Pavlo

Thank god for that, I thought one of us had lost it there.

Fatigue is deffo more an issue in tension. If fatigue wasn't an issue (nice thought) if it didnt fail on the first cycle, it would last pretty much forever (nice thought again).

Back to the thread however.

Mark at lateral performance does some great stuff for subaru engines.

"Engineer to Win" by Carroll Smith has good, easy to read explainations on fatigue, materials, surface finishes, heat treatments etc. I would recommend it to anyone doing any sort of detailed work on car, and wanting to know the reasoning behind part design and specification.

Paul

Andy.F

At last !!!!!!!!!

MrContro

Hello again,

One thing that I would like clarifying is...

I understand that when mapping an engine you are juggling a number of parameters to get to the most power efficient but also safe operating conditions without causing engine knock.

The parameters that affect this are AFR, ignition and boost.

From what I understand, knock is basically the fuel mixture burning in an uncontrolled way, this is caused by temperatures in the cylinder exceeding the stable ignition point of the mixture.

(In the following assume that we cannot change the intercooler or turbo to reduce in cylinder temperatures we have to the engine as it is.)

So by juggling the above parameters what you are trying to do is in effect reduce the in cylinder temperatures to an acceptable level, the end result regarding engine power efficiency is dependant on how you have tweaked the parameters to do this.
For example... if the current engine map is causing knock you may have to alter any 1 or all the parameters by varying amounts, am I right in saying that when you for example retard the ignition, you are in effect are reducing the peak cylinder pressure/temperature, this is how the knock is reduced ?

Is it better to reduce the boost, richen the mixture, retard the ignition or what.

Can anyone refer me to some usefull information regarding this ?

Feel free to correct me on any of the above :-) lol

Any help would be greatly appreciated

Andy.F

Depends on the circumstances really, the mixture should be the last resort IMHO (assuming it is correct to start with). Reduce the boost if the det is temperature induced. Retard the ignition if it is due to fuel quality.
Others with more mapping experience may have different views ??

R19KET

Like Andy says, det can be caused for several reasons. From high intake temps, to a carbon build up on the piston crowns.

One problem, is identifying what id causing the det. If we assume that the AFR is correct, reducing either the boost, or the ignition is going to cost power.

If the problem is due to excessive heat, and we have addressed the IC, then we need to make sure the turbo is correctly sized, and not causing the problem.

Next, it would be worth trying increased fuelling, because regardless of what we believe the best AFR to run is, some engines will work better, with a richer AFR.

Lastly, fit water injection. Fit the jet close to the throttle body, and use it purely for det control/in cylinder cooling.

With the correct jet, you could just inject enough water to solve the det issue, but if you fit a larger jet, you could lean the AFR out a little, and advance the ignition even more, to give more safer power.

With regards to rods, I was always under the impression that "tensile" strength was the issue, hence the concern over the rod bolts, and why the better rods use ARP2000 bolts.

Mark.

MrContro

BTTT

hypoluxa

I was also under the impression that the rod loading is squared per 1000rpm.?

rex11

the tensile load is squared...hence the double in rpm=4 fold tensile increase, good catch.

If your really want to know what factor is the best variable for reducing knock, but keeping power aas high as possible, I could design an experiment for you that will tell you what the greatest influencing factor is. We could also get a localized regression of power output to parameter settings if you can get some dyno time. Let me know if your interested.

AJKS

Just remember that 'stress relieving' is FAR more important in mechanical systems than it is in the bedroom... Do what EVER you can do elimate stress concentrations - no sharp edges, post machining stress relief (through tempering and quenching or shot peening etc), etc, etc. Often, the most important design variable is the correct material choice (plus grade, fabrication method (cast, machined, etc)) for the GIVEN application that will determine whether factures will occur at stress concentrations (does the material need to be more elastic, does it need case hardening).

I also second the comment re Carroll Smith's Engineer To Win book (and Prepare To Win). Its pushing 20yrs, but I often find myself going back to it time and time again (Ive actually being re-reading sections over the last week) - I actually use it to brush up on material eng stuff more than I use my more 'academic' text books.

Adam

tweenierob

Bttt for an interesting read..

Rob