Idf's......horns or filters??

[MIGHTY 8]

Have had rectangular filters on forever, and just wanted to gather thoughts out there on the horns.

[maytag]

see here:
http://www.fiatspider.com/f08/viewtopic ... 30#p157889

The info in that link is as empirical as any I've ever seen on the subject. It was forwarded to me from Jeff (sptcoupe) who has probably spent more time with these carbs than anybody SHOULD in a lifetime.

[manoa matt]

Also ditch the screens on top of the horns. They do nothing to filter, except a bolt or nut, and actually steal away the horsepower the horns added in the first place.

[maytag]

Also ditch the screens on top of the horns. They do nothing to filter, except a bolt or nut, and actually steal away the horsepower the horns added in the first place.

!!?? Matt, that's absolutely untrue. Sorry dood!
the ones I had on my horns (before I ditched the horns) will filter any particles larger than .012" (120 microns) and they are proven to restrict aiflow by less than 2% as long as you are between -30df and 350df

is 120 micron filtration enough for a daily-driven car that get's oil changes every 4k miles? nah. but for a "toy" or a race car, that get a high level of maintenance, 120 micron is WAAAAY sufficient.

[manoa matt]

Sorry dude, those are not my sentiments, rather what I have read many, many, many, many, many, many, many, many times on the Guy Croft forum and in his books.

Just look at the ram pipe chart. The radius of the ram pipe is CRITICAL to the flow and subsequent HP gains. Bigger the radius = bigger gains. If your horns look like #6 and you stick filter screens on them, you end up with a #5, maybe even a #4.

The filter screens basically eliminate any radius, and cause turbulence.

[maytag]

Just look at the ram pipe chart. The radius of the ram pipe is CRITICAL to the flow and subsequent HP gains. Bigger the radius = bigger gains. If your horns look like #6 and you stick filter screens on them, you end up with a #5, maybe even a #4.

well... that's where I can't argue with ya... 'cuz you are absolutely correct. I knee-jerked, and responded to what many people assume is a screen-door filter, when in fact it is much more than that, and I've used them successively on MANY vehicles. You yourself made a claim that they "filter nothing other than a bolt or a nut", as I recall....

But when it comes to changing the shape of the horn, (and therefore airflow) you are absolutely right on the $$

[leeputmanjr]

I have horns on my IDF's....with the screens.

I was paranoid about sucking in loose nuts, rocks, dust, debris, bugs, birds, and small children ...

The one thing I'll say about the horns ... they certainly seem to increase the IDF noise! If you like that, you're good-to-go

Another note - my '74 Spider with it's 2000cc motor - with the the curved-top RamFlo filters, I can fit a smooth hood, with no issues. With the horns & screens - I had to bump-up to a small-bump hood. (Get it? 'bump-up'?)

[ward00]

Hello - the link to the empirical data in this thread does not work. Can anyone opine on what length horn / velocity stack is optimal for dual IDFs on an 1800 cc with street cams and headers? Thanks

[cormac]

Ward -

it is an old link the f08 (in link)needs to be changed to f15, tip for old links that any might have, seems to work for me

or here is link corrected
http://www.fiatspider.com/f15/viewtopic ... 30#p157889

[ward00]

Although the link you provided works and points to a post with a photo of a cat, the post or clicking on the cat does not provide any info about the horns?

[cormac]

I just told you how to get to the topic mentioned by another...no idea if the info original poster said was there, after all there are 6 pages and there is info about horns...you might have to look thru the pages

[ward00]

Thanks, google says that longer horns are better for low end torque and shorter for hi end torque. Once I get everything tuned for no stacks, I'll try the horns to see if low end torque can be improved with them.

[ward00]

I found this formula for determining velocity stack length vs optimal power - its probably for a conventional engine, but I wanted to see what result the calculation will provide

L = 1100(T)/R

where L = length in inches from valve seat to the end of the stack
T = # of degrees the intake valve closes After Bottom Dead Center (ABDC) - 75* max
R = RPM @ desired power range

Anybody have a ball park figure what the distance from the valve seats of a 1756 head to the top surface of a 40 IDF carburator with no stack attached is (ballpark is ok)?