I've been reading about Variable Valve Timing and it seems like it does have it's merits. You can get a very efficient amount of power out of a very small amount of displacement. Hondas 240HP VTEC for example is a very solid engine...now as far as I understand VVT simply sets the valve timing to be more efficient over the entire RPM range, so instead of having low, mid, or high power bands you get a high level of efficiency between all power levels allowing a lower displacement but someone comparative amounts of power compared to conventional OHV designs. (I'm a n00b here so I may confuse things)

My question is, if you have a 240HP VVT engine (Be it mechanical where it has different settings for high/low or a computer controlled which gives maximum efficiency at all RPMS) against a 240 OHV engine with it's power band in low-mid RPMs, assuming that both vehicles weight the same, will the VTEC motor of 240 HP run the 1/4 as fast as an OHV 240HP motor? Like....as I understand it the VVT maximizes both high/low, allowing for a high HP rating, which controls max speed, but does it provide the same kind of torque numbers you'd want when running the 1/4?

In short, will the 1/4 still be ruled by low reving big blocks 350+ci motors, or will technology some day take over? Like alot of foreign cars that rev to 9k and have 500HP, vs domestic big blocks that rev to 6k, but have the same 500HP, is displacement going to remain the main factor in drag 1/4 ? Is it unfeasible to have a rev range that high when going that short a distance?

While I'm at it, I know DOHC is simply 2 cams, with more valves per cyclinder for better breathing for more power, why does ford have a SOHC? Why have SOHC? Is it better then conventional OHV design? What are the gains?

 

the 240hp v-tec motor you are referring too makes 150ft-lbs at 7500rpm
a comparable 305 truck engine making 240hp will probably make 300ft-lbs at 3000rpm or so

so no... those to engines in the same car would certainly not have the same 1/4 time, not by a long shot

that said... identicle large displacement engines, one with vvt and one pushrod actuated, the vvt will rhomp on the pushrod

also.... vvt are always dohc (intake cam and exhuast cam) and will have 4 valves/cylinder
it will have significantly lighter valvetrain and easily spin much higher (more power) and also 4 valves/cyl is of course much much better than 2

ford's sohc engines are 2 valves per cylinder, so one cam is sufficient (but there is no possibility of vvt)
this is because it's cheaper....
though in a lot of cases its actually cheaper to make a dohc engine because sohc cams are more complicated grinds

sohc is better than pushrods and and dohc is better than sohc (i suppose a sohc valvetrain driving 4 valves per cylinder could possibly be lighter, but would not allow for vvt)

 

Is pushrod cheaper/easier to produce/maintain? If so, is that why OHV design is still around? Because VVT is obviously the choice of the future.

So it is true then, no matter what you do, you truely can't replace displacement?

 

pushrod engines are most definitely easier and cheaper.... as for more reliable..... tough question, i'd lean toward no, but they're far from unreliable

i suppose some sort of electric supercharger that made constant boost at any rpm would be about the only replacement for displacement....


the other thing about those 2.0 liter s2000 engines, the v-tec kicks in at 6k rpm i beleive, so until 6k rpm you're drivng a honda civic....

still... it is quite impressive being a production engine that can run 8000 rpm all day without breaking a sweat

another cool thing i'll let somebody chime in about is solenoid actuated valves...
the thing about vvt in today's high tech engines is it isnt TRULY variable, it advances and retards the cam timings, the duration remains the same
increasing the cam duration at higher rpm's will REALLY make a big fat torque curve
i beleive gm's solenoid actuated engine will debut in the corvette in 5 or 6 years?

 

VVT and VTEC: As Jimmy said, VVT changes the phasing of the intake and exhaust cams. If just the exhaust is varied, like in the GM 4200 inline six, you have variable lobe separation angle (LSA) which can be used to help emissions, power and economy both at part throttle and full throttle. If you vary both intake and exhaust, you can even influence power, etc. more.

VTEC uses two different sets of lobes on the intake cam, I believe. Yes, the change from mild lobes to wild lobes occurs in the upper revs.

The Honda S2000 with it's 240 hp from 2L isn't all that fast even at it under 2800 lb.weight. You have to row it around with the gear shift.

