Gabbing about 212 Hemi ports

[TheInspiredFool]

SIZE="4"] Back story and goals: We are building a yard kart for a small yard. Max speed of 20mph and for adults as well as children and teens. Instant torque and mid range torque is what we are looking for. Gearing will be appropriate and a 30 series TAV2 will be used to help with our goals.

So we took the new Predator 212 Hemi apart to remove plastic governor and see what manufacturing flaws there might be and make sure nothing crazy happened during the assembly process that might affect the longevity of the engine. Then I took a good look at the ports.

Is it just me or do these ports look about 25% too big?? The port bowl and short turn radius is obviously horrible. It's no wonder why these engines are sluggish on the bottom end. Yeah, they are small engines but they could definitely have a bit more torque down low and have a bit wider power band. I understand the mass production aspect and since it leaves such a low efficient flow pattern the size is acceptable for stock performance. It runs ok and is still a bargain for $99. But if you want to take time to tinker and gain performance my first goal would be to work on the short side radius and tighten the port to improve velocity.

It's pretty obvious to me that if someone where to take the time to work the ports in a configuration where the cam, bore, stroke and rpm are close to stock that one would straighten out the port and tighten them up some. So I went on the interweb to look at port jobs to get an idea of what others have done. What did I find? They all hog them out. Nobody is tightening them up some to keep velocity up.

Second guessing myself I decided to do a little math and double check my initial thoughts. Since I didn't currently have a dial indicator or degree wheel to check the exact cam specs to calculate piston speed and all that I searched box stock class rules and other resources to obtain the cam specs for the 212 Hemi. I then plugged them into the various formulas to calculate max port volume, cross sectional area min and max, etc with differing variables that would have an affect of determining optimum port volume and cross sectional area. Yup, ports too big.

What am I missing here? Maybe I am wrong?
I see people taking the time to work on the ports for lightly modified configurations but they just add volume and laminar flow and never address the low velocity inherent with the over-sized cross sectional area throughout the port and bowl area.

I think a pretty good amount of low and mid end power can be gained without affecting power at max rpm (up to valve float with stock valve springs) as well as a much more responsive throttle response. The stock port volume, if properly worked, can support most moddest engine builds and if you work them to improve laminar flow they become too big, loose velocity and only build bigger power in the upper range of rpms.

So that's my thoughts. Why not tighten the ports up if you want to gain power for a typical yard kart?
Why does everyone ignore the oversized ports when doing port work?
Other than raising the port side on the short radius turn why don't people tighten the port up?
Why do the tinkerers not tighten the ports up on pure stock engines just to gain more usable power?

(This should be good... LOL)

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[BigWes]

Ok, you are looking for 20mph correct?

You could have gotten that right out of the box without taking anything apart.

I have a governed 212 with nothing more than a stage one that'll make 40. The engine has never been into. It'll do donuts on asphalt in a tight turn. I know it's mainly a result of the live axle but it's still spinning an 18 inch tire that's very wide on asphalt. I have no complaints about bottom end torque from the little engine. I guess I have experience with much worse. The 212 does a good job.

You'll find with some research these engines were designed as multipurpose engines not just use for go-karts. Remember to it is an air cooled engine as well and a portion of that cooling comes from air flowing through the combustion chamber. When you restrict that cool air and fuel from flowing into the cylinder the head temps will increase drastically. It won't last long at high temps.

Generally speaking people open up the ports to flow more air and fuel. If they want to optimize torque they will install a mathematical correct length intake runner to optimize velocity. I don't know the math nor do I care. I find the engine performs very well within a given set of parameters and aftermarket parts will empty your pocket and make your head spin.

But by all means. Decrease your port volume and tell us how that works out.

 

[TheInspiredFool]

Thanks BigWes.

What I was getting at was that our yard can only support a top speed of 20mph and since that is where it will be used and a top speed of 20mph is about all that we need I wanted to focus on low and mi-range torque so that adults could have fun and experience quick acceleration while riding it. I also pointed that out because large ports normally support higher hp gains in the higher rpms. Since our kart will be in very short stretches from very low speeds I wanted to focus on how to make the kart more efficient for our specific needs at just off idle to mid-range and how to optimize the efficiency for our purpose.

