pyrometer installation

[lostagain]

I would like to install a pyrometer for my turbo installation. It would be good to see the EGT under load so I can back off if it gets too hot. I looked into it a while back and found that the "wire" off the thermocouple is 6 or 8 feet at most. Does any of you have a pyrometer on your dash, and how is it hooked up? I was told that a 40 foot regular low voltage wire would not send the correct reading to the gauge. Any solutions out there? Thanks.

[TomC]

If you have a 2 stroke engine-whether it be turbo'd or not-you don't need a pyrometer.  If you have an electronic engine, whether it be 2 or 4 stroke-you don't need a pyrometer.  The only engines you really need a pyrometer on is mechanical 4 strokes that have been juiced up and are mainly using manual transmissions, since an automatic will not allow the engine to lug.

If you do absolutely feel you need one, the temp bulb is installed AFTER the turbo.  The only way I can think of to have an accurate reading to keep the wire short is to have a gauge panel in the engine compartment with a video camera on it to watch from the driver's seat.  This is done many times with large yachts. Good Luck, TomC

[JackConrad]

We installed a pyrometer on our MC-8 8V71. We placed the thermocouple in the pipe after the 2 exhaust manifolds combine into one. The wires on the thermos couple were about 8' long.  We ran them to 2 empty terminals in the rear panel. From there we ran 14 gauge wire to 2 empty terminals in the front panel and 2 wires from there to the gauge. It appears to be accurate as best I can tell. At idle the gauge doesn't move off 300 (lowest gauge reading). Under normal flatland driving at highway speeds, we run 450-550. On grades it climbs to about 750 (at which point I shift down) and it comes back to about 650-700. Even if it is not exactly accurate it definitely gives you an immediate reading of an increase in engine temperature. As soon as we top a grade at 700 and let off the throttle for the downhill coast at no throttle, the gauge is back to 300 in less than a minute. Throttle application also shows in less than 1 minute.  Hope this helps, Jack

[lostagain]

Thanks Tom and Jack, great info.
Tom, why don't I need a pyrometer on my bus? It is 4-71 DD that I just turboed. I was advised by several DD mechanics not to change pistons, just don't lug it or abuse it. It would be fine if I drove it myself. I don't even know the EGT value under normal load. Although Jack's post gives me an idea. If 700 is hot, then I don't need to worry about my pistons melting since it would take 1200 to do damage (or so I've heard). If this is the case, then I don't need a pyro gauge. Tom what do you think? Any more insight into this would be appreciated, as I need to understand completely before I do something or not do it. Thanks guys.
FYI: I've rebuilt the exhaust in 5" from 4", since the turbo outlet is 5". The new muffler is a big oval thing with baffles, but you can see right through it so it should be fairly free flowing.

[tekebird]

the pyro offers an almost instant response as to engine temps.......while your coolant temp gauge has some lag.......you should be fine with engine coolant gauge

[TomC]

If I remember right, you are not changing the injectors?  If that's the case, your engine will actually be running cooler with the turbo since it will have an over excess of air coming into the engine to make combustion more complete.  You have to worry about exhaust temp when you see black smoke coming out-that's a sure way of overheating the engine. This is why I turbo'd my bus, since at 7,000ft I had to really watch my foot pressure on the gas pedal so not to produce alot of smoke.  Because of the nature of 2 strokers and the fact they already pass alot of air, it would be very hard to overheat the engine.  If you do increase your injector size (which I would do in your shoes-to N75's) and stay within the Detroit size that they originally use, you should be alright.  For instance, on 8V-71's, the largest truck injector engine that was offered was using the 7G80 injector on a aftercooled block for 400hp and 1200lb/ft torque.  Some go higher-like Don Fairchild on his own bus has (if I remember right) 125 injectors that will give you around 625hp and 1875lb/ft torque!  That's where you have to be careful!  But with your N65 injectors, your engine without turbo puts out 150hp and 400lb/ft torque.  Now with turbo, you'll be putting out 163hp and 488lb/ft torque.  I don't know if you have one piece or two piece pistons (you can pull one of the side oval ports and look at the pistons through it), but most likely you have two piece if it has been overhauled in the last 10 years.  You could do what I did and add an air to air intercooler with 75 injectors for a total 188hp and 562lb/ft torque-which will take you real close to the original output of the 6-71N as equipped with the 4104's.  Lots that you can do-inline 71's are very receptive to huge increases in power since they have twice the connecting rod bearing area that the V's do, and the same main bearing size.  Good Luck, TomC

[lostagain]

Great info Tom, thanks again. I am staying with the N65's for now and see how it goes. N75's maybe later. Work in progress...
I was going to fire it up today, but I got the wrong size V-band clamp for the turbo flange. So it will have to wait a day or two till I find the right size clamp. So I won't bother with a pyro. The last item I need now is some exhaust wrap, mainly because the turbo and pipe are really close to the fire wall under the bed. I'll keep you guys posted.

[Stan]

You can run long distances (hundreds of feet) from a thermocouple if you use the proper lead wire. If your thermocouple is type K then you have to use type K lead wire.

When I was considering a turbo on a 4-71 I got the same story from Detroit, to install a pyrometer and watch the temperature on hard pulls.

[NJT 5573]

Jack described a situation that shows why you should cool the engine before you go over the top of the hill. His engine is cooling 400 degrees in under 1 minute. Thats a lot to ask a head to do! Tom related that Don's running a drivers injector that really needs a pyro because it makes alot of power and I'm sure it could seize a piston if it was not driven correctly. If you don't have a computer motor that will shut down if it looses its water a pyro can save you alot of money. With a bus engine in the back, if you break a radiator hose and dump the water there is a good chance you will burn the engine up because if there is no water, the water temp will read cold. If that happens and you have a pyrometer you will see the exhaust temp climb right off the gauge and you can shut it down and save your engine.

[Jerry32]

I purchased my guage from an outfit in Pitsburg and it came with a long wire for a pusher. I was running a juiced up cummins so frequently hit the 1200 + mark.  Jerry

[NJT 5573]

Gotta love those Cummins pumps!