Weber Jetting For Altitude

[type26owner]

I'm going from sea level to 4500 feet for the GGLC trackday at Reno/Fernley. My mixture is 12 to 1 at sea level. What kinda mixture can I expect for 4500 elevation if I don't change the main jet settings? The engine is completely stock at about 9:1 compression.

Can I make it over Donner Pass 7000 feet elevation without fouling the spark plugs completely? TIA!

[Foxie]

Without going into carbutettor gas and fluid dynamics, I've gone over the Gotthard, Simplon, Furka, all around 7,000 passes in the Alps, Stelvio on 11th September 2001 at 9,045 feet, and last October, Col de L'Iseran at 9,070 feet.

Never missed a beat, but you need a big radiator and fan(s) on the climb up.

Sean Murray

[type26owner]

Hi Sean,
I've had my Elan out on racetrack going 10/10 before when the ambient temperature was 40C. Fan would come for about 20 seconds at the end of the straightaways and cool it from 105C back down to 90C no problem. My main temperature problem these days when the ambient is 10C or below is my engine runs at only 80-85C. The thermostat opens at 90C and that means I'm overcooling most of the time and no water is circulating through cooling system. I'm afraid that puts me real jeopardy of suffering from cavitation corrosion in the waterpump. That would really suck to take out my new waterpump in this way. Always thought a front license plate would obstruct the airflow of through the front grill too much and now I find I need install it to do that exact thing for me to correct the actual problem. Intuition is sometimes not any help.

Anyways getting back on track, you don't know the air/fuel mixture you're using then I presume? Knowing that bit would greatly help me decide whether the altitude was a real issue to be concerned with or not. Thanks!

[Foxie]

Keith,

I don't have a figure for my air/fuel ratio since I put in smaller jets since my last rolling road outing, but it's still fairly rich.

My engine temp almost never goes over 85 C.

I'd say if you are rating your cooling for racing in 40 C temps and climbing twisty mountain passes, you are bound to have considerable overcapicity in less demanding situations. I have a full width Stanpart radiator with two 10" fans.

I can't say I've ever heard of cavitation damage on Twincams, but I'm ready to hear about it.

I suppose the simplet way to deal with overcooling would be to fit a partial/adjustable blind on the radiator.

Sean

[type26owner]

Sean,

I suppose the simplet way to deal with overcooling would be to fit a partial/adjustable blind on the radiator.

I need to find the time to re-jet my engine to the stoichiometric point (14.7:1). Running the mixture I am is causing part of the overcooling problem. There's more fuel going into the engine then there is oxygen to burn it so the latent heat of vaporization of the extra fuel has a huge effect on the throughput of heatflow in the engine. The issue of finding a set of main/air jets that does not go bonkers from the two-phase flow effect is dainting. By bonkers I mean that the mixture leans out at high rpms. Getting the damn thing to not suck it dry is the tricky part.

Not sure that cavitation effect applies to the twinkcam or not. It's a real possibility though and the prevention is simple so appying a cure is a prudent thing to do in any case. In any case the other things it does is reduce my heat coming out heater by about half. Also when I do bury my foot it abruptly opens the thermostat and gulps overly chilled water. Not good for engine when the temperature gauge plummets down to 60C in about one second.

[sk178ta]

Keith,
I`m frequently amazed by the time and effort you put into analysing the vagaries of the thermodynuclearophonicalarisation of various parts of the twincam!! I have had occasion to seek your advice in the past, to good effect ........however......... loads of British classic car rallies routinely cross the European alps and I`ve never heard of anyone making ANY adjustments to compensate for the altitude.
Likewise the cooling, I would have thought water pumps would have been failing by the minute in cooler climes had this been a problem. Is it too obvious to just change your thermostat if you are concerned?
In no way wishing to denigrate your broad technical knowledge in things twincam, it does seem to me that the blokes who have all the problems are the ones who are forever fiddling under the bonnet and know 10 times as much as me. I`m a great believer in getting a professional, preferably old and experienced, guy to set everything up properly and leave well alone, bar routine checks.
Though not convenient to people who spell tyres with an i, I can heartily recommend Dave at High Peak Auto Classics 01298 7008 at ?29.50 per hour.
I had 4 successive Elans in the 60s and 70s and used a similar, now dead, bloke. I well remember him saying that Lotus`s reliability reputation was largely tarnished by owner`s mis-guided enthusiasm for fiddling under the bonnet.
Keith, please don`t take this as a criticism of your undoubted ability, I merely make the point that less gifted home mechanics (like me) can probably save money and heartache by keeping things simple.

[type26owner]

sk178ta,
Thanks for the advice. Had a conversation with Mike Ostrov a few weeks back about whether or not posting technical stuff