I know that its easy to achieve 20mph with a 6.5hp engine. I was just noticing the size of the ports and figured that I could easily gain more low and mid-range torque and hp if the ports were properly worked and tightened to improve velocity at low valve lift. I figure I would put it in a thread to see what others thought and see if there is a reason why this isn't done by any of the diy'ers that our in the karting community/hobby.

About cooling the engine: With smaller ports you might loose a tiny bit of volume in the high rpms but you gain velocity in all areas. So you would have a better rush of air into the engine and helps to scavenge the hot air from the combustion chamber after the power stroke soI would think it would help to keep the engine slightly cooler, especially at low rpms. I will see if I can find any research papers that give any temperature result variances concerning port size to engine temp in air cooled engines. Very interesting. Thanks for that, BigWes.

---------- Post added at 11:58 PM ---------- Previous post was at 11:32 PM ----------

I don't know, maybe it's just me. I'm a tinkerer and obsessed with efficiency and making things perform better for my specific needs or in general over all. I just figured that I would have been able to find others who would have taken the time to fix the ports to be more efficient at low and mid valve lift to improve low and mid range hp and throttle response especially since there is already a good shape to the port to improve the short turn radius flow and it's unlikely that you would loose any peak flow to affect peak hp in the stock or even mild built configurations. I mean, it's only a $100 engine, or even a $30 head, it's not like an expensive race head or your daily driver.Why not give it a shot and see if you can make your fun kart more of a blast to drive? It's almost free to do and only takes some time. It seems to me that a small, low hp, low rpm single cylinder engine would respond even better to smaller ports (re: tightening to the correct size for correct velocity and max flow for application) than a larger or multi-cylinder engine would. What am I missing here?

 

[BigWes]

You sir, are missing the hemi version of this engine. That is exactly what you are missing!

Look into that one! I think it will not only be more to your liking it will be more fun to tinker with!

I have a few. It has way better off the shelf flow characteristics.

Do yourself a favor and check it out. Or do me a favor and check it out.

My reply wasn't intended as a bad response. If it came off as much I apologise.

Look into that hemi 212 though. I think you will like it better than the non hemi.

 

[TheInspiredFool]

You sir, are missing the hemi version of this engine. That is exactly what you are missing!

Look into that one! I think it will not only be more to your liking it will be more fun to tinker with!

I have a few. It has way better off the shelf flow characteristics.

Do yourself a favor and check it out. Or do me a favor and check it out.

My reply wasn't intended as a bad response. If it came off as much I apologise.

Look into that hemi 212 though. I think you will like it better than the non hemi.

Thanks BigWes. I understand that you were not trying to post a negative comment but it seemed that you had missed my intention for the post. I only gave the goals of speed and purpose for the kart so that the reason for gaining more low and mid range power were realized and it was more clear to the readers that off throttle response and mid range power would be far more important that total cfm hp in the high rpms.

The engine that I have IS a hemi. Yes, the port and valve flow is better but it can be improved. The port size is adequate for stock applications if you don't take the time to reduce the short turn radius cliff or work the valve shroud. My reason for starting the thread is to answer a few questions:

1: If you take the time to take material out of the port by reducing the sharp edge of the short radius bent and work the valve stem shroud then the port becomes more efficient (less turbulent) so you loose velocity that could be gained. If you take the time to do port work why not take the time to do the math to see what the minimum and max port cross-sectional area will be best for the current engine combination to optimize velocity?

2. Once the port is opened up and the port becomes more efficient the size of the port doesn't need to be as big to support flow at higher rpms. So why do people not take the time to tighten the port up to increase velocity?

3. Why do people continue to hog out the ports?! I see pics on the interweb of ports with a cross-sectional area large enough to flow enough CFM to support 60+hp thats going on an engine that will only produce 16-26hp?

I know that the stock configuration with a new intake and exhaust, geared properly with a torque converter would be plenty for our needs. But since I noticed the ports and I know we could gain a good deal of efficiency by softening the radius of the short turn. But once you improve the laminar flow efficiency, and thus the total flow efficiency, the ports become oversized because you can now flow much more CFM. Since the engine only needs a max CFM of x at 5,300rpm but now can flow much more than our required x we are now giving up velocity for no gain at all. We could now tighten the port cross-sectional area to gain velocity. As long as you don't exceed velocity to introduce sonic choke or reduce max CFM below needed flow at max rpm there is a very good chance of gaining efficiency at ALL rpms.

