World's first FT86 Anti-Reversion,(A/R) Header

[Hyper4mance2k]

Originally Posted by SirBrass

It's times like this that make me wish I'd majored in mechanical or aerospace engineering instead of EE.

Thanks for the lesson (without the math... otherwise I'd need to go dig up my old college notes).

I majored in Political Science LOL. I only know this stuff becauseI have spent the vast majority of my free time over the last 20 years readingabout cars. I never sold a book back in college and I think my automotivelibrary trumps my collegiate library.

[SirBrass]

Originally Posted by Hyper4mance2k

I majored in Political Science LOL. I only know this stuff becauseI have spent the vast majority of my free time over the last 20 years readingabout cars. I never sold a book back in college and I think my automotivelibrary trumps my collegiate library.

I get distracted by many interests, and now with wife (who is a lawyer, so that makes it worse :P ), I have even less of a budget to fund them all .

Like "cascams, or get that RC heli & transmitter I really want..."

Recommended reading for us engineers who want to know more would be helpful, though .

[RobertPaulson]

Originally Posted by s2d4

If someone spends money building a high rise out of tissue paper, would you also thank them for spending money and showing you that it doesn't work?

not only would i thank Donald Trump, but i'd set that bitch on fire.

[KoolBRZ]

Originally Posted by Hyper4mance2k

Valve timing has aboslutely nothing to do with compression ratio. Small amounts of overlap exist for a reason; they increase cylender flow rates by allowing the intake ports to remain open longer. Thus, the incoming intake charge helps expell exhaust gasses.
Where do you learn these things? I suggest reading a book on basic automotive engineering, or taking a class before you go any further. I'm not trying to be a jerk, but seriously... Go take a class at your local CC, or UTI, or something, anything. You know the basic terminology, but your understanding is fundamentally flawed. I really am starting to think you might just be the biggest, most epic troll and you're just pranking everyone.

There are no books to read about dual AVCS tuning. It's too new. Our motors have electrically adjustable hydraulically actuated intake and exhaust cam adjusters. In the past there were lots of motors with an adjustable exhaust cam, but very few had intake and exhaust adjustable. If the intake cam is advanced and the exhaust cam is retarded there is so much valve overlap that the exhaust pushes out some of the intake charge coming in. This lowers the peak pressure in the cylinder, and it's as good as lowering the compression ratio. This overlap is used for better economy, not for more power. When more power is needed both intake and exhaust cams adjust for no overlap up to a certain point, then gradually move to give more exhaust overlap while leaving the intake cams at TDC. In the past a turbo car had to run low compression to keep from pinging itself to death, now people are turboing this car with 12.5:1 compression. Most of the rules in your old-timey petrol motor handbook no longer apply. You gotta start thinking outside the box if you want to understand the inner workings of this engine.

[Ultramaroon]

Originally Posted by KoolBRZ

I gotta start studying if I want to understand the inner workings of this engine.

fify

You think you have the basics but once again you've shown us just how much you're deluding yourself. SMH

[burdickjp]

Cam timing isn't a new phenomenon. The effects of timing are well known. It being dynamic is relatively new, but even that has been around for over a decade. Even so, it doesn't suddenly change the thermodynamics of the engine.

[Hyper4mance2k]

Originally Posted by KoolBRZ

There are no books to read about dual AVCS tuning. It's too new. Our motors have electrically adjustable hydraulically actuated intake and exhaust cam adjusters. In the past there were lots of motors with an adjustable exhaust cam, but very few had intake and exhaust adjustable. If the intake cam is advanced and the exhaust cam is retarded there is so much valve overlap that the exhaust pushes out some of the intake charge coming in. This lowers the peak pressure in the cylinder, and it's as good as lowering the compression ratio. This overlap is used for better economy, not for more power. When more power is needed both intake and exhaust cams adjust for no overlap up to a certain point, then gradually move to give more exhaust overlap while leaving the intake cams at TDC. In the past a turbo car had to run low compression to keep from pinging itself to death, now people are turboing this car with 12.5:1 compression. Most of the rules in your old-timey petrol motor handbook no longer apply. You gotta start thinking outside the box if you want to understand the inner workings of this engine.

Volumetric efficiency changes, not compression...
Once again you're wrong. Bosch first developed variable valve and cam timing for planes durrig... world war 2.

