5-speed Q

[maxnix]

I don't get why people think pushrod engines are "archaic" while OHC engines are not.

Quite simply, it follows from the concepts of reciprocating mass and variable valve event timing, and now variable valve lift. To be kind to the pushrod V8 in particular, we will not even mention multivalve heads.

None of these are avaiable on a pushrod engine. Hence, they are less efficient.

[ScottJackson]

Oh, but yes it is available in pushrod engines. Check to new Viper V10 for proof. I understand that for an ultra high rpm engine pushrods can be detrimental. But at what cost? For a street engine, I bet a person would be completely unable to tell the difference between an equivalent (same compression, rpm range, idle quality) pushrod engine of the same displacement as a DOHC engine. If you want the best, don't even use valve springs. They are an old-fashioned cheap way of closing valves. We all NEED a F1 engine in our street cruiser with a 20,000rpm redline that will bog and die if we try to leave a stop light at less than 6,000rpm As far as rotational mass, I bet 4 cams take more energy to spin than a single cam actuating pushrods. The rocker arms are offset by the VH's followers. I'm not saying the VH is a bad engine. It's a fine engine, but if you want a lot of power without having to spend a load of money and a big headache, a good pushrod engine is tough to beat, and it fits in a small space easily. Like I say, both are fine, but for a typical application of 8000rpm and less, good luck being able to tell the difference in seat-of-the-pants feel assuming both are equivalently built and of same displacement. The beauty of the pushrod design is you can build very large displacement cheaply while being able to swap it in the place of a much smaller displacement DOHC engine... and it's cheap, easy, effective. Comparing a 7.5:1 smogger 350 chevy from 1975 to the VH isn't fair because it's not the basic design of 2 valves and pushrods making it such a dog. It's the cam, cam timing, intake, compression, combustion chamber design, ignition timing, and exhaust which is holding it back.

[maxnix]

Granted, for street, not much difference in everyday performance, but in high rpm power when passing, a world of difference.

[ScottJackson]

Yes, if comparing a low performance smogger engine to the VH, the top end power is lacking. But it's so easy to bring a pushrod engine up to modern specs that it'd be stupid not to if you want any higher rpm performance at all. If you hit 9000+rpm while passing, then yes, I would spend the extra $$$ on a built VH, but I could get just as much acceleration out of a bigger displacement engine without having to rev it up nearly as high. If you just love the sound of 9000+rpm and that's a requirement, yes, I fully support building and modifying the VH or a similar DOHC engine over a pushrod engine, so long as you don't actually care much about how little total power it makes compared to something like an equivalent priced and external sized 10 liter big block Ford (can be built on a stock block, unlike the bbc) that will only rev safely to 6000rpm while making gobs more power.

I just re-read my post. I'm not trying to be too confrontational even if it sounds that way. Just presenting my side and logic is all.

[maxnix]

But same thing, even at 6K rpm, the DOHC will have a lot less reciprocating forces and therefore last longer due to lower spring pressures, less friction, etc. Can't arue it on volumetric efficiency either. In a truck, OHV makes sense. In a car, I still like being able to rev freely.

I remember a Cadillac that dropped it's bottom end in the 70's trying to keep up with my 2L Alfa four at only 110 mph for five minutes. He had at least 3 times the displacement and twice the pistons.

[ScottJackson]

and how many more lbs of weight did that caddy have (and frontal area)? As for rev-ability, you should check out some hot rods at a nearby auto event this summer. Some of them are slow revving blubbering POSes, but those built by owners who know what they're doing and care about street performance rev very quickly, up and down. It really is too bad that U.S. auto makers for a couple decades made really low compression low rpm V8s that gives them a bad reputation.