anybody know where the nhra rules are published online?
i have a feeling most classes are in fact restricted to pushrod v8's

383backinblack, any technical reasons ohv pushrods are better? other than that they are 'bigger and badder'
from an engineering standpoint, i would beleive a W16 engine of the same displacement, dohc 4 valves/cyl, burning nitrometh would make a lot more power
but then again there are none so i cant say it for a fact

i think leman's races are somewhat open on engine designs... they are mostly but not entirely dohc engines i beleive, mazda's rotary mopped them all up one year but then yes then they did ban engines with no pistons

 

Actually, that response wasn't to be taken so literally. Yes, the engines are displaced in cid not cc, my mistake. Not to overshadow the point that was made I hope.
Torque per liter? Never seen that as a measure of efficiency. What about bmep?? Then again, one must define efficiency.

-Mindgame

 

well torque per liter is a good measure of how much fuel and air you can jam into a cylinder and get it to the flywheel

in a sense making more hp just means you're spinning the engine faster

obviously i'd be more impressed with an engine making 500hp at 6000rpm than 500hp at 20,000rpm

and also not with an engines 500hp at 3000rpm that is 5 times the size of the engine that made it at 6000rpm



.....that wasnt a good explanation, but torque per liter is a good measure (not all encompassing) measure of a good engine

i think it also shows small dohc engines, in this sense, are better
....too bad nobody makes BIG BIG BIG dohc engines we can get without buying a ferari

 

I am not, in the least a Honda man, but there are 4 cylinder Honda OHC dragsters that are turboed making over 2,000 HP (have no idea what the hottest is, I don't follow them). Obviously these are custom blocks of course with very thick cylinder walls and plenty of webbing etc.

One advantage of OHC is the cam profile, maybe a small advantage but one, very aggressive opening ramp (almost flat) and about a normal closing ramp. Another is less valvetrain weight, less fricton, there are plusses and minuses to both sides, but SOHC is more efficient and again allows for small side benefits which are great in high RPM racing engines.

Some people still love Flathead Fords, but those certainly are not horsepower demons by being an excellent design, while you can build anything to make power some things will get more out of less and thats just the way it is.

 

If were talking street car, and wanting something easy to work with when lowering compression or changing cam profile, then pushrod is easier to work with. Valvetrain geometry gets screwy when you play with compression or cam base circle/profiles with OHC stuff. I'm not a fan of chain tensioners either, so again its a give and take, some ways I like one some another.

 

sure, if your looking for power vs. complexity an OHV motor beats the ever lovin sh*t out of a DOHC motor. and with proper setup will almost always make as much if not more power. Granted the higher racing classes are restricted to run OHV motors (like nascar) but look at the cars that do have OHC motors. they make about the same power, and they are far more complicated.

the thing is, if you could make a top fuel motor work with DOHC and make more power, someone would have already done it on an exhibition car.

 

so what are those reasons its technically superior again backinblack?

i'm with dr mudge that i'm not a honda man, but i'm not an idiot, i have an engineering streak in me

the honda guys are right (in some respects)
YES their engines make more torque and power per liter
YES they are technically superior
but no their cars are not faster even if it has a big spoiler.... and the above mentioned isnt worth **** right after you lose a race and cry about it

and the cars we drive ARE faster (but sorry back in black its not because they are 100% better in every arena no matter what even if god says otherwise)

when i look far a fast car though, i get myself one thats got some displacement
and when i might wanna hotrod that car, i make sure its a chevy small block
i could get a toyota 4.7L truck engine, but couldnt do **** to it once i got it and it'd probably be stuck under 400hp NA unless i spent 30 grand on it

 

Well, we as americans have been working the pushrod engines for some time now.... we know how to make real power with them and it just keeps on getting better with technology. The fact remains that even high level race only engines of the pushrod variety have their limits. That limit is not in the bottom end... hell a top notch motor hardly ever breaks a bottom end part. The real failures come in the valvetrain and from there we always see a limitation on what we can do. To get more power per cubic inch, as one of out prominent memnbers stated here a while back, you need rpm. The more revs you can turn, the more power you can make. The limit again is in the valvetrain... larger valves are heavier and even when they're larger (valve area in relation to piston area) they're still not as good as having more smaller/lighter valves and greater valve-to-piston-area. So you get the best of both worlds the multi-valve way. More valve-to-piston-area and better valvetrain stability = more rpm and higher output.
Then again, we could all go to Top Fuel tech and run around with dry sump oiling systems, aluminum connecting rods, 2 super-thin-ring pistons and the like. Where is the real world in that scenario?

