Friday Video : Link to the 518 awhp dyno video (VAG Motorsport GT25 S4)
03-02-2007, 07:41 PM
#31
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Rod bolts have little to do with handling power as they become stressed in putting the
piston back to the top. More of an RPM vs small end + piston weight problem.
Breaking a rod from too much power would be a compressive failure and would collapse the beam of the rod and leave the cap intact along with the bolts.
Breaking a rod from too much power would be a compressive failure and would collapse the beam of the rod and leave the cap intact along with the bolts.
03-03-2007, 05:05 AM
#34
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No disrespect sir, but I have a degree in structural engineering. I have spent many hours in the...
lab performing stress analysis on all sorts of real world scenarios.
As far as what you are talking about it depends on the configuration of the rod. In the case of the 2.7 you are completely wrong, the rod bolts are installed through the cap and threaded into the rod. Max yield is experienced on the downstroke. This is where any yield will cause an "egg-ing" and an out of round condition occurs and normally causes problems, such allow the bearing to spin, and stresses that can travel up and down the beam during this deflection.
If you are collapsing a rod it is not from too much power, its from improper tuning. In my experience the OEM parts can normally handle the power you are trying to make within reason. It's the guys who are trying to make it the wrong way and get caught up in the dyno moment. Knock, Heat and Foolish-ness is what leads you to your broken parts.
No matter what people may say, on a VAG motor the tools are out there to data log and see excessive knock and corrections. These conditions exhibit stress and forces far more than any peak cyl. Tq you can make. If you push, they break.
As far as what you are talking about it depends on the configuration of the rod. In the case of the 2.7 you are completely wrong, the rod bolts are installed through the cap and threaded into the rod. Max yield is experienced on the downstroke. This is where any yield will cause an "egg-ing" and an out of round condition occurs and normally causes problems, such allow the bearing to spin, and stresses that can travel up and down the beam during this deflection.
If you are collapsing a rod it is not from too much power, its from improper tuning. In my experience the OEM parts can normally handle the power you are trying to make within reason. It's the guys who are trying to make it the wrong way and get caught up in the dyno moment. Knock, Heat and Foolish-ness is what leads you to your broken parts.
No matter what people may say, on a VAG motor the tools are out there to data log and see excessive knock and corrections. These conditions exhibit stress and forces far more than any peak cyl. Tq you can make. If you push, they break.
03-03-2007, 06:26 AM
#37
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Guess it was bound to happen...
<img src="http://pictureposter.audiworld.com/55192/waterfest-005web.1.jpg">
<img src="http://www.vagmotorsport.ca/gallery/Steve+S4+GT25r%27s/image/700/Steeve+GT25+S4+017.jpg">
<img src="http://www.vagmotorsport.ca/gallery/Steve+S4+GT25r%27s/image/700/Steeve+GT25+S4+017.jpg">
03-03-2007, 07:51 AM
#39
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All good points on the bolts..
And I can understand the points you have made.
Don't agree 100%, but such is life on a car forum.
Riddle me this. If your CF's are mostly 0's (117 motor octane fuel), A/F about 12:1 and all the other typical related deto parts (plugs, ring lands, head gasket) all look and measured factory fresh. What broke the rod? And how can a better tune have saved it?
I am sure if I would have had cylinder pressure monitoring equipment in that motor I could have keep the peak pressures below what is deemed critical... To be honest I have considered purchasing the equipment.
Could of - should of.
Since we are on the subject and you seem to feel like sharing. What are your thoughts on the "Limits" of the 2.7?
Don't agree 100%, but such is life on a car forum.
Riddle me this. If your CF's are mostly 0's (117 motor octane fuel), A/F about 12:1 and all the other typical related deto parts (plugs, ring lands, head gasket) all look and measured factory fresh. What broke the rod? And how can a better tune have saved it?
I am sure if I would have had cylinder pressure monitoring equipment in that motor I could have keep the peak pressures below what is deemed critical... To be honest I have considered purchasing the equipment.
Could of - should of.
Since we are on the subject and you seem to feel like sharing. What are your thoughts on the "Limits" of the 2.7?
03-03-2007, 08:02 AM
#40
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Re: Jeff, honest question, how much power was this making? Can you share more details on the setup?
-100% factory motor (not the AMU which has the factory high output parts)
-GT turbo.
-117 motor octane fuel on really racy timing maps.
-In fifth gear it could make 25ish psi close to 3000 rpms. About the situation where the failure occured.
-Lot's of rod poping potential power per cycle.
-AF ranged from 12.3-11.4:1.
Mostly 0 CF's.
-Piston crowns looked like a 1000 mile factory fresh motor.
-Rings lands 100% intact.
-Head gasket intact.
-Never lost a plug.
-Rod bearings perfectly intake and had normal wear for a motor with 60ish K.
Besides making less power per cycle how can a tune affect this?
-GT turbo.
-117 motor octane fuel on really racy timing maps.
-In fifth gear it could make 25ish psi close to 3000 rpms. About the situation where the failure occured.
-Lot's of rod poping potential power per cycle.
-AF ranged from 12.3-11.4:1.
Mostly 0 CF's.
-Piston crowns looked like a 1000 mile factory fresh motor.
-Rings lands 100% intact.
-Head gasket intact.
-Never lost a plug.
-Rod bearings perfectly intake and had normal wear for a motor with 60ish K.
Besides making less power per cycle how can a tune affect this?