04gtod

iTrader: (3)

I keep reading that exhaust closing events affect driveability more than any other event but they don't say how or what the ideal closing point would be.
Any experts that really know?

Formulated

iTrader: (16)

It might only be an issue with regards to valve overlap. The later the closing, the larger the overlap, generally. Usually, intake valve closing is most important when chosing and installing a cam, as it will determine how high the engine has to rev to make power.

Old SStroker

I'm sure that there are some who really know. Do I think they will post in this thread? Not hardly, as the Duke would say.

I'M NOT a cam expert, but I suggest there are many things that affect driveablility as well as power and torque curve shapes. Unfortunately engines are as least as complex as women. I have yet to figure out which one event is most important to either.

04gtod

iTrader: (3)

Maybe I should have been more clear. What valve events combined with a cam with a good amount of overlap make it easier to tune and more street friendly?

Old SStroker

Maybe I should have been more clear. All of them. Go directly to your cam guy/engine designer with your desires for your engine/vehicle combination.

Perhaps PZ and PG will chime in.

Tom@SpeedInc

iTrader: (5)

The exhaust closing point will have effect on overlap. So will intake valve opening point.

I don't think a camshaft has one key component that will make or break the setup

generally I like to see IV and EV have some .050" duration during overlap, FWIW. This will vary from a cam only setup to built motor.

danf1000

iTrader: (2)

Valve events are not altogether an unknown. At risk of drawing in the post police, here's my take, at the lowest level possible.

Intake valve closing affects efficiency of compression stroke and plays on the inertial flow effect of the incoming air to time the ability of the air to cram into the cylinder, even after the intake stroke is over. More velocity from more RPM results in a later IVC to take advantage of this, generally at a disadvantage to low RPM compression stroke efficiency.

Exhaust valve opening gives a head start to release of the high pressure spent gasses even before the power stroke is closed. Earlier is indicative of high RPM as the entire time to release these gasses diminsihes with RPM. Earlier release, however, negates an otherwise power-producing segment of power stroke that would be used at lower RPMs. Good for boosted though to balance a higher volume of pumped in air during intake valve opening.

Overlap as a combination of intake valve opening before exhaust valve closing assists a scavenging effect of the inertia of the exhaust gasses, creating a vaccum wave that assists kickstarting initial intake flow. Detrimental to emissions and fuel economy if taken too far as raw intake mixture is sucked directly out of engine if the duration is too long.

Overlap is almost free here (other than fuel) as it is detrimental to idle quality, but actually enhances LS1 low-RPM torque. IVC, IMO, is the hierarchically the first factor.

However, the direct application of experience WRT similar combinations will give desired result to your combination. Get advice or spend some time finding and comparing similar combinations. Let others get scared off from playing around with this.

Own words, short, simple. Flame on.