There is something to be said about bench testing and number pushing not being a very good idea in terms of screwing with ports, however, when the numbers point to a difference between good efficiency and poor efficiency so large it becomes a pretty sure thing that an increase in performance could be had by following the numbers.

There is enough room to create a great short side radius, straight port, a shear and anti-revision wall and still flow enough to support 117% (@ 85% BSFC) of the max CFM needed with a stock cam/engine combo at out max rpm.

I just don't know why I can't find anyone who is doing it. They are either leaving them with the small amount of material removal or hogging them out more. The only thing I can think of is that maybe these engines are not susceptible to low velocity detrimental port flow... Which seems like that would be false. It seems like these small single cylinder engines would be more responsive to proper velocity ports and would see a greater amount of gains throughout the rpm range and even gain power at max lift and in the high rpm range.

 

[BigWes]

I don't know. I'm not a racer. I tend to leave the ports alone myself. I do have a non-hemi I was thinking of polishing on the exhaust side to reduce friction but not really to open it up any.

I love to see what others do but I am one of those guys that believes that if I really need that much more power then maybe I should just get a bigger power plant.

I'll go with a bigger cam and some better parts but I myself am not going to go all out to try and modify an engine to squeeze every ounce of possible power out of it. At some point it becomes an issue of diminishing returns. The engine will become its own destructive force if you will. It's just a matter of time before it will not be able to contain its own parts. There are plenty of people that flow bench heads. But these guys are always going for max flow.

Yes. I did misunderstand you I'm sure. I got an old buddy that lives up north. He does mini tractor pull stuff. He has a flow bench and everything he does is for max top end flow.

When I get home from work I'll send you a PM later if you want and maybe get you set up with a place a little different.

---------- Post added at 01:46 PM ---------- Previous post was at 01:40 PM ----------

To add to above: I mean I'm not going to try and make a 6.5 hp engine make 20 hp.

I might throw a few nice parts into it though

But I'm not going to personally like weld the fins and girdle it up to hold it together or put in a stroker kit, or bore and sleeve it...and I don't hold anything against anyone who does! I just don't think I will...

 

[TheInspiredFool]

I understand that. I just figure that I can gain more power sooner in the rpm range and gain a better throttle response by doing some port work. I am all about efficiency and getter the most out of what you have while gaining reliability. If a stock hemi makes lets say 9.3hp at 5,400rpm and 13 ftlb tq at 4,600 I would expect to make eek out 9.6hp @5250rpm and 13.2ftlb tq at 4,300 but have better throttle response, better pull and instead of making 3.5hp at 3,500 it would make 3.8hp at 3,200 where the torque comes on sooner, builds faster and has a more flat curve further into the rpm range. Nothing that will destroy itself... Just getting more efficiency out of what is already there. Plus its just fun tinkering around when you have time to do so. I polished the combustion chamber earlier just for kicks. Let me know if anyone wants to see a pic.Working on things is kinda like meditation for me... It kinda grounds me and sets be in the right spot.

I will probably build a flow bench pretty soon as well as a small engine dyno. Once I get into something I end up custom building everything and getting pretty nerdy with math, research, custom built single board computer systems, custom built programs.... It gets pretty bad lol I am an autodidact polymath with a deep desire for knowledge, obtaining efficiency and customizing things to better fit my exact needs or goals.

 

[BigWes]

Hey man, if you build something that works everyone here will surely love to see it. Make your thread heading a little more inviting and add some pictures and I'm sure they will come.

This place is kinda like fishing. The better your bait, the better your your bite. Just don't do it my way...but anyhow, there are a few boards on facebook you can look into as well. Just search for all the related 212 racing and engine building type stuff.

 

[TheInspiredFool]

Hey man, if you build something that works everyone here will surely love to see it. Make your thread heading a little more inviting and add some pictures and I'm sure they will come.

This place is kinda like fishing. The better your bait, the better your your bite. Just don't do it my way...but anyhow, there are a few boards on facebook you can look into as well. Just search for all the related 212 racing and engine building type stuff.

