Motorhome turbo operation questions

[master53yoda]

I gave it a short (20 mile) run today and have a couple of questions. This is a 24' class c motorhome.

1. I turned up the pump 1/4 turn while i had the intake off and it was easy to get to. I drove it a little before i got the turbos hooked up. when i got into it the EGT spiked to the 1400 range in a couple of seconds and pored black smoke. I wasn't expecting that hi EGT.
2. With the turbos and inter-coolers complete, on a long hill (most Semis do this hill at about 45) where i could get into it and hold it at full throttle doing about 65 without the overdrive in so the RPMs were running about 3000, I had about 9PSI boost but the EGT never went above 900 in the 30 seconds or so I was at full throttle, no black smoke at any time. Does this mean that I need to give it more fuel and any idea how much to turn on the pump. It seems to have plenty of power. I think it would have gone up to 70 if I would have drooped in the overdrive as i backed off about half way up the hill, when i did the EGT dropped into the 725 range.
3. Is there any reason to turn up the fuel if the power level is sufficient for my needs. It is about as responsive as my 1/2 ton with the banks turbo is.

[DmaxMaverick]

If you want more power, and likely a shorter service life, turn it up. If you have enough power, I don't suggest any more fuel. Sounds like you have it very near optimal for a 6.2, if not spot-on. More pressure and/or EGT can be catastrophic. The 6.2L, in stock internal form, does not have treated piston crowns like a 6.5TD, and may be +2 on the CR. 900°, pre-turbo, is about as high as you want to sustain on your engine, and post-turbo, is in the red for more than very short periods. About 7 PSI is recommended for it, as well. Sounds like you have a built-in safety margin.

It appears to me that your miles of plumbing has dramatically increased the effectiveness of your CAC system. With that much pipe exposed to ambient air, I might have opted to not use cooling cores, at all. That's a LOT of surface area. Very nice, in any case, on the whole package.

Also, consider a complete glass-wrap (header tape/wrap) of your pre-turbine exhaust tubing. This will help get more heat energy to the turbos, and increase their efficiency.

[master53yoda]

Thanks Dmax

The pyro is in the exhaust manifold, I bought the exhaust wrap tonight as i can see heat effect on the oil hoses that are close (3 or 4")to the exhaust piping running up to the turbos. I had thought that I would wrap it before winter in any case but I'm going to do it before it goes any further.

Was that 1400+ EGT that i saw before hooking up the turbos normal for an over-fueled NA engine. I would think that kind of temp would hammer the pistons even without a turbo or does the higher turbo combustion pressures have some to do with it as well..

[DmaxMaverick]

Good call, not waiting to wrap the pipes. That much heat that close to rubber is never a friendly situation.

You can't really compare N/A vs. Turbo temperatures. The mechanics is very different between the two. It is common to see higher EGT's N/A on a gage, but that's not really a true representation of the actual internal condition. The probe samples the gas temperature it is surrounded with. N/A exhaust is significantly less dense, and at a much lower velocity. This causes the probe to be exposed to heat units for a longer period. The probe does not sample/measure heat units, only the environmental collective heat. Higher density and velocity also transfers more heat units away from the combustion chamber, but not at on a linear scale to what you see on the gage. I don't know of anyone or institution who has conducted a study on this event, and I haven't done it myself, so I can only "guess" at the actual comparative result. #2 Diesel fuel has a specific combustion heat unit (temperature) that is constant, with the only variable being the molecular quality of the fuel, as a collective quantity (some "stuff" in the fuel is not actually #2, such as water, gasoline, additives, so has variable characteristics, tank to tank, day to day). That said, 1400° is very high for a N/A 6.2L (or any 6.2, for that matter), but does not mean damage done. 6.2L N/A engines are very tolerant of extremes. A well cared for N/A can last 500K+ miles with only minimal service (which isn't as rare as you may think, I know of several, including my 85), while the same engine with a turbo will be significantly less. They become more sensitive to the extremes. There are exceptions to every standard, of course.

[master53yoda]

I wrapped all the piping and took it for a run and now have a new problem. I'm blowing substantial amounts of oil past the rear main seal when working the turbo. I suspect that i have excessive crankcase pressure under boost, because there is no leak when at an idle even after 45 min run time, but there is no vacuum on the line up from the turbo at an idle.

I ran one 1/2" hose from the oil fill tube back to the turbo inlet pipe between the filter and the turbo. This is about 10 FT of hose. the connections on the vapor capture tank are only 1/2".

do i need to remove the capture tank and run two 3/4" lines one to each turbo, if so will i need to also reinstall the CPV control. With the lines each being 10' long will 3/4" be large enough.

[DmaxMaverick]

1/2" hose is too small. 3/4" hose may be too small, for your application. The CDR system on most all OEM's runs about 12" of 3/4" hose. 1" may be large enough. You may have to configure the nipple entering the inlet to allow eduction to help "pull" a little vacuum. Make sure the line does not have any dips (like a P-trap), and is downhill all the way from the engine to the inlet. If there are any points that could allow pooling of condensed oil vapor, it will block all flow. Are you still using the CDR? If not, you should. It won't help with your current problem, but will prevent excessive crankcase vacuum, which is just as bad.

[master53yoda]

1/2" hose is too small. 3/4" hose may be too small, for your application. The CDR system on most all OEM's runs about 12" of 3/4" hose. 1" may be large enough. You may have to configure the nipple entering the inlet to allow eduction to help "pull" a little vacuum. Make sure the line does not have any dips (like a P-trap), and is downhill all the way from the engine to the inlet. If there are any points that could allow pooling of condensed oil vapor, it will block all flow. Are you still using the CDR? If not, you should. It won't help with your current problem, but will prevent excessive crankcase vacuum, which is just as bad.

I had removed the CDR put will reinstall it. Will 2ea 3/4" hoses be big enough one to each turbo or do you think i need to go to 2 ea 1" hoses The turbo inlets are only 2" total.

[DmaxMaverick]

Definitely install the CDR.

I suggest a single 1" (or larger) to the area of the turbos, then Tee 3/4" to each. 10' is an awful lot of hose volume, and a lot of surface area friction. One larger hose to the rear will do several things to help the situation. It will take up less space, have significantly less internal surface area, have greater hose volume for the area it occupies, and one less piece to mount and keep track of.

Another option would be to use an air pump and keep it all under the bonnet. It could be pressure switched, so it would only work when necessary, and you could continue using a vapor capture system. A small car smog-air pump would work well for this. Compact and simple, with a lot less plumbing to mess with.

[master53yoda]

Problem resolved, I ran a 1" metal tube (emt conduit) from the engine back to the turbos and then ran 3/4" hoses to the turbos i have about 2' of hose total.

I fabed an oil separation tank at the engine with a drain line back into the engine and also installed a separation tank in the back by the turbos, this tank drains into the turbo oil scavenge pump. The 1" metal line runs between these two tanks.

I drove it about 20 miles and had no rear main oil leak so this problem should be resolved.

Thanks again for the input.