Supples’ Pub

So with the announcement of the new LS3 engine featuring a 0.2L displacement bump from the LS2, ~30 more HP, and variable valve timing, a question popped into my mind. Where do GM’s famed OHV engines have left to go?

 
Pushrod valve actuation system 

Overhead Valve, or pushrod, engines have been the bread & butter of GM for decades. The famous, and still virile, Small Block Chevy engine has been going strong since 1955. Sure it has gone through many improvements over the years, transforming into the LT series 2nd gen engines in 1992 (introduced in the Corvette), then the LS series 3rd & 4th gen engines. The wikipedia links embedded in this paragraph offer a good overview of the different engines and changes.

A cylinder head sliced in half shows two overhead camshafts—one above each of the two valves.

Now GM has dabbled in Overhead Cam engines before. The LQ1 was a dual overhead cam 3.4L V6, making a very respectable 200-210HP @ 5200rpm and 215ft-lb @ 4000rpm. Found in early-mid 90’s GM vehicles like the Monte Carlo Z34, it has a good amount of pep to it, I’ve ridden in one before. It lacks the down-low torque of a good old OHV engine, but still has plenty of power. Anyway, there are lots of reports of problems with those engines and that is probably why they were discontinued.

So looking to modern day engine offerings, you’ll see a bit of a change. V6’s are still available in OHV configurations, like the High Value engine lineup, but the High Feature engines sport DOHC. The claimed smoother engine operation of an OHC setup, combined with needing to stay competitive in power output, has probably led to the increase in mid-range models sporting OHC engines. Let’s not forget, some of Cadillac’s high end offerings feature the Northstar DOHC V8 engine.

LS7 Engine

But the true high end performers in the GM family - Corvette, GTO (ahem), SSR, CTS-V, etc - are still based on the good ol’ OHV designs. The monstrous 427ci 7.0L LS7 powers the Corvette ZO6, good for 505HP. The 350HP 5.7L LS1 is a stalwart model in the LS series family, having powered several years of F-bodies, Corvettes, and even a year of the GTO. Let’s not forget the first “Gen-IV” LS engine, the 6.0L LS2 400HP/400TQ which offers incredible performance, ULEV emissions rating, and gave the Corvette a V6-like 18/28MPG EPA rating.

Now we have the LS3, the next evolution in LS series engines. It has a slightly larger displacement than the LS2, plus variable valve timing, and likely some other internal tweaks for a ~8% increase in power. The LS2 featured 0.3L displacement increase with better flowing heads and a slightly hotter cam than the LS1, for a nearly 15% power increase. The 505HP LS7 goes for a massive 7.0L displacement for a 26% power increase, along with of course better breathing thanks to revised heads and cam.

One engine I didn’t mention here was the LS6, which was a tweaked 5.7L making 405HP but with more high end power rather than the traditional super-fat torque curve. The LS2, which directly followed the LS6, offered the same overall power but with more low & mid-range torque in a more fuel efficient engine.

My guess is that we will see something like the LS1->LS6->LS2 transition occur with the LS3. A new design will be formulated to provide the same or better performance, better fuel economy, better emissions, and lower cost than the previous model. This will likely be evolutionary in the one or two designs after the LS3, but at some point a more revolutionary design will come along that will be positioned as the fundamental performance engine and still out-do the best of the best from last generation.

The question I pose to those who are more attuned to mechanical technical knowledge than myself, is where does OHV have left to go? Where do we go next? Will the LS4 be a 6.5L 450HP OHV VVT engine? Will the fundamental elements of the LS7 make up the next generation LS engine, offering up the once-upon-a-time hotrod engine as a base model? Or will GM switch tracks entirely, and find OHV has grown long in the tooth to be a widespread engine design in a world where competition is fierce, fuel economy constraints are tightening, and performance must still grow? Will the C7 Corvette or 6th-gen Camaro feature an OHC performance engine? By gosh, what if the high end performance offering was a super-tweaked small displacement V8 or a high displacement screaming V6? (Please no…)

Tell me what you think will happen. Do you know someone who might have a unique thought on this topic? Send them here, I’m interested to see where this discussion can go

All images courtesy Wikipedia