The never ending debate

[GoCougs]

(Laconian: Split from Colin's Vette ZHZ review)

It's just like his hate-on for pushrod engines.  The Chevy LSX and Chrysler Hemi, IMO, have proven that pushrods are every bit as capable as OHC.

It's an inherently lesser-performing technology objectively discussed ad naseum both here and in automaker power train design departments the planet over.

It is no coincidence that there are no pushrod I4 or 6 cylinder engines anymore that aren't literally decades-old legacy leftovers (i.e., Chrysler's 3.8L).

[ifcar]

It is no coincidence that there are no pushrod I4 or 6 cylinder engines anymore that aren't literally decades-old legacy leftovers (i.e., Chrysler's 3.8L).

I think the GM 3.5-liter was new in 2004.

[SVT666]

It's an inherently lesser-performing technology objectively discussed ad naseum both here and in automaker power train design departments the planet over.

It is no coincidence that there are no pushrod I4 or 6 cylinder engines anymore that aren't literally decades-old legacy leftovers (i.e., Chrysler's 3.8L).

Pushrod V8s and V10s (in the Viper's case) are just as capable as their OHC counterparts, are lighter, and more compact.

[565]

    Not this shit again...

[ChrisV]

Sure I have a clue, and I've mentioned it myriad times; functional-wise, it's one dynamic structural member performing three disparate jobs (left spring, right spring, anti-roll bar) simultaneously and development-wise it's inherent variable rate and wheel travel issues, and tuning difficulty.

Only with expensive and complicated technology (i.e., ZR1's second-generation magnetic particle shocks) have GM engineers come close to combining the performance and livability of a high-performance coil suspension one would expect in a high-end sports car. My bet is that, should it ever come to be, the C7 will have coils.

If you have objective opinions to the contrary, try bucking up. Calling names simply makes you look like you can't technically challenge what has been written.

I've already gone over the tech ad nauseum. So now, it's more appropriate to note how fucking stupid you actually are.

There are no wheel travel issues, compared to coil springs in the application we're discussing (no Corvette or Porsche or BMW is going to have noticeably different suspension travel)

One side of the transverse leaf is no more affected by a bump on the other than the left side of a car with coil springs is affected by a bump on the right side. It also is lighter, has less unsprung weight than a coil spring, and by being mounted lower has a lower CG than a coil spring. it may do part of th ejob of the anti-roll bar, but that ends up beiung a side effect of the springing, rather than a separate job it has to do (i.e. it isn't working any harder in anti-roll than it doies as a simple spring. In fact, that's one of the benefits: it adds that ability for free, making the entire suspension more efficient and lighter)

As for being variable rate, so are the coils in a BMW M3 or a Porsche 911. That's not a hindrance at all.

The ONLY real disadvantage is in a race car situation, it's harder to swap out different rate springs for different tracks or different drivers. So in race car form, the Corvettes revert to coil-overs when the rules allow. (the other two disadvantages being cost of manufacture and in stigma from ignorant morons).

It is no coincidence that there are no pushrod I4 or 6 cylinder engines anymore that aren't literally decades-old legacy leftovers (i.e., Chrysler's 3.8L).

Inline engines are a different animal than V engines. And inline 4s don't carry the issues of severely using up underhood real estate by making the heads slightly wider. they also are typically much smaller displacemetn engines that require, by virtue of being smaller displacement, more rpms to provide the what used to be race car levels of power that consumers demand these days, so the added breathing of 4 valve heads are not just a benefit, but a necessity. Larger displacement V engines, OTOH, have no need of that complexity to make useable power, and are better served by being physically smaller and less complex.

[GoCougs]

Hey, I'm completely dumbfounded as to how "I" created this thread (I did not)...

[Laconian]

My bad, I was halfway through splitting the topic when the sky fell at work.

[GoCougs]

I've already gone over the tech ad nauseum. So now, it's more appropriate to note how fucking stupid you actually are.

Hmmm...

There are no wheel travel issues, compared to coil springs in the application we're discussing (no Corvette or Porsche or BMW is going to have noticeably different suspension travel)

I noted this critique in the design realm (i.e., constraint) of things.

