Intake tuning for your quads

[rthy]

I have written a decent size article with all the info from here and more, here it is:



I am interested in peoples feedback

[SpotterOne]

<div class='quotetop'>QUOTE (Sam_Q @ Jan 9 2008, 11:13 AM) </div>Just read it, that is excellent.

The only suggestion I have is that there isnt much information of the airbox principle. One of the major failings of the standard plenum on a single throttle body 4AGE is that it isn't big enough, and the engine runs out of air. Most of the airboxes in the pictures aren't much bigger (if any), which would seem to me like it sort of defeating the purpose? Also, there is some wisdom that suggests that the wall directly opposite the end of the trumpets should not be exactly square to the trumpets to prevent additional resonance. I don't know how much difference it makes, but its out there.

I'll use some of that data soon, when I start making my bent trumpets.

Leo

[rthy]

<div class='quotetop'>QUOTE (SpotterOne @ Jan 10 2008, 09:26 AM) </div>Just read it, that is excellent.

The only suggestion I have is that there isnt much information of the airbox principle. One of the major failings of the standard plenum on a single throttle body 4AGE is that it isn't big enough, and the engine runs out of air. Most of the airboxes in the pictures aren't much bigger (if any), which would seem to me like it sort of defeating the purpose? Also, there is some wisdom that suggests that the wall directly opposite the end of the trumpets should not be exactly square to the trumpets to prevent additional resonance. I don't know how much difference it makes, but its out there.

I'll use some of that data soon, when I start making my bent trumpets.

Leo
[/b][/quote]

thanks Leo, you have some interesting points, but apart from the section where I say the rough rule is that the airbox should be equal to the engine displacement I was unsure what elese to add, theres just too much contraversy in that area. Also your sujestion about the outer wall of the airbox being parallel to the opening is something I havent ever heard of it and I never thought of. I would take an eductated guess and say your right on this one though because even though theres nothing to back it up it makes sense. I just had a brain wave, I have a book that has some good information and a diagram of what is ideal, I will re-read it and write my own version of it with my own diagram. Thanks for the tips

[SpotterOne]

<div class='quotetop'>QUOTE (Sam_Q @ Jan 10 2008, 03:11 PM) </div>Cool. I should probably clarify what I MEANT and couldn't get out in print!

What I was thinking was that the standard plenum/intake is probably in the region of 1.6lt, which fits in with the stated ideal, but I think your statement regarding "bigger is better" is more correct. Dyno graphs of 4AGE's with a small amount of help in breathing (ie extractors) often show a dip at the top of the rev range, most likely due to it running out of air in the plenum. That is with a standard single throttle body, so the theory stands that with all the extra breathing from the ITB's, more air is required, and hence and even BIGGER airbox being required.

I dont know how much the effect of the perpendicular wall theory affects the standing waves, but if it isnt any harder to put a 5 degree angle on it, how could it hurt? The theory makes perfect sense to me from when I used to play with subwoofer boxes (MANY years ago!) where you would purposely change the angles to stop the box from "booming". Those waves weren't standing though, and a whole lot bigger, so I don't know how relevant it is.

[rthy]

yeah I hear you, I will try and write something in soon and that diagram I was talking about

[ae86rally]

So after reading this I thought I might post a pic or two of mine


pics in next post


they are nearly 350mm long and any on who thinks is doesnt rev better come for a drive. it has a rev limiter set at 7800 rpm for longevity of the motor it would rev way past it easily, you don't even see the shift light in first gear!!.
quote from the guy who had them designed

o Inlet manifold rocks. Currently in long trumpet mode (13.9inches from valve head) for mid range torque. Shorten to 12” at the trumpet end for 10%+ more power. But it simply harder to drive with short trumpets made easier if you have a different diff ratio. Long trumpets = 4.5K – 7K power range (as per the cam specs – 288 deg.duration, 7.5mm of lift). Short trumpets: 5.8K – 7K+.

edit - current ratio 4.875:1

to drive the car, its a dog below 3000 understeers, then starts to get going but when it hits @3800 it transforms, it takes off with a kick (I used to drive high powered 6 and 8 cylinders before this) the balance and steering of the car transforms into the easiest car ive ever driven, change to second at @7600 (no need to rev it any harder but you could if you wanted to)and it accelerates just as fast, have run out of road before I've had a chance to wind it out in third. custom close ratio box helps too.

[ae86rally]

[rthy]

interesting...

thanks for the pics and info

[gunbz-r]

another option for bell mouths could be jelly moulds, havent tried it but alot of size and degree of roll on the moulds make it worth while to look into.

[rthy]

I will have a look at that, thanks for the tip