Jobro

iTrader: (2)

That is wikipedia.

Slides

It is how the variation in timing is achieved which can allow a different duration with a cammed setup, Jobro isn't a fool.

Some systems just use the same lobes & vary the cam angle vs drive gear/wheel (and thus crank timing).

The VTEC uses a completely different lobe, this allows both different duration & lift in the top end, much different effect and would be a better indication of whether or not combining early opening with the later close is of much benefit or not.

Piston motors can have pneumatic in addition to the desmodronic (or pick your brands moniker) poppet valves or rotary valves. Rotary valves are heaps better, I had an SAE magazine article on it (from the guys that were supplying Williams? in F1 before the ********* banned it), they are looking to get into the production or performance market, they gave a honda CR 450 more torque everywhere from 3000 - 12500rpm (ie beyond poppet valve rev limit) & the better tumble/swirl they provide allows for less ignition timing for peak torque & use of lower octane fuels or higher compression ratio. The head was also smaller & lighter.

Also, considering average EMP and Intake pressure doesn't really give you a lot when considering overlap conditions, you really need dynamic pressure readings, people close the exhaust late & intake early not just for port area but because you get low pressure on the exhaust side at he end of the stroke which does help suck intake through.

rotoryota

I guess I'm mostly speaking of the 3-6k range. I could care less about 0-3k. I could launch at 7k on my streetport consistently....and launching 8k with the bridge is a coin toss. At this point I'm thinking that leaning out the low/mid range should help my problem. I'm also going to freshen the motor since it's the off season.

rotoryota

I think that pulling timing only works well when used on the 2step. Anti-lag is used to spool the big turbos. It's a combo of retarded timing and and extra fuel.

t-von

iTrader: (8)

Ok that's good to know because some of us don't look at the 3-6k range as low end. Many people can get confused and give the wrong advice if we don't know what actual range your concerned with.

peejay

I agree to that.

When I did my half bridge, meaning I just took my street port and cut the eyebrows into the secondaries (small eyebrows: 30mm high starting about 10-12mm above the tension bolt hole, 5mm thick bridges, no rotor housing cutting), I found that I had to take a lot of fuel away from the 1200rpm and 800rpm cells. The 2000rpm to 5500rpm cells required a lot MORE fuel, to maintain the same AFR as before.

As far as variable valve timing is concerned... the OEMs have a lot of concerns different than us enthusiasts. They spread the lobe centers apart at idle to minimize overlap for a smooth idle, and now that I think about it they may be wanting to open the exhausts earlier in order to build/keep heat in the conveter. Then, at low RPM loadings, they close it up to get the intake closing earlier (more torque at those low revs) and get some overlap for beneficial exhaust reversion, so they can get away without an EGR valve. Then at higher RPM they close the intakes later for more high-RPM torque.

Driving a dual variable timing vehicle with a scantool plugged in is a real eye-opener. They really shift those cams around a LOT. GM seems to even incorporate it into their idle strategy. I've greatly simplified the scenarios they are concerned about, of course, and the more sophisticated systems use a 3D mapping for cam timing.

There's a LOT of piston engines out there without cams! (Ever hold a gas-powered weedwhacker or chainsaw?)

Jobro

iTrader: (2)

I'm in the process of watching the 87 and 88 and 89 F1 GP atm (86 is done). I plan to watch 79 through to 2010 over the next year or so. Its pretty clear Honda's engines were more efficient than anyone elses during the end of turbo era whilst still producing competitive horsepower. It is suggested BMW had the highest peak numbers and general highest straight line trap speeds for a given race. Ferrari were hopeless, they could make the numbers but without the economy and blew SO MANY engines pushing the lean limit trying to get the same mileage of the Honda.

PS Senna was not god, just REALLY good, with a good race attitude and during the times he dominated the best equipment by a long way