Lotus Elan

Compression Ratio, Cam duration and fuel Octane rating

PostPost by: rgh0 » Sun Jul 16, 2017 12:14 pm

Looking for some advice on what other people do

I have normally used Avgas for race fuel with a 100 / 105 RON octane rating. As i understand this Octane rating it is 100 RON at lean cruise conditions in an aircraft and 105 RON is the upper limit of the actual Octane rating at standard Octane test conditions. The use of Avgas is being phased out for historic racing over the next two years here in Australia

I have previously normally used a 12.5 to 13:1 compression ratio with a range of cams from 290 to 320 degree duration.

I am currently building a new race engine and need to decide what compression ratio to use given the phase out of Avgas. I am planning to use a .46 lift 300 degree duration cam in this engine as I believe this is the sweet spot for my Elan on the tracks I race on. More lift leads to to long a duration and loss of mid range torque needed on the slower tracks , less duration limits lift and looses to much top end power for the long tracks

The choice of fuels in the future appear to be as follows

1. 98 RON pump premium unleaded with non lead octane booster giving around 100RON
2. 100 RON unleaded racing fuel
3. 105 RON unleaded racing fuel if you can get it which appears to not be easy currently

Interested in what other people are doing for fuel and compression ratio in their racing twin cams with various cam durations

cheers
Rohan
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PostPost by: richardcox_lotus » Sun Jul 16, 2017 7:08 pm

Can't help with the specifics Rohan, but maybe you need to think about it from the worst scenario point of view.

I.e if you turn up at a circuit expecting a certain level of fuel to be available, what would be your options ??

You don't want to travel a long way to compete to find you would only damage things if you were to venture out.

I'm sure you've done it already but what advice have you had from the circuits? Can the organising clubs mandate anything for their events ?

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PostPost by: holywood3645 » Sun Jul 16, 2017 11:55 pm

May be a good idea to have a conversation with Tony Ingram or John McCoy
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Last edited by holywood3645 on Mon Jul 17, 2017 4:44 am, edited 1 time in total.
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PostPost by: Panda » Mon Jul 17, 2017 4:40 am

Hi Rohan,
In our 2.0 alloy block twin cam with .440" lift and 272 deg at .050" and 12.2 compression, we are using BP 98 octane unleaded with octane booster to bring it to at least 100. We have had total reliability in the NSW CSCA series for the last 2 years. With our previous 1700cc engine at 12.5 cr and same fuel, we also had no problems whatsoever with the engine. The head was as per your excellent recommendation, an SAS unit finished by Tony Ingram
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PostPost by: holywood3645 » Mon Jul 17, 2017 4:57 am

Do you have a dyno sheet?
Hp and torque no's
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PostPost by: nmauduit » Mon Jul 17, 2017 9:36 am

I'm working on building a 711 block to test head porting (when I eventually get the parts back from the UK machine shop that is...) and will look into knock/detonation via sensors (Bosch 0261231142 , one at the front, one at the rear). Target compression ratio will be 12:1 to run on the local premium gas which is 98 RON (yet in neighboring Germany/Switzerland/Belgium you can get 100 RON , e.g. Shell V-Power or equivalent).

Typical octane enhancer can help compensate for a detonation tendency, at a cost (about 0.30€/l for 2 points and up):
http://tetraboost.com/info/dosage/
For the devoted enthusiast there is also the possibility to order special race gas (NB: non FIA), costly but reliable:
http://www.elfcompetition.com/packaging.asp

I'm planning to work the heads with in mind to attenuate hot spots in the chamber, experimenting the help of coatings, target compression ratio being 12:1 to begin with (camshafts would be Newman PH5 0.443" 280°, or possibly QED 450 0.445" 298° to be confirmed, on 1.4/1.625 valves ; McCoy 450 may be of interest 0.44/0.43 280° though I could not get any confirmation or even reply from them; Kent 145 "Vegantune" 0.445" 280° that I can't find anymore; also with less lift Kelford 148-B 0.425/0.415" 278/288° and 148-C 0.43/0.412" 292°; then there is always the option of ad hoc profiles...). To be worked out will be to set the knock sensor detection threshold, which would switch the ignition curve to a retarded version during the development phase.

One question I have in mind, along the line of a previous discussion on camshaft timing, would be the relevance of detuning the camshafts a bit to help run on stock gas for road use, and use additive only for track use after resetting the timing...
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PostPost by: rgh0 » Mon Jul 17, 2017 11:15 am

Thanks for all the input, it is all extremely valuable, especially from Alan and your experience using 98 RON premium unleaded plus octane booster in race twin cam heads and cams similar to mine.

It looks like I can get away with 12.5 compression ratio on 100 RON (either 98 pump fuel plus octane booster or 100 Octane racing fuel), especially with the 300 degree seat to seat duration inlet cam I am looking at. I will stay with a shorter duration exhaust cam as this improves mid-range torque without significant loss of top end I believe.

