Wastegate dilemma

[220bhp]

I am rebuilding my head and have two wastegates, one still has the anti tamper disc l,and the spring length is 97mm. the other one has the the anti tamper disc missing, and the spring is 82mm,and the distance from the top of the cap to the screw is 7mm.
both have the same number of coils,and appear to be of the same gauge wire.so which one should I use

[Rusty]

82mm sounds like an ABY item. The pre-load on the spring is about 46mm for an ABY WG. For an ABY cap, this represents around 8 turns of the adjuster from it being flush with the top of the cap.

HTH

[220bhp]

Andy the short spring came from the doner car,it belonged to Neal at all audi, its a
3b,but it is quite possible that he fitted another spring.The longer one spring came from my own 3b,which as far as I know has never been changed.
As I am now running an rs2 setup,I wondered which one to use.I take it from your post that the shorter spring would be the one to use. I appreciate your help, as I amstanding with spanner in hand.

[Rusty]

If you can, measure the springs. AFAIK, the ABY and ADU use the same spring. It has a spring rate of around 3 N/mm, which is pretty soft.

Dimensions are approximately -

Length = 81mm
Outer Diameter = 38.5mm
Wire diameter = 2.8mm
Coils = 4

Pre-load (measure the gap between the cap and base with the cap just sat on the base) = 46mm

If the spring is significantly different, then it's not an ABY one.

You can adjust the pre-load with it on the car between 0.2 and 0.5 bar. Se it to give 0.4 bar approx with the N75 unplugged (electrically).

HTH

[UrS4boy]

Stock vs 1.9 Bar Wastegate springs

You can adjust the pre-load with it on the car between 0.2 and 0.5 bar. Se it to give 0.4 bar approx with the N75 unplugged (electrically).

0.4 Bar (about 6 psi) is the stock mechanical boost setting above which the ECU via the N75 will raise the boost. Many people have removed the anti-tamper "plate" at the top of the wastegate and turned the spring perch down about 6 turns (clockwise). This increases the base mechanical boost, which to some people, improves the response when you go from no boost to boost.

Other people, such as me, have gone with a 1.9 Bar (absolute) wastegate spring. This provides about 0.9 Bar base mechanical boost (about 12 - 13 psi). This seriously increases the "snap" on initial throttle tip in. However, IME, you have to raise the spring perch up (screw it up, anticlockwise) from the stock position because if you don't the rate of boost rise is faster than the ECU can cope with and it freaks out. Fun once you get it dialed in. Here is a photo of the 1.9 Bar spring (left) and the stock spring (right):

[Rusty]

Having tried a few springs, chosen after modelling the WG behaviour, I have to say that anything other than a stock spring requires a specific map to avoid the car running like crap or doing damage.

[Error404]

OT but does anyone know of somewhere to buy springs like these from? Not neccessarily wastegate springs, but similar size / rate etc

[4WheelDrifter]

Stock 3B spring for reference:

[Rusty]

OT but does anyone know of somewhere to buy springs like these from? Not neccessarily wastegate springs, but similar size / rate etc

What do you want...

[UrS4boy]

Having tried a few springs, chosen after modelling the WG behaviour, I have to say that anything other than a stock spring requires a specific map to avoid the car running like crap or doing damage.

Disagree. I have been running an "unmapped" 1.9 Bar spring (with the perch turned up) since 2007 and liking it a lot. No "running like crap" or damage.

But hey...each to their own.

(Car by the way is a 93 UrS4 AAN, fully RS2'd with MRC Stage 3 RS2 software)

[Rusty]

Different setups perhaps. My chipped ABY did not like it at all.

[220bhp]

So what do's my 97mm spring come from I wonder,as I said Ido not think it has ever been tampered with.

[UrS4boy]

Different setups perhaps. My chipped ABY did not like it at all.

You probably needed to turn the perch UP (from the stock position). I would try it again, starting with the perch all the way UP and then screwing it down bit by bit until the ECU doesn't like it, and then turn it up a notch.

[Rusty]

If you turn the perch up, it's no longer a 1.9 bar spring... I had a spring that adjusted between 1.7 and 2.1 bar. There were few gains from 1.7 bar and it didn't like anything higher, so I removed it. Swapping to more aggressively mapped chips had a more desireable effect than using the spring and showed none of the running problems when coming on boost.

On my stock setup, a 1.9 bar spring cracked at 1.9 bar but the tailed off to 1.4 or 1.5 bar at the top end. Some more testing would most likely have shown that a stiffer spring with the same pre-load force (giving the same WG crack pressure) would have tailed off less but I was already at 5x the stock spring rate and decided to leave it there. A custom map would tune the N75 to complement the spring perfectly and make the car run withing the correct limits and thus a lot happier.

After modelling and then testing, I was able to calculate WG crack pressure to a decent degree of accuracy and could then set the WG and spring up to give me what I wanted, as well as purchase off the shelf springs to use, which are a lot cheaper than parts sold by a tuner...

The longer spring sounds like it's got more pre-load and thus may give a higher WG crack pressure than a stock spring.

[220bhp]

Whats the differance in lenght of stock aby.adu, aan, 3b,if any