Max boost varies-- normal?

The_Josh_Bear

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Hey guys I've been turbo'd for a while now and have noticed that my max boost numbers vary quite a bit.
I tow a trailer most of the time my pickup is moving so keep that in mind, I always have about 4k+ behind me.

So for example, WOT going up hill with 4k in tow at 70-74mph I can pin the 15psi gauge, just barely.
But sometimes going up the SAME HILL, same load same day, it'll only hit 12psi.
What gives?? Is that normal?

I figured that maybe it was cool morning air vs hot afternoon air but that actually doesn't seem to be much of a factor at all, once I started paying closer attention.

Thoughts?
 

Thewespaul

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Where do you have your timing set at? I’ve found I have lower egts with just a disconnected wastegate and not locking it close. If you force all the exhaust through the little turbine it really chokes the engine and shortens your life of the turbo.

Do you have a mechanical lift pump? You may have less fuel pressure with less fuel in the tank making the ip deliver less volume. If the engine is cold you may be seeing more of less boost because the cold advance solenoid is still activated, so that’s something else to consider.

What egts are you seeing?
 

Macrobb

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I've only been able to get about 11 out of my Ford Factory turbo for the last number of months. Added a Wicked Wheel, I'm now getting 14 under the same conditions.

As far as why it varies, maby your wastegate is sticking open just slightly, due to crud/rust buildup or something?
Or, maby your throttle cable is sticking slightly and you aren't getting "WOT" sometimes?
 

The_Josh_Bear

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Where do you have your timing set at? I’ve found I have lower egts with just a disconnected wastegate and not locking it close. If you force all the exhaust through the little turbine it really chokes the engine and shortens your life of the turbo.

Do you have a mechanical lift pump? You may have less fuel pressure with less fuel in the tank making the ip deliver less volume. If the engine is cold you may be seeing more of less boost because the cold advance solenoid is still activated, so that’s something else to consider.

What egts are you seeing?

Not sure on my timing exactly, I have a meter and have timed it at 6*BTDC, but it never ran as good down there. Tried 8.5 and it still ran better cold than hot. So I've advanced it by ear using the Allen on the advance plunger lever, it's really a great way to get just a little adjustment here or there.
Honestly i think my balancer has slipped cause it's a dog at stock timing numbers. It's running well now since my last adjustment, I'd like to know where it's at but not now with the front clip work.
I could un-bolt the wastegate, I got better spool with it locked shut which was the purpose. Looking at the turbo map for the 093 it's basically right in the heart of the map at 15psi and 2800rpm so I doubt its hurting it any. Why would it shorten the life of the turbo?

I have the 9-11psi Facet Duralift. Holds about 6psi cold at idle and drops to 3psi revving in the driveway. This is a post-filter reading too.
Its only 6psi at idle because I have the check valve on the fuel filter header installed, so it bleeds pressure.
I'm not terribly pleased with the ability(or lack) of this pump to supply our system under high load. I dont have a gauge in the cab though, cant say much for numbers when actually under way.
 

The_Josh_Bear

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If you hit 15 PSI, that's damn good. Fuel from different Stations, Cool air, Humidity, head or tail winds, all can make a small difference.

Good points, and I'm sure to some extent that's contributing. Except the fuel part, itll all be in the same day same hills same fuel. But windage and temp and humidity certainly change.

I've only been able to get about 11 out of my Ford Factory turbo for the last number of months. Added a Wicked Wheel, I'm now getting 14 under the same conditions.

As far as why it varies, maby your wastegate is sticking open just slightly, due to crud/rust buildup or something?
Or, maby your throttle cable is sticking slightly and you aren't getting "WOT" sometimes?

My cable is solid, I get the full stroke for sure. Great point though, it's something I had to address in the past.
Cant say for sure on the gate. It was very clean when installed and I run the poo out of this engine. I got a good spool increase and about 2psi better max boost when I bolted the gate down.
Max EGTs didn't change really at all. They go right up to 1150 and slowly climb after that both before and after the gate lockage.
 

Macrobb

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I have the 9-11psi Facet Duralift. Holds about 6psi cold at idle and drops to 3psi revving in the driveway. This is a post-filter reading too.
Its only 6psi at idle because I have the check valve on the fuel filter header installed, so it bleeds pressure.
I'm not terribly pleased with the ability(or lack) of this pump to supply our system under high load. I dont have a gauge in the cab though, cant say much for numbers when actually under way.
You need to do this. Add a gauge. Chances are, it goes to 0 under WOT conditions, and the pump is sucking fuel. This massive change in input pressure(6 psi to 0) will also affect timing under load, making it retarded at the high end.

Honestly, unless you get a really good electric setup(that can actually push ~4 psi under WOT) and a regulator to keep it at that pressure, go back to a mechanical pump. I've found the pressure-demand curve to be extremely flat - last check I was running 4 at idle and 3 at WOT(post filter).

Also, if you are having issues that make an electrical pump much better(drainback, hard starting etc), you have a problem in your fuel lines/switchover valve/pickup. Fix that. It'll run much better when you've fixed whatever problem you have, electric or mechanical.
 