Thanks for the tips. It seems like fully unpacking your thoughts and giving full explanations on here is considered "Gabbing" as in talking too much so I figured I would be upfront about the fact that I will be gabbing the heck out of the subject like I realize I tend to do. I guess it's more to do with not wanting to hear the complaints about how much I type or discuss than about attracting the maximum amount of views. But I definitely get your point.

I will think about making a build thread. It just seems like the majority of people on forums now-a-days just try to nit-pick your every word, argue and aren't open to fresh ideas that might go against the popular consensus. I have already reduced the short side radius and worked the valve stem area on the intake port. I am still wondering why others haven't tightened the ports on this at this stage. I am pretty confident that it would be beneficial to tighten the ports up some to gain some velocity but I can't get past why I can't find ANY pics online of ANYONE doing so... So it has me second guessing myself.

 

[landuse]

This place is kinda like fishing. The better your bait, the better your your bite. Just don't do it my way...but anyhow, there are a few boards on facebook you can look into as well. Just search for all the related 212 racing and engine building type stuff.

That is correct about all forums I am on a few, and if you don't post something inviting it is like a graveyard in your thread.

On the other hand, it doesn't take much to excite us either!!

 

[mckutzy]

Now the more finer points of technicalities with these motors are a little hard to digest for me, but over the years I have heard from various sources here who work with car engines and other engines and then these clone type engines... One thing that seems to ring with them all... they dont translate across from the bigger engine well.
Something about them(the clones) just is off physically, which theoretically should apply, but doesnt....
An example I can think of off hand(now more like a desired effect), is valve float to act as a limiter gov. We allow the engine to achieve this state for a governing effect, without the throttle limiter in place. A standard larger car engine with this effect would be detrimental to achieving more power and revs(as I understand)......

So as for the Port sizing to a specific range, more on the lower stock side..... Most dont venture into the head let alone the optimizing the stock range... and if they do, Most go for more flow and power for higher ranges of the motor's capabilities.

I am however interested in this as Im trying to get a little more info on the technicalities of these guys.... Id like to see what you come up with...

Flyinhillbilly has some good work done on his racing karts and other work on the Hilbilly dyno.....
A simple dyno rigged up... Aparently he got some fairly good results too...
http://www.diygokarts.com/vb/member.php?u=25088

A few others who worked heads with fluid and flow testing... Have to do a search.

 

[Flyinhillbilly]

I race unlimited modified dirt karts, and the bigger, the better as far as I’m concerned with the ports. My best head flows 96cfm at .425 lift, and it’s a beast.
What you’re talking about doing it seems to me is keeping the rom low and improving torque. In my eyes, make it flow, make it rev, gear it for a 20mph top speed, and it’ll be stupid powerful. Probably to the point that I wouldn’t even advise doing it.
There more than one way to skin a cat.

 

[TheInspiredFool]

That is correct about all forums I am on a few, and if you don't post something inviting it is like a graveyard in your thread.

On the other hand, it doesn't take much to excite us either!!

Thank for that landuse

---------- Post added at 03:18 PM ---------- Previous post was at 02:27 PM ----------

Now the more finer points of technicalities with these motors are a little hard to digest for me, but over the years I have heard from various sources here who work with car engines and other engines and then these clone type engines... One thing that seems to ring with them all... they dont translate across from the bigger engine well.
Something about them(the clones) just is off physically, which theoretically should apply, but doesnt....
An example I can think of off hand(now more like a desired effect), is valve float to act as a limiter gov. We allow the engine to achieve this state for a governing effect, without the throttle limiter in place. A standard larger car engine with this effect would be detrimental to achieving more power and revs(as I understand)......

So as for the Port sizing to a specific range, more on the lower stock side..... Most dont venture into the head let alone the optimizing the stock range... and if they do, Most go for more flow and power for higher ranges of the motor's capabilities.

I am however interested in this as Im trying to get a little more info on the technicalities of these guys.... Id like to see what you come up with...

Flyinhillbilly has some good work done on his racing karts and other work on the Hilbilly dyno.....
A simple dyno rigged up... Aparently he got some fairly good results too...
http://www.diygokarts.com/vb/member.php?u=25088

A few others who worked heads with fluid and flow testing... Have to do a search.

