• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Low boost & black smoke with ATT

Got a couple quick runs in today, I think I can safely say the loose hose was the problem. At WOT I can instantly pin 10 psi and 3000 rpm and maintain it up to about 70 mph or maybe 80. And I think I can safely say it is reaching 70+ a whole hell of a lot quicker than it ever has before. Still got smoke but I'm not really worried about that, it's only during that period when the throttle is opened and the truck is rearing up on it's hind legs and trying to get underway. Once we have forward momentum the smoke settles down to a reasonable level. Still enough to thoroughly piss off someone in a Prius, but not unhealthy looking (to me).
Now I am even more impatient to hook the trailer back up and go attack that hill.
I think I need to find someone to race!
 
I've still got some issues which I think may be speed sensor related, ever since I had the tranny problems and tried changing the speed sensors, I haven't had functional cruise control and no highway speed topend. Any application of throttle from a good highway speed will eventually result in the motor bucking and puking and falling on it's face. Maybe the larger tires confused the 4l80es electronic controls too much. With stock tires and exhaust I could max out at 105mph. Like I've said, my speedo is useless, but I definitely feel like I've gained some topend with the ATT. It used to be if I were travelling at estimated 65-75 and hit it, it would slow down. Now I think I can probably see 85-90 before that happens. But I'm reasonably sure it's not fuel delivery or mechanical, I think it's an electronic issue with vssbs or electronic tranny controls. No biggie, I don't need to go 100, I'm just happy I can pounce onto the highway from an onramp fast enough to merge at full speed now.
More I think about it, with the 33 inch tires and 4:10s, 4 speed with OD and the available rpms left, this truck would probably otherwise be able to go faster than would be prudent for an old truck with 6 half-worn mud tires and an out-of-balance driveshaft.
 
Dan,
I'd race you but, well...my 6.5 is bigger. :rolleyes5: Besides, you'd never know exactly how fast you would be going.:D It sounds like you're having VSS problem, thus no cruise, speedo, etc. But I'm glad you took my advice on the loose hose issue....more than most over look this. As for the black smoke, I feel that's a lack of air issue, the intake has to be choking @ the filter.... We have a more free-flowing turbo now that moves more cfm than the factory stock turbo, so the intake has to be 'opened' up now...just as we did our exhaust systems. Think about it.
 
I wouldnt suspect it is his air induction, since others with 97s dont have that issue, unless there is something actually wrong with his. And there really is no way to move more CFM through a fixed space without increasing the pressure, so thats not really a player. If there is any air flow increase it would be due to the reduction in exhaust backpressure at high boost, so less exhaust gasses are left to expand after the exhaust stroke, but that is only like 5% max more airflow at 10+ psi boost.
 
And I did not mean it that you dont get more power with the ATT, because with it not having to do work to compress exhaust gasses, all that power is freed up to go to the wheels, and less waste heat is generated.
 
Hopefully, we can get some dyno data in the future but for now I think the fact that the engine pulls stronger and gets better fuel economy proves there was a positive change in efficiency of the engine. You don't get a 1 to 3 MPG increase in fuel economy from a lot of bolt on items. :eek:
 
Slim Shady said:
Hopefully, we can get some dyno data in the future but for now I think the fact that the engine pulls stronger and gets better fuel economy proves there was a positive change in efficiency of the engine. You don't get a 1 to 3 MPG increase in fuel economy from a lot of bolt on items. :eek:
Click to expand...

:iagree: :yesnod: :grouphug: The 6.5 Family!
 
mrbucbuck said:
We have a more free-flowing turbo now that moves more cfm than the factory stock turbo, so the intake has to be 'opened' up now...just as we did our exhaust systems. Think about it.
Click to expand...

It's not complicated to actually know, rather than guess, what degree of restriction an intake/air filter system presents. It takes a gauge (often cheap on ebay - with the correct scale/range) that can read vacuum just before the turbo, with adequate resolution. Here is an example:

http://cgi.ebay.com/Dwyer-Magneheli...in_0?hash=item5635296803&_trksid=p3286.c0.m14

As a reference point, the filterminder's common on diesels typically trip somewhere btwn 15-20" water. This equates to around 1.5" Hg, so you need a gauge capable of reading smaller pressure differentials than the common automotive vac gauge.
 
I went another route that demonstrates the same point, boost out vs drive pressure to make the boost, boost/drive is nearly 1:1 ratio 2-3 psi which get you to 70-75 mph, once you get above 3psi drive starts climbing to approx 2:1 drive to boost, whereas with GM turbo I recorced 3x-4x sometimes drive pressure, dirve pressure is influenced by overall flow restriction out of the turbo itself, since Diesels thrive on airflow to make power, closer to 1:1 the better you will be; hands down ATT is superior than the GM turbo, also some guys are reporting with addition of the ATT their filter minder (vacuum) now also pops on hard acceleration they werent seeing with the GM turbo so that also another indication the ATT is pulling more air
 
Turbine Doc said:
I went another route that demonstrates the same point, boost out vs drive pressure to make the boost, boost/drive is nearly 1:1 ratio 2-3 psi which get you to 70-75 mph, once you get above 3psi drive starts climbing to approx 2:1 drive to boost, whereas with GM turbo I recorced 3x-4x sometimes drive pressure, dirve pressure is influenced by overall flow restriction out of the turbo itself, since Diesels thrive on airflow to make power, closer to 1:1 the better you will be; hands down ATT is superior than the GM turbo, also some guys are reporting with addition of the ATT their filter minder (vacuum) now also pops on hard acceleration they werent seeing with the GM turbo so that also another indication the ATT is pulling more air
Click to expand...

