Snorkel sizes to motor size?

[nicbeer]

Hey,

Just wondering if there is a rule of thumb for making a snorkel for size of snorkel pipe for engine size.

Eg: i am thinking of putting a 3" system for the snorkel for my zook. 1.3/extractors/exhaust/cam. std carb for now.

cheers

nic

[cutzook]

i have 3 inch on mine. works really good. i am still running standard motor with extractors and thats about it

[CHOPS1]

Hi nicbeer

I just put a 3" pvc one on mine on the weekend, Works great.
Unless your going to plumb it straight into the airbox making your own hole, i dont think it matters. Have a look at mine on the suzishop forum, put pics up lastnight. It gets restricted at the original intake anyway and there is the air filter which only lets so much air through.

Chop

[J Top]

The size of the filter box inlet has little to do with the size of your snorkle.
The longer the intake the greater the restriction and the harder to breath.
3" should easily feed 2.5 litres, depending on number of bends, length of
runners etc.
J Top

[CHOPS1]

Correct me if i'm wrong, but a pipe that is 3" at one end and 2" at the other has restriction albeit small as opposed to a pipe that is 3" at both ends? Its like blowing in a witches hat!

Chop

[nicbeer]

was thinking maybe a bit of a turbo effect as it will try ram the air through the 2" outlet.

Thinking of changing the inlet on the airbox as well. gonna try anyway.

cheers

[sudso]

was thinking maybe a bit of a turbo effect as it will try ram the air through the 2" outlet.

I would have thought the same. I mean, on my Rodeo V6 the air filter inlet is facing the inner guard at the top of the wheel arch with not much gap between the two so doesnt have cold air induction like a lot of cars.

You would think that a forward facing air inlet in the open would improve air speed through the whole line over an inlet thats cramped up in a nook and cranny of an engine bay trying to gasp for every cubic litre of air around it.

[Screwy]

3 inch for the V8

[chimpboy]

Ram effect is not going to be significant in any fourby I've ever seen. It's going to be insignificant until you're going very, very fast.

See:

(nb an inch of mercury is two psi so 1.0" Hg = 0.5 psi)

I was really hoping that someone would post up a good rule of thumb for snorkel size but nobody has!

There is a lot of information about air intake size unrelated to snorkels ie the throttle bore, and I'm kinda thinking that would be as good a rule of thumb as any for vehicles that, let's face it, are not really aiming for formula 1 engine tuning. BTW I am not saying the following is correct, it's just an idea since nobody else answered with any numbers!

I think it's sufficient to look at it in terms of horsepower, since any motor making the same horsepower will want basically the same amount of air - so engine capacity isn't that important in itself.

So consider that a 900hp F1 car has an air intake of 20-25 square inches which is equivalent to a 5" or 6" diameter hole. I'm thinking that a particularly grunty fourby might make 300hp, which suggests it would want about 8 square inches of air intake, which is only an approximately 3" snorkel.

Extrapolating from the F1 car and some other cars I could find figures on, air intake of a given diameter would be good for horsepower as shown below, before starting to interfere with power. I think the length of the snorkel matters, and this theory ignores that. I don't know how much it would matter.

If someone with more engineering skillz can tell me this is terrible reasoning that would be great. In the meantime I plan to use this theory to make me feel okay about having a 3" snorkel:

Code: Select all

Dia.          Area         Power
1"             0.8 sq. in.  30 bhp
2              3.1           120
2.5            4.9           190
3              7.1           270
4              12.6          480
5              19.6          750
5.5            23.8          900

I dunno what kind of power the 1.3L zook motor makes but I really doubt a 3" snorkel would create problems.

What do you all think of this approach? Another approach would be to consider the area of the inlet valves that are open at anyone time and aim for maybe double that area for the intake. Of course nothing would substitute for actually testing on a dyno with different snorkel sizes. And then there's the idea of a tuned length snorkel where the pressure wave from the last cylinder hits just as the valves are opening on the next cylinder... but anyway...

Jason

[nicbeer]

Nice maths.

I was hoping for something simple as well.

Mainly going for a 3" as it is the esiest ram head to find.

cheers