Engine/Transmission (1994 - 1998) Max boost for HX35-12

[Archive]

I want to know if there is anyone who has gotten more than 40-41 psi from their stock turbo?

I could easily get 39 with just a little camplate surgery on my puny 160 hp pump.

I have since added the Diamond B 370 injectors. My max boost still hits the brick wall at 40 psi. I suspected my tiny delivery valves weren't allowing sufficient fueling.

I then added propane injection. I have my system set to come on at 16 psi. The propane alone adds 6-8 psi of boost when it comes on. Still though, 40 psi is my max.

Any thoughts? I searched through the archives for hours, but I've never heard of this "limit" before.

Thanks,
Chris

'94 2500 4x4, auto, custom fuel plate, 370s, scotty air, homemade propane injection.

 

[Archive]

Mine also maxes out at 40-41 PSI. I had 37 - 39 before moving my #11 TST Plate all the way forward and I excepted to get more when I pushed forward. But it stops at 40 - 41.

I believe this is because of the exhaust restriction the small housing has. It won't allow anymore. I have even unhooked the waste gate and no effect. I have unadjusted my TST boost elbow now and only get 38 before the waste gate opens. Having the extra 2 PSI didn't lower EGT any.

------------------
Dee'sel
97 2500 Club 4X4 3. 54, Forrest Green/Driftwood, LSD 5 speed, K&N Air filter RE0880 & Psychotty, TST #11 all the way forward, #12 for winter, AFC spring kit, Geno's Exhaust Blanket, TST EGT gauge & TST 0-60 boost gauge in A Pillar, Hypo clutch ass. , Cat-be-gone, 4" Dynomax Bullet muffler, Crome 4" turn down, AmsOil ser 2000 75W-90 in Trans, Geno's trans filter kit, AmsOil ATF In Transfer case, AmsOil 15W-40 Oil W/ Bypass system, AmsOil Ser 2000 75W-90 in front & Rear ends, Lund Winter front, Leer Cab Level Shell Driftwood , 235/85R16 Goodyears, Dyno'd 342 HP *NRA/USPSA member and proud of it*

 

[Archive]

Your engine is better off with a larger turbine housing and less boost. It's easy to damage the turbo when letting off it quickly at such high boost (couple hundred thousand rpm too!). I bet your enigne's mx egt is pretty high too, and that is a good way to crack the head at the valve seats.

Some folks use boost numbers as a measure of performance and hp. Boost is at best an approximate indicator and ideally your engine will make just enough to burn the fuel and help cool the exhaust. If you hve access to a good dyno, you can expect to find a performance increase going to the 16 cm2 housing with similar or lower boost numbers. The internal clearances of the turbo also affect the amount of boost you will get.
Hope this helps.
Joe

 

[Archive]

Thanks Joe,

I know I need a bigger exhaust housing. I am holding off for the HX40-16 though. I was just curious as to why 40 seems to be a brick wall with the stock turbo.

Enquiring minds want to know. #ad


Thanks for the tip,
Chris

 

[Archive]

I used to have boost pressure "bleed" off to limit it to 45 psi with around 350hp, with it wired shut I could attain 53lbs. with my "stock" turbo and 4" exhaust, 360degree K/N, the center were the silencer ring goes cut out.
Adam

 

[dcash]

i dont know if its gonna do any good to reply to an old thread but i thought i might give it a try. adam, explain more what you did to your turbo. cut center out? very interesting.

hope you read this,

du$ty

 

[Jim Fulmer]

dcash

What he is refering to is the area between the inlet and the housing surface, if you take the silence ring off it's the area under it, this is nothing new, gassers have beeen doing this for years. It's suppose to fool the turbo into thinking it's bigger that it is (this is what I was told)



Jim



Nice location!

 

[SlyBones]

In some threads a while back discussing turbos and efficiency maps, the best I recall the efficiency map of a stock HX35 ended at about 36psi. Which ( I thought I learned in those threads ) means that beyond that the turbo is working too hard and is heating up the air. So now the boost is ADDING to your egt's and not reducing them.

 

[Forrest]

One of the TDR's had an article comparing the backpressure of the 12 & 14cm housings on the HX35. I think the 12 looked like 70something psi of backpressure at 30psi. The 14cm housing was over 50% less. The backpressure @ 40psi must be huge.

 

[Don M]

It is Forrest. Real high.



Don~

 

[BigBadDodge]

Only mods I have are a #10 plate slid all the way forward and a 4K kit, I get 44psi

 

[BigBadDodge]

Only mods I have are a #10 plate slid all the way forward and a 4K kit, I get 44psi

 

[BCFAST]

Guage accuracy aside, mine goes right thru 45#... . I only did it once and my wallet got scared, so I backed out of it gently.

 

[Snow man]

I dont know this for usre,but if boost goes over 37 psi,the superheated air would nor only increase EGT's but reduce power as well. i just switched my housing to the 14cm,and I did get a little more lag,but my EGT's came down about 100 degrees at WOT on 5x5,and the motor revs a little easier,boost went down about 2-3 psi on average from 39 to 36. It takes al ong time to hit 1450 now,it used to hit in almost instantly when you nailed it on 5x5.

 

[jimk]

Drive pressure

Don m I have a few questions, I know that this must take a lot of time so I appreciate the time as I am trying to learn.

If the drive pressure can be reduced and maintain the desired boost, will the drop in drive pressure result in increased torque. If I understand that the drive pressure are just pumping losses.

So for the guys who wont the most bang for the buck, The hx35 with a 14 or 16 is the best? If the auto is used and a 89% convertor, and the standard transmission.

Besides the strength, what is the main reason for running a marine camshaft, more lift, increased duration, or rate of lift at . 050 . What do you reccomend to make 350 hp as for as turbo size and camshaft type. I wont power and good mileage, and I wont to be able to have a reliable and dependable truck .

Thanks again Jim

 

[Jff24Gordn]

well, ive hit 48 with my hx35 - 12cm2

 

[HoleshotHolset]

What's this about removing the center section on the inlet side of the compressor housing? This is news to me.....

That little setup in there looked like a restriction to me... . but I've just been driving with it in there.



How did you all take it out? Dremel/etc? And how careful do you have to be in polishing the nubs down after you grind everything down?



Matt

 

[AWM]

70# of exhaust drive pressure ?, I thought the stock exhaust springs were only rated at 30# Bob

 

[Don M]

Originally posted by AWM

70# of exhaust drive pressure ?, I thought the stock exhaust springs were only rated at 30# Bob

Nah, that is a misconception I shared with you at one time too.



The blues are about 65-75lbs @ 50mm and the whites are about 144- 157lbs @ 50mm.



Don~

 

[WadePatton]

Where are the efficiency discussions? I'm searching and not finding.



FTR my 35 has been to 42+ with a fueling box and stock injectors.



I'm working on reducing it's peak operating pressure by drilling the boost fitting.