Little Red Devil

[VWindahouse]

Lol only 52.5* mate. Pretty surprised at how well the Polo's perform in that department! But I guess the front top and bottom bumper grilles are pretty massive.

The vents will really come into play when the massive open pod filter gets here and when the flat bottom splitter goes on. The passenger side vent is over and just behind where the pod is going, creating flow straight into and over it especially with the existing 3" duct feeding up from underneath. And will need more engine bay ventilation in general when the splitter goes on because it's going to cover the entire of the bottom of the engine bay

[VWindahouse]

So had fun today thinking up a rear diffuser. And also got around to shading my tail lights which is long overdue on account of hating the Polo's for like... forever.

Well the verdict on the diffuser is maybe too much trouble than it's worth. Here's a pic of what your Polo looks like with no pants on



As you can see it's near on impossible to get any sort of upward angle from the spare wheel well that's not too severe. So now thinking of just helping air flow. Any hatchback acts as a parachute at the rear therefore increasing drag the faster you go. I have a few ideas but started with the trusty hacksaw From this



To this



Investigating a couple of products at the moment which might help also and make things look more factory as well as B/Racecar

Happy with the lights also





Cheers.

[VWindahouse]

Quick update time starting with something not seen too often.



Yes it's a dump pipe but not your conventional type This has a 4" expansion chamber that runs for 9" right after the 3.5" inlet, then down to 3" and flanged after the cat at 2.5" to meet the millteck catback.





There is a bit of science behind the expansion chamber which was highlighted to me by a cluey fellow with an Audi TT on Vortex called Marcus_Aurelius.

But first the big picture goal. So I've read that advancing timing doesn't actually increase cylinder pressures if done safely. This means that rods remain safe if the boost remains at requested levels with no spikes down low. However the adverse affects of too much timing advance is knock and EGT's rising to dangerous levels. So I want to see if I can hit the 200fwkw mark safely and to do that I need to make sure there is no back pressure affecting the little Ko3s turbine which creates high EGT's. Now our Polo's are lucky in that our DP design is fairly linear with no severe 90* angles the exhaust gases have to take directly after the turbo's hot side, so the only real thing that will increase back pressure is exhaust diameter. I have read everywhere that the magic diameter for 300bhp plus is 3". So my 2.5" system won't be helping and is increasing back pressure and EGT's.

But there is also something else and this is where the science part I mentioned before come into it. Here is the post Max made explaining;

Firstly, the expansion-chambered downpipe provided a huge improvement in spool-up time. It was there and very noticeable from the first WOT pull after the install. But at the track, it became very clear that this thing is a success and a must-have for anyone that takes turns in Motorsport conditions. It just made the car a rocket coming out of slow turns where spool time would be taxing any turbo car. The best way I can describe what it did in the spooling characteristics, is the car slingshots out of turns now, instead of steadily accelerating from them.

Secondly, in terms of the physics behind it, there shouldn't be any loss of velocity but in fact improved flow out of the hotside. Normally, airflow coming out of the turbine wheel is in a spiral shape (the speed of the spinning wheel dictates the direction of the flow, which could be either following the blade rotation or spiralling in a counter rotation). This spiral effect is not ideal for flow and also reduces the gases velocity. By expanding the area right after the turbine, you effectively allow the otherwise spiraling exhaust flow to become turbulent. When the flow becomes turbulent (whirlpool-like), it allows the gases to move faster away from the choke point (turbine wheel and housing size). This is why you're able to achieve an improvement in flow and velocity by doing this. The closer to the exducer you can expand, the more effective the result will be, but obviously we all have to deal with space and packaging restrictions.

I don't have the dyno data to quantify the results over the entire powerband, and didnt log/compare peak EGT differences yet. However, I can already say that the improvement in spool alone is well worth it for applications like mine and yours. Stay tuned and the raw data will be available in this thread as soon as the car is back and running again.

The dynamics involved in providing expansion to the spirally gases:



... and a bit of explanation of the concept (better than mine ).