Thanks, mckutzy.

Yes, I was weary of valve float as well. I guess when you have tons of people doing it without failure for years you can kinda rely on the tried and true method. For me, I think of the camshaft lobe sweeping around, loosing contact with the lifter and then sweeping back and slapping the lifter. One would think that doing that 100's of thousands of times would eventually break a lifter or atleast wear the pushrod or rocker arm or something out until failure or very diminished performance.

"So as for the Port sizing to a specific range, more on the lower stock side..... Most dont venture into the head let alone the optimizing the stock range... and if they do, Most go for more flow and power for higher ranges of the motor's capabilities.

I am however interested in this as Im trying to get a little more info on the technicalities of these guys.... Id like to see what you come up with... "

I can understand that most people that keep the engines near stock won't tinker with ports but I figure that there should be others like me who customize everything to optimize efficiency and performance that would have tried this. Even those who build them up slightly should still (in theory) be left with ports that could be optimized for more velocity and still have a cross-sectional area that would support total CFM needed for desired hp goals at max lift for peak hp at max rpm.

I guess I will go ahead and try it and see how it works. I would prefer to build a dyno and flow bench first but I don't know if I want to put this on hold to monkey around withboth of those projects firrst. Maybe I will see what all I already have that I could use to build just a flow bench. I can always go back and do testing for comparison. A flow bench would be pretty great for tightening the ports properly while maintaining max CFM though... Hmm...

Well, I will keep you posted

---------- Post added at 03:59 PM ---------- Previous post was at 03:18 PM ----------

I race unlimited modified dirt karts, and the bigger, the better as far as I’m concerned with the ports. My best head flows 96cfm at .425 lift, and it’s a beast.
What you’re talking about doing it seems to me is keeping the rom low and improving torque. In my eyes, make it flow, make it rev, gear it for a 20mph top speed, and it’ll be stupid powerful. Probably to the point that I wouldn’t even advise doing it.
There more than one way to skin a cat.

"I race unlimited modified dirt karts, and the bigger, the better as far as I’m concerned with the ports. My best head flows 96cfm at .425 lift, and it’s a beast."

Thanks Flyinhillbilly. That sounds like a freakin blast (unlimited modified dirt karting) and would love to get into that! Thats what I read about these engines. I understand it in a race engine that is wide open all the time, especially since you gear for it and it's doubtful that you have any very low speed corners to deal with. Plus I bet it's a rolling start as well. I wonder just how much low end power it gives up on these engines or if they really are not as susceptible to loss of port velocity as other engines are.

"What you’re talking about doing it seems to me is keeping the rom low and improving torque. In my eyes, make it flow, make it rev, gear it for a 20mph top speed, and it’ll be stupid powerful. Probably to the point that I wouldn’t even advise doing it.

There more than one way to skin a cat."

Well, kinda. I am just looking to make the engine more efficient for our needs. I could gear it to top out at 20mph but that would be completely insane and definitely unsafe for children and teens, as well as most adults LOL. Plus it would be a belt and tire shredder.

I just figured that I could gain more usable torque in the bottom and mid range without affecting the top end. It would be better to engage the TC at a normal low rpm engagement speed with the engine a bit more powerful at engagement rpm. We come to a near stop pretty often and there are not any higher speed corners. It's like building a kart for the worlds smallest road corse. A stock 212 hemi would be pretty fun geared right and set up how I am going to set it up. I am just a tinkerer and experimenter who likes to find solutions to make things more efficient.

Here's how it went: I already had the engine apart to properly remove the governor so I figured I would do a little port work once I saw the short side radius cliff. Once I got to looking at it I realized that if I improved the laminar flow the total flow would improve nicely but imagining the cross sectional area of tge port when I was finished I was worried that I would loose volumetric efficiency due to a drop in port velocity. So I looked around the web and could only find those who have done a modest removal of material and nobody seemed to worry about loss of velocity. They only suggest not hogging them out but there is no mention anywhere about tightening the ports up a little to improve low and mid valve lift flow. I figure that a low hp, single cylinder engine would be benifit much more to porper port velocity but it has seemed to either just go completely ignored or there is no benifit from it, which I can't understand. That's when I figured I would start this thread, explain my thoughts and see if I could get a definitive answer before screwing up my brand new engine lol. I might just have to try and see what happens I guess.

