OMG!!! Twins Rock part II

[T. Baker]

Jese Diesel Freak,

Give the guy a break! I think what he did is cool. I don't think he is offering a bunch of garantees. If you don't like his sytem build you own or buy a different one. It takes time to get all the test info. Were not talking a big company here. I am all for grassroots engineering - lets not squash this kind of creativity. I'd like to have drive pressure too when he gets around to it. But it does need to be compared to somthing, so a base line needs to be established for different power levels and different turbos. Who has all that info? Does everyone want drive pressure info. before they buy an HX40 etc. ?

 

[Diesel Freak]

yeah, yeah, yeah... I'm a jerk.

 

[KatDiesel]

Originally posted by T. Baker

Give the guy a break! I think what he did is cool. I don't think he is offering a bunch of garantees. If you don't like his sytem build you own or buy a different one. It takes time to get all the test info. Were not talking a big company here. I am all for grassroots engineering - lets not squash this kind of creativity. I'd like to have drive pressure too when he gets around to it. But it does need to be compared to somthing, so a base line needs to be established for different power levels and different turbos. Who has all that info? Does everyone want drive pressure info. before they buy an HX40 etc. ?

What he did is fine and dandy and creative... more power to him. However when he intends to sell this setup to someone (yes they have been listed in the classifieds since 9/30/02) then drive pressure should be one of the first things tested. When playing with turbos the drive pressure will tell you alot. You don't need a baseline to compare it to... ..... you simply measure the combination and see if its working effecently or not.



I would imagine most poeple don't ask what drive pressure is like when buying turbos, because they either don't care or don't know what it is and how it is important. Drive pressure was discussed when I purchased my turbo.

 

[csutton7]

T. Baker--all Mark did was put the waste gate somewhere else--all other info he got from people who've done alot of testing---now that doesn't mean that what he's done is not a worthwhile system, but without the #'s who knows if it's really any different than what's been done before and has been tested ---I think that is the bottom line--and these guys are right if you're going to sell something you should know everythging about it--and if I plunked down 4k I'd like to know if the system is not due for premature failure--wouldn't you???... chris

 

[T. Baker]

Kat,

how do you tell if it is working efficently if you don't have any #s to compare it to?

Chris, if he just copied existing systems except for redirecting the waste gate to the big turbo then it seems performance should be somwhat similar. It makes sence to me to use the waste exaust to drive the big turbo instead of wasting the energy out the exhaust. The parts he is selling are way less than 4k. I am happy to have the oportunity to buy them at my own risk. I have not seen him make any claims about his system being better than the others avaliable. He is just offering the chance to build a system that is the same as his for those that choose to.

I don't knock anybody wanting to know the drive pressure before they were to buy it. I also don't knock him for offering a system that is not proven as long as he is not misrepresenting it. If I decide to have twins somtime I will probably have to design and fab my own set up because of my IH scout set up. I thank Mark for the info he has shared about his project just like I thank everyone else for info on how to BOMB my engine. I learned it all here on the TDR from others who did all the experamenting. Without people sharing on this site I guess I would have had to go to Banks or some other big company and pay out big $ to get any performance.

 

[Diesel Freak]

now for the nitty gritty



I am pulling these numbers out of my butt..... however I think they are close.



if a HX35/12 is operating by itself at a PR of 2. 4 (21psig of boost) I would assume drive pressure is very close to 20-22 psi.



Then we add a large turbo running also at a PR of 2. 4 to feed the HX35. The large turbo by itself needs 10-20 psi of drive pressure.



so total drive pressure if the load is shared equally between the turbos is 30 to 42 psi and boost pressure is 70 psi. (drive pressure is just a educated guess)



if I use a large wastgate on the small turbo to dump to the large turbo and in the process end up with a pressure differential less than 20-22 psi across the small turbo's turbine then the small turbo slows down and operates at a lower pressure ratio. However since the small turbo has slowed down and we still want 70 psi of boost, the large turbo has to speed up and operate at a higher pressure ratio than 2. 4.



so now the large turbo is spinning faster..... due to higher drive pressure. . 15-25 psi... . and the load is not shared equally between the turbos and total drive pressure may even be higher than 45 psi.



Marks system should have dual external wastgates (the HX35 has one because the OEM wastgate only vents off the aft three cylinders) he should also have one on the big turbo.



UGH I need to get a life!

 

[KatDiesel]

Originally posted by T. Baker

Kat,

how do you tell if it is working efficently if you don't have any #s to compare it to?

You test it... . and find the best drive/boost ratio for whatever setup your working on, single or twins. What it was stock... . has nothing to do with what it might be now.

 

[T. Baker]

Diesel Freak,

What makes sence to me is that you want the HX35 to do most of the work below 2k rpm and then the turbos begin to share the load and at higher RPM and CFM you want the big turbo to do more of the work so the engine is not choked by the little turbo. Why should they be balanced all the time? I'd guess that that BHT3B is big enough not to overboost most trucks under 450 HP.

That is the range they run at when on 855 Cummins without waste gates.

