Lotus Elan

Dyno results, not good

PostPost by: pauljones » Thu Jul 12, 2018 3:48 pm

Id take it out.

I pulled mine out not long back. Only to change a split coolant pipe but easier with engine out.
The job is a long day or a weekend depending on how often the kids demand attention. Hardest part was undoing the exhaust.

I ran some boring simple maths, lift/valve diam.
360÷1.5625=0.2304
What this means is less than 0.25 and its the valve seat area/throat/venturi, that is the primary obstruction for air flow.
You could measure the hole and see what the difference is as a percentage of intake valve diam. In theory the hole should be 85 to 90% of the valve, or a simple check is about the same size as your exhaust valve.
If its smaller you may be getting a restriction in which case id reccomend a clean up of this area and valve angles cut to suit low lift bias.
It also means fitting a bigger cam would be wasted unless that porting was done. Incidently a 0.450 lift gives 0.288 so would need work further up the port to suit. This then gets into cross sectional areas as the port itself may become restrictive sooner than the valve seats.

Off course all the above may be of no relevence, it may just need a good setting up.
Kick the tyres and light them fires...!!!!!!!
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PostPost by: m750rider » Thu Jul 12, 2018 4:27 pm

Dan

As has been said, the engine doesnot have to come out to time the cams.

Remove the radiator and fan and you'll have clean access to the front of the engine. You will put the degree wheel on the crank pully and work from there. Pretty simple really. I think I read in one of the answers someone said about an hour to do it - I must be slow cause it took me much longer than that, but certainly not hard to do. Just requires patience and an accurate gauge. It's been a while but I think both of my cams required offset dowells. These were stage 2 cams from Dave Bean.

Good luck

Bob

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PostPost by: Chancer » Thu Jul 12, 2018 5:25 pm

collins_dan wrote:My memory is that the car seemed quicker with the L2 cams, but who knows if that was really true or if it was just the difference in sound. The L2 cams had a great sound and seemed to rev very quickly, but it could all be an illusion. Could be the head just has bad flow characteristics.

Thanks, Dan


I think that is the telling statement, it all points to the cam timing not being correct.

Dont throw money at an unecessary rebuild that could leave you with even more incorrect set up or incompatability, set the cam timing first, you will know from the second the engine picks up revs that you have made a major difference.

i say this as someone that bought a S/H vehicle, a Suzuki Jeep, I knew them very well, had owned several, this one just did not quite seem right, lacking a little sparkle, I felt it wasn't like my previous ones but could not say for sure, PO had changed the head gasket so I thought it could be all sorts of things but checked the cam timing first, the mark was misaligned and moving it one tooth made it just as misaligned the other way, 50/50 chance so I moved it.

The second I fired it up and it zipped up the RPM's I knew I had resolved the problem and I also realised after driving it that the performance and response had been seriously lacking yet it had been so hard to tell.
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PostPost by: collins_dan » Thu Jul 12, 2018 5:36 pm

The reason I was thinking I would have to pull the engine was due to the low compression numbers. From some people's posts, I am interpreting that as being the big contributor, from others, it seems that they are thinking cam timing is still the culprit despite the markings being correct. Maybe I try to get someone to help me time the cams and shim the tappets correctly without pulling the engine, then re-run dyno. If its still low, then pull the head and address the low compression and possibly porting at that time. Dan
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PostPost by: nmauduit » Sat Jul 14, 2018 3:46 pm

collins_dan wrote:The reason I was thinking I would have to pull the engine was due to the low compression numbers. From some people's posts, I am interpreting that as being the big contributor, from others, it seems that they are thinking cam timing is still the culprit despite the markings being correct. Maybe I try to get someone to help me time the cams and shim the tappets correctly without pulling the engine, then re-run dyno. If its still low, then pull the head and address the low compression and possibly porting at that time. Dan


first checking the actual valve timing will tell you a lot: if the timing is significantly off (e.g. a slipped tooth is 10.6° - also take note if the chain was under adequate tension before, understanding why the timing became so off is important), setting it correctly may restore some static compression on all cylinders, as later than required inlet closing (which would measure as not enough BTDC opening) when the piston is on its way up for compression will enable less volume to be effectively swept into the chamber.
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PostPost by: Davidb » Sun Jul 15, 2018 1:14 am

I absolutely agree with nmauduit. It is not difficult and will eliminate one possible source of your problem.
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