shatner saves said:
THe only real disadvantage to pushrod engines is they can't rev to the moon. (at least not cheaply) but then again most OHC engines don't rev past 6500.
I wish Ford would build a new pushrod engine, The Hemi, LS1, LS6 , LS2 all kick ass. The new 3 valve Fords are looking good, they seem to have the power of the DOHC V8's but lower cost of SOHC.
The new 4.6 3v motor makes 300 hp on 87 octane fuel and it is meets ULEV 2 emmisions standards. Imagine what a 5.0 or 6.0 litre engine running 11:1 compression would do.
Pushrod engines with a single camshaft also makes running multiple valves, cam phasing, or VTEC type systems really difficult.
I applaud GM for sticking with the technology. That new vette motor is a very impressive powerplant, but it's development potential is fading fast.
Just take a look at the new "daisy" motor. An atmospheric motor, making over 600 hp from 6.4 litres. Not bad.
Pushrod engines with a single camshaft also makes running multiple valves, cam phasing, or VTEC type systems really difficult.
I applaud GM for sticking with the technology. That new vette motor is a very impressive powerplant, but it's development potential is fading fast.
Just take a look at the new "daisy" motor. An atmospheric motor, making over 600 hp from 6.4 litres. Not bad.
shatner saves said:
Displacement on demand is easier to do on a Pushrod engines. Starting in 05 some Chevy trucks with the 5.3L and the Hemi V8 in the 300C and Magnum will have DoD.
GM will have pushrod V8s with 3 valves and VVT in the next year or two. The 3.9L V6 going into the 2005 Pontiac G6 is a new generation of pushrod V6 that has DoD and VVT. The 3 valve version will be 270HP. The 3 valve heads are said to add 10% HP the the GM V8s.
Pushrod engine are less expensive to build and lighter and more compact than ohc. The LS6 also gets better gas milage than any DOHC V8 on the market. The GM 3800 series III (which is an old school engine) has been reworked and now meets SULEV standards.
I got a pic of the 3 valve V8, I hope it loads
I agree that Ford needs a larger bore spacing V8. Particularly for trucks, Ford needs a V8 that can go to 6.0L while having a stroke that is less than 3.7"
Unfortunately to do this Ford would need to spend a massive amount of $$ on new tooling. I just don't think that Ford is in a position to spend those $$ right now. So in the mean time Ford should develop and sell the 5.8L V10 engine. It could be made with most of the same tooling that Ford already has. An all aluminum SOHC 3 valve 5.8L would deliver as much if not more HP that GM & Chrysler will be able to get out of their pushrod V8's, will weigh about the same and not be much larger. V10 friction losses will be slightly higher than the V8's, but gas mileage could be close to the big displacement V8's with proper development.
Unfortunately to do this Ford would need to spend a massive amount of $$ on new tooling. I just don't think that Ford is in a position to spend those $$ right now. So in the mean time Ford should develop and sell the 5.8L V10 engine. It could be made with most of the same tooling that Ford already has. An all aluminum SOHC 3 valve 5.8L would deliver as much if not more HP that GM & Chrysler will be able to get out of their pushrod V8's, will weigh about the same and not be much larger. V10 friction losses will be slightly higher than the V8's, but gas mileage could be close to the big displacement V8's with proper development.
Z28x said:
Not exactly a model of simplicity (or high rpm stability). Although I hear the next Z06 might use this type of cylinder head, so, we'll see. As I said, running multiple valves is an issue.
I really don't see how this configuration is much simpler, lighter, cheaper or more compact than the sohc 3v geometry in the mustang. You save the cost of some length of chain, tensioners and one camshaft. In return, you get pushrods (24 of them), more rocker arm bulk (24 of those) and the lash adjusters reciprocate as well. In ford's design, they are stationary. Friction and reciprocating mass are going to be much higher and overall mass probably isn't much different Those intake rockers and shaft mount have to weigh at least as much as one of fords cam's. And, with all those pushrods all over the place, GM still gets to do the "coil-not-exactly-on-plug" ignition, so throw in 8 plug wires, which other designs do away with. If I'm not mistaken, the spark plug holes are just visible in the picture, next to the forward-upper exhaust manifold bosses. That cylinder head machining seems pretty involved as well. GM's going to have headaches with the tolerance stackups. Overall cylinder head height is probably a bit lower but it is definitely wider in this configuration.
DoD is cool is a cool idea. Although, GM was going to do that on this vette, but decided against it because it cause some chassis resonance issues (you could tell it was running on 4 cyl). That's from the MT article. Although, the vette still gets amazing milage without it.
In the end there is no relacement for displacement, regardless how you actuate the valves. Although, the new 4.6 makes 75 more hp, 15 lb-ft more peak torque, and has 1000 more useable rpm than my 5.0, and it still runs on pump gas and gets the same or better mileage in a heavier car. It also does this while motivating 6% less displacement. I think that's significant.
And, I don't care what anyone says, this is just plain cool:
http://www.wrljet.com/fordv8/427sohc.html
3 valve SOHC and 3 valve OHV probably arn't that far apart on cost. I beleive the 3 valve pushrod still uses 16 pushrod. 1 pushrod operates 2 intake valve. DOHC is the one that cost a lot more.
I've read GM is working on Cam-less V8 engines, I can see this being the way all engine go in the future
I've read GM is working on Cam-less V8 engines, I can see this being the way all engine go in the future
There is one pushrod and one (huge) rocker that operates the 2 intake valves. The exhaust valve has the pushrod coming up through the vee that pushes on an intermediate rocker that shares the common shaft with the intake rockers. The intermediate rocker then pushes on a shorter pushrod that actuates the second exhaust valve rocker that actuates the exhaust valve. Hence 24 pushrods and 24 rockers. The rockers look like investment cast or powder metal pieces that should be quite strong but have considerably more bulk than the stamped steel roller followers used in the new 4.6.
It's the exhaust side that makes me consider tolerance stack-ups. You've got 2 pushrods and 2 rockers actuating the exhaust valve and the machining for the secondary rocker pedestal is definitely not that straightforward. I'm sure it'll work fine in a truck, where you generally don't see much more than 5k RPM, but it's rev potential is probably limited.
Here's an interesting article on some other engine tech. I especially like the offset crank idea.
http://www.sae.org/automag/techbriefs/12-2002/page3.htm
It's the exhaust side that makes me consider tolerance stack-ups. You've got 2 pushrods and 2 rockers actuating the exhaust valve and the machining for the secondary rocker pedestal is definitely not that straightforward. I'm sure it'll work fine in a truck, where you generally don't see much more than 5k RPM, but it's rev potential is probably limited.
Here's an interesting article on some other engine tech. I especially like the offset crank idea.
http://www.sae.org/automag/techbriefs/12-2002/page3.htm
I am sure that a 5.4 3v modular motor (to even up the displacement) with VVT and camming as aggressive as the LS1/2/6 (as has been noted in other threads, the LS-series V8s are cammed FAR more aggressively than the 4.6/5.4s, even when you take into account the overhead cam-factor) would produce similar numbers to what the LS2/LS6 are putting out, if not surpass them by quite a bit.
Last I heard, International is looking at doing away with camshafts on their big diesels as soon as 2007. Their hydraulic system is not suitable for passenger cars (bulk, revs) but is ideal for a slow revving highway tractor.
BMW and Lotus have been working on solenoids for a while. Infinitely variable timing, lift, duration while controlling intake and exhaust independently would be HUGE. Apparently, the systems they have been testing have shown promising reliability, but they use a lot of power, requiring a 24v or 48v system, and they have a long way to go making them quiet enough.
BMW and Lotus have been working on solenoids for a while. Infinitely variable timing, lift, duration while controlling intake and exhaust independently would be HUGE. Apparently, the systems they have been testing have shown promising reliability, but they use a lot of power, requiring a 24v or 48v system, and they have a long way to go making them quiet enough.
SadbutTrue said:
VVT does not necessasarily do anything to increase peak HP. In an engine with fixed valve timing you have to pick a compromise for cam timing between low end torque, peak HP and emissions. So from most engines VVT gets you around those compromises and better optimizes power at low & high RPMs. The biggest effect that adding VVT to most engines is to broaden the torque curve.
The Cobra R engine probably had its cam timing optimised for peak HP so adding VVT would most likely not add any more HP, but could improve torque across the RPM range.
However, I'd imaging that since the R engine was built Ford has learned other things about engines. Don't the FR-500 heads flow better than the R heads? They've also come up with better intake manifolds and could come up with better cam profiles too. On the other hand engines have to meet stricter emissions regulations today than back with the R was made.