During a particularly high rpm autocross day, rodney decided to say hi. Maybe I'll find out more during the tear down. Unfortunately this means I won't be running the new engine this high. My gearing is such that I keep tapping limiter during runs but shifting to 3rd would cost time.


Let the smoke out

Is that what I think it is

 

Well, if shifting to 3rd only costs time, but revving that high costs entire engines... I know which one I would pick to do.

 

shocked not shocked...

I read a lot of stories of K motors coming apart when driven hard constantly. Mostly on the actual track. Totally turned me away from wanting to do the swap.

 

Most of the blown up K stories I've seen have included high revs and/or modified valvetrains. Mine has been reliable (so far), but I have stock cams and am shifting at 7500.

 

You're also pushing what, 350 WHP through that engine?

I sympathize though, with the gearing on my car I'm hitting limiter a lot as well. I've tried grabbing 3rd on some of our courses but I'm rarely able to leave it there for any amount of time. I thought the 3.6 would keep the gearing pretty usable, but it's still a bit shorter than I'd like. I've considered going even shorter to make 3rd more usable and accepting that 2 shifts are going to be necessary.

 

Bummer man. Out of curiosity, are you using a stock balancer?

 

RIP! At the end of the day it's motorsports and this is gonna happen. I think the biggest benefit of the K is cheaper replacement motors when it does. I.E. a 350whp capable BP is gonna cost a heck of a lot more to replace!

 

Ouch. Sorry to hear/see that. Fire's got a great point, though. I'd be way happier replacing an unopened K than rebuilding a forged BP after an incident like this.

Just asking because I'm not as versed on these motors, 350whp is probably close to the limit of the stock rods, no? What makes you say the failure was rpm-related rather than torque related? I'd imagine that motor could make pretty serious torque down low depending on the turbo size.

 

Yeah, I’ve had vibration issues with my Z3 that winds out to 7900. I’m dialing it back to 7600.

Sorry about your block, BTDT.

I’m just about over my K-swap.

 

Ya, I can't get a taller gear and vitours are so short. I need go back through my logs and see just exactly what rpm and for how long it was running that high. I don't yet know that it was rpm related but my gut says ya. I had been running 7600 limit until this summer when I read Kpower's 7800 "recommended" red line. The last autox had a lot of limiter areas and shifting to 3rd wasn't gaining any time. Well now I know.

Stock crank pulley. Internal balance shafts are removed for this swap.

Anyways, engine arrived for less than $1000 shipped. I hope the internals that I need aren't damaged on the old engine.

 

After some late-night drunk chats at the last event, I started a rabbit hole about piston speeds and forces. I then simplified things down to speeds, because my grasp of physics comes from watching Wile E. Coyote.

I present to you a chart of some random, high-revving engines and their mean piston speeds. In m/s, because deal with it. I've overlaid the redlines I found for the stock engines, except the 2ZZ-GE, where you see two red zones - Lotus and others used this higher redline.

I will draw your attention to the correlation-is-not-causation of redlines falling suspiciously at or near 24m/s.

I'm not going to set my redline at 24m/s because that would cut out a large chunk of where I'm making power. My engine is achieving peak power at 7300rpm and only loses about 4% of that number out at 7900rpm. I'll use 7600rpm and hope for lower carnage.

 

Hmm, then my destroked LS could theoretically spin to 8600RPM... what a glorious sound it would make!!!!

 

Absolutely! That’s exactly how these things work. Just promise you’ll record it.

 

The bottom end would likely survive, but the valve train I think would come apart. IIRC the parts in my valvetrain setup have been spintron tested to 8000 with stability... I would expect valve float and destruction well before 8600rpm since im not on a solid roller and dont have monster 500+lb springs.

 

Our race engines on king of the bagger bikes are running nearly 27 m/s mean piston speeds. We've ran higher in the early years of the series, but have been rulebook regulated for quite some time. Reliability is a challenge with that type of mean speed, so it's fair to say no privately funded enthusiast would be happy with the compromise of rebuilding motors this frequently. F1 sits around 25 m/s speeds and manages to keep things fairly reliable. I really don't love making correlations between a built v-twin bike engine, an exotic F1 engine, and a factory commuter car engine, but piston speed is generally a pretty hard metric to design around as the physics are difficult to beat. Not surprised seeing most OEM's around 24-25 m/s mean speed for OEM redline..

All that said... I had my 230whp K24A redline set to 8500 which it occasionally ran up to in order to prevent a shift... Never had an internal part become an external part with doing so

 

This is awesome. I read somewhere that 25m/s is usually highest target by manufactures.

 

Old school engine builders that taught me, used to talk about respecting the 5000 ft/min rule. That stuff used to be common knowledge I thought.

 

This may also be part of my problem. I ran the car all the way to cut-off just about every lap. I’m thinking about changing my rev lights so I shift before that point. Knowing that my maximum power happens just before redline, I’m probably waiting too long to shift.

Also for me, it’s less about engine internals becoming externals than it is about not shaking the car into so many pieces every event. I’m starting to think that the K24A has fewer vibration issues than the K24Z.

 

Yeah, they also used to talk about respecting the 2 liter rule...

 

FTFY. You’ve been racing the 402.336 meter track for too long!