Ok, looking for some technical info here. I am very interested in drive pressures at defined boost levels and flow rates. This ultimately reveals the effiency of the turbo. I can push my stock HX35 to 35#, but I am sure I have a bunch of drive pressure and I am making plently of intake air heat. I am sure alot of you guys are measuring drive pressure, or have access to the elusive Holset maps..... What are some typical drive pressures seen or shown on maps for the following:

Stock HX35 with 12cm^2 housing... about 350 HP and 30# boost
HX35 with 14cm^2 housing about 350 HP and 30# boost
Hybrid HX35/40 with 14cm^2 housing about 350 HP and 30#
HX40 with 16 cm^2 housing about 400 HP and 35#
Piers HX40 " "
KSB1B " "
aurora 2000 " "
Pius' Bell USB " "

Ok OK I know I am asking alot here but with over a thousand members I should be able to get at least half of this filled out!!!!!

Zino

 

Come on guys! HELP!!!!!!!!!!!!!!!!!!!!

 

Excellant topic -

In additon to the drive pressures needed to get that boost, I wonder what typical egts would be.

 

I'd venture to say most of us are off the efficiency range of our chargers, with backpressure exceeding boost by quite a bit.

IIRC, at 35psi of boost, the stock charger gives you 45psi of backpressure
jlh

 

Is that from real testing? I would have guessed you'd see a lot more than 45psi...

 

Well, we will find out this weekend. I will hook up a gauge and check the drive pressure of my stock HX35 at 35# boost. Its easy enough to do, after all, we all have that 1/8" NPT tap in the manifold we made for our EGT thermocouple, just pull it out, plumb in a guage with some tubing, run it through the window and go for a ride !!

Come on guys with other chargers.... do the same and post results !!!



Zino

 

I saw a thread that had the B/p numbers in it at different pressures for the HX35. The numbers I posted are what I remember-- not necessarily so.

 

Anyone care to explain "drive pressure" and "back pressure" when used in regards to a turbo.

 

Its the exhaust pressure in the exhaust manifold prior to the turbine. Its the energy that 'drives' the turbine hence drive pressure.

 

Yes, TIP or turbine inlet pressure is also referred to as back pressure.

TIP is measured between the turbine inlet and the exhaust valve runners. Generally in the manifold. Many things effect TIP and there are trade offs of too much and too little.

In general terms, higher TIP has the extra velocity to turn the turbine faster and apply more TQ to the turbine shaft. Allowing larger wheels on the compressor side. On the downside, the higher the TIP the higher the pumping loss you have on the exhaust stroke. As the piston is moving up toward TDC the pressure left in the cylinder has to be "pumped" out by the rising piston. This causes a loss of crankshaft power from the resistance. Lowering any pumping loss will always result in higher crankshaft power. Caveat being: if you lower the TIP too far and lose the TQ you need to drive the turbine wheel you will lose power as well. Its a balancing act.

Low TIP can cause a laggy turbo, and if the engine load is applied too fast and too soon as in sled pulling...a low TIP can really get things out of balance and the power output can fall off exponentially.

Twin turbos help the TIP be lower than the intake manifold pressure by compounding the atmospheres.

TIP is best measured using a chamber or snubber between the gage and the measuring point to help reduce pulsations at low speeds. If you are only concerned with total TIP at higher RPM you generally dont need the snubber. The pulses are all but gone as far as the gage can read and the pressure is very constant.

Zino, TIP for your scenerios is not a constant. Too many variables from fueling levels, etc.

In the past I measured over 70 PSI of TIP using an HX35/12 @ 45 PSI of manifold pressure. For most of your applications listed it is always higher than 1 to 1. This is NOT always a bad thing.

Don~

 

I think I followed all you said, after reading it twice. So TIP, Drive Pressure and Back Pressure are all the same thing??? Sorry for the stupid question but this thread is the first time I heard back pressure related to anything other than an exhaust, which it kind of, sort of, is. I'm so confused.
RJ

 

Don M -

Thanks for the explaination -

Is there an ideal ratio (or range) of TIP to boost?

If so what would it be?


Thanks

George

 

Yep, TIP is the best terminology among turbo performance guys anyway. I was always going around saying "drive pressure" or "back pressure" to my turbo guy the last few years. He is from Germany and says he "does not know what that means, unless I am speaking about TIP" He cracks me up. He spent 8 years with Ferrari as the cheif engineer in their Formula One program. From a semi Texas Redneck like me he gets a good laugh too.

TIP is better in the higher than intake pressure range in the lower RPM bands. Say leaving a stoplight or a rounding a corner with little boost. The higher the TIP, the faster it will spin the turbo. The 3rd gens with stock turbos and big fueling are running 90-105 PSI of TIP on the top end at 50 PSI in the intake manifold. Not good for power, but they spool that turbo like crazy on the low end to control emissions and smoke.

Once power comes up and you have the turbo cranking...the lower the TIP the better to reduce pumping loss. Less than manifold boost pressure to TIP ratio. 1 to 1 is always talked about, but it would be better if it was say .85 or less to 1.
The problem with this is if you load the engine down and the RPM is reduced quickly the TIP may not be high enough to continue the boost pressure you need to maintain or recover fast from the RMP loss. Sled pulling seems like a good place to have somewhat higher TIP numbers. As the weight is increased on the chassis from the weight box the engine is loaded heavily. A higher TIP would help keep things going and keep the boost from dropping off from the reduced RPM and corresponding CFM of air from the lower RPM range. Just the opposite is true with a dyno truck for big numbers. Lower TIP is good. The load is small and the easier things are flowing the better to make the most power.

I hear 1 to 1 ratio and "dont exceed 1 to 1", etc. IMO it just depends on what you are trying to accomplish. Most street driven trucks will and generally need at least 1 to 1 and really drive better around town and light to light. Spool up is better, economy is generally better, etc. Of course Dyno numbers suffer some, but a few moments on a dyno and the higher RPM band power is not what 99% of us want or need.

VGT or variable turbine housing were the answer we were all looking for and still hold some merit in the future once the parts and reliablity come up. Price is still high and the ability to control them are somewhat behind. You almost need a neural controller to think for itself and change the geometry as the engine is lossing or gaining RPM, fueling levels, TIP, etc.

Don~

 

Absolutely, positively, without question the variable turbine housing is what we need. Holset has a few. Cost is of course the issue. As for control, us properly valved guys allready have the computing power on board to effectively control it !!!!
lacking that, I am sure that using a pnuematic ratio controller you could build your own variable exhaust housing and control it with three inputs: drive pressure (turbine inlet pressure) boost pressure, and throttle position. I very much would like to get my hands on one of those variable exhaust housing HX35's !!!

PS: All these aftermarket turbo guys will HATE variable exhaust housing turbos, because they will just about put them out of business!!!!!


Zino

 

Graciously stolen from Gunracer1's post on diesel place:

Turbo______CFM______Racing HP____Daily HP
HX35______600________420_________330
HX40______800________560_________440
T66_______800________560 _________440
B1________900________630_________495
H2E_______1000_______700_________550
HX50______1000_______700_________550
HX55______1050_______735_________578
HT3B______1100_______770_________605
T76_______1350_______945 _________743
HT60______1400_______980_________770
B2________1500_______1050________825
HX60______1550_______1085________853
T88_____1450-1750__1015-1225____798-963
HT4B______1800_______1260________990
Big Brother_1900_______1330________1045
T91_______2000_______1400________1100
HC5A/HX82_2450_______1715________1348
T100______2600_______1820________1430
T105______2900_______2030________1595

That what you're looking for??

brandon.