Exhaust Crossover confusion

[Tom Lins]

I am confused over the temp readings I get using a non-contact temp gauge on the intake manifold.

I drove from the storage facility we keep our GMC at to my house (about 10 miles at 70 mph)
When I got into my driveway I opened the engine cover and measured the following temps.

End of left exhaust manifold 450 deg F
Top of choke stove 277 deg F
Top of runner to next cylinder fore or aft 225 deg F
Top of end of manifold fore and aft 217 deg

I was expecting the temp on the top of the choke stove to be higher if the crossover was not blocked.
The reason I was measuring the temps is to attempt to determine if my crossover is blocked short of pulling the manifold.

I guess another question I wonder about is if the factory choke would work at all if the crossover was blocked.
This all feeds into why I had 2 FI-Tech units fail after very short periods of time.
The first after about 800-900 miles and the second after 250 miles.
The engine runs fine now with the carb back on it.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
GMC Dealer Training Tapes
http://www.bdub.net/tomlins/

 

[john r. lebetski]

Another permutation other that open or blocked would be restrictors. That's the Cinnabar practice as it retains some warm up benefit and the factory
choke works fine. If they have worked on it they can probably look up service history
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Tom Lins]

> Another permutation other that open or blocked would be restrictors. That's the Cinnabar practice as it retains some warm up benefit and the
> factory choke works fine. If they have worked on it they can probably look up service history

I will have to contact them since this coach was in Kansas with the original owner for 30 years and there were some receipts from Cinnabar with it
when we bought it.
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
GMC Dealer Training Tapes
http://www.bdub.net/tomlins/

 

[Matt Colie]

> Another permutation other that open or blocked would be restrictors. That's the Cinnabar practice as it retains some warm up benefit and the
> factory choke works fine. If they have worked on it they can probably look up service history

Thanks John,

That was what I was going to add.

From experience, those intake temperatures are about what I would expect. The exhaust you saw was maybe a little low, but I measured it with a
thermocouple on the exhaust flange.

This is memories from when I was McCord's (RIP) aftermarket we were supplying OE to the Chrysler (RIP) V-engine line. I was also using those tools
for aftermarket parts. While it was not an issue with the port fuel versions both the RPD groups FI and Carb were complaining about heat burning the
paint off the intake passage. So, I got a carburetor engine and did some dyno time. We changed aftermarket to a restrictor on one side only. The
other side remained a steel flange insert.

The OE parts just had flanges at both sides, but it also had a far smaller cross port than the 455 does.

Matt - the dynoland refugee
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit