stepping outside for some fresh air, 200x(ish) air intake questions.. and MATH! lol

[OldNo437]

the intake plans have been laid on my silly overengined machine, one problem I have on my build I need to get mud free fresh air and about 200cfm worth. problem is going the stock 200x route (through the backbone) is the bottleneck (about 100cfm total supply) now, from my math the engine is only capable of a max cfm of 137.74cfm (39.67 ci x 12000rpm) / 3456 < formula lol and that is an unrealistically high number, as that doesn't factor the restrictions like valves, intakes, the flow delta of the air filter (eyes glazed over yet?) and everything else in the way. and it seems it would only be a bottleneck at over 8k rpm, but that's the point of a high winding 4 cylinder, rev the crap out of it :D

I'd like to duct air somewhere under the seat, or anywhere really. but the problem I see is that everything honda seems to either draft from the neck area, or above the seat plastics. so anyone have any suggestions as to a good duct that's below the plastics, but won't have me cleaning the air filter every 10 minutes. the way the airbox is designed, it will be kinda a P.I.T.A. to get to the air filter, not impossible but something I'd rather avoid...

heres a pic from my other thread.. I have a clean slate, fresh is coming from the lid of the box, and can come from any spot on the lid.

https://i.imgur.com/CPVP3l9.jpg

[El Camexican]

A turbo charger may be your best bet. Build a small sealed air box behind the carbs and then mount the fresh air intake like a snorkel with the filter on top. The added power can't hurt.

Short of that some individual K&N oiled pod filters with Outerwear covers on them may be the easiest way to go if you can stay clear of water.

[wonderboy]

I've never thought about this problem from your perspective, but I have a couple thoughts:

1. Your looking for CFM = cubic feet of air per minute. I think your math is wrong. 200 cc is 0.007 cubic feet. If I use your 12,000 RPM (Waaaaay to high for this engine) keep in mind you only get 1 intake event for every 2 revs of the crank. So you move 0.007 cubic feet of air for every 2 revolutions of the crank. Just multiply 0.007 * 12,000 and divide by 2 = 42 CFM. At a more reasonable 8000 RPM, you would get 28 CFM.

2. The flow through a duct is not simply a fixed number. It will be a certain flow rate at a particular pressure differential. You won't get flow without a pressure difference across the duct. So, the flow rate of the factory intake system is not really something easily calculated without some flow analysis software or a flow bench.

[barnett468]

.

Your engine is not 100% volumetrically efficient so you should not use 100% efficiency to calculate your air requirements.

PS - Besides, you will never be able to use all the power of that engine in a 3 wheeler anyway so have less available air then it is capable of using won't make any difference.


PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR AND THE ONLY PERSON ON 3WW WITHOUT AN EDIT BUTTON OR A STAR :Bounce

[OldNo437]

hmm food for thought on the intake, yes I'm well aware of the multiple non real world figures, I'm never going to get a good answer as to the VE of this engine, so over estimate. as far as engine goes, im seeing 200cc and 1 intake event per 2 rotations, but its a 650cc engine with 4 intake events per 2 crank rotations.. I agree 12k is high, but using your formula, but with 650cc I get a result within 1 cfm of my first calculation, so at least i think I've got the formula right, so, so far with my err to high calculation at 137 at WOT which is unrealistic, as thats the engine as a straight no loss air pump with more than likely a chassis which won't utilize the power anyhow, so basically hook it to the backbone lol.. I used "rule of thumb" cfm ratings from exhaust pipes, at what ever they were, I know this isn't anywhere near exact, but I need at least something in the ballpark to go off of..

[OldNo437]

ok so, to make this more accurate anyone know a ballpark VE for a cb650? given its close to 100hp / liter I would say its pretty efficient. but guessing again.. also I know CFM is dependant on the restriction, any tips to make this more accuate? I think the bottleneck might come down to the holes at the neck.. but I really want to get a closer evaluation...