Exhaust manifold/boost levels

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Exhaust manifold/boost levels

Postby needlenose » Wed Dec 25, 2019 1:48 pm

I've been running a '92 5.9 in my '94 Ford F350 conversion for about 5 years now. The engine is completely stock except for a 3/4 turn on the fuel screw and a 16cm turbine housing. I can max about 15psi towing a 10Klb load. I'm reading that it should be around 20psi stock, more with the fuel screw and turbine changes.

I used a military 90* exhaust manifold to get the turbo away from some plastic a/c parts under the hood. It bolts right up, but it's significantly larger than the stock manifold. Could this be the reason my boost is low?

I'm just wondering before I dismantle stuff and start looking for boost leaks. Thanks!
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Re: Exhaust manifold/boost levels

Postby PToombs » Wed Dec 25, 2019 5:19 pm

To me it sounds a little low but not a lot. Has it always been about 16? If it hasn't changed then I doubt if it just started leaking. You can make a tester from a 4" fernco rubber plumbing coupler, a 4" PVC cap, and an air fitting. Drill and tap the PVC to screw in the air fitting, put the PVC into the Fernco and clamp it down, and put it on the turbo inlet. Be careful, when you add air it may blow off and damage the alternator. Just add air until you are holding 15 or so and start looking for leaks. Windex or spray cleaner works good on the IC.
pete

Just enough power to break everything behind the crankshaft.
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Re: Exhaust manifold/boost levels

Postby needlenose » Wed Dec 25, 2019 6:06 pm

Yeah, it's been the same since I did the conversion. I drove the engine in a '92 D250 for 14 years with the 21cm. But I never had a boost gauge, so I don't know what the boost was with the stock manifold. I guess the opening into the hot side is still the same size, so if the engine is still producing the same amount of exhaust, it will still produce the same pressure/volume at the turbine; it just may take a few milliseconds longer? I had just heard that with turbos, you want to keep the exhaust as hot and compressed as possible so it will expand in the turbine and exhaust. So not really sure if changing the mani hurt anything.

I'm just hoping I find a leak in the piping.....
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Re: Exhaust manifold/boost levels

Postby PToombs » Sat Dec 28, 2019 3:57 pm

I don't think the mani made that much difference. Check all the clamps, and check where the intake plate mounts to the intake. Sometimes the bolts get loose or the gasket gets sucked in.
It's possible the IC is bad. My truck made 16ish psi of boost and I thought it was fine, then I hooked up the trailer and put my JD LA on and was shocked when the EGTs went from the normal 7-800 to 13-1400! I checked the IC with a spray soap and it looked like a bubble machine. I made a bypass pipe from exhaust pipe and ran the truck for a while until I got an IC for it. I was surprised how much boost I had with the pipe. :lol:
My truck lived in the winter salt until I got it, no wonder it was rotted out.
pete

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