Bad news. Threw a rod and blew up my RS2ed 3B engine

[S2central.net]

So lets say the spark is destined for #5 (and I think the firing order is 1-2-4-5-3) - are you saying that the spark can jump *inside* the dissy cap from the rotor arm to #3 because the impedance is too high inside the #5 chamber ?

That would sure by painful as #3 is next up on the firing line.

Do you have any data for resistance/impedance measurements with varying boost pressure ?

I have never heard of this weird phenomenon before... I wouldn't have imagined the resistance values to be that different with boost.

WOuldn't an uprated single coil be able to overcome the additional load factor - thats got to be easier than a coil per cylinder approach.

[EspenW]

I'll dig up some links for impedance vs. boost. I thought this was pretty well known. Same reason why it is recommended to reduce spark plug gap when chipping turbo engines like the 1.8T.

[Acidburn]

I know some early turbo'd fords suffered quite a bit with this so most had to change over to the later management.

[S2central.net]

Every day is a school day eheh. I'll have to search this one down. Weird alright...

So the correct rotor arm has ~11mm tip whilst the Audi & Bosch info calls up a 17mm tip.

What is the correct part number then 052 905 225 C ? Family album lists that as 10mm for the 3B.

[LHD_Kid]

Every day is a school day eheh. I'll have to search this one down. Weird alright...

So the correct rotor arm has ~11mm tip whilst the Audi & Bosch info calls up a 17mm tip.

What is the correct part number then 052 905 225 C ? Family album lists that as 10mm for the 3B.

Paul,
If you buy 052 905 225 C, you will end up with an 18mm rotor arm... I know, as I had one when I was trying to replace my own rotor arm...(this was the number on the part itself)
Might be worth a seperate thread on this, but it is in lots of places on here....
As far as I could tell, Audi could not supply the correct rotor arm, period. I ended up grinding down the wide one, although I think there is a toyota one which fits....
Chris


Edited to add, I have been reliably informed that 052 905 414C is the part number for the correct narrow tipped rotor arm, but I have no personal experience of getting one...!

[waad_uk]

I'll dig up some links for impedance vs. boost. I thought this was pretty well known. Same reason why it is recommended to reduce spark plug gap when chipping turbo engines like the 1.8T.

Yeah its true. It follows paschens law...

http://en.wikipedia.org/wiki/Paschen%27s_law

Breakdown voltage of any gas is a non-linear product of gap and pressure.

There is a different paschen curve for each gas/gas mixture.

[S2central.net]

Maybe my brain is having a slow day cos its MOnday, but the graph linked from that wiki site seems to show lower breakdown voltages as the gas pressure is reduced.

The non-linear element here is the tricky bit of course, and the graph will be different for each gas as you say...

1bar is about 750Torr according to http://www.unit-conversion.info/pressure.html

I've not been remotely worried about rotor arms before as I have the ABY of course. This is certainly some good info that needs to be easily found. I'll add an update to S2central in due course.

Paul

[EspenW]

Yeah its true. It follows paschens law...

http://en.wikipedia.org/wiki/Paschen%27s_law

Breakdown voltage of any gas is a non-linear product of gap and pressure.

There is a different paschen curve for each gas/gas mixture.

Excellent

[EspenW]

Maybe my brain is having a slow day cos its MOnday, but the graph linked from that wiki site seems to show lower breakdown voltages as the gas pressure is reduced.

The non-linear element here is the tricky bit of course, and the graph will be different for each gas as you say...

1bar is about 750Torr according to http://www.unit-conversion.info/pressure.html

I've not been remotely worried about rotor arms before as I have the ABY of course. This is certainly some good info that needs to be easily found. I'll add an update to S2central in due course.

Paul

Starting point of the x-axis is high vacuum (higher breakdown voltage at high vacuum, then voltage drops to a minimum at low vacuum, then climbs rapidly with increased boost)

[S2central.net]

There's some crazy people out there - LOL - this site came up in a Google for sites on Paschens law... Bonkers stuff

http://www.angelfire.com/co/rwrwrw/prop01.html

[EspenW]

There's some crazy people out there - LOL - this site came up in a Google for sites on Paschens law... Bonkers stuff

http://www.angelfire.com/co/rwrwrw/prop01.html

Good stuff. Engineering is fun

[S2central.net]

Starting point of the x-axis is high vacuum (higher breakdown voltage at high vacuum, then voltage drops to a minimum at low vacuum, then climbs rapidly with increased boost)

Yes I see that... So remembering this graph is just for air... the breakdown voltage of the gas INCREASES with increased pressure past that sweet spot.

Guess we really need a graph for air/fuel mixture to understand where the non-linear points are and how they might apply at circa 1.7bar.

All this Paschens law stuff is interesting... If I interpret that graph correctly it would indeed mean that (say) 10k volts of spark energy might find it easier to jump the air gap inside the dissy than across the plug gap in the target cylinder... But that is SOME big jump when you think the spark-plug gap is about 0.7mm and the fast moving rotor arm is about 10-15mm (guesstimate) from the wrong place. It deffo makes sense that a wider / bigger rotor arm would make this worse.

Thanks for the education on this one.

[GazzaG60]

the rods are same as on most of the non tall block vw 4v pots also.

16vt guys rate them at around 360-380lbsft before issues. rod bolts are changed to ford 289 mustang ones (arp) for strength. they are far cheaper than the arp audi/vw ones bout 1/4 cost. tyhats for rpm over 7k and over say 300hp.

the rest is in the tuning...and the fuel.

[S2central.net]

Thats a good trick, calling up Ford 289 rod bolts from ARP...

If the part numbers are different, does anything need to be done to fit them ?

Thats about 500Nm torque capability on Gazzas 16VGolf info - pretty much in line with the 500-550Nm commonly talked about here.

This spark jump appears to be the root cause though - seeing as we appear to have confirmation of use of the wrong / larger rotor arm.

Paul

[shlab]

Joe,

I just read something from RockinV8Q on Motorgeek about this. He had a 200 20v at 400whp on stock bottom end. And he made a very valid point. Why try to work AROUND fixing the problem instead of going to the source. The truth is that ANY rod will bend if exposed to pre-ignition. So building up the motor will only subdue the fact that it'll break sooner or later. So do what Keith (rockinv8q) recommended. Send your distributor out and get it completely rebuilt and add a narrow rotor on top with a brass gear on bottom. Utilize some good spark plug wires (Magnacor) and let er' rip.

The question is .. what causes spark hop? Is it play in the shaft of the distributor or is it infact that distributors CANNOT handle this horsepower/rpms?

I personally think, before you add more money into a motor, invest in rebuilding your distributor and magnacor wires.

Emy