1.15 ar for towing

[danzick]

I've been messing with my s475/stock kit for a lot of years now trying to get egts where I think they should be. I'd love to drop 100 degrees, but id be happy with 50. Imo my boost is low for grade towing. With the cruise at 70-75 climbing a grade with around 10k for a trailer weight, I'm only running 30 psi, maybe 35. Even at 70 and running 4th it's hard to keep it under 1300 degrees. Would swapping to a 1.15 housing bump the boost and lower the temps? I have the boost T completely closed trying to get more boost, but it just doesn't help for towing at part throttle.

 

[Chevy1925]

The stock turbo should be opening its gate by 22-25psi to the 475 so it stays in its map. If you have the gate shut, 475 can’t get enough flow and stock turbo is trying to make all the boost which puts its outside its map and like you don’t even have twins. Hence high egts at part throttle.

You might be getting more boost at wot because drive pressure is opening the factory gate to then drive the 75.

 

[danzick]

So to do this, do you use a compressor to put 25 psi to the regulator and watch for the arm to start moving?

 

[Chevy1925]

You can do that but I’d start at 15 or 20psi first or base it off the boost gauges. Watch total boost to see about when the 75 is starting to make boost. At 20psi, my 483 would be making 5 psi. By 25psi, 83 was up to 10 and all increasing amounts of boost were dependent on the 483 from there (total boost only increased the same amount as the 83)

You can base it off best egt’s as well. A drive pressure gauge is really the best way to get it set for optimum performance

 

[danzick]

Great thanks. I'll start with setting it so the arm starts moving at 15 psi? I'd like to give power driven's turbo tuner a try, but it says production in July and our next trip is early July. Wot performance is becoming less and less important to me the older i get.

 

[Chevy1925]

Set it there, test drive and adjust from there.

 

[gmduramax]

Have you tried leaving the wastegate line completely open, back to stock?

 

[danzick]

I had it there when I first did the kit and the egt temps were very high above 1500 on full throttle runs so I turned it up some.

 

[gmduramax]

Something isn’t right, they shouldn’t hit 1500. How much power does it make? And more boost isn’t always better.

 

[danzick]

Well I get that. It was making around 38-40 with an unrestricted gate. I closed it up to make about 50 and the temps went down about 200 degrees and it pulled much better. It made 617 and 655 when I had them load the dyno harder.

 

[PureHybrid]

What turbine and housing are on it now?

 

[danzick]

Box stock. 96/1.32

 

[rcr1978]

I'd get the 1.15 housing especially if you elevation is 5000+, the 475 will come on a little quicker about 200rpm and 3-5psi more from the big charger. Wonder if your wastegate is fukd to= not sealing? Mine didn't last long with the stock charger it busted the gate arm off, like within the first 100miles. Tried a bigger valley and a 480 but the valley one I have now is just to lazy down low and lacks part throttle boost for towing.

 

[danzick]

I checked that. I was wondering the same thing. According to my camera it seals good and looks like new. I do worry about it. I pull long grades where I see 1300+ sustained for minutes on end. And yes. My home elevation is 4500 ft. My truck rarley sees below that. Mostly above.

 

[Chevy1925]

What’s your outside temp? What’s the tunes hp level you are running? What injectors?

 

[danzick]

Oddly enough, ambient temperature doesn't seem to play much of a roll unless it's like 40 or less. All stock fueling. I'm not sure what the hp levels are for tuning. I do know that there is only about 50 degrees difference between tune 1 and 4 for towing. That's why I think there is a problem with my turbo tuning. On my "stock optimized" tune it still runs 1250 plus egt but with a lot less power.

 

[Chevy1925]

Yeah I would agree. You should be 1100 max on stock optimized. That’s wide open high rpm.

At that altitude, even up to 7k ft, the spool up of the 475 isn’t the issue for what you have going on. I was at 12,000ft on a 1.32 and 480 and spooling the stock ihi was waaaay harder than the 480 lol

 

[Bdsankey]

I think you may have a wastegate issue like others have said. Check where it is set at. Kennedy Diesel makes an adjustable "boost increase valve" or you can find another way regulate the air going to the wastegate diaphragm.

 

[danzick]

thought I should update this. I had 4 decent grades to climb round trip. I jimmy rigged my compressor regulator into my cab with some long vacuum hose. I found the opposite of what we were thinking. If I turn the regulator all the way out, it will shut all air to the wastegate. I found that shutting off all boost to the wategate was worth about 5 psi increase in boost and 100 degree drop in egts. that truck has never towed that good. some of the grades were a few miles long and the truck would be into it pretty good for a few miles and towards the top of the hill, it would just start to get close to 1300. most of the climb it was under 1250, which i find totally acceptable for sustained towing. best part, that was in 5th gear at 72 mph. Before, about 1/4 of the way up the hill, it would already be at 1300, and I would have to lock out OD and run it the rest of the way up at 65 in 4th still running at least 1250. it was cool playing with the regulator, because I could open the gate and immediately watch the boost drop from about 30 psi to 25 and the egts would climb past 1300 fast. without letting off the gas I would close the gate and watch the temps settle back down under 1250. I still might try that 1.15 housing out to see if I can get the temps closer to 1200 while running steep long grades.

 

[Chevy1925]

How much boost was the big turbo making?