What is the upper hp limit on stock rods?

[Knight Rider S4]

It has been suggested to me that "the 3B which had an inferior ignition system which leads to preignition which = BROKEN RODS. Alot of it had to do with people using the incorrect distributor cap (yes there is a difference= narrow points)"

Is this the real problem with the 3B that doesn't occur with an ABY or ADU (or AAN)?

(I am not being argumentative, just curious).

Think someone is getting there wires crossed here with retarding ignition to create more HP with higher boost levels

[a4kquattro]

Think someone is getting there wires crossed here with retarding ignition to create more HP with higher boost levels

I think what dave is referring to is "spark hop" which occurs when the spark arcs arcoss the distributor rotor to the WRONG CYLINDER causing disasterous preignition. I'd personally feel safe taking my own AAN powered car to 400 *wheel* hp on stock internals, no problem.

[prosty]

I have a crazy friend who uses a GT40R and 150hp nos and stock rods, his URQ has gone 11.1 on the dragstrip, he's really crazy but this year he's finally rebuilding the engine..

The bigger hotside the less backpressure, and that also relieves the rods from bending. My guess is that this causes the stock rods to bend with and rs2 turbo.

[UrS4boy]

I think what dave is referring to is "spark hop" which occurs when the spark arcs arcoss the distributor rotor to the WRONG CYLINDER causing disasterous preignition. I'd personally feel safe taking my own AAN powered car to 400 *wheel* hp on stock internals, no problem.

I seem to have opened a can of worms that might be relating bent rods to spark hop on a 3B distributor because the wrong rotor has been used:

http://www.sjmautotechnik.com/trouble_shooting/20vboost.html#rotor

I have zero 3B experience because in Canada we got zero S2s and we didn't even get the 200 20vt with the 3B that the Yanks got. Seems they (the Yanks) have had 3B spark hop problems when a normal 7A rotor is used instead of the proper 3B rotor.

SO...now I don't know what to believe about HP, torque and bent rods. I am, however, very pleased that my AAN does not have a dizzy.

[Jamo]

I seem to have opened a can of worms that might be relating bent rods to spark hop on a 3B distributor because the wrong rotor has been used:

http://www.sjmautotechnik.com/trouble_shooting/20vboost.html#rotor

I have zero 3B experience because in Canada we got zero S2s and we didn't even get the 200 20vt with the 3B that the Yanks got. Seems they (the Yanks) have had 3B spark hop problems when a normal 7A rotor is used instead of the proper 3B rotor.

SO...now I don't know what to believe about HP, torque and bent rods. I am, however, very pleased that my AAN does not have a dizzy.

All you need to know is that rods like any other component have a limit. The closer to the limit you run them the more likely hood they are going to bend.

The primary rod bending force is torque and then bhp.

Think of it this way, torque is how hard you've been punched in a fight, bhp is how many times you got punched in a fight.

You can get hit hard once by the torque you get knocked out ( bent rods )

You can get hit slightly less hard ( lower torque ) but repeatedly more times ( high bhp ) and through fatigue you'd get knocked out ( bent rods ).

[UrS4boy]

All you need to know is that rods like any other component have a limit. The closer to the limit you run them the more likely hood they are going to bend.

The primary rod bending force is torque and then bhp.

Dude: I am not a Noob. I understand about hp and torque. I just wanted numbers. The "spark hop" theory (not mine by the way) suggested that the bent rods in the 3B in the thread quoted in an above post were not due to the RS2 turbo but to other factors, e.g. spark hop causing pre-ignition and the piston being forced upwards against a downward travelling and expanding flame front.

Personally, I am happy with the 550 Nm (405 lb ft) answer. If others want to attempt higher levels of hp and torque on stock rods, good luck to them.

BTW - I checked the Family Album on the crankshaft bearings. As far as I can tell, they are the same for an ADU (RS2) as an ABY (or AAN). Rod bearings are different.

[caterpillar]

conrods

org conrod are not safe anyway: have you rebuild the engine or have the big hp in the mind: by new conrods
sorry for the advert: www.stenparnermotor.se / H-profil staker
the cheapest alt.

[Audi_CQ]

This is a never ending story without an answer
Details in setup is one thing(small turbo with large pumping losses but strain on rods even if not showing as power on dyno) and factory toleranses in the rods is another.
The simple answer is : if in doubt, change rods

[a4kquattro]

also, are we talking about WHEEL torque or flywheel torque?

In my experience, the single biggest factor that determines how hard you can push the internals of a motor is the quality of the tune...

[EspenW]

Picking up an old thread here..

