I am trying to understand the limits of a 12cm housing. I have read a million times that it will restrict things on the "top end" but am not sure what that refers to. Does this refer to boost or to engine speed. For example, when one puts in a 3200 governor spring, but is only making 28 psi of boost is there a chance that the housing is a restriction. Or does this only really apply when the turbo is exceeding the efficient boost (32psi ish for an HX-35?)?

Basically I am just wondering at what point a 12cm housing is to small. Keep in mind that I am at a high altitude, so it takes more turbo speed to create boost for a given compressor size. Would it be effective to upgrade the compressor wheel on a turbo that has a 12cm housing to keep things cool as long as the resulting boost was still in the efficient range for the turbo?

Finally, is there a way to tell what compressor wheel is on an HX-35 without removing the housing? I know that the 60mm wheel has 6 fins, how many do the smaller HTT and stock wheels have? I noticed that the housing on the HTT upgrade in another thread is all nice and shiny like to one that is on my truck so I figure it would be looking into. The PO got the turbo from someone who went to a bigger turbo, and wasn't terribly savvy about what had been done to it.

Thanks a ton for your input!

 

Where exactly are you? How high is high elevation?

I top out at about 28lbs of boost with the wastegate shut on my 12cm housing. Pulling the same weight/same grade I like the 12cm much better. Spoolup around town is about the same but spoolup under load with the 12 is much faster. I've got mine ported and the center divider milled completely out down to the scroll in preperation for water/meth. But i'm definately not going back to anything bigger!!

 

The 12 cm housing does pretty well until you have enough fuel to get over 300 HP.

In your scenario, a bigger compressor would be the best way to lower EGT.

Measure the hole, that will get you close to what wheel size you have. Most likely you have a 56 mm wheel.

2nd gen compressor housings weren't painted engine color. A natural aluminum turbine housing is not a sign of an upgraded turbo.

 

A 56mm wheel is usually 8 blades, and 54mm (from a 24v truck) is 7 blades, and just as efficient as the 56mm!

Chris

 

the 12cm housing becomes a restriction just as a 2" exhaust would.It only allows so much exhaust out,even with the wastegate fully open,it starts becoming a real big restriction over 350hp.As RPM rises over 3000,with added fuel,airflow increases beyong what the 12cm was meant to flow.You can measure the restriction it poses with a drive pressure guage.You can also go too big on the housing,and your top end flow will be good,but you will have turbo lag,excess smoke,and weak bottom power end on take off until you get some boost.You want a good balance of both,the smallest exhaust housing you can run that keep drive pressures,egts and cools for the level of fuel you have.

 

Oops, I guess I need to update my info so that my location shows up. APWatson, I am just over the mountains, on the Western Slope. My truck lives at 7,600 feet and I use it a few thousand feet lower and a few thousand feet higher than that regularly. As you know, the hills are big, long, and steep. I haul a 7000lb trailer on a fairly regular basis, occasionally as much as 14,000lb. Your set up is pretty much exactly what I was thinking using the 12cm housing, 190 injectors and a bigger compressor. How do you like it? You mentioned that you were going to put on a water/meth system. Do you have EGT issues? All the time or just when heavily loaded?

Thanks also for the info on compressor ID. I am sure Wannadiesel is correct that it is a stock compressor wheel, but given the source of this turbo, it is worth checking on since it will take me all of ten seconds to yank the intake hose off and look.

 

You are correct I have egt issues when loaded. I have a travel trailer weighing 6200lbs dry empty, so figure 7500-8000lbs with water/gear/etc.. and I have to back out of it when pulling the hills and drop to 3rd gear because of egt's. I have the IP maxed out and advanced really far, but i'm pretty sure its dying(lower idle when hot with A/C on) so i'm not sure how it would compare to a fresh pump as far as the dynamic timing goes.

But egt's are fine unloaded, before the 190 injectors I could climb eisenhower at 80mph with spare pedal and could speed up from 40mph if I got slowed down.

So i'm going to try the bigger intercooler first to see if that'll help then water/meth.