Worth it to go from 3.73 to 4.11

[skyhighsami]

I am swapping a LQ9 in my Yukon with worked 243 heads and ported Fast 102 with headers and BTR Stage 3 truck cam. I have a Yank SS3600 converter and 4.11 gears and Auburn diff. My question is will the SS3600 too much converter for the Yukon or should I send it back to Yank to have the stall speed changed, and would it be worth swapping the 3.73 gears out for 4.11s? Either way I plan on installing the Auburn diff for it's extra strength but with the 218/224 .553 .553 110LSA stage 3 cam in essentially an iron block with 10.9 CR would the switch to 4.11 gears be enough of a change to be worth it? I am on 315/35/20 tires that are 28" tall and I realize the 4.11 will cause the cruise RPM to go up but only around 300-500 rpm in OD. Would the added gearing and SS3600 converter be worth the tradeoffs for the off the line performance.

 

[OR VietVet]

While the 4.11 gear will give you better off the line grunt it also means you are sacrificing size at the pinion gear and therefore some strength. What is the final outcome you are looking for?

 

[skyhighsami]

Well I have a Trailblazer SS which came from the factory with 4.11 gears and a LS2. While the Yukon will be no where near as rowdy as my Trailblazer is now with it's 11.8 CR 416ci LS3 but my goal with my Yukon has been to build my Yukon how GM would have if a SS version had been made. That being said the converter, cam, Fast 102 with 4" intake will basically be an upgraded SS if you will. I won't be able to tow with it since it is as low as it is and will have a converter be it the SS3600 or is restalled to a lower stall speed. Either way the converter will be a Yank SS be it a 2800 or 3600.

 

[OR VietVet]

Ok, well you have my opinion on the gear ratio. Keep it in mind when you drive it and romp on it and the wear and tear over time. I did a bunch of off road rock crawling over the years and seen 4.11 and 4.56 gears shred them selves because of the weaker pinion if romped on in the rocks or mud running. It happens, is part of the fun. I ran 4.56 gears with Detroit lockers at both ends in one ton running gear. I had 38" tires. My stroked small block 400 put out enough power. I had to be careful of those gears. I saw guys with rigs like mine running 5.13 gears that replaced gears all the time. It is what it is.

 

[skyhighsami]

Well my Trailblazer lives on M&H 325/45/17 with stock 4.11 gears in the 14 bolt and I relentlessly beat on it and it makes 200hp more than what I expect from the iron LS2 going in my Yukon and it will never see a tire as sticky. Once I swap the converter in my Trailblazer I'm expecting low 1.5 60' and am not concerned with the R&P life. I'm mostly interested in the swap from 3.73 to 4.11 and if it's worth it and if a SS3600 is too much converter for a full size SUV.

 

[Mechanic421]

Ok I run a lq9 with Vinci 208-216 570-578 Cam,I think 115 lsa circle d 2200-2400 stall. 3.73 awd and have the same question. I pull a trailer on a regular basis. I tow in 3D and was thinking 4.11-4.10 would do me justice. But too scared to regear and still have to tow without using OD. I think the only benefit I would get is no downshift up large hills.

 

[skyhighsami]

What's your overall tire diameter? Because when I went from 32" tall tires on 24s to 28" tall tires on 20s and just the tire diameter change was nice. I doubt you could make that kind of change but making the change to your front and rear diffs would be extremely expensive unless you do the work yourself. I towed with a Yukon XL and Silverado lowered 4"-5" and 5"-6" with a 4" drop hitch flipped upside down and it did great towing 7 or 8k lbs. If you are near Central Alabama I have a set of 28" tires on some Nissan Titan 18" wheels that if you towed your trailer here we could toss them on and see what you think. I think the swap I made was equal to changing to a 4.09 or close to it if I remember right. While I don't plan to tow with my Yukon I am 100% sure I could. If I don't put the SS3600 in but I am putting a 40k transmission cooler in it, but I am thinking about putting it in when we pull the transmission to build it. If I keep the stock converter a flipped 4" drop hitch and air in the bags on 315/35/20 28" tall tires I wouldn't bat an eye on towing with it. If you could get online and figure out the tire diameter that would equate to swapping to 4.11 gears maybe pick up some cheap used tires to drive on and tow on for a while to see what you think. You might be able to pick them up for a 100 or so to just try.