 

[65ShelbyClone]

I figure I would put it in a thread to see what others thought and see if there is a reason why this isn't done by any of the diy'ers that our in the karting community/hobby.

Some big reasons I can think of are:
1.) The community is largely comprised of people just getting acquainted with engine fundamentals.
2.) Good (accurate and reliable) information is, as usual, hard to find while misinformation is not.
3.) Many who have the accurate and reliable information got it by their own money and hard work and use it for winning races, paying the bills, etc. and aren't willing to publish their trade secrets.
4.) Most of those same people build high-rpm engines for racing, not the stock RPM band.

About cooling the engine: With smaller ports you might loose a tiny bit of volume in the high rpms but you gain velocity in all areas. So you would have a better rush of air into the engine and helps to scavenge the hot air from the combustion chamber after the power stroke so I would think it would help to keep the engine slightly cooler, especially at low rpms. I will see if I can find any research papers that give any temperature result variances concerning port size to engine temp in air cooled engines. Very interesting. Thanks for that, BigWes.

Cooling from the intake ports is negligible for our purposes. If it wasn't, then engines would run hotter under low throttle when airflow through the port is low. Plus all the heat picked-up from the port walls just ends up back in the chamber.

The 212 hemi head is not an advantage over the inline head IMO(even with larger valves; that suggests a worse port design). Stock flow is only marginally better, if at all, and the hemi is harder to port for high flow. The short-side radius is angled closely into the seat and has very little room for smoothing. What some people do is blend the SSR into an epoxy hump on the port floor and make the SSR as large as possible. It helps get the air to make that turn without entirely shooting across the valve. That, and the hemi has no quench which is bad with high compression.

With inline heads, some porters focus on getting the air to completely shoot across the valve and have very little SSR and some have success with that. The hemi's valve is tipped upward into the flow path and makes that harder to get away with, yet it has a worse SSR that makes a conventional approach harder.

 

[Flyinhillbilly]

I get what you’re wanting to do, and I under your reasoning behind it. My thing is that like you said earlier, what works in car engines do t translate well to these engines. There’s one guy that put a stage two on a predator and legitimately doubled the horsepower. That blew me away, there’s no way that it should’ve done that in my opinion. Another thing is that 30hp for these engines in race trim is not uncommon, and if you think about the hp per ci, it’s well beyond what even the best car engines will do naturally aspirated.
I’m interested to see how this plays out, I’m all about experiments and learning, and I look forward to know if it’s a yes or a no. I honestly have no idea how it’ll play out.

 

[BigWes]

Some big reasons I can think of are:
1.) The community is largely comprised of people just getting acquainted with engine fundamentals.
2.) Good (accurate and reliable) information is, as usual, hard to find while misinformation is not.
3.) Many who have the accurate and reliable information got it by their own money and hard work and use it for winning races, paying the bills, etc. and aren't willing to publish their trade secrets.
4.) Most of those same people build high-rpm engines for racing, not the stock RPM band.



Cooling from the intake ports is negligible for our purposes. If it wasn't, then engines would run hotter under low throttle when airflow through the port is low. Plus all the heat picked-up from the port walls just ends up back in the chamber.

The 212 hemi head is not an advantage over the inline head IMO(even with larger valves; that suggests a worse port design). Stock flow is only marginally better, if at all, and the hemi is harder to port for high flow. The short-side radius is angled closely into the seat and has very little room for smoothing. What some people do is blend the SSR into an epoxy hump on the port floor and make the SSR as large as possible. It helps get the air to make that turn without entirely shooting across the valve. That, and the hemi has no quench which is bad with high compression.

With inline heads, some porters focus on getting the air to completely shoot across the valve and have very little SSR and some have success with that. The hemi's valve is tipped upward into the flow path and makes that harder to get away with, yet it has a worse SSR that makes a conventional approach harder.

Ok, as far as how air flowing through the engines ports effects cooling the cylinder goes I suppose I wasn't explaining myself and the effects of it very well. All airflow matters especially cold outside air...relative to the hot engine.

