Lotus Twin Cam Alternative Valve Springs

[rgh0]

As a result of challenges selecting a valve spring type to use in a competition cylinder head on my bench that I am currently building I have engage on a quest to better understand the design details of all the spring packs currently available on the market by buying and measuring and testing all the unique valve spring types I can find.

I will document in this thread the results of that investigation which I am part way through as I make progress.

However my first question is that I have found 4 suppliers of 7 unique alternative valve spring designs for a non standard twin cam engine design and I would like to know if people are aware of any others.

The 4 suppliers I know are:

QED (2)
Tony Ingram (1)
Dave Bean (3)
Omnitech - John McCoy (1)

I have been told that Wilcox also does a unique spring of German origin but their web site photo shows QED springs and I have been unable to get a reply from them so far if they do something different also. I have also been told that early Porsche 911 springs can be used in a high lift race twin cam but have no expereince or contacts in this area, maybe that is the source of the Wilcox alternative also.

All the rest of the usual Lotus suppliers appear to use the same springs as one of the 4 above as far as I can tell, though I may be mistaken.

Does anyone know of any other unique non standard spring suppliers that I should be following up apart from those I have listed above.

I am happy to keep buying and testing valve springs but I have 10 sets here now and I dont want to buy more duplicates of the ones I already have.

cheers
Rohan

[lotocone]

Isky valve springs were used in my twin cam 6-7 years ago. The engine was built by Barry Sale at PHP Racengines, Wauconda, Illinois, USA. Sorry, I don't have any details on the springs. I just remember that he preferred them to stock springs.

The email address I have for PHP is [email protected]

[rgh0]

Hi Bob
Thanks for the Isky reference i will investigate further

cheers
Rohan

[ardee_selby]

Rohan,

Out of interest. What testing will be involved?

Cheers - Richard

[blacklotus]

Hi Rohan, I had a Hart in my S2 (now swapped into other Lotus) and I can tell you that they were "selected" 911 springs as when I rebuilt the head and searched around for springs a shop recognized them. The tight tolerences of the Hart design doesnt give much breathing room between spec gap, full lift and coil bind. Probably in the .010 to .030 max area. Valve to valve gap when both closed is vital. When rebuilding another performance head I had an unpleasant experiece using Beans springs (not because of a quality issue) { i was planning on using these newer springs in the Hart next time its out as the coil bind gap gives MUCH more room to breath} because when i had the valves grooved for the keepers I went by his fitted length spec'd in his book. BIG mistake, new pistons etc. I spoke with him once I bought another set of his springs and compared old and new and found to be the same, and he said "you have to shim the springs"----(I have rebuilt my Hart and so far have survived the trip over 10,000rpms numerous times so I am not a total idiot) ----after checking all sets it was evident that instead of fitting at specified 1.280, they need to be fitted at 1.180, makes a big difference at 8000rpm. Survey of local shops, 1 always checks pressures (after I gave full account of issues) other 2 said they would go by the fitted length, why give a fitted length if they don't meet the required pressure?
Dont know if this helped but hoping this info might be of some use.
Take Care
Robert

[rgh0]

Hi Robert
Thanks for the confirmation that 911 springs are a possible alternative. I just now need to find somewhere where I can get some design details for them. Lots of guys racing 911's in my class I will start by talking to them but most are cheque book racers so I will probably need to talk to their $100k race engine builders!

For most of the springs I have tested so far there are substantial differences between the nominal instal dimensions quoted by suppliers and the actual dimensions to achieve the right seat load ( 60 to 80 lbs) and full lift load ( 180 to 200 lbs) in a competiiton twin cam. Like you say you really need to measure each spring and test its load versus deflection and coil bind height to confirm an installation design before you cut steel to set a valve height.

cheers
Rohan

[rgh0]

Rohan,

Out of interest. What testing will be involved?

Cheers - Richard

Hi Richard
I am measuring each spring types dimensions to calculate a spring rate and coil bind height and testing them to determine the actual spring rate and coil bind height to see how close they align with the calculation. The measured spring rates vary from the calculated ideal as the coils never compress evenly affecting the number of working coils in practice as they compress

From the measurements, calculations and tests I can figure out target installation dimensions for a particular cam lift and valve pocket depth and other valve train details.

cheers
Rohan

[bill308]

Hi Rohan,

Brilliant project.

Would it be possible to collect some metallurgical info too?

Perhaps:

alloy
fatigue strength
manufacturing process (cold work, heat treat, other?)

I don't know how much information a supplier is willing to share. One would hope the good guys would provide some of this info just for the asking.

Bill

[rgh0]

Hi Bill

I dont know how much the suppliers would know about the materials in their springs or how they were made. The only way i could get dimensional and spring rate information was to buy them and measure it myself as what the suppliers can tell you is incomplete and approximate only.

All the springs I have appear to be conventional spring steel that has been shot peened. The Tony Ingram ones are polished but I presume they were shot peened before polishing. Reports of spring failures in competition twin cams are pretty rare and I suspect most of those that do occur are from wrong installation rather than excessive material stresses.

The nominal design target for maximum spring stress is less than 65% of the typical 240,000 psi yield to avoid fatigue failures and this is achieved by all the springs I have got so far.

cheers
Rohan

[vstibbard]

Rohan. Mahle-Knecht also do valves springs, when in UK the top engine builders used them in TC's BDA, FVCs etc, I thought at the time (80-90's that Ken Snailham at QED used them, in discussions Ed Winter who ported and set my head up, as I bought all the parts from QED.

V

[vstibbard]

Rohan, further to my last post I think you'll find the 911 springs are actually produced by Mahle-Knecht, I can check as Bruce Tyson in Melbourne is rebuilding my 2.8RSR engine at moments as it has all new gear.

V

[rgh0]

Hi Vaughan

Maybe the springs QED sell are the same "german sourced" springs that Wilcox sell which is why they look the same in the photos on the Wilcox web site. Maybe they are both sourced from a 911 spring done by Mahle-Knecht.

Interesting how the various threads of information merge

cheers
Rohan

[SJ Lambert]

Just from looking at the numbers, one of my mates thinks Tony Ingram may be using an Isky spring or that they are a spec that's very similar?

[rgh0]

Does your mate have any details on the Isky spring he thinks matchs the Tony Ingram one ?

I had a look at the Isky spring list and none is identical. The nearest i can see is the VWE-006 and the 3405 both of which could be used but both slightly different from the TI spring.

cheers
Rohan

[prezoom]

Rohan,

Yes, it is very interesting in how information merges. The Isky VW springs, exhaust and intake, I also used in my Nissan A series engines. The 1200 engine would hit 10,600 in the dip, at the old Road Atlanta. Never had a valve spring failure. Also used them in the 1300 and 1400 engines.

Rob Walker
26-4889