i think ford needs to return at least its powerhouse (F350, f450) trucks offer an engine with pushrod design, modular engines are great for a balance between a useable power band and fuel economy + emissions control...but pushrod design has so much better power to offer, a fuller longer power curve...
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1990 F150 4X4 XLT Lariat 302 5spd
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Like a motor has any clue where its cam(s) are located concerning powerband.
Where do people come up with this stuff??????
I can't imagine where people get this stuff either! Bore/stroke ratio, compression, programming, etc. are what make a difference in power delivery. OHC designs have the advantage of lower reciprocating mass and the easier adaptation of four valve heads and variable valve timing, although both are possible with OHV motors too, it's just harder to do. (For a OHV motor with variable valve timing, check out the new Viper V10).
Like a motor has any clue where its cam(s) are located concerning powerband.
Where do people come up with this stuff??????
Very true. I guess they don't recognize that most pushrod engines are very large. Size does matter. When towing, there is no replacement for displacement.
Emissions is what is killing big blocks. To get the same power out of smaller engines (for emissions), you have to get it at higher RPMs. Push rod engines has so much more reciprocating mass that OHC is the logical way to go.
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2004 XLT Regular Cab, Short Bed, 4X4 with 5.4 and 3.73.
Very true. I guess they don't recognize that most pushrod engines are very large. Size does matter. When towing, there is no replacement for displacement.
Emissions is what is killing big blocks. To get the same power out of smaller engines (for emissions), you have to get it at higher RPMs. Push rod engines has so much more reciprocating mass that OHC is the logical way to go.
Quote:
Originally Posted by snowdog79
I can't imagine where people get this stuff either! Bore/stroke ratio, compression, programming, etc. are what make a difference in power delivery. OHC designs have the advantage of lower reciprocating mass and the easier adaptation of four valve heads and variable valve timing, although both are possible with OHV motors too, it's just harder to do. (For a OHV motor with variable valve timing, check out the new Viper V10).
Check out the GM 6.2.....it uses VVT also!!!
Reciprocating mass is a viable debate.
I believe that a pushrod motor may actually have LESS RECIPROCATING mass if it's a V type motor...and also an inline motor with DOHC has an extra cam to turn.
The debate is whether pushrods are considered reciprocating.
In theory, pushrods are a detriment as far as valvetrain stability.....but GM LSx motors seem to have a handle on that.
I don't don't think there is any debate that multivalve technology most certanly benefits from DOHC architecture......
I've always thought the 2 valve wedge SOHC MOD motor to be more complicated then it needed to be.....but it was a stepping stone to later 4 valve (and goofy 3 valve) designs.
Last edited by DOHCmarauder : 10-05-2007 at 04:25 PM.
I believe that a pushrod motor may actually have LESS RECIPROCATING mass if it's a V type motor...and also an inline motor with DOHC has an extra cam to turn.
The debate is whether pushrods are considered reciprocating.
In theory, pushrods are a detriment as far as valvetrain stability.....but GM LSx motors seem to have a handle on that.
I don't don't think there is any debate that multivalve technology most certainly benefits from DOHC architecture......
Back in my wasted youth, the debate was between OHV and flat head motors. OHC were only found in exotic European cars and Fiats. I found out early that OHV engines don't like high RPMs. You would get valve float and sometimes bent pushrods. I think the pushrods, rocker arms and lifters held the valves open at high speeds because the spring had to push them back in addition to closing the valves.
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2004 XLT Regular Cab, Short Bed, 4X4 with 5.4 and 3.73.
Back in my wasted youth, the debate was between OHV and flat head motors. OHC were only found in exotic European cars and Fiats. I found out early that OHV engines don't like high RPMs. You would get valve float and sometimes bent pushrods. I think the pushrods, rocker arms and lifters held the valves open at high speeds because the spring had to push them back in addition to closing the valves.
Right on.....it's known as valve float. And like you said, it's the inability of the spring to close the valve. Modern tech and lighter valve trains have allowed higher RELIABLE revs with pushrods than ever thought possible.
And TRUE OHC designs actually have the cam lobe DIRECTLY on top of the valve stem.....adjustment is done by shims between the two.
Most of the automotive OHC designs use a rocker or finger follower so that a hydraulic plunger or lifter takes up the slack. In other words, the cam lobe does NOT act directly on the valve.
The new Ford 3.5L V6 in the Lincoln actually uses a lobe on tappet method....supposedly no need for adjustment for at least 150,000 miles.
Most high performance DOHC bilkes also use this method......but adjustments are more frequent.
Last edited by DOHCmarauder : 10-05-2007 at 07:45 PM.
Back in my wasted youth, the debate was between OHV and flat head motors. OHC were only found in exotic European cars and Fiats. I found out early that OHV engines don't like high RPMs. You would get valve float and sometimes bent pushrods. I think the pushrods, rocker arms and lifters held the valves open at high speeds because the spring had to push them back in addition to closing the valves.
I know you didn't axe me but solid lifter BOSS 302's could rev to 7,000 RPM but needed constant valve adjustment.
Modern day OHV motors run around 6,000 RPM safely.
DOHC motors run 7,000 RPM PLUS with a lot of the limitation being the accessories running too fast!!!
Torrque and low speed power is dependant on filling the cylinder quickly....that's why big, slow revving motors make all their power down low and then basically run out of breath,
What's cool about VVT is you can "restrict" the opening which speeds up cylinder filling making a smaller motor have decent low end.....then as the revs rise, open up the lift/duration to let all the air the motor can handle in for that top end charge.......much easier to do using VVT with multivalves.
Look at the Tundra motor some time (sorry for the blasphemy) every bit as much low end torque as the 5.4 Ford with over 100Hp more at the rear wheels.
And Ford has just as many resources/parts to do it also!!!
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