TB upgrade, V6 vs VR4

[Gly]

well in my pursuit for more power outa the N/A V6
i decided i would fit the VR4 intake plenum to the V6 as it just looked bigger.

got it all off and everything would bolt on with no hassel,

i decided i would keep my original TB...

this is where i noticed my original TB is much larger than the turbo one...

and so was the inlet on my original plenum... bugga! so now i have to get the VR4 plenum machined out to remove the restriction.

so my question to Turbo owners... why have you not done this?? (turbo plenum with n/a TB)

heres a few quick pics of the plenums

also why are the plenums so different, on all the previous 6a series the turbo and n/a plenums have looked the same,
even the 6g series have the mor traditional looking plenum.

why has the 6a13 n/a plenum been changed so much??
to restict the true power of the motor?

[bradc]

your stock plenum looks a lot more restrictive than the normal vr-4 one, I don't know why the throttle body is bigger though. strange.

[You See]

Bring on Dyno day I say! :D

[Gly]

gotta get the vr4 plenum bored out first, ended up putting the stock one back on.

[Kenneth]

I think I expressed my supprise to you at one stage that the turbo TB/manifold was bigger than the NA one...

Usually the NA manifold and TBs are designed to flow better. If you look at the NA manifold, you can also see that it is designed to distribute the air more evenly over all 6 cylinders. when you are force feeding the plenum, its not such a big deal, but with NA, if you dont distribute the air evenly you will get one or 2 cylinders running leaner (possibly dangerously) than the others.

I remember the TB on my 1.8GDI galant being at least as big as the one on the VR-4. Wouldn't be supprised if the NA V6 TB flowed better. Would be interested to see the NA manifold too.

To be honest, I wouldnt use the turbo manifold on your NA as it looks like the NA manifold has been designed especially to make sure the air is distributed evenly across all cylinders.

[bradc]

Even if the inlet to the plenum is bigger on the NA one, the actual manifold part looks very restrictive on the NA, probably designed as you said Kenneth to make sure the airflow to each cylinder is the same.

[Gly]

If you look at the NA manifold, you can also see that it is designed to distribute the air more evenly over all 6 cylinders. when you are force feeding the plenum, its not such a big deal, but with NA, if you dont distribute the air evenly you will get one or 2 cylinders running leaner (possibly dangerously) than the others.


basically what i was thinking...

but why have they only used this design on the 6a13na, when they've stuck to a much more coventional design on the 6g72 which is a v6 na aswell.

but wouldnt it be more likly to run rich, on a couple of cilinders, due to a lack of air??.

[Kenneth]

basically what i was thinking...

but why have they only used this design on the 6a13na, when they've stuck to a much more coventional design on the 6g72 which is a v6 na aswell.

but wouldnt it be more likly to run rich, on a couple of cilinders, due to a lack of air??.

Yes and no. dont forget that you O2 sensor only monitors the AVERAGE AFR over 6 cylinders. so, lets say you have 2 running rich, 2 running lean and 2 running fine... O2 sensor will still show ok as the gasses mix before being metered.
At high load, this could become dangerous.


Even if the inlet to the plenum is bigger on the NA one, the actual manifold part looks very restrictive on the NA, probably designed as you said Kenneth to make sure the airflow to each cylinder is the same.
If you look side on Brad, I think you might find that the NA runners are taller... in which case the area for intake may be at least the same.
What we need to do is find one, cut off the plenum and do some measurement.

Another way though, is to fill them with water and see which holds the most. not the best way due to differences in the plenum, but would be interesting anyway.

[The Vee]

Think the n/a manifold is also designed to produce more torque as it does not have the aid of the blower.

[Kieran]

So, based on what I'm reading here, I wonder what would happen with a V6-24 TB on a VR-4?

[bradc]

Kieran, it would possibly restrict the turbos even more

[Kenneth]

Kieran, it would possibly restrict the turbos even more

what, being bigger? :P You high? :pimp2:

[bradc]

I mean the restrictive bit in the middle of the plenum where the air goes into each of the runners.

[Kenneth]

Thats the plenum, not the throttle body.

I cant see it being any more restrictive than the VR-4 plenum... so long as the internal diameter of that bit is bigger than the plenum diameter on the VR-4, it could flow better.

Thing is that NA requries a bit more thought and tuning of intakes if you want them to perform well... in a turbo application it doesn't really matter.

[stevec205gti]

Inlet manifold design is not just a simple case of the bigger the bore the more power unfortunately.

For a NA engine, changing the bore of the runners as well as changing the length of each runner will alter the characteristics of the engine. For example, as a very general rule, the longer you make the runner the lower down in the rev range you'll get the oomph. Then you also have to start taking into account pulses in air flow created by opening and closing valves, and you can also use this to good effect by suiting the runner design to increase performance at certain revs. You also have to consider to some extent the robbing of charge between runners at certain revs.

As already mentioned, this has less of an effect with forced induction, so it wouldn't be that surprising that the NA inlet manifold will give you greater performance overall than the turbo one