-Mindgame

 

The Bugatti Veyron uses the W-16 cylinder configuration (8._ liters in disp. and about the size of a big block V8). 4 banks of 4 cylinders and 4 turbochargers (one for each bank). Also 4 valves per cylinder. AND it has all-wheel drive with a 6 or 7 speed gearbox. 1006hp and 9__ft.lbs from the factory and 8 sec timeslips. But they cost $750K and only 50 a year are being built. Volkswagon, of all things, invented and produced the engine.

Go steal one, put nitro in it, turn up the boost and tell us what it runs.

Either the pushrod or the modular is all I'll use. I won't trust a solenoid with my engine. No sir-ree.

 

I wouldn't say all that much more complex, just more PITA factor during setup.

 

the point is this....the engines could make alot of power...but they dont....

im sick of people crying about "horsepower per liter" some [EDIT: deleted by moderator ] kid was saying how his car had 100 HP per litre....i was like thats great dude, but your engine is 1.6 litres. in my book that sucks....and i come from an engineering background Im pretty well versed in the details of VVT and DOHC technology. there are 2 problems here..

first they dont make the damn engines big enough....make a 500ci V8 with VVT i bet it makes some power.

secondly, being "technologically superior" doesnt always mean something is better.....in the case of engines alot of times all it means is a more complex machine with far far more parts and chance for failure.

 

well there ya go.... we agree a 500ci v8 dohc engine would make more power (actually v12 would be better but i dont think ya wanna hear that), thats what we were saying all along

my beef was earlier you said look at racing for the best technology, and the best is pushrods

now i'm not sure but i think an sohc engine has less parts than a single cam engine (plus one cam and chain, minus 16 pushrods and lifters and rockers)


by the way, why doesnt anybody make a no-holds barred exhibition dragster, nitrometh burning..... tires as wide as ya like, as much displacement as ya like, as much boost as ya like.... it would be madness
probly would be a good idea to remove the driver also all they do on the top fuelers is keep it in the lane and keep their foot on the gas

wonder how fast it would go....wonder what the limit on displacement making it faster would be

 

if top fuel could use the pro-mod style engines running on 100% nitro im pretty sure they could get into the 3's pretty deep. those engines are about 800ci on the average.

there are more parts on a DOHC or an SOHC motor, because of hardware required to retain the camshaft on top of the head. but like i said before, just because something is more complex doesnt make it better.

 

Actually, NHRA prohibits Top Fuel dragsters from running over 500 cubic inches. They can get away with this small displacement b/c there are no coolant passages in the blocks; they're one solid hunk of iron. 6.0:1 CR and 50+ psi of boost help as well.

I'm an engineering student as well and yea, all these new technologies are cool and effecient but are impractical at some point. The OHV is proven technology and its simpleness is what makes it so effective. In 10 years or so these new technologies may become as practical and reliable as the OHV. Then the OHV will be phased out. Ford's new modular platform has unreal potential that in time will be unleashed. Let's face it, 4 valves will out flow 2 valves in any given bore b/c of the greater valve curtain area. And these new cam manipulating abilities will give a much more broad and efficient powerband. You know it will happen sooner or later.

 

Some thoughts:

TF blocks are aluminum.

In a 4.5 second pass the engine turns over about 800 revs, or 400 firings in each cylinder. By halfway down the strip, the spark plugs are toast, and the glowing (1400F) Inconel exhaust valve is enough to keep the fire lit.

Most of the power comes from the fuel; 90%(max. allowed by NHRA) nitromethane (CH3NO2). When burned nitro releases oxygen. There is another, non-combustion nitromethane reaction in a TF engine which is responsible for maybe 25% of the power. Ask your chem profs about this.

So much fuel is injected (1.5 gal per second) the engine is on the verge of hydro lock. Combustion of nitro is so slow ignition timing is 50-60 deg. BTC and burning continues all the way into the exhaust stroke.

GM & Ford went in different directions for rear-drive V-8's a few years ago, and invested billions in the design, development and tooling to produce their newest V8s. Most of them are used in trucks, of course. The Mustang, Corvette (and Camaro/Firebird) usage is a vey small % of the market. GM's GenIII has fewer parts than the modular Ford, so production costs, and long-term ownership costs are probably lower. Performance seems to be right up there.

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.

Hey, add a second, variable phase cam in the block, and the pushrod GenIII gets harder to beat with OHC and more valves.
I predict a long future for the OHV V8.

My $.02