88crxSi

its a chain effect.. if you have the exhaust open a lil while the intake opens, as stated above, you might loose a lil boost, but, the exhaust being PUSHED out by the intake spins the turbo faster...

Spenser

thats probly why since my cam gear gear skipped a tooth my car has been spooling up way faster

Engloid

I see some really confused people making statements that simply can't be true in every case.

The best post was (I won't bother quoting) the one about how every engine will be different. No, I'm not being sacrastic, as this is true.

Overlap does NOT, in itself, cause lower pressure. Think about it...if you have a turbo that can fill your cylinders with the set psi of boost way before the intake valve shuts, then why not leave the exhaust open and let the turbo run free....then shut the exhaust valve and get the cylinder filled just before the intake valve shuts.

In other words, if you can pump the approriate MASS of air into the cylinder within the last 10 degrees of crank rotation, why try and get it in there on the first 10?

I don't think you'll be getting much exhaust reversion with a log manifold. Simple physics says that air moves from high pressure areas to low pressure areas. When going from a small port to a runner that's significantly lower, pressure drops, as does velocity.

The implication is that these log style runners, although cheap and easy to build, they are very large. This slows velocity. Having smaller runners would increase spooling, and likely never limit you on the top end. Take a look at some of the Supra headers....many use runners that are smaller than most guys use on honda engines.

Honda16hb

because if you're just letting it blow through you could over spool your turbo

but the fact is a turbo isn't exactly a free flowing device, it blocks up the exhaust and uses exhaust energy to spin, it's not just a hollow device that lets exhaust pass as it pleases.

J-SMITH69

Engloid

Isn't that what your wastegate is for? Isn't the purpose of a blow off valve to keep your turbo spooling?
===========================
Yes, and by NOT trying to cram boost in during the entire intake duration, and having overlap, you are allowing air to go through the engine and continue to spool the turbo with the intake valve open.

So if we say that your turbo can put air into the cylinder in 20% of the time that the valve is open, you'd rather cram it in during the first 20% of the time and then have your turbo fighting to keep that pressure....thus slowing the turbo? I think I'd rather have it freespinning and then jam the air in during the last 20% of the time the intake valve is open. Think about it a bit...this is likely what this guy achieved by putting in more overlap.

warric_k

I'd sooner listen to engloid than stop drinking.

if that makes sense.

Reddy

Kyle put the crack pipe down

warric_k

holy crap kyle, you said that?

the duration that the exhaust valves would be open at the same time as the intake will most definitely not over spool a turbo... totally different from running with a charge pipe disconnected.

redemption will follow only with you ridiculing someone, me not excluded.

Engloid

Sometimes you gotta wonder if people really have a grasp on the concept behind a 4 stroke engine to begin with.