Are Exh pushrods more stressed even in NA applications?

[Warp Speed]

Why is the exhaust valve lifted less than the intake?

In inches or area?
In what application does this change and why?

Not sure, that's why I'm asking?!?

[Stan Weiss]

Why is the exhaust valve lifted less than the intake?

Because, in general, low lift flow is more important on the exhaust side. In general, high lift flow is more important on the intake side. Yes, a generalization. So it is not so much that you are trying to get lower lift on the exhaust. It is that you are trying to get higher lift on the intake. Ducking!

paulie

Really?!?
Low lift flow is important to the exhaust?
How much does an exhaust flow at initial opening?

What is my pressure differential during my low lift?

What cylinder pressure should I want to have ABDC?

Stan

[GARY C]

Why is the exhaust valve lifted less than the intake?

In inches or area?
In what application does this change and why?

Not sure, that's why I'm asking?!?

My understanding is pressure differentials across the valves and why this may change with some boosted or nitrous applications but I am sure you already knew that.

[gruntguru]

Why is the exhaust valve lifted less than the intake?

Well the simplest answer is - because the exhaust valve is smaller.

Curtain area = valve head area when L=D/4.

[plovett]

Because, in general, low lift flow is more important on the exhaust side. In general, high lift flow is more important on the intake side. Yes, a generalization. So it is not so much that you are trying to get lower lift on the exhaust. It is that you are trying to get higher lift on the intake. Ducking!

paulie

Really?!?
Low lift flow is important to the exhaust?
How much does an exhaust flow at initial opening?

What is my pressure differential during my low lift?

What cylinder pressure should I want to have ABDC?

Stan

Yes. I think the pressure differential is high when the exhaust valve cracks open and relatively low when the intake valve cracks open.

Are you talking ABDC after the power stroke? In a perfect world all the energy of combustion would have went into the piston and rotating assembly, but I don't think it works that way in practice. Is that what you are getting at?

[plovett]

I think you would have a net gain in power if you could use all the combustion pressure on the power stroke and have a zero pressure differential on the start of the exhaust stroke, even though you would not be able to evacuate the exhaust gasses as well, as only the piston coming up would be doing the work?

You would certainly want different cam timing if you could that. LOL!

[hoffman900]

Dr. Andrew Randolph of ECR in his NASCAR Engines 101 lecture said best power is made on the exhaust side when the expansion loss is balance to the pumping loss. In the example he gave, it’s about 20hp for each...

It’s interesting reading Honda papers, on even their motorsports stuff, in that they refer to inlet flow as pumping loss as opposed to mass flow.

Maybe people need to rewire how they think of things.

[BradH]

Why is the exhaust valve lifted less than the intake?

I'm curious... did you ask this question to the poster who made this statement because:
(a) you didn't agree with him and were looking to debate it, or...
(b) because it's true and you wanted to see if he understood why?

[Warp Speed]

Why is the exhaust valve lifted less than the intake?

I'm curious... did you ask this question to the poster who made this statement because:
(a) you didn't agree with him and were looking to debate it, or...
(b) because it's true and you wanted to see if he understood why?

It seems to be the accepted trend lately by most, but I have no idea why?

[3V Performance]

Why is the exhaust valve lifted less than the intake?

I'm curious... did you ask this question to the poster who made this statement because:
(a) you didn't agree with him and were looking to debate it, or...
(b) because it's true and you wanted to see if he understood why?

It seems to be the accepted trend lately by most, but I have no idea why?

I believe its because most are still chasing flow bench numbers on the exh. Exh ports are HUGE today. Less lift is helping control the rapid blow down.

[CharlieB53]

Would it be advantageous to grind ex valve/seat to maximize low lift flow?

Intake angles for high lift flow?

Is this already a common practice?

[ClassAct]

I'm curious... did you ask this question to the poster who made this statement because:
(a) you didn't agree with him and were looking to debate it, or...
(b) because it's true and you wanted to see if he understood why?

It seems to be the accepted trend lately by most, but I have no idea why?

I believe its because most are still chasing flow bench numbers on the exh. Exh ports are HUGE today. Less lift is helping control the rapid blow down.

I've been squeezing exhaust valve and port sizes down for close to 10 years now. I make the port as quiet as I can, and whatever it flows, it flows.

[ClassAct]

Would it be advantageous to grind ex valve/seat to maximize low lift flow?

Intake angles for high lift flow?

Is this already a common practice?

I wouldn't grind any valve job to maximize low lift flow. This has been thrashed out here many times.

[GARY C]

Would it be advantageous to grind ex valve/seat to maximize low lift flow?

Intake angles for high lift flow?

Is this already a common practice?

I have often wondered if you combined that with a much later opening and maximize the lift for evacuation what would happen? I am sure it has been tried but I don't see anyone doing it or if they are they ain't talking about it.

[paulzig]

I believe its because most are still chasing flow bench numbers on the exh. Exh ports are HUGE today. Less lift is helping control the rapid blow down.

Like the analogy of the shook up beer can, open it quickly all the way vs just slightly cracking it slowly...