One side of the transverse leaf is no more affected by a bump on the other than the left side of a car with coil springs is affected by a bump on the right side. It also is lighter, has less unsprung weight than a coil spring, and by being mounted lower has a lower CG than a coil spring. it may do part of th ejob of the anti-roll bar, but that ends up beiung a side effect of the springing, rather than a separate job it has to do (i.e. it isn't working any harder in anti-roll than it doies as a simple spring. In fact, that's one of the benefits: it adds that ability for free, making the entire suspension more efficient and lighter)

Unless you've redefined basic beam theory in the past 47 minutes, this wiki entry plainly shows basic beam theory as it applies to the transverse leaf, and plainly illustrates the phenomenon I described; here's a cropped FEA analysis from said entry:

As for being variable rate, so are the coils in a BMW M3 or a Porsche 911. That's not a hindrance at all.

The ONLY real disadvantage is in a race car situation, it's harder to swap out different rate springs for different tracks or different drivers. So in race car form, the Corvettes revert to coil-overs when the rules allow. (the other two disadvantages being cost of manufacture and in stigma from ignorant morons).

Variable rate wasn't the critique, it was the ability to get the desired range of variability owing to both the material and inherent design of the spring itself.

And you're being generous on the C6R

Inline engines are a different animal than V engines. And inline 4s don't carry the issues of severely using up underhood real estate by making the heads slightly wider. they also are typically much smaller displacemetn engines that require, by virtue of being smaller displacement, more rpms to provide the what used to be race car levels of power that consumers demand these days, so the added breathing of 4 valve heads are not just a benefit, but a necessity. Larger displacement V engines, OTOH, have no need of that complexity to make useable power, and are better served by being physically smaller and less complex.

No, they are not different animals. Neither do OHC engines "severely" use under hood space; 3.5+L DOHC V6s in such small vehicles as an IS350, Rav4, 370Z, G6, et al., both transverse an longitudinal configuration, plainly shows that it's a non issue.

Pushrod engines in the I4 and 6 cylinder are virtually non existent owing to the profoundly more competitive nature of these segments, exactly as you state; the fundamental engineering principles you implicitly acknowledge do not magically go away with cylinder count.

Further, t is also on coincidence that the only two automakers in the world that make appreciable numbers of gasoline pushrod engines are now in bankruptcy.

[GoCougs]

My bad, I was halfway through splitting the topic when the sky fell at work.

No problem, however I believe HEMI666 should've been the topic "starter" as he drew first blood in his out-of-the-blue pushrod apologism.

[r0tor]

I'll put money on a 6.0L DOHC engine with variable valve timing would fit in the engine bay of a corvette and produce more power and have a broader torque curve

[2o6]

Really, if it's producing loads of power, or good fuel economy I don't see the point of this debate.

[SVT666]

I'll put money on a 6.0L DOHC engine with variable valve timing would fit in the engine bay of a corvette and produce more power and have a broader torque curve

Would it fit under that really low hood?

[TBR]

Really, if it's producing loads of power, or good fuel economy I don't see the point of this debate.

I agree. Looking at the results of the LS series of engines, what's the point of this argument? Lots of power in a light package with respectable fuel economy, what's wrong with that?

[r0tor]

Would it fit under that really low hood?

if you can put a supercharger ontop of the current one and it fits - then yes and without a problem

[SVT666]

if you can put a supercharger ontop of the current one and it fits - then yes and without a problem

The supercharger fits between the cylinder banks, not on top like on the GT500.

[SVT666]

I agree. Looking at the results of the LS series of engines, what's the point of this argument? Lots of power in a light package with respectable fuel economy, what's wrong with that?

Exactly.  It's different methods of achieving the same thing.

[GoCougs]

The supercharger fits between the cylinder banks, not on top like on the GT500.

It can't - that's where the camshaft, lifters and pushrods live.

It sits on top of the block:

[SVT666]

It can't - that's where the camshaft, lifters and pushrods live.