Thewespaul

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The map is for the flow of the turbo with the wastegate connected, with it unable to open you are restricting the amount of flow and forcing all the gas through the turbine which spins the turbo faster than it’s designed to go, which cooks your chra and heats the intake charge. I’ve made more power with less boost by using a boost controller to open the wastegate once I’ve reached the boost level I need to burn the fuel I have. Boost has nothing to do with power production, it’s just a measurement of restriction and indicates how hard you are pushing your turbo
 

The_Josh_Bear

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The map is for the flow of the turbo with the wastegate connected, with it unable to open you are restricting the amount of flow and forcing all the gas through the turbine which spins the turbo faster than it’s designed to go, which cooks your chra and heats the intake charge. I’ve made more power with less boost by using a boost controller to open the wastegate once I’ve reached the boost level I need to burn the fuel I have. Boost has nothing to do with power production, it’s just a measurement of restriction and indicates how hard you are pushing your turbo

Well if that's how it works, then I agree with you. You've probably forgotten more about turbocharging than I even know in the first place! My thinking is that since it's a *compressor* map, and shows pressure ratios all the way up to 29.3psi whoever made the map wasnt taking any wastegate into the equation. Obviously you'd never even get to 15si with the gate functioning, let alone 20, etc.

For reference this is the map I'm referring to, first map on this post over on FTE: https://www.ford-trucks.com/forums/1218095-the-idi-turbocharger-thread.html

So whenever I get the front end situated I'll reinstall the actuator and just leave it unplugged, see what we see then.
 

The_Josh_Bear

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You need to do this. Add a gauge. Chances are, it goes to 0 under WOT conditions, and the pump is sucking fuel. This massive change in input pressure(6 psi to 0) will also affect timing under load, making it retarded at the high end.

Honestly, unless you get a really good electric setup(that can actually push ~4 psi under WOT) and a regulator to keep it at that pressure, go back to a mechanical pump. I've found the pressure-demand curve to be extremely flat - last check I was running 4 at idle and 3 at WOT post filter.
Also, if you are having issues that make an electrical pump much better(drainback, hard starting etc), you have a problem in your fuel lines/switchover valve/pickup. Fix that. It'll run much better when you've fixed whatever problem you have, electric or mechanical.

Yeah that seems to be the next step in the fuel delivery situation. I have a pressure/vac gauge I could ziptie up front like you did pretty easily, actually.

Thankfully at this point I dont have any of the classic air intrusion problems that I know of...but of course I've had the epump on there for some years now.
 

Thewespaul

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Well if that's how it works, then I agree with you. You've probably forgotten more about turbocharging than I even know in the first place! My thinking is that since it's a *compressor* map, and shows pressure ratios all the way up to 29.3psi whoever made the map wasnt taking any wastegate into the equation. Obviously you'd never even get to 15si with the gate functioning, let alone 20, etc.

For reference this is the map I'm referring to, first map on this post over on FTE: https://www.ford-trucks.com/forums/1218095-the-idi-turbocharger-thread.html

So whenever I get the front end situated I'll reinstall the actuator and just leave it unplugged, see what we see then.

Im no turbo expert by any means, that map is for the compressor side so like you said it wont matter at all whats happening on the hot side, it only deals with the cold side air flow and at your boost level you should be in the 75-65% efficiency range and around 100,000 rpms which is just the crest of acceptable rpms on a journal bearing turbo. Thats not really a problem at that boost pressure for the cold side, but the hot side of these turbos are significantly smaller, and rely on the wastegate to make up the difference in flow. If there was a map for the hot side I imagine 15 psi would be pushing it quite a bit more than on the cold side.

Im by no means telling you that you cant do this on your truck, Im just trying to help get more information out there. Ive pushed the factory turbo to 27 psi but not for long, as long as you have the fuel to back it up the turbo will keep building boost, regardless of the configuration of the wastegate. When I made 27 i had the wastegate unhooked with no adjustment done or boost controller used
 

The_Josh_Bear

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Wow thats a lot of fuel on the stock turbo! Nice, I'm surprised that's possible with the WG just unhooked.
I appreciate any help you or anyone is willing to give me, I've read a lot about turbos but this engine is the only one I've ever "played" with.

I tried googling the 100,000rpm limit for journal bearings and never found anything in that range
The only real number I could find was over 6,000rpm PER SECOND!(360,000rpm) and the other reference was once the turbo is "off the map" it is in danger of being over-sped. Do you have a link to information on overspeeding a turbo? I'd like to read up on it if possible.

I'd like to get a gauge for the drive pressure and actually have numbers to test out different things like this. Or a differential gauge, if they exist. Not that I need to spend more money...
 

Thewespaul

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That’s not on a stock pump, it’s an experimental pump I built that’s on version two now, I go through it in the shop truck thread.

And I read that in a turbocharging theory book, the author I found when reading up on porting. I’ll see if I can get a picture for you
 

Jim Sisson

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I don’t know if this is pertinent, most of my experience is with 1693 and 3408 CAT's, on highway logging trucks and logging equipment. I had some of them running up to 40 psi of boost, but just having a worn-out motormount would cause a 3 to 4 psi fluctuation in manifold pressure. When a operator would complain about lack of power, I would make sure that the motor mounts were allowing full throttle. Just a little wear made a ton of difference.
 
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The_Josh_Bear

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I don’t know if this is pertinent, most of my experience is with 1693 and 3408 CAT's, on highway logging trucks and logging equipment. I had some of them running up to 40 psi of boost, but just having a worn-out motormount would cause a 3 to 4 psi fluctuation in manifold pressure. When a operator would complain about lack of power, I would make sure that the motor mounts were allowing full throttle. Just a little wear made a ton of difference.

Why would the mounts affect the throttle cable?
 

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