Hx-40wii safe boost on stock compression

[Edzzed]

I read most if not all threads here but I wonder, if air can be measured as a volume, as well as can be measured by flow, as well as can be measured by boost being in pounds or kilopascals. It is also measured by pounds per square inch or foot as in how much air weighs. We all know air at sea level weighs about 14 pounds. Does anyone know how many pounds per square inch or feet the gm8 vs. the att vs. holeset flows. To put it a better way, if one cubic meter of air weighs x pounds does one move more pounds vs. the other turbos. and if so which one. And is the ratio significantly more or nearly the same.

 

[RI Chevy Silveradoman]

Just a heads up, Buddy didnt contradict himself once. Everything in that post is consistent, and correct. Its to bad we have the attention span of a golden retriever, otherwise maybe a post that was longer than 4 lines might have the chance of being understood.

Let's keep the personal insults out of this thread, NOW! If you agree to disagree, then say so. Insults are not welcome here! PLAIN AND SIMPLE. Take heed of the warning.

 

[Pillow]

Wow. I appreciate the deeper insight although fluid dynamics is not my strong suit. lol

I cannot explain why, but my HX40II does just fine at 20PSI on my Burb with 200K.

Cooler temps and less boost at cruise than the GM-X. The feels much less stressed while doing its day to day. The bonus and "proof" in my mind is the boost in fuel economy all other factors being the same!

FWIW most days boost never goes over 10PSI. Even when I get on it I still try and keep it below 15PSI. At 20PSI I think I am out of fuel anyway and is just a waste (I have more to do, like FTB mod).

 

[96Sub1500]

Wow, this forum has really gone down hill. Every thread is a bunch of blow hards pretending to be engineers arguing with each other and laying out veiled insults.

To the OP, two turbos at the same pressure and air temp will flow different amounts of total air mass. Our engine is only 6.5l when it is sitting in the OFF posistion. At any other speed, the volume per cycle does not stay constant. It's called volumetric efficiency. That is why fuel maps are never linear.

A turbo with high back pressure will cause a engine to achieve the same intake pressure with lower flow. So what pressure a stock engine can "take" is directly related to what turbo you are using because it will cause other issues such as high egt's. This isn't Wikipedia theory, it's based on 15 years of reprogramming ecu's and tuning fuel maps.

 

[RI Chevy Silveradoman]

Good discussion and debate is healthy. If we stay on topic, we do much better. There are several great and knowledgeable members here. Let's stay focused and stay positive and work with each other. :thumbsup:

 

[millsroger]

Any engine has a constant volume expressed in cc or ci. RPM x volume then divide by two eqals CFM at atmospheric standard pressure and temperature. That results in a specific Mass Air Flow which is an expression of weight not volume. To get more HP you need more air mass in a specific volume than standard pressure will provide. That requires a compressor of some kind. Standard pressure at sea level, or one Bar, is (+/-) 30", or 15 psia or Zero on a typical gauge. An additional 15psi above that is actually 30 psia or 60" of MAP, or two Bar. If the temperature of the air at both pressure levels was the same then the Mass Air Flow would double and if you then keep the Air/Fuel ratio the same you get twice the HP. (this discounts all other system inefficiencies and there are lots of them) All compressors increase the temperature so the MAF does not go up directly by CFM. Do not confuse CFM with MAF---they are two different animals.

 

[millsroger]

Here are HP calcs;

Required air flow in pounds per minute = BSFC times HP times air fuel ratio then divided by 60

BSFC is defined as pounds of fuel divided by horsepower per hour, typically 0.6

Required manifold pressure in pounds per square inch is calculated as:

460 + manifold temperature, times 639.6, times MAF in pounds per minute,
then divided by:
RPM divided by two, times displacement in cubic inches, times the volumetric efficiency

Mass air flow =
Volume of air in cubic feet per minute times air density in pounds per cubic foot.
Sea level air density is 0.076 pounds per cubic foot

As can be seen, CFM is only one factor in calculating MAF

 

[Chopchop]

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

Quick question so I’m trying to Install

1. HX40II in my truck 1999 c3500 6.5
2. I’m trying to get my truck to hold 25- 30 psi
3. What mods do I need to install

 

[ak diesel driver]

Stock compression ratio? If so good luck

 

[Will L.]

Welcome.
Everything I say is meant with humility and politeness. Take no offense, it will be hard to answer such an open question without knowing perimeters. You noticed they quickly fell to argument above.

