hmmmm. good topic. something that will probably always be debated. I'm no expert in this field and never will be. Here are some questions and ideas to throw out there for you guys that would know though.
- Fuel - obviously with our motors we can take this out of the equation I would assume as the injectors take care of the delivery.
So, the next question we need to look at is where do we want the power? I would think modifing the ports for low-mid is going to be differnt for mid-high.
Then the next question is we have to figure out how to move the maximum amount of air into the chamber in relation to the power we are looking for.
There has to be some sort of equation or something out there to figure out if a chamber is x size it will take y to fill it or something like that.
Another thing to think about is force the air is placed into the chamber maybe? Equal amounts of air transferred from one chamber to the next without any force behind it will only yield the same amount fo air. I think this is wherere the velocity idea comes into play as maybe with the air possibly having more force coming into the chamber the end result is actually more air in the chamber???
The last part of the entire question is then the air flow. I would think the path the air needs to flow needs to be as uniform as possible? I would think any large areas would create pockets that result in dead space and disrupt the flow of air. As would any small restrictive areas?
The Velocity Myth
The velocity over size arguement also focuses on 1 big factor. OK, if your ports are big enough then yes you will suck in the most air, but you will also loose air from the cylinder faster as the compression stroke starts compared to a smaller port. So not only is it the size but it is the geometry of the intake that makes a difference.
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funmachines
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My .02:
Velocity isn't a myth and there is no free lunch. There is a lot more capability at low speeds with EFI than a carb but it doesn't change physics. If you have large ports with short runners that fill well at high rpm you give up some low end and mid range. Higher velocity with smaller ports and longer runners will fill the chamber better at lower rpms but will run out of flow at higher rpms. Some sophicticated motors use variable valve timing and variable runner length/cross section to reduce compromises.
Velocity isn't a myth and there is no free lunch. There is a lot more capability at low speeds with EFI than a carb but it doesn't change physics. If you have large ports with short runners that fill well at high rpm you give up some low end and mid range. Higher velocity with smaller ports and longer runners will fill the chamber better at lower rpms but will run out of flow at higher rpms. Some sophicticated motors use variable valve timing and variable runner length/cross section to reduce compromises.
When we first started porting the heads there was an overwhelming worry about losing velocity and exhaust port reversion that nobody wanted to to really change the heads away from stock much. "your going to lose low end " was the cry. Thats when 50 hp seemed so far out reach. Then we started taking chances and experimenting . We dropped the d porting on the exhaust and started opening up the intake. Then 50 hp was attained and surprizingly no torque or power lost anywhere. Then came bored throttle bodies and velocity stacks. And when I slapped on the first cyclone 55 was here with 35ft pounds of torque. Anyone who drove that quad will tell you its not wanting for low end power. I wish I had cataloged every head as the porting progressed to where it is now. They have changed a lot in just a few years. Trial and error.
Im no wizard with head design but I know what has worked so Im sticking with it.
Im no wizard with head design but I know what has worked so Im sticking with it.
QUOTE (cannondale27 @ Jun 4 2007, 07:52 PM) <{POST_SNAPBACK}>
Anyone notice the new Can-Am has a 46mm throttle body and 38mm intake valves?Hmm bored throttlebody on ours is 46mm and Intake valves are 38mm.Works great.We need to go bigger now!
The new Can-Am is also using an IACV... I'm wondering what their setup is like, hopefully not similar to ours...
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cannondale27
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cannondale27
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QUOTE (funmachines @ Jun 10 2007, 11:26 PM) <{POST_SNAPBACK}>
My .02:
Velocity isn't a myth and there is no free lunch. There is a lot more capability at low speeds with EFI than a carb but it doesn't change physics. If you have large ports with short runners that fill well at high rpm you give up some low end and mid range. Higher velocity with smaller ports and longer runners will fill the chamber better at lower rpms but will run out of flow at higher rpms. Some sophicticated motors use variable valve timing and variable runner length/cross section to reduce compromises.
Velocity isn't a myth and there is no free lunch. There is a lot more capability at low speeds with EFI than a carb but it doesn't change physics. If you have large ports with short runners that fill well at high rpm you give up some low end and mid range. Higher velocity with smaller ports and longer runners will fill the chamber better at lower rpms but will run out of flow at higher rpms. Some sophicticated motors use variable valve timing and variable runner length/cross section to reduce compromises.
I agree this should eventually happen (torque/lowend loss) but it hasnt yet only price we are paying is MPG has gone down.Going to be trying hard to make it happen though in next month or so.If there is still no lowend loss well then should be some BIG #'s.Now reason I called it a myth is because up until fuel injection alot of the motors were actually making thier ports smaller and smaller going for velocity.I have seen a few very knowledgeable engine builders actually say their porting or lack of it on intake helps fuel delivery.Thing is they were talking about fuel injected motors.I know F1 cars have variable valve timing for performance but I cant think of others that do it for anything other than emissions and gas mileage.Example is our Camry.Yes you can feel the cam timing take effect but motor is a complete mutt until then.Could the cam timing actually be limiting performance with mpg in mind then allowing it late in rpms?Now the variable intakes on Motorcycles are definitly performance enhancing but they are taking advantage of RamAir effect at higher speeds not same thing as velocity.The few cars that have it I bet thats not the case.
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funmachines
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I think it is great that real development of higher power levels is continuing with Dale motors. It sounds like the point of diminishing returns has not yet been met with the larger ports.
A couple more thoughts:
There are quite a few examples of higher end car motors that take advantage of variable cam timing. BMW's have been using variable cam timing in many motors for quite a while. They are routinely pulling over 100 hp/l and meeting emissions and fuel economy standards, with better low end and midrange to go along with the top end. etc. The new 600 hp Dodge Viper has variable cam timing too (first for an in block cam).
Examples of variable runner length include many current Mercedes, Ferrari 360 and 550, many Porsches, and the Lotus designed ZR1 corvette motor from a while back or the SHO Taurus motor. Extremely complex and expensive to implement. It's not needed for turbo or supercharger motors.
You are right, there are many design compromises made for automotive engine that we don't have to be concerned with. I'm so happy that we don't have to worry about smog inspections...
Thanks to all that are continuing the real world development of these motors and sharing the benefits.
A couple more thoughts:
There are quite a few examples of higher end car motors that take advantage of variable cam timing. BMW's have been using variable cam timing in many motors for quite a while. They are routinely pulling over 100 hp/l and meeting emissions and fuel economy standards, with better low end and midrange to go along with the top end. etc. The new 600 hp Dodge Viper has variable cam timing too (first for an in block cam).
Examples of variable runner length include many current Mercedes, Ferrari 360 and 550, many Porsches, and the Lotus designed ZR1 corvette motor from a while back or the SHO Taurus motor. Extremely complex and expensive to implement. It's not needed for turbo or supercharger motors.
You are right, there are many design compromises made for automotive engine that we don't have to be concerned with. I'm so happy that we don't have to worry about smog inspections...
Thanks to all that are continuing the real world development of these motors and sharing the benefits.
QUOTE (haydug @ Jun 11 2007, 12:32 PM) <{POST_SNAPBACK}>
How did we gain H.P. by using smaller intake valves in 2002 with no mapping experience, & completely stock motor?
Thats a valve mod we are still using. I dont like to talk much about it because that mod walks a fine line reliabilty wise. The valves are cut as small as possible to offer less resistance. Its kind of like tricking the head into thinking it has bigger standard valves.