16v vs. 32v?

[InfernoOrangeSS]

Let me preface this by stating I am by no means an engine expert, so don't beat me up if I am asking a dumb question...


I have heard that the Mustang 5.0 has 32 valves, and the Camaro SS has 16 valves. It is my understanding that the 32 valves will help the engine "breathe" better in the 4 stroke process. I have been told the 32 valves gives better power. It makes sense to me, but again I have limited knowledge on engine power/modding, etc.
My question is why wouldn't Chevy go with 32 valves on the SS? Is there some reason that they decided with 16 over 32?

[archtaan]

The Mustang and Camaro engines are fundamentally different in their head/cam designs. The Mustang is a DOHC motor while the Camaro is a pushrod OHV motor. 4 valve heads cost more due to needing 2 cams per head on a dual cam motor. There is also a packaging concern because the engine is usually wider with the bigger heads. OHV motors like the Camaro breathe just fine and have an advantage in making torque. A dual cam 4 valve head like the Mustang has better rev range as seen in a higher redline because of less moving parts. The cams actuate the rockers(usually) as opposed to the Camaro style where the cam actuates a lifter, a pushrod then the rocker. Some say the 4 valve engines run smoother, have better timing control, better emissions and are more fuel efficient. The Vette, Z06, ZR1, CTS-V, Hemis are all 2 valve OHV motors.

[Rock36]

That is a complicated question, but a lot of it has to do with the basic engine design/layout. Simply put, the 5.0L has 32 valves total, 4 valves/cylinder (2 intake valves, and 2 exhaust valves), the LS3 has 16 valves, 2 valves/cylinder (one intake and one exhaust) Your 4.6L 3V has 2 intake and 1 exhaust valve.

The Coyote engine and all Modular Ford engines are an overhead cam design. This design generally makes it easier to and gives more flexibility to cylinder head design/geometry and typically makes it easier to have more valves.

The Camaro engine is a pushrod design. There have been 4 valve per cylinder pushrod engines, but there are a lot of good reasons to stick with 2 valves in a pushrod engine; for instance simplicity and fewer moving parts.

Generally speaking more valves do provide better air flow into the cylinder, but better airflow can be developed in other ways than number of valves. You can increase the air flow in a 2 valve design by going with larger valves, but that increases valve train weight and can lower the ultimate redline of an engine. Having more valves allows more air flow, and keep smaller lighter valves moving in the valvetrain.

But I imagine adding more valves to the LS3 wouldn't yield enough extra power to really be worth the extra effort in head design, block design, etc.

Others will probably go into greater detail, but that is quick run down. Really there are a lot of factors driving this, much more than I've mentioned.

EDIT: Here is a good link to check out, its about camshafts, but valve and camshafts go hand-in-hand:
http://www.howstuffworks.com/camshaft.htm

[InfernoOrangeSS]

Many thanks to both of you for excellent explanations! Makes perfect sense now. I appreciate the info without being treated like I am a retard.

[chain777]

Originally Posted by archtaan

The Mustang and Camaro engines are fundamentally different in their head/cam designs. The Mustang is a DOHC motor while the Camaro is a pushrod OHV motor. 4 valve heads cost more due to needing 2 cams per head on a dual cam motor. There is also a packaging concern because the engine is usually wider with the bigger heads. OHV motors like the Camaro breathe just fine and have an advantage in making torque. A dual cam 4 valve head like the Mustang has better rev range as seen in a higher redline because of less moving parts. The cams actuate the rockers(usually) as opposed to the Camaro style where the cam actuates a lifter, a pushrod then the rocker. Some say the 4 valve engines run smoother, have better timing control, better emissions and are more fuel efficient. The Vette, Z06, ZR1, CTS-V, Hemis are all 2 valve OHV motors.

I agree with most of what you said except the torque comment. The only advantage the LS has in making torque over the DOHC Ford is displacement. If the Ford matched the displacement of the Chevy, the Ford would be making more torque throughout the rev range. It's not just the DOHC and 4 valves, but the TiVCT (variable cam timing).

