View single post by NigelK
 Posted: 07-28-2018 01:40 pm
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Joined: 07-16-2014
Posts: 196
Dear All

I've just got my GT back from Lotusbits with the latest (and definitely final) engine upgrades. Upgrades as follows - i) gas-flowed CNC ported head with new valve guides and valve seats cut to fit Lotusbits oversized waisted valves, ii) Kent L14 cams inlet and exhaust (similar to Lotus 104 cams), iii) skimmed and matched inlet manifold, iv) Lotus spec 10 ignition system (Lucas 45DM4 distributor / AB14 remote amplifer and coil) replaced with mapped ignition system (crankshaft mounted trigger, DTA S40 Pro ECU with throttle position and temperature sensors, plus coil pack).

Troy at Northampton Motorsport, with help from Dave from Lotusbits, then set the car up on the rolling road with tweaks to the ignition and some leaner main jets. The chart shows engine hp, engine torque and lambda before (dotted lines) and after (solid lines) the upgrades.

Peak hp has increased substantially from 183.6hp at 6,850rpm to 204.8hp at 7,050 rpm. Peak torque has increased marginally from 167.1lb-ft at 5,000rpm to 171.5lb-ft between 4,900-5,700rpm. Both power and torque are generally lower below 4,500rpm, as would be expected with more airflow in the head and different cams. There is still a significant power and torque dip on the dyno plot, albeit at 200-300rpm higher than before. The lambda figures would suggest this could be an over-fuelling issue, certainly the dip was more pronounced before Troy fitted leaner main jets. There is probably little more I can do to fix this dip, short of going full EFI which I do not want to do.

And in any case, I do not notice the dip in everyday driving. In fact there is noticeably increased tractability at lower revs with the mapped ignition. There is a pronounced boost in power and torque at 3,000rpm, although nothing too raucous. However the car now really takes off at 5,000rpm making overtaking a breeze with the large bore exhaust emanating a lovely 4-cylinder snarl. Lots of fun!

Best wishes,

Attachment: Dyno results 250718a.jpg (Downloaded 89 times)