`85 Postal Service Golf Restoration: 16V ITBs etc.

Yamaha ran a variable length intake on the mid 2000 R1's, seemed to work very well but a lot of work to fit to a car (unless you can use complete airbox).

 

@daNpy: As I can see your setup is a bit dfferent since you are running a intake manifold, which provides some more intake length. Depending on your cams and your desired rpm it still maybe a bit too short. Also depending on how long your throttle bodies are my guess is that 70-90mm trumpet length would be a fitting setup. Consider I am calculating the complete length from valve seat to the end of the trumpets.

@KeithMac: Yes, it is a very interesting idea and Yamaha did it very well. I think for most projects, especially street applications, the effort and also the time spent on the dyno is quite high.

 

Since we are discussing this topic: I collected the different calculation methods from Forums, scientific papers and books.

Following collection was gathered:

- Formula taking the intake diameter into account (Forum)
- Fomula without diameter (Forum)
- Helmholtz Engelmann method (Thesis paper)
- Honda Nakamura (SAE paper)
- Honda Nakamura BDC (SAE paper + my own tweak to calculate)
- Heissler method (from his book)

As already stated, every calculation was a bit different from each other, and the only method which was showing different results was the Engelmann-Helmholtz method, but this method is rumored to be not very acurate.

These are the results - the calculated ideal intake length, depending on the desired rpm, measured from the valve seat to the end of the trumpet (in cm):



As you can see, the results are really close, especially the results of Heissler, Nakamura and the formula with Diameter from a forum. Since I trust the calculations from Heissler and Nakamura the most, this will be my target area. I also would like to have the rev limiter somewhere between 8000-8200 rpm to stay in a relatively safe area. Now it makes not much sense to have the peak torque come right at the rev limiter, but about 700-900 rpms before. Also keep in mind that at half the targeted rpms, the effect will also take place, just not in the same magnitude. I plan on making the intake length 410mm overall.



Substracting the already given length by the intake ports, the throttle bodies and some other things like gaskets etc (will also come to that later) I will need an air horn length of 191mm (How fitting for a MK2 ).

This seems really long until you start to look at properly tuned race engines. This one for example is from a friend of mine (Büchl Motorsport built it). It is a 1.6l revving to 10k. Thinking of the theory we discussed until now it puts things more into proportion.

 

Don't forget, injector placement has an effect too.

 

Yes, Injector placement needs for sure to be considered. I wanted to place them quite close to the head because of emissions and idling, I am using Bosch 4-hole injectors so the spray pattern should be good. Also the injectors are reasonably sized, I hope it does not negativley impact the overall performance too bad.

I can show you a picture of the first "prototype" of the intake trumpets. It was merely a test to see if we can print it like this, the angle etc. are definetely not final. I would have waited with the first prototype but my friend was eager to try this on his 3D printer - I did not complain



Also I was worried about the temperature in the throttle bodies and therefore in the injector and fuel gallery, so I stole a technique from the carburetor guys and made a phenol plate to shield the throttle bodies from the heat of the cylinder head:

 

In the meantime, I ran into some problems on the parts for the timing belt covers. First I finished sculpting the planes, which worked well.


After that it was time to paint the covers wo get a nice and even finish. This did not work so well as the paint did seep through tiny holes of the epoxy layer into the foam and dissolved it. I made this slight increase in this area to have a little bit more space for the adjustable camshaft wheel. Well, in the end I scraped out all the foam and redid the complete thing with epoxy resin.



At least, the lower part came out nice.


And so I started with the last preps before moulding:



Perhaps now it gets more clear what my mission with these parts is?

 

Gfk or carbon?

Lovely bit of work there.
Possibly even more so than painting, preparation is EVERYTHING.

Will you make more than 1 set?

 

Let's say 3 or more?

 

Tristan, your second guess was 50% right:


If everything goes well, I will make a small run if anyone is interested. Tomorrow I will de-mold the first attempt. However I will only offer any parts for other people if I am satisfied with the quality, so we`ll have to see how things turn out. The first attempts for sure will be not of good quality standard so you`ll have to be patient with me

This is how I made the molds:

 

Awesome, if anything, i prefer Aramid.

If you make any that aren't "pretty", but are still race car usable, I might be interested.

 

As I have the problem my engine won't start when hot (heat soak), I am also interested in the phenol plate gasket if you're able and willing to make one (or) more.

 

Tristan, if I have some parts with only cosmetic imperfections I'll let you know

daNpy, I can ask the guys from work if I can do a run on the waterjet cutter. I made mine by hand and it's a nightmare

 

I just measured the length of my intake. It's 24 cm for the ITB's and manifold. The trumpets are 4cm.
I don't know how deep it is to the valves. Approx 3 cm I guess?
That would make 31 cm in total. Looking at your graphs, I would need at least 50 cm to have the max torque at 6000 rpm

Yes I know I am discarding the differences between our engines, but when I see the differences in calculation methods I am guessing there wouldn't be like 5+ cm difference?

 

https://clubgti.com/forums/index.ph...and-maximum-porting-dimensions-thread.193826/

I can't recall exactly the inlet port length in the head casting, but if you follow the centre line of the port it's more than 3 cm on a 16v.

 

that looks like a lot more than 3 cm indeed, thanks Tristan

 

It is 95mm as far as I can recall, but I'd have to look in my documents to be sure.

So your intake length currently is approximately 37,5cm. Assuming your cams are a tad less aggressive than mine, you should probably aim for 42-45cm (just a guess). Always keep in mind that running too long is way less critical than running too short.

 

I can mount longer trumpets and am currently busy re-placing the radiator so that wouldn't be a problem, but I still have to run with an airbox otherwise I will be sent off the track (again). So the airbox limits my trumpet lengths anyway.
I never meant to build the fastest angine possible by the way, I just want to have fun on the track. The engine has no mods tot head other than the cams.
Catcams 7661221 (283°/279° - 247°/243° - 11.50mm/11.50mm - 3.00mm/2.65mm) are fitted in my engine. And as I can keep up with (or pass) almost all 325i between 1980 and 2010, that's quite a lot of fun nowadays.

A power measurement is found here. 195 hp, 149 bhp. Note that this is without airbox and 60 mm horns fitted and a rather cold outside temperature (at 18°C it's 190hp).

 

Your engine has a very healthy power curve! It also pulls nicely up to the limiter.

I would make the trumpets as long as the airbox allows it, It seems like it`s a very driveable setup and it does not have a large torque-dip or something like that so there is no actual need to improve anything drastically.

Unfortunately I am still waiting for the clutch package to arrive, so I am not able to install the engine. But at least I finished the floor on the inside, I put some sound deadening on because I want to be at least a bit comfortable. Also the new shifter needed to be introduced to it`s future working environment:



Also a friend of mine is building a hillclimb Scirocco 1 and he was casting whels for his build and fortunately, he was kind enough to also make a set for me since I really love this kind of wheel. Perhaps some people know it - originally the design is from Spiess:

 

Oh, that's really rather nice.

 

I also have to start practicing again welding the Aluminium, and I had to make a bracket for the brake booster vacuum pump, so I thought why not combine both? If you ask yourself why in hell I need a brake booster - the vacuum generated by the engine is too weak because of the cams.

Cutting Aluminium is the worst:

Tacked & welded:


As you can see, the welds are inconsistent, but it`ll do the trick this time: