Turbo over-boost?

[Ramboy]

This question came up during my recent tow from Kerrville, Tx to Bakersfield, Ca. I was towing a GCW of 24,200 lbs. and I had no trouble hitting 40+ lbs. boost . I only did this a couple of times as I had been told that this exceeded the operating parameters of my HX-35 with 14 cm2 housing. If the maximum boost for an HX-35 is around 35 lbs. , how does it continue to increase boost?

Phil

 

[jimnance]

Boost

Boost can be affected by atmospheric issues such as outside temperature, high barametric pressure, low humidity, etc. In theory your computer is controlling the wastegate to limit boost to a particular figure, but if the computer is keeping the gate closed and letting the turbo go wild then these factors will influence the ultimate boost you can see.

 

[Don M]

The HX-35 will not last too long making 40 psi. Mine went about 12,000 miles making 38 and crapped out.



the turbo will continue to build boost past 35 regardless of what the reccomended maximum boost is. Personally, I feel the HX35 is over before 35 with the stock pinwheel.



As the load increases the boost will too and inclines only add to the boost increasing.



larger loads may require you to wastegate more exhaust out.



Don~

 

[Don M]

the computer does not control your wastegate on the 14cm housing. The banks big head wastegate is probably set for the truck being unloaded and in the lower altitude air of Texas.



Loaded up you might need to adjust the wastegate to help lower the peak boost.



Don~

 

[jimnance]

boost

Personally I would worry about repeatedly exceeding 30 lb of boost for long engine life. But if all you want to do is go fast, crank-er up!

 

[Don M]

Your right about that... boost equals dead stock turbos and shorter engine life. I have about 200,000 on my old 12 valve and for 45,000 miles of it has been bombed past 350HP.



So far so good, but I know the end is closer now.



Don~

 

[Ramboy]

Even though I saw the high boost a couple of times, as a rule, I keep the boost at 30 or below. If it starts to really head up, I just downshift. Thanks for the info.

Phil

 

[JR2]

Your tubo will build boost up to the wastegate setting (assuming you have defeated the Map sensor so it will not defuel the engine). What ever that setting is is where your boost drops off. The key to getting good performance is to run your turbo in its efficiency range. Once a turbo gets out of its efficiency range it actually generates heated air and this increases EGT. I think I would adjust your waste gate back to around 32-35 psi.



I ran my little HY35 9cm turbo to 40 psi for a while and the EGT got way out of hand. I have since replaced it with a PDR HX35 with the waste gate at 35 psi. It runs like a dream and for the most part keeps the egt's in check.