exhaust port size?

[exhausted]

2 cycle engines are a completely diferent animal and how can you combine exhaust on that?

[hotrod]

You are absolutely right, but when do multiple cylinders not interact in the manifold?

When they share no manifold like individual port injection, and independent exhaust pipes.

That was actually my point, of mentioning that issue.
Single cylinder research only works for examining basic processes, and establishing working hypothisis to develop in the full engine.
I understand that things won't directly scale to muliticylinder engines due to the interactions.

yamaha had a straight four cyl 2 stroke awhile back... basically 2-twins bolted together. we did our initial testing on the twin and then tried it on the four... just didn't add up.

Did you find out why it did not cross over? That is just as important as finding that it would.

In some areas of research though you can establish very useful data working on an isolated cylinder. For example all the basic research NACA did on water injection, fuels research, octane sensitivity to cylinder head temp, piston crown temp etc. were first examined in isolation on a single cylinder research engine and then moved to a full muliticylinder engine. That also allowed them to examine the interaction effects as they had two cases to work from one without and one with interaction so they could identify exactly what sort of interaction was taking place and why.

For examining trends in certain processes, like the effects of themal coatings, heat transfer through the head etc. instrumenting a 16 cylinder radial or a V-8 is way too complicated. Much easier to examine the simple case first and work out the basic physics and processes then see how they apply in a live engine.

Larry

[exhausted]

Hotrod;
There are areas where exhaust stuff does not cross over. Single cylinder engines do not have to worry about reversion from other cylinders in the system!
A lot of things happen in multiple cylinder engines that minimize header length and size calculations based on single cylinder engines that otherwise work fine.
On the exhaust side of things, I believe we could learn a lot more about how much velocity during blowdown we can get to. The Blowdown event is from EVO to to lowest point of pressure in the cyllinder. It happens all by itself and is sufficient to overpower any other waves coming up the pipe, at least for a while. A great analogy I use is a hand grenade. When one goes off it will clear the room! well there are 533 grnades going off in an engine every two revolutions of the crank at 8000rpm's and they wreck havoc.

[exhausted]

Correction, sorry guys I got ahead of myself there. 533 grenades per second, not two revolutions, sorry!

[SWR]

On the exhaust side of things, I believe we could learn a lot more about how much velocity during blowdown we can get to. The Blowdown event is from EVO to to lowest point of pressure in the cyllinder. It happens all by itself and is sufficient to overpower any other waves coming up the pipe, at least for a while.

If I model an engine in EA Pro,and I make the exhaust port smaller than stock while everything else is the same,the blowdown event is fast enough (peaks at 1750 or so fps and it flows well),then it's strong enough to subdue most anything coming back up before overlap...and it usually makes more power (as a trend). Wonder if that's "theoretical proof"..?

[MadBill]

Correction, sorry guys I got ahead of myself there. 533 grenades per second, not two revolutions, sorry!

JIC you haven't yet unearthed all the subtleties of the ST Forum Calvin: When you make a post, an EDIT box appears at its top right. If you want to change something, just click on it and you can do so. Bonus: if you're quick enough to spot it before anyone else replies, no note about editing appears on the revised post.

[randy331]

Exhausted, I've read several of your posts where you say ex ports, and or the exits, are too large, and your finding power with a reduced csa header pipe, vs the port exit. I can see that on non all out engines, but are you saying that the top running PS/comp eliminator heads/engines have power to be gained with a smaller header, than port exit?? Are they running a too large of ex port? Darin Morgan gives specific average air speeds for the throat, and port exit (when measured on a flow bench), the speed difference from throat to exit tells me he intentionaly expands the port a certain amount from the throat to exit. He also says he can easily make the port flow more by making it larger, but it will cost power. I'd have to belive he also tried a smaller port than what he chose to use.
They can make the ex port any size they want.
Is he expanding the ex port, because he's bandaiding a too large of header? He, or other top engine builders/cylinder head people, haven't tried smaller port/headers combinations?

Randy

[exhausted]

Exhausted, I've read several of your posts where you say ex ports, and or the exits, are too large, and your finding power with a reduced csa header pipe, vs the port exit. I can see that on non all out engines, but are you saying that the top running PS/comp eliminator heads/engines have power to be gained with a smaller header, than port exit?? Are they running a too large of ex port? Darin Morgan gives specific average air speeds for the throat, and port exit (when measured on a flow bench), the speed difference from throat to exit tells me he intentionaly expands the port a certain amount from the throat to exit. He also says he can easily make the port flow more by making it larger, but it will cost power. I'd have to belive he also tried a smaller port than what he chose to use.
They can make the ex port any size they want.
Is he expanding the ex port, because he's bandaiding a too large of header? He, or other top engine builders/cylinder head people, haven't tried smaller port/headers combinations?

Randy

I would like to know what he is thinking also! I have probably built headers that have been on his heads. I have, he used to be with Reher wasn't he? There are a lot of different headers out there so I can not see him coming up with any formulas based on headers.
David bought several sets from me over the years for his PS car and some customers. While I have spoken with David about some of my issues, I never got to deal with Darin. I never built anything experimental for them, maybe they tried some headers from someone else or did some themselves. I do know that you have to be very careful with that transition at the head or you will lose any gains to flow loss! Higher velocity headers do not grow on trees!

[exhausted]

Thanks Mad Bill, I am clawing my way up the learning curve!

[exhausted]

SWR; What peaks at 1750 fps?