You are given the simple and correct answer by AK DieselDriver above- luck. Yes, I agree. That is what made the difference many days at the racetrack for me.

More directly: You need knowledge.
Running a stock compression 6.5 at 30psi - I’ve done it several times both single large and smaller twin turbos.

You need to understand that you were building a dragster engine by doing that, not an engine is built for lasting 20,000 miles. You need to understand that it is not a question of IF you’ll blow a head gasket, warping head, twisting the block: you WILL do damage it’s just a question of how well you build the engine as to WHEN it happens in 1000 miles or in 18,000 miles. Do not be confused, you will not get over 50,000 miles doing it, regardless of money spent. I lived decades trying high compression with high boost. My current build has a set of 18:1 pistons going in for a reason. That concept of high compression plus high boost is simply not the best.

Moving forward assuming that you are trying to build a toy not a Street driven pick up to get to work with:
True deck the block after the block filler (at 60% jacket capacity) has cured 60 days. Ignore the difference of spec ring gaps for cylinders 7&8 and gap them the same as the other 6. Reversed coolant flow going in all 4 ports and out the pump ports using positive pressure pump, not an impeller pump. Head studs, oring the block and copper head gaskets.

Note equalizing the ring gap - unequal pressure will warp the head in minutes under that cylinder pressure. So having the rest of the system balanced should go without saying, but for the benefit of readers that don’t know how to build a race engine- the rotating assembly has to be balanced, the injector pump output has to be balanced, and injectors have to be balanced. Without this imagine an engine running 25% less power in 1 cylinder- as the block and head flex if one is not moving as much as the others, it will open the gap and blow the head gasket in minutes. I had it happen before the truck made it half way down the 1320 before. As to the bottom end of the engine- full girdle, scat crank.

I suggest a short study of blown alcohol dragster engine concept. Because the cylinder pressures you will create with that high compression you will create is in that category.

Starting with better flowing heads to help fight the heat complications would help too.
Top cooling system is a given must.

If you are intending on using this as a towing or daily driven truck on the street and not doing $10,000 worth of build, just throw studs in with felpro +.10 gaskets, ignore the how to stop head stud leak write ups done and just gob on ultra grey to the threads. Have junkyard engine #2 done at same time so next month or so when this one goes, you can just swap engines because it is faster than doing both heads in the rig. And you have the truck running the same day each time. Still balance the pistons/rod assemblies but dont bother with crank and machine costs. Just use a scale and home tools. The failure rate will make machining costs not worth it as you go through engine parts. This way doing it with my friends when we were young was some of the funnest times we had wrenching- so if this is the route- enjoy it! I miss those days.

 

[Jaryd]

You are definitely going to have to drop compression. What are doing about fueling it? DS4 or DB2?

 

[WarWagon]

Quick question so I’m trying to Install

1. HX40II in my truck 1999 c3500 6.5
2. I’m trying to get my truck to hold 25- 30 psi
3. What mods do I need to install

What else has been done to the engine? What, exactly, are you trying to accomplish? You have not provided much info so we assume stock: share if it isn't.

You have picked a Duramax DI low compression number for the turbo PSI and appear to be applying it to a high compression 21:1 IDI engine. I never ran more than 24 PSI on a ARP head studded 6.2 with the HX40II. Not because I picked a SANE number of 24 PSI: it's because I couldn't get any more boost out of the HX40II and the sun blocking black smoke when I was trying was impressive. However with 14 PSI of boost out of a bigger ATT turbo I got nearly the same Dyno numbers : the TQ and HP traded winners with one or the other winning but not both. Doing it with 10 PSI less boost IS a winner.

My suggestion from above is don't just focus on the boost number: it's not the only thing that matters.

 

[93detroit]

Listen to the fellas giving you hard earned and expensive advice! I have an hx40wii with an honest HX35 compressor and housing. I enlarged the wastegate port to 13/16" from 9/16", and had the exducer housing bored 2mm to lower drive pressure and boost at highway speeds. With a fully cranked (but stock) 4911 db2, I can only build 10psi at 2k rpm (my wastegate is so loose, it may not be seated tight against the housing- even at idle! This is on an unopened 2006 Optimizer. Maximum boost is 15psi. In addition to the relatively weak design (which is what everyone is telling you), my theory (which I am not smart enough to explain mathematically), is that the faster you spin the engine, the more boost you can reliably hold. Building 20psi at 1700rpm puts strain on everything for a much longer period of time (on the power stroke) than at 2700rpm. Don't lug it! I have 12k hard miles on my combination so far.