Yet, another reason to "open up" the intake plumbing right.
 
Well, that same 'math' was what damned the ATT in the first place, these numbers said the turbo would never work on a 6.5........yet for all those who own one...I'll not go there. I have a headache, and you know why....well, I don't either. Just another point on how what's deemed to 'not' be able to work.....does, and very well!
 
Youll notice no one has posted any math to show that an airflow increase is there. I have done the math to show that it is a 5% airflow increase, taking into account cylinder size, stock compression ratio, cylinder temperatures and exhaust backpressure.

You can only increase airflow by increasing the displacement, make more room in the cylinder for air, or increase RPMs.

The ATT accomplishes it by making more space in the cylinder for fresh air, because with the more free flowing exhaust more of the exhuast gases are pushed out. But not all of it, because of the backpressure is greater than the boost pressure and the intake stroke is expanding, whatever is left in the compression ratio size of the cylinder will expand back into the cylinder, because it cannot be scanvenged, because of the backpressure. With half the backpressure that equates to 5% more space for compressed fresh air to enter the cylinder.
 
Here we go again!....


Danny boy why not properly calibrate your VSS so speedo is correct? You'll notice a huge quickness in shifting, especially 1-2 shift.
 
The Math would say that more flow would transfer less heat. Less Heat in the turbo could mean lower oil temps. Then by transitive relation that would mean you have less blowby. Because the boiling point of diesel fuel and vapor state of oil deposits is equal to the inverse ratio of waste heat which when proportionate to hot air can cause excessive confusion.

I don't know, that was intentional bullcrap, my blowby does seem less now, but I have changed oil types 3 times and been venting it for the last 6 months. I will say that with venting the blowby I think I see a little bit higher oil pressure and get a little splatter around the dipstick now, so if youre going to vent make sure its and easy path for it to rise out of. I still intend to hook it back up once I make an oil fill cap with a large hose connector and just suck it out of there instead.

I have always had a lot of visible blow-by, which I think is more oil vapor than fuel vapor.
 
Last edited:
As the "more flow with less boost" discussions continue (for the past ~2) to confuse, here is a post intended to add clarity & better understand "airflow" in a turbocharged engine.

Please note my intent is to help/promote a better understanding of turbochargers - ANY turbocharger. I've run & experimented with many different turbos (on quite a few different engines) over the past 18 years.

A solid understanding of this stuff doesn't have to cause so much brain pain.

Start by focusing on the density of the air in the cylinder when the intake valve closes. The mass/lbs/# of O2 molecules in the cylinder at that time is what matters.

At the point when the valve closes, cylinder filling stops - the cylinder is at a certain volume. The piston is at this same point in the cylinder when the intake valve closes, everytime. When cylinder filling completes, the volume of the cylinder is always the same.

What differs throughout the range the engine/turbo runs in, is the density of the air-charge fit into the same size cylinder(s). Again, the volume the air-charge is fit into is the same, EVERYTIME, under EVERY operating condition. Not trying to be a smart-ass here; just emphasizing an important point.

Forced induction increases the air-charge density.

As density increases, more O2 molecules are put into the same volume cylinder. The 2 variables impacting air-charge density are air pressure (boost) & air temperature.

Consider 2 different turbochargers (eg. an ATT & a GM-X) operating on equivalent 6.5's at the same rpm - but making different power levels at the same fueling level. Both turbo's have pressurized their engine's intake tract to the same air pressure (boost) - 10 psi.

The one is making more power (almost certainly) has a higher density air-charge in the cylinder when compression begins.

Since the cylinder volume is the same, and the air pressure is the same, the remaining variable to impact density is air temperature. Equivalent volume, equivalent pressure, lower air temp means higher air-charge density. Higher air temp would result in lower air-charge density.

As it so happens, many ATT owners report higher power levels (at a given boost level), and lower IAT's (air temperature) than with their GM-X turbos.

Specifically note that I did not use the volumetric term CFM (cubic feet per minute) in the explanation. CFM can't describe air-charge density, until you know both the air pressure & air temperature in that cubic foot.

Boost pressure & intake air temps are constantly changing as the engine runs under different conditions. This is why it is of limited utility to say "flowing more cfm" when describing different turbo's installed flow characteristics. I believe what they're trying to say is the turbo is getting "more" air into the cylinder. CFM just isn't a particularly good term to describe this.

Perhaps use of CFM is due to folk's familiarity with the term being used to describe/compare flow capabilities of things like cylinder head intake/exhaust ports, or carburetors. These CFM ratings are at standardized air pressure & air temperatures. Same with turbo compressor specs - eg. when you see a compressor spec'd at 850 cfm @ 15 psi, there should be fine print nearby stating the compressor outlet air temp.
 
You must log in or register to reply here.
Back
Top