What would cause temp differences between cylinders?
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Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
What would cause temp differences between cylinders?
As a result of having some carb problems which were causing the front 4 cylinders to run rich and the rear 4 to run lean, it appears that even when all seems to be well, I am picking up some differences in temps. I am using a infra red heat sensing gun. I checked the tail pipe temps and found there was a 50 deg difference in temp. The number 5 and number 8 cylinder seem to run the hottest. The rear 4 cylinders on average will be hotter. I am begining to suspect an internal intake leak. Trying to figure out a way to check that without pulling the intake.
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
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From: Bogart GA
I am hoping that it is only an idle thing and at higher RPM the distribution evens out. Hard to check. I am using a 2 inch spacer as well. I was thinking also that maybe I am pulling a little to much air through the secondies. I may close them a bit to see if it has any impact.
Thread Starter
Melting Slicks
Joined: Nov 2000
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Likes: 53
From: Bogart GA
That is what the average difference between the front 4 and rear 4 cylinders. My number 8 is at about 280 and number 1 is at 180. The folks I purchased the carb from said the bend the secondary linkage to close the butterfly valves a little more.
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
When I dyno an engine I find that exhaust temps will be all over the place at anything other than WOT. When the throttle blades are only partialy open they will direct fuel in an eratic manner. It is not unusual to see temperature variation of 200-400 degrees at idle and light throttle.
The intake manifold can only strive for equal fuel distribution at WOT. Then I try to achieve a variation of all cylinders within 100 degrees. An exceptionally ported head and intake combination may get you within 50 degrees EGT but that would be very rare case.
The intake manifold can only strive for equal fuel distribution at WOT. Then I try to achieve a variation of all cylinders within 100 degrees. An exceptionally ported head and intake combination may get you within 50 degrees EGT but that would be very rare case.
Thread Starter
Melting Slicks
Joined: Nov 2000
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From: Bogart GA
Thanks for you reply, that puts my mind at ease. I am going to try to move my PCV line to the front manifold vacuum port. The large rear line I think was intended for the brake booster line. It may be sucking to much air into the secondies causing a lean mixture. At least at the primaries I can adjust the idle circut. If I can get them within 100 deg I will be happy. I saw a diff with my Edlebrock carb as well but it was not as much. I had the PCV hooked up to the front port on that. Thanks again Pete!!
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Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
Getting vacuum lines hooked up correctly and unleaking is a critical first step to tuning! 
Otherwise you can be all over the place for no apparent reason. And that includes your headlights, and everything under the dash!! Personally I don't know if there's any different between the front and rear large ports, but hooking the up the correct way is a safe and easy bet 
-Chris
Otherwise you can be all over the place for no apparent reason. And that includes your headlights, and everything under the dash!! Personally I don't know if there's any different between the front and rear large ports, but hooking the up the correct way is a safe and easy bet -Chris
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
I have been through the entire vacuum system, rebuilt all the actuators and the under dash dash pots and rotory valve. She will hold a vacumm for about 15 minutes after the car is shut off. The front port pulls from the primaries which at least have idle screws to adjust. With the greater adjustibility I am hoping to be able to balance it out better. Now I am just sucking more air at the secondaries making the mixture lean. I also doubt that the rear valves were set up that way.