[Zeke.Malvo]

Originally Posted by shaffe

Ok so OHV are more efficient and make more power and are lighter/ better packaging.

Why is every other GM motor an OHC design then? Why does the colorado have an OHC engine?

They WERE lighter, but with the technology they need to compete with DOHC, they no longer have that advantage. They come in weighing the same roughly now. And they are no longer cheaper as well, which used to be an advantage too. And they do not make "more power", just look at the Mustang vs C8. The base v8 Mustang is out powering it. The advantages the current OHV does hold is packaging, and low end torque production.

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[whiteboyblues2001]

Originally Posted by Zeke.Malvo

They WERE lighter, but with the technology they need to compete with DOHC, they no longer have that advantage. They come in weighing the same roughly now. And they are no longer cheaper as well, which used to be an advantage too. And they do not make "more power", just look at the Mustang vs C8. The base v8 Mustang is out powering it. The advantages the current OHV does hold is packaging, and low end torque production.

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An OHV engine of the same displacement will be VERY much lighter than a DOHC engine, and much smaller too. That is why you can have more displacement by going with OHV.

Also, the technology to get the fuel efficiency and emission are employed on BOTH designs, so weight was added to both. In fact, when you deploy variable valve timing to the DOHC design, it adds more weight than when deployed on an OHV engine because you need four hydraulic actuators rather than just one.

Case in point: Coyote vs. LS3. LS3 was a bit lighter and smaller. Coyote vs. LT1, LT1 was a bit smaller but a bit heavier due to DI. New Gen Coyote vs. LT1, the LT1 is a bit smaller and lighter because the new Coyote added Dual injection. But the main thing to remember is that the LT1 has 6.2 Liters of displacement where the Coyote is 5.0. More displacement is more torque under the curve. If you shrunk an LT1 to 5.0 Liters, it would be significantly smaller and lighter than the Coyote.

[Mr. Wyndham]

Originally Posted by whiteboyblues2001

An OHV engine of the same displacement will be VERY much lighter than a DOHC engine, and much smaller too. That is why you can have more displacement by going with OHV.

Also, the technology to get the fuel efficiency and emission are employed on BOTH designs, so weight was added to both. In fact, when you deploy variable valve timing to the DOHC design, it adds more weight than when deployed on an OHV engine because you need four hydraulic actuators rather than just one.

Case in point: Coyote vs. LS3. LS3 was a bit lighter and smaller. Coyote vs. LT1, LT1 was a bit smaller but a bit heavier due to DI. New Gen Coyote vs. LT1, the LT1 is a bit smaller and lighter because the new Coyote added Dual injection. But the main thing to remember is that the LT1 has 6.2 Liters of displacement where the Coyote is 5.0. More displacement is more torque under the curve. If you shrunk an LT1 to 5.0 Liters, it would be significantly smaller and lighter than the Coyote.

It would also be less powerful. Displacement drives performance on OHV engines moreso than OHC.

But that's the thing, isn't it? Two different answers to the same performance question...and the regulation that's driving it all: emissions.

[whiteboyblues2001]

Originally Posted by Mr. Wyndham

It would also be less powerful. Displacement drives performance on OHV engines moreso than OHC.

But that's the thing, isn't it? Two different answers to the same performance question...and the regulation that's driving it all: emissions.

Yes, exactly. If you started at the beginning of this thread, you know that the simplified equation for HP in and ICE is HP=RPMs * Torque(at that RPM). So, you can increase HP by increasing RPM's or by increasing torque. So, if you increase RPM's you get more peak power, but it is only increased at the top of the RPM range. If you increase torque, you increase HP everywhere on the RPM range.

[Mr. Wyndham]

Originally Posted by whiteboyblues2001

Yes, exactly. If you started at the beginning of this thread, you know that the simplified equation for HP in and ICE is HP=RPMs * Torque(at that RPM). So, you can increase HP by increasing RPM's or by increasing torque. So, if you increase RPM's you get more peak power, but it is only increased at the top of the RPM range. If you increase torque, you increase HP everywhere on the RPM range.

[Norm Peterson]

Originally Posted by whiteboyblues2001

An OHV engine of the same displacement will be VERY much lighter than a DOHC engine, and much smaller too. That is why you can have more displacement by going with OHV.

I'll give you that the heads will be smaller and lighter, but not that the block need be. Perhaps the biggest reason Ford's modular engines are so physically large compared to their displacements is because they started with an essentially 'square' bore & stroke - unlike the LS and current LT series engines, which are somewhat "oversquare" (bore bigger than stroke). The 'square' configuration forces a relatively longer stroke, which also gets multiplied by the desired rod length to stroke ratio when determining the block deck height dimension (kind of a double-whammy), which is where the heads start.

