What is the reason for breaking rods. I'm boosting at 9psi and making only 380ish hp and 310ish ft/lbs torque. Guys with TT setups are making 400/400 with 6-7psi and they seem to break more frequently. So what gives? Boost or HP?

 

It's the torque man. Centrifugal s/c's have poor torque due to low boost at low RPM's, which is why we see less rod failures with s/c's. TT however has full boost at 3-3.5k rpm's which puts alot of pressure/torque on the rods.

 

So it's due to stress caused by the resistance of the crank to spin? Not due to the lack of space (air) at TDC due to being full of compressed air.

 

What do you think about running an 11psi pulley then. I have one sitting in my garage that just stares at me. I heard it's too much for the intercooler to handle the charge. I may try it for kicks.

 

Are you talking about the 2.87 serp pulley ? Mine is staring at me also.....lol...Ive got a post at 350Z . Greddy makes a relief valve to prevent boost spike . Was wondering if we could make this work for us . Vent off any thing over 9 or 10 psi and be able to get into boost sooner with the 2.87 pulley

Couldnt afford it when young...gonna play when Im old

 

As far as the TT breaking rods....yes I believe it is the trq down low that is doing it.

Couldnt afford it when young...gonna play when Im old

 

I agree. Hopefully one day I'll get my Stillen S/C and nothing will break and the car will last long.. haha.

Thanks - Joey Avino

 

Cylinder pressures that are two high cause rods to fail. Particularly, the peak pressures reached in the combustion chamber. Compression by itself doesn't cause this. The combustion process, it's timing, the fuel mixture can all play a role in this. Higher peak pressures generally lead to more torque, but it's not exactly linear with HP. Most of the extra torque an engine makes is created after the peak pressure point. While peak pressures will still rise a 100% increase in torque may only be a 50% increase in peak pressure.

"So it's due to stress caused by the resistance of the crank to spin? Not due to the lack of space (air) at TDC due to being full of compressed air. "

Yes. But perhaps not in the way you might be thinking. When accelerating a car, there is always resistance. An object in motion wants to stay in motion and an object at rest wants to stay at rest. In order for a car to accelerate, it must fight the urge to stay at rest. The faster you want it to accelerate, the more it has to fight this physics law. So the stress on all parts becomes greater.

But to answer the original question, no, torque does not cause internal engine parts to break. The presense of more torque means you are probably experiencing higher cylinder pressures. These higher pressures put up against the car's resistance to motion or acceleration puts the load on the rods. And it's not necessarily the torque down low, but the torque present at any RPM. Torque output is highly related to cylinder pressures. This being the case, the failures can certainly occur at higher RPM boosting as well as lower RPM boosting.

Keep in mind I am only referring to compressive rod failure as opposed to tensile(which involves higher RPMs).

 

DONT DO IT!!!

everyone knows that the story of 'that guy' who ran the 287 serp is only a myth.....

on a quiet and clear night, i can still hear the whine and whizz of that 287, as his ghost boosts down the road.....

:^)

ps- there is no clearcut solution to your question..... too many variables to discount! the s/c, with linear boost, will lend itself to less stress loads (yet other issues arise)

<P ID="edit"><FONT class="small"><EM>Edited by esemes on 09/21/04 04:58 AM.</EM></FONT></P>

 

Scott....So you never ran that 2.87 pulley did you ? So why lie about it ?

Couldnt afford it when young...gonna play when Im old

 

[sarcasm] nahh.... never ran it....... just pushed the car w/ it on...[/sarcasm]

c'mon...

 

Well we know now why it didnt mess up your jackshaft and it did mine .!!!!!!!!!!

Couldnt afford it when young...gonna play when Im old

 

boog-

i hope you can interpret my sarcasm bro....

wait, maybe i didnt even have a voirtech either..... or a g35...

heck, im not even old enough to drive!!

c'mon already!!

i wont take credit for anything, but jeeze...... i am 100% legit

for god's sake, i sold the blower WITH the 287 still on it .......

((maybe i should get a note from the dealer??))

hope you were kiding

es

 

Esemes, your car was so clean, I'd be suprised if you even drove it.

Boog, he ran it on his car, but never tuned it to see what it could really do. I think that's what he was implyin- "Who cares if you had it, if you can't share experiences on the forum it's like you never had it." type statement

 

thanks craig....

coming from a guy that has the most outstanding looking infiniti i have ever seen, that means alot!!

and yep, i did run it (observing double digit boost levels at 6K) , i felll short of proper tuning....

the only way (IMO) that i would think this can work (and i do believe it can), is tolower your shiftpoint, remapp accordingly, get a stiffer spring for the bov (or replace altogether), and maybe an enlarger I/C)...

of course, you could just mapp for it, and see how everything reacts, but i am speaking about what i think would be the optimum way to benefit from the added boost levels.... (maybe a watersparay on the i/c, or the CO² i/c kit??)

worth a shot, imo (if for no ther reason than to prove that it fit and does spin as i reported)

ese