I agree with the pre-ignition theory. Most all rod failures happen on the 3B engines, and this is most likely due to use of the wide rotor. The E*KA even lists the wrong rotor (17mm tip), so it is easy to get the wrong one. The correct one has a 11mm tip.
Think about this: a bone stock RS2 will produce approx. 380bhp on a (very) cold winter day. People have bent rods with power levels lower than this. It is highly unlikely that Audi and Porsche would equip a flagship model like the RS2 with rods that would have a safety factor so close to 1.0 (and even below 1.0).
Something else: a rod (or any structure) deforms when it is bent past its elastic limit, into what we call plastic deformation (permanent deformation). A rod that would go plastic at, say, 360hp would have substantial elastic deformation at power levels produced in an ADU on a normal 10deg day. (Factory hp is rated at 20deg C (DIN) and increases with decreasing temps, etc). A flexing rod is not a good way to transfer torque to a crankshaft, as it absorbs power. This means that a stock rod with a (mythical) deformation limit of 360-400hp would display noticeable flex in a stock RS2. This is not likely.
Pre-ignition is what kills most rods. The poor rod get the force of the combustion in its face as it is on the way up, instead of a "gentle" push in the back as it is on its way down. It is the same as the difference between a head on collision going 60mph and being rear ended by a car doing 70 while you're going 60.
Rods can bend at "low" power outputs due to high boost or lots of ignition advance, since this increases the temperature in the combustion chambers and increases the risk of pre-igntion, so, an engine producing 400hp @ 1.5bar due to a well flowing head is less likely to bend rods than one that produces 400hp @ 2 bar.

Most rod failures happen at low rpm, this is no wonder, as the risk of detonation is the highest at low rpm/high torque (more heat, and each knock event has more time available to occur). Detonation superheats the metal of the chamber, and can easily lead to pre-ignition.
Note that 034 claim their (up to) 450hp 3071 kits to be fine on stock internals.
Also, people have logged 500hp+ at the wheels on 16v turbos on stock rods, the load per rod equals 700+ flywheel hp on an I5..
By all means, aftermarket rods is a good idea, since they increase the factor of safety, but I believe that the stock rods can take a lot more punishment than people give them credit for, and that the failures most of the time are due to other factors than high hp/torque.

[S2central.net]

also, are we talking about WHEEL torque or flywheel torque?

In my experience, the single biggest factor that determines how hard you can push the internals of a motor is the quality of the tune...

Why dont the 'murricans just say 'at the wheels' ?

This 'wheel torque' term slays me - too easily confused as a lazy of way of meaning flywheel or even lazier way of saying 'at the wheels'.

Jamo's analogy is curious but effective nonetheless.

That nitrous monster could be crazy bhp at the redline but not have enough torque in the midrange to bend rods - thats a characteristic of a huge turbo with large free flowing hotside that only blows strong way up the rev range.

For me 500Nm is a safe number leaving some margin to 550Nm where I feel you get into the scarey zone. Thats a flywheel number - why would a conrod care about anything else ?

Paul

[EspenW]

A stock RS2 produces approx. 500nm at 3000rpm on nice winter day (-30degC) in Northern Scandinavia. There is no way Porsche did not take this into account when they spec'ed rods for the ADU. Considering material fatigue and production tolerances, a 500nm safe limit would mean that the RS2 would have a safety factor of 1.0 (safety factor= max sustainable load/max load in use) under environmental conditions that it would definitely see in some countries. Porsche knows better than that
Rods bend around peak torque because that is where the engine is most likely to develop detonation and pre-ignition (max torque = max thermal efficiency= most heat).
Heat combined with low rpm that allows knock to take place= best conditions for detonation, pre-ignition and banana shaped conrods

[S2central.net]

I don't have an RS2 datasheet in front of me but my memory is of something around 420Nm - presumably spec'd for nominal ambient conditions of 20 celsius. Whilst its correct that an RS2 on factory software does NOT reduce boost at cold ambient I would be gobsmacked if its pushing 500Nm at 3000rpm high up in the Nordics. Are we talking normal pump fuel here or something exotic ?

What data do you have for this statement ?

I'm not looking for an argument here - just a bit amazed is all !!!!


Paul

[EspenW]

Data using the SAE J1349 equation for dyno correction due to environmental factors.
(all dynos use this or the similar DIN equation in order to standardize power output)

Here is an online calculator:

http://www.csgnetwork.com/relhumhpcalc.html

Note that the J1349 is developed for NA engines. Waste gate controlled FI engines are less affected by ambient air pressure (lose approx half the power of NA at altitude).
Nobody seems to know if FI is more affected by temperature change than NA.
FI will gain less from the increased density of the colder air, but they might gain more due to increased intercooler efficiency, especially cars that are on the knock limit.

[EspenW]

On the topic of wheel horsepower:
When using a rolling road, wheel horsepower and wheel torque is what is actually measured... flywheel horsepower and flywheel torque is what is guessed
(unloaded coastdown measurement will not represent tranny losses generated under load). The MAHA dyno uses advanced algorithms to come up with a flywheel number, but it is still not a measured number, just calculated. Most other dynos just add a guesstimate or fixed percentage (also wrong, since tranny losses have some components that constant and some that are depending on load)