RS2 remap - will it bend the rods ?

[Jonas_R]

Yes ask SteveH



http://www.s2forum.com/forum/showthread.php?t=1352

Yeah but then again it is a 3B.

[4WheelDrifter]

I'm pretty sure the number I have heards is around 125Nm per rod (mk 2 golf guys) which would be 625Nm on S2.

Also I'm sure that the bend rods was on 3B with the rotorarm and due to pre ignition. Never heards of bend rods on RS2 setup with multi coil setup.

The torque figures smell about right to me.

A good map won't bend them, it's the slightest amount of detonation when pushing the envelope that does.

Mine has rods but I've water injection just to protect it at the top. Mapped without it though.

As Darren points out, it's not just torque that can bend rods, detonation can too. So watch out for cheap generic chips when running high power/torque.

[prj]

Detonation bends rods. To bend them with torque you'd need more than 800nm at very low rpm.

Bigger issue is metal fatigue. Where they can snap for no reason.

[vti2]

Friend of me is Running 469hp and 600nm on stock Engine Mappen at MTM, they say Big torque Numbers under 3000 rpm will Bend rods. Everything above this rpm is No problem.

[EspenW]

Friend of me is Running 469hp and 600nm on stock Engine Mappen at MTM, they say Big torque Numbers under 3000 rpm will Bend rods. Everything above this rpm is No problem.

Interesting. So major problem at 2950rpm and all golden at 3010rpm?
Do they have a reason that does not involve detonation sensitivity for this?

(there is one, but it does not have a on/off behavior at a certain rpm and is actually affected by piston weight, etc).

As PRJ mentioned, detonation is the key here. Torque is the result of average cylinder pressure during the expansion phase. You can have high torque with low peak pressure (but high average) and low torque with high peak pressure but low average pressure.

Relation to boost:
As a general rule, when you double the boost, peak cylinder pressure goes up by only approx. 20% (but average pressure and torque/power by much more). It is the peak pressure that can bend a rod.
However, increase timing from for example 10 to 20BTDC and you increase peak pressure by around 100%.

Torque is a decent proxy for peak cylinder pressure, but far from an absolute one.

And: let us not confuse the spark hop induced damage on the ancient distributor type ignition systems with bona fide torque induced damage. That spark hop issue at high boost on the 3Bs (and likely after fitting the wrong rotor....) has generated so many myths and misconceptions on the I5s. Almost like the ''backpressure makes torque myth''.

Check these curves out:
The blue curve is my torque curve measured at the wheels. That is 461lbft/625nm at the wheels. There is likely a certain drivetrain loss, so torque at the crank is likely 15-20% higher, ie. +/- 750nm.
The yellow curve is torque at the wheels of a built I5 of a acquaintance of mine. That engine pulled 467whp on the road (but 515whp on a Mustang dyno with different cams). Rated at around 700hp at the crank (with the hotter cams).
As we can see, I make way more torque, way earlier than this 700hp engine.
Now, this discussion is about torque, but it sort of puts to rest the old notion that rods must be changed at 400hp (crank)

[vti2]

I assume that to get high torque Numbers at low reis you will Need to advance timing and pull boost up, These three factors combined with low revs will Bend your rods. We allways Bend rods when we go to overboost (2 bar) under 3000 rpm.

[EspenW]

I assume that to get high torque Numbers at low reis you will Need to advance timing and pull boost up, These three factors combined with low revs will Bend your rods. We allways Bend rods when we go to overboost (2 bar) under 3000 rpm.

Check out a chart that shows knock sensitivity vs. rpm.
The engine is much more prone to detonation at low rpms, as there is more time available for a knock event to occur.

However, at higher rpm, the inertia of the piston causes a tensile force in the piston that will offset some of the compressive force.