IS GM capable of making a small block DOHC

[Firefighter]

GM can and has made these types of motors they simply choose not to for cost/weight/overall dimensions.

Personally I'm not looking forward to the thought of having to buy 2 or 4 cams and a 30' timing chain because I want to do a cam swap. Never mind 32 valves to have to get worked on and start thinking about buying all of those in titanium or sodium filled, what about checking all of those springs and retainers etc... just too much to achieve a similar goal IMHO.

They can be cool though. There is another thread around here comparing the Coyote motor to the LS3 and it's a never ending thread of tit for tat. Someone pointed out the AMG 6.3L making 631hp and 468tq with an 8k redline what I find interesting is that it's TQ number is down so much compared to HP.

[DGthe3]

You can't make a 5.7L DOHC engine the same external size (I assume thats what you meant by 'profile'?) as a 6.2L pushrod. They're a couple inches taller & wider. To compensate, you'd have to take a couple inches off the stroke. Now you've got half the displacement as the pushrod engine. You could make up a little bit of the 'lost' displacement by boring it out. But even then, there isn't much room to increase the bore on a small block over the 4.06" on the current 6.2L engines. The overall displacement limit would be somewhere between 3 and 3.5L. You could increase the bore spacing, but that a) makes the engine longer and b) causes a massive increase in cost. But besides that, the resulting engine would be redicously oversquare. Something like a 5.6" bore on a 1.75" stroke. It could be done, but the thing would be wildly impractical for street usage.

Originally Posted by Firefighter

GM can and has made these types of motors they simply choose not to for cost/weight/overall dimensions.

Personally I'm not looking forward to the thought of having to buy 2 or 4 cams and a 30' timing chain because I want to do a cam swap. Never mind 32 valves to have to get worked on and start thinking about buying all of those in titanium or sodium filled, what about checking all of those springs and retainers etc... just too much to achieve a similar goal IMHO.

They can be cool though. There is another thread around here comparing the Coyote motor to the LS3 and it's a never ending thread of tit for tat. Someone pointed out the AMG 6.3L making 631hp and 468tq with an 8k redline what I find interesting is that it's TQ number is down so much compared to HP.

Yep, its not like DOHCs are a magic bullet that simply make an engine better. They are heavier, taller, more complicated, and more expensive than a pushrod engine. Its also much harder to implement cylinder de-activation, though it can be done (I think it involves shutting down an entire bank of cylinders). Now, given the fact that the 'ancient' pushrod engine in the C7 has managed to provide the best combination of power and fuel economy of any car ever (which, by default, includes everything with a DOHC) I don't think they made a mistake by sticking with pushrods.


as for the AMG 6.3, its not that torque is down (it makes about the same as the new LT1), its that it has a very high redline. Since horsepower is a function of rpm's and torque, an engine that spins faster while making a similar amount of torque is going to make more power.

[derklug]

The next big step will be cam-less engines with Piezio-electric(or some alternative) valves that are individually fired for any timing and duration profile the engineers require.

[GretchenGotGrowl]

Originally Posted by derklug

The next big step will be cam-less engines with Piezio-electric(or some alternative) valves that are individually fired for any timing and duration profile the engineers require.

Mclaren is already working on this. Reduces the size/weight of the engine quite abit.

[menendez1293]

Originally Posted by derklug

The next big step will be cam-less engines with Piezio-electric(or some alternative) valves that are individually fired for any timing and duration profile the engineers require.

Originally Posted by GretchenGotGrowl

Mclaren is already working on this. Reduces the size/weight of the engine quite abit.

So is koenigsegg. They have actually put a cam-less motor into a Saab and have driven about 60K Kilometers in about 2 years with zero issues.

[Firefighter]

Seems very doable with today's tech. No cam reduces rotational mass quite a bit (I imagine) and you are a computer tune away from a new "profile"...

