Hx-40wii safe boost on stock compression

[Dylly]

Im sure the answer my question is hidden among the 30+ pages of posts on this turbo ... as a matter of fact i feel like i read it there at one time but...

What boost can this turbo deliver on stock compression and stock head gaskets? I was sure i would be able to push it up past the 15psi max with the gm8.

 

[Jamin6.5]

with out a inter-cooler 15psi. but that is more cfm than the gm x turbos had. my truck with the gm-5 turbo would not hold more than 10 psi when working. sure it would hit 15 but not stay there. with the hx-400wii it will hold anything i want. but if you go over 15 air intake temps get high. At 15psi with the hx it pulls great too. i love the way my truck drives now.

 

[Dylly]

An intercooler should have nothing to do with boost numbers... or very little due to the increase in density of cooler air. Also the cfm at 15psi will be the same regardless of turbo granted the compressed air temperature is the same between the two. I also have almost every bolt on performance enhancer including water/ meth injection so im not really worried about the intake temperature.

I would have assumed that the lower back pressure numbers with this turbo would allow higher boost numbers to be achieved... safely

 

[Jorge6.5]

Your right, the lower back pressure in the turbo will allow a safe increase in max boost assuming your motor is in good running condition. I have the same turbo on my truck and the motor breathes my runs smoother and takes less effort climbing hills. I'm really really considering adding an ata front mount intercooler now that I have a turbo that can support more airflow

On obdII should be able to push about 20psi with stock tune without an issue

 

[Dylly]

I definitely read your thread, Jorge, when you were trying this turbo. Its one of the main reasons im likely going tobinstall it, with all the positive feedback... except for some manufacturing flaws and maybe longevity issues, but im taking baby steps here when it comes to turbos... im sure ill go for a genuine holset eventually.

My truck definitely has an aftermarket heath performance tune.. but if your talking about when it will code due to over boosting... that might be the same as a stock tune but im sure i can fool the map sensor into seeing less boost if i have to.

But with stock head gaskets and stock compression.. no internal mods and a healthy engine... 20 psi is attainable? And safe?

 

[Jorge6.5]

If you have the Heath tune you should already had the defuel/limp mode tuned out of it. As for internal mods there shouldn't be any required assumming your motor is in a good running healthy condition. Head studs would be a good idea

 

[sshewins]

Dylly, the HX40WII is way more efficient than the gm junk, no secret there. But to say the cfm would be the same regardless of boost would be somewhat incorrect. What gmx's push at 15 psi, the ATT and HX40WII will do at a lower psi. So the cfm would stay the same, but the boost numbers won't be close.

At least that's my take on it.

 

[buddy]

Dylly was correct, the CFM is exactly the same through the engine at the same boost level. The mass flow is exactly the same at the same IAT. But because it is more efficient there are gains with larger turbos with lower IATs. The definition of efficiency is basically how much mass are you flowing compared to the same boost at ambiant temp. The higher the efficiency range you are in on the compressor map the less it will heat up the air, thus flowing more mass. But the CFM through the engine remains the same. There is a CFM difference at the inlet of the turbo depending on the IAT difference, but always equivalent through the engine cylinders, its a fixed volume pump.

So more air mass at 15psi of boost is the most appropriate way to describe it, because the GMx transfers more heat to the incoming air. volume and mass flow are entirely different.

If you are looking for what is a safe boost level, a stock 6.5 can handle 20psi of boost. the issue is how fast do the IATs climb and backpressure choke the engine into the ground. The small GM turbo contributes to high engine strain and early detonation from high IATs, such that your engine self destructs much more easily. So the safety is not only about cylinder pressure, but cylinder temperature and how it affects the whole combustion cycle and head temp that can deform between the 5-bolt pattern and help compression destroy the gasket.

 

[littleboy]

Dylly was correct, the CFM is exactly the same through the engine at the same boost level. The mass flow is exactly the same at the same IAT. But because it is more efficient there are gains with larger turbos with lower IATs. The definition of efficiency is basically how much mass are you flowing compared to the same boost at ambiant temp. The higher the efficiency range you are in on the compressor map the less it will heat up the air, thus flowing more mass. But the CFM through the engine remains the same. There is a CFM difference at the inlet of the turbo depending on the IAT difference, but always equivalent through the engine cylinders, its a fixed volume pump.

