Thread: Radius Cut Vs Velocity Stacks for intake. Are there results anywhere?

Has anyone actually made back to back testing between the two? Does that actual lip on a stack REALLY make a difference? Motor is a stock 20V with N1 cams and Cam Gears. Im in the process of putting together an excessive Plenum build for my 20V and wondering if making stacks/machining them on a bottom plate actually does what we all think? Obviously it is much cheaper to just port a radius on the bottom plate. It seems to work for a lot of peeps on here. I understand stacks are needed for an ITB set up whether its a plenum or open build..but what if it was just a standard plenum and not ITB?

Thanx in advanced everyone.

Charlie

Radius Cut



Velocity Stacks

This is a good question not getting any love of course. If there is one thing known it adds to runner lenth....good for a street driven vehicle...maybe the stack it self only provides a way to tune the manifold to make maximum power at a specific rpm, neither is superior perhaps.

The only test that springs to mind recently is 'almeragt' with his custom xcessive plenum with stacks.
The results arent back to back against a regular xcessive plenum so its not a direct comparison. Non the less, the results showed good gains.

I have no personal testing to offer yet, just some known theories and points to consider:
The raised stacks add taper to the runner.
The raised stacks have better positioning to draw air in all directions with less friction, as opposed to dragging air along the plenum floor.
A big throttle body is required in order to see the gains on the N/A intakes.
The intake tube length and size affects power output.
Radiused plate floor entry is preferred for boost as the engine is force fed and stacks are an obstruction.

In what way do they affect? Longer or shorter is better?

It seems the larger 4" diameter intakes like the pipe as long as possible.

I have made more power on the hand made radius cut than the elevated velocity stack on a custom manifold not back to back test.
All I can say its get the plenum kit for the 20V intake manifold and get the plate and runners ported as much as possible on the plate side to remove the reverse taper and you should see gains from 10-15 whp keep intake as long ans straight as possible!!!
I would not go any bigger than 3.5 inches on the intake piping!!

This is pretty much the insight I have as well. No testing, but if you plot the pressures around a horn during the intake stroke you'll find the horn will draw air in from below itself and around just as easily as it does directly in front. Because of this, it makes sense to design a plenum around a horn that lets air come in from all angles, even below. So goes the theory anyway.

If you don't have the space around the horn to make a plenum like that, then you will be limited and a radiused plenum floor starts to make more sense.

Interested in the results, if any?

Payu, thankyou again and thankyou for everyone's responses as well. I was advised also that if i could get my hands on a VET bottom runner/intake, it would be more beneficial than the 20V one due to the larger diameter oval ports. Still doing my research. Like Ben Fenner and Sr20-Autech..the theories behind the stacks are what make me consider doing this. Unless someone does some testing on both in the near future, i will likely try the radius cut/port first. If i do come up with some more extra $$ and my motor isn't too beat up, then ill try the stacks as well and post my findings. They are STILL, IMO though, not an easy and cost effective test because when you do the stacks, you still have to factor in stack diameter, height, and other things to consider to be most effective with MY motor. Man..this NA game really isnt cheap but man i love doing this.

i agree with many of the opinions here. for me, the key to making the best power is the "right" formula to make both the exhaust and the intake work with the resonant frequency's offered by the bore/stroke of the motor, and the duration and lift of the cams. what that is i have no idea...., but i've been looking at whats made the best numbers, especially with n1 cams, as they seem to be a "constant" in ve builds (lol). jamie marsh has stated the ideal intake length (is that 2nd or 3rd resonant? nfi) of an intake won't fit in a B or N series engine bay, so we are compromising and looking at the lesser ideal resonant lengths that work. he say's ideally 7.5-10 inches (intake length). another prominent guys says 8-9 inches is good. i figure its there somewhere. jamie's just finished an xcessive n1 intake for me (9inches). Almera GT's intake is (i figure) about 7-7.5inchs, his torque peak is a pretty high 6700rpm. If the intakes near banging on the firewall, its a start.

the world needs more Payu's... just tells it how it is, and backs it up with the 1/4 mile time slips.....diamond.