Overhead cam VS pushrod design? Which is better?

[jmortensen]

OK, you caught my math error. I suck at math, sorry about that. I still don't buy your parasitic loss argument. 32 valves, springs, retainer, and keepers is still a lot of mass.

I'm fully capable of understanding the hypothetical, but I don't make my decisions on what engine to put in my car based on hypotheticals. If you want to that's just peachy. You can extend that theoretical advantage over a hypothetical pushrod L6 to theoretical infinity. ;-)

As for me, I'll do what ACTUALLY makes the car faster. I don't need a hypothetical advantage, I need a REAL advantage. For this reason I keep comparing the engines that exist and get installed into cars that actually exist. Why do you insist on referring to a hypothetical advantage? Does that gain you any traction here on planet Earth?

[Walter Moore]

It is worth noting that in the U.S. only G.M. and Chrysler still sell OHV engines. G.M. only uses OHV in the small-block V8, and some of their larger V6 passenger car engines. Their 4, 5, and 6 cylinder truck engines are all either SOHC or DOHC engines.

But Ford has abandoned the push-rod technology altogether, at least for street engines. I noticed recently that the Lincon Navagator ahead of me had a DOHC (32 valve) V8.

(Well Ford may still sell a OHV V6... I don't recall...)

If you want to make an OHV engine turn 10K RPM you have to use titanium push-rods and rocker arms. The NASCAR teams do things like that because the rules say they HAVE to use OHV engines, NOT because they are better.

If some people WANT to stick a SBC in the front of their Z car, so be it. It is a free country, and as long as it is YOUR car, who am I to say you are wrong.

I have owned many cars with OHV engines. I have driven many G.M. products, and one Ford product WAY past 200K miles. I have two Chevys at home right now. But I believe that the soul of a car is its engine, and I will not be yanking the engine out of my Caprice to stick into the Datsun.

If I wanted to drive a Corvette, I would have bought one...

[thehelix112]

Jon,

I don't make any decision about what to do on my car based on what people say on an internet forum. For me its a place to maybe learn a little. If you are taking peoples on internet forums' words at to what is best for your zed you're in strife IMHO.

The topic posed many questions, the main one (as per subject line) is a broad scoped question which I interpretted differently to you. Not to worry.

There is no question in my mind that a N/A V8 (almost any) will kane a N/A L6 (almost any). So if you don't have the budget to go forced induction, the choice is relatively clear, if less than optimal. Whats a VK56 worth these days and will it fit?

But I don't know why you'd muck around with N/A stuff as I mentioned earlier. And as soon as you got forced induction (turbocharged especially) there is not as strong a case to go V8 unless you are chasing 1000hp+.

Anyway, I think I'm repeating myself so I'll sign off this topic. Enjoy

Dave

[jmortensen]

I have owned many cars with OHV engines. I have driven many G.M. products, and one Ford product WAY past 200K miles. I have two Chevys at home right now. But I believe that the soul of a car is its engine, and I will not be yanking the engine out of my Caprice to stick into the Datsun.

If I wanted to drive a Corvette, I would have bought one...

I believe that my car doesn't have a soul. My car also doesn't have a name, and I don't talk to my car in anything other than a joking manner. I think it is an assemblage of parts that makes a machine. I control what parts go into the machine, and when those parts make a machine that pleases me, then that's when it's doing what I want. When parts break my car is not "sick" and since I have it torn apart right now it is not being "vivisected"... ;-)

I don't want a Vette either. Too heavy. I do envy that assemblage of parts under the hood of a Vette though. Last time I checked it weighs less than my assemblage of parts under my hood and makes a good 75 hp and 100 lbs torque more than my current assemblage.

I don't make any decision about what to do on my car based on what people say on an internet forum. For me its a place to maybe learn a little. If you are taking peoples on internet forums' words at to what is best for your zed you're in strife IMHO.

So if you learn something from somebody on the internet and you implement changes based on what you learned... oh nevermind.

There is no question in my mind that a N/A V8 (almost any) will kane a N/A L6 (almost any). So if you don't have the budget to go forced induction, the choice is relatively clear, if less than optimal. Whats a VK56 worth these days and will it fit?

V8 costs about the same as a turbo. I'd rather have the V8 personally.

