Re-Gear question

[8lug]

Hey guys, I can't get my EGT's down!! My last option is to re-gear. To get back to stock I need 4.33, haven't heard of that for a 14 bolt. I've seen 4.10s 4.11s and 4.56s... But I also thought I saw some 4.27s. Does anyone know where I can get 4.27s front and rear for my '06 LBZ?

Thanks.

 

[adeso]

I don't know of one, what are your EGTs? I had/have no issues with 37 and 35s now towing

 

[PACougar]

Are they bad towing or just driving down the road? How high are they getting?

 

[mackthehack]

X2 how high are they?

I thought the 72 vvt runs a little hot.

For the gears check out Randy's ring and pinion. Yukon, Superior. I have been running Superior 4.56's with 39's and now 37's with no problems.

Are you worried about your egt's when normal driving, dd, towing, racing, sled pulling or on the freeway?

The 4.10's with 36-37's would be good for mpg's and if I remember correctly will lower the rpm range at freeway speeds. But with those gears you lose a little bit of low end torque for driving around town.

4.56 give alot of low end torque and due okay mpg wise on the freeway.

I think 4.33's will be a nice middle ground for those tires.

If I were you I would try 4.11's and retune to accomodate for those gears.

 

[8lug]

Sorry, been away, Normal driving, cruise on 70 miles/hr I can break 1250 on a normal highway hill. Towing I hit 1400 on a slight incline with an empty trailer, I haven't been able to tow a load. if I down shift to 5th while unloaded and 4th with the empty trailer my EGTs come down to manageable but unloaded, flat highway, 65-70 miles/hour 10-1050

 

[Chevy1925]

Imop, you need tuning work. I tow 12k on a tune thats still not fully optimized and at 1800rpm, 70mph its runnin at 800-900*. Around town or highway it sees 600 on the flats and 800 max on inclines. 1000 on the big hills if im lugging it unloaded

Thats on 37s and stock 3.73. The only reason i may switch to 4.10 is for the little extra grunt from 60-70 without downshifting from 5th to 4th

 

[8lug]

I think it's a turbo issue, I never had an EGT problem before. I've towed with 36's for over 175,000 miles no issues. I did RDL Manifolds, Up pipes, Down pipe, EGR delete, Banks Technicooler, AFE Hot Side Pipe, 72mm Danville VGT, DSP 5 Mark @ Danville Tuned, ARP Head Studs, Fass 150, Ported Rail Fitting, Shims, PCV ReRout and instant hi EGT's. MPL Motorsports had it for tuning, got about 200 degrees better, and that's where she sits.

I figure with the exhaust work, the intake work, the intercooler and pipes and the water meth I shouldn't have an issue...but I do!

 

[8lug]

I pulled over 20k for a short ways, it included 2 long hills, no issues. I pulled a large bobcat and dump trailer thousands of miles, now I can't pull the trailer empty.

 

[mackthehack]

Imop, you need tuning work. I tow 12k on a tune thats still not fully optimized and at 1800rpm, 70mph its runnin at 800-900*. Around town or highway it sees 600 on the flats and 800 max on inclines. 1000 on the big hills if im lugging it unloaded

Thats on 37s and stock 3.73. The only reason i may switch to 4.10 is for the little extra grunt from 60-70 without downshifting from 5th to 4th

How long have you been running that size of tire and stock gears?

I ran 39's with stock gears for a year and hated it...

 

[Chevy1925]

Since 2006. I honestly cant justify the cost in switching yet. I even have a set of front 4.10 gears sitting here waiting for me to pull the trigger.

Maybe i need to ride in a truck with gears and a load but it seems the twins more than make up for the difference. If i had the stock turbo only, you bet id swap gears.

 

[Harbin_22]

Have you checked for boost/exhaust leaks? Do you have a drive pressure gauge? How much boost are you making while these EGT's are high? A log of vane position and boost while in that area might help.

 

[PACougar]

Unlikely but is it possible you have a bad gauge or damaged thermocouple?

 

[8lug]

Appreciate that Cougar, I put in a second set of gauges and second TC just to be sure!

Harbin - I'm sure Ted checked for boost leaks after the install. I make a ton of boost. I do not have a drive pressure gauge. I make maybe 5lbs on the highway, maybe 10-15 when I hit a hill, 40+ when I goose it.

Where do I measure drive pressure? What is normal? And how do I lower it??

Thanks guys!

 

[8lug]

Bump, where is a good place to measure drive pressure and what is optimal??

Thanks.

 

[adeso]

You can get a gage and tap it off the other manifold the same place you did for EGT probe, but you need a bunch of tubing to let it cool down before it gets to the gage. The ideal DP is 1 to 1 ratio with the boost but with the VVT you won't see that, a lot of DP tells you that something (99% of the time the VVT turbine) isn't flowing what you need it too and the restriction is causing the EGTs to rise. You can see where it starts to diverge from a close to 1 to 1 and I bet that is where your EGTs start to go up quick. You fix it with a more open turbine and tuning

 

[Capt.D]

One thing to remember if you decide to re-gear is make sure the ratio is available for both ends...I have a friend that was re-gearing and bought the rear first and when he had the money found out that ratio wasn't made for the front.....I'm sure it's rare and all but just a thought.

 

[8lug]

Excellent, thanks guys, I planned on ordering fronts and rears together but that is a good point! Thanks.

I have a couple extra ports on my up-pipe, I'll see what I can do, a regular boost gauge will work if it's cooled enough?

 

[8lug]

You can get a gage and tap it off the other manifold the same place you did for EGT probe, but you need a bunch of tubing to let it cool down before it gets to the gage. The ideal DP is 1 to 1 ratio with the boost but with the VVT you won't see that, a lot of DP tells you that something (99% of the time the VVT turbine) isn't flowing what you need it too and the restriction is causing the EGTs to rise. You can see where it starts to diverge from a close to 1 to 1 and I bet that is where your EGTs start to go up quick. You fix it with a more open turbine and tuning

And that makes perfect sense... I was thinking I needed more boost, but it's possible I need to open it up freer flowing instead!

 

[adeso]

And that makes perfect sense... I was thinking I needed more boost, but it's possible I need to open it up freer flowing instead!

balance is everything! you gain nothing from over driving a comp out of the MAP, and while it helps the lower end spool you need to watch how much fuel you put to a turbine. You get a lot of pulse in the manifold so you need either a sensor that can damp it out or something like a crimp to damp it out, search around and you can find out what guys are doing for dp gages

 

[8lug]

Will do, thanks!