[chaoskaze]

^ That's interesting to know. Never thought a plane need something like that. Wonder wut Honda planes is like lol.

[wparsons]

Originally Posted by KoolBRZ

There are no books to read about dual AVCS tuning. It's too new. Our motors have electrically adjustable hydraulically actuated intake and exhaust cam adjusters. In the past there were lots of motors with an adjustable exhaust cam, but very few had intake and exhaust adjustable. If the intake cam is advanced and the exhaust cam is retarded there is so much valve overlap that the exhaust pushes out some of the intake charge coming in. This lowers the peak pressure in the cylinder, and it's as good as lowering the compression ratio. This overlap is used for better economy, not for more power. When more power is needed both intake and exhaust cams adjust for no overlap up to a certain point, then gradually move to give more exhaust overlap while leaving the intake cams at TDC. In the past a turbo car had to run low compression to keep from pinging itself to death, now people are turboing this car with 12.5:1 compression. Most of the rules in your old-timey petrol motor handbook no longer apply. You gotta start thinking outside the box if you want to understand the inner workings of this engine.

So much mis-information...

First, dual variable valve timing has been around for well over a decade.

Second, without knowing the valve timing in relation to BDC, knowing how much overlap you have doesn't tell the full story. If you get overlap by advancing the valve timing you'll get more scavenging (assuming a good header), but because of the timing you won't be losing compression.

How exactly does the exhaust push the intake charge out?

You're more likely to lose intake charge (or compression) by keeping either the intake or exhaust open as the piston passes too far past BDC than by having good overlap.

Some overlap is good because scavenging (high exhaust velocity creating a vacuum in the cylinder) will pull more intake charge into the cylinder. On a turbo or supercharged engine you don't need (or want) as much overlap because you're already forcing the intake charge in under pressure and will just blow it right out the exhaust. If anything, more overlap gives worse economy and emissions because you'll lose some intake charge out the exhaust.

You might want to take a look at what the intake and exhaust cam timing actually looks like in a datalog compared to throttle and rpm...

http://www.datazap.me/u/wparsons/jul...6&zoom=193-430

http://www.datazap.me/u/wparsons/jul...7-680&mark=611

[Turdinator]

Originally Posted by Hyper4mance2k

Volumetric efficiency changes, not compression...

Cam timing does have an effect on the dynamic compression ratio. It is why on NA engines when you go to larger duration cams higher static compression ratio is recommended.

This is the first link that came up in google and will give you an idea about it.
http://cochise.uia.net/pkelley2/DynamicCR.html

I don't agree with a lot of what OP says but don't automatically shoot him down because of who he is and potentially add to the misinformation. I think @Dimman was on the money.

[burdickjp]

Originally Posted by Turdinator

Cam timing does have an effect on the dynamic compression ratio. It is why on NA engines when you go to larger duration cams higher static compression ratio is recommended.

This is the first link that came up in google and will give you an idea about it.
http://cochise.uia.net/pkelley2/DynamicCR.html

I don't agree with a lot of what OP says but don't automatically shoot him down because of who he is and potentially add to the misinformation. I think @Dimman was on the money.

Dynamic compression ratio is a misnomer. There's nothing dynamic about it. What they're looking at is trapped volume and the ratio between trapped volume and compressed volume. Trapped volume compression ratio is probably the more correct term.

[Turdinator]

Originally Posted by bur****jp

Dynamic compression ratio is a misnomer. There's nothing dynamic about it. What they're looking at is trapped volume and the ratio between trapped volume and compressed volume. Trapped volume compression ratio is probably the more correct term.

Perhaps, but is an accepted term and there is information on it out there.

EDIT: The forum thinks your name needs to be censored.

[burdickjp]

Originally Posted by Turdinator

Perhaps, but is an accepted term and there is information on it out there.

EDIT: The forum thinks your name needs to be censored.

When you get into real research from smart people who get their doctorates in things like this, such as Blair, Heywood, or Taylor, you won't find it.

Most people using the term dynamic compression ratio do so in ignorance of what's important and why. Sometimes they get it right, but usually in an indirect way.

[Poodles]

Originally Posted by bur****jp

When you get into real research from smart people who get their doctorates in things like this, such as Blair, Heywood, or Taylor, you won't find it.

Most people using the term dynamic compression ratio do so in ignorance of what's important and why. Sometimes they get it right, but usually in an indirect way.

Much like "backpressure."