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A lot of references are made to improving and/or best optomizing intake air velocity, especially at lower / less than WOT operating conditions. Would like to get some of the knowledgable folks to elaborate on components and factors that control / regulate air velocity.
Example: Many references are made to maximum amount of head flow, But also that good head flow is NOT a good indicator of air velocity under certain conditions.
I guess what I am looking for is a basic primer on what to look for and/or how to utilize these factors in determining a build . Especially in reference to fuel injected engines.
 

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head flow

Well my take on it is... And this has been said many times before, Build an engine with heads the suit the intended use. If your build is for a heavy bike riding two-up you want heads the dont have huge valves and large ports the would suit a Dyna build. Taking the budgit route use stock heads that are reworked. The SE CnC just dont seen to work all that well. They can also be tuned up, but you factor in the cost of the heads and then have someone work them over its getting pretty pricey. Long story short, smaller ports and valves for more bottom end grunt. High air speed is a good trade for alittle extra peak flow number.
There are aftermarket heads mentioned in this forum that might make things look different though. Im sure you'll get more input form others on this subject.:whisper:
 

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Cam Choice???

Your cams duration also plats a major part in velocity. Durations of 220 or more cause the valves (intake&exhaust)to be open at the same time for a few degrees of crank rotation. This is known as overlap. At slow RPMs overlap causes a small amount of reversion screwing up your intake velocity but at high RPMs this effect is reversed by helping fill the cylinder with the out going exhaust gasses causing a vacuum pulling fuel & air through the intake valve as it opens. Hope this helps, its hard to simplify
 

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Air Speed

First thing is, that bigger is not always better when it comes to throttle body size, or carbs for that matter. We have seen, via Joe's Cycle Repair, (link from our site), incredible power with t/bodies as small as 48mm on 95" builds. The intake manifold shape is extremely important, as too large can harm there also, causing lack of cylinder fill, in spite of a good head, and vise versa.
The correct combination for the intended application.
Scott
 

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This is a well guarded secret for head porters and you will probably only get generalities on this subject. Take our R&R stage 2-1/2 heads that will give 105-108 torque and hp with cnc porting and virtually the same numbers but rev much quicker (2-4 seconds) with the welded and cnc ported stage 4's. Then use the stage 5 which are larger ports, larger intake valves, and larger TB and get a very fast revving- in the 120's torque and hp with the same 95".
Head porters seem to pay close attention to cross sectional flow area when designing ports for different size engines and also consider piston demand caused not only by bore but stroke. There is a lot going on here.
With a throttle body it's just an air passage and your injectors are what is atomizing the fuel so are not as prone to velocity as a carb so as much air as you can pack into that high velocity port along with the right amount of fuel, the engine will use it. Seeing the results of these on the dyno is amazing, the larger TB's seem to have a positive effect on detonation also.
 

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I am only posting so i can track this post, too much good Info here, keep it coming [email protected]: :coffee: :corn: :corn: :corn: :corn: :corn: :corn:
 

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With a throttle body it's just an air passage and your injectors are what is atomizing the fuel so are not as prone to velocity as a carb

I would partially agree with this. IMO every piece of hardware from the air inlet initial entrance to the valve head and even the shape of the chamber influence velocity (and could be carried further to include all the way out to the exhaust tip). In most cases we can't leverage pulse wave tuning (packaging) but if we could the whole intake tract is very influential EFI or carb and VE over 1.0 becomes achievable.
The motor only needs so much air and if the TB is grossly oversized these quick rev times cited can be discounted due to a lack of velocity at WOT and lower speed ranges. Therefore IMO a motor with the PROPER sized and proportioned intake tract will be the quicker reving unit. On the dyno the evidence would be more torque under the curve.
 

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The motor only needs so much air and if the TB is grossly oversized these quick rev times cited can be discounted due to a lack of velocity at WOT and lower speed ranges. Therefore IMO a motor with the PROPER sized and proportioned intake tract will be the quicker reving unit. On the dyno the evidence would be more torque under the curve.[/QUOTE]

Yes, this is why I believe that most companys having engines certified by EPA are using EFI's to pass emissions because most of the testing done is in the low rpm range close to lugging so the injectors atomizing the fuel better plays a positive role in this. So the companys like R&R who have certified big inch engines with carburators clearly have a better understanding of velocity and how to keep the fuel atomized. Here the guage is the hydrocarbon levels, how cool the engine runs, and the power.
 

