fuel injection intakes

[hontrx265r]

With all this talk about fuel injection and my curiousity of intake design theory growing. I thought I would present some questions for you guys to ponder and comment. So the last thing I need for my crf is my intake/airbox.. Basically to not get to lengthy with this, I'm trying to decide... should I build a traditional airbox setup (open box with whatever intake tube fits) Or should we be a bit more scientific with it. By building a correctly tuned runner, plenum intake to optomize intake volumn/pressure? Ive been doing alot of reading and basically with these items built properly up to 130% flow can be obtained at a desired rpm range by tuning runner length/taper, and plenum size creating basically a forced air effect. My real questions is, is this effective on an engine of only 450cc displacement? I'd really like some opinions on this.. The only intake I've seen that actually uses this theory in our industry is on the cannondale atv... Yet people still put a straight velocity stack and filter on the throttle body for gains? Why? Again that will give you best PEAK hp but is that really where the power is needed, or does it make a happier dyno guru?

[C41Xracer]

it would probably help to have something designed correctly, air velocity helps alot too. I dont thhink a clamp on velocity stack and filter will cut it but i could be wrong

[hontrx265r]

I'm pretty much set on building a runner and plenum box system. I already have it sketched I'll probably put it in cad tonight. Maybe I can post a pic. I am really just wondering if its going to matter due to the engine size? I know it can't hurt. But I just want to know what people think about the idea vs a traditional airbox. Not really a debate on which to use.

[witech]

The intake boxes that came on the cannondales were designed to make the intake quieter and locate the filter up front . It did a great job. The price paid was a 4+ horsepower loss over a pod filter with a properly designed intake funnel. The power gain was everywhere. I did a dyno test of intake runner length as well and found shorter was better.

[pinitatv]

Hey John (WITECH) when did you start hanging out in the hybrid section??

I think you really have to take a look at the space you have to work with, the 50mm throttle body is hugh so you are going to have a tough time routing a decent sized intake track to it. I'm not sure exactly where the throttle body sits but it won't be easy fitting something decent between the left frame rail and the rear shock.

To answer your question on will it make a difference, YES. The 2 things that matter most exhaust and intake, if done right it equals HP. Keep in mind Honda has spent a lot of time developing the intake and exhaust on the new motor. I've personally found with the pre FI CRF motors the best intake was from the bike but it won't fit in a quad so the next best thing is something reasonably short with a good size filter. Most of my experience is with a taper bored carb and a large tuned bell. With the tuned bell I was told it didn't matter how I got the air there as long as it wasn't a smaller dia that would create restriction. The bell would do the rest.

97rocks and I spent a good amount of time on the dyno testing exhausts and intakes on the early crf's you should hit him up.

[hontrx265r]

witech.. yea you would know about cannondales and although I do know that it did make more power with an open filter (had one one my walsh dale) on those units I believe there were limitations on intake because of going around the stem. Pinit. I totally agree that they have done their homework at honda and looking at that intake and box is what really started to get me thinking. Its not as it appears on the outside. On the outside it looks like a quad (big funnel basically) But inside it is a runner that is dimensioned properly that drops into the box (ie. plenum) However inbetween that runner and plenum is a filter and that is what I would think would be the problem. It would seem to me that the filter would have an affect on those refracting pulses going in and out. I want to let that be a clear passage way and install my filter on the outer portion where the air is drawn into the plenum .. Like I said I'll draw it in cad and post it up. But I'm sure your getting the idea. Of course I can't put a stack and filter directly on this throttle body in this application not an option. I am however taking the twist out of the laeger subframe rail that is a bit of an intrusion. So the runner will be clean... no dimples dents or weird stuff.

[97Rocks]

Yeah, I'm on board with pinit. Basically what we found is the left hand frame rail and shock is in the way for what the motor wants. Shorter seemed better, but you are restricted by the frame rail. Anyone who tells you just put on the ole pvc pipe adapter to a jumbled up filter from a 84 pinto should be slapped. We spent time on this and basically, If I could build a frame.... I would design the intake part first!! PM me ifn you want any suggestions/specifics on what we came up with.!!!

[jcs003]

i dont know alot on the subject. but, what i have discovered in my research in adapting an EFI for a 250r is: length and diameter of intake tube have an effect on the tune. but i have learned that with the mapping software/systems available and with a savvy EFI tuner you can build your map to suite your set-up. wheter it be stock modified or custom.

this sound like things you already might know, but it couldnt hurt to state.