Lotus Elan and Lotus Elan Plus 2 Forums

A totally excellent thread, just what the forum is about.
Well done!!

rgh0 wrote:I went to a longer duration and higher lift inlet cam of 0.46 lift and 300 degrees seat to seat to try to compensate while leaving the 0.44 lift 285 degree exhaust cam.

Spent a day on the dyno and did many runs, trying many things. I had used 36mm chokes previously but ended up trying 38mm chokes which gave more top end with no loss of mid-range torque. Also found my fuel pump was not keeping up at the top end and losing pressure so did the dyno work with a temporary set up - new pump and fuel line to go in next weekend !

ok for richness: it was not because of a risk of detonation then. From previous threads I would think you have used a composite head gasket, not the MLS kind, hence I would infer it is about 1mm compressed height (unless you had a special one made - can't seem to find different heights these days)

I'm sure the day was busy setting carbs and ignition (what max advance by the way? did you push till you'd see a decrease in performances?), but did you get to try different cam timings than McCoys recommendations, then if so what did you end up with?

looking forward to read from the outcome on the track...

nmauduit wrote:........ok for richness: it was not because of a risk of detonation then. From previous threads I would think you have used a composite head gasket, not the MLS kind, hence I would infer it is about 1mm compressed height (unless you had a special one made - can't seem to find different heights these days)

I'm sure the day was busy setting carbs and ignition (what max advance by the way? did you push till you'd see a decrease in performances?), but did you get to try different cam timings than McCoys recommendations, then if so what did you end up with?

looking forward to read from the outcome on the track...

Yes after a number of dyno runs concluded this particular build likes to be richer than most. The dyno guy likes to run a little rich just to be on the safe side but this also gave the best power.

The composite fibre head gasket was 1.1 mm uncompressed and around 0.7 compressed. The head chamber was 41.0 cc, The head was an original thickness low compression Stromberg head before the McCoy conversion. The larger valves loose a little volume but opening up around the valves and matching volumes I ended up back were I started in terms of chamber volume. With the other build details and a 7 cc intrusion volume for the pistons I ended up with around 10.8 compression ratio which was close enough to the 11:1 nominal target and comfortable on straight 98 Octane without any additives

The dizzy I use is a billet machined copy of a Bosch body that was used in escorts built in Australia but fitted with roller bearings, it otherwise uses standard Bosch components. I use 911S Bosch points that are no longer available but I think I have managed to buy up the last few from NOS suppliers on the internet so I have a life time supply (If not I know how to modify other available Bosch points to the needed specification) Static timing setting is 12 crank degrees and the dizzy has 20 crank degrees of advance giving 32 crank degrees total advance. The advance is a straight line from zero at 1000 crank rpm to maximum at 4500 crank rpm. The advance is about 2 degrees less than I had used previously when using Avgas in higher compression but otherwise similar engines.

Valve timing was inlet MOP of 106 degrees ATDC and exhaust MOP of 108 degrees BTDC
I did not try different cam timings this time but I have adjustable sprockets fitted and I will do some cam timing runs when I have some more time and more money after some experience with this build on the track. The dyno guy is a racer who I have parked next to in the paddock and he really knows his stuff, but a full day on the dyno is not cheap so i use my dyno time after deep thought to ensure I maximise my learning. Wish I could afford a dyno in my garage but i don't think the neighbors would be happy

During the day a number of the dyno guys rally and racing mates dropped by for lunch and they enjoyed the sound of a twin cam at full throttle and 7500 rpm close up they were all surprised what a 1600 twink could do on pump fuel.

On the track at Phillip Island Historic meeting in a few weeks and it will be interesting to feel the improvement. Whether it shows up in track times depends on the driver and I am getting older and slower at about the same rate that the car is getting better and faster

cheers
Rohan

thank you Rohan for all these insights and your open mindedness !

Regarding the Dyno, I must admit I am toying with the idea of building one around a Telma truck retarder, for engines (not a rolling road) cost would be a few grands and the plan would be to share it between some Lotus TC and Jaguar straight six (my workshop partner races in E-type) : refining the engineering is a convenient loophole when one cannot hope to refine the pilot...

Ah yes, the old saying "The older I get, the faster I was" keeps creeping into the equation. When I approached my mid 70's, I realized my time had come.

Hi Rohan,

Do we know if CAMS have done any testing of their Aproved lead replacement additives,
namely
i) Valvemaster
ii) Redline Lead Substitute
iii) Penrite Valve Shield
iv) PM 800 Fuel System Conditioner
v) Elf Millesim

on engines and fuel tank systems across the types of competition vehicles under their umbrella in readiness for 1 July?

If they have, it would be very helpful to get a copy of the data......

I dont know of any quantified testing. i know a few guys who have used some of them with mixed results so i have tried to avoid putting additives in and aimed to build engines that will run on straight 95 octane pump fuel.

cheers
Rohan

In the absence of any empirical data it could be s case of ?befriend a pilot? month for me!

I?ve got triple trouble on the integral fuel tank/tub sealant as well as lubricity & detonation concerns (on two motors!)

A friend who has a similar spec twink to mine but who wants to stay with a high compression engine has been experimenting with all the additives versus the Elf unleaded racing fuel. On the dyno not much difference between 98 octane with any of the additives but on the track the Elf racing fuel appears to be quicker. He broke the outright lap record at Winton for group S yesterday so it must be working well.

cheers
Rohan

rgh0 wrote:A friend who has a similar spec twink to mine but who wants to stay with a high compression engine has been experimenting with all the additives versus the Elf unleaded racing fuel. On the dyno not much difference between 98 octane with any of the additives but on the track the Elf racing fuel appears to be quicker. He broke the outright lap record at Winton for group S yesterday so it must be working well.

cheers
Rohan

http://www.acs.total.com/en/racing/raci ... 02-en.html

I've been told of similar improvement with racing fuel ("offered" at track location here for race events, though at least twice the price of pump fuel - only a bit cheaper if you buy 50l or 200l containers, then one isusually not allowed to manipulate fuel on the premices), and they actually advertize is as such :

- anti detonation / knock (would have about 4 point more in octane grade equivalent)
- same cartography as sp98 (our local high grade pump gas)
- performance gain

some friends use it for qualifying...