Lotus Elan

Ideal rod length for std crank and L block desk height

PostPost by: vstibbard » Fri May 11, 2018 1:24 pm

I'm keen to clarify the best rod combination for a Lotus TC using std crank and L block deck height, assuming max bore to 1600 cc.

Can you let me know rod length and also piston gudgeon pin to deck heights, and any recommended suppliers.

Cheers

V
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PostPost by: rgh0 » Sat May 12, 2018 4:07 am

Hi Vaughan
Nothing much wrong with the standard combination But if your a long rod fan then 1600 rod length, BD rod length or long BD rod length can all be made to fit with suitable custom deck height pistons, though the Long BD rod is getting to be a very tight fit and does not leave much room for the rings. JE Pistons will make you pretty much anything you want.

I have attached a table of the various combinations.

block rod and stroke combinations.pdf
(149.77 KiB) Downloaded 79 times


cheers
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PostPost by: vstibbard » Sat May 12, 2018 5:14 am

Thanks Rohan, I was interested to know if the long BD rod was able to used. Appreciate the table.

Cheers

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PostPost by: SJ Lambert » Thu May 17, 2018 2:19 am

I’m using rods on 5.23” centres in my scratch built motor - they’re going well.
Ford Escort Mk1 Lotus Twin Cam
Elfin Monocoque (Twin Cam)
Elfin Type 300 (Holbay S65 - 120E) mechanic

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PostPost by: CBUEB1771 » Thu May 17, 2018 2:17 pm

Shouldn't this also involve a discussion of what use is planned for the engine? Generally the longer the rod the lower the side thrust loads on the piston and lower peak acceleration of the piston. This should help get to higher engine speeds. The shorter the rod the higher the peak piston acceleration and better cylinder filling at lower crankshaft speeds I think it is best to decide want you want he engine to do and then decide on the best components to achieve that goal. BTW, thanks to Rohan for sharing is geometry data.
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PostPost by: vstibbard » Fri May 18, 2018 12:04 pm

Good question, I'm in early stages of planning build of road/track day car, max 1600cc 10.8:1 with McCoy 450's using DCOE 42's 34mm chokes, 1.625 inlets. As its not a race engine, I'm prepared to tryout one of the maxspeeding steel crank/rod wide journal sets simply because the lotus cranks are getting on now and cost of preparing etc goes a fair way to cost of new, especially as I'm after the rods anyway.

At this time I'm going to get a set of the McCoy 450's to initially try out in a 1760 tall block engine I've got that's currently running cams that were the ones to use in the Sydney Lotus club in the 80's called Kawasaki grind from Waggott Camshafts the dyno sheets say 244 deg duration at .50" and 380" lift, 1.625 inlet valves, ported with 1760cc with 10.3:1using points ignition, DCOE42's with 34 mm chokes, the power peaks at 143bhp at 6100 and hits 140bhp at 5500 through to 6600rpm when it starts to fall off. Torque is 110ft lbs at 2900 115ft lb's at 3200 120ft lbs at 4000 130ft lbs at 4500 134ft lbs at 5100 which it holds above 130ft lbs until 5700 before slowly falling to 123 at peak power.

All in all a nice engine to use in an Elan, but a more modern cam with higher lift and the short duration will fill in the mid range, initially I was going to try QED420's but these seem to make similar power albeit a bit more low down, then as in planed engine capacity will be higher, felt more lift and duration would be ok, I was interested to hear about the Q450's but little is said about them and Rohan said McCoy 450 over the QED 450's so I'm happy to try that route with this engine initially as I'll be using the head off the 1760cc for the new engine. The head on the 1760 had L1's fitted in the past so spring pockets had been machined when I bought it, I'm hoping I'll get away with spring and cam change only and avoid a rebuild as the engines done very little work.

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