Race Engine Forum UK

Hi G,

I have a question for you. You (GC) recently did a test of the 205 GTI 8v inlet manifold which showed about 10% loss in flow because of "wierd entry profile". This caused my and some others to think. Could the black plastic manifold used in the 306 XSI 2.0 8v actually be quite good? There are really many good things about this 306 xsi inlet. This is especially aimed at doing the popular XU10 head conversion on the 205 1.9 gti's, since you can avoid porting the head to use the GTI inlet by using the 306 inlet instead..

Good things about the plastic inlet manifold: 10mm larger throttlebody (than 1.9 GTI inlet), quite large inlet "tubes", the angle that the air enters the head is good, and the injectors sits high so that hey do not disturb the airflow... The bad things is the the angle from the "air container" to the 4 inlet "tubes" is more than 90 degrees, and the manifold in general does not fit that well in the 205 engine compartment... Other than that i do not see many bad things about this manifold?

About the GTi inlet manifold i read one of your (GC) flow tests. This showed that the angle that the air enters the head is really bad, and it actually proved a loss in flow of about 10% as i recall. Furthermore the injectors sits low and can therefore help "blocking" or "disturbing" the flow of air. And also it has a 10mm smaller throttle body than the 306 XSI inlet manifold...

I think a flow test could be quite interesting, so we can compare these inlet manifolds... (Especially if you perhaps have an XU10 head and an XU9 head to test the inlets on. It would be perfect! And we could then also really find out whether or not the XU10 conversion is really worth it)

Looking forward to hearing your answer G, and thank you! (If someone doesnt know which plastic manifold i am referring to, then just do a quick search on Google --> Images for "306 XSI engine" or something like that)

Stefan

Stefan,

I've looked but am sorry but unless you can give me detailed photos of the individual inlet manifold I cannot answer this.

GC

Hi G

Ill take some photos of the 306 manifold asap. You have some photos of the 205 gti inlet manifold yourself since you tested it a while back (believe it was in your thread in the "Cyinder Head" forum called "The effect of portmatching" or something like that).

Stefan

Sure!

It is good photos of the other manifold I need. This is all presupposing it actually fits the 1.9 205 GTi...

GC

Hello Guy!

I made a few pics from the 306 XSI manifold, because I'm interested in your opinion too. I hope the quality of the pictures is ok for you.
On the first photo you can see that the pipes are round and not square like the 205 GTI ones. The inside diameter is 35mm. So I think the ports on the 205 GTI head need to be alingned to the manifold. The fourth picture shows the XSI manifold mounted on a 205 GTI Head. It fits perfectly, except from the mismatch of the ports. Possibly it hits the radiator when it is mounted in the car so that there some customization is necessary. On the last photo there's an original manifold of a Peugeot 205 GTI 1.6/1.9 on the head for camparsion.

Michael

Michael,

thanks for the excellent photos and also for being patient. It does take a long time to form some of the replies in such a way that they will be useful/interesting.

I have put notes on the photos to indicate how I think each will behave. It would be hard to judge which manifold (cast or plastic) might be better without putting the items on a head on a flowbench. The design of both tells you straightaway that they are designed to fit the car as an over-riding priority. They are both 'plenum' designs - less powerful than fully separated runners, the plenum being there to damp out pressure wave effects. Great idea if it damps out pressure waves (pos/neg) that we don't want at particular points in the rev band but my exp of plenums is they also damp out beneficial waves that we DO want !

My annotations on the photos are all based on direct exp of flow behaviour on my Superflow rig.

Obviously in both cases I have only talked about the airstream. The influence on pressure waves (given that pressure waves acting towards the inlet valve greatly augment the airspeed and cylinder filling), I can't really comment on that and frankly, there is no need to.

GC

Hello Guy!

Thank you for this detailed answer. No I understand why the 205 GTi manifold lost so much flow on your flowbench when it was mounted on the head. But the ports in the 205 GTI head aren't horizontal like in your drawing, even worse, they are a bit upturned.
By the way, there's also a plastic version of the 205 GTI manifold which has a smooth surface inside. I think this one flows better than the cast aluminium one and is the one to go for.

Best regards

Michael

Yes,the ports are ramped upwards, I forgot.

G

So G, you would think that the original 205 gti manifold will flow better when used with this head?

If I had to choose - yes I would use the aluminum one above. Though of course I would rather flowtest them back to back to be sure. I just don't like the look of the angle of the plastic one relative to the ports, that can cause a massive on-head loss.

GC

Hello Guy!

Would there be an improvement of flow if I would mill an angle on the mounting surface of the manifold like in the picture below?

Best regards

Michael

I just do not know. Things like that have to tried on a flowbench.

GC