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