On pushrods . . . they are subject to lateral deflection along their length, so you can't open valves operated through them as fast as you can with more direct-acting mechanisms, especially since the greater mass of bigger valves + pushrods + lifters then requires the valve springs to be stiffer to control it all at any given rpm.

Also, the technology to get the fuel efficiency and emission are employed on BOTH designs, so weight was added to both. In fact, when you deploy variable valve timing to the DOHC design, it adds more weight than when deployed on an OHV engine because you need four hydraulic actuators rather than just one.

Being able to vary the intake to exhaust phasing is a benefit more readily achieved in a DOHC design. Viper managed it, but there's got to be a reason Chevy hasn't tried it in a production vehicle yet.

You can comfortably fit about 3.65 total inches of valve diameter in a 4" bore OHV (2.05" I + 1.60" E). But you can fit two 37mm intakes and two 32mm exhausts into a 3.70" bore. The difference in total intake and exhaust curtain areas at any given amount of lift is significant, to say the least.

Case in point: Coyote vs. LS3. LS3 was a bit lighter and smaller. Coyote vs. LT1, LT1 was a bit smaller but a bit heavier due to DI. New Gen Coyote vs. LT1, the LT1 is a bit smaller and lighter because the new Coyote added Dual injection. But the main thing to remember is that the LT1 has 6.2 Liters of displacement where the Coyote is 5.0. More displacement is more torque under the curve. If you shrunk an LT1 to 5.0 Liters, it would be significantly smaller and lighter than the Coyote.

I don't think it'd be physically as much smaller as you want to believe (bore and stroke being in cube root relationships to displacement). The bigger problem would be that in a comparable state of tune to its current 6.2L size it'd only be putting out around 375 HP with a similar torque figure.


As mentioned before, it does come down to where (and how) you want to be operating. Some prefer more torque down low (and this admittedly suits automatic transmissions better), while others would rather work with higher revs when they're "playing around" and aren't as concerned about torque @1500 - 2500 rpm because they aren't using it all when they're down there anyway.



FWIW, I don't hate pushrod engines.


Norm

[whiteboyblues2001]

Originally Posted by Norm Peterson

I'll give you that the heads will be smaller and lighter, but not that the block need be. Perhaps the biggest reason Ford's modular engines are so physically large compared to their displacements is because they started with an essentially 'square' bore & stroke - unlike the LS and current LT series engines, which are somewhat "oversquare" (bore bigger than stroke). The 'square' configuration forces a relatively longer stroke, which also gets multiplied by the desired rod length to stroke ratio when determining the block deck height dimension (kind of a double-whammy), which is where the heads start.

On pushrods . . . they are subject to lateral deflection along their length, so you can't open valves operated through them as fast as you can with more direct-acting mechanisms, especially since the greater mass of bigger valves + pushrods + lifters then requires the valve springs to be stiffer to control it all at any given rpm.

Yes, but the bigger issue with trying to rev a pushrod engine high, is there is so much mass for the spring to push back when the valve is closing, that at high RPM's the cam rotates but the spring can't catch up, so then the lifter starts hopping off the cam. Once that happens, engines are prone to dropping a valve.

You can comfortably fit about 3.65 total inches of valve diameter in a 4" bore OHV (2.05" I + 1.60" E). But you can fit two 37mm intakes and two 32mm exhausts into a 3.70" bore. The difference in total intake and exhaust curtain areas at any given amount of lift is significant, to say the least.

Yes, but as I pointed out in an earlier post on this thread, the point of NOT going to DOHC is that you can have greater displacement, which means larger pistons and cylinders, which can accommodate a larger valve. So the difference in flow thought the head is not as much as folks imagine because they are comparing two valves vs. one in the same size package. But that is not the case in practice. The OHV engine will have larger cylinders. And if you aren't going to rev to the moon anyway, you don't necessarily need the extra flow that four valves would provide (unless you add boost to the design). Take the two Coyote intake valve and calculate the cross sectional area, and compare it to the one in the LT1 and they are a lot closer that you would think.

Look at it this way. An ICE is nothing but an air pump. You can make a little pump and turn if faster, or a smaller pump and turn it slower and get the same exact air flow. But the one running slower won't need the extra benefit of having four valve, because it never spins fast enough for one to cause a limitation.

I don't think it'd be physically as much smaller as you want to believe (bore and stroke being in cube root relationships to displacement). The bigger problem would be that in a comparable state of tune to its current 6.2L size it'd only be putting out around 375 HP with a similar torque figure.

Agreed, I never brought this up because it over-complicates an already too wordy explanation.

As mentioned before, it does come down to where (and how) you want to be operating. Some prefer more torque down low (and this admittedly suits automatic transmissions better), while others would rather work with higher revs when they're "playing around" and aren't as concerned about torque @1500 - 2500 rpm because they aren't using it all when they're down there anyway.

FWIW, I don't hate pushrod engines.


