Audi V6 Throttle, Afm, 240cc Injectors

[stux 0]

Hi,

I have read about swapping Mi16 throttle body (TB) for Audi 2.6 V6 (6 pin) one

http://forum.205gtidrivers.com/index.php?s...rottle&st=0

and I decided to do it myself.

 

The differences:

- Mi16 – 38 and 38mm throttle plates;

- V6 – 35 and 52mm throttle plates.

However the entrance to the Mi16 TB is bigger. And it is narrowed just before throttle plates to 38mm, that is why one can think that diameters of the butterflies are not the only thing to be considered.

 

The inlet side of a V6 TB is smaller than Mi16 one, but the choke area is about 36% bigger. There is also one thing that in my opinion should be mentioned and CW noticed it:

“… the top butterfly is restricted by the body itself (a smaller air hole than the butterfly itself) …

Top butterfly 35mm (but inlet hole for it is 24mm)

Bottom butterfly about 52mm

 

Using 24mm as the top butterfly size, the VAG throttle body increases the inlet area by about 12% over the Mi16 one.”

Unfortunately it is true!

 

I decided to swap Mi16 TB for V6 one and find out if I can measure some better acceleration time from 0 to 160km/h (about 100mph). Unfortunately I didn’t notice much gains. I’m positive that with V6 TB it isn’t worse but I’m not sure if it’s better either. If there is any difference it is not more than 0.5s (in both cases about 15.0s).

So if someone write that after this modification it “goes like hell”, or it “gives 10hp more”, or “It was quick before but now it’s a lot quicker. More power and torque through the rev range.” It must be a placebo effect.

 

The only noticeable difference for me is the smoother ride at low throttle openings, because only the smaller butterfly opens first.

 

Perhaps one day I’ll check the differences on RR, till then I’ll be using V6 TB.

 

I have vacuum and fuel pressure gauges and in both cases vacuum was 0.0bar and fuel pressure 3.2bar at max throttle, through whole rev range (to the rev limit 7200rpm). I have a huge OMP air filter so it doesn’t restrict flow much. (conclusion: standard mi16 TB do not restrict flow)

 

I also measured voltage at AFM and it was the same max 4.68 – 4.70V at ~7200rpm. Max AFM flap opening gives 4.80V.

 

To say more about AFM:

at 1000rpm is above 1V;

at 2000rpm about 2V;

at 3000rpm about 3V;

at 4000rpm about 4V.

 

The higher the revs the differences are small. That is why I think that what I’ve heard from my colleagues from polish 205 forum is true: The ECU read signals from AFM only to 4500rpm, further all depends on fuel and ignition maps programmed in it (naturally only at full throttle).

So untrue is that bigger TB can not work properly with standard AFM because of higher flow.

 

Perhaps V6 TB can give more noticeable gains with hotter cam/s or/and with slightly raised fuel pressure at higher revs.

 

PS. I swap standard 213.9cc injectors to 240.2cc (XU10J2TE) ones and it was definitely to much fuel. Acceleration was worse and at full throttle was to rich – voltage at lambda sensor 0.92V (max) compared to 0.88V (max) with standard injectors.

240cc injectors with 3.2bar give almost the same amount of fuel as 214cc ones and 4.0bar.

 

PS. PS.

My engine is:

Fully rebuilt XU9J4 DFW. Forged JE Pistons 83,5mm. Flowed, ported, polished and skimmed head (1mm). Compression ratio 11,0:1. 3 angle seat and valves. Balanced and lightened bottom end (lightened flywheel 1kg). OMP air filter. Magnecor Competition KV85 & NGK sparks

 

 

Photos of the throttle swap:

Edited May 31, 2007 by stux

[C_W 3 1 Cars]

I tried this one and the older Golf 16v Mk2 body and it's the latter that doesn't have the "restriction" in the top butterfly; I'm not sure why this engine was fitted with a bigger body than the Mi16 let alone the V6 engine . Anyway I tried the Golf one and it felt better sometimes but full throttle felt like it was leaning out or something as it felt best on 90% throttle.

[stux 0]

As far as I know the more cylinder the same throttle body will cope with more power. According to A.G. Bell (moder engine tuning) 4-cyl 190bhp, 6-cyl 240bhp, 8-cyl 300bhp - all with the same throttle body.

Edited May 31, 2007 by stux

[C_W 3 1 Cars]

Ah that does make sense! as they're only filling a cylinder at a time.

[skeggyrik 3]

C_W i read though the whole of the post from the other year earlier on. So did you stick with it or revert back to the Mi one?

 

Did anyone ever get any Rolling Road info on the "upgrade"

 

I could never justify going the bodies, ecu route so anything helping the standard set up is a benefit.

In the end though there's still the AFM stuck on the end of it all.

[stux 0]

In the end though there's still the AFM stuck on the end of it all.

 

There are no problems with AFM, because vacuum in plenum is 0,0bar at full throttle (AFM is not a restriction in this case), and above 4500rpm the ECU doesn’t use AFM signal.

[boombang 2]

I had the VAG one too but found it fine top end (171bhp @ 7'100 RPM) and it improved throttle control and round town economy a hell of a lot.

 

The second body doesn't open until 1/2 throttle (guesstimate) and can really feel when it is going to open so can pootle with just the smaller throttle open.

[cybernck 400 1 Cars]

stux> due to your scientific approach to things, i'd recommend you

equip yourself with VEMS WBO2+EGT to closely monitor fueling and

exhaust gas temperature side of things :-).

[veloce200 3]

I tried this one and the older Golf 16v Mk2 body and it's the latter that doesn't have the "restriction" in the top butterfly; I'm not sure why this engine was fitted with a bigger body than the Mi16 let alone the V6 engine . Anyway I tried the Golf one and it felt better sometimes but full throttle felt like it was leaning out or something as it felt best on 90% throttle.

 

KR engine is a work of art in compactness and bulletproof performance but they did indeed reduce the size of the manifold - early versions had 50mm runners which is mad for road car! People may have noticed my leaning towards the 8v in the pug. in the Golf I'm 16v all the way!

Edited May 31, 2007 by veloce200