Jugs temperature
#21
02-28-2006 | 09:40 PM
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From: Pocono, Pa-Brooklyn, NY
#23
03-01-2006 | 02:03 AM
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RE: Jugs temperature
I'll start by mentioning that this topic has re-opened my eyes to wanting to understand this in even more detail. With that, my best feedback is...
I would imagine a longer intake duration for the front would help, but then might cause other issues (pressure overlap). Better that the intake manifold be biased towards the front and perhaps the spark advance account for it (too bad the Sporty doesn't have EFI, yet). Which, is probably why this phenomenon is much less prevalent in the BT's (and airflow cooling of the front jug becomes more of a factor with the BT's).
I wonder the same thing! Although, there are a lot of variables in that situation - I'm curious to try and find out...
Hey, no prob - you bring up some good points... As to cooling airflow and exhaust orientation as contributors - no doubt, but comments from HD techs need to be placed in the context of whether they're talkin' BT's and EFI as opposed to a Sporty with a single carb and its own funky intake...
Drats - you got me wanting to find that out too! :-)
Hmmm, dunno about that one. And yep - plug reading isn't as simple as just pulling it once in a while to see if it's fouled or burnt up. Also, regular ol' pump gas can create inconclusive results (as compared to knowing what consistently happens with pre-mix that you know you batch exactly the same way each time) - plug read results have to be pretty darn obvious to be a definite indicator.
Cool! I have (half-owner, actually) a Piper Tomahawk (PA-38) - 4-cyl horizontally opposed. I've only cracked 100 hours recently so my experience probably isn't as deep as yours, but again ya got me thinkin'... Next time up I think I'm going to do the same and look at EGT's and CHT's while in different configurations. But, results would only apply to my situation (the Sporty again being a somewhat unique case - although I kinda wish my plane could make the potato-potato sound!). Hmmm... a Sporty-based experimental - wonder if anyone's built one?...
I wonder that one too! I'm sure someone has if HD hasn't - in fact, I've al
Big Cholla
If there is a difference in the amount of cylinder fuel charge drawn in between the cylinders, couldn't H-D engineers take that into account and grind the cam lobes for the intake valves slightly different giving the front intake a slightly longer duration than the rear?
If there is a difference in the amount of cylinder fuel charge drawn in between the cylinders, couldn't H-D engineers take that into account and grind the cam lobes for the intake valves slightly different giving the front intake a slightly longer duration than the rear?
I also wonder what percentage of cooling effect is contributed by air/fuel mixture and by outside airflow.
I am not trying to be a pain in the a** on this, but I have heard from many H-D mechanics that the rear cylinder tends to run hotter than the front strictly because it is subject to less cooling air flow and because the exhaust pipe points to the rear and gets much less cooling air than the front exhaust pipe.
I vaguely remember some experimentation by H-D on their flat-track 750cc and 1000cc engines by switching cylinders to have both exhaust pipes facing the rear and then again with both facing front. Do you know of any results of those experiments?
On my '05 XL 1200 R, I have examined the plugs after a true shut down from 70/75 mph with a magnifying glass and could tell that the front plug was running the coolest. I have lots of experience in racing single cylinder two-strokes and single cylinder four-strokes and can read a plug.
I used to own an airplane with a six cylinder horizontally opposed air-cooled engine with a six position Exhaust Gas Temperature gage. I could see that the rear two cylinders always ran just slightly warmer than any of the other four. By flying the airplane in a "Yaw", I would watch the rear cylinder on the "sheltered" side warm up slightly over the other one that was receiving more airflow.
I wonder if H-D or anyone else for that matter have published any definitive studies on cylinder head temps during normal use.
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