Camshaft question

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MOPARMAGA

MOPARMAGA

" The other hard member"
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Hey a-body folks,
I have a question hopefully someone has experimented with.
Question is & I'll try to ask this as best that I can. With the camshaft having 4 events 1 being intake closing it has effects on dynamic compression & effective stroke.
Seems like most of the drag race Camshafts in the 260°-270°@.050 close around 68-80 degrees after the piston is on its way back up (valve still open)
Would there be a benefit of having a cam ground so the intake valve closes sooner?
My 471 should be around 11.8:1 static & is race only.
 
My thought is no. I would think you would want the intake valve open a bit longer to allow as much air and fuel into the cylinder as possible, especially in a race only engine. The only thought I have about closing it sooner is building more cylinder pressure. I wonder what a cam grinder would think.
 
RammerJammer75 said:
My thought is no. I would think you would want the intake valve open a bit longer to allow as much air and fuel into the cylinder as possible, especially in a race only engine. The only thought I have about closing it sooner is building more cylinder pressure. I wonder what a cam grinder would think.
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That was my thought "cylinder pressure" good, do we have any cam grinder dudes on fabo ?
 
Not that I'm aware of. Racer Brown seems to be a common one around here as well as Bullet. The thing is with the cylinder pressure, I'd say this engine will live above 5,500 or 6k RPM right? I would think the cylinder fill would be more important at higher RPM.
 
RammerJammer75 said:
Not that I'm aware of. Racer Brown seems to be a common one around here as well as Bullet. The thing is with the cylinder pressure, I'd say this engine will live above 5,500 or 6k RPM right? I would think the cylinder fill would be more important at higher RPM.
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Good point, probably be up to 6800-7000 at the line
 
RammerJammer75 said:
Not that I'm aware of. Racer Brown seems to be a common one around here as well as Bullet. The thing is with the cylinder pressure, I'd say this engine will live above 5,500 or 6k RPM right? I would think the cylinder fill would be more important at higher RPM.
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I just read a great article from reher Morrison, looks like cylinder filling is better at higher rpm. Question settled
 
MOPARMAGA said:
I just read a great article from reher Morrison, looks like cylinder filling is better at higher rpm. Question settled
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Do you have a link to that article, I like to read it
Thanks
 
The higher you want to rev it,
the later the intake has to close;
to allow "time" to get the oxygen in there; it's always about the oxygen. The problem is that our atmosphere is only about 21% oxygen by volume, so our poor engines end up being huge nitrogen pumps; around and around it goes.
If you close the intake earlier,with no other changes, then the engine slows pumping sooner, and peak horsepower moves to a lower rpm, usually losing some in the process.

The late closing intake usually only causes problems in the lower 1/2 of the rev-range; from idle to maybe 3000/3500 rpm.
 
Talk about a hair splittin question.
 
There is another way..

Go roller. Roller cams faster ramp speeds. The valves open and slam shut much faster than flat tappet cams. The valves are open wider for a longer period of time which makes for much more flow. More flow = more power.
 
roccodart440 said:
There is another way..

Go roller. Roller cams faster ramp speeds. The valves open and slam shut much faster than flat tappet cams. The valves are open wider for a longer period of time which makes for much more flow. More flow = more power.
Click to expand...
Thanks Going roller.
 
MOPARMAGA said:
Yeah I make thoughts sometimes
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Just remember...a dyno and the numbers it produces has limitations just like any other tool.

So two cams and appear similar and make the same or similar power curves can and will behave differently in the car. That’s why cam selection isn’t splitting hairs. A custom ground cam will always produce results that can’t be measured on a dyno.

Larry Morgan wrote in an article way back in the late 90’s that he spent the entire offseason testing only cams. He went through a drum of fuel doing it, which is huge amount of dyno pulls.

I’d bet you could lay the vast majority of the power curves over each other and it would look like the same line. Yet at some point, they had a decision to make as to which cam with their engine was the one to test in the car.

The point is cam timing is critical if you want the best power, driveablity and overall performance. Things like how well the engine recovers RPM off the Transbrake or off the pedal and how well it it recovers RPM in the gear changes. The more gear changes, the more critical that aspect of cam time becomes.
 
yellow rose said:
Just remember...a dyno and the numbers it produces has limitations just like any other tool.

So two cams and appear similar and make the same or similar power curves can and will behave differently in the car. That’s why cam selection isn’t splitting hairs. A custom ground cam will always produce results that can’t be measured on a dyno.

Larry Morgan wrote in an article way back in the late 90’s that he spent the entire offseason testing only cams. He went through a drum of fuel doing it, which is huge amount of dyno pulls.

I’d bet you could lay the vast majority of the power curves over each other and it would look like the same line. Yet at some point, they had a decision to make as to which cam with their engine was the one to test in the car.

The point is cam timing is critical if you want the best power, driveablity and overall performance. Things like how well the engine recovers RPM off the Transbrake or off the pedal and how well it it recovers RPM in the gear changes. The more gear changes, the more critical that aspect of cam time becomes.
Click to expand...
Thank you for the great reply, that makes sense.
 
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