So more air mass at 15psi of boost is the most appropriate way to describe it, because the GMx transfers more heat to the incoming air. volume and mass flow are entirely different.

If you are looking for what is a safe boost level, a stock 6.5 can handle 20psi of boost. the issue is how fast do the IATs climb and backpressure choke the engine into the ground. The small GM turbo contributes to high engine strain and early detonation from high IATs, such that your engine self destructs much more easily. So the safety is not only about cylinder pressure, but cylinder temperature and how it affects the whole combustion cycle and head temp that can deform between the 5-bolt pattern and help compression destroy the gasket.

If this was true why do we run turbos that have double the cfm ratings on the 6.5 and they run cooler and make a ton more power??? If all turbos flow the same cfm at the same boost there is no point to a bigger turbo! Bigger turbos flow more cfm at similar boost.

 

[buddy]

If this was true why do we run turbos that have double the cfm ratings on the 6.5 and they run cooler and make a ton more power??? If all turbos flow the same cfm at the same boost there is no point to a bigger turbo! Bigger turbos flow more cfm at similar boost.

Thats not true. Go do the math or physics/chemistry. Its a physical fact. The engine is a fixed pump, it only flows 6.5L of VOLUME per 2 revolutions. At the same temperature that 6.5L is the same mass. When the temperature is lower, there is more mass at the same CFM through the engine, but more CFM through the turbo comparatively, because it will take more ambient temp air to make 15psi of boost at 100F than 15psi of boost at 200F. But its still only 6.5L of volume every 2 revolutions, no matter how much boost you have. And its still the same mass when you have the same boost at the same air temp regardless the size of the turbo. This is why sometimes too big doesnt help.

It does not matter what the turbo is rated for, that doesnt mean thats the actual CFM it is outputting at a given boost pressure. CFM and pressure when presented with the right demand will give you the max that a turbo is rated for.

The reason they work better is the efficiency of the turbo in two ways. One being the actual compressor map efficiency where it shows you how much mass you get in relation to the pressure due to less heat transfer. And the other is the backpressure efficiency. Backpressure is parasitic to your horsepower and also often very detrimental to the exhaust stroke scavenging effects or lack thereof. So backpressure robs horsepower a couple ways too.

 

[littleboy]

Naturally aspirated you are correct. However once you start putting boost through the engine you start increasing cfm. The more fuel you throw to the engine the more heat you have there for requiring a larger turbo to keep temps in the happy range and to keep the turbo from over spinning so it stays in it's efficient range. Example , if i had an hx-40 on my truck and i added more fuel pushing my turbo to 30 psi . Now it's running hot and not clearing up the smoke ,so.... i put an hx-55 on. Now i'm still running 30 psi, but i'm clearing up my smoke. That tells me that i am pushing more volume through my engine keeping things cooler and hopefully happier. You can't tell me a bigger turbo doesn't increase volume through an engine.

 

[buddy]

Youre talking about AIR MASS, you passed more mass :hihi:, not volume through the engine. An intercooler is rated for CFM, do you ever find one rated for the same high CFM as the turbo? No, because it goes off the CFM of the engine, it doesnt care that you took 2 cubic feet of air and made it fit into 1 cubic foot of air with a compressor. Its just passing that 1 cubic foot of air that used to be 2 cubic feet of air. So yes, the turbo compressor inlet sees more CFM than its outlet, thats basics of compression.

If the air is lower temp, then the CFM at the compressor inlet will be greater, but if you have two turbos of different size, both pushing the same boost at the same IAT, then the CFM and mass is all the same.

 

[littleboy]

Youre talking about AIR MASS, you passed more mass :hihi:, not volume through the engine. An intercooler is rated for CFM, do you ever find one rated for the same high CFM as the turbo? No, because it goes off the CFM of the engine, it doesnt care that you took 2 cubic feet of air and made it fit into 1 cubic foot of air with a compressor. Its just passing that 1 cubic foot of air that used to be 2 cubic feet of air. So yes, the turbo compressor inlet sees more CFM than its outlet, thats basics of compression.

If the air is lower temp, then the CFM at the compressor inlet will be greater, but if you have two turbos of different size, both pushing the same boost at the same IAT, then the CFM and mass is all the same.

Lol, i can get whatever size ata cooler my heart desires. I disagree. A bigger wheel will move more cfm, period!

