Part Two: The Intake Port

[Mastermind]

Ok so we've covered the exhaust port in exhaustive detail (pun intended).

http://opeforum.com/threads/part-one-the-exhaust-port.7279/

Now let's look at the intake port.

Let's talk about angles, shapes, texture, finish, opening and closing points.

How about intake tract length?

Is there a point that too much intake is bad?

Can too short of a duration hurt performance?

Should carb size be considered when deciding duration?

What about primary or case compression?

 

[kkemp]

I'm looking forward to this one . The intake confuses me more than the exhaust for some reason.

 

[XP_Slinger]

This is where I've got some ground to make up. The dynamics of the intake aren't nearly as clear in my head. My current thought is in keeping velocity up for 2 reasons. First, proper atomization of fuel through the carb. Second, to fill the case quickly and efficiently. The other priority to me is closing the intake soon enough to build sufficient case pressure for movement up through the transfers. Now I'm gonna eat popcorn..lol

 

[merc_man]

Part two already. Lol

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[Mastermind]

This is where I've got some ground to make up. The dynamics of the intake aren't nearly as clear in my head. My current thought is in keeping velocity up for 2 reasons. First, proper atomization of fuel through the carb. Second, to fill the case quickly and efficiently. The other priority to me is closing the intake soon enough to build sufficient case pressure for movement up through the transfers. Now I'm gonna eat popcorn..lol

We agree on many things here.....

I'm gonna kick back and let some folks get in here. Like yesterday's topic, this will really get going when everyone gets off of work.

 

[Stump Shot]

I don't feel like I graduated part one yet. Lol

 

[Mastermind]

I don't feel like I graduated part one yet. Lol

We can still post in that thread.......just don't wanna let this series go stale.

 

[merc_man]

I don't feel like I graduated part one yet. Lol

I know its a lot of info in 24 hours.

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[merc_man]

We agree on many things here.....

I'm gonna kick back and let some folks get in here. Like yesterday's topic, this will really get going when everyone gets off of work.

Thats when ill be just starting work. Gonna miss it it all then be up til 1 AM like last night trying to catxh up.

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[Stump Shot]

Question; (yes, I know you all hate me by now Lol) If after lowering a cylinder all it can be lowered and the skirt of the piston still is hanging down into the intake tract with the piston at TDC, can the bottom of the skirt be marked and material removed if there is plenty of support for the piston? Any thing else to look for, or reason not to do this?

 

[Mastermind]

I like a pretty short intake duration. I just build working saws, so I think about fuel economy. I worry that excessive spitback might drown the air filter. I feel like a short intake makes a better idle and off idle transition.

There are other folks that like a longer intake duration........sorta like @mdavlee likes a higher exhaust. He can make that work.

I know @blsnelling uses a longer intake duration, and Brad has built some damn strong running saws with a longer intake duration. I can't seem to make that work for me. That doesn't mean that either way is right or wrong.......just a different approach.

I've come to the conclusion that the port timing numbers actually make up only a small part of the way an engine really performs. It's the whole package that makes different ideas and build philosophies work. So, we can cover all this stuff in detail, but you have to try things your own way in the end to figure out what really works for you. Hopefully these threads will educate you enough that you can at least have an idea of where to begin.

 

[Mastermind]

Question; (yes, I know you all hate me by now Lol) If after lowering a cylinder all it can be lowered and the skirt of the piston still is hanging down into the intake tract with the piston at TDC, can the bottom of the skirt be marked and material removed if there is plenty of support for the piston? Any thing else to look for, or reason not to do this?

That will add to intake duration.

 

[Stump Shot]

That will add to intake duration.

Which could be good as long as it shuts off in time?

 

[Mastermind]

Which could be good as long as it shuts off in time?

Could be good......or bad. lol

 

[Stump Shot]

Could be good......or bad. lol

Here we go again dot dot dot

 

[Fruecrue]

Would shorter intake duration give better case compression?
Does a saw with tight transfers benefit from more case compression?

 

[Mastermind]

Would shorter intake duration give better case compression?

Yes, but it can be argued that more case compression hinders performance by adding more rotating resistance.

Does a saw with tight transfers benefit from more case compression?

Good question.....and not one I have a solid answer too.

 

[Redfin]

Which could be good as long as it shuts off in time?

I think I understand what your thinking Steve but intake duration is measured from when the port opens till closing.

Cutting the skirt to give more time at tdc gives more duration from closing the port later. Was I off base on your quession?

 

[Stump Shot]

I think I understand what your thinking Steve but intake duration is measured from when the port opens till closing.

Cutting the skirt to give more time at tdc gives more duration from closing the port later. Was I off base on your quession?

So the time of events is more important than the port not being fully open, I think I'm starting to see.

 

[Mastermind]

I think I understand what your thinking Steve but intake duration is measured from when the port opens till closing.

Cutting the skirt to give more time at tdc gives more duration from closing the port later. Was I off base on your quession?

Thanks John.

Sometimes I'm as thick as a brick.

Good explanation.