Air Flow

[hubeerjw]

I started crunching some numbers today after having taken off my carbs and intake and noticing the oval shaped intake ports. The stock carbs are 35mm (and if I am wrong with anything I say, please correct me) and the top/circular part of the intake is 36mm. The intakes then "blend" into an oval shape that I measured to be 30mm by 40mm. This is the same shape/size as the intake on the heads. If we take the area of these openings we will get the following:

35mm Circle (diameter) = 9.62cm^2
36mm Circle (diameter) = 10.17cm^2
38mm Circle (diameter) = 11.34cm^2
30mmx40mm oval = 10.07cm^2

I threw in the 38mm circle because I recently purchased some 38mm carbs off eBay hoping to get them installed on the VMax at some point. I wanted to know if anyone knows what the intake and exhaust valve sizes are and where the most restriction would be located? If it is at the valves, then I will not bother with trying to remove material in the oval parts of the intake and head. If the valves will allow more flow, then I would think it would be in my best interest to try and match the carb size with my intake/head size. I have calculated that an ellipse measuring 36mmx40mm would match almost perfectly with the 38mm carbs. That would mean removing only 3mm of material at the center of the intake at both the top and bottom. If you throw V-Boost into this, all my theoretical numbers go out the window. I talked with Shawn a while back and I believe he had his heads flow tested to 120CFM. Shawn if you are willing to read through this whole thing, do you know if they tested your heads at 28inches of water depression and what did they use for exhaust restriction (diameter of exhaust pipe?) Now I'm no way an expert in any of this and will take in any comments or criticism. I have also read how port size and velocity all play an important part with HP, throttle response, etc. Maybe I am over-complicating things, but if I'm going to spend the time on certain projects, I would like to get as much out of it as possible. Sorry for being so longwinded.
Thanks,

Jeff

 

[lankeeyankee]

I dont know about all them numbers. During my 85 engine rebuild I noticed the same thing with the intakes.
Yamaha either didnt spend much time or they had there reasons. I took my chances and expierence and broke out the dremel and about 9 hours.
But here are my intakes.

 

[one2dmax]

there are reasons the ports are shaped as ovals and not 100% round. Airflow works best on those kind of transisions,

Sean

 

[hubeerjw]

there are reasons the ports are shaped as ovals and not 100% round. Airflow works best on those kind of transisions,

Sean

That makes sense... especially with the dual intake valves, but I am wondering if I will be wasting my time with tryintg to install 38mmm carbs... From all the threads it sounds like there it more HP to be gained by going to them, but what else could be gained by going to what Lankee has done? I may try to model this up into a 3D cad software and see if I can schmooze one of our analysis guys to see if he can provide any input. I think a nice smooth "blend" or transition with the same amount of surface area will provide the best results or least restriction.
Thanks Lankee and Sean for posting!

Jeff

 

[one2dmax]

You can definetly benefit from blending in the area and port matching the intake. You can also benefit from enlarging the inner diameter of the intakes too.

Sean

 

[KJShover]

You can definetly benefit from blending in the area and port matching the intake. You can also benefit from enlarging the inner diameter of the intakes too.

Sean

+1 Portmatching, mild porting and low profile valves can yield some good gains. The company that did the head on my XS did a bang up job. made great power. They had the exhaust ports where huge and smooth as glass. The intakes were large as well, but they left a mild "texture" for lack of a better term (felt like relly fine sandpaper) when I asked them about this, they said it aids in the atomization of the fuel.

Lemme tell ya, the bike had a totally different sound to it with the ported head, and a definate increase in power. After all an engine is not much more then a big ol air pump. Being flow is horsepower and size is torque. The more efficient you can make the pump, the more hp will be freed up.

 

[lankeeyankee]

I am by no means a head porter. From what I have read, the obvious is to have the intakes to match the head ports, the exhaust to match the exhaust pipe entrance. Never want to smooth the intake due to what the previous post wrote you want the air and fuel to be mixed when entering the combustion chamber. On the other hand you want the exhaust ports to smooth as a babies ass!
I just matched my head ports to the intake and exhaust. I did open up the exhaust around the valves and its route to exit hard to explain. And polished polished polished to an almost chrome finish in the complete area of the exhaust. Does anyone else have any tricks on the VMAX head?