At the race meetings I compete in here typically the fuel available currently is premium unleaded, 100 Octane racing fuel and Avgas ( plus 85% ethanol and alcohol which is of no interest). In the future when Avgas is phased out I don't know if 105 Octane race fuel will become more readily available. Moving to 98 unleaded plus Octane booster will be good as it will enable me to drive the car more on the road than I have been able to do in recent years since use of Leaded fuel on the roads was banned :D


cheers
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PostPost by: vstibbard » Sat Jul 22, 2017 4:34 am

Rohan,

I sold an S1 last year with 1594 cc running 11.6:1 comp, steel bottom end its been tuned to use BP Ultimate 98 Octane, later head, cams are Kent with slightly longer duration and lift than QED 420's. Idles at 800rpm, does not detonate, get hot and pulls like a train its on 45's with 34mm chokes. Iv'e done lots of dynoing over the years with Alfa's, Lotus and Porsche and this has proved to be the most stable quality fuel and makes more power than Shell V Power. With the Porsche (2.8RSR twin plug) when rallying I use Octane booster as a pre caution.. makes me feel happier running it to 8K all day, the engine had done 12 years of motorsport before being sent of now for refresh, pistons looked fine heads not cracked, signs of detonation!

Only thing I'd mentioned is it has two sets of plugs one for track days that are colder plugs as it tended to foul up these with lots of idling, gentles part or cruise throttle on the road.

I'm was planning on asking John McCoy to prepare a new SAS head for my 26R with his cams (I'm currently running the original matching number Cosworth). Who would you recommend, John or Tony Ingram?

Hope this helps with your next step.

V
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PostPost by: rgh0 » Sat Jul 22, 2017 5:58 am

vstibbard wrote:Rohan,

I'm was planning on asking John McCoy to prepare a new SAS head for my 26R with his cams (I'm currently running the original matching number Cosworth). Who would you recommend, John or Tony Ingram?

Hope this helps with your next step.

V


Thanks it again confirms I should be able to run 12 to 12.5 on 98 premium unleaded plus octane booster.

I also run cold plugs on the track (NGK BP8ES) and warmer plugs on road (BP7ES) and and when doing hillclimbs warmer still ( BP6ES)

As for who to get to build a new SAS head up for you It really depends on what your detail preferences are. Personally I prefer the spring setups that Tony Ingram or QED use but prefer John McCoys cams. Either John or Tony can build you a good head. If I was not doing it myself and using Johns cams and getting a head built for me then I would probably use John to do it.

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PostPost by: 1owner69Elan » Sat Jul 22, 2017 7:51 pm

Regarding getting a new SAS head setup you won't go wrong with either Tony Ingram or John McCoy. Question will be who is available and can get the job done in a reasonable time frame (less than a year). Tony has a lot of experience with the SAS heads. In fact, it was his recommendation to me on the SAS head that steered me in that direction.

I talked to both John and Tony and then ultimately settled on Dave Vegher (on Tony's recommendation) as Dave was closer to me (Northern California). Dave took the SAS head(that I ordered directly from SAS) and redid the seats (he felt they were not quite large enough from SAS for 1.625 inlets. SAS didn't agree - but no big deal). Also, Dave did some porting, other mods, high lift cams. etc. Dave did a full engine build for me. Very pleased with ultimate product dynoed at : 181hp, 143 torque in a stroked street engine (under 7K revs) with Weber 40's.

I suspect that Dave would only be interested in a full motor build. Tony readily supplies prepared heads only. John always seems to be super busy.

Lead time from SAS can also be an issue. Mine took almost 2 months to receive. I wanted a street port which is non-standard.
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PostPost by: elandoc » Wed Jul 26, 2017 3:02 am

Panda wrote:Hi Rohan,
In our 2.0 alloy block twin cam with .440" lift and 272 deg at .050" and 12.2 compression, we are using BP 98 octane unleaded with octane booster to bring it to at least 100. We have had total reliability in the NSW CSCA series for the last 2 years. With our previous 1700cc engine at 12.5 cr and same fuel, we also had no problems whatsoever with the engine. The head was as per your excellent recommendation, an SAS unit finished by Tony Ingram
Alan P

HI Alan,
I was afraid to go over 11:1 on my last build (rally engine BP 98), but I'm building a whole new car to be 100Kg lighter and was hoping to source a 2 litre BDG or similar for a bit of fun. Is yours a Wilcox?
Patrick
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PostPost by: SJ Lambert » Thu Oct 26, 2017 4:14 am

rgh0 wrote:...........
.............
I have normally used Avgas for race fuel with a 100 / 105 RON octane rating. ...............The use of Avgas is being phased out for historic racing over the next two years here in Australia

.....

cheers
Rohan



Rohan, do you think there's any likelihood of a reprieve on the Avgas phase out?
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PostPost by: rgh0 » Thu Oct 26, 2017 9:36 am

Talking to the Group S eligibility officer his opinion was that for group S and N which are production car based it would definitely be banned but for some of the open wheeler classes that have always used Avgas since they were new it may be retained at least for some period.

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PostPost by: Panda » Fri Oct 27, 2017 8:30 am

Hi Patrick (elandoc) I have just seen your post tonight. My 2.0l alloy block is a Cosworth casting which was supplied by Paul Truelove, when he was still in business. I can't remember from where he sourced it in the UK.
I built the rest of the engine myself, and touch wood it has been very reliable racing in the CSCA series here in NSW.
cheers Alan P.
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PostPost by: nocones » Mon Nov 06, 2017 2:39 am

Hello
i built a twin cam stroked to 1658, long rod's, 14.1 to 1 Compression, don't know duration cam but is almost .500 in lift cam. I run VP E85 for fuel. Fuel injected
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