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I was watching a video on camshafts (not here), and they said cam lobe lift (peak valve lift) will affect piston to valve clearance.
I have heard this many times, and it is technically not true. Peak valve lift occurs at the installed centerline of the cam, around 100-115 degrees after TDC. At this point the piston is over 70% down the cylinder bore. If you had a 3″ stroke crank, the piston would be over 2″ from TDC.
The only way peak valve lift relates to piston to valve clearance when selecting a cam, is that when you pick a cam with more duration, it usually has more lift.
It is the cams duration and installed centerline that will affect the piston to valve clearance.Another one is a piston with a short compression distance (Pin to top of piston), will have a shorter piston skirt, and rock more in the cylinder bore.
I think this is confused by the fact the shorter compression height pistons are normally used in stroker engines, but the compression distance (pin location in the piston) does not directly to piston skirt length. Many times the higher pin location will make the piston more stable, except on the intake stroke, all other strokes, compression, power, and exhaust, it will be more stable, so it really does not need the extra weight of a long skirt, and in a stroker application, the skirt may need to be shorter so it does not protrude too far below the bottom of the cylinder bore and interfere with the crank and rods.
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[quote=”Evil-i” post=176840]What drives me nuts is when people tell me you stroke an engine by adding longer rods. :pinch:[/quote]
First I heard of that one, but funny.
There seems to be many based on cams, carbs, and exhaust, like there is a magical version that is way better than all the rest.
There’s also the popular misconception that premium gasoline makes more horsepower.
No, it doesn’t. If your car runs fine on regular or mid-grade gas, it won’t run any better on premium, as far as HP is concerned. There may be some cleaning benefits from the higher detergent additives, but that has nothing to do with the energy content of the fuel.
Many of these are the truth, but not the whole truth. So general information is generally true. Just like you can have two cams, both with the same lift and duration, even LSA, and they can be totally different due to the shape of the lobe.
[quote=”Evil-i” post=176913]There’s also the popular misconception that premium gasoline makes more horsepower.
No, it doesn’t. If your car runs fine on regular or mid-grade gas, it won’t run any better on premium, as far as HP is concerned. There may be some cleaning benefits from the higher detergent additives, but that has nothing to do with the energy content of the fuel.[/quote]
Depends on how the engine is built and if it’s tuned for higher octane. If the engine is not tunes for the higher octane it can actually decrease power due to the longer burn time of the higher octane fuel.
[quote=”Jasonw1178″ post=177003]Many of these are the truth, but not the whole truth. So general information is generally true. Just like you can have two cams, both with the same lift and duration, even LSA, and they can be totally different due to the shape of the lobe.
[/quote]A agree with what you are saying, except you need to mention the lift and duration is the “Advertised”, or taken at just the one point. If the two cams did have the same lift and duration at all the points of the lobe, then they would be the same.
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