They offered no proof that I could see. Somewhere farther down they backstepped and admitted "some gains....but not as much as our plenum", and then followed up with some sort of attempt at electronic hypnosis: "you will buy our plenum...we are the best...power does not come cheap...you get what you pay for"

 

Not to throw a wrench in the works......but....
Did you also check out the angled spacer that Altered Atmospheres is working on???
It's design is closer to the Crawford concept of equalization of the front.
But then they have the problem of bolt /washer design on the angled top of the plenum.

 

...and most likely the slight differences between the Crawford and the Motordyne (with stock plenum) and the wedge-shaped spacer (with stock plenum) are the way the air flows due to the shapes of the plenums and the additional volume under the plenum. The combination of more plenum volume and the shapes will have slightly different airflow effects with each. I'm not sure which is better at evening out the airflows, but they ALL seem to be increasing it overall. Each cylinder would have to be tested individually, which is nearly impossible, but what the heck.

 

Yea, this seems to be the $25,000 question now, will be interesting to hear from both sides on why they decided on the design they chose, or maybe they didn't even consider the other after seeing some nice gains with what they first tried. It's quite possible that as long as you raise up the rear, the height increase in the front may not make much of a difference...

 

Uhhh...
I think you have it backwards...it's as long as you raise the front...the increas
e in the rear may not make much of a difference...

But I know what you meant .

 

VFRguy,

i think copbait as a thing for a lil junk in da trunk, which is why he said to raise up the back..

 

Copbait,

I did consider the angled approach but decided it wasn't necessary.

Pressure drop decreases with the square of the flow area. As the height above the runners is increased linearly, the pressure drop decreases asymtotically. And the pressure drop at runners (1 & 2) decreases at a much faster rate than all the others. Hence there is an automatic balancing effect. In theory they will still never be equal, but then again, they will be so similar that it no longer matters. So from a pressure drop point of view, the cirteria is met with a straight design.

From a cost point of view, an angled spacer will cost much more to make, and in the end, not really make much, if any, difference in HP. (At least that's how I see it. We'll have to see comparative dynos to really know.)

There is also an advantage of keeping the angle of the stock plenum the same. You get to keep your strut bar and/or your engine cover.

Then there is also the added internal plenum volume gained by keeping all sides raised equally. This helps to keep the internal pulse flow charecter smoothed out to a more consistant and continuous flow. Hence, less dynamic losses and less average pressure drop. Pulse flow can be advantageous but that gets really tricky to optimize.

Oh yeah, I almost forgot to add... Almost any plenum mod is going to be better than stock. There really is a flow restriction going into runners 1&2.

Tony

 

When I raise mine up, the room clears out.

 

Hehe you guys

Yea I must have gotten it turned around...I meant whichever side has the restriction, which I now know to be the front.

I do agree that some junk in the trunk is a good thing tho =)

 

Hydrazine, thanks for the dyno runs. Do you have the TORQUE data from those runs as well? I think that would be very interesting and important to see also.

Nissan (hopefully) spent a lot of time doing flow testing on their plenum, so it would make sense that using the existing design while adding some height to the plenum would take advantage of the Nissan engineering. If only the intake didn't make a U-turn into the plenum, that would improve airflow tremendously!

 

Here are the torque plots, sorry that the series is out of order.

The green line is from my previous dyno run on the same dynapack, but that run was in 4th gear. The rest are in third gear (automatic).

 

I'm eagerly reading this thread for developments, but I agree that the only way to convince some of us is to do a back to back to back (stock 3 runs, spacer 3 runs, stock 3 runs) comparison with no other variables. That would, without a doubt, establish gains. The simplicity and value of the mod speaks for itself, but I'd like to see what a mere 3/8" can do for the engine - with Crawford let out of the equation.

 

I agree--I'd like to see stock plenum, then stock plenum with 1/4" and then with 3/8", etc. (though you might have heard this request more than once). You can throw in a Crawford dyno run also. All of this would be excellent.

 

i'm going to do some dyno tests on my car. hold fast guys. will post results as soon as i get em.

 

Yea, im wondering about the A/F as well.. sorry to be at the end of the line .. but im curious!!!