Safe rev-limit with Wasted Spark

[SprinterTRD]

If your worried about unburnt fuel in the then use "fuel cut" for the RPM limit type!

[Sean]

I'm trying to work out why my main bears were all loose after a teardown with only dyno time on the engine. We stripped the engine after each engine dyno session and everything was perfect. Then on the last strip down all the shells were loose; this was over a period of 4 dyno sessions and about a week.

Were the main caps loose, or the shells were loose in the caps and block?

[uvii]

^
I am now using fuel cut for the limit function, but this wouldn't do if I were to implement TC.

It's the shells in the big end, sorry if my description was a bit crap. They were all tested during the rebuild and all were in spec (they had just been serviced).

[stevieturbo]

If bolts in your engine have come loose, it is certainly not a fault of the ecu !!

[uvii]

Really, I never would have thought....

This is something that has been observed before on other engines. The current assumption is large backfires are causing the shells to get 'hammered'.

I am just trying to understand the events that are likely to have caused the issue and prevent them happening again.

[bbs16]

I think you should re-check the housing diameters of the connecting rods if the shells are becoming loose?

[Sean]

Uvii, I would think detonation is a much more likely cause of the loose shells than backfires. If you are getting backfires you can hear they are in the exhaust (mostly ) Is this engine boosted or atmospheric?

We run wasted spark in an aspirated v8, with rev limit and TC set to ign cut and never have a problem with rod bearings, and it gets in to the TC HARD at times.

[uvii]

Yeah, I agree, but A) there is no sign of detonation at all; B) the car was on its 'running in Map' which runs low boost and low Rev Limit; C) each previous strip down was fine and it had just come off long engine dyno sessions at full boost.

The only thing that we can think that correlates is hitting the Rev Limiter and this was true for another similar engine.

Clutching at straws, I agree, but I just wanted to check if there was anything obvious i'd missed.

[Holmz]

Yeah, I agree, but A) there is no sign of detonation at all; B) the car was on its 'running in Map' which runs low boost and low Rev Limit; C) each previous strip down was fine and it had just come off long engine dyno sessions at full boost.

The only thing that we can think that correlates is hitting the Rev Limiter and this was true for another similar engine.

Clutching at straws, I agree, but I just wanted to check if there was anything obvious i'd missed.

Well with a 6-cly you could run CoP as 6 units with an m800. That would totally alleviate any chance of a spark on the off-cycle. This is the only sensible option, if it is in fact an issue at all.

[Sean]

Just wondering, what is the engine? Have you read this thread.....

viewtopic.php?f=11&t=734&p=3469