just wonderin

[SVTballa]

i was just wonderin why does chey still use a 16 valve pushrod engine unlike sohc and dohc engines like everyone else is using. the z06 is an effin animal but wouldnt it be better with dohc so it can have more valves. whats GM secret with the ohv?

[Dyno247365]

Originally Posted by SVTballa

i was just wonderin why does chey still use a 16 valve pushrod engine unlike sohc and dohc engines like everyone else is using. the z06 is an effin animal but wouldnt it be better with dohc so it can have more valves. whats GM secret with the ohv?

The secret is experience. The pushrod has been around for so long that it's been perfected, and if you ask me always sounds amazing.

[WEF]

I've always wondered why we didn't get a big Northstar.

[Dyno247365]

Originally Posted by WEF

I've always wondered why we didn't get a big Northstar.

You mean bigger than 4.6L? The thing is, I say if it ain't broke, don't fix it and the OHV is GM's signature V8.

[TEXAS-HOTROD]

That's really a good thought.
High horse power numbers might be cool, but it's torque that gives the grunt that sets you back in the seat.
A push rod engine will always make more torque than an over head cam engine. It doesn't make any sense, but that's just how it is. Corvette has always been on the leading edge of automotive technology, and even though a push rod engine sounds low tech, it by far out performs the others.
The Z06 makes 500/500 (or more) with push rods and 3 valves per cylinder. The viper makes 500/505 (I think) from 10 cylinders, 8.0 liters and over head cams. Ford needs the boost from a super charger to make its 500/500 numbers, and that's in a car that costs $150K+.
Even as sophisticated as the hand-built Cobra engines are (were), they lacked the impressive power that they should have had and torque was almost nonexistant. The North Star, as well as the Cobra, needs to be wound up before it's internals come into play. Making a cam swap? Forget it, it now takes an expert to handle that task.

A cam/bucket design will lift the valve only as much as the cam lobe is tall. If the lobe is .50", the valve lift is only .50" The standard rocker arm ratio for a push rod is 1.5:1. So if the lifter travels .50", you get .75" valve travel. The valve can be actuated faster and with roller cams/lifters, there's more flexability with lifts and durations. Simply adding a 1.6:1 rocker set can add more performnce (in older engines) and earlier Chevy big block rockers are available in 1.7:1 ratios. I would guess that Chevy uses a 1.6:1 or a 1.7:1 rocker ratio in the new engines to make such fat torque. That's up to .85" of valve lift from the same .50" cam lift.
I guess if the LS1 (6.0) in my truck can pull a loaded car trailer down the highway, an LS2 (7.0) can make a Vette really fly around the track.

[corning_d3]

Plus pushrod engines come off the line way harder than an OHC/DOHC, since the torque develops sooner. I watch pusrod v-8 engines develop 7000 to 8000 horsepower, although not for very long. I've never saw even the hottest DOHC put out that many ponies..