The S2000 engine gets 240 hp @ 8300 or 152 ft-lb at power peak.
That's impressive torque/liter at power peak. Of course, max torque is 153 ft-lb @ 7500. (It looks like a flat top end torque curve). Even with more gear due to the high rpm (compared to the LS1), that's only equivalent to 250 ft-lb or so at torque peak, and below that it sucks.

As for VVT with pushrods, it's quite possible, and IMO, maybe on the near horizon. Look closely at the LS1. There's room for a second cam directly above the existing one. Make the lower cam non-variable intake, drive the exhaust cam from the intake and use the variable mechanism from the 4200 and you have variable exhaust at a reasonable price. That could make our LS1's even better than they are now. My guess is maybe 8-10% more grunt with same or better emissions and economy at cruise.

I'd bet on this LONG before solenoid actuated valves.

My $.02

 

Honda's VTEC sports two sets of intake and exhaust lobes, effectively varying duration, lift, timing, and LSA. Also, VTEC motors feature dual stage intake manifolds: long runners for down low; short runners for up top.

That said, Honda's VTEC is more the exception that the rule. Most other variable valve timing set-ups only change the timing, typically through varying the length of the timing chain. Very simple mechanically for the dividends in power, torque, idle, and emissions improvement.

 

Ya know - the LT5 (ZR1) motor used a very primative VVT setup.
405HP in 1995 - that was pretty impressive at the time. It took an extra 100+cid from a Viper to go faster

 

the LT5 did not have a variable valve timing setup...it was a regular DOHC setup....4 cams, 2 on each side. but nonetheless it was a very complex motor.

to quote car crafts why imports suck article from last year on VVT,

Us: old tech, OHV pushrod v8 making 450 ft/lbs
them: state of the art, VVT electronically controlled engine making 150ft/lbs

'nuff said

 

Heres some more info on V-Tec and VVTI for you guys
http://autozine.kyul.net/technical_s...gine/vvt_1.htm

About the motors, well you got to remember, if they are geared right, they can run the same speed, but in real life no. The smaller motor would need many more gears to keep up with the bigger motor with less gear. Its all basicly about power under the curve multiplied by gearing.

 

No - the ZR1 had a low RPM and high RPM cam; thats why the powerband is so flat

 

no it didnt...not at all. i think you need to look into the lt5 a little more carefully. there was absolutely no VVT tech on that motor. the torque curve is that flat because its a DOHC motor with 4 valves per cylinder.

that technology didn't exist at the time, and if you read the specs on the the LT5 you will find that its just a regular DOHC setup....except its on a v8 and it was in the early 90's so it was a bit more impressive. there were not seperate low and high RPM cams. each cylinder bank had 1 intake valve camshaft, and one exhaust valve cam shaft. so there were total of 32 valves, and 4 cam shafts.

if you want to take a look for yourself...all the lt5 specs are available at this link.

http://www.zr1.net/ZR1_specs.html

 

Is it not possible to have a an LT1 cam perform like a Vtec cam? Dont remember if it was DocMudge or Skardom that told me that long time ago someone made a cam that went from stock driving to like a small shot of Nitrous in the upper rpms. just like Vtec. I would Love teh specs on that cam.

 

Maybe it was the infamous "rubber cam lobe". The faster the engine turned the more the rubber stretched and the more lift and duration increased.

Durability was a bit of a problem, however.

 

hehe

 

LoL, ahh yes, the rubber cam...

VVT is not the same as VTEC, not at all, VVT would be awesome to have but... these are American engines were talking about, wait 10 or 20 years after it becomes commonplace in other cars (not just the Porch), then maybe we'll get it.

There are other evolutions inbetween this fancy pants stuff, and the older OHV stuff, don't forget OHC when they first came out, my 73 has an OHC setup and people are making 300 streetable HP out of 2.8-3.1 liter setups, in 1970s engines... For someone willing to rev it out a bit more, I would not doubt more than 350 HP, still streetable.

VTEC seems neat, but VVT is definately more advanced, and would be awesome to have and be able to play with it, imagine an almost optimal 'cam' for every RPM range through the band.

Every once in awhile someone talks about the Coate's 'spherical rotary valve' engines, if the stuff honestly has no sealing problems, it seems like that would be fun to play with, although the wide top end profile may make it a pain to fit in a car that isn't DOHC stock (wide top end).

Then we have electronic valve actuation, yummy.