"While 4-valve (or 5-valve) heads can theoretically outflow 2-valve heads, they often don't. Curtain area isn't everything. Also with 4.6 to 6+ liter V8s, practical rpm ranges to around 6500, which is still quite doable for pushrods."

In my long years in this industry, I have never seen evidence of that. Quite the contrary actually. 5 valve is generally always superior in design to 4 valve and 2 valve designs are less efficient yet in terms of Cd throughout the lift curve and maximum volumetric efficiency. Brake horsepower per liter is always proportional to the ratio of lift area to piston area. An excellent point made in one of the other posts I read through.
Pushrods work? Of course they do, Roger Penske showed us some years back that a pushrod engine can be very competitive -given rule breaks- but the Ilmor he debuted was built specifically for that purpose and used a pushrod merely 58 mm in length. Penske knew, as any good engineer would, that designing a valvetrain with a high enough natural frequency would be the key to success in that engine. Those of you not so fortunate in building your own cylinder blocks will have a much more difficult time of it.
Regardless, much of this multi-valve debate has been shown in the research of Aoi, Nomura, Taylor and Matsuzaka to name a few. I feel that the subject is a moot one but still it goes on. If pushrod/2v per cylinder designs were superior then we'd be designing 2v cylinder heads for our F1, Indy and Prototype engine development programs.
In all of this you have to keep a few things in mind. An engineer often wants to go one way with a design only to run into a roadblock. That roadblock being money. When you look at the cost of the american pushrod engines you so love you see an excellent cost to performance ratio. The employment of technology makes for a better vehicle but it does not come without costs. Also keep in mind that the prime goal of an engine development program for OEMs is not only performance, even more so here in the UK.
Cheers,
Nick Hayes

 

Correct me if I'm wrong, but OHV engines are pushrod engines, for the most part, right? OHV just stands for Over Head Valves, which kind of came next, after the flathead design.

But OHC (over head cam) engines are technically OHV engines, because the valves are in the same relative position as the pushrod type engines.

Just my $.02

 

Cosworth

Nick,
Are you in any way involved in Cosworth's CART or Nascar programs? Just curious.

-Mindgame

 

No quarrels with any of what you said, Nick. All I meant was that some well developed 2-valve heads flow extremely well, and some 4-valve heads don't, in spite of having the extra valve area.

Case in point: Zed-06 5.67L Corvette engine manages 71.4 hp/L. 4-valve 4.6L Ford SVT manages about the same (69.6 hp/L) both at 6000 revs. Both are GM and Ford's high end NA versions of their flagship engines. It would be interesting to compare lift areas to piston area ratios for these two engines.

When Ford needed more grunt for the newest Cobra, they supercharged the 4.6 to about 85 hp/L rather than go for 20% more hp/L, which would probably have required many more revs. Unfortunately the torque/L wouldn't respond as well.

Of course multivalve is the way to go in race-only engines (rules permitting). Absolutely no quarrel there.

Regards,

Jon

 

There is a Nick Hayes at Cosworth, I believe:

http://www.grandprix.com/gpe/cref-haynic.html

 

Now that's an eye opener! Not everyday you see a motorsports professional's resume on the internet.
Nick, what brings you to an f body message board? Just my curiosity running abound.... hope you'll be sticking around!

-Mindgame

 

You're right, sorry. I was thinking about some other class.

As far as nitromethane, we have taken a look at it in our lectures. The "complete fuel".....a hydrocarbon with its own oxygen source attatched to it. One of the pros said that it is actually impossible to inject enough nitro into the engines with the rpms they turn(short of shooting it in with a fire hose and displacing too much oxygen to get a good burn cycle).

From watching the indy guys, it seems as though we won't be using valves and cams for too much longer. I forget the term for it, but that "valve bar" (solid bar with notches cut in it that acts like a valve) setup is the way to go. I'm still looking into this so called "valveless engine". If you know anything about where I can find more info, PLEASE tell me where. A 3.0L V10 turning 15K rpms is bookin' it too boy!

And please be patient with me ol' timers, this young grasshopper is still learning. This engine stuff is starting to blow my mind.

Nice of you to stop by Mr. Hayes. Now stay here!

 

you guys are bringing up some good points....thats exactly what i was getting at with the simplicity of the OHV engine. The problem with the 4+ valve heads is that they often dont realize any large flow benefit until higher RPM.

I knew the cube limit in TF was 500, we were talking about a possible exhibition car with a huge cube engine to test the outer limits of power capability.

when you come into complex engine setups, you have to weigh the benefits.....if you have a state of the art DOHC multivalve VVT engine that is only slightly better, then you have to do a cost benefit analysis. is it really worth it? in most cases i think not

 

With VVT yes, with OHC no, less parts.

 

Not really, the cam sits over the valves, so how is this more parts?

There is either a lifter or a rocker, but not both (sounds wierd doesn't it), and a chain from the crank to the cam, or a belt, and then a spacer in your size of choice between the valve tip and rocker/lifter.

This is less parts, not more, and ultimately this is why there is less frictional drag on the engine and also less requirement for high spring pressures.

 

No argument, for a street car, who wants to spend $1,000 to replace the cams in a quad cam engine. The engine will also weigh more, and the top end is pretty big in a DOHC car.

 

One of the big negatives with DOHC motors, and even SOHC motors, for that matter, is they are not in production long enough to get a following in the aftermarket. Sure there are companys that make upgraded VTEC cams, but usually they get rid of the standard lobe, and use the VTEC lobe all around. I mean, the SBC, and the 5.0L have over 40 years of use, and tons of tuners have had time to "enhance" the engines, to make more power. The modular motors have been around since, what, 94? And the Honda motors change every few years, so the available parts for those engines are going to be more expensive, and less readily available. That's the price to pay for technology.

 

I think the TF guys get enough nitro in there. They are on the verge of hydrolock; there is as much volume of liquid nitro as there is space above the piston at TDC.

The nitro reaction I was referring to was not combustion; more like 'cracking'. I don't remember the exact term, nor many of the details.

The "valve bar" you mentioned is quite old, and reappears regularly in literature and forums. Perhaps this is what you are referring to:


http://www.ls1tech.com/ubb/cgi-bin/u...c;f=1;t=007612

15K rpm? Even the F1 engine guys who mention numbers are talking in the 17-18+ range. At 18K every lb-ft of torque is about 3.4 hp, but only about 2.9 at 15K. Here's a case where bigger (faster anyway) is probably better.

 

bmw-williams hit 19k a little while ago..... that is insane
doesnt piston speed eclipse flame speed at that point?
thats another scratch against "v8 no matter what", when you get mores like 4.5" and bigger for drce engines, that is a long way for a flame to have to burn when you're turning some serious rpm's

not that i wouldnt mind having a twin turbo big block...... ooooh man
my favorite muscle car is actually a dodge viper.... the viper coupes are goergous, but being that i'm in school i'm just getting a trans am.... poor me

 

because the cam doesnt just sit on top of the valves....there has to be supports and bearing surfaces, plus all the chains and gears, which makes the front of the engine a mess, and any work on the valve train much more complicated