Norm

Agreed, and I don't hate DOHC engines either. They each have their place depending on the engineering goals. The truth of the matter is you need both RPMs and Torque to make power. But as you decide to produce peak HP higher and higher in the RPM range, that comes at the cost of low end torque (and hence HP) in the RPM range relative to peak power. So, for my personal enjoyment (and nothing else) I prefer engines that put out an equal amount of peak torque and peak HP. That usually puts peak power at about 6,000 RPMs or so. If they are not equal, I like a little more HP than torque. Both the LT1 and Coyote fit my ideal performance range, so I am good either way. I'm just not big on engines that don't rev far enough because it's like driving a diesel. It puts you back in the seat initially, but then falls flat right away. Some of the turbo 4 cylinders are like that today (but not nearly as exaggerated example as the diesel). You have to short shift them. And I also don't like the peak HP too high because it takes forever to get to the fun part of the power band, and it becomes all about shifting and modulating the clutch like a two stroke dirt bike. I like the happy medium in between the two extremes. It gives you power everywhere. The LT1 puts out just about the same peak HP number, but it also puts out about 315 lb-ft of torque at 1,000 RPMs. That's some low end grunt! And it puts out 400 lb-ft at about 2,200 RPMs and keeps it over 400 until peak HP at 6,000 RPMs. It's just powerful everywhere, not just up top.

[Norm Peterson]

Originally Posted by whiteboyblues2001

Yes, but as I pointed out in an earlier post on this thread, the point of NOT going to DOHC is that you can have greater displacement, which means larger pistons and cylinders, which can accommodate a larger valve. So the difference in flow thought the head is not as much as folks imagine because they are comparing two valves vs. one in the same size package. But that is not the case in practice. The OHV engine will have larger cylinders. And if you aren't going to rev to the moon anyway, you don't necessarily need the extra flow that four valves would provide (unless you add boost to the design). Take the two Coyote intake valve and calculate the cross sectional area, and compare it to the one in the LT1 and they are a lot closer that you would think.

Quick and dirty, the intake areas are close (not surprising, given that the power outputs are similar and they're both working under the same emissions and fuel economy pressures). What's important is that it takes the OHV motor having a bore about 10% bigger in order for that to happen. IOW, the OHV design has to be bigger at least in the bore dimension in order to get that much valve area into it.


Side note, that tiny bore is one thing in particular I don't care for about the modular-design Ford motors. I feel that a 93-ish mm bore (3.66") is really better suited to 8-cylinder displacements between about 4.0L up to 4.2L.

Side note #2, there actually have been a couple of pushrod 4-valve designs for the older-gen SBC. The LS would have been a better starting point


Norm

[metros11]

Originally Posted by whiteboyblues2001

Yes, but the bigger issue with trying to rev a pushrod engine high, is there is so much mass for the spring to push back when the valve is closing, that at high RPM's the cam rotates but the spring can't catch up, so then the lifter starts hopping off the cam. Once that happens, engines are prone to dropping a valve.

A prime example of this is the LS7.

[whiteboyblues2001]

Originally Posted by Norm Peterson

Quick and dirty, the intake areas are close (not surprising, given that the power outputs are similar and they're both working under the same emissions and fuel economy pressures). What's important is that it takes the OHV motor having a bore about 10% bigger in order for that to happen. IOW, the OHV design has to be bigger at least in the bore dimension in order to get that much valve area into it.

I don't have to have bigger pistons, I want to...

Side note, that tiny bore is one thing in particular I don't care for about the modular-design Ford motors. I feel that a 93-ish mm bore (3.66") is really better suited to 8-cylinder displacements between about 4.0L up to 4.2L.

In theory, having the slightly undersquare setup that the Coyote has and 4-valve design would lend itself well to forced induction, as compared to the 2-valve oversquare of the LT1. But it is not ideal for N/A high HP. To be honest, I think the rod ratio is a more important factor here anyway, so I am getting a bit to far down this road...

Side note #2, there actually have been a couple of pushrod 4-valve designs for the older-gen SBC. The LS would have been a better starting point

The issue I have with 4-valve pushrod is there is still too much mass to rev high, so the 4-valve is kind of not fully utilized.

Truth be told, what's really holding back the pushrod design in terms of being able to raise the RPM's of peak HP is the emission standards (IIRC cold start emission is tough here). You can buy Chevy's heads and cam for the LT1 and get 535HP right out of the box. Or you can just buy the LT376/535 crate engine right from Chevy. 535 N/A HP with all that low end torque would make a nice replacement in an SS 1LE if that person's engine blew up. That would be a blast at the track!

[Norm Peterson]

Originally Posted by whiteboyblues2001

I don't have to have bigger pistons, I want to...

It's always nice when somebody goes and builds something - whatever it might be, not just engines - the way you'd prefer to see it built.



Norm