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

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MIGHTY 8
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Idf's......horns or filters??

Postby MIGHTY 8 » Tue Oct 02, 2012 6:44 pm

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

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maytag
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Re: Idf's......horns or filters??

Postby maytag » Tue Oct 02, 2012 6:49 pm

see here:
http://www.fiatspider.com/f08/viewtopic.php?f=5&t=14494&st=0&sk=t&sd=a&start=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.
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

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manoa matt
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Re: Idf's......horns or filters??

Postby manoa matt » Tue Oct 02, 2012 8:16 pm

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.

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maytag
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Re: Idf's......horns or filters??

Postby maytag » Tue Oct 02, 2012 8:32 pm

manoa matt wrote: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! :wink:
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.
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

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manoa matt
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Re: Idf's......horns or filters??

Postby manoa matt » Tue Oct 02, 2012 9:53 pm

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.

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maytag
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Re: Idf's......horns or filters??

Postby maytag » Tue Oct 02, 2012 11:08 pm

manoa matt wrote: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.... :wink:

But when it comes to changing the shape of the horn, (and therefore airflow) you are absolutely right on the $$
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

leeputmanjr

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

Postby leeputmanjr » Wed Oct 03, 2012 12:15 pm

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

Postby ward00 » Mon Mar 26, 2018 12:54 pm

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
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cormac
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Re: Idf's......horns or filters??

Postby cormac » Mon Mar 26, 2018 2:00 pm

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

Postby ward00 » Mon Mar 26, 2018 3:31 pm

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?
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cormac
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Re: Idf's......horns or filters??

Postby cormac » Mon Mar 26, 2018 7:03 pm

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

Postby ward00 » Mon Mar 26, 2018 7:26 pm

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.
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ward00
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Re: Idf's......horns or filters??

Postby ward00 » Thu Mar 29, 2018 7:44 pm

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)?
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