Peak RPM/HP

General engine tech -- Drag Racing to Circle Track

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11secAvanti
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Re: Peak RPM/HP

Post by 11secAvanti » Tue Dec 04, 2018 10:25 am

Thanks to everyone for the feedback insight. A second question. At idle rpm (say 700) the A/F can be tweaked for the highest vacumn readings on the engine. So the change in A/F changes the rpm point. Cam and other dimensions are fixed and not changed. But one does notice a change in rpm based on solely adjusting the A/F at idle. Soo, if say the rpm were held at a steady load of 5500 and ONLY the A/F was again tweaked and changed.

Would this change swing the rpm reference level again? And if so wouldn't that swing the Peak HP/RPM point? And if "yes" wouldn't this mean that an ideal A/F ratio can determine the Peak/HP/RPM point? thanks

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Re: Peak RPM/HP

Post by Brian P » Tue Dec 04, 2018 11:30 am

Unclear what you would be attempting to achieve by doing that. The lean and rich limits of air/fuel ratio will be quite different with no load on the engine than they are at full load or part load, with different limiting factors setting those bounds.

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Re: Peak RPM/HP

Post by MadBill » Thu Dec 06, 2018 1:43 pm

carbureted AFR is very sensitive to load as well as speed. Another way of stating a reply is: "If you adjusted AFR for maximum RPM, re-setting as necessary to maintain 5500 in neutral, all you would achieve is the lowest fuel consumption for operating at 5500 in neutral. It would have no relevance for any real world condition."
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Re: Peak RPM/HP

Post by swampbuggy » Thu Dec 06, 2018 3:33 pm

Cylinder heads and manifold. Mark H.

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Re: Peak RPM/HP

Post by 11secAvanti » Fri Dec 07, 2018 9:13 pm

Not, not netural but under load from say a dyno or a vehicle under acceleration. Example: When my leaf blower starts to run out of fuel I notice the engine will momentarily speed up ( air is the load here). The carb is leaning and so A/F is changing and I notice the rpm starts momentarily to increase. Sooo is not the A/F ratio playing a big role in where the Peak HP/RPM is
on say a graph chart. thanks.

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Re: Peak RPM/HP

Post by steve316 » Fri Dec 07, 2018 9:33 pm

don't confuse 2 cycle with 4 cycle engine

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Re: Peak RPM/HP

Post by MadBill » Fri Dec 07, 2018 11:35 pm

11secAvanti wrote:
Fri Dec 07, 2018 9:13 pm
Not, not netural but under load from say a dyno or a vehicle under acceleration. Example: When my leaf blower starts to run out of fuel I notice the engine will momentarily speed up ( air is the load here). The carb is leaning and so A/F is changing and I notice the rpm starts momentarily to increase. Sooo is not the A/F ratio playing a big role in where the Peak HP/RPM is
on say a graph chart
. thanks.
You're right, the revs increase as the fuel runs out because the engine is tuned rich of maximum power and thus makes more power and can spin the air impeller faster, but peak power RPM (as opposed to the actual HP) is not substantially affected. Optimizing AFR is one of the biggest variables in dyno tuning an engine.
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Happy is he who can discover the cause of things.

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