Competition Blew up my DD Jammer turbo

[Cooker]

Do you have a link to Holset's site with that info on the 40. I was under the impresison that it mapped out at 38-39 PSI?

 

[Forrest Nearing]

their maps aren't very accurate with efficiency lines, etc. but 0. 4 kg/sec is about 55lbs/min. 4:1 total pressure ratio at sea level is just shy of 45psi (3 atmospheres over 14. 7psi)



38-39 might yield more power due to cooler charge temps, but my wastegate is touchy... it's either 35psi w/ crappy spool up or 40-42psi w/ great spoolup. I chose the latter.



here's the map off their site.

 

[HoleshotHolset]

Forrest: I have yet to find a map for an HT3B... since you found the map for the 40 so easily, perhaps you have run across one for an HT3B... ?



Matt

 

[Forrest Nearing]

I don't have one, but I'll see what I can dig up!



Forrest

 

[SRadke]

Originally posted by Forrest Nearing

Their maps aren't very accurate with efficiency lines, etc. but 0. 4 kg/sec is about 55lbs/min. 4:1 total pressure ratio at sea level is just shy of 45psi (3 atmospheres over 14. 7psi)

This I understand but can someone smarter than me help me to read that map? What is Kg/sec and what can I compare it to?



-Scott

 

[Forrest Nearing]

compressor maps measure air MASS (lbs, kgs, etc. ) NOT VOLUME (CFM)



the kg/sec is a metric measurement... (Holset is an English company) IHI maps are the same way. I'm used to standard measurements found on Garrett maps which read in lbs/min (their maps are also much more defined and have seperate efficiency islands... basicly the closer to the center of the map, the more efficient you are.



general rule of thumb on a gasser at sea level is 10lbs/min = 100hp. I've done the math a number of times, and it works out pretty dang close.



diesels are a different animal because they can make hp at VERY rich air/fuel ratios (though EGT's get hot) but I looked at stoich for gas vs. stoich for diesel, and it's not that different... I calculated it for 12. 5:1 A:F for gas (which is what I shoot for on turbo gas applications at WOT) and it came out to like 12. 2 for diesel, so I went ahead and stuck w/ the 550 number (doing the calcs on . 4 kg/sec comes out to just shy of 55lbs/min)



anyhow, the numbers on the vertical scale on the left represent the pressure ratio...



1:1, 2:1, 3:1, 4:1, etc. so the 4 represents a 4:1 pressure ratio over atmospheric. at sea level (I'm at 300ft) atmospheric is 14. 7psi, I usually just round it to 15 for quick glances. so 4 x 15 = 60, but you've gotta subtract the atmospheric pressure, which gives you ~45psi. (actually a little less)



the quick/easy way is to just subtract 1 from the pressure ratio number and multiply by 15. often, you're not looking at a round number on the left, so go ahead and multply by 14. 7 for a more accurate number.



I'm lucky to be down near sea level, so I don't have to really compensate for altitude, but there are rules of thumb for that too (but I've forgotten them/don't have them in front of me)



bottom line is: for most guys making in the 400rwhp range, I don't see a problem pushing an HX40 past 40psi... now, you may not be making peak power because the farther out on the map you are, the more inefficient (HEAT) the compressor is, so you run into diminishing returns at some point, but from a purely mechanical standpoint as far as the turbo's shaft and bearings, spinning it that fast isn't going to cause it to die on you... letting off the throttle instantly at peak boost WILL though!!!



your mileage (and boost levels) may vary



Forrest

 

[SRadke]

Thanks Forrest, excellent lesson. I had to read it three times and do a bunch of unit conversions but I get the idea. Idealy you're right in the middle of the green loop. Now if I only had a book of these so I can figure out which turbo is right for me.



-Scott

 

[Forrest Nearing]

not even necessarily right in the middle...



go to www.turbonetics.com and click on compressor maps on the left, and just take a look at all those maps... you'll get a better idea of what different efficiency islands look like.



I agree though, I wish Holset would produce some REAL maps!!!

 

[SRadke]

Thanks again Forrest. As long as I've got you here I have another question. None of those maps stretch higher than 4:1 pressure. Assuming this is about 45 psi how do guys get away with pushig the big turbo in a twin setup up to 70 or 80 pounds of boost? Are they just so big that efficiency does not matter?



-Scott

 

[Swayse]

Originally posted by RonA

Since you already have an hx-40 down pipe, it probably wouldn't take more than 90 minutes to install the usb on your truck. Your buddy shouldn't mind since it's already used. that way you could try one before you buy one(rhyme). Then you could help him put it in his truck.

RonA

That's a great idea, but he lives 4 hours away. There is still a chance I might get your turbo. The way I understand it, Bell USB turbos don't like cams and low rpm, they will sneeze. He has a cam in his 12 valve and runs 315/75/16 tires with a 3. 54 axle and an auto. So his 70 mph cruising is about 1600 rpm, from what he tells me. I hope it works for him, but if it don't I'm next in line. Oo.

