Intake Manifolds - Page 2

BlackJack · 06-24-2010, 06:05 AM

you "can" have a 3500 upper and 3400 lower, but if you're going ported on that 3500 and stock on the 3400, well..... it seems like there would not only be a bottle-neck so to speak, but seems there would also be a "shelf" as it were for the air flow to get around since the 3400 ports are already smaller than the 3500.

XanderWiFi · 06-24-2010, 11:20 AM

So unless you do a full conversion there really isn't any point is there?

WhiteV6 · 06-24-2010, 07:15 PM

A 3500 upper ported for a 3400 lower on a stock 3400 lower is still going to improve flow over a stock 3500 on a stock 3400 lower. The advantage to the 3500 upper is the plenum volume, and the broader powerband it will give you. It is best to port everything to match the parts, but you can certainly run a ported upper on a stock lower just as you can run a ported lower on stock heads.

XanderWiFi · 06-24-2010, 10:28 PM

That poses another question: what is plenum volume? I thought ported just improved airflow compared to a stock. So why would a ported be better than a stock 3500 when you still have the stock 3400 lower bottleneck regardless of ported or stock 3500s?

WhiteV6 · 06-25-2010, 04:15 AM

The area inside the upper intake between the TB and the runners for each cylinder.

The first bottle neck is the air filter. Then the intake tubing. then the maf. then tb. then upper. then lower. then heads. Why do you put a larger TB on a motor and gain power if all those other bottle necks are still in place?

Redog · 06-25-2010, 02:41 PM

^^ He knows all with this topic. Years of reseach.

I have Stage 2 upper and lower (both 3400) from his site and I feel a difference.

To do an upper, you'll need about $8 in gaskets, no RTV, and 6 bolts (10mm) on the mani, 2 on the TB (13mm), and 2 holding on the coil bracket (10mm or 13mm I forget)

mbeals · 06-25-2010, 03:22 PM

Quote:

Originally Posted by XanderWiFi

That poses another question: what is plenum volume?

Plenum volume is voodoo magic. Think about an engine with one intake runner per cylinder fed off of its own bore in the carb/throttle body. If the cylinder starts outflowing the throttle body, the manifold bottlenecks and you lose top end power. Instead, if you introduce a larger, shared volume of air, as the heads
start out flowing the carb/tb, it has a reservoir to pull against, drawing a vaccum. The bigger the plenum, the easier it is to draw a vaccum, but that also means you lose response.

It was a big deal back in the day because carbs were a limiting factor....it was hard to just make a bigger carb. So you either kept adding carbs, or you added plenum volume.

Now this is the part I don't get. With modern MPI engines, plenums should not be necessary. You could use a tunnel ram intake with zero plenum volume and completely isolated runners....no need to worry about mixture or atomization at all in the intake manifold. Yet intake manifolds are still the same as they used to be and (some) engines still show improvements by adding plenum volume. I've even asked old time engine builders who have designed intake manifolds and manifold turtles, and they just say they know it works because it does.

WhiteV6 · 06-25-2010, 07:43 PM

Hard to run a MAP sensor without a shared area between all the cylinders. Its also hell on a MAF to deal with all those intake pulses. When the intake valve closes, it sends a shockwave back up the intake runner. The added area is a buffer between the intake pulses and the MAF. Most independent throttle setups use alpha N fueling, which is RPM vs TPS. Great for the track, not so simple for the street.

Plenum volume and throttle body size are just like carb sizing and plenum area, only we don't have to deal with vacuum at the throttle body to draw fuel in and disperse it to each cylinder.

XanderWiFi · 06-30-2010, 09:23 PM

Quote:

Originally Posted by mbeals

Plenum volume is voodoo magic. Think about an engine with one intake runner per cylinder fed off of its own bore in the carb/throttle body. If the cylinder starts outflowing the throttle body, the manifold bottlenecks and you lose top end power. Instead, if you introduce a larger, shared volume of air, as the heads
start out flowing the carb/tb, it has a reservoir to pull against, drawing a vaccum. The bigger the plenum, the easier it is to draw a vaccum, but that also means you lose response.

Just to reiterate so I make sure I understand. The bigger the intake (ported 3500 etc.), the more air it will draw in so the cylinders have a continous flow correct? More continuous flow or an "air reservoir" so to speak-equals more power? But why would a loss in response time be the result? Seems like I would take a loss if I did the conversion or did not do a conversion-just depends on what area I want to take the hit in.

White-are you saying if I did this I would need to extend my tubing from the throttle body to the intake to diminish the shut off backflow that interrupts the MAF? What if I just opted to upgrade to ported/polished 3400s-what would be the complications with that?

WhiteV6 · 06-30-2010, 10:48 PM

No such thing as continuous flow. When the valve shuts, the pulse keeps moving towards the valve, which has also created a wave back up the runner.

You are trying to make this much more complicated and involved than you need to be. The ported 3500 upper isn't going to kill throttle response and will offer the best powerband.

XanderWiFi · 06-30-2010, 11:19 PM

I got ya. Just back me up a bit. Is there a simple metaphor that can be used? I'm just not a mechanic...I feel I could do this, but I want the ducks in line and such. Sorry if my ignorance is bugging you guys...

WhiteV6 · 07-01-2010, 11:10 AM

You don't need to worry about the MAF, any tubes, or plenum volume. I am not a mechanic either. I deal strictly with performance. Unless you are building a custom intake, none of the details for making a custom intake really mean anything. The MAF/pulse thing doesn't apply in the least with a 3500 upper. If you want to learn how all that stuff works, there are books dedicated to the topic. It gets quite specific and detailed the more you read up on it.

If I try to explain anything in general terms, it just snowballs.

XanderWiFi · 07-01-2010, 11:16 AM

I see. Thanks for trying.

XanderWiFi · 12-27-2010, 07:10 PM

Ben, what is the best setup you would recommend on wot-tech? I see the packages and such but I wonder if there is a setup you find to be the best?

Redog · 12-27-2010, 10:59 PM

^^ depends on your budget. Take a look at his site, he's got lists of stuff from Budget to all out

XanderWiFi · 12-27-2010, 11:34 PM

no budget. Which set is the all out?

xXManwhoreXx · 12-28-2010, 10:30 AM

Quote:

Originally Posted by XanderWiFi

no budget. Which set is the all out?

DIY than... get a dremel and go to work...

XanderWiFi · 12-28-2010, 01:16 PM

That's...not an intelligent suggestion...

xXManwhoreXx · 12-28-2010, 03:50 PM

Quote:

Originally Posted by XanderWiFi

That's...not an intelligent suggestion...

There are tons of DIY porting tutorials on the internet... I have done 2 of my cars

XanderWiFi · 12-28-2010, 05:51 PM

I am not even sure I will be able to get the produced ones in my car without destroying my engine let along produce them myself. I'm a play-around mechanic and nothing more. And we all know how internet tutorials can turn out...I say tomata, you say tomato and such. I'll take the product straight from the professional, with the professionals advice and have it no other way.