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94-98 Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect...NO ADVERTISING

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post #25 of 92 (permalink) Old 06-22-2010, 02:16 PM
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Keep your temps low so you do not melt pistons or warp turbine wheels on the turbo.
I know there will be plenty of people that disagree but think of this as a rough guide: sustained temp of 1100
1200 for 30 seconds,
1300 for 10-15
1400 for 5
higher... why??? Thats why they make bigger turbos and products for better airflow like the tunnel ram, 3pc manifolds, cams, water injection, porting etc

Keep your boost low so you do not blow your head gasket.
Keep your drive pressures low so you do not create a restriction on the exhaust side causing unnecessary boost/restriction or blow your head gasket
Do not overboost as you will overspeed the turbo and run the turbo beyond its efficiency range = hot boost and less dense air = less effecient and expending MORE energy to be less efficient.
hy35 =280hp 28psi
hx35= 300hp 32psi
35/40=350hp 35psi (bigger compressor wheel but same 3" turbine outlet and bad wastegate design)
hx40 or he351 =400hp 40psi (4" outlet, he351 has good wastegate and super40 wheel, but 9cm housing so I am putting it slightly behind the super40 with 16cm housing)
s300 57/65/14 (like superB) or super40=425HP 42psi
s300 62/65/12=450HP 42psi
s300 62/71/14=500HP 45psi

You can run bigger/hotter than the list, but expect decreased turbo life, head gasket problems and risk overheating cylinders 1 & 6 which run hot anyways. (a good stock turbo is still worth $300, a blown one is worth $0-100 if it can be rebuilt)

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post #26 of 92 (permalink) Old 06-22-2010, 02:35 PM
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Quote:
Originally Posted by jkidd View Post
Keep your temps low so you do not melt pistons or warp turbine wheels on the turbo.
I know there will be plenty of people that disagree but think of this as a rough guide: sustained temp of 1100
1200 for 30 seconds,
1300 for 10-15
1400 for 5
higher... why??? Thats why they make bigger turbos and products for better airflow like the tunnel ram, 3pc manifolds, cams, water injection, porting etc

Keep your boost low so you do not blow your head gasket.
Keep your drive pressures low so you do not create a restriction on the exhaust side causing unnecessary boost/restriction or blow your head gasket
Do not overboost as you will overspeed the turbo and run the turbo beyond its efficiency range = hot boost and less dense air = less effecient and expending MORE energy to be less efficient.
hy35 =280hp 28psi
hx35= 300hp 32psi
35/40=350hp 35psi (bigger compressor wheel but same 3" turbine outlet and bad wastegate design)
hx40 or he351 =400hp 40psi (4" outlet, he351 has good wastegate and super40 wheel, but 9cm housing so I am putting it slightly behind the super40 with 16cm housing)
s300 57/65/14 (like superB) or super40=425HP 42psi
s300 62/65/12=450HP 42psi
s300 62/71/14=500HP 45psi

You can run bigger/hotter than the list, but expect decreased turbo life, head gasket problems and risk overheating cylinders 1 & 6 which run hot anyways. (a good stock turbo is still worth $300, a blown one is worth $0-100 if it can be rebuilt)
i just got my boost and egt gauge in. under wide open throttle with the tq converter locked i will run 1200-1240* for about 4-8seconds. cruising down the road at 76mph i run 920-960* pulling a pretty good hill, i run about 860-880* flat ground. under full spool stock hx 35 turbo im putting out 33-34psi, my drive pressure at 76mph on flat ground is about 3-5psi and pulling a hill about 12-15psi. let me know if this is acceptable or not jacob, thanks

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post #27 of 92 (permalink) Old 06-22-2010, 03:33 PM
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drive pressure is the pressure on the exhaust side instead of the intake side.
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post #28 of 92 (permalink) Old 06-22-2010, 03:47 PM
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drive pressure is the pressure on the exhaust side instead of the intake side.
so do i need to put a boost gauge in on the exhaust side?

