Just finished these runs.

Boost EGBP

5 PSI 6 PSI
10 PSI 11 PSI
15 PSI 16 PSI
19 PSI 20 PSI all @ 2200 to 2500 RPM on numerous runs and WOT.

18 PSI 21-22 PSI @ 3000 - 3500 RPM

No my x-over isn't leaking, checked it before the runs and retorqued the bolts and i doubt i could get 19 PSI boost if it was.:ro)

Here's a new pic of my wastegate controller since i've changed it.

So up to 2500 rpm you had 1 lb. more backpressure than boost? Who was it that was saying that after 12 psi boost the back pressure was astronomical? :rolleyes: No, CR I know it definitely wasn't you :ro) thanks for the info. something to chew on

Where is your tap physically located?

What's with the Small Breather/Filter?

Where is your tap physically located?

Where did you tap into to get your exhaust back pressure? I'll bet it's after the turbo in this case. Looking for pressure before turbo. After turbo would be exhaust system back pressure > tail pipes, muffler. Pre-turbo pressure is the pressure needed to determine engine/turbo efficency. The engine cross over pipe is a good location to tap into.

Where did you tap into to get your exhaust back pressure? I'll bet it's after the turbo in this case
I'll take that bet!

I tapped pre-turbo in the boss below the turbo on the underside across from the pyro probe, been tapped there since doing my heads, just had it plugged until i got the fittings and stainless hose to get pressures. So this is not in the exhaust after the turbo and its not in the x-over, if pressures are higher in the x-over i can't see it being by more than a pound anyways. My testing confirms with my truck that back pressure is not something to worry about.

Small breather is a test i just put on, seems to have helped somewhat, going up hill unloaded OD 65 MPH i was able to obtain 21 PSI and hold it for a good 10 seconds. So now i only have another 5 PSI to go to make 26 PSI....lol

Stock GM-x turbo too?

Pressure would not be higher in the cross pipe, that was just a suggested location. Suggest having the gauges checked, your readings seem faulty. Need matched mechanical gauges for this test. The stock turbo at that boost level is highly restrictive. Get two gauges and a regulator and "T" them together to see if they are evenly matched.
Glad to see your doing some testing instead of guessing, Looks like your on the right track.

Stock GM8 turbo. I'm very sure the gauge is accurate to at least within 2 PSI but i can check that against a deadweight later just to see. Its a quality oilfield fluid filled mechanical gauge with 6" face, reads in PSI and KPA.

So what pressures do you think it should be at?

A little color for the post. 79mm or 92mm, what do you think?:ro)

Looks like your a little rich on the fuel curve.

Need two gauges = matched. Oilfields have neat gauges. Get you a pair and hook them together with a regulator for a comparison, then test.

>So what pressures do you think it should be at?< You already won one bet now you want to put me on the spot for double or nothing? I'll go with your test results after you meet the parameters given.

That mirror writing should not say, "objects in mirror closer than they appear".

It should say, objects in mirror don't appear at all.

Now, let me ask this question here: (cause I'z don't knowz de answer)

If you are measuring your EGBP, would the reading be not different if you have incomplete combustion as such seen in the above pics? Just thought I'd throw that out fer discussion.

Black smoke = high EGT's? doesn't it?

With a few gross math figures, you're gonna need at least 26 psi boost to help burn that extra fuel . . . maybe more. How many rolls of duct tape are you gonna need 'round ye ole engine block?

Pics aren't of when i did the EGBP tests, that smoke is just taking off before spool up (which i think is to slow) and hitting the throttle, very little smoke on the EGBP tests @ 60+ MPH. Here is WOT 65 + MPH on the first hit of the throttle.

I have some Westers mirror stickers that say "Objects in Mirror Soon Dissappear"........lol, just haven't put them on yet.

My tap was dead center of EGR upper manifold and the 40 psi was verified with 2 different gauges at 15+ boost

You have peaked my interest. Show and tell rules. Lotz of traffic on this tread all of a sudden. People across America and foriegn countries too, want to know
"what kinda Maple Sryup is CR runnin' in that thing!"

My tap was dead center of EGR upper manifold and the 40 psi was verified with 2 different gauges at 15+ boost

Not sure about a reading there or what it would do. I will verify my gauge against another to see if there equal. If not i'll do the test again!:D

"what kinda Maple Sryup is CR runnin' in that thing!"

DSG secret formula conditioner??? Nah.... just gotta be the mods...

I should be checking out on building an IC tomorrow.... unlike anyone here as seen i'm sure. Once again oilfield technology applied to the 6.5. I'm also in the middle of making a new upper intake.... kewl..

Great work on the EGBP test CR. That's some serious cloud tho..

My tap was dead center of EGR upper manifold and the 40 psi was verified with 2 different gauges at 15+ boost

TD: I'm just still wrappin' my brain around these numero's. Was your reading taken with stock or improved exhaust?

Great work on the EGBP test CR. That's some serious cloud tho..
It was very, very windy too. Wife wants to take some pics from the outside to post here....lol.

