Lotus Elan

CAMSHAFTS

PostPost by: paros » Mon Oct 17, 2005 7:51 am

Hi
I would appreciate any ideas people may have for cams on an S4 Elan I race over here in Greece. So far this year the car has won every race BUT the competition is getting closer, so fo 2006 I need another 15 bhp.
I use the car a bit on the roads - say 500 miles a year so a wild cam is not on the agenda.
Currently the engine is plus 040 - although owing to a long story and bad Greek machining the squish is poor and a set of new pistons next year is aclled for to restore squish [ currently only .004 of the piston land protrudes above the block face ].
The carbs are 45 DCOE and the cams are QED 420 with 10.9 : 1 cr. The cams are great, and are similar to Burton's BLF14 with .410 of valve lift and 285 degrees duration. Ideally I would like a cam change that I won't have any other engine maods to do, as there are no machine shops on the island. The engine is taken to 7500 in races and has a new EN19 crank and lightened flywheel, large bore 4:2:1 manifold from TT. I had even wondered about the L1 but this old technology and thus any ideas please?
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PostPost by: steveww » Mon Oct 17, 2005 8:48 am

What the engine needs is more lift not more duration, alas more lift will require some machine work to the head. :(

Has the head been flowed and ported? There is definately more power and torque in there above standard.
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PostPost by: rgh0 » Mon Oct 17, 2005 11:10 am

If your valve gear will take higher lift you could try cams with around .44 inch lift and 290 to 300 degrees duration eg The Dave Bean 104 profile at 300 degrees and .44 inch lift or from John McCoy at Omnitech Engineering who has a profile of 290 degrees and .44 inch lift. Valve gear that will take this lift without machining the valve pockets is available but it needs careful design and component selection and correct placement of the valves in the head.

If your valve gear will not go more than your current .41 inch lift and you dont want to replace all the valve gear then you could try a longer duration cam up to 300 degrees. The L1 cam was .41 inch lift and 300 degrees. More modern replacements with similar timing have faster lift and produce a little more power. The problem with the longer duration cams at around 300 degrees is that you will loose torque in the 3000 to 5000 rpm region for only a little gain in top end performance and in the end it may not be faster around a track.

Your current engine based on your description should be producing around 150 to 155 hp at 7500 rpm if everything else is done right (especially the porting) . A L1 style profile may give you 160 to 165hp at 7500 to 8000 rpm. The McCoy cam will give you around 170 to 180 hp at 7500 to 8000 provided the porting is good enough for the .44 lift to work properly.

If you just get a new cam ensure the base circle you specify matches your current cam as the cams from differenct manufacturers use different base circles as their norm.

regards
Rohan
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PostPost by: paros » Mon Oct 17, 2005 1:51 pm

Thank you both for the quick replies!
I had assumed I may need to look at more lift and not extra duration for the reasons you mentioned.
However the figures for potential power increases from the L1 and McCoy are very interesting.
The head has been flowed and ported by the way but I forgot to mention has the Sprint size of valves - another reason I pictured a need for faster and higher opeing of the valves. My guess is that I have around 135 to 145 bhp - I supect nearer the 135 figure although the cars it is beating, at fast circuits such as Serres [ GTAM Alfa for example ] makes me hope for 145!
To accomodate .44 lift I will need longer valves and different retainers - not impossible.
This is the route I think I will have to start investigating after this weekends race
Thanks again
Richard
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PostPost by: steveww » Mon Oct 17, 2005 7:50 pm

Paros,

You mention you have fitted the TTR 4:2:1 exhaust manifold and system. I am thinking about fitting one of these this winter. How is the clearance between the manidold and chasis rails? Any hints / tips / pictures you could share?
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PostPost by: mct340 » Tue Oct 18, 2005 3:06 am

Steve,
Are you still running strombergs? I'm thinking of sending my head to McCoy for the sex change but would like to be talked out of it.... (if it ain't broke don't ...etc.)
Mike
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PostPost by: paros » Tue Oct 18, 2005 6:48 am

Steve
Yes the TT exhaust will fit BUT you will need a regular supply of replacement knuckles and fingers!
THE TRICKS ARE AS FOLLOW
You need to carve out apiece of the chassis to get clearance.
The cross member beneath the sump is best removed [ and A roll bar ] and a removable replacement made.
The studs need shortening and I usually find I remove all but two of the studs - by the way K nuts are the only nuts with the right clearance.
Remove left hand engine mounting and lift engine as far as possible.
Now start fighting - it is like a Chinese puzzle!
I gave up at one stage years ago and went for a coffee - my wife came out and just lifetd the pipes into place - in other words get the alignment right and it goes in easily.
It is a nicely made sysytem and the welding is good - not mandrel bent thoughand some slight collapsing of the bends.
An old friend in the UK who prepares twins tells me the Y piece should be inches longer for more torque.
It is so cramped around the exhaust that I don't think any picture would show much other than blood stains
Best of luck
Richard
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PostPost by: rgh0 » Tue Oct 18, 2005 9:45 am

Richard

You really need to go to 1.625 inlets and 1.4 exhaust valves and port to match these valves to get the maximum benefit from your current cam and any potential future cam.

