TxDiesel007

Guys

i used to have the notion, that lets suppose A phatshaft 66 turbo was just that, a turbo that would produce 66 pounds of efficient boost. I got this notion from the HX 35 turbo.. Now if this is so, should the HX 35 have a 35 mm compressor wheel? and produce 35 pounds of boost efficiently? Or is this not correct on all turbos?

IE how much boost can a Phatshaft 66 or other larger compressor wheel turbos produce? i seem to have that notion that it is 66 lbs... am i correct?

Also twins.. IN twins, lets say one was to run an HX 40 as a large turbo, and an HX 60 as a larger turbo, would that also make the set produce 100 total PSI if there were no wastegate or other conditions? I have heard of turbos making upwards of 100 lbs of boost, but im certain that they are much larger than a 60 and a 40.....

I finally understand (somewhat) how twins work, and they are a very strong possibility in my truck in the future. I just need to better understand just how much boost can a large single produce efficiently? and someone to clear up that twins total boost issue....

Thanks guys

Rick

HOHN

No. mass flow in lb/min has no linear correlation to compressor diameter. An HX35 typically has a 56mm comp wheel and flows .46kg/sec. An HX40 flows .53kg/sec, and typically has a 60mm or 62mm wheel.



Nope. Boost if a function of how much resistance the engine poses to the air being supplied by the turbo. If you put the same turbo on an engine that's half the size, you'd have about double the boost.

Again, the "66" means compressor diameter (in mm), not mass flow in lb/min. But the diameter alone doesn't mean much at all. You can have a 56mm compressor setup to flow 30lb/min, and a another 56mm compressor setup for 40lb/min-- but the latter will be much less efficient and have a lot narrower useful range (or it might be totally useless).


The boost a large turbo makes depends on it's compressor map. Boost itself doesn't matter much-- you are more concerned with MASS. HOW MUCH AIR is getting in there. Boost alone won't tell you this, because there are temperature and density variables. A turbo making 50psi of superheated boost will make less power than one making 40psi of cool, dense boost.

The theoretical limit to how much boost a compressor can make is the "choke" point of the compressor.

Again, nor correlation of numbers. It's not a matter of hx 40 makes 40psi, and hx60 makes 60psi. And you can't take 40+60=100.

You need a lot bigger turbos to make 100psi of boost. A typical hx40 and hx60 combo will make about 70psi of boost.
In twins, you have to think of pressure ratios. In other words, how much is a turbo multiplying air pressure.

Say you live at sea level, where air pressure is 14.7psi. If your turbo makes 14.7 psi of boost it is "boosting" TOTAL air pressure to 29.4psi (14.7 from the atmosphere, plus another 14.7) This is where you need to use "absolute" pressure (which accounts of atmospheric pressure) vs "gauge" pressure (which does not). The problem is that a guage reads "0" when there's actually 14.7psi from the air around you. So you have to add back in the 14.7psi ambient air pressure that the gauge ignores.

So at 14.7psi boost on your gauge, the engine is getting 29.7psi total. This is a "pressure ratio" of 2:1. At a 3:1 pressure ratio (PR), the engine sees 44.1psi, but your gauge will show 29.7psi.

Twins work because of this multiplication. Say you have a single turbo operating at a 3:1 PR. You'd see 29.7 on the gauge. To get high boost numbers, say 58.8psig (on the GAUGE), you'd have to have a PR of 5:1. A turbo is very inefficient trying to multiply pressure so much.

Instead of one turbo running 5:1 PR, what if you went to twins with each turbo only running 3:1 PR? Each turbo is now more effient (lower PR). The first turbo make 29.7psig ("gauge" boost) and feeds it to the second turbo.

Now, yoru second turbo is also multiplying air pressure. But instead of just getting ambient air, it's now "force fed" air from the other turbo. So its 3:1 PR isn't multiplying 14.7psia (total, or "absolute" pressure), instead it's multiplying the 44.1psia that the other turbo is feeding it.
so the 44.1psia timesthe 3:1 PR gives you 132.3psia!! Subtract your ambient, and your seeing 117.6psi of BOOST.

So, it's all about the pressure ratios. That's why twins work so well when set up right.

The lower the PR, the more efficient the compressor can be made to be. Staging compressors (like twins do) allows better overall efficiency.


Your welcome. But I suspect you have some homework to do based on your flawed understanding of turbo sizes relative to mass flow and boost levels. They are only loosely related, and you can't draw much useful info from just compressor size or boost numbers, and CERTAINLY not model numbers (like hx35!).


Justin

got...DIESEL?

knowing how to read compressor and turbine maps as well as being able to do the math associated with volume/mass and temperature influences are a must if you're not going to buy an out of the box set of turbos. And even if you do buy a set, knowing how they work fundamentally is a must to get them tuned. Garrett has a nice tech essay on their spin off site...i believe turbobygarrett.com...that will get your feet wet to understanding the principals and even a basic understanding of how to read a map, and where all the measurements come from that we use to spec our turbos. I suggest that as a first read....then start gathering maps as you can get your hands on them and study them before even breaking out the torches and tigs.

zukgod1

Now thats what I call allot of GOOD info.

dan

TxDiesel007

Thank you very much Justin!

its for people like you who explain these things to people like me that this site is as solid as it is.. Many thanks once again for your good information.... I printed this up so i can read, learn, and observe...

Rick

Diesel Freak

Also, Maximum Boost by Corky Bell is a must read!!!!

Then there is my little research paper from last year.

http://www.nwbombers.com/membersites...reak/Final.doc