[jmarkaudio]

In the mix of all this, if you are making the port smaller, to gain velocity, to combat reversion. Unless it is already too big wouldn't the exhaust duration need to be longer to allow for proper scavanging? And where do you decide what is too small? I would think this would be determined on the flow bench and dyno. Now you have to change the cam and cylinder head that was researched with whatever dyno headers was originally used. On an engine such as a Pro Stock or Comp engine, you would change a lot. I think there is power in having the right exhaust port/header combo, but you can't forget that getting the air/fuel mix into the engine is the primay goal. After that you figure what is the best combination of cam duration, cam timing and exhaust port/header size to get the exhaust out.
Now I have read as of late that PS intake runners have gone to a slight funnel shape, tapering smaller as it gets closer to the valve. Maybe the exhaust needs the opposite, like the laval nozzles in a prior part of this post, but instead of the restriction being below the valve maybe it needs to be farther in the tract like in the first 12" of the primary or at the exit of the port. This would means the exhaust port needs to be larger up to that point. After that, you have steps to expand outward. I would think you would want to get a little ways from the valve into a relatively straighter part of the tract.
Maybe barking up the wrong tree, but I'm getting a little curious about all this as I have to come up with headers for my SB2.

[randy331]

Now I have read as of late that PS intake runners have gone to a slight funnel shape, tapering smaller as it gets closer to the valve.

Are you saying the intake runner/port has a diminishing rate of reduction in csa as the runner/port gets closer to the intake valve? Or it just gets smaller as it gets closer to the valve?

Randy

[SWR]

SWR; What peaks at 1750 fps?

Blowdown velocity. If I "shrink" it smaller than the size giving me that velocity,it loses power...

[exhausted]

In the mix of all this, if you are making the port smaller, to gain velocity, to combat reversion. Unless it is already too big wouldn't the exhaust duration need to be longer to allow for proper scavanging? And where do you decide what is too small? I would think this would be determined on the flow bench and dyno. Now you have to change the cam and cylinder head that was researched with whatever dyno headers was originally used. On an engine such as a Pro Stock or Comp engine, you would change a lot. I think there is power in having the right exhaust port/header combo, but you can't forget that getting the air/fuel mix into the engine is the primay goal. After that you figure what is the best combination of cam duration, cam timing and exhaust port/header size to get the exhaust out.
Now I have read as of late that PS intake runners have gone to a slight funnel shape, tapering smaller as it gets closer to the valve. Maybe the exhaust needs the opposite, like the laval nozzles in a prior part of this post, but instead of the restriction being below the valve maybe it needs to be farther in the tract like in the first 12" of the primary or at the exit of the port. This would means the exhaust port needs to be larger up to that point. After that, you have steps to expand outward. I would think you would want to get a little ways from the valve into a relatively straighter part of the tract.
Maybe barking up the wrong tree, but I'm getting a little curious about all this as I have to come up with headers for my SB2.

OK, I have to go a little further now into this situation.Invariably, we find that the exhaust duration can be shortened when utilizing current header technology such as I am pushing. Yes, this is one of my points. If your header is not helping you you need more duration and a bigger valve. in order to help because you are pushing more than you need to! Over the three years I was involved in PS truck, what we found was that you could use a smaller exhaust valve at least wih my headers. This also meant you could use a larger intake valve which should help you understand where this is all pointng. The more you can use the power that is left in the exhaust side of things the more air you can get in. I am sorry, but this is reality. I have been helping some Stocker guys lately and some of them have changed their cam timing, to smaller exhaust lobes and wider lobe centers and always pick-up. The next step after that is more intake duration becasue the exhaust side is getting out of the way sooner, you can go to places with the intake you could not go before! More and more people are dicovering merged collectors. From my corner they do cahnge things for everyone, but depending on other parts of the system, they may not translate into more usable power.
And to stoke the fire a little more, unless you are testing with a accelerometer and not a load dyno, you are not seeing everything you need to know! I can not tell you how many times I have seen some of my headers lose power on a dyno but run better at the track! I have seen it in Cup and NHRA. I call the phenomena an engines transient response. How well a motor can recover from sudden piston speed changes and to a lesser extent just go from one rpm to another. It is my strong belief that unless you are pulling the load and measure how fast the engine is doing the work, you are missing this important part of tuning an engine. Measuring torque instantaneously and calculating power gives you a static number. Accelerating a mass and measuring the time it takes is the only realistic measure of an engines ability to do work. That is why there are a lot of people that know you do not race a dyno or a flow bench for that matter. The last test is the accelerometer, the car! This situation is always more evident when we get into the "sizing" part of an engine. How big to make the intake runners and how big do we make the exhaust side! etc. It is my decided conclusion after 16 years of building headers for many top professionals, we have not explored "smaller" enough.
Bring on the whining!
And to answer another of your questions, yes for years I have seen PS engine builders use a old set of headers in their dyno room while their "race headers" were out on the road. sorry , those days are over! If you are not working in every test with the correct header you are wasting time and money!

[exhausted]

SWR; What peaks at 1750 fps?

Blowdown velocity. If I "shrink" it smaller than the size giving me that velocity,it loses power...

Well there you go!
My point is head guys should look at this because I think the area growth from the bowl, as well as the valve size, should be controlled in the head and not "attached" on in the header? follow me? You would not believe the confused look on head guys faces as they think of all the air flow they might lose! If the header is brought online, you gain?
As in other posts here, there is a limit I can reduce area and not lose power. It is a shifting target but reality for me, and if the customer is not willing to push the envelope I can not go there. That is one reason I have decided to try and rattle some cages here in this forum, the more me and head guys can get together we can help each other and our customers.