 

[skyhighsami]

I might even try that myself with my Titan 18s after the motor goes in. Just a super cheap way to see if the swap from 3.73s to 4.11 gears is really worth it.

 

[Chert_Detective]

Is that LQ9 a fresh assembly, or has it been in something else that you know the dyno numbers and powerband of? What throttle body size and header dimensions? That's not much lift for a ported manifold and heads. Those heads won't taper off in cfm until high .500 to .600" and with a good manifold in front of it I imagine the difference between .500 and .600 lift cfm would be worth the swap to a .600 cam if it's still on an engine stand.

But you need to look at powerband and weight. I think a 3600 converter would be fine with that engine.

I have a Cricle D 3400 in my 08 Yukon and went from 3.42s to 4.11s and it was a night and day difference down low and mid range but the converter still isn't performing like I need it to. After talking to Circle D, PTC, TCI, and Sonnax they all recommended a 4500-4600 based on weight, gearing, and powerband. Up top I didn't really notice anything. But I think that's because I need to spin it up to 7200 or so instead of 6000 lol.

 

[skyhighsami]

The LQ9 is something I bought and it will either have some stock 243s or some mildly worked 243s my mechanic has I just haven't looked over them yet. The intake is a Fast 102mm and I will get a 102mm throttle body for it. I will end up building a 4" intake using an elbow off the throttle body with a straight section where I will put the LS7 MAF I have. Then another 4" elbow pointed towards the ground with another straight section and a 4" opening air filter

 

[skyhighsami]

The reason I was planning to use that BTR Stage 3 truck cam which is 218/224 .553 .553 110 cam was that I could use stock LS6 valve springs and stock pushrods. So the valve train will live alot longer and not be as noisy. BTR said a LQ9 with the 243s, Fast 102, and exhaust I was planning on will make 420-440. So I'm basing what I said off what I was told. I would run one of their LS2 cams but with the amount of lift they have it will be much more difficult on springs and they will only last 20k or so. If you have a Yukon XL and are running a 3400 then that makes me feel better about running a Yank SS3600 in my Yukon. That Yank is the best converter I have had on a stock to mildly cammed LS2. I still have one in my Trailblazer and with the bigger motor and wilder cam it really needs a 4200-4400 stall. I like it so much I have considered have them restall it but they insist I only need a 3800 which I am sorry but they're wrong. Too many extremely knowledgeable people have said 4k-4500 for me to settle for only a 3800. Besides it only 60' a 1.8 now and with all the power and suspension my truck has on a tire as sticky on there I have it should be in the low 1.5 range. I think I've decided to go ahead on the 4.11 because either way I am putting the diff in so swapping gears isn't that big of a deal.

 

[TheAutumnWind]

What's your overall tire diameter? Because when I went from 32" tall tires on 24s to 28" tall tires on 20s and just the tire diameter change was nice. I doubt you could make that kind of change but making the change to your front and rear diffs would be extremely expensive unless you do the work yourself. I towed with a Yukon XL and Silverado lowered 4"-5" and 5"-6" with a 4" drop hitch flipped upside down and it did great towing 7 or 8k lbs. If you are near Central Alabama I have a set of 28" tires on some Nissan Titan 18" wheels that if you towed your trailer here we could toss them on and see what you think. I think the swap I made was equal to changing to a 4.09 or close to it if I remember right. While I don't plan to tow with my Yukon I am 100% sure I could. If I don't put the SS3600 in but I am putting a 40k transmission cooler in it, but I am thinking about putting it in when we pull the transmission to build it. If I keep the stock converter a flipped 4" drop hitch and air in the bags on 315/35/20 28" tall tires I wouldn't bat an eye on towing with it. If you could get online and figure out the tire diameter that would equate to swapping to 4.11 gears maybe pick up some cheap used tires to drive on and tow on for a while to see what you think. You might be able to pick them up for a 100 or so to just try.

that is a small tire. What rpms do you see on the highway with 3.73s? I'd bet 4.11s with that tire would be more like 4.56 with a 32

 

[Chert_Detective]

Well not an XL but still 5700 lbs lol.