 

[HoleshotHolset]

Scott said: "Assuming this is about 45 psi how do guys get away with pushig the big turbo in a twin setup up to 70 or 80 pounds of boost?"



The big turbo in a twin setup is not producing 70-80psi in most setups. Since turbos will compress air above and beyond their inlet pressure... all you have to do is feed the smaller turbo with a few pounds of boost and it will make huge boost out of it. Normally, the small turbo is trying to compress air from whatever pressure the atmosphere is... . so there's no compounding effect. Make sense?



Matt

 

[SRadke]

So the big turbo is in it's map at say (guessing here) 30 psi and the small turbo compounds that to 60 or 70 psi? Which is why the map is a relative pressure ratio on the Y axis rather than just a pressure. I think I've got it. Does the map not change a little after you've compounded the pressure being fed to the turbo?



-The question guy

 

[HoleshotHolset]

The big turbo is well within its map when it is acting as a secondary or primary (depends on how you see the world... ).



Say the primary is putting out a nice cool 15psi (since it's WELL within its map... )... . the little turbo then compounds that 15psi based on it's own map.



Since you are compounding - neither turbo has to go very deep into their compressor maps.



The map of the little guy doesn't change - but the numbers you input do. Compressor maps are based on pressure ratios @ sea level (one atmosphere)... . if you feed the little turbo a few atmospheres... . you can use the compressor map to figure out how much you can compress what you're feeding it to stay within the map.



Matt

 

[SRadke]

So even as you compress the air and it becomes more dense the map doesn't change? Something must change. At the very least it must not have to spin as much rpm to provide the same compression because the air is denser. I guess that is irrelavant, a map is a map.



-Scott

 

[HoleshotHolset]

As far as I'm concerned - that last statement is correct.



Matt

 

[Forrest Nearing]

well, the Holsets seem to be more efficient at higher boost, but there are some big garretts that'll stretch up there.



BUT, with a twin setup with one blowing into another, lets say you've got one turbo operating at 3:1, pressurizing the air to about 30psi... then you blow that into the inlet of another turbo operating at 2:1... it's "atmospheric" pressure is 30psi, so you end up DOUBLING that an ending up with 60psi



that's why twins are so great for generating high boost pressures. the compressors are allowed to operate in the heart of their efficiency range. This keeps charge temps and EGT's nice and cool!



Forrest

 

[Forrest Nearing]

sorry, I answered before reading the 3rd page! LOL!



bottom line is that pressure ratio on the left is the key... you're looking at an efficiency map for the mass of air compressed at a particular pressure ratio...



if atmospheric is 14. 7psi, you base your boost output on that. if atmospheric is thinner due to altitude, you gotta consider that too!



if "atmospheric" is 20-30psi due to a twin setup? now you're having fun!!!



Forrest

 

[therabbittree]

hey matt maybe you can figure out what my hy35(9cm ex0 and hx55(27cm ex) ar gonna do. . i broke a ear off my h1c today so i threw the hy35 on ended up with the manifold mounted normally as the hy wouldn't work upside down because when clocking it the waste gate actuator wouldn't move much... i definately am gonna need that wastegate we spoke about now . . i fabbed my flanges and started the bends i should be cool soon. . just gonna make sure i support it well with some extra fabbed brackets...

later

Deo

\x/ Hillfolk!

 

[HoleshotHolset]

Deo: I'll give you a call later.



We can talk 'twins' for a while.



Matt

 

[Forrest Nearing]

not quite...



if the first charger is making 20psi based on a 14. 7psi atmosphere, it's operating at a 2. 36:1 pressure ratio...



now, if you have the second charger operating at the same pressure ratio you multiply the atmospheric (20psi) by 1. 36.



if you're operating at a 2. 36:1 pressure ratio, you subtract one atmosphere, and multpily by atmospheric... IE: 14. 7 atmospheric at 2. 36:1 ratio = ~34. 7psi ABSOLUTE, but you need to subtract the atmospheric pressure to give you the amount of pressure OVER atmospheric... 34. 7 - 14. 7 = 20psi on the boost gauge (pressure above atmospheric)



so, if you put 20psi on the inlet side of the big turbo and ask it to operate at 2. 36, subtract an atmosphere and multiply 20 by 1. 36 and you get 27. 2... not very much, but 2. 36 pressure ratio isn't very much for these turbos!



these Holsets operating at 3:1 are hardly stretching their legs... (subtract an atmosphere and round it to 30psi) ask the next turbo to do the same thing, and you get 60psi.



it gets a little gray because the pressure ratios usually aren't the same... the bigger turbos tend to be more efficient at higher boost levels than the smaller ones...



so say you've got a small turbo that's wastegated at 30psi and a big turbo that's still very efficient at the 50psi range (4. 40 pressure ratio) so your multipliers would be 2. 38 and 3. 40... what's 50 x 3. 40?



it's a lot of efficient boost!



that's why you see guys with twins making "only" 60-70psi reporting that their EGT's are essentially a non-issue... because the turbos are in the absolute core of their efficiency range and are barely breaking a sweat.



hth,



Forrest