[DGthe3]

As a little side note ... its been rumored that the next gen small blocks could be getting a 3 valve per cylinder overhead valve engine, reducing the flow advantage that the 4 valve DOHC engines have.

[InfernoOrangeSS]

I am curious as to why Chevy uses the pushrod, and not the OHC.
I thank you again for helping me out with that. I think it would be interesting if Chevy went to the OHC with their greater displacement.

[Southern Comfort]

My assumption is the cost of development & manufacturing 4v don't yield enough power to lure a buyer to any model. At least, not like a blower.
Consider Cadillac Northstar vs their current offering CTS-V.
Been there. Done that.

[assasinator]

Originally Posted by TungstenGT

Let me preface this by stating I am by no means an engine expert, so don't beat me up if I am asking a dumb question...


I have heard that the Mustang 5.0 has 32 valves, and the Camaro SS has 16 valves. It is my understanding that the 32 valves will help the engine "breathe" better in the 4 stroke process. I have been told the 32 valves gives better power. It makes sense to me, but again I have limited knowledge on engine power/modding, etc.
My question is why wouldn't Chevy go with 32 valves on the SS? Is there some reason that they decided with 16 over 32?

4 valves does not always mean 'breathes better'. there are some limits that need to be placed on that assumption.

for example, modern high flow chevrolet ports are huge by small block standards. They have to be for the 300+ cfm they flow. it doesnt mean low end loss in the sense it used to. the engines have grown with the port size and flow increases, IE, trying to use a l92/ls3/l76 head on a big bore short stroke 5 liter engine would be a mismatch. there would be almost no low end torque.

if you have an engine that can use 4 valve and 2 valve heads, the 4v will usually out power the 2v and be more flexible. IE, a 4 valve pushrod head for the LS3. it would likely murder the 2v in use now. you have to figure that even with a small 4v cam a LS3 could easily make 500-600hp and be 50 state legal.


google unshrouded valve area. it explains some of the reasons, but its complex. you have to compare the two types on the same engine.

[LOWDOWN]

Consider the LT5 engine, '90-'95, in the C-4 Corvette ZR1. DOHC, 5.7L and a highest rating of 405 hp. With another 15-20 years of engineering development, and expanded to 6.2L displacement, 500 hp wouldn't have been too optimistic...if not a few more. But its co$t$ were prohibitive, compared to what an LS7 eventually offered...

Consider, also, GM's recent announcement of the 100,000,000th Small Block. To do a clean-sheet-of-paper replacement optimized for DOHC architecture would "strain" that direct relationship...let alone co$t a ga-zillion in development/retooling...

[DGthe3]

Originally Posted by TungstenGT

I am curious as to why Chevy uses the pushrod, and not the OHC.
I thank you again for helping me out with that. I think it would be interesting if Chevy went to the OHC with their greater displacement.

Mainly cost. Its been said that GM can crank out OHV V8's for about the same price as what most manufacturers build a modern V6 for. There are also weight benefits to an OHV design.

Originally Posted by assasinator

4 valves does not always mean 'breathes better'. there are some limits that need to be placed on that assumption.

for example, modern high flow chevrolet ports are huge by small block standards. They have to be for the 300+ cfm they flow. it doesnt mean low end loss in the sense it used to. the engines have grown with the port size and flow increases, IE, trying to use a l92/ls3/l76 head on a big bore short stroke 5 liter engine would be a mismatch. there would be almost no low end torque.

if you have an engine that can use 4 valve and 2 valve heads, the 4v will usually out power the 2v and be more flexible. IE, a 4 valve pushrod head for the LS3. it would likely murder the 2v in use now. you have to figure that even with a small 4v cam a LS3 could easily make 500-600hp and be 50 state legal.


google unshrouded valve area. it explains some of the reasons, but its complex. you have to compare the two types on the same engine.

