Plenum upgrade "Real performance or Hype"?

[Jake Raby]

We use modified IPD arrangements on most Stage II engines. In my experience, until you add 400ccs, a point of compression, some real port work and etc , the gains are minimal.

I have seen stock engines make less power with them, back to back on the dyno.

[jaykay]

Originally Posted by Jake Raby

We use modified IPD arrangements on most Stage II engines. In my experience, until you add 400ccs, a point of compression, some real port work and etc , the gains are minimal.

I have seen stock engines make less power with them, back to back on the dyno.

I understand that the IPD arrangement has the potential to direct and accelerate the intake air left and right giving more "authority" to the charge, but I have always been concerned that it would restrict acoustic pulses side to side (perhaps this is not a valid concern). Especially when the resonant flap in the cross tube is shut. One can see that the design has evolved with different types of relief holes through the "divider blade" perhaps to mitigate this very issue.

Just a guess:

The engine is drawing the intake air in and the divider could potentially disrupt side to side (one plenum feeding the other) cylinder filling in certain cases (engine rpm and flow rates).

It would look like this design would be much better suit to forced induction where bank to bank acoustics would be covered off by positive pressure before the divider blade

[Jake Raby]

No, on an normal aspirated engine the short side radius is always where the greatest air speed and velocity will be found. On the flow bench, the long side can have a pitot tube introduced and you'll find no velocity, or a slight vacuum.

This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.

The short side is where the men are separated from the boys, and it doesn't mater what it looks like, all that matters occurs on the flow bench.

[j.fro]

This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.

Ouch!

I think that is exactly what they did, how else can a:

2.7L 986 have 217 HP, ~80 HP per liter
3.2L 986 have 250 HP, ~78 HP per liter
3.4L 996 have 300 HP, ~88 HP per liter

I agree with this, and there is further evidence from the current 3.4 liter engines: 350HP in a 911, but only 315 in a Boxster S.

[Jake Raby]

Originally Posted by j.fro

This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.

Ouch!

I think that is exactly what they did, how else can a:

2.7L 986 have 217 HP, ~80 HP per liter
3.2L 986 have 250 HP, ~78 HP per liter
3.4L 996 have 300 HP, ~88 HP per liter

I agree with this, and there is further evidence from the current 3.4 liter engines: 350HP in a 911, but only 315 in a Boxster S.

There's more to it than that... The 986 engine uses the same cams as the 5 chain, 3.4 996, they are even stamped as such right on the cam blanks.

The cylinder head ports and castings are also the same, BUT the 3.2 chambers are 3-4ccs smaller, for the smaller bore size.

4 valve engines respond aggressively to bore size increases, the 3mm difference in bore size between the 3.2 and the 3.4 is HUGE in regard to swept volume, and chamber filling. The entire intake system is different as well, as the 986 intake runners are longer and thinner and extend from the plenum chambers all the way to the cylinder heads without interruption. The 3.4 996 does not do this, at the 70% point it breaks away and changes to a more effective aluminum intake runner that bolts to the head.

The plenum areas are also larger.

We find huge gains with intake manipulation, but thats not meaning bolt on items-

Porsche knew that the engine in the Boxster was in the right place, and the engine needed a handicap to keep the performance differentials between the two cars so the 911 would remain the flagship.

Because of this, we have always been able to increase the percentage of power increase more with the 986 engine more than its 996 counterpart. Its not uncommon for us to produce 100HP more than stock from a 3.2S engine for a totally street able engine, on pump gas, with a red line that can be reduced 500RPM lower than stock.

[jaykay]

Originally Posted by Jake Raby

No, on an normal aspirated engine the short side radius is always where the greatest air speed and velocity will be found. On the flow bench, the long side can have a pitot tube introduced and you'll find no velocity, or a slight vacuum.

This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.

The short side is where the men are separated from the boys, and it doesn't mater what it looks like, all that matters occurs on the flow bench.

Yes agreed but I am talking about bank to bank flow pulses over the divider blade where you see relief holes......normally that would be a dead area yes

[Jake Raby]

Originally Posted by jaykay

Yes agreed but I am talking about bank to bank flow pulses over the divider blade where you see relief holes......normally that would be a dead area yes

Those holes are for lightening the casting, not performance. A pitot tube in that location will show zero air speed.

[Hawaiian Driver]

Thanks Guys, you've really given me great info. I think I'll just leave that alone. Don't really need more power, just have the itch to tinker with things. This is a mod I can live without. Reward vs effort isn't there