 

[Dylly]

That is good news. Everything that Buddy stated is 100% correct, and i thank you. I've taken a couple of thermodynamics classes but we never assessed a turbo, just centrifugal pumps, which act the same as a turbo but don't factor in the effects of back pressure, or any strains on a system in general. I do have a good understanding of pump efficiency curves which leads me to believe that littleboy's larger turbo could have been operating in a more efficient point on the curve doing something similar to what the ATT and HX-40wii do for our 6.5's... Allow the engine to get rid of hot combustion gasses easier and not work as hard spinning a bigger turbo at the same psi.

Jorge: I know head studs would be a good idea but i have no interest in putting them in for the sake of putting them in... I am going to build an engine with lower compression, girdle, headstuds, fire ringed, you name it, etc.. I just need to find a good 599 block and have it ready to go for when the time comes... I just don't want to fix what isn't broke... yet.

 

[Dylly]

I disagree. A bigger wheel will move more cfm, period!

Of course it will, but not at the same psi, that's not an assumption, thats fact. There are other factors that need to be considered when there is a bigger compressor and inducer, and housing, and etc etc are used... its a domino effect. For example, you put larger sized tires on your car/truck - at the same speed, your tires turn slower, your engine runs at a lower rpm, BUT that does not necessarily convert into better fuel milage.

 

[Dylly]

Also, I remember reading something about a 10 vs 12 blade compressor wheel on the HX-40ii? Which one was preferred/ should be requested?

Thanks again

 

[sshewins]

Ok, my bad. Sorry Dylly, I was thinking that with a larger/more efficient turbo I could theoretically move more volume and mass. Here me out on this, so you know where I was/am coming from. Air compresses and I was figuring that with a given volume (6.5), the gmx could hypothetically push twice the air volume. And a larger volume could be realized by a larger turbo pushing (again hypothetically), say three times the volume. Keeping in mind air compresses. What I don't know is at what point the air can no longer be compressed. That's where i was goin.

Owww, my head hurts now...

 

[THEFERMANATOR]

A larger turbo CAN move more air at the same boost pressure. If you have an engine with a mass air flow sensor this is VERY evident. I know my logs of Peps truck showed ALOT more airflow at 22 pounds of boost than my stock engine does at 25. His engine is slightly lowered compression than mine, but were both running 01 LB7's.

 

[buddy]

A larger turbo CAN move more air at the same boost pressure. If you have an engine with a mass air flow sensor this is VERY evident. I know my logs of Peps truck showed ALOT more airflow at 22 pounds of boost than my stock engine does at 25. His engine is slightly lowered compression than mine, but were both running 01 LB7's.

Yes, MASS AIR FLOW, that is more mass, people just incorrectly apply the theories to volume (CFM is a volume flow). And its not voodoo that a larger turbo automatically means better mass flow. To increase mass air flow you need to increase boost or lower the air temp. If you do not lower the IAT, then you don't increase mass flow at the same boost. So the GMx at 8psi of boost and IAT of 150F will flow just as much mass as an HX40 at 8psi boost at 150F IAT. However, the at 15psi the GMx is already a heating element so IATs are typically higher so it doesnt flow as much mass as an HX40 or ATT at 15psi. That and improvements in exhaust flow also help the larger turbos, with very little to do with the intake air flow.

 

[buddy]

Also, I remember reading something about a 10 vs 12 blade compressor wheel on the HX-40ii? Which one was preferred/ should be requested?

Thanks again

To me, the 10-blade turbine is recommended, but seems the sellers have no idea they even exist, and won't ask suppliers to provide it. Its just random. Seems most original purchasers got the 10-blade and now everyone gets 12-blade.

The 12-blade should spool a tad faster, but the 10-blade operate better before having to pop the wastegate, lower boost when not needed. The 10-blade on WarWagons suburban still spooled real quick right out of the box, and Raceday ran the 10-blade turbine. You can buy 10-blade 76mm HX40 wheels aftermarket as well if wanting to swap to it. The alternative is just get the larger 16cm^2 HX40, which will also behave better under load, but spooling more at like 1500rpm vs 1100rpm for the smaller housing. That and the smaller HX40WII is an easier fitment, with smaller exhaust V-band and compressor outlet lines right up with stock intake.