[mobiuslogic]

So like the title says, I couldn't sleep and started think about volumetic efficiency and more importantly, how to improve it. Now the volumetric efficiency is of course the ratio of manifold pressure to absolute pressure. The piston will always take in the same volume of air, but the pressure relative to absolute (ambient) pressure dictates the volumetric efficiency.

And so I thought on....with our V6 engines, 2 intake valves will always be open on the intake cycle at the same time. Thus the intake charge will always be split almost equally in half. Now if the pressure has already dropped in the manifolds due to obstructions like the air filter, MAF, throttle body, and of course the mythical e-ram

, then the best way to increase VE is to relieve these obstructions. But how much is needed? And that became the basis of my though process for the half hour preceeding this.

Now the intake valve head has a diameter of 40mm, so unless you go to bigger valves, 40mm diameter is the best possible size to hope for for the intake's diameter. 40mm diameter has an area of (pi(r^2)) which is (3.1416(20^2))=1256.6mm^2. Double this for the 2 valves open at a time which = 2513.27mm^2. So logically, we should have an opening and all openings to the upper manifold with an area of 2513mm^2. Now if we work this backards and divide 2513 by Pi we get ~800 and then take the square root and we get a 28mm radius, or 56mm diameter. Pretty damn close to the stock 55mm design.

Now all this makes me wonder. Why do our stock intakes have what seems to be a big restriction when they are really just the right size? Why does Jason's intakes at 80mm and an area of 5026mm^2 give such big gains, or do we even know how big exactly the gains are? Do his intakes actually increase VE or do they just make the engine work easier?

And it's now that I realize that all this has really been 1 long incoherent rambling on due to the fact that I really just gotta stop drinking soda so damn late. And I guess to answer your question Patrick from quite a while ago:

QUOTE

Do you sit around your bedroom trying to think of the most whacked out way to squeeze 2hp out of your vulcan?[/b]

I guess it's apparent that I really truely do.

-mobiuslogic

 

[mobiuslogic]

Because it's a V6 there is always going to be 2 valves open at the same time, each on a different cylinder and at a different point on the intake cycle. Regardless, it was late but I got the answer I think I was looking for in that:

"it's better going with a P&P on an optimum sized intake than going to a bigger sized intake or TB"

Like I said, it was late. Oh well.

-mobiuslogic

 

[mobiuslogic]

Originally posted by Patrick Norris@Jan 16 2004, 08:49 PM
valve overlap but not 2 at the exact same time.

Thats the term I was trying to imply. Yes 2 valves will be open, but correct not at the sametime. However it will still be drawing air in threw 2 valves at all times, regardless of what point of the stroke they are in. And I do agree the 55mm TB and MAF are still too small.

-mobiuslogic

 

[mobiuslogic]

QUOTE

drank a few beers[/b]

I'm only 19, but what dad doesn't know won't hurt him.

QUOTE

Anyways, it is people like you that have invented so many goodies that are present in our everyday life[/b]

I'll take that as a compliment, I think...Heh.

QUOTE

Hmmmmm,  450HP,  500 TQ,  150 MPG  on 87 octane......[/b]

I'm working on it.

:zoomsmiley:

Ok but seriously. Yeah, I thought about it some more and the area of the 2 valves compared to the MAF is right on. However because of casting irregularities, the intake velocity is reduced. A port and polish should be fine because the engine doesn't have to work against the irregularities. However going to a larger MAF/TB will slow down the air coming in. So the real question is which upgrade gives the most power:
1) P/P upper and lower intakes with stock MAF and TB
2) Upgrade MAF and TB only.
3) P/P and bigger MAF and TB

Of course logic says #3, but are they really necessary after the P/P. I could see them being needed with forced induction or even N2O, but are they really a big deal after the P/P on a NA engine?

-mobiuslogic

 

[mobiuslogic]

Originally posted by Bob Gervais@Jan 17 2004, 06:16 AM
The stock Vulcan MAF is 65mm. As you said before, the stock TB is 55mm.

No wonder I can't find a 55mm MAF adapter. Thought they were the same size.

-mobiuslogic