Exhaust Temperature

[Pete]

There have been discussions on the need to keep the combustion temperature up on Detroits, but no numbers I can find. I am measuring the temp at the head to exhaust manifold flange and getting around 475 degrees at 1800 RPM on both 453N engines in our 48 LRC. At this RPM even these engines are lightly loaded and I am even considering going down to 1700 RPM, as a drop from 7.9 knots at 1800 RPM to 7 at 1700 RPM will increase the mileage from about 1.4 NMPG to 2.0 NMPG. But, want to be sure to keep sufficient load on the engines to keep them healthy. Anyone know what exhaust temp should be maintained for continued good health?

Pete

 

[Brian Degulis]

Measure at the exhaust manifold discharge before the turbo if you have one. Anywhere between 400 to 700 is very good for continous running.

Brian

 

[Genesis]

Yeah, you can't measure at the flange and get an accurate reading, however, from what you're seeing its PROBABLY ok.

The best place is a pyrometer at the output of the manifold before any crossover pipe to the showerhead (since you mentioned Naturals; the ideal is BEFORE the turbo, not after, although most marine setups with turbos have the pyro tap AFTER the turbo - that's less useful.

 

[Pete]

The exhaust on my 453N's are very simple. The exhaust manifold is closed loop water cooled, which next attaches to an exhaust riser which has the shower head as it attached to the low temp fiberglass exhaust pipe just before the muffler. Thus, the exhaust gas flow is out of the exhaust head ports into a water cooled exhaust manifild into a dry exhaust riser, past the shower head into the fiberglass pipe on the way to the muffler. The only point in the system that is not subject to water cooling are the exhaust manifold entry ports flanges that attach the exhaust manifold to each cylinder of the head. That is why I am measuring the temperature at this point. Any later in the system will be cooled to some extent. Thus, I am requesting temperature information at this point to make sure I sufficiently load the engines for good health. Thanks for the help.

Pete

 

[Brian Degulis]

At the manifold discharge (the dry riser) Yes there may be some cooling efect from the water cooled manifold although very little. But it doesn't matter your trying to see if the engine is running within design parameters set by the manufacturer. The manufacturer wants it measured at the manifold discharge so they have factured in any cooling efect for you. Don't over complicate it if your using an infra red just pick what you thing will be the hottest spot on the dry riser. The infra red won't be as acurate as a pyrometer but should be close enough to see if your in the range.

Brian

 

[REBrueckner]

I ran 3-53N's for several years on an 40 ft Matthews...great engines but a little wobbly on idle vibration....yours are likely a bit smoother...I also ran 6V53's for many years at about 1800 RPM....always clean running...except when the cork gasketed hand hold cover would occasionally slip loose....

You can run those forever in the 1600/1700/1800 range without any concern...likely even lower and at that modest RPM they will last forever if you use them enough....That temp you are getting is influenced by the adjacent water cooled portion of the exhaust manifold and likely doesn't mean much...but the higher compression of naturals means "no worry, mon"...I'm surprised it read as high as it did....

 

[Dan Mapes]

We're hoping to take a long trip south this year, and I have install pyrometers in the elbow out of the turbo prior to the shower. Yes I was wishing it was earlier.
But I figure if I shoot a couple of the exhaust ports and note the pyrometer at that rpm, I should have a reasonable means of keeping the engines at temperature.
These are 6-71TIs rated at 340. 400-700 at the head exhaust port ok for these also?

My biggest concern is the lack of oil pressure at low rpms for the sake of economy.