Cam timing and reversion solutions

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77cruiser
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Re: Cam timing and reversion solutions

Post by 77cruiser »

joespanova wrote: Sun Nov 19, 2017 6:47 pm The headers ARE 1.875 Hookers.......as far as the primaries , they are indicated in the catalog as 30-38 inch primaries.............and since I am not using any of the extensions I have to guess , right now , they are close to 30 inches long.
What's on it for collectors?
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Re: Cam timing and reversion solutions

Post by statsystems »

77cruiser wrote: Sun Nov 19, 2017 7:00 pm
joespanova wrote: Sun Nov 19, 2017 6:47 pm The headers ARE 1.875 Hookers.......as far as the primaries , they are indicated in the catalog as 30-38 inch primaries.............and since I am not using any of the extensions I have to guess , right now , they are close to 30 inches long.
What's on it for collectors?

That was my next question.
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Re: Cam timing and reversion solutions

Post by joespanova »

3.5s............not merge or anything fancy..........the original collectors . These are a Hooker 2304 adjustable "race" header.
Recall , as I already stated.......this engine WITH the same everything has had clean ports.
No one has suggested ( well maybe one guy did ) the connection with the new carbs. I HAVE seen "trace" reversion evidence in the ports , but nothing alarming.Nothing like this...........
FAST FORWARD TO THE NEW CARBS.....and tons of reversion.
My attempt at stopping all this is to stick the 112 LCA cam back in and ask Patrick WTF he thinks. If I thought it was vac pump related ( not effective ) I would assume I'd only see oil contamination in the chambers and exhaust ports. The exhaust ports look very normal.Read that light gray and dry.
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Re: Cam timing and reversion solutions

Post by ptuomov »

Isn’t the earlier suggestion in the thread the likely explanation? There’s reversion with both carbs in certain operating modes. However with the old carb the engine was lean in those operating modes, with the new carb it is rich. The same exhaust reversion causes more soot in the intake ports with the new carb. Kind of would make sense to me.
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Re: Cam timing and reversion solutions

Post by joespanova »

ptuomov wrote: Sun Nov 19, 2017 9:27 pm Isn’t the earlier suggestion in the thread the likely explanation? There’s reversion with both carbs in certain operating modes. However with the old carb the engine was lean in those operating modes, with the new carb it is rich. The same exhaust reversion causes more soot in the intake ports with the new carb. Kind of would make sense to me.
Who the hell knows .......anythings possible. Right now I'm looking at valve events as well as carbs.
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Re: Cam timing and reversion solutions

Post by naukkis79 »

joespanova wrote: Sun Nov 19, 2017 2:53 pm I've wondered the same thing................but evidence from Kaase's video illustrates how counter productive reversion is and how blow back into the intake can be very severe. So any effort to reduce that has to be beneficial?
Frankly I'm surprised this topic hasn't drawn more interest.
My guess is still cam timing has to be changed , at least on this engine , with these heads , with this induction . Others , apparently have different results.
Changing cam timing couple of degrees changes nothing. With radical cams individual runner carb setup you will hear wot reversion crisply clear and see fuel pushed back from velocity stacks but that only happens at low rpm before power band. Actually with most IR-setups wot reversion is pretty audible and it stops exactly at same time as engine gets into powerband.

But late intake power hurt reversion won't show up in manifold or carbs, actually cycling fuel washes everything clean. It's closed-throttle reversion which blackens things - and badly so if part-throttle afr is very rich - and also if it's extremely lean and backfires back to intake. But that's usually pretty audible.
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Re: Cam timing and reversion solutions

Post by modok »

The intake ports of many engines can be totally coked with carbon. No definite relationship to cam timing at all.

I agree it would be caused by the conditions being such that it builds up and does not get washed away. Why did you have to de-carbon a model-t as often as we change the oil today? what changed? mainly the oil and fuel.
Perhaps the oil or fuel you are using is not burning clean for some reason. The carb could be a reason.

If it runs great, then I would not really be suspecting a mechanical problem, more of a chemistry problem.
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Re: Cam timing and reversion solutions

Post by joespanova »

Actually , changing cam timing "may"? If spreading the lobe centers' and keeping the intake CL in about the same location ( lets say 107-110ish ) then wider lobe centers would open and close the exhaust earlier ( helping ) with the blow back? No?
Trying to tune it out with headers would be an "exhausting" proposition , pun intended. Lots of work and looking , there.
Carbs ( I run 2 ) could be very rich at idle..........this suggestion by Patrick James who spec'd the carbs. I'll certainly look at that
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