Back Pressure Data

[Gwoody]

I have some data on back pressure to share, this is from an 06 Dodge that we ran some data logs on. This is a stock manifold and turbo, the drive pressure is double the boost in the higher boost ranges. The data is in the attachment.

[zstroken]

Why can't you attach it as a graph? :)





Series1 is drive, Series2 is boost.

[Gwoody]

I was pretty tickled I even figured out how to get it on here as an attachment. However, if someone wanted to convert it to graph, that would be good...................

[01PPUMP]

Why can't you attach it as a graph? :)

Not everyone is as smart as you.:kick:

[Gwoody]

Not everyone is as smart as you.:kick:

D... engineers!!!:bow:

[zstroken]

Not everyone is as smart as you.:kick:


Who pulled your chain? :lolly:

[01PPUMP]

No one just glad to be alive.:Cheer:

[zstroken]

No one just glad to be alive.:Cheer:

I can pull my own. I bet you can too!

[PSUCE]

So if I understand this correctly, a stock truck seeing 35# of intake/manifold pressure with 70# backpressure, the head gasket is actually holding 70# boost?

[Scooter's Roofing]

So if I understand this correctly, a stock truck seeing 35# of intake/manifold pressure with 70# backpressure, the head gasket is actually holding 70# boost?

no, it's holding 70psi of drive pressure...

it takes the 35psi of boost and compresses it 17.5 times which = 612.5psi... then when you inject fuel, the cylinder pressure skyrockets far higher still!!!!

70psi is nothing

[Gwoody]

So if I understand this correctly, a stock truck seeing 35# of intake/manifold pressure with 70# backpressure, the head gasket is actually holding 70# boost?

Yeah, those mult layer gaskets are good!!!!!!!! I have retorqued the factory bolts to 125. This was with tthe smarty on 3.

[Scooter's Roofing]

70psi of drive is NOT 70psi of boost... 70psi of boost compressed 17.5 times is 1225psi!!!

[Gwoody]

70psi of drive is NOT 70psi of boost... 70psi of boost compressed 17.5 times is 1225psi!!!

I agree Forrest, cylinder presuure increases as boost does, point taken.
I was pointing out that the CR gaskets are pretty d.... tough.

[Scooter's Roofing]

now that I'll definitely agree with! :)

they'll take a lot more than 35psi :D

[Gwoody]

I suspected the drive pressure was a little high but I was really suprised at it being about double the boost once we hooked everything up to gather the data.

[PSUCE]

no, it's holding 70psi of drive pressure...

it takes the 35psi of boost and compresses it 17.5 times which = 612.5psi... then when you inject fuel, the cylinder pressure skyrockets far higher still!!!!

70psi is nothing

Sorry, meant to say drive pressure. :bang Still wasn't thinking right as you pointed out in your previous posts about the compressing of the boost.

Has anyone played around with this on the other generations? Just interested stock how they would all compare. I realize that as they depart from stock they are all different, but just wondering.

[DIESEL_POWER]

I have some data on back pressure to share, this is from an 06 Dodge that we ran some data logs on. This is a stock manifold and turbo, the drive pressure is double the boost in the higher boost ranges. The data is in the attachment.

It wont do that for long, your at a 2:1+ ratio now. you need a bigger turbo or you need to gate the turbo down about half the boost your seeing now.

[OrangeNV]

If dp is only 70 psi how does it effect hg failure if cylinder pressure is over 1000psi?

i love hearing opinions on this subject

[Krazeeun]

I dont think drive pressure in most cases is a major player in head gasket failure... it's more about peak cylinder pressure, is it not?

[PSUCE]

If dp is only 70 psi how does it effect hg failure if cylinder pressure is over 1000psi?

i love hearing opinions on this subject

This where I was trying to get to with my original post. Would it be the duration of the event? i.e. a "peak" of 1000psi vs a continuous 70psi? Also with a lopsided ratio, at what point (if ever) would one have to worry about reversion?

[XLR8R]

If dp is only 70 psi how does it effect hg failure if cylinder pressure is over 1000psi?

Simple - it doesn't.

I dont think drive pressure in most cases is a major player in head gasket failure... it's more about peak cylinder pressure, is it not?

TIP can reflect combustion pressure like EGT indicates cylinder temp... neither is necessarily an accurate measurement of the critical numbers.

No HG ever failed from blowdown pressure in the exhaust tract.

This where I was trying to get to with my original post. Would it be the duration of the event? i.e. a "peak" of 1000psi vs a continuous 70psi? Also with a lopsided ratio, at what point (if ever) would one have to worry about reversion?

Duration of the pressure is insignificant when it's an order or two of magnitude less than peak combustion pressure.

