Lotus Elan

Rod length question

PostPost by: Witofthestaircase » Thu Oct 17, 2019 11:55 am

No doubt my failing but I’ve searched the forum and elsewhere without success for the following information which will be, no doubt, answered faster than the delay, when at the front of a London traffic light queue, between the change from red and the sounding of the horn of the car immediately behind. My question: What is the required conrod length for a ‘standard’ compression height tc piston in an un-decked 711m 1600 block with a ‘standard’ 711m 1600 crankshaft? Is that recipe problematic beyond the normal tall block adaptations? Thank you
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PostPost by: avro » Thu Oct 17, 2019 12:30 pm

In short the rod length required would be 5.150” but as there is not a stock rod available at that length you would have to have a set of steel rods made. There are 5.100” narrow journal rods readily available off the shelf but the wide journal rods to suit the standard crankshaft may prove a little more difficult to find, although l have purchased them in the past at that length.

Options :-
If you are using the standard compression height Twin Cam piston then the conrods required are the standard 1600 crossflow items that would have originally come with the 1600 crossflow crankshaft and block.
Approximately 0.225” will need to be machined from the block face and a spacer plate will be required to increase the height of your existing front covers.
In addition to that you will require a longer set (3) of front cover to head bolts, a longer timing chain tensioner plunger, a longer 122link timing chain and a spacer to sit under the head to block breather tube. All the parts are available from either QED or Burtons.

The head stud holes in the block may require tapping out slightly deeper to stop the bolts bottoming out in the holes.
They will not require drilling as the holes will be deep enough, but the use of a 7/16 UNC plug tap will take the threads to the bottom of the existing holes.

If you do not want to machine the block face to that extent then a higher compression height piston set and a pair of taller front covers (with a modular water pump) are available from Burtons. You can then use the 1600 crossflow conrods and retain a full height block.


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PostPost by: 2cams70 » Fri Oct 18, 2019 5:35 am

Why do you want a tall block? The engine is sweeter and freeer revving in stock 72mm stroke form.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2015 Honda City 5spd.
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PostPost by: rgh0 » Fri Oct 18, 2019 12:22 pm

Yes i love a 1600 cc twink at 8500 rpm in a race engine but for a road car a 1700+cc long stroke twink is hard to beat for mid range torque and good top end power at 6500 rpm---- needs the right cams and porting and tuning of course to get the best... the details make all the difference :D

cheers
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