08-11-2014, 09:07 PM
I did a crap load of research into precup related shenanigans back along...
The result I came out with is - go direct injection or leave them the f*ck alone! I've seen people ceramic coat them to keep the heat out, however this generally causes problems, most I've seen - the coating flakes off - no matter what you do, the precup is DESIGNED to run intensely hot, when running, this provides better, more instantaneous ignition, especially when the coolant temperature is down and during cruising, improves economy and combustion quality - this is one of the main ways the IDI engine is infact better than Direct Injection. High power levels accelerate the cracking, but you take apart any stock 90hp XUD9 and the precups will be cracked... I've only ever see ONE drop a cup.
Also if the precup is cooler, you get more noise - half the reason IDI engines were invented in the first place was for NVH reasons, the precup being hot is for the same reasons that most DI and late XUDs have twin-stage injectors and now on Commonrail, multi-burst injection - all to reduce noise...
I personally don't think unless you went down the road of different design injectors with more up-to-date precups (read Kubota...) you'd see any benefits... End of the day, going from 9 > 11mm is the only difference in the actual injection rate per crank degree/mS, when you crank the max fuel, you're doing nothing but increase the duration - hence IMHO there's little need to have larger precups... You're shoving the burning fuel mix through the hole at the same rate no matter whether it's idling or making 200hp - it just takes longer to do so.
The Merc OM603 and OM606 is an Indirect motor, no adjustments to the precups (admittedly of a different design..) and they're making happily up to 600hp with reasonable reliability... Just the slight issue of blowtorching pistons instead.
The result I came out with is - go direct injection or leave them the f*ck alone! I've seen people ceramic coat them to keep the heat out, however this generally causes problems, most I've seen - the coating flakes off - no matter what you do, the precup is DESIGNED to run intensely hot, when running, this provides better, more instantaneous ignition, especially when the coolant temperature is down and during cruising, improves economy and combustion quality - this is one of the main ways the IDI engine is infact better than Direct Injection. High power levels accelerate the cracking, but you take apart any stock 90hp XUD9 and the precups will be cracked... I've only ever see ONE drop a cup.
Also if the precup is cooler, you get more noise - half the reason IDI engines were invented in the first place was for NVH reasons, the precup being hot is for the same reasons that most DI and late XUDs have twin-stage injectors and now on Commonrail, multi-burst injection - all to reduce noise...
I personally don't think unless you went down the road of different design injectors with more up-to-date precups (read Kubota...) you'd see any benefits... End of the day, going from 9 > 11mm is the only difference in the actual injection rate per crank degree/mS, when you crank the max fuel, you're doing nothing but increase the duration - hence IMHO there's little need to have larger precups... You're shoving the burning fuel mix through the hole at the same rate no matter whether it's idling or making 200hp - it just takes longer to do so.
The Merc OM603 and OM606 is an Indirect motor, no adjustments to the precups (admittedly of a different design..) and they're making happily up to 600hp with reasonable reliability... Just the slight issue of blowtorching pistons instead.