Sam's build thread

[Sirocco20348]

How would you match up the polo throttle body to the gtir intake manifold?? Polo TB If it's the same size as the mk4 i recall it being 3" entry.

MK4 cup cars and other professional mk4 racing cars seem to use the stock large port intake manifold.

What do polo cup cars use?


Frazero racing mk4 golf British touring car championship partial picture of throttle body/intake manifold.. once again looks stock.. Possibly ported.




Nothing fancy!

[sambb]

Ok so I found these old pics of my Polo plenum versus the Audi S3 Mk 1 plenum. What I'm trying to work out is if the drivers side feed Audi mk1 TT and golf 4 gti intakes are the same as this, because this S3 mani actually looks quite a bit bigger in the plenum compared to the Polo than I remember.
I guess my thinking was that the S3 and TT both had 225hp from factory with the larger turbo so if the factory designed the plenums this way then that would better suit my future Golf Mk6 GTi turbo upgrade. But if the stock Polo one looks the goods (and it does look closer to the GTiR plenum than the S3 one) then I'm more than happy to stick with it and I want to do anything to retain throttle response. Its my understanding that all the intakes Golf 4, S3, TT and Polo run the same throttle body so thats a constant between them. Also they are all small port heads/inlets which is definitely what I want to stick with.
That Mk4 intake posted above is the one I was thinking of getting. It looks much more consistently shaped and doesn't have the big undulations and cutouts in it to clear engine bay bits. It definitely retains its fatness further down in front of Cyl 4 more than the Polo one which tapers more like the GTiR one does.
The GTiR one is quad throttle from factory yeah or is that a GTiR plenum with aftermarket adapted throttle bodies?

[HaydEn]

Gti-r is factory itb


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[Sydneykid]

Also they are all small port heads/inlets which is definitely what I want to stick with.

Why? The reason for small ports is to keep up the airspeed, which is important in an N/A engine but next to irrelevant for a turbocharged engine. All that small ports do is increase the boost because of the restriction that they present to the airflow. Boost is after all a measure of the engines restriction to airflow and it's airflow that makes horsepower not boost. In simple terms I'd much rather have an engine that makes, say, 300 bhp at 15 psi than one that makes 300 bhp at 25 psi. There is less load on the turbo plus less heat generated which means a smaller intercooler and/or lower inlet air temps. Of course there are lots of other benefits, lower combustion pressures, lower water and oil temps, less time spent recovering to full boost (lag), etc. Larger valves (particularly exhaust) for the same reason.

Personally I'd be looking for a cylinder head that fits on the engine with the largest ports and valves that I can find.


Cheers
Gary

[sambb]

These show the difference between small port and large port inlet mani ports, and also a small port head being taken out to large port. The turbo 1.8T 20V's were all small port. The only large ports were naturally aspirated ones out of passats etc. Exhaust ports and valve sizes were the same irrespective of inlet port size. So basically the factory made all the turbos small port. From listening to 1.8T 20V circles the consensus seems to be that below 300-350hp you will loose response with a big port head. Is that because despite the larger port you still only have the same valve sizes. That coupled with the fact that i'll probably never go over a GT2560 size turbo is what had me thinking small port would still be the go.
The other option is a large port manifold off an NA car and then get one of those half inch think phenolic spacers machined to take the large port runner in the intake down to the small port entry at the head. Any merit in that?

[Sirocco20348]

Australian delivered mk4 golfs (AGU) are all large port. There are other large port 1.8t motors aswell - AEB...

1.8T 20V Engine codes FAQ | Club GTI

[sambb]

you're joking. Hmm interweb bum steer then. But all naturally aspirated engines are large port yeah? Whats the going rate for a large port head?

[HaydEn]

you're joking. Hmm interweb bum steer then. But all naturally aspirated engines are large port yeah? Whats the going rate for a large port head?

$100 or so. See them cheap all the time, most of the time they have a bottom end attached to them for that price though.


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[sambb]

ok another thing then... I read this and that about using NA cams. They seem to have more or less the same minimal overlap but a lot more lift. Some say do the inlet and then the more mental the engine gets go to the NA exhaust cam as well, but then other peoples put up dyno sheets where they make zero gain and loose bottom end. Any experience with NA cams from the Mk4 guys?

[Sydneykid]

My view is that turbo charged Golf's especially from MK5 onwards (and Polo's) have twin goals, performance and fuel economy (which is also heavily emissions related). Hence the small ports which, together with turbo sizing, promotes low rpm torque (really low rpm), such as making boost at just above idle. This gives the instant shove in the back (performance) plus negates the need for higher rpm (economy & emissions). Conversely the N/A engines need the larger ports to make decent performance (less torque, more horsepower), but in doing so they sacrifice the really low rpm torque, need higher rpm to make horsepower and hence result in increased fuel use and emissions. That's why we have 1.4 litre turbo engines making the torque of a 2.5 litre N/A engine with the emissions and fuel usage of a 1.4 litre engine.

IMHO the smaller ports (in the later turbocharged engines) has far more to do with fuel economy and emissions than some small low rpm performance gain. Since, in competition, we only care about performance, making more horsepower at lower boost levels is the target.

On camshafts, it's all about matching, for example if you have a camshaft set up that works really well from say 4,500 rpm to 8,000 rpm then you need to size the turbo to match that. It's no good trying to match a 2,500 rpm to 5,500 rpm turbo to those cams. Playing around with the cam timing can make a small difference, for example (in Evo's and Skylines) advancing the inlet cam 4 degrees and retarding the exhaust cam 2 degrees means making the same boost 500 rpm earlier.

There is no real substitute for matching the turbo sizing with the rest of the engine hardware, so have your targets firmly in mind before you start. If you want an engine that makes good boost (torque), say, at 2,000 rpm then small ports and turbo cams are the go. If your aim is good horsepower at say 7,000 rpm, then big ports and N/A cams are more likely to help with that.


The Garret GT2560 is the standard turbo on the S15 200SX, they are OK for around 310 bhp at about 1.2 bar. A common upgrade on 180SX/S13 with the CA18 (1.8 litre), they are very responsive but run out of airflow (efficiency) at around 6,250 rpm. Personally, for a competition biased car with rods and pistons, I'd be looking more in the BW 6258 sizing and running it at around 1.5 bar for 360 bhp. Still well in their 76% efficiency range at 145,000 shaft rpm and they can run at 75% all the way down to 0.7 bar for around 220 bhp at 95,000 rpm. They also can handle 2.2 bar at 75% (155,000 rpm) for the same horsepower (~360), OK for an engine with lots of restrictions, so they are very flexible. Handy if you want to use the same turbo on an existing (unopened) engine while you build a decent one.


Cheers
Gary