Intake manifold, keeping the lid on sonic boom

Status
Not open for further replies.
Joined
Jun 3, 2003
Messages
4,413
Location
BC, Canada
I was looking at the new Mercury Marine 4.5L V6 intake manifold
and wondering what inspired the design.

The engine is 4.00X3.60".

Perhaps the stroke was not increased to 3.75 to keep intake velocity manageable.

In last month's Hot Rod magazine LT4 vs Hemi on the cover, a GM tech engineer
discussed the intake manifold with the supercharged engine.

When the intake velocity is transitioning from sub-sonic to supersonic,
would a sonic boom occur inside the intake manifolds on both of the above examples?
 
No, a sonic boom is a build up of sonic waves along a leading edge. In this case, the air itself is moving, there is no leading edge. Also, it is exceptionally difficult to achieve supersonic speeds in automotive intakes, the friction caused by running air that speed by plastic or metal that is not totally and perfectly smooth becomes a problem; very small imperfections cause very big disruptions to flow. Would be interesting to know how they did it. You sure he wasn't talking about air inside the supercharger? The outer edges of the impeller can sometimes be supersonic.
 
Could an exhaust influenced low pressure condition or sonic wave during
valve over-lap be the need for the intake manifold design?
 
Originally Posted By: used_0il
Could an exhaust influenced low pressure condition or sonic wave during
valve over-lap be the need for the intake manifold design?

What valve overlap? It's a forced induction engine that is not dependant on exhaust gases to create the intake charge. In turbocharged engines there can be valve overlap as long as the intake charge is moving fast enough (otherwise the gas would flow exhaust -> cylinder -> intake). The higher exhaust gas pressure keeps excessive intake charge from venting out the exhaust. But in a supercharged engine that is not so, the intake charge can just get blown by the top of the cylinder (cooling it slightly, which can be of benefit) then out the exhaust. It's not efficient, thus from-the-factory supercharged engines normally have minimal, if any, overlap.
 
Perhaps my two examples were not very good ones to learn from.

How is "ram-tuning" achieved in a non-boosted application?

One would think, considering the name, that a very high intake
velocity would be required to achieve "ram-tuning".

If the valve timing just an on/off switch without sufficient overlap
to create exhaust influence, then the ram effect velocity must be
generated by the piston movement and the intake manifold design.
 
Originally Posted By: JHZR2
What's the significance of going up to 3.75" from 3.60"?



I'm going to guess because of more air being pumped per stroke must have some effect.
If coming through the same orifice then velocity would have to increase to move more air.

Just guessing.
 
That is what I was thinking Clevy.

Also if the original engine design had a stroke of 3.50 inches for example,
increasing the stroke to 3.60 would allow the use of existing pistons
by milling .050" off of the top.

By increasing the stroke to 3.75 without a significant increase in
connecting rod length, would put too high of a demand on the intake port.

We saw that already once or twice with the increasing displacement of domestic V8s.

The engines grew, but the heads and intake manifolds remained the same.

One big exception to that rule was the Ford 302 Boss.

The 302 Boss had an intake port large enough to drive a bus through,
but not enough cubic inch to get port velocity.

(I know the language is Hill-Billy, but I know you can follow it.)
 
The 302 Boss concept went one step in the right direction when drag racers
stroked the engine to 332 CID.

With the increase in displacement, the compression ratio could be increased.

It was hard to get the compression ratio very high with 302 CID without everything touching.

The three things that increased the port velocity in the 332 Boss, was of course the increase
in displacement, the increase in compression ratio and the piston moving away from
TCD faster.
 
Originally Posted By: used_0il

The engine is 4.00X3.60".
Perhaps the stroke was not increased to 3.75 to keep intake velocity manageable.