So now I can be assured that with the no immediate restriction caused by a 3" flange which would be half an inch smaller than the turbo hotside outlet, and the 4" expansion chamber going into the full 3" system with 100 cell cat and ceramic coating, I have given the turbo optimum efficiency with next to no back pressure or spiraling gases either spinning faster and or in the opposite direction to the turbine keeping EGT's at bay.

So next up is to install the DP and hookup the air fuel gauge, then it's off to the dyno to play with the timing up to the point of knock to see what power we can see.

Oh and also got the alloy TIP ceramic coated also

[Eddy]

Hoyhoy.

Seems like your getting very serious Ant.

[VWindahouse]

Haha yes mate, giving this a red hot crack

[jasn78]

Hey Ant, Porsche club day at willowbank must be around again soon hint hint

[sam_vw]

Little Red Devil

Great work mate! Is there much clearance around the 4" expansion chamber to the bulkhead etc?

[VWindahouse]

Hey Ant, Porsche club day at willowbank must be around again soon hint hint

Not a bad idea mate, you keen?

Great work mate! Is there much clearance around the 4" expansion chamber to the bulkhead etc?

Cheers Sam TBH I didn't get to see the trail fit but he tells me there's not much.

Also enlisted the help of Gav and his grinder in reducing some rear end drag















Also borrowing an idea from the Honda drag boys that should be here soon.

[VWindahouse]

And got a baffled sump from Forge that looks pretty nice

[VWindahouse]

One step closer to some free flowing goodness





And massive thanks to Greg from Carformance for this very nice 42DD stainless tip



And here is the idea stolen from the Honda Civic drag boys



Installed in the bumper to free up drag they have seen an increase of 4-5mph trap speed for the 1/4 mile But a total pita to install on the Polo as the Polo's bumper is curved and these thick alloy plates are not So got creative and bent them around a ceramic pot plant to get the right curves. Took ages. Then primed, positioned and drilled.



And marked



Then the fun part





And after 3 hours or so, done!



Sorry really crap pic, will grab a better one tomorrow.

[team_v]

looks pretty hektik Ant.
I didn't realise how much under body restriction there was on these cars at speed.

[VWindahouse]

Yeah heaps apparently Clay. A hatchback coupled with a rear torsion beam suspension set up is no friend to efficient aerodynamics.

But doing my best to fix that

[Polo GTEye N9]

Hi Ant, well done. Thought that you were going to vent the rear bar, somehow. More photos?
Any additional NVH from the vents? They look quite good.
Have you abandoned fully the idea of rear diffuser?
Cheers Al

[vwthunder]

Sorry really crap pic, will grab a better one tomorrow.

Wow love these, they look awesome, really do suit the race car theme, well it isn't really a theme is it !!!

[VWindahouse]

Hi Ant, well done. Thought that you were going to vent the rear bar, somehow. More photos?
Any additional NVH from the vents? They look quite good.
Have you abandoned fully the idea of rear diffuser?
Cheers Al

Cheers Al! No more NVH than before luckily. Most of that was a result from ditching the rear seats. But that was soon drowned out by the turbo whistle and now the induction noise since the bonnet vents went in. For a small car it sure does sound angry

Yes I don't really think a perfectly functional rear diffuser is an option with this car. So the plan is to just get rid of anything from a drag perspective. All that's really left now is mounting the new muffler a bit higher in the tunnel as there's a tonne of room up in there



and moving the exhaust hanger next to the outlets to the right hand side between the muffler and spare wheel well

Wow love these, they look awesome, really do suit the race car theme, well it isn't really a theme is it !!!

Thanks mate, they're another mod that I was a little worried about but thankfully worked out well. Haha yes it's a just a theme until next year I guess. The real pressure starts in the way learning how to drive in absolute anger to do all this prep work justice.

Got some better shots this morning





I'll finish painting the rest of the chassis black when I get a chance so it all looks nice and stealthy.



It's pretty clear these will do the job of evacuating the air pretty well