Currently, I’m running a 1900k with 285H Piper cams on a Emerald ECU with forged and balanced internals. The engine has been running strongly now for over a year, regularly revving to +8000rpm with no issues.
I have just had a track outing where the car was used in anger; I found that in 5th gear, the engine felt like it was rev limiting to 5500rpm - I managed to replicate it a couple of times with no sign of smoke from the exhaust (by means of looking out the back window).
I’m a little confused as to what it could be. Just last week, it felt reluctant to rev out in 4th gear over 7000rpm - so I checked and gapped the sparks, ensured the HT leads were away from the crank signal wire and that seemed to cure it, now it appears to have shifted the fault when flat out in 5th gear (oddly enough).
It would appear that the fault happened when the engine had done a few high speed laps (the track consists of two high speed straights with a sharp bend either end)
For info, I run a mocal oil cooler, with a DVA sump baffle.
I cant seem to figure this one out, although the only thing I have noticed is that the exhaust manifold has cracked at the collector welds…quite badly. I’m positive that this is from an old incident where by I had to have the manifold repaired in the past. Could this be causing the issue?
Ben, whip the crank sensor out and see if the end is bent or loose. I had this a few times on my old K series at high revs. Might be worth trying a new sensor.
[quote=SeanB]Ben, whip the crank sensor out and see if the end is bent or loose. I had this a few times on my old K series at high revs. Might be worth trying a new sensor.
Sean… [/quote]
Hi Sean,
Thats one thing I never thought of! I’ll whip it out and replace it for a spare one I have.
So, new crank sensor now in place and its still doing it. It appears to be temperature related - a few very heavy laps and working the engine hard seems to have this RPM limit still. I use a a good quality oil, Mobil 15W50 and as mentioned above, a thermostatic oil cooler. So, I’m now thinking this is either fuel or ignition related - is something breaking down when hot?
The leads are magnecore and are about 4yrs old…perhaps I should change the plugs?? They have about 4000miles on them.
As you have an Emerald, why not hook up a PC and the logging and see what it says when it’s going wrong? Just watch the throttle, ignition timing and fuel. If the problem comes on after a couple of laps it should be easy to see if it changes.
what are the other options available? Magnecor appear to have been the market leaders for many years now - at least in terms of the online Lotus brigade.
Esprit, sorry to butt in but just caught up with you and your car. Absolutely wonderful.And what a relief for you. Would you mind posting up the engine spec elsewhere on exiges, please?
Apologies for dragging this thread up and taking soooo long to update!
I finally got to the bottom of this strange RPM limit…the standard crankshaft has failed around the end counter weight. I guess the RPM limit was due to the crack expansion when hot causing the crank pickup sensor to alter the air gap thus causing strange rpm inputs to the ECU.
It eventually failed allowing the counter weight to become detached which also allowed the flywheel to have plenty of backlash!! However, no damage to conrod 4 or journal, so nothing more expensive was damaged as a result (phew!)
I’m pretty sure the failure has occured due to abuse i.e being unsympathetic with the clutch and using a Torsen and sticky tyres
Could have been a lot worse but I’m in the process of rebuilding at the moment, just waiting on a few parts.