But I don't know why you'd muck around with N/A stuff as I mentioned earlier. And as soon as you got forced induction (turbocharged especially) there is not as strong a case to go V8 unless you are chasing 1000hp+.

I can only tell you what I know, and since you've said you won't be reading this there isn't much point anyway. I've come up against a VG30ET 240, a couple L28ET 240Z, a Z31 Turbo and a couple of Z32 Turbos (one with over 500 hp) at autoxes and road courses. Haven't found one yet that was faster than my L28. I'm not saying that my car is the fastest thing on the planet, because it isn't and I know better. But I'd rather have 400 NA hp than 400 boosted hp just for the lack of lag and the linearity of the power. I've heard people say you can build a turbo without those problems, I just haven't seen it in a Z yet.

[CoastGuardZ]

You know, I was just thinking that "cam in block" or "push-rod engines" keep getting refered to as OHV. It's not being compared to a Briggs and Straton 5hp lawn mower. So why is this? The valves in a OHC are also placed above the pistons, so isn't it also an OHV?

Just a little food for thought, if you're hungry that is.

Nate

Also If one can't "afford a turbo" so they go with a V8 (which also will require a new tranny) maybe it's time to reevalute your hobby.

If I wanted a race car I would have bought a race car. j/k

[Walter Moore]

Yes, I suppose that OHC engines do have valves in the head so they COULD be called overhead valve, but the "standard" name for the push-rod style engine is overhead valve. When you say overhead cam the fact that the valves are in the head is assumed.

By the way, weren't there overhead valve aircraft engines years before they adapted the design to cars? I know that there were DOHC engines running at the Indy 500 well before 1920, but didn't the 9 cylinder rotary aircraft engines of WWI have an OHV configuration? Certainly by the 1930's they did.

[GunnerRob]

You know, I was just thinking that "cam in block" or "push-rod engines" keep getting refered to as OHV. It's not being compared to a Briggs and Straton 5hp lawn mower. So why is this? The valves in a OHC are also placed above the pistons, so isn't it also an OHV?

Just a little food for thought, if you're hungry that is.

Nate

Hi Nate.

I believe, in the early days of average American engines, that the valves were in the side of the block, in the verticle position, and were actuated by a cam that was mounted in the lower end of the block (see picture below). So, when the OHV engines were introduced, they apparently were marketed as the new "OHV" valve engines.

If I'm way off base here, please let me know. I hate to be wrong.

[e_racer1999]

^^like a flathead ford...

[Phred]

Ok, I'll toss some fuel on the fire. The oldest engine I have built was a 1927 Wright nine cly. radial aircraft engine. It was the same type (not the same one) that Lindberg flew across the Atlantic. It, like all radial aircraft engines has a OHV layout. These engines have a big (over a foot in dia.) flat cam disc that is attached to the crank. Roller lifters move long pushrods which move rockers, and valves. 1750/1800 RPM was max.

GunnerRob is right about the valves in block, known as flatheads, because they had a....flathead. Go figure. Just like the Briggs engines BTW.

Walter Moore-There were two completely different designs of aircraft engines in WWI. The coventional radial, and another French built bizzare thing called a LeRohn rotary, Wherin the crankshaft was attatched to the fuselage, and the entire engine spun around the crankshaft!! It had no throttle, just an on/off switch. No wonder they lost the war.

Phred

[Aussie Zed]

GunnerRob is spot on. Initially side valve engines were the most commonly used due to their simple design, it wasn't until the '30s when a few top end manufacturers really started to use OHV engines as common place. There are exceptions, of course, some sports manufacturers saw the benefits in OHC engines such as Bugatti, which even had DOHC engines in the '20s (type 40, 3 valves per cylinder).

As for which layout is better... How many OEMs do you se changing from a pushrod to an OHC design? And how many do you see going the other way?

[CoastGuardZ]

As for which layout is better... How many OEMs do you se changing from a pushrod to an OHC design? And how many do you see going the other way?

That is an outstanding point. Are OHC's more efficient? Therefore making them easier to meet emission standards? Possibly smoother or quieter? There's got to be a reason.

Flame on!

Nate

[bemmerguy714]

If I wanted to drive a Corvette, I would have bought one...

With all the money we put in these Zs we probobly could buy a Vette! :cheeky: I dont think i would want to thou.