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I am having trouble following the logic here. We are discussing intake tract velocity and the R&R heads are being held accountable for making or breaking a build and the ability to EPA certify? The R&R heads work WELL but there are many other acceptable alternatives. I have nothing but praise for the part, I own them on my own ride but this isn't about the merits of the R&R engine development program or their heads. The heads are just one, important granted, part of the equation and I know R&R "gets it" as does King of Cubes "get it" but what about the rest of the parts like the filter cover, filter, velocity improvements can be had there, for example the Doherty AF setup with velocity stack integrated, and then the TB. They are not all the same and even the 50mm SE unit which may be an impressive number seems to be a slouch barely worth the price of admission compared to the stocker. So let's take a more broad view and get off the R&R drum beat for a minute. Other companys "get it" too and we really are talking about IC engine theory here anyway not who has the latest or greatest parts. TB oversizing is not as smart as one may be lead to believe and a few HP on top sacraficed may be a small price to pay for an easier to tune well running motor with more roll-on power and those touted quick rev times we all are hearing about. I cite well respected company owner Doug Coffee with that statement backed up by Mike Stegman also well respected NOT AN ENDORSEMENT FOR LATUS MOTORS OR HEADQUARTERS.
Regarding emissions I could build a very clean motor, EPA legal as far as tailpipe emmissions are concerned (not compliant due to the test sampling requirements and costs involved) that by virtue of the size (124") made respectable power and was smooth and long lasting and there would not be one R&R part to be found on it. S&S has many EPA compliant engine packages for custom builders, not endorseing them or the motors either just another source.
My point we all know R&R is a top notch outfit enough already.
 

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Do you mean like how the cam and the valve works up to the opening of .2562 L/D ratio and then after that the port takes over and the smooth transition that occures and the velocity that you want to port to so that at the rpm's of your engine when you size everything correctly with the rate of change of the cams that your fuel doesn't fall out of suspension or slow down where it balls up where it starts to burn- that it combusts also at the highest rpm that it doesn't go to supersonic and if you can port the heads and have the control of the cams, the valves, and the ports to do that, your in a regime and the higher you can make that happen the more efficient the engine runs?
 

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We could talk this till the cows come home and it would be of no interest to the majority except individuals wanting to enter the head porting field. My personal views are a little far out and non-mainstream and not too geared toward plug and play parts, which most seem to prefer, so would likely bore the average hop-up enthusiast.
If anyone is really interested in learning more about port flow dynamics there are several good books by Vizard, Heywood, Taylor, Ricardo, Maleev, Heisler. One of my favorites in my library is Theory and Practice of Cylinder Head Modification (1971), by David Vizard.
Another series of books that are really informative are the Denish books. When it's all said and done at the end of the day you learn that all of the cool tuning techniques that could really make these hogs fly are practically impossible due to packaging constraints. Also the odd fire, pushrod, air cooled siamesed intake motor is just design limited. Nonetheless many tuners are making enough power to far exceed the chassis and riders ability in a lot of cases. With a motor the size of the 155 a very mild state of tune would get the job done. A well tuned 124 is an animal and requires no frame mods.
 

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I would agree that a poor running 155 is an animal compared to a good running 124 but the same high velocity principles apply to both. We have hundreds of 95" engines out there with over 100 torque and hp working well as with 124"'s in the 140's. The new PSI carb is another example of intake velocity improvements. Testing on an S&S 96" engine resulted in 9 more torque and hp and more linear power that came on 600 rpm sooner, all redesigned and tested by that company you don't want me to talk so much about.
 

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psi carb

The PSI "Big Air" carb I feel is not for your average Joe public. I have alot of tuning expierence with these carbs in a different racing application and it seems most people just cant get the tune right. These carbs in the wrong hands will be a tuning nightmere for most. My MHO only here:whistle:
EFI with a ThunderMax is going to be way more user friendly:beer4u:
 

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Randy I am not picking on you, I have the utmost respect for your knowledge and products from Hyperformance and R&R Cycle. The security of being a business owner with a value added relationship as you have is priceless, I know been there and done that.

"poor running 155"

So lets' take a look at this. Just because a motor doesn't make 1.1hp/cu in doesn't necessarily mean it is poor running. In fact it may be very efficient if it was purposely designed and optimized for less / a lower speed range and more tolerant of lower octane fuel. BSFC and emissions could be phenomenal. We always assume the "good running motors" are on the high side of what is typical for the engine type.

Regarding a carb or TB, I often have imagined an air valve that worked like an aperture lens diaphragm. Airflow valve that is always centered.
I have no experience with the PSI so can't comment on how it works in the field, I do certainly like the design concept.
 

