Lotus Elan

Racing High Lift Valve Springs

PostPost by: rgh0 » Tue Jun 23, 2009 11:28 am

I am currently looking at doing a production run of high lift valve springs and retainers. I have used what Dave Bean and Elan Factory supply in the past and while these were excellent products I think that they all have issues in terms of stiffness and design installed height that limit their flexibility and make application to a range of engine designs a challenge. I have been doing some analysis and with a local spring manufacturer believe there is a better and more flexibile design possible. Still some way to go but it looks promising.

From my analysis it looks like all the current suppliers adopt a "near enough" standard stock spring they can buy to keep cost down rather than do special production runs of a purpose designed spring to suit a range of typical twink applications. This is an admirable approach but makes engine building more complex than it needs to be - as they need the 3 or 4 alternatives they offer to cover the range of possible applications. I beleive a single purpose design spring set can cover almost the full range of possible twink applications making the build much more simple.

So 2 Questions to judge what size production run I should be looking at for supply beyond my own needs

1. Would people be interested in a better high lift valve spring that could be used in a wide range of applications from standard .36 lift to full race .50 lift cam with a single spring and retainer set. The cost would be the similar or less than from the usual suppliers especially if I can do a run of around 500 units ( 60 engines worth) I can use a reasonable amount for my own engines but sixty is probably all I will build in the next 20 years so a little more than I really want to order today. Not looking for any committment just trying to judge interest at this stage

2. Does anybody have some QED competition high lift springs ( I think they have 2 types) I would like some measurements to analyse and compare with the Dave Bean and Elan Factory springs. If you have some I can send a spreadsheet which shows the measurements required and has the springs on it I have currently analysed.

If I go ahead with a production run I will publish the full design data on LotusElan .net so people can do further runs in the future if needed. I am doing this to support and simplify my own engine building rather than make money

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Rohan
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PostPost by: msd1107 » Tue Jun 23, 2009 5:45 pm

Rohan,

Since you mention .5" lift, I presume these springs are suitable for use with reduced base circle cams and longer valve stems. True?

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PostPost by: rgh0 » Tue Jun 23, 2009 8:52 pm

Yes
I believe I can come up with a design that can cover the full range of installations from standard valve lengh and standard cam base circle to full race .5 lift cams with 0.98 base circle and long stem valves and give maximum flexibiliy to change cams without changing valves and springs.

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PostPost by: rgh0 » Fri Jul 10, 2009 8:15 am

Surely someone in Europe has some QED race spec springs they can measure up for me ?

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PostPost by: Dag-Henning » Fri Jul 10, 2009 8:38 am

Hello Rohan ! Yes, I am running the Q55 race-pack, and can do some checks for you. What is it you want to know ?

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PostPost by: rgh0 » Fri Jul 10, 2009 11:40 am

If they are installed in the engine to hard to measure. You need to have some out of the engine to measure but the data I am looking for is as follows:


For both the inner and outer springs

1. Free Length
2. Spring wire diameter
3. Number of working coils
4. Spring outside diameter


From these I can work out the spring rate, design installed height and load and full lift load and clearance to coil bind at full lift and spring material maximum stress.

I have pretty much finalised my design but a comparison with what QED Q55 springs would help me confirm that the improvements in installation flexibility I am seeking are worthwhile pursuing versus what other suppliers currently provide.

Currently sitting here measuring and drawing up 5 different spring retainers I have to also optimise these as well.


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PostPost by: Dag-Henning » Fri Jul 10, 2009 12:00 pm

- it's ok, I have some new sets on the shelf. Will get back to you over the weekend.
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PostPost by: rgh0 » Fri Jul 10, 2009 2:26 pm

Dag
Thanks for doing that
I have sent you pm with 2 spreadsheets which show the dimensions I need for both the springs and retainer

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PostPost by: SJ Lambert » Thu Mar 03, 2016 9:33 am

I've been reading with interest today some thoughts by Keith Duckworth on his views as to the fundamental requirement of valve surge minimisation & that one of the ways of achieving it is through the use of "interference springs" in which the inner spring is a push fit inside the outside spring, causing both coils to rub together when in use. Is the concept one that is still actively adhered to these days?
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PostPost by: rgh0 » Thu Mar 03, 2016 10:52 am

There is certainly some light interference between the inner and outer springs of some of the sets I have tested.

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PostPost by: vstibbard » Thu Mar 03, 2016 11:38 pm

Rohan, have you tried beehive type valve springs in any of your engines?

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PostPost by: rgh0 » Fri Mar 04, 2016 9:20 am

No. I have only tested or used in engines commercially available double cylindrical springs.

I have not done any detailed analysis of conical springs in a twin cam but I dont think any real advantage would accrue from their use.

i.e.
The twin cam has very restricted space for the spring to fit in. I suspect you would struggle to design a conical spring that fits and produces the need seat and nose loads with any significant weight or resonance saving for the total valve train.

The conventional double cylindrical springs with standard diameter stem big valves and titanium spring retainers are good for 9000+ rpm which is about as fast as you want to try to run a twink unless you have so much money or passion you can afford to do rebuilds after every 30 minutes of running and have handcrafted springs designed to be made for you engine :D

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PostPost by: nmauduit » Sat Mar 05, 2016 5:04 pm

Are there race springs of a very different free length than standard springs ? it would seem to me that a somewhat longer free length springs would be beneficial for high lift/long stems applications, leaving more room to avoid coil binding.

If I take (e.g. from http://www.lotus-europa.com/manuals/tcwork/tech/ ) the stock spring rates (62 lb/in inner 188 lb/in outer) and free length (1.13 and 1.45) I get for a standard engine an installed force of 57lb and full lift force of 142.

When using the same springs with .08 shims I get 85 lb installed force and 196 lb full lift force for my target lift of .443 (210lb if one wanted to push to 0.5 lift) without considering binding - so it seems to me that the stock springs in long version (to match long stems and give more room before binding) would do just fine in high lift applications.

What would be the race springs specs (free length, rate) available ?
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PostPost by: rgh0 » Sat Mar 05, 2016 9:54 pm

Here is a spreadsheet that covers a range of standard and competition springs I have tested. Which is best depends on the exact design of the other valve train components you are using. Normal practice for high lift cams is to use a smaller base circle for the cam and a longer valve and thinner follower which in combination gives more room for a longer valve spring that can accommodate the higher lift without over stressing.

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spring load ranges.xls
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PostPost by: nmauduit » Sat Mar 05, 2016 10:24 pm

Thank you Rohan, I have 2 sets of springs I'll check tomorrow to figure out which, if any, would fit. With the new guides and seats I got the head fitted with race valves and springs, and was surprised by the amount of shimming it came back with (about 3mm, more or less the length of stem added) : I'm not after absolute maximum lift, but that stroke me as not optimal for helping with coil binding... if longer springs were available.

I'm not sure yet about camshaft - actually I was discussing with someone on the forum offering one for sale, but he became little responsive after I asked about the base circle... and vendors are not so clear either (I've asked regarding Newman ph5 and McCoy 450 ...) - maybe they are just overloaded with spurious demands... and prefer to keep the mystery around camshafts details of any kind.

meanwhile I have more time to balance the chambers. But I'll need the final camshafts for head line boring, as per the machinist requirements.
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