rears, 285s, 152k. It has a Suncoast transmission with lockup TC. Banks exhaust. KDP killed. K&N cold air intake.

I just had guages installed. Pyro and boost. My question has to do with boost. When I get on it a ton in overdrive--say, when I am ramping up to an interstate, the boost guage goes to 40 or a little beyond. My mechanic says the stock turbo (which it appears I have) should only hit 32 or so, and the fact that it is going to 40 or better means that someone has replaced some of the internals of the turbo. Does this sound right? what kind of mod can you do to a stock turbo?

I cannot ask the previous owner, since he is dead, so I gotta ask the knowledgeable folks here, who probably know more about my truck than the previous owner, anyway. thanks for any replies.

 

I'm new to the whole diesel scene, although I've been involved with turbo cars since I was a teenager (honestly, that was just a few years ago but I've accomplished a lot ). My gut instinct says that a stock Holset should be able to push the Cummins higher than 32psi, but I'm sure some more educated guys will chime in and tell you for sure.

 

Boost over 35psi with a stock turbo just generates heat (high egts) and can cause the turbo to fly apart.
If you're adding lots of fuel, wastegate is blocked or the exhaust is restricted (clogged cat) you can easily exceed the design map of the stock turbo.
My feeling is someone has blocked the hose to wastegate if you're getting that high of boost.

 

Completely blocked, or are you meaning a bleeder valve or ball bearing/spring style valve? If it was completely blocked I would think that it would boost infinitely until it would blow the turbo and/or engine apart.

 

35-38 psi is about max efficient range on these turbos

Sounds to me like what Bill said is correct, and you might have a fuel plate or other mods as well to get that high boost, not sure if it will do 40 psi with a stock fuel plate...

Rick

 

I have a #8 fuel plate. And no cat, by the way. And no muffler. The mechanic seemed to be saying that you could put different internals in the stock turbo to make it withstand the higher boost without flying apart. I do not understand this at all, as I am sure is clear by now.

"Sounds to me like what Bill said is correct, and you might have a fuel plate or other mods as well to get that high boost, not sure if it will do 40 psi with a stock fuel plate..."

Assuming the turbo is entirely stock, then I need to keep the boost at 38 or below. That much I can do, and save fuel at the same time. If anyone knows what he could be talking about re: modification of the stock turbo, let me know.

 

Well there is such a thing

as a 35/40 hybrid turbo. The stock HX 35 can be sent off to HTT or some other shops to be machined and you can run an HX 40 compressor wheel for a little bit more efficient boost. Im not sure how those turbos hold up as im running a stock 35 with a 14cm housing with my setup. The only other turbo mod that i know for a 35 is a wastegate mod, which crossdrills the exhaust divider and allows all six cylinders to gate instead of only three, which lowers ur EGTs and drive pressure a bit.

IMHO for what its worth, twins or a better single are the way to go, i dont see a sence in modifying an HX 35 when u can save that money and a bit more and get a good and proven single, anyways

If you do not know how to adjust your wastegate, (hook it back up if it is blocked, A rubber line behind the AFC connects to a steel line that goes to the wastegate, ) you can always pull your fuel plate a bit back, back off the starwheel and AFC while you are at it, but again it all boils down to right foot control if you are good at keepin up with that.

Best of luck and hope it helps

Rick

 

(have had the truck since July) and folks on here are patient and VERY helpful with the newbies. I really appreciate it. I will let you know if the turbo flies apart!

 

Ill let u in on a hint

I ran mine to 44 psi a few times and it didnt blow up (thank god) but it wasnt for too long or that long, Simply because the pyro told me to back off (once i see the needle on the yellow and red on the color coded pyro i backed off) the Stock turbo will produce nothing more than hotter air that will hurt your egts much passed 38 psi, now with the twins setup it never sees more than 24 psi max (what its gated at). U should be fine, just take care of your ride and it will take care of you

Rick