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TOMPAGLIA2 said:
A lot of references are made to improving and/or best optomizing intake air velocity, especially at lower / less than WOT operating conditions. Would like to get some of the knowledgable folks to elaborate on components and factors that control / regulate air velocity.
Example: Many references are made to maximum amount of head flow, But also that good head flow is NOT a good indicator of air velocity under certain conditions.
I guess what I am looking for is a basic primer on what to look for and/or how to utilize these factors in determining a build . Especially in reference to fuel injected engines.

Tom

In easy terms a head that has great flow numbers IE .. CFM may not have good velocity. This can be caused by many items, such as t/b size, air cleaner flow volume, size of port, choice of valve size, and valve shape, cut on the valve and seats, cam choice, exhaust system etc.

So when you are talking velocity it will translate into head porting, and the total package. A mild port job can help or it can hurt the performance if not done correctly. Properly ported for a certain cam, compression, exaust, you should get more flow and increased velocity with those two working as a team you get a head that has increased VE.

In a nutshell I do not feel that a head that is ported is going to work well with all packages. This would be the reason for a shop to ask many questions. Bike, type of riding, cam that is being used, exhaust, induction system. With that info and more you can talior a head to produce power where the rider needs it. There are many shops that port heads as you know. Some will and do produce a very good peak number, but many times these leave the rider with a engine that will be lazy at lower rpms. The rider may not even know that it is lazy until he rides a bike with a kit that can rev faster, pull harder enven though the peak number is very close to his own.

It is a hard thing to get your mind wrapped around until you can ride it , feel it, once you have done that it becomes clear as to what a head that can produces great velocity feels like and what the power should feel like.

Example a car has a 0-60mph time of 7 seconds and makes 300 hp 300 tq, same car same hp but it can go from 0-60mph in 5.5 seconds. That is rate of acceleration, that is what you get with a head that can produce a higher VE rate. It makes for a very snappy feeling bike.
 

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Discussion Starter #16
Appreciate everyone's input. A lot of good info. Education goes a long way in making build decisions.
What might be some of the key indicators in determining and/or what to look for in purchasing a good head job ( no jokes please - I may have really opened the door on this one).
 

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Look at the people who have the best understanding of all of these different events that have been mentioned in this post. For instance one that has not been mentioned, exhaust to intake velocity ratio. This is the critical value that determines how much port scavenging is being utilized to draw more intake air in for cylinder fill. Two things that show up when this isn't right is poor bottom end torque and a hot running engine. Hope this helps
 

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Effects of high intake velocity:
- Prevents entrained fuel from falling out of the flow stream onto the port and manifold walls. This can lead to funky air/fuel ratios.
- Creates a velocity-supercharge effect as the intake valve is closing, allowing volumetric efficiency to go above 100% at high engine speeds.
- Improves throttle response.
- Improves turbulence and burn in the combustion chamber.

You can get high intake velocities by choking the intake port, but then you'll get less total mass of air/fuel flowing into the combustion chamber at WOT. The secret is to maximize the port's efficiency, and that's where the experienced porter's black magic comes in. You want the maximum mass to flow into the combustion chamber through the smallest port possible. Port efficiency is usually measured as a ratio of flow vs. valve area (at any given lift). For a loaded bagger, you might want stock valve sizes with ports done by an experienced porter. For a Dyna, you can use a larger valve and have the same porter do his thing. It'll raise the rpm where the power peaks, but for a Dyna you don't need that much bottom end anyway. Once you've got your heads done, pick a cam that lifts the valve to about 25 - 29% of the valve diameter for the bagger and about 30 - 35% for the Dyna. Sorry for rambling.
 

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Randy did make reference to L\R and L\F in a previous post. I am in agreement with what you say but with the stock TB configuration siamesed and uneven fire, right turn into the head in a very short radius IMO this over 100% VE is a bit of a bench racing fantasy but I could be wrong. Set the motor up like a XR1000 then we would have a new story or just flood it with cubic inches and then it doesn't matter
 

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nw_guy4_fun said:
Randy did make reference to L\R and L\F in a previous post. I am in agreement with what you say but with the stock TB configuration siamesed and uneven fire, right turn into the head in a very short radius IMO this over 100% VE is a bit of a bench racing fantasy but I could be wrong. Set the motor up like a XR1000 then we would have a new story or just flood it with cubic inches and then it doesn't matter
Sorry I can't show you the flow sheets, but a 160 cubic inch Sportster motor running at 7000 rpm calculates to just about exactly 325 cfm at 100% volumetric efficiency. On the dyn, that motor drew almost 390 cfm through the flow meter while it produced 275 hp (rear wheel) @ 7000 rpm. That calculates to something like 120% VE. S&S Pro Stock heads.
 
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