Just switching to a 4 valve design won't yield a ~30% improvement in hp on the LS3. Not in and of itself at least. To see those sorts of gains, you'd have to make it much higher revving. But they could give a 2 valve pushrod engine an 8000 rpm rev limit if they really wanted to.

[Rock36]

Originally Posted by TungstenGT

I am curious as to why Chevy uses the pushrod, and not the OHC.
I thank you again for helping me out with that. I think it would be interesting if Chevy went to the OHC with their greater displacement.

I can't speak for GM specifically, I can just share my own general understanding. There are still advantages to a pushrod design engine. The pushrod engine is the simplest design in general. For instance it only needs one camshaft operating, vs 2 cams in a SOHC (one camshaft per head), or 4 cams in a DOHC (two camshafts per head). All those extra camshafts, require a much larger set of timing chains, tensioners, gears, etc. to drive all of them. Typically this makes SOHC/DOHC engines larger and heavier than pushrod (OHV) engines of similar displacement.

A good snapshot example of what I'm talking about is this:

The latest BMW M3 uses a 4.0L DOHC (4V) V8 engine, now this engine weighs around 445 lbs all together, if my source is correct. It is important to also note that BMW made significant weight reduction efforts to get the engine to weigh 445 lbs. Now compare that to the "giant" 7.0L LS7 engine in my Z06. The LS7 weighs around 458lbs, and is a 2V engine. There is only a 13lbs difference. So despite the fact my LS7 has an extra 75% displacement, it only weighs an extra 3%. That is a great trade off in my mind.

Now the advantages of the 4.0L BMW engine are more apparent when you consider that the specific output for the 4.0L engine is around 103.5 hp/liter (414hp total). While the LS7 only makes 72 hp/liter (505hp total). The BMW engine spins past 8000 rpm (in large part due to its overhead cam design), and the LS7 only spins to 7000 rpm.

Very very generally speaking GM is able to use greater displacements due to their use of pushrods. GM has used DOHC (4V) V8 engines with their Cadillac Northstar engines, and if you take a look their largest displacement for their Northstar series was 4.6L naturally-aspirated and a 4.4L supercharged engine. Also generally speaking, DOHC/SOHC engines can spin to higher rpms easier, while pushrods typically run larger displacements in a tighter overall package.

Finally, GM likely still uses pushrods (OHV) engines because they still work for GMs purposes, are still competitive and allow them to hit specific price targets. I imagine it is the same for Dodge/Chrysler to a degree as well. Why does Ford still use a live-rear axle in the Mustang?... because simply speaking, Ford has made it work and kept it competitive without having to R&D a new rear suspension for now.

Again these are all general trends that I speak of. You could make a pushrod spin to 8000 rpm, but that would require very expensive and light weight valves, springs, pushrods etc. You could have a large displacement DOHC engine like the 6.3L DOHC V8 that Mercedes AMG uses, but again EXPENSIVE!

[LOWDOWN]

Keep in mind GM, CYD Nov/11, has sold 785,000 Trucks (Chev/GMC/Cad) and 75,000 Cars (Camaro/Vette/Caprice/CTS-V) with predominantly OHV V8 engines. The generally superior torque of the OHV design is well-played in those vehicles...

[CamaroSpike23]

Originally Posted by TungstenGT

I am curious as to why Chevy uses the pushrod, and not the OHC.
I thank you again for helping me out with that. I think it would be interesting if Chevy went to the OHC with their greater displacement.

part of it... is the addage of "if it ain't broke, don't fix it"

GM has proven time and time again that you don't need DOHC and all the other stuff to make a strong, cheap, and reliable engine.

