Con-rods stresses: inertial+combustion forces

[bigtoe]

Im new here so treat me gently..LOL..I used to build LOT or Rally engines when i was in my early 20's.None were turbo charged but i used to use very high CR's and dependant on engine size etc very high revs.

I found a cheap way to rods that were VERY strong.I used ones out of diesel engines.They take a lot of lightening the need to be dynamically balanced but they have plenty of meat at either end to playwith and i used to mix and match bearings etc no problem.

All you guys need to do is find a rod thats the same length, or very close and let the engine shop do the rest.

[KramRS2]

Hi Marco,

After this very good post and some discussion by e-mail, I’ll test your theory this weekend. I’ll do a fine tuning to the ECU and rise the boost to something like 1,55bar. It will be flat, from the point it makes this boost until redline.
I use only 102 octane fuel (now widely available here via BR fuels) and use 5-6º more time advance over the stock map. Remembering, I use K&N conical filter, stock intercooler, stock MAF, no cats, 3pol exhaust, almost stock turbo (with a bigger compressor wheel).

How much power do you think I can make?
Do you think that I can leave the RS4 behind?:nana:


This is my first post, and I would like to congratulate every one here for this amazing forum.


Best Regards,
Mark

[Pisobiker]

Hi Mark,
nice having you on this forum.

Well, as I already said, from a "mechanical stress" point of view, engine wont be hurt by using 1.55 bar boost at redline, given all the fuel and ignition management are correct and exhaust + overall engine temperatures are kept in the safe range..... and of course given your turbocharger cold side is capable of managing such a boost with the engine flow requirements at redline.

You told me your RS2 k26 7200 has a modifyed cold side impeller that should give more flow, but without a map its hard to tell if you really got the ~ +13% more flow required in respect to the 1.25 bar boost at redline known (around many tuners) to be the real top for the RS2 turbo cold side at redline. Modifyed impeller for higher flow rates, moreover, will probably negatively affect low rpm flow with a surge line presumibly shifted a little higher in the rpm.

Apart from that, given your turbocharger will be OK, since cold side maps usually show impeller constant speed curves decreasing quite sharply while reaching the choke line, it seems to me you'll be underworking your cold side at engine midrange if using "only" 1.55 bar boost.
With such a boost capability that you claim at say 7000 rpm, your boost curve may look much more like that:

0.80 @ 3000
1.30 @ 3500
1.80 @ 4000
1.80 @ 4500
1.75 @ 5000
1.65 @ 6500
1.55 @ 7000

This way you'll have much more push in the midrange with a 1.8 peak boost that is told to be whitin safe limits for the 7200 (but as said, your modified impeller could not be able to manage that peak boost).


Anyway, I can guess that with a good fuel+timing setting and 1.55 bar boost at 7000 rpm you could get over 400 hp, probably around 420/430 with ~ 42 kgm of torque (@ 7000 rpm).

Keep me informed on how your testing goes, and..... good luck beating RS4s



Ciao

Marco