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new air filter=interesting effect

Hellbent

Hellbent

NAXJA Forum User
Location
san diego, california
thought this was kind of interesting...
among the several other small mods i've done to the renix,(5.0 injectors, high altitude cps, etc, etc) i put on a 59.5mm bored-out tb on along with the rusty's tb spacer. now this tb was advertised as "no whistle". i don't care if it whistles, sings and/or dances, so long as it flows more air. i put it on, and if it did whistle i never heard it. so the other day i replaced my paper air filter with an accel kool blue filter(made by k&n's european division-it's a blue k&n), now i have a fairly prominent turbo-like whistle under medium loads between about 1500-3000rpm or so. would this be because the new filter flows that much more air? or does it just not muffle the noise like the paper filter did?
 
it's just a drop-in replacement filter in the stock airbox. i think the new filter just doesn't muffle the intake noises as much as the old paper filter. the exhaust rumble at idle is somewhat louder now also. the whistle is quite funny, it causes people to stare when i take off from a stop.
 
your flowing more air, causing the whistle and the louder exhuast note.
paper or whatever filter it is, isn't going to muffle noise that well, the sound is coming from the TB/S not the air box anyway. sound may pass back to air tube, but a filter won't muffle it that much. the sound is just your TB breathing better. My TB did the same when
I bored it out myself, I took it back off and polished down any sharp edges at the bottom of it... no more whistle.
 
thanks, that makes sense. the jeep seemed a little peppier; not much, but noticeable. i thought about pulling off the tb in order to round off the iac window and assorted sharp edges, but i don't really care about the noise. in fact, it's pretty amusing.
 
mine sounds like compressor surge/ blowoff valve when it shifts from 2nd to 3rd...... its just pullin a lot of air, which is nice
 
maybe a duck call? that would turn heads!
 
Food for thought: Just how can a bored-out TB flow more air than a stock TB at any other throttle position than wide open? If, for instance, 1/2 throttle position of stock TB equals 2000 RPM at 70MPH, how could the bored-out TB draw any more air at 2000 RPM? The whistle and other noises you here, in my opinion, are due to surface angle changes brought about by the boring, and by the filter change, not from more air flow.
 
xjbubba said:
Food for thought: Just how can a bored-out TB flow more air than a stock TB at any other throttle position than wide open?.
Click to expand...

3.14159265358979323846...........pi is your friend. area of a circle and all that.
 
It's because the filter flows more air than the Jeep needs. There is some sort of turbulence/ vaccum thing going on... but I'm no engineer.

I do know that I run a cone filter on my tow rig (Dodge 5.9) and it used to whistle. I just installed a Magnaflow muffler in place of the stock muffler, and haven't heard a whistle since. Strange, but it makes sense.
 
as a test i put the paper filter back in......lo and behold the whistle nearly disappeared, it becomes very, very faint. put the hi-flow back in....hello whistle! weird.
 
I have a spacer but not from rustys. I think I got a coupon for $50 from summit racing and bought the spacer from them. Only thing I noticed from it was a whistle at about 2500-2900 rpm. I'm kinda glad I didn't pay full price for it. I'm thinking I would be better off without the spacer and boring my throttle body at home.

For now, I tell people it's my turbo. ;)
 
"3.14159265358979323846...........pi is your friend. area of a circle and all that."

Just because the TB can accommodate higher volume flow, doesn't mean higher volume is flowing. The amount of air the engine needs is not determined by the TB size. It seams that the only time the additional, POSSIBLE, flow from an enlarged TB would be realized, would be at the point the engines needs exceeded the stock TB's ability to flow enough air; this is generally only at WOT.
 
xjbubba said:
Just because the TB can accommodate higher volume flow, doesn't mean higher volume is flowing. The amount of air the engine needs is not determined by the TB size. It seams that the only time the additional, POSSIBLE, flow from an enlarged TB would be realized, would be at the point the engines needs exceeded the stock TB's ability to flow enough air; this is generally only at WOT.
Click to expand...

perhaps i'm failing to understand your logic. an iac motor works this way, no? at any throttle position, even wot in some circumstances, there is a restriction(high vacuum) under the throttle plate. bigger opening = more air flow all the way up to wot, regardless of throttle position. if the motor can pull all the air that the head can flow through, say a 60mm tb, then a 62mm tb would be of no benefit in terms of max airflow at wot. but it would still flow more air at 1/4 throttle opening than the 60mm opening.
 
if the motor can pull all the air that the head can flow through said:
That's my point. I do agree that more air would flow at the 1/4 throttle opening with the larger TB. Increasing the TB's bore does effect more air flow with respect to the "skinny pedal" movement--making the engine more sensitive to throttle position, but more air than the engine needs for a given load and RPM does not occur with a bigger TB. I don't think a stock 4.0l Jeep engine will gain meaningful horsepower if the only modification is boring out the throttle body; however, I wouldn't argue that point because I've not spent much time considering performance mods for the 4.0. It would seem that head work in the area of valves, cam, exhaust, along with a better intake manifold and larger injectors would be required to increase the need for additional air flow, and thus, a larger TB.
Click to expand...
 
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