That being said, no engine design is perfect. There are drawbacks to each engine out there, OHV or OHC

Originally Posted by Rock36

I can't speak for GM specifically, I can just share my own general understanding. There are still advantages to a pushrod design engine. The pushrod engine is the simplest design in general. For instance it only needs one camshaft operating, vs 2 cams in a SOHC (one camshaft per head), or 4 cams in a DOHC (two camshafts per head). All those extra camshafts, require a much larger set of timing chains, tensioners, gears, etc. to drive all of them. Typically this makes SOHC/DOHC engines larger and heavier than pushrod (OHV) engines of similar displacement.

I wouldnt necessarily say that the pushrod engine is the simplest. but thats based on your definition of simple. you can run a SOHC engine with fewer parts than an OHV engine. yes, you have two camshafts and two timing chains (sometimes you can run one), but you no longer have pushrods, rockers, and lifters. Instead, you have the cam pushing directly on the valves, which IMHO, is "simpler".



A good snapshot example of what I'm talking about is this:

The latest BMW M3 uses a 4.0L DOHC (4V) V8 engine, now this engine weighs around 445 lbs all together, if my source is correct. It is important to also note that BMW made significant weight reduction efforts to get the engine to weigh 445 lbs. Now compare that to the "giant" 7.0L LS7 engine in my Z06. The LS7 weighs around 458lbs, and is a 2V engine. There is only a 13lbs difference. So despite the fact my LS7 has an extra 75% displacement, it only weighs an extra 3%. That is a great trade off in my mind.

Now the advantages of the 4.0L BMW engine are more apparent when you consider that the specific output for the 4.0L engine is around 103.5 hp/liter (414hp total). While the LS7 only makes 72 hp/liter (505hp total). The BMW engine spins past 8000 rpm (in large part due to its overhead cam design), and the LS7 only spins to 7000 rpm.

actually, part of the reason the BMW engine spins past 8000rpm is largely due to the size of the rotating assembly. you can build an LS7 to spin past 7k, but it will cost you.

Very very generally speaking GM is able to use greater displacements due to their use of pushrods. GM has used DOHC (4V) V8 engines with their Cadillac Northstar engines, and if you take a look their largest displacement for their Northstar series was 4.6L naturally-aspirated and a 4.4L supercharged engine. Also generally speaking, DOHC/SOHC engines can spin to higher rpms easier, while pushrods typically run larger displacements in a tighter overall package.

Finally, GM likely still uses pushrods (OHV) engines because they still work for GMs purposes, are still competitive and allow them to hit specific price targets. I imagine it is the same for Dodge/Chrysler to a degree as well. Why does Ford still use a live-rear axle in the Mustang?... because simply speaking, Ford has made it work and kept it competitive without having to R&D a new rear suspension for now.

Again these are all general trends that I speak of. You could make a pushrod spin to 8000 rpm, but that would require very expensive and light weight valves, springs, pushrods etc. You could have a large displacement DOHC engine like the 6.3L DOHC V8 that Mercedes AMG uses, but again EXPENSIVE!

what about a BBC spinning past 9500rpm?

Originally Posted by LOWDOWN

Keep in mind GM, CYD Nov/11, has sold 785,000 Trucks (Chev/GMC/Cad) and 75,000 Cars (Camaro/Vette/Caprice/CTS-V) with predominantly OHV V8 engines. The generally superior torque of the OHV design is well-played in those vehicles...

Remember a big part to play in the superior torque is the displacement of the engines.

You could have an OHC engine that makes gobs of torque down low, but it would fall on its face in the higher rpm. There's a balance to be reached. with most OHC engines, they are smaller displacement than OHV engines mainly due to the extra physical size from all the extra components.

for a comparison, I'll pull the specs for the 95 Lambo Cala that makes 400hp at 7200rpm and the LS3 that also makes 400hp at 5900rpm (not apples to apples, but for this comparsion it will do)

the engine in the Cala is a 3.9L DOHC V10
the engine in the Camaro is a 6.2L OHV V8

the Cala engine is just over half the size of the Camaro's, yet has 2 more cylinders. the cylinders in the Cala are tiny compared to the Camaros. The Cala can rev to the moon, but the Camaro can pull the moon down with its torque.