It sits on top of the block exactly as with the GT500's 5.4L:

My mistake.  I thought it sat right in between the cylinder heads and barely increased the height of the engine at all.

[GoCougs]

My mistake.  I thought it sat right in between the cylinder heads and barely increased the height of the engine at all.

Yeah, you guys do that a lot.

[2o6]

Yeah, you guys do that a lot.

What's that supposed to mean?

[ifcar]

What's that supposed to mean?

It means "I will trumpet this mistake in this and every other OHV debate to suggest that everything my detractors say is just as inaccurate."

[sportyaccordy]

if you can put a supercharger ontop of the current one and it fits - then yes and without a problem

Its not just the height, it's the width. And it's not just the size, it's the price. Plus what does it matter? The new Vette makes like 450HP from 6 liters and gets good gas mileage. As much as I like to tech-snob, the LSx series of engines works. The 5.4L DOHC in the new Cobra needed a supercharger to make the same power. Within the realm of mass produced V8s you don't have that many making that kind of power. And DOHC heads are definitely bigger than OHV or even SOHC heads- to write that difference off as negligible is negligent IMO.

[Eye of the Tiger]

Can't we just compromise and have an OHC pushrod engine?

[GoCougs]

It means "I will trumpet this mistake in this and every other OHV debate to suggest that everything my detractors say is just as inaccurate."

First, the supercharger issue raised is independent of valve train configuration.

Second, it was an error indicative of rabid defenders such as ChrisV.

Third, you're generous in using the word "debate." The market decided this long ago.

[Cobra93]

I was ready to go order a Camaro SS until I found out it's ugly little secret.

[2o6]

It means "I will trumpet this mistake in this and every other OHV debate to suggest that everything my detractors say is just as inaccurate."

If so, that was very immature.

[GoCougs]

I was ready to go order a Camaro SS until I found out it's ugly little secret.

Oh, no, I'd definitely recommend that. I think it's one of the best vehicles GM has built in a very, very long time, and best of breed by a long shot.

[Onslaught]

I fail to see why people give a fuck about this shit. As others have pointed out, it works well so what's the big deal?

And the market decided the future of the rotary too. I'm just happy that Mazda ignored it just like Chevy with the pushrod.

Don't like them? Don't buy them.

[ChrisV]

I noted this critique in the design realm (i.e., constraint) of things.

Unless you've redefined basic beam theory in the past 47 minutes, this wiki entry plainly shows basic beam theory as it applies to the transverse leaf, and plainly illustrates the phenomenon I described; here's a cropped FEA analysis from said entry:

And when you hit a bump with one side of a coil spring car, the car body moves up on that side, and transfers downward force to compress the other side's coil spring in almost exactly the same manner. Each side still affects the other. and if you make the coil spring stiffer, the problem gets worse. they end up doing the job of anti-roll just like the leaf you show, and to the same degree (which is barely any). The picture you show shows a spring deflection unattainable in an actual car (effectively that would equal pushing one side of the car down approx. a foot from static, which would make that side of the car actually a few inches UNDER the pavement.) in order to get ANY visible deflection of the opposite side.

Simply put, in the REAL world (on the street OR track) the deflection of the opposite side is at MOST barely measurable, and then only an issue if that side itself is on a billiard table smooth surface and the car body doesn't move even a fraction of an inch when hitting said bump.

Variable rate wasn't the critique, it was the ability to get the desired range of variability owing to both the material and inherent design of the spring itself.

Apparently not as much of a problem as you think as it's done quite well by both the factory and aftermarket.

No, they are not different animals. Neither do OHC engines "severely" use under hood space; 3.5+L DOHC V6s in such small vehicles as an IS350, Rav4, 370Z, G6, et al., both transverse an longitudinal configuration, plainly shows that it's a non issue.[/quote]

And I've seen a Ford 351cid V8 under the unmodified hood of a Focus, and an LS400 DOHC V8 under the hood of a PT Cruiser. Doesn't mean that they only take up as much room as the stock 4 cyl. If it can be done by a homebuilder, why can't big DOHC v8s fit in an economy car from the factory ALL the time?