With the sprint valves and porting to suit you are right in assuming a 135 to 145 hp type of number for your current engine. Bigger valves , bigger porting, a higher lift cam, 36 mm chokes and a big exhaust system brings the performance you are looking for at your 7500 rev limit.

I use socket head bolts to mount my exhaust both because with the larger ports and pipes no room to get a spanner on the nuts and to hard to fit a big exhaust if the studs are still in place. I use plenty of antisieze on the socket head bolts and have never had any problem removing them or stripping the threads in the head over many years and many removals and replacements. It is easy enough to helicoil the head if you do strip a thread anyway. What is the tail pipe diameter on the TTR headers, you need at least 50mm pipe and a 50mm straight through flow muffler.

Rohan
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PostPost by: steveww » Tue Oct 18, 2005 10:24 am

Rohan - the TTR system IIRC has 1.6" headers to 2" pipe and muffler. I had the head off last winter and found that taking all the studs out made things much easier. Rohan idea on the socket head bolts sounds good.

Richard - Thanks for the tips, I will let you know how much blood I loose fitting the TTR system. I have just replaced the carb side engine mount so I know exactly what you mean.

Mike - Yep the car is still running on the Strombergs and is getting around 130 bhp at 6000 - 6500 rpm. With the TTR exhaust system fitted and the carbs flowed I should be able to push this to around 140 bhp and fatten up the torque curve lower down. With a bit of work you can nearly match a Weber engine for road use and the Stromberg engine will have a better torque curve. If you want all the techie details just ask. A lot less expensive that a new Weber head :shock:
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PostPost by: patrics » Tue Oct 18, 2005 9:09 pm

Hi Gents,
TTR has two different diameter exhausts for sale - 2" and I think 2 ?, any thoughts on which to choose?
Regards
Steve
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PostPost by: steveww » Tue Oct 18, 2005 9:13 pm

The 2" system is OK for engines up to 165bhp. If in doubt give them a call they are happy to discuss these things.
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PostPost by: paros » Thu Oct 27, 2005 12:42 pm

Thanks for all the replies and I am investigating what I can do for 2006 - bearing in mind the zero machine facilities here in Paros isalnd!

I mentioned the lack of squish but no one replied about this. Is it as important as I thought? I always worked to a squish dimension of around .013", meaning the land at the o/d of the piston had to be about .012 high. Gasket being .025 thick.
Mine owing to sub contracting some machining to Athens 2 years ago is only .003. To correct it means a set of new pistons.
Any advice please?
Richard
ps last race only .03 seconds behind a near new GT40 in practice but after 3 laps of the race the throttle cable came unstitched. Tyre waer was impressive but with only 1/3 peadl travel what else can you do!!
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PostPost by: type26owner » Thu Oct 27, 2005 2:00 pm

IIRC, BRM recommended .030" on their race engines. According to a calculation my father did back in the sixties at 9000 rpms the gap would be nearly zero. It does this on the exhaust stroke and not the compression. The forces were nearly 18,000 pounds exerted on the conrod.

I always have to machine the clearance of the squish deck and the the relief pockets for the valves in the piston whenever a new set is installed in our BRM. We use JE pistons now. Back in the sixties we made our own pistons from some experimental forged billets we got for free from Kaiser Aluminum. It was some of the first ceramic filled aluminum ever made. Wonderful stuff! We had no more cracking of the pistons after that.

Can't remember the exact type of piston we order but here's the recommendation that JE gives for the squish deck.
http://www.jepistons.com/pdf/piston_instrc2618.pdf

Here's an interesting technical article which has nothing to do with squish deck stuff but I'm including it just for the hell of it.
http://www.jepistons.com/pdf/2005-proseal.pdf
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PostPost by: rgh0 » Fri Oct 28, 2005 9:46 am

I normally run the piston land about .020 inch below the top of the block deck. This ensures the piston does not interfere with fire ring on the head gasket if there is some some overlap of the fire-ring with the bore.

It is hard to guarrantee the fire ring does not overlap given all the tolerances on the assembly and the distortion when the head gasket is compressed unless you have a head gasket fire-ring bore about 5mm more than the cylinder bore.

The squish thickness is thus the compressed head gasket thickness plus a little at around .040 to .050 inch. Dont know if totally optimum but it makes a reliable engine without much downside.

I like Keith use JE forged pistons that I final machine the intruder height, pockets and land to achieve the exact clearances and compression ratio I want.

Rohan
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PostPost by: twincamman » Tue Nov 01, 2005 10:11 pm

u :shock:
Last edited by twincamman on Thu Jan 17, 2013 11:50 pm, edited 1 time in total.
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