Reversion is always an issue that must be considered - small turbines & tight exhaust A/Rs require less overlap & higher LSAs in the cam profile to avoid diluting the fresh intake charge with excessive combustion byproducts... hence the 600 series' "in-cylinder" EGR, courtesy of the OEM bumpstick's tight LSA.

[paulb]

Reversion is always an issue that must be considered - small turbines & tight exhaust A/Rs require less overlap & higher LSAs in the cam profile to avoid diluting the fresh intake charge with excessive combustion byproducts... hence the 600 series' "in-cylinder" EGR, courtesy of the OEM bumpstick's tight LSA.

Common wisdom, but all to often mis-understood. Good comment.

Paul

[Gwoody]

I attached a log of a run after installing a new turbo that I have been testing. Huge improvement, drive pressure is usually less than boost. Take a look at the attachment and let me know what you think.

Thanks

Garry

[zstroken]

Pretty Graph.

[Gwoody]

Pretty Graph.

Yes it is, Thanks.

[C111]

it takes the 35psi of boost and compresses it 17.5 times which = 612.5psi.

Sorry, it doesn't actually work that way.

If what you said were true why does my engine make 350psi compression when, by your math, it should only make 255psi (12.1altitude x 21.1 CR)? At 255psi my engine would have massive blowby and barely start.

[Mopar Muscle]

What are you using to data log? What are you using for pressure sensors?

[Gwoody]

What are you using to data log? What are you using for pressure sensors?


The data logs come from the electronic controler that controls the turbo. The controler sends commands to the actuator that changes the exhaust flow that drives the turbine wheel. I beleive the sensors are made by Honeywell.

[Luken]

How has the new setup been working when towing?

[Gwoody]

How has the new setup been working when towing?


Towing with this charger is a huge improvement over the stocker. Some of the places I tow is the same roads. One area I go through I usually have the cruise set on about 78 mph and I leave it there till the egt hits just under 1300. I have to take the cruise off and usually top the hill around 68 or so with the egt just under 1300. With this set up I am able to leave the cruise set on 78 and it tops the hill around 76-77, with egt of 1250. I attached a pic from the compressor side of this turbo.

[G1625S]

Cool thread! The he351vgt on my 96 is controled by a spring I found on the shop floor and holds right about 1:1 give or take up to 45psi. The engine 'sounds' much happier at full boogie...I can only imagine the drive pressure with the stock hx35. Wish I'd had my d/p gauge then for a reference.

[Gwoody]

Cool thread! The he351vgt on my 96 is controled by a spring I found on the shop floor and holds right about 1:1 give or take up to 45psi. The engine 'sounds' much happier at full boogie...I can only imagine the drive pressure with the stock hx35. Wish I'd had my d/p gauge then for a reference.

With this unit it comes with the software to be able to log all of that with a laptop. I attached a pic taken during the install on my 06.

[G1625S]

Pretty dern cool! How much and whereabouts do you tow? Even driving at that speed around here will get a guy in trouble[laugh]

[Gwoody]

Pretty dern cool! How much and whereabouts do you tow? Even driving at that speed around here will get a guy in trouble[laugh]

I live in Missouri and the towing was intersate. They don't usually bother you if you are under 80. The tow is another truck that weighs 8000 and I think the trailer is around 6000.

[Gwoody]

Here is a pic comparing the factory 3rd gen turbine housing to this one.

[Gwoody]

Here is a couple of pics of the complete unit. These were taken for the brochures that are in the works.

[91shelbydaytona]

Sorry, it doesn't actually work that way.

If what you said were true why does my engine make 350psi compression when, by your math, it should only make 255psi (12.1altitude x 21.1 CR)? At 255psi my engine would have massive blowby and barely start.

i believe what should be looked at here is dynamic compression ratio rather than static...

[C111]

i believe what should be looked at here is dynamic compression ratio rather than static...

That still doesn't explain his logic/math for an engine with less than 100% VE.

[Gwoody]

A couple more pics, shows how the 3rd gen elbow fits on this housing, also a comparison of the openings.

[oldturbonut]

Here is an interesting video on you tube showing a guy in a 02 3500 Dodge comparing his boost vs his back pressure. http://www.youtube.com/watch?v=vsFhaIqH-6c

[homewrecker]

So what turbo is Gwoody running? Did I miss that?

[Gwoody]

So what turbo is Gwoody running? Did I miss that?

The turbo in the video is the same one that I have on the 06 that the graphs are from. It's an awesome piece of engineering!!!

[Flowmeister]

I'm not too smart about drive pressure but doesn't a 2:1 DP mean the engine isn't running efficiently meaning lowering it should bring better fuel mileage? I know this is a narrow question but am wondering what happens to fuel mileage when driving easy with a bigger turbo or TH?