Performance questions
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Elder User
Joined: Nov 2004
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From: So. California
Performance questions
I am familliar with the pushrod motors but I wonder how much a difference 4valves makes over two. Does a 4 valve have better throttel responce than a 2 valve with the same total valve area? Most of the modulars today apprear th be 3 valves so if the cam had extra exaust duration to compensate would it make up for 3 vs. 4 valves? I get the impression that overhead cams ramp faster at the valves than pushrods.
thanks...
thanks...
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Elder User
Joined: Nov 2004
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From: So. California
Velocity and intake manafold? So four valves with the same total valve area of a two valve motor will have faster air velocity due to smaller valves. If the 4.6L 4V is a healthier breather than I would be inclined to think it wold make more peak hp than a 5.4L that has 3 valve unlelss a cam like a 253/274 duration cam from comp cams could make up for the single exaust valve. Still you could make up for the lack of toruqe on the 4.6 compared to the 5.4L with a close ratio transmission and lower gears or a high stall and low gears on an auto I think.
Post Fiend
Joined: May 2006
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From: Central Florida
Gears can't make HP, but the multiplier in a TC can show some increase.
The 3v motor has a variable valving, the valve's duration changes. I don't know if it's done by RPM, vacuum or Throttle position. I want to say the 3v motor produces another 40 hp bone stock over the 2v and the the 4v is about 25 hp over the 2v bone stock.
I believe the velocity difference is partly because of valve location and intake runners. Which is why I am waiting for an aftermarket casted head and intake.
The 3v motor has a variable valving, the valve's duration changes. I don't know if it's done by RPM, vacuum or Throttle position. I want to say the 3v motor produces another 40 hp bone stock over the 2v and the the 4v is about 25 hp over the 2v bone stock.
I believe the velocity difference is partly because of valve location and intake runners. Which is why I am waiting for an aftermarket casted head and intake.
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Elder User
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Well I just figured that if my gears were closer together I would keep my rpms up higher where I have more torque. If it torques out nice from 3-6k I would not want to be turning 2000 rpm after an up-shift from 5500 rpm. If the 3 valve is better breathing than the 4 valve then that is nice because the 4v is more complicated and has some scarcity about it $$$$. And if it takes one cam to drive a 3v and two to drive a 4v that breathes only as well as a 3v then I think I would take the 3v which seems to be common.
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
3v is DOHC and one of the cams moves to change the duration. The 4v uses 2 fixed cams and is less computer-complicated.
Don't get me wrong, gears can make it feel peppier. I loved my change from 3.73 to 4.56.
Don't get me wrong, gears can make it feel peppier. I loved my change from 3.73 to 4.56.
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