Topic: "Uh, did you toss the airbox?"

[Gerry Hull]

Have been trying to make best decision on air filtration/induction for a new build of a 550. I pulled out the airbox/plenum and marveled at all the free real estate I had now where I could do things like bring the electrics inboard, put in an oil cooler or tank etc.

I am glad I held onto that airbox, though. My gut sense is that this crappy looking piece of plastic has an extraordinary amount of engineering in it, and a power drop by replacing it with filtered, screened or even unscreened velocity stacks is likely.

Putting the whole issue of filtration and top-end longevity aside for a moment, pretend it is not an issue (it is, but the consequences of choices is already well-known)

What I am most curious about iis the effect that air temperature at the intake opening (wherever it is) has on power, and how much. Fortunately there are a number of science articles online, I've been scanning them since I woke up.

One summarized exactly the sort of equation I am looking for: "every 5 degree rise in temperature will result in a 1 percent drop in power in internal combustion engines". Other articles may hypothesize a different equation, but this one seems sensible enough to use as a starting point.

A velocity stack will be drawing from turbulent, preheated air directly behind it. The airbox with the intact side snorkel will be drawing from air that is probably as close to ambient temp as you could get.

My guess is that the temperature difference is more than enough to justify keeping the airbox/snorkel. If ambient temp is 70, and temp right behind a stack intake (with or without pod filters is 100, that 30 degree rise in intake temp equates to 6 percent power drop, or about 2 hp.

Setting aside that method of computation, I believe there would be value in knowing the temperature difference at these two points, as measured by real people on real bikes.

It's one of the few things that we could establish as near-certainty, with nothing needed but, say, 5 or ten guys going for a ride with two cookie thermometers. Anybody out there curious to know?

Other researchers may have

[web]

Given where the OE airbox draws, blocked by the seat, side covers and all, I doubt it gets much cooler air than stacks.

That may not have been a design goal either, if you consider cold climates...

[Tracksnblades1]

Perhaps the OEM airbox was designed around Helmholtz's findings.....

[Gerry Hull]

It's something I'm curious about. I am not sure myself which option is best for air intake. Automakers go a long ways to have the air intake as far away as possible. Does it make a meaningful difference on a bike where air is drawn in? I don't know. But a cookie thermometer would be more valuable than any formula or scientific paper. Unfortunately I don't have a rolling bike, or I'd find out myself.

Perhaps I'll just use 4 big shop vac hoses, one clamped to each carburetor, have them run out of the frame and up my back,  bungee them to the top of my helmet. Do you think re-jetting would be needed?

[Deltarider]

Perhaps I'll just use 4 big shop vac hoses, one clamped to each carburetor, have them run out of the frame and up my back,  bungee them to the top of my helmet. Do you think re-jetting would be needed?

You mean like ram air style? I'd like to see a picture of that. BTW, what is a cookie thermometer?
 

[Don R]

   I wonder how much automotive design is based on scientific theory and how much is just what is known to have worked before.   
  I read a Bonneville Salt Flats team was experimenting with an automotive air conditioner based intercooler to reduce the intake temp. But, I never heard any more so it's either a secret or it didn't work. K&N did a lot of work on air scoop size and found in testing that a large opening causes more drag than the small supercharging effect produces but no one believed it and few racers bought the small opening scoop.  I put a pressure sensor on our dragster scoop and at 175 mph it reads about .5 psi

[Gerry Hull]

Ok, so, dragster scoop grafted onto helmet-top shop vac snorkel assembly. Cookie thermometer stuck in ass for temperature regulation?

DONE.

[Don R]

 Sounds right, please get photos. 

[754]

5 degrees causes a 1 percent drop after what temperature.  What is optimum  ?

[Gerry Hull]

it was pretty straightforward, probably derived from laws of gas temp, pressure, density. Which are all basic linear algebra equations if I remember right. The secondary effect on emissions and soot is where it gets complicated, debate-ridden.

Power-wise, drawing from the coolest air possible is a certain win, always results in a) free horsepower, b) greater resistance to detonation, and 3) a cooler running engine.

The question is how much. Is it worth rethinking how I build my basic air intake system.

F1 designers will go to absurd lengths to have their intakes out of the oven-hot slipstream of air coming off the cars ahead of them. I'm not trying to design an F1 car, just a basic intake/filtration system for a 45 year old motorcycle. But since the same rules apply- but how much? I like facts.

Any two thermometers that read up to 120 degrees would provide positive confirmation. Tape one at the snorkely nerdy oem intake, and tape the other near the carb openings, near the end of those little rubber stacks, but in front of the airbox. Ride speedy. While you couldnt check them mid-ride, those mercury thermometers are so sluggish I don't expect the reading would change much in the ten seconds it took to pull over and check it.

I am barrels of fun, yes?

[Don R]

 True, my carbs are drained and there's salt on the roads around here, so I ain't the guy.
  I would think something like a V max air intake might be the nutz. Both sides, out in a clean cool air stream. I was just noticing the short air filters on my Weber carbs. some sort of a short air horn might help them, if it didn't close it off too much. I think K&N made the stub stack to sit on a Holley carb. it was supposed to be worth 10% more flow.

[Gerry Hull]

I'm going to make self nuts if I noodle over this anymore.

Solution: keep the plenum section and the little rubber velocity stacks. Go to O'Reilly's get K&N filter from the "2Fast and Furious Wannabe" shelf. Adequate airflow assured. Plenum blocks direct heat from engine.

If needed, I can stuff area with icebags. FINISHED.

[754]

 I ask because we have ice raced a 750 in 0 degree F weather,  and it did not seem to pick up significant power..

[desertrefugee]

  I would think something like a V max air intake might be the nutz. Both sides, out in a clean cool air stream.

Conceptually, yes. But the Vmax scoops (at least the first generation ones) are purely decorative.  I have had three first Gen Vmaxes over the years.   Loved each one dearly.  There was banter in the Vmax circles about plumbing the intake tracts into the scoops, and I think a couple of guys actually did. But, I don’t recall any grand revelation with regard to increased performance. 

[vik351]

Interesting what Hondaman has to say on this subject. to quote him...

" Airbox: Using the OEM box, I would make a long tunnel to the rear of the bike and breathe down a tube to feed the bottom of the box. I've outlined those reasons in other posts"

Wish I could find the outlined reasons in the other posts... did a search ... 

vik...

[Gerry Hull]

The important number is not the ambient temperature but the degrees difference between ambient temp and the temp of the air that the intakes are drawing in.

Hondaman's ductwork would bring that temp difference down to near zero, which is the ideal.

In real life, the higher the temp difference, the greater the hp loss from drawing hotter air.

There are ez install lightweight ducts that can be dirtectly mounted to the plenum/airbox in the same "Fast n' Furious wannabe" sections of auto parts stores.

It's not likely I'll ever know the exact gain. I could estimate it once I had a rolling bike and could measure the temp difference myself. Perhaps it means only .5/ 1 horsepower. No one could feel that. But three or four little gains like that start to add up.

A 20 degree temp difference would tell me that a velocity stack set up, with or without screens and pod filters- is a bad decision.

I love the 550 engine as it is- the power range, its look and feel, its reliability- so my aim is in making it efficient and reliable as possible, and aim for a 4-5 hp increase as a secondary benefit.

This three dollar adapter opens up induction/filtration options to anything I want- either more ducts or any 3" inlet auto filter I want. They have all kinds of ducts and adapters that fit right on.

Say, do you have photo of that Vmax snorkel you could put up?



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