Lotus Elan

weber carbs and piper cams LOTBP285 ultimate road

PostPost by: lotus_elan_s4 » Tue Jun 19, 2018 1:16 pm

hi all,
did someone try the LOTBP285 ultimate road cams with 40 weber carbs?

i'm using the weber 40 dcoe 18 carbs, with the weber sprint setup (jet,idle, ..) taken from the workshop manual ( weber 40 dcoe 31), but i think the engine could have some more power. do I have to use a better weber setup or maybe a different type of carbs to get a better performance? dellortos? 45 webers?
some experiences?

thanks in advance
kai

piper cams specs taken from the web page ...

LOTBP285
Ultimate Road
Cam Code LOTBP285
Application Ultimate Road
Power Band 2000-7000
Power Increase 16BHP
Duration Inl 280?
Duration Exh 280?
Valve Lift Inl .384"
9.75mm
Valve Lift Exh .382"
9.70mm
Timing Inl 30 - 70
Timing Exh 70 - 30
Full Lift Inl 110?
Full Lift Exh 110?
Lift AT TDC Inl .090"
2.28mm
Lift AT TDC Exh .088"
2.23mm
Valve Clearance Inl .008"
.20mm
Valve Clearance Exh .010"
.25mm
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PostPost by: lotus_elan_s4 » Fri Jun 29, 2018 12:01 pm

hi,
i found one big mistake in my weber setup, the choke size was 30 instead of 33 .. well, seems to work better now :-).
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PostPost by: rgh0 » Sat Jun 30, 2018 1:39 am

The Piper cam is not that much different than the standard sprint cam with a little more lift ( .392 lobe versus .360) and a little more duration( .280 versus 272 degrees). The sprint 40DCOE jettings should work OK as you have found but a trip to a rolling road dyno is probably worthwhile to fine tune it further.

The quoted power increase look like its versus the SE cam engine of 115 hp with a 12 hp increase quoted for the BP270 cam which looks identical to a 126hp sprint cam specification and a 16 hp increase quoted for the BP285 cam giving it 130 hp which is about right for just the cam swap in an otherwise standard engine

The .392 cam lobe takes you over the lift that the standard valve train components can normally handle. I hope you have replaced the springs at least with something that can accommodate that lift without binding. The Piper data does not show it requires changing of valve train components but it should

cheers
Rohan
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PostPost by: lotus_elan_s4 » Tue Jul 03, 2018 12:12 pm

Hi Rohan,

you are totally right, I was looking for a not so expensive solution to get some more power (something near the sprint specs) when moving from a Stromberg head to a Weber, so the idea was just to change the cams and modify the head. The head was modified for unleaded fuel, spring inlet valves and the valve springs were replaced (as i remember i took something similar offered for Kent cams). Its working fine for me and the power output is ok, it seems that I have to invest in a rolling road dyno to get a better result .. many thanks :)
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