wastegates / blow-off-valves

[mudguppy]

a waste gate is there only to limit max boost .the reason the waste gate turbo it better is because it flows more on the compressor side and the exhuast side . so it can make more boost at lower speeds without overfueling. it can take more fuel . the c and d turbos are pretty restrictive and cause overfueling due to restricting the air and exhaust . this is how you can get more boost at lower rpms with the waste gate turbo without melting the engine with high egts.but the engine can still only take so much stress this is where the waste gate comes in

this is both very confusing and mostly incorrect. the only correct concept in this post is that the waste gate limits the turbo output. however, that is not the reason for a waste gate.




a waste gate is added to a turbo for these 3 reasons:

1. to limit turbo speed at high engine rpms and prevent catastrophic turbo failure when matched to a specific engine (this is the primary reason)
2. to reduce drive pressure to safe levels (preventing headgasket failure), again, depending on engine design constraints
3. to allow a smaller turbo to be used on a larger engine or to decrease turbo response time - the smaller size allows for quicker spool-up, yet waste gate prevents turbo over-speed.

the non-gated turbos on the deuces are large enough that the multi will not produce the air/fuel high enough to overspeed the turbo. also, because the multi fueling is not that high, drive pressures do not climb out of safe levels.

basically, turbos run off of fuel [read: exhaust] - add fuel and you decrease spool-up, increase turbo speed, drive pressure, and output (aka "boost"). the multi can't push enough fuel to stress the turbo. and if it does, other things fail long before the turbo does.

'porting' the turbo just improves the volumetric effeciency by reducing restrictions that cause higher pressure differentials. this will decrease the drive pressure which allows the turbo to operate a bit more effeciently. this efficiency increase will show by a [slight] increase of compressor output volume ("boost") and can allow more fuel to be run through the engine until drive pressure reach danger levels again.

think of it as work - the easier job it is to get flow through the exhaust, the easier it is for the turbo to push air. same principal as a free-flowing exhaust on a gas motor: easier out, easier in.

modern turbos have much better effeciency maps and have many more compressor and turbine wheel options to better match engine sizes and performance.

 

[Beerslayer]

.if you have a ldt 465 1d you can switch out to a lds 427 turbo and turn the fuel up you will double the boost and see a huge increase in power

I have the LDT 465 with D turbo. Where might I find one of these fine LDS 427 turbos?

The only time I am pushing the EGTs up to the limit is on long hills. If I really pour the fuel to it, max boost I get is about 11.5 and about that time the EGTs tend to hit 1100, I then quit and downshift.

 

[jesusgatos]

Thanks for posting Ken. So what's your take on adding an external wastegate to one of these engines? Waste-of-time/money?

I've only fired-up the engine in my driveway since re-installing my turbo, but I'll definitely let you know about the boost & EGT's once I get it back on the road. My sprag-case **** it's pants, and I've got a new air-shift case, but I've been putting off installing it...

 

[Crackerjax]

I have the 427 turbo... that ken rebuilt for me and I run about 7 psi at 300-400 feet above sea level. I have not turned up the fuel.

 

[ken]

Jesse, In my opinion you have the best turbo for your set up. It is the closest mapped turbo for these engines. And you should be able to increase your fuel rate enough to really make the truck pull at higher elevations. The LDS turbo is much larger. And works quite well. I have one one my M52A2. But i dout it would be worth the time,effort and cost to swap to one.
Mud guppy, The multi can push enough fuel to stress these turbo's I have oversped a few of them and they make i nice heartstopping sound when they explode.

 

[jesusgatos]

You think my D-series turbo is ideal for the LDT, or for the LDS engine I just bought? I can't tell what turbo this is, can you?

 

[ken]

Jesse, It sure looks like a "C" turbo. Notice the adaptor at the back of the turbo. This is to mate up with the 5ton exaust pipe. This turbo will proude less air flow and boost than the one you have now. Got any better pics?

 

[jesusgatos]

Thanks Ken. I don't have any other/better pics, but I'll be able to let you know if you're right when I go pick it up sometime before the end of this month.

 

[poppacap]

Iinstalled a 5ton in my duece

hey guys,I have had my truck for 8 months or so,and it was a great runner till the oil idler gear sheered off and lost oil pressure.So she locked up now I need an engine so I picked up a 5 ton motor rebuilt in the crate,the swap was straight forward.She started right up but smoked really really bad .The turbo was putting out 18 to 20 psi then quit making boost .Engine oil was flying out the exhaust.the seal went bad in the turbo.I put the original turbo on and it took care off the problem.But it still gives 18 to 20 psi .Now I can ask the question ,is the boost level safe? any feedback would be awesome ,thanks

 

[topo]

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