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Manifold temperature
https://slantsix.org/forum/viewtopic.php?t=59239		 Page 1 of 1
Author:  coconuteater64 [ Fri Mar 04, 2016 3:56 pm ]
Post subject:  Manifold temperature
Recently there was a discussion on carburetor icing and manifold temperatures. So I hastily bought one of those cheap Horrible Freight laser temperature gauges. I don't know how accurate they really are, but the numbers were at least consistent in five checks.

The engine is a stock 225 with dual Dutra exhaust and a Holley 350 cfm carburetor on an aluminum adapter. It's at full operating temperature and the ambient temperature outside is 58 degrees Fahrenheit.

The number one exhaust was the coolest at 354 degrees; the rest were between 377 and 384. The adjacent intake runners were 184 for the number one cylinder, and the rest were all around 218 to 227 degrees. This was measured about an inch from the head.

But what really surprised me was the base of the carburetor. The cast iron manifold was 84 degrees where the adapter is bolted on, and the base of the carburetor was 58 degrees.

Now do you see why carburetor heat is necessary?
Author:  Wesola78 [ Fri Mar 04, 2016 4:37 pm ]
Post subject: 
Yes I do. :shock:
I already thought it was important based on my own experience of doing without it. :cry:
Author:  mcknight505 [ Fri Mar 04, 2016 7:04 pm ]
Post subject: 
I just got home after about a 30 minute drive and shot my exhaust with my temp gun and they are running about 550 to 600. Should I be concerned?
Author:  coconuteater64 [ Sat Mar 05, 2016 6:42 am ]
Post subject: 
No. They do get that hot! Mine had been idling in the driveway for 15 minutes when I tested it so no doubt it was cooling off.

One thing I did notice was how much cooler the number one cylinder runs compared to the rest. I guess it's because it is the closest to the thermostat, but I was surprised by how much cooler it was.
Author:  Dart270 [ Sat Mar 05, 2016 7:56 am ]
Post subject: 
That's curious. Usually, the conventional wisdom is that #1 runs hottest because the water goes from the radiator outlet (bottom, cold side) through the block (toward the rear), then through the head (toward the front). So, the water would be hottest right where it exits the head at the thermostat. I have found the most wear (rockers/pushrods) on #1 over the years on sustained roadcourse running and assumed it was hotter.

Hmmm,
Lou
Author:  Old6rodder [ Sat Mar 05, 2016 10:37 am ]
Post subject: 
Gentlemen,

What I see on the stocker is
entry from the rad at the base of #1 left,
flow to the rear and up the left side through the block,
and rear to front left in the head favoring the left side,
with the bypass middle front.

This would seem to have the #1 cyl wall coolest, and the #1 chamber top warmest.
Just deduction, as the only thing I've ever measured has been the head, and that only by feel, so any differences were strictly relative.

When I went to an aft rad set-up on the 'Brick I plugged all the transfer holes between the block and head, deleted the bypass, fed both from the back, and hooked the water pump inlet to the therm housing.
Thus it went from the rad to the head rear,
head front to water pump,
water pump to block front,
and block rear to rad,
with no crossovers between.

This ran the head cooler than stock, and though I hadn't measured it, I expect the cyl walls a bit hotter.
Author:  wjajr [ Sat Mar 05, 2016 4:44 pm ]
Post subject: 
Quote:
The number one exhaust was the coolest at 354 degrees; the rest were between 377 and 384.
I have registered slightly lower #1 intake runner temperature in relation to the other five with engine running, and figured it was from a direct hit of air flow from fan, and its shielding of that air flow from the other five.
Quote:
But what really surprised me was the base of the carburetor. The cast iron manifold was 84 degrees where the adapter is bolted on, and the base of the carburetor was 58 degrees.
This is normal due to the expansion of gasses or liquid (air/fuel mixture) as it flows more rapidly and is somewhat compressed as it flows through carburetor, and slows down and expands in larger plenum of intake. This the same thing when one feels cold spot when spraying air from a spray can onto a part of his body.

Under certain conditions this flow through a carburetor can lower temperature of local surfaces directly below carburetor enough to freeze moisture suspended in ambient air to form frost or ice.

I had this icing occur just the other day when running my old tractor with an up draft carburetor and un heated manifold. After a several minutes of fast idling frost formed on outer surface of intake manifold and top of carburetor making a 4 inch x 3 inch patch. Later that same morning I was using a map-gas torch to remove undercoating, and that same ice formed on neck of torch where compressed gas passed from orifice expanded mixing with air as it passed to end of torch to be burned.
Author:  coconuteater64 [ Sat Mar 05, 2016 6:06 pm ]
Post subject: 
Oh, I know about carb icing. It happened to me last weekend at 1100 feet. It's much easier to correct in a Cessna than a D100.

I did the test just out of curiosity because somebody else was asking about carb heat with headers. I have dual manifolds and it has always run like crap in the winter. Now I know why.
Author:  Louise76 [ Sat Mar 05, 2016 6:17 pm ]
Post subject: 
I always assumed that #1 spark plug loaded up more than the others due to running cooler because the stock fan blows cold grill air only on the front of the cast iron block, never mind the coolant system. 75,76 Darts
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