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post #29 of 92 (permalink) Old 06-22-2010, 04:05 PM
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not needed for most trucks, but is helpful for tuning the wastegate to where you want it. try to stay at 1:1 ratio of boost and drive pressure.

for example: if you were to be at 50psi say on an he351 your drive pressure will probably be closer to 70psi
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post #30 of 92 (permalink) Old 06-22-2010, 04:27 PM
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Originally Posted by jkidd View Post
not needed for most trucks, but is helpful for tuning the wastegate to where you want it. try to stay at 1:1 ratio of boost and drive pressure.

for example: if you were to be at 50psi say on an he351 your drive pressure will probably be closer to 70psi
how would you keep the tubing from melting with the temps gettin 1000* plus? also do you think my exhaust temps are good or should they be lower?

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post #31 of 92 (permalink) Old 06-22-2010, 04:51 PM
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use copper tubing for drive pressure.

your temps seem to be in the norm.
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post #32 of 92 (permalink) Old 06-22-2010, 08:37 PM
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Quote:
Originally Posted by jkidd View Post
not needed for most trucks, but is helpful for tuning the wastegate to where you want it. try to stay at 1:1 ratio of boost and drive pressure.

for example: if you were to be at 50psi say on an he351 your drive pressure will probably be closer to 70psi
I always thought it was impossible for drive pressure to exceed the exhaust valve spring rating.
35 psi stock or 60 psi modded.

Bill
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post #33 of 92 (permalink) Old 06-22-2010, 09:07 PM
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I always thought it was impossible for drive pressure to exceed the exhaust valve spring rating.
35 psi stock or 60 psi modded.
Maybe someone who knows more than me can explain better. The 60# valve spring are supposed to be 60# greater than stock.

As I understand it the drive pressure is the pressure that is between the exhaust manifold and the turbo. Those with wastegates closed off or running a turbo with a small non-wastegated housing can have a big restriction if they do not have a wastegate that allows the the extra air to bypass the turbine wheel reducing the pressure and helping to keep the turbo from overspeeding and creating excess boost leading to even higher drive pressure.

for instance the 71mm turbine wheel is called the LDP or low drive pressure wheel and because drive pressure is lower (and slightly more mass of the larger wheel) during normal driving the turbo does not spool as well, but at higher RPM and higher boost it allows the air to flow more freely out of the engine and manifold.

As for max drive pressure being limited by valve spring seat pressures... I am not sure how it would limit it because the design of the manifold, turbo/wastegate and to a small degree the exhaust would be the greates contributing factors.
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post #34 of 92 (permalink) Old 06-23-2010, 09:32 AM
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Shouldn't the output for turbos be limited by so many times barometric pressure, instead of total psi? I drive at 0-500 ft and have a 62/65/12 turbo. At my level 48 psi apears to be inside the map, whereas someone in Denver is pushing it at 40psi. Is that right, or is there more to it than that?

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post #35 of 92 (permalink) Old 06-24-2010, 11:30 AM
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My main experience with drive pressure is from installing exhaust brakes.
I was told by BD if you exceed the valve spring rating by blocking off the exhaust with the brake at higher rpm that the pressure will max out the spring rating while the valves are floating and getting damaged.

Bill
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post #36 of 92 (permalink) Old 06-24-2010, 07:24 PM
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Illflem I work mostly with the vp44 trucks which have greater spring pressure. I had not really looked into it for 12v. That information is good to share. I'm sure you know more about exhaust brakes than me. If I remember there are some design features to protect the engine from the scenario as you discussed, like a small hole in the plate that blocks off the exhaust flow, and they tell you to get the 60# over springs for at least the exhaust side. Wish I had more info to contribute specific to the 12v.

Drothgeb You are right that a turbo will be out of its map earlier at a higher altitude. The maps are for a pressure ratio. If you are at sea level it is 14.7psi absolute pressure, double is 29.4psi which would read 14.7psi at sea level. for each 1000ft in elevation you lose roughly 0.5psi. If you were at 6000ft your absolute pressure would be roughly 11.7psi and so it is harder for the engine to get more air because it is less dense.
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