Best highway RPMs
 

I am installing an LS3 engine and a 4L70 transmission. I do believe the overdrive in the 4L70 is .70. I have installed 275 40 20 tires with a 28.5” diameter in my 2 wheel drive Blazer. The truck has an open differential with 3.08 gears. I am trying to decide if I will eventually go to 3.73 or 4.11 gears. What is the most comfortable and efficient RPMs for an LS3?

3.73 should run about 22XX and the 4.11 should be about 25XX. If I can I “may” install a taller tire in the future if it will fit?

Thanks
Mark

Re: Best highway RPMs
 

I don't have an LS, but an 'ol run of the mill Vortec 350/4L60 with 210k on it. I have 295/45/18 which is about the same size as urs, mine has 3.42s in it. IMO, it's a good happy medium. Acceleration is OK, but then I can do 100 without the tach bouncin' off the rev limiter. Would go more, but need to tune out the speed limiter. It keeps pulling till it hits 100.

Re: Best highway RPMs
 

Best is subjective. Best for accelerating? Best for gas mileage? For vibration and noise?

Re: Best highway RPMs
 

I mentioned "What is the most comfortable and efficient RPMs for an LS3?"

Engine longevity, noise, comfort, mileage?

Re: Best highway RPMs
 

2500 won't be bad depending on exhaust. As with any build in a enclosed vehicle like a car, suburban or blazer in your case. Exhaust choices will be a bigger make it or break it item then rpm.

I was towing a 5000 pound trailer yesterday up the grape vine doing 3500 rpm. Engine ran smooth, and no excessive noise. I couldn't hear it over the talk radio program I was listening too either. I have the 4.3 LV3.

Personally I like 4.11's, but alot of that depends on available traction.

In my opinion any gear from 3.55's to 4.11's will be a great all around gear.

Re: Best highway RPMs
 

i dont have my LS3 going yet...but all the other swaps ive done i try to shoot for 2000rpm at 65...
it is more than my 13 z71 turns...but the 2k seems like its my sweet spot for power,mileage and noise
but my LS3/tr6060 was in front of 3.31s but when i get it in the truck, ill shoot for 2k at 65 on it as well

Re: Best highway RPMs
 

3.73s with my 28.5" tires at 70 MPH in overdrive at 70 MPH calculates to 2155.

I "think" that might be a good choice. I plan to drive it for a while with the 3.08s just to see if I want a little lower or a lot?

Re: Best highway RPMs
 

In that case lower is better as evidence by the factory. When they make a gas mileage version of a vehicle, axle ratio's and resulting rpm's go down.

Re: Best highway RPMs
 

I have 4:10's in my LS swapped 68 C10. I choose the 4:10's because I installed a T56. I now have a 4L60E in the truck and I would go with 3.73 if I was to do it again. The 4L60E or 4L70E a have pretty low first gear so you should have good performance off the line.

Re: Best highway RPMs
 

Thanks for the replies and opinions!

Re: Best highway RPMs
 

My Dad's truck with LS whatever rolls down the highway 75 mph at 1500 rpm. None of my vehicles would do that. My Buick used to chuggle below 1800 rpm. Never had a vehicle that could cruise the highway at 1500 rpm's.

Re: Best highway RPMs
 

Fwiw My 2010 Camaro SS has the LS3’s nearly identical twin L99, same basic engine just afm and vvt added. It runs about 2K at 60-65, when driven right I can get closer to 25mpg on long interstate trips.when I took it to Vegas a few weeks ago I averaged 23 on the way there with lots of “spirited” romps passing cars on the 2 lane roads I take on that trip while averaging about 80 mph. It pulls pretty hard for a mostly stock car. One of the more popular mods for the Camaro Guys is 3:91 gears however, obviously they pull quite a bit harder with more gear. I wouldn’t hesitate to run it 2K@60. Your 275/40/20 tires are the exact size the SS Camaros run, and the automatic cars have a 3:27 rear gear. The 4l70 won’t have the double overdrive that my 6L80 has but at .70 OD for the 4L70 and .67 final Od in the 6L80 they should be pretty close. 3rd gear in the 4l70 @ 1:1 should wake it right up and should pull pretty hard when you want too. You’ll enjoy 3:73’s I believe.

Re: Best highway RPMs
 

Thank you for a lengthy and informative first-hand experience. I do agree I think 3.73 gears are going to be my sweet spot. I will probably drive it for a season with the open differential 3.08 gears just to see how it feels or until I break something.

Re: Best highway RPMs
 

[quote=Thealien;8875448]I mentioned "What is the most comfortable and efficient RPMs for an LS3?"

Engine longevity, noise, comfort, mileage?[/qu

Yup