[Truck Norris]

Originally Posted by Angrybird 12

Actually that wasn't completely designed by GM it was a joint design with Lotus and was built by Mercury Marine.
http://www.corvettemuseum.org/specs/.../history.shtml

Never said it was designed by GM, in fact I said nothing about it's origins or development... just it saying it fit under a C4's hood just fine and had massive power potential.

Originally Posted by Firefighter

Seems very doable with today's tech. No cam reduces rotational mass quite a bit (I imagine) and you are a computer tune away from a new "profile"...

+1

Cam swaps are becoming a thing of the past with the performance potential of DOHC with variable valve timing on both the intake and exhaust. You can have a smooth idling, mileage friendly V8 one second and an all out high hp high screamer the with a wicked idle the next all thanks to independent valve timing and probably reason why domestic push rod engines get stuck with cylinder de-activation and gas guzzler tax's while DOHC power plants don't. GM has stuck to push rod V8's for one reason....... MONEY. Theres a reason why supercar builders like Pagani have AMG engine's.

[Angrybird 12]

Originally Posted by Truck Norris

Never said it was designed by GM, in fact I said nothing about it's origins or development... just it saying it fit under a C4's hood just fine.

Well the question was "Is GM capable of making a small block DOHC?", when you brought up the LT5 I was just noting that GM did not completely design the motor alone and they didn't build it. Nothing about it fitting under the hood.

[KMPrenger]

Originally Posted by GretchenGotGrowl

Mclaren is already working on this. Reduces the size/weight of the engine quite abit.

Originally Posted by menendez1293

So is koenigsegg. They have actually put a cam-less motor into a Saab and have driven about 60K Kilometers in about 2 years with zero issues.

Yep, saw a video about the koenigsegg version. Pretty impressive to me.

Smaller, lighter engine, which is considerably more fuel efficient, and more powerful. Its a huge win all the way around.

[Number 3]

Originally Posted by Angrybird 12

Well the question was "Is GM capable of making a small block DOHC?", when you brought up the LT5 I was just noting that GM did not completely design the motor alone and they didn't build it. Nothing about it fitting under the hood.

Sorry, but the fact that GM elected to outsource a LOW volume engine has ZERO to do with whether they can do it on their own.

[Angrybird 12]

Originally Posted by Number 3

Sorry, but the fact that GM elected to outsource a LOW volume engine has ZERO to do with whether they can do it on their own.

I don't think I ever said they couldn't..... I was saying the LT5 engine wasn't that's all....
I know since then GM has designed and built their own DOHC V8s.

[fielderLS3]

Can they build it....of course they can. Why couldn't they?

The question is, do you want them to build it. There are reasons GM has stayed with the pushrod 2-valve design, as that configuration has certain advantages both in packaging, and power/torque characteristics.

They could easily build a smaller, higher revving V8 to make similar power, but do you want them to go down a road that will ultimately end with trading torque for revs? Or put another way, what would you rather have, the new 4.3L version of the small block with 285 hp, or a Chrysler Pentastar or Ford Cyclone, all of which make about the same power on paper?

[Truck Norris]

There are plenty examples of DOHC V8's that make just as much torque as they do horsepower. For example the 2000 Cobra R made 385hp at 6,500rpm and 385tq at 4,250rpm with its DOHC 5.4L. Making low end torque is in the cam profiles and not wether or not it has DOHC.

[fielderLS3]

Originally Posted by Truck Norris

There are plenty examples of DOHC V8's that make just as much torque as they do horsepower. The 2000 Cobra R made 385hp at 6,500rpm and 385tq at 4,250rpm with its DOHC 5.4L. Making low end torque is in the cam profiles and not wether or not it has DOHC.

Yeah, but the Corba R was kinda a unique example, and you're unlikely to see anything like that in a high volume, mainstream engine. In my experience, with cars normal people can actually drive, I've never driven a DOHC with a truly strong low end, that made as much torque as horsepower (at least not in NA form). But pretty much all of the OHV engines I've driven, and the ones still in production today, make either the same or more torque than horsepower.