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Old 05-29-2012, 05:39 AM
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low boost question

my 97 psd is having trouble building boost at low rpm. at 2500 it will build up to 21 psi in a few seconds. but between idle and 2000 it has trouble.
If I hit a hill at 2000 rpm and 10 pounds of boost it will gradually drop, but at 2500 it will continue to accelerate and build boost. could this be a wastegate issue? maybe out of adjustment and leaving the door cracked?
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Old 05-29-2012, 01:45 PM
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No wastegate on these. What mods are done?
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Old 05-29-2012, 05:31 PM
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tymar intake, 3 inch downpipe to 4 inch, no cat or muffler. thats about it.
its a 5 speed.
so whats the wastegate looking thing under the turbo with the linkage going to it?
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Old 05-29-2012, 11:08 PM
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That's the Exhaust Back Pressure valve. It blocks off the exhaust to aid in warm ups and makes for a decent exhaust brake when you put a switch on it. If your getting 21psi, it's not likely causing any problems. Your powerband doesn't really kick in till 1800+RPM. Are you seeing 10psi empty or while towing? Hills flats? Once your up to speed and there is little load, the boost will drop.
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Old 05-30-2012, 06:49 AM
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its pretty consistent whether im loaded or empty. I was towing when I was having the boost drop uphill. Shouldnt it build boost under load all the time?
It seemed like it had the powerband effect like you said. any way to make that kick in sooner, or is that the nature of the beast?
I would like to learn more about hooking up the switch to the exhaust bypass valve like you said.
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Old 05-30-2012, 08:12 AM
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Quote:
Originally Posted by JSchuricht View Post
Your powerband doesn't really kick in till 1800+RPM. Are you seeing 10psi empty or while towing? Hills flats? Once your up to speed and there is little load, the boost will drop.
This guy is 100% correct, but he's wrong. CORRECT... you are dropping out of the powerband. But unlike the superduties, where the powerband is at 1500rpms for max torque, our trucks dont make torque until 2000rpms. Our OBS trucks make max hp at 3000rpms also. So basically, you need to spin these motors out to make power. Thats the nature of a V-Series diesel. They love rpm's.

Quote:
Originally Posted by TOW RIG View Post
its pretty consistent whether im loaded or empty. I was towing when I was having the boost drop uphill. Shouldnt it build boost under load all the time?
It seemed like it had the powerband effect like you said. any way to make that kick in sooner, or is that the nature of the beast?
I would like to learn more about hooking up the switch to the exhaust bypass valve like you said.
The truck cannot build boost if you aren't spinning the motor enough rpm's to lite the turbo. Like I said above, our v8 powerstrokes make max torque at 2k rpms, and max hp at 3krpms. These trucks need rpms.
No, there are ways around this. A chip, first of all, when combined with an intake and exhaust, will fix a LOT of those boost issues. It will boost sooner, and boost harder. But a lot of people like to ditch the stock 1.15 exhaust housing and install a 1.0 housing. Some people will say it will cause higher egts blah blah blah, but it wont. I know LOTS of people on this forum running the 1.0 exhaust housing, and they love it. This housing will allow damn-near full boost between 1600-1800rpms. So a 1.0 exhaust housing combined with a chip, exhaust and intake would be a nasty combination.

It's an exhaust backpressure valve, and it's used to heat the truck up faster in the cold, and it's used to sustain oil temp when it's cold so the truck doesn't wet stack. The amount of flow-obstruction it provides is so minimal, I dont think it even shows up on a dyno (or its something like 5hp). I'd just leave it, or maybe hook it up to a 3way switch.
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Old 05-30-2012, 11:57 AM
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thanks for the insight. So does the computer control the boost?
I have a edge programmer Im gonna put back on, If it doesnt help, I will just drive it like hell.
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Old 05-30-2012, 12:02 PM
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also, the 1.15 exhaust housing. what is that refering to?
the pipes behind the engine going from the manifolds to the turbo?
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Old 05-30-2012, 12:05 PM
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Quote:
Originally Posted by TOW RIG View Post
thanks for the insight. So does the computer control the boost?
I have a edge programmer Im gonna put back on, If it doesnt help, I will just drive it like hell.
Edge is absolute junk and will trash your transmission very quickly.

Quote:
Originally Posted by TOW RIG View Post
also, the 1.15 exhaust housing. what is that refering to?
the pipes behind the engine going from the manifolds to the turbo?
The exhaust housing is the rear of the turbo where the downpipe attaches to. It's what spools up the compressor. The 1.15 housing is very slow spooling, but boosts HARD in the top-end. International uses it on our trucks because we dont have intercoolers stock, so the 1.15 housing keeps egt's in check. Super Duties come with a .84 housing stock, which is part of the reason why the boost so much lower than we do. But often times the super duty guys get rid of the .84 housing for the 1.0 housing because it lacks mid end power and top-end power and creates too many drive pressures.
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Old 05-30-2012, 12:36 PM
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The numbers on exhaust housings refer to the size of the inside of the housing. This is a VERY general description though! If you want to know more, you will need to start reading a ton on turbos. Going from a 1.15 A/R housing to a 1.00 A/R housing is a reduction in the opening of the exhaust path entering the turbo. This creates more velocity at lower air flow (lower engine rpm) and causes the turbo to spool sooner in the rpm band.

Before you decide you need a different housing, make sure you don't have PRE turbo exhaust leaks!! This can cause the same issues.

Also, a tuner won't control boost pressure without a wastegate. It will however bump up the fuel which creates more heat and drives the turbo harder creating more boost and likely sooner also.
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