So as you were saying about the engine heating up at idle as the airflow decreases we need to consider the combustion cycle has decreased and energy output of the engine has decreased as well, thereby decreasing heat output. Does it make a drastic impact on upper cylinder temperatures? Who knows. The fuel mixture really makes a difference though. You can make a little more power by running a bit lean at the cost of higher head temps and also you can run a little richer and drop your head temps at the cost of a minute amount of power. That's pretty much a proven fact.

Is it negligible with these small engines? Yeah, who cares I guess. I think you could measure the effect with the right equipment though.

Some engineer decided to implement a rear cylinder shutoff on Harley Davidson air cooled engines when outside air temp exceeds a certain temp. It just moves air through the cylinder in an effort to cool the entire engine when you're sitting at idle. Does it work? Yeah, it's annoying sitting on the vibrating thing...but whatever works.

 

[TheInspiredFool]

I get what you’re wanting to do, and I under your reasoning behind it. My thing is that like you said earlier, what works in car engines do t translate well to these engines. There’s one guy that put a stage two on a predator and legitimately doubled the horsepower. That blew me away, there’s no way that it should’ve done that in my opinion. Another thing is that 30hp for these engines in race trim is not uncommon, and if you think about the hp per ci, it’s well beyond what even the best car engines will do naturally aspirated.
I’m interested to see how this plays out, I’m all about experiments and learning, and I look forward to know if it’s a yes or a no. I honestly have no idea how it’ll play out.

Thanks for the reply, Flyinhillbilly. I am just worried that the normal formulas don't actually appy to these engines and I screw it up lol I could just toss it back together and I know that I will be able to achieve what I want with it. Its just the experimenter in me that wants to see if I can eek out some more power and throttle responsiveness out of it on the bottom and mid range.

Maybe because it's a single cylinder engine it's less susceptible to lower port velocity because there is no other cylinders affecting and disturbing the pulse waves in the intake or exhaust portions that other engines have to deal with?

Well, I will mull it over for a bit and see whether I decide to try it. It would be nice to have a flow bench going into it. I will keep you updated.

 

[BigWes]

Yeah but if you mess it up they're cheap. You can buy a new one!

 

[TheInspiredFool]

Yeah but if you mess it up they're cheap. You can buy a new one!

Very true!

 

[65ShelbyClone]

Thanks for the reply, Flyinhillbilly. I am just worried that the normal formulas don't actually appy to these engines and I screw it up lol

They still apply. Be leery of the overly simplified formulas you might find in places like Hot Rod magazine or something. They often round-off numbers, shorten decimal places, make assumptions about the engine, and then condense it into some constant where all that monkey business is not visible. The more variables you have to plug in, the better.

If you can make the port smaller with the same or better flow, then the engine should make more power under the curve.

Its just the experimenter in me that wants to see if I can eek out some more power and throttle responsiveness out of it on the bottom and mid range.

You probably won't get noticeably better throttle response without lighter parts and/or a pumper carb. Singles have the disadvantage of 720° firing. At low rpm, response to a throttle snap is delayed until the next intake stroke comes around. Then there's going to be a lean AFR spike as fuel starts moving and the port walls get wetted.

Incidentally, a throttle chop causes the AFR to rock bottom briefly as that fuel is pulled off the ports under low airflow. Fortunately it seldom affects driveability.

Maybe because it's a single cylinder engine it's less susceptible to lower port velocity because there is no other cylinders affecting and disturbing the pulse waves in the intake or exhaust portions that other engines have to deal with?

No, they're affected the same way. It's less noticeable the less power an engine makes. There again, most people trying to get more power out of these engines are also spinning them a lot higher.

It would be nice to have a flow bench going into it. I will keep you updated.

If you're not after actual flow numbers, then a simple flow bench that provides only comparative results would be simpler and easier to build. Dynos can be done that way too, but the only real difference is the data collection. Might as well make it spit out real numbers.

Some engineer decided to implement a rear cylinder shutoff on Harley Davidson air cooled engines when outside air temp exceeds a certain temp. It just moves air through the cylinder in an effort to cool the entire engine when you're sitting at idle. Does it work? Yeah, it's annoying sitting on the vibrating thing...but whatever works.

That's to keep the hotter rear cylinder from overheating though(and by extension, the rider sitting over it); it doesn't cool the front one.