway.

[dirt track racer 81]

Glad to see you look outside the box from what most people run.

[zeake]

i put 4.10s in my truck and noticed a good diff