The Velocity Myth

[cannondale27]

All those who are stuck in the carb days need to wise up.Fuelinjection does not need velocity on intake it just needs air and lots of it.Here is proof.My Phazer snowmobile.

4 stroke 500cc two cylinder motor 85hp I believe at crank.

Big throttlebodies 48.5 mm.Two of them!Another interesting.No I.A.C.V. yet it still has a fast idle when cold.Not sure how they do it.

[Canniboomer]

....those are two very deep-set butterflys. I think we are looking at built-in velocity stacks!, LOL.... let's throw one on a dale!

[cannondale27]

Velocity stacks are in airbox.Hey I figured out the I.A.C.V. its opened and closed by the coolant.Basicly just a small thermostat.And it looks adaptable to our throttlebody.I hate our IACV no other offroad machine I know of uses a stepper motor based IACV.They are either manual like LTR or something like this.Reason must be that the steppers cant take off road enviroment.I am definitly going to try this method.Only downside is a small coolant line needs to be t-ed in to one of our and run to this.Is even attached with two screws like ours.

[azcannon]

Steve Why not create manual one that is easy to adapt so we can control it and verify it isnt messing up anything

[wanablaze]

This coolant based one might actually be easier. Just tap the outlet from the water pump as long as it can be made to fit. Good find, Steve. Manual would work, too, but I'd prefer an automatic one.

[timbomoose]

With new technology old technology doesn't always apply. Snowmobiles are a great example since they put out some extreme power. Your phazer is an excelent example, 4 stroke 80hp 500cc 2 cylinder fed by 2-48mm throttlebodies.How can it run the velocity is not there? Oh wait its fuel injected,Yeah baby! On my polaris switchback it is also fuel injected and has 2-46mm throttle bodies,but is a 2 stroke 600 cc 2 cylinder an is 125hp.The carb version has 2-38mm carbs(old tech) and is 120hp with alot less broader powerband at the peak hp.Fuel injection lets us have more than a carb could ever. Another thing on snowmobiles is that they all have roller bearings at least at the output shaft where all older models had ball bearings to hand the extra load from the extra hp just like our Dales!

[cannondale27]

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!

[Happyboy]

This isn't a black and white issue. Velocity exists and it works. All that matters is what works on the motor you are talking about. If you go too big then yeah, you won't get enough air coming in---its a fact. If you can't form a vacuum then you can't get air. So its a balance of volume and velocity. What Tim and John have done is what works. They try something out and then dyno it. That is a must. Gratz to them for thinking outside the norm.

[wistech]

The real velocity issue is drawing air in at WOT at low to mid rpms . With a carb you need air moving at a minumum speed to create a low pressure for the jetting system to be able to draw fuel from the float bowl . If you make the ports to big air speed will slow down to the point where no carb will work very well at low rpms. Look at how complicated the carbs are on jap quads nowadays. This is why seriously ported race engines many times need a very high idle to keep the engine running with a carb. Old school carb porters needed to find a balance point with a flowbench between going to big for high rpm power and keeping the engine driveable . We are really not dealing with a vaccum . The piston creates a low pressure area on the downstroke and atmosheric pressure forces air into the intake trying to balance it out.
Now with fuel injection there is a lot of leeway for intake size. With huge porting and big throttle bodies atmospheric pressure has a lot less resistance going down the pipeline which allows for more air and fuel to burn for more power especially at higher rpms. Efi has no worry at all about air flow and velocity . It will atomize and deliver fuel regardless of velocity. You just need to change the map to compensate. The 1000 ecm is perfect for this because it has infinite adjustments. The 500ecm has a slight issue because at low rpm you cannot turn the fuel down lower than 10% on the mil tool. This is why we had a problem running rich with it and installed a pressure regulator that helped lean out the mixture at low rpm.
If you can run a stock map on a supposed high performance Dale engine and get a good afr with just a flowrate then the porting is not far off from stock and so will be you power.
Ever wonder why 45hp was the norm for even the hottest race engine for several years? Those guys were porting the heads just like the carbed engines.

[Happyboy]

very good point. makes sense too. you are sooo gonna make me go and read again.