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Erfan Afshar
Dodge Dakota
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2/14/2002
10:10:21
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 Subject: Diffrence between Push rod motor and OHC
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What are your guys preferences when it comes to motors? DOHC or Push rod? What are the plus and minus of both.
Thanks
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Demon-Xanth
Dodge Dakota
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2/14/2002
13:07:54
| RE: Diffrence between Push rod motor and OHC
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OHC allows for better valve placement and less reciprocating mass in the valve train. However it places a signifigant additional highth when compared to pushrod engines. Meaning you can't fit as long of a stroke in the same width of engine, reducing the displacement of the engine.
Note that the difference in highth between a DOHC engine's head (w/ came) and a pushrod engine's head.
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Joel
Dodge Dakota
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2/14/2002
13:37:41
| RE: Diffrence between Push rod motor and OHC
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Pushrod motors (318, 360) have power down low right away. The max torque can be delivered right way at low RPM's. Excellent for towing and pulling stumps.
OHC, like the 4.7 delivers torque later. You can drastically tell the difference between them when you step on it. I prefer pushrod motors because the power is there all the time, no waiting. Lots of GM motors are this way too including the vette, camaro and trucks. The pushrod motors can be just as efficent as OHC motors and deliver power sooner, the LS1 and LS6 are perfect examples of that.
Joel
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hehasnoidea
Dodge Dakota
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2/14/2002
16:16:19
|  RE: Diffrence between Push rod motor and OHC
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ohc vs push rods has NOTHING to due with torque. The 4.7 makes practically the same torque as the 5.2 beacause of its more efficient design. The reason a 5.9 makes around 50 lbs of torque more is DISPLACEMENT!!!! A 4.7 design in a 360 cu displacement would far out torque any pushrod 360.
Bottom line ... overhead cams are the way to go!!!
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scat pack
GenIII
2/14/2002
16:17:56
| RE: Diffrence between Push rod motor and OHC
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Actually it's more the cam profile that determines where that power hits, not pushrods. Bigger cubic inch motors will have more torque down low. Please also realize 4.7 is single overhead cam design, DOHC would have 2 cams in each head, one for intake valves, one for exaust. Pushrod design is not as efficient as OHC. Can you guess which I prefer ? Just be patient while the performance aftermarket catches up and enjoy the new technology.
2K RC 4.7 4x4
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hehasnoidea
Dodge Dakota
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2/14/2002
16:18:25
| RE: Diffrence between Push rod motor and OHC
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http://coulterc.home.mindspring.com/hemi/hemi.html
Just thought I would add some proof
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Duner
Dodge Dakota
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2/14/2002
18:48:22
| Now There's a Torque Curve!
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Everyone should follow that link and take a look at the hp/torque curves that were in that magazine article. It's pretty obvious that they didn't get that torque curve from testing one! hahahaha
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R Middleton
Dodge Dakota
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2/14/2002
20:23:25
| RE: Diffrence between Push rod motor and OHC
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I have two pushrod engined vehicles. I have no
complaint, I have had the privlidge of piloting a
few real fast DOHC cars and I gotta say that I
really dont't have a prefrence.
I'd like to point out that every last NHRA
Dragster and Funnycar uses a PUSHROD engine with a
hemispherical head for maximum perfomance. What
conclusion can we draw from this information.
I always thought probably due to my mopar slant on
world views that one of the greatest advantages to
the Hemi head were the port paths, and the
sparkplug location at near top center of the
chamber, as a result having a DOHC engine allowed
the plugs to be inserted into the head in the
center of the combustion chamber.
IMHO the bottom line is head design and valve
layout seem more important than what actuates the
valves and it is easier to get things to line up
with an OHC setup but perhaps not neccesarily any
better.
I'm no engineer I just read a lot of Mags and
stuff. If you really have to know drop an E-mail
to Richard Ehernberg from Mopar Action/Mopar Now!
Hes an SAE and he know his stuff.
Peace.
Middy.
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Hersbird
Dodge Dakota
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2/14/2002
22:15:16
| RE: Diffrence between Push rod motor and OHC
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What I don't understand is this 4.7 Hemi talk. The 4.7 is not a Hemi, and there is more to a hemi then just hemispherical shaped heads. They also need an opposed valve arrangement. Nascar actually outlawed opposed valves not the hemispherical combustion chamber. The 5.9 and 5.2 are definately wedge motors so in that since I guess the 4.7 is more of a Hemi, but a hemi it is not. The new 5.7 (true) Hemi is actually closer to the 5.9 in its design. It is a pushrod motor very similar to the current 5.9 with better heads. The latest rumor flying around (and I want to stress rumor here) is that the new 5.7 hemi heads will be able to be retrofitted onto the 5.9's and 5.2's. There is really nothing better about either design and both have probably been around just as long. I believe the Ford Flathead was sort of both. It had the cam in the block but it activated the valves directly (used a very ineficiently shaped cumbustion chamber to accomplish this.) You could say pushrods and rocker arms are inefficient, but then a OHC v-8 with 5 feet of timing chain spinning around the front is not exactly perfect.
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Big59er
Dodge Dakota
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2/15/2002
10:49:16
| RE: Diffrence between Push rod motor and OHC
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This is kind of a newbie question.
Say I had an air induction/Ramair hood of somesort, and I were to retro fit my 5.9 with those 5.7 hemi heads your talking about. That would'nt effect anything else on the engine would it? I mean... would everything still fit underneath the hood and what not?
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Hersbird
Dodge Dakota
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2/15/2002
13:54:13
| RE: Diffrence between Push rod motor and OHC
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If, and it's a big IF, the 5.7 hemi heads could be retrofitted onto the 5.9 it would also require a new intake manifold and exhaust manifolds for sure. The new intake manifold may not leave the throttle body in the same exact spot, front to back, left to right, and up and down. So it would probably require some modification to make any cold air setup work.
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NeedForSpeed
Dodge Dakota
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2/15/2002
16:05:03
| RE: Diffrence between Push rod motor and OHC
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Wonder how much HP the hemi heads would add to the stock 5.9.
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scat pack
GenIII
2/17/2002
08:44:49
| RE: Diffrence between Push rod motor and OHC
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The old hemi head may have been a great design, but the real reason its in all the funny cars (yes, Mustangs, Camaros, you name it)is that its the only BLOCK strong enough to handle all that power ! To infer its because its a pushrod design would be false.
2K RC 4.7 4x4
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