Okay so it sounds like you're still mid way in the planning stage. I'm not unhappy with the driveability of this converter, it's great on the street. It just isn't putting me in the powerband at the tree. I can footbrake to 3400 and it's not close to pushing through the brakes. It went 1.87 60' and should be low 1.70s so I feel ya there.

While that cam, heads, manifold package may not be ideal.. it's not going to hurt anything or cause a drop in power, it just won't be optimum. Which sounds like that's what the Trailblazer is for anyways. So if that is the case then run the 3600 and a cooler, and put the 4.11s in. With a 315/50/17 Mickey and 4.11s Im turning just under 2500rpm at 70 and about 2250 with the daily Toyos on so it's not as bad as you think.

 

[skyhighsami]

It's been a while since I drove it so I don't remember but my Trailblazer has 4.11 and 28" tires and it turns 2500 I think at 70. I will double check tomorrow on the interstate.

 

[skyhighsami]

Well not an XL but still 5700 lbs lol.

Okay so it sounds like you're still mid way in the planning stage. I'm not unhappy with the driveability of this converter, it's great on the street. It just isn't putting me in the powerband at the tree. I can footbrake to 3400 and it's not close to pushing through the brakes. It went 1.87 60' and should be low 1.70s so I feel ya there.

While that cam, heads, manifold package may not be ideal.. it's not going to hurt anything or cause a drop in power, it just won't be optimum. Which sounds like that's what the Trailblazer is for anyways. So if that is the case then run the 3600 and a cooler, and put the 4.11s in. With a 315/50/17 Mickey and 4.11s Im turning just under 2500rpm at 70 and about 2250 with the daily Toyos on so it's not as bad as you think.

I'm not going for a max effort build. I really just want a LS2 so 243 heads on a LQ9 is the same thing for a fraction of the price. The exhaust, intake manifold, and CAI I'm planning on putting together will help the motor especially with a cam. If I can comfortably make 420whp I'm all for it. The cam I picked I am leaning toward is what BTR suggested. I obviously don't plan on taking my Yukon down the track on a tire or anything. I will make some runs down the track for sure but not on a radial. Hell if it runs a low 14 I'll be pleased.

 

[Chert_Detective]

Just don't get max efficiency confused with max effort. If it's still on a stand, now is the time to make sure everything will work together happily. Sounds like you've got the direction pretty much figured out.

To come full circle though and the purpose of the thread. I think you'll be happy with 4.11s

 

[gat0r]

generally....to me, 1 step up in gearing doesnt sound worth it... unless you will be squeezing every drop of performance out of your ride.

on highway its like a 300rpm diff (or less) 3.73 vs 4.10/4.11


if you were jumping like 2 or more sets difference, then it would be noticeable


since it reads like you will be doing mostly track time... go for it.
plus like you said you will already be doing diff work, so its right there.


either way, you do you.
let us know how it works out.


sounds like it will be rowdy & fun.


i need to get mine out to track sometime, but really want LTs & driveshaft first

 

[S33k3r]

Here's a chart that might also help you: https://auto.howstuffworks.com/auto...NQKBDnTn4kiOp3jzOnCFJO0u-U7FLDpsX3NRGgrj4hZt8

 

[Dantheman1540]

I'm not going for a max effort build. I really just want a LS2 so 243 heads on a LQ9 is the same thing for a fraction of the price. The exhaust, intake manifold, and CAI I'm planning on putting together will help the motor especially with a cam. If I can comfortably make 420whp I'm all for it. The cam I picked I am leaning toward is what BTR suggested. I obviously don't plan on taking my Yukon down the track on a tire or anything. I will make some runs down the track for sure but not on a radial. Hell if it runs a low 14 I'll be pleased.

Do you plan to dyno at any point? I'm getting my tune sorted out for a dyno run later this month possibly. I'd love to see 400whp with my setup.

 

[skyhighsami]

Yes after we get it installed and running it will go to the exhaust shop to have the ORY mated to the exhaust and then we will put it on the dyno to tune it. Then to track to further tune it the street tuning.