4 x 3.6 is a common dimension, also the same dimensions used in the 3.0L inline-4 that's been in production for 20+ years.
my guess would be merc used those numbers to take advantage of existing tooling and production and parts commonality. using a stroke of 3.75 would be less common if not custom, and cause geometry problems with regards to crank centerline, rod length, and so on.
if you look up a piston speed calculator, you'll see even for ridiculous rpm and stroke of 4" the piston speed and crank rotation is 1/10 the speed of sound at best, so intake velocity is never near that. if the merc 4.5L v-6 shares a lot of common features of the gen3 and gen4 LSx motors like crank mounted oil pump and cylinder head dimensions then my guess is they worked off the existing GM platform and chopped 2 cylinders off.

as for the intake manifold design on the 4.5L i haven't found pics or looked it up yet. hopefully the genius's that came up with the merc 3.7L 470 didn't design it.
 
In the 4.3L V6 topic, back a few pages now, I mentioned "and not the 60's all over again".

During that decade we saw engines grow in displacement with out corresponding increases
to the intake flow capacity.

GM's 5.3 V8 strikes a good balance between engine size and cylinder head flow capacity.

Moving the same heads onto the 5.7L would likely be a sensible CID limit without causing
intake velocity issues.

To apply that theory to the 4.3L V6, unless better heads are available, an increase in
engine size will not likely achieve a corresponding increase in usable power.

This matching of engine size to cylinder head flow is not unique to any one manufacture.

I picked two or three engines from Ford, GM and one from Mercury Marine.
 
Last edited by a moderator:
When your intake flow goes supersonic, the air flow behaves a bit differently than it does subsonic. The port calculations, shape, cross section etc go out the window when you have to consider supersonic flow. The air doesn't hug the port walls (short radius), starts skipping around, and creates odd pressure waves that really mess with flow numbers.

Stroke effects PEAK flow numbers through a port more vs bore diameter increase to achieve the same displacement. A 500ci engine with a 5" stroke will pull more peak flow than a 500ci engine with a 4" stroke (assuming same TOTAL air flow). Total flow will will be the same, but the PEAK flow will be greater with a longer stroke per given displacement.

High intake velocity (subsonic) is a good thing if you maximize the engine to take advantage of it. High velocity air has more energy (F=mv^2) that can be utilized to fill a cylinder. F1 engines achieved VEs of 130% normally aspirated. Only problem is that intakes that don't have variable runner/variable plenum setups give away power on either side of the RPM they are optimized for. More optimization= more power losses the farther you move away from the tuned RPM.
 
With variable runners, plenum and valve train we can optimize tuning inputs and dynamic compression for load and RPM.

By retarding the camshaft at low RPM and high load conditions, the compression ratio is effectively reduced, lowering peak cylinder pressures.

With variable intake runners and plenum, the velocity can also be matched to air-flow demand and RPM.

Late valve timing from a retarded camshaft position may also increase intake velocity.

With increased RPM, depending on the load, the camshaft may be advanced to obtain a higher dynamic or operating compression ratio.

To supply an increase of intake flow at high RPM and load, the plenum size may be increased and a secondary intake runner utilized.

Intake charge flowing out of the exhaust port during valve overlap is eliminated by grinding the camshaft on a wide LSA.
 
Last edited by a moderator:
If you have an engine apart with a cylinder
head on, try this experiment.

Take a spark plug out and push a piston on a
connecting rod up into the cylinder until it
stops against the head.
Install the spark plug and see how far you
can move the piston by pulling on the rod.
That simulates an engine with a very high
compression ratio.

Take the spark plug out and pull the piston
down the bore one inch. (25.4 MM)
Install the spark plug and once again see
how far you can move the piston by
pulling on the connecting rod.
That simulates an engine with a very
low compression ratio.

The above, demonstrates how compression ratio
affects intake velocity.

If the intake valve is left closed while the piston
is moving down the cylinder, a very low pressure
condition is created above the piston.

Intake port velocity can be increased by delaying
the intake valve opening point.
 
Last edited by a moderator:
Status
Not open for further replies.
Back
Top