Anyone here ever look at the turbo flange on the exhaust and turbo bottom, not sure what you guys got but mine don't line up in a perfect square, offset about 1/4" so i did a very small amount of dremel work on it just to smooth the corners some, was thinking about matching it up perfect but wasn't set for all that grinding when it was off.

Good Work there CR. I bet that gauge is like the ones I work with and they get checked twice a year and can't be off very much at all. Let us know how the second gauge reads too. That will be interested to see, I believe your testing location would be the best place for back pressure working against the turbo.
Keep the good work coming

I was thinking he was running his boost gauge and his Back pressure gauge to compare, least thats what I thought I understood him to be saying.

DP I was not using the scan tool for a gauge, no way to hook it up, it only goes to the OBDII port. No bets anyways, thats more joking than anything. Even if the gauge was 10 PSI off (which i doubt) its still a far cry from TD's numbers and gives me peace of mind the EGBP isn't too high when i'm killing this thing with boost.

I was thinking he was running his boost gauge and his Back pressure gauge to compare, least thats what I thought I understood him to be saying.
Yes i was comparing boost to EGBP using my boost gauge and another on the exhaust manifold, my boost guage is accurate with the scanner, dead on!):h

One more question for TD. What turbo are you using? Just so we are comparing apples to apples.

GM-8, the delta though may be S vs F intake system and reading center of EGR, to compare I need to tap where he is reading or for him to read where I'm reading.

May be some delta T there, but not delta P - turbo is the restriction to both banks, and the crossover pipe is larger, more direct shot, so pressure would equalize.

Fall of 2000 I ran some Boost vs EBP tests, posting results on the Page, coincidental with the 18:1 Project Truck running out of steam over 15psi Boost during accel/time testing.

At 7-8psi Boost, EBP was hard pegging a 20psi gage, wastegate under factory oem PCM control, 3.5" custom exhaust, no charge-air cooler.
EBP post-turbo avg ~1psi.

Those DP Project Truck runs determined the max perf of a GM-8 - marine mechanical IP, 18:1 pistons, balanced, port-matched, charge-air cooler, 4.10 gears, opened intake and large exhaust systems - and those results have been re-proven many times over.

I may need to re-plumb an EBP gage for some further tests on BH v2.0 chip.
Dooley's are considered commercial vehicles here in Texas, and as such are subject to spot-check by THP, with restrictions enforced at State Insp events, so plumbing was removed to get the Sticker.

CR's results are, more than a little, interesting................................

Ok i've made some more runs using my boost gauge for EGBP and this is what i've got this time, a little different but still very reasonable and pretty darn accurate too as the boost gauge read perfect against the scanner since picking it up. My first readings were out at most 3 PSI on the top end. I was using a 35 lb autometer boost gauge on this run.

Boost EGBP

3 PSI 5 PSI
6 PSI 8 PSI
8 PSI 10 PSI
9 PSI 12 PSI
10 PSI 13 PSI
12 PSI 15 PSI
16 PSI 20 PSI All @ 2200 to 2500 RPM

19 PSI Boost WOT gave 25 PSI EGBP, i was only able to hit 25 PSI EGBP once on numerous attempts WOT up to 3500 rpm, speed limiter or high IATs cut me out @ about 96 MPH.

Boost pic pegged @ 21 PSI. (Not a EGBP pic)

Russel, great info.
Your truck is screaming for a turbo upgrade.

Just waiting for you to send me one...lol ;)

Geeze i thought i'd get more response from my final numbers? They are accurate.
:jawdrop: :confuzeld

I fully expected you to post numbers close to what you did.

I've mentioned before that I've watched a lot of Powerstrokes that have an EBP sensor from the factory, and they follow pretty close to what you posted, just a couple #'s more than boost pressure under load.

Although they do show WAY higher EBPs when the engine is cold and the exhaust gate on the turbo is partially closed.

You have still peaked my interest. I'm only a student here.

I'd like to hear some ideas too.

Your truck would be the perfect application to test our experimental upgraded GM-8 Turbo too, give comparison on spool speed, boost pressure and EBP.

i assume your talking about the turbo you mentioned to me in one of our PMs? what about running a T3/t4 hybrid turbo instead of the stock Gm8s or is it too small or big i dont know which it would be.. (cross post: thats the info i was looking for when i asked about the specs on the gm8 not the map turbine size and such)

The biggest problem with running a totally different turbo is hooking up the intake and exhaust.

Using a different exhaust housing would mean some serious work would have to be done to connect it to the down pipe, but not impossible.

As I also mentioned to you in our PMs, I'm not a turbo guy, this was the product of a conversation I was having with our in shop turbo guy (25 years experience) and he made it into reality.

i know my bad. and my apologies.. i know this.. your a pump guy though ;) i'm done posting though don't want to accidently hijack

Your truck would be the perfect application to test our experimental upgraded GM-8 Turbo too, give comparison on spool speed, boost pressure and EBP.

Whenever your ready i should be.

The stock turbine housing is just to small to accomodate the amount of exhaust in a serious hp. upgrade.

Hey TDG Tell us all more about the GM8 of which you speak so that we all may learn more ???

No don't let the cat out of the bag just yet:eek: , let me test it first!!!:lol: