L14 Kent cams

[miked]

For weber head motor.

Has anybody fitted above. I have a big valve head with some port work just complete. To fit big bore manifold etc. Everything else is standard. Good nick and all balanced etc. I Am after some advice on carbs jetting and chokes for a start point. Also dizzy advance curve advice etc.

Was told that cams would possibley move BHP up to around 140 mark delivered well below safe RPM for standard kit.
At present I have couple of DCOE 40 31's ready with big valve spec' jet and chokes.

If L14 is not known, I have all the data.
Any Help?? I understand it is a bit of a, "how long is a piece of string question".

Thank Mike

[mark030358]

Mike,
I fitted L14 cams to my europa. I used std dizzy and carb specs (dellortos). Cannot remember cam timing details, sorry. However, the car didnt feel like a 140 bhp motor but I didnt have any porting done though.

cheers
Mark

[elan_fan]

I did think that a true L14 profile required a counterbore of the spring platforms to prevent coil binding.

[Dag-Henning]

- that would depend on the cam base diameter, the length of the valves, height of the seats, type of springs etc. Counterbore of spring platforms would, - to my opinion-, be something to try to avoid....

DH

[steveww]

The cam lift is 0.41" thus you might need the QED valve springs to prevent binding but this really depends on the base circle of the cam. The duration is 282 which is fine, the twinc needs lift not duration. Depends how good your head porting is (who did it?) you should see around 140bhp @ 7000rpm

[rgh0]

Fitting a 0.41 lift cam will normally require a range of mods to the rest of the valve train to get it to work right. The cam itself should be ground on a 1.05 to 1.10 inch base circle versus the standard base circle of 1.20 inch to make room for the valve mods below and still have shims in the normal range

You then need

1. Long valves (approx 4.0 inches overall length)
2. Thin steel bucket followers, at a 1.05 base circle you may get away with the standard thickness followers depending on other setup details.
3. High lift valve springs designed for the longer installed length provided by the longer valves.

You also need to have the valves in the right location in the head and not too far recessed. Most heads have had a lot of work done on them over the years and you need to measure them carefully to understand what your starting with before you add a highlift cam. If you dont know how to measure up the head and calculate what is needed to get this setup right find someone who does or an engine shop who specialises in racing twincams to help you.

You have multiple choices of valve position, cam base circle, valve length, follower thickness, shim thickness, spring type, that can be made to fit in the space available but not all the choices work reliably well.

Dont forget to check valve clearances with piston and valve train clearances in the head at the higher lift before turning over the engine.

Output depends on porting and valve sizes, carbs, exhaust and compression ratio and how many revs your bottom end can handle. With 10:1, standard bottom end and 6500rpm limit, standard valves sizes, reasonable porting, good big bore tubular headers and straight through muffler and 33mm choke webers the quoted 140hp is a good target to expect. Pushing to a 7000 rpm limit, bigger valves, top quality porting, bigger 36mm carb chokes you will be getting close to 145 to 150hp

With 33 mm choke Webers start with the standard Lotus settings and then dyno the engine to get final settings. You also need to get the advance curve right on the dizzy - aim for a static setting of around 10 crank degrees with around 16 - 18 crank degrees of centrifugal advance coming in linearily from 1000 to 3000 rpm to give a total of 26 to 28 degrees total max advance. You can get away with a 20 degree centrifugal advance and run with less static advance. Setting up the correct timing on the dyno to match your fuel and engine can be worth a final few hp.

Rohan

[miked]

Wow! thanks for replies.

I understand the advance bit and carb chokes etc..
I have purchased new valve springs and caps from QED. These are meant to be for higher spec'

The engine work is by Bill Bannister at Bamber Bridge Preston. He does a lots of twin cam stuff in our area. I believe he does lots for Richard at Banks for the Europa's. I obtained new valves from QED, just normal length big valve spec. Bill makes his own valve seats. So I am not sure what to think. I thought he was going use longer valves since I had the sprint cams reprofiled. It sound like my shims are going to get thicker.
Am I being silly (about compression) in thinking there may be some tolerance with the valve position in the seats and how they are made.


Mike

[rgh0]

Mike

If you dont use longer stem valves then you run a risk of spring coil bind or the retainers hitting the top of the guides or the followers bottoming out in the head. Even if you avoid all these interference problems you will end up with too high valve spring loads on the nose of the cam. You want to keep the load under 200lbs other wise you will wear the cam and follower very quickly. The high lift springs have a longer design installed length to work properly with longer valves and give clearance for the high lift cam and correct spring loads.

If you recess the valves in the head either deliberately or due to worn and recut seats then you can end up with it working with standard length valves but the head will not breath as well due to the valves being shrouded by the seat they are recessed into and you loose a lot of the benefit of the high lift cam as well as lowering compression ratio.

Rohan

[miked]

Rohan,

thanks for your help. I am concerned. I will have a word with him and stop what is happening. Hopefully he has not touched anything and I can swap the standrad length for longer at Donington.

Mike

[rgh0]

Mike

When modifying a twin cam head for higher than around .38 valve lift it is really critical to understand each of the valve assembly components and how they are being integrated together so that the whole assembly works right. The guy you are using if he has lots of twin cam experience should know that and should be able to give you a drawing or spreadsheet that shows how he intends to get the right set up in terms of component dimensions, clearances and spring loads in your specific head.

Unfortunately there is no standard solution as each head was slightly different when new due to fairly loose machining tolerances adopted by Lotus and now after 40 years with rebuilds of varying quality they all vary greatly and a setup that works in one head may not fit in another.

If your interested I can send you a copy of the spreadsheet I use to set up a cylinder head.

Rohan

[miked]

Rohan,

I am intertested in seeing your data. I can see what you are saying about all the important factors. I woud like to think that our man knows his stuff. I will have to be subtle when asking.

Thanks Mike