Simply put, you can't rewrite physics on a V engine. A pushrod engine given the same displacement is physically smaller and more compact. Sometimes shorter, but always narrower and less tall. When differing displacements come into play, the difference is even more striking. My Lexus DOHC 4 liter V8 is the smallest and lightest of all mass produced DOHC V8s available, and it's physically much larger than the Ford small block V8 I'm replacing. the 5.0 fits in the Comet with room to spare for exhaust and the like. The shock towers will have to be entirely removed and new suspension created in order to accomodate the extra width of the lower displacement Lexus engine.

Pushrod engines in the I4 and 6 cylinder are virtually non existent owing to the profoundly more competitive nature of these segments, exactly as you state; the fundamental engineering principles you implicitly acknowledge do not magically go away with cylinder count.

Actually, they do, as the need to rev high to make usable power goes away as cubes climb. And as cubes climb, the need to be more compact and lighter for displacement goes up.

And of course, cost and complexity goes up pretty fast as cylinder count goes up in V configurations. While a DOHC I4 has twice as many cams and valves as a pushrod 4 cyl (like the old Iron Duke), a DOHC V engine has 4 times as many of each. So while teh friction inducing surfaces of a DOHC 4 is only slightly more than a pushrod or SOHC 4, the DOHC V engine has a LOT of new friction inducing surfaces in comparison, from 4 times as many cam gears, and much longer cam chains/belts and many more chain/belt tensioners, it has 4 times as many valve guide surfaces, 4 times as many cam followers riding on the camshafts, 4 times as many rockers or shims between the cam and valve, 4 times as many cam bearing surfaces, and only misses out on the 16 surfaces where the pushrod meets the lifter.

The DOHC will have one short cam belt/chain with one tensioner, which is about the same as a pushrod or SOHC 4. And the head, while wider, is not appreciably wider with the exhaust and intake factored in. it only has twice the bearing surfaces and valve guide surfaces in 4 valve form, but the loss of the pushrod friction surfaces is a more significant factor than in the V engine. So yes, the engineering principles do in fact change as cylinder count and layout change.

Further, t is also on coincidence that the only two automakers in the world that make appreciable numbers of gasoline pushrod engines are now in bankruptcy.

Sorry, but the pushrod engines have nothing to do with their bankruptcy. There are a LOT of factors that have contributed to that, from unions, to brand mismanagement, to piss poor quality control (and ironically, the highest quality is in those pushrod engines, themselves).

[Sigma Projects]

I'll put money on a 6.0L DOHC engine with variable valve timing would fit in the engine bay of a corvette and produce more power and have a broader torque curve

Pushrod engines can have Variable valve timing. GM already using it on a bunch of their engines. I think they plan to eventually make a 3V Pushrod (the thought was thrown around for the C6). All of the new Vortec 6.0 and 6.2 V8s GM puts in their trucks/SUVs have VVT. Pushrods just have a hard time making those ultra high REVs that OHC motors are more capable of.

I mean I'm sure everyone has seen the epic difference between the 5.0L pushrod Ford and the 4.6L OHC? I mean I know the 4.6 isn't the most compact of motors when it comes to OHC engines, but the difference in size is staggering.



Yea I bet a 6.0 DOHC setup would make more power than 6.0 OHV, but I really don't think it would fit very nicely in the corvette. I'd need to find some dimensions on some 6.0 DOHCs. But here is the 4.6 (I think this is not the SC version) XLR next to C6, same chassis.  



I'm sure there are some dimensional tweaks. But as you can see the relatively small northstar V8 kinda fills up the bill quite well.

Or look how CTS's engine bay looks with the V6 compared to the LS6 V8



I found pics of the shock mounts uncovered so it's easier to look at the passenger side shock mount and see where the engine sits.

There is a reason why the SBC is dropped into anything that has 4 wheels... sometimes ones with 2, lol.


Edit: just read your post ChrisV, haha yea if one thing GM did right it was those Pushrod Engines, lol.