 

[Greg Boardman-RIP]

I think Diesel freak has a good point. Not to take a thing away from Mark either. Drive pressure is a must on R&D. If you have a HX40 that builds 40 psi of boost with a 12cm housing you will have a drive pressuer that is through the roof. That is why we buy from vendors that have tested their stuff. Do you think DD or Piers didn't run a Drive Pressure guage on stuff while testing. I am sure DD does. Just told me yesterday. Drive pressure needs to be in the same ballpark as boost. Say 38DP and 40boost. Excessive drive pressure is caused by a restriction in the exhause housing and causes heat. It is like trying to blow air out of a straw. It will come out the sides of your mouth if you blow hard enough. Try blowing through a paper towel holder... ... That is kind of a cheesie way of putting it but it is the middle of the night.

 

[T. Baker]

Greg,

Most turbos have a lower drive presure than boost at some point. It is called the cross over point. The problem is that it is a faily narrow band. At higher flow the drive pressere goes up compared to boost. The whole goal of all this turbo work is to get the turbos to work efficiantly over a much broader RPM and power bands.

 

[Greg Boardman-RIP]

Well I am still trying to learn as I go along. I will just watch from the sidelines for now. Thanks for clearing that up. Greg

 

[TxDieselKid]

this is from LONG ago........

you want a base line? HERE it is... ...

Originally posted by Piers

Here's a little data to ponder.

HX35/12 housing at 40lbs boost has about 72lbs drive pressure.

HX35/14 housing at 40 lbs boost has about 55lbs drive pressure.

HX35/16 housing at 40 lbs boost has about 45lbs drive pressure

Now bolt on an HX40/18 housing, no fueling changes and you get 46lbs boost, but only 40lbs drive pressure. More boost with less drive pressure = lower air temps. For each 1 degree you raise intake air temps, your exhaust gas temps go up by 1. 4 degrees.

Andrew

 

[Mark_Kendrick]

now that everyone is done pulling numbers out of their butt.



Does anyone know the drive pressure of Nowel's twins? how about enterprise? I didn't think so.



There are a lot of factors that affect drive pressure. enough that the pressure needs to be on a curve not a stated #. I lack the data aquisition equipment to record the drive pressure compared to boost and rpm accurately.



I would rather not say than give a wrong answer.



I can say that drive pressure is reduced greatly from the single turbos that are applicable to our engines.



As for longevity, nobody abuses parts like i do.



Later,

Mark

 

[KatDiesel]

Originally posted by Mark_Kendrick

now that everyone is done pulling numbers out of their butt.



Does anyone know the drive pressure of Nowel's twins? how about enterprise? I didn't think so.

I bet they do. Thats the point. Noone said you had to give out the info. However unless I have misunderstood you, you haven't even measured it as of yet? Just trying to get you to measure it... ... . you might be surprised at what you find.

 

[TxDieselKid]

HX35/12 housing at 40lbs boost has about 72lbs drive pressure.

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HX35/16 housing at 40 lbs boost has about 45lbs drive pressure

correct me if I'm wrong, but you want boost pressure to be higher then drive pressure. unfortunaly we all know what Mitchell uses now. i'd be willing to bet if you ask nowel, and maybe mitchell, and were VERY serious about buying, they might tell you.



Andrew

 

[T. Baker]

Andrew,

Boost higher than drive presure only happans at a turbos most effeciant range. It is somtimes called the cross over point. Drive presure to boost changes with CFM flow of air and exaust. You keep giving drive presure to boost info that is only good for one flow amount totaly disregarding how it changes with engine RPM. Like Mark said dirve and boost pressure are on curves. 40 psi boost at 300 CFM will take one drive presure and 4O psi boost at 500 CFM will take another drive presure. Changing the size of the exhaust housing just changes where the turbo is most effeciant. Turbos still work fine when drive presure is higher than boost. But they work at there best when drive pressure is lower. This tends to be around peak engine torque it you have a turbo that is near stock.

 

[Diesel Freak]

Mark measuring Drive pressure is easy.



First find a loading type dyno (mustang)



Seccond call Blue Chip and ask them what the peak fueling RPM is for the FMS.



Third install a 0-100 psi gauge in your pyro port on the exhaust manifold.



Fourth run the engine at full load with the FMS on kill and peak fueling RPM.



This should give you worst case drive pressure at peak HP.



Why peak HP and not peak Tq... ... the air demands are higher at peak HP than at peak Tq.

 

[Diesel Freak]

T. Baker, those numbers TDK gave you are worst case full load drive pressures at peak Horsepower. Which is exactly what I want Mark to measure.

 

[Mark_Kendrick]

I didn't say I can't measure it. I can't record it. looking at 2 gauges even a split second apart isn't accurate enough. The best I can do is give a ball park... in the rain at 100 + mph in a 6-700 hp truck. you get the picture.



I am hoping for some dyno time today or tomorrow since we're not racing.

 

[TxDieselKid]

Originally posted by Mark_Kendrick

I am hoping for some dyno time today or tomorrow since we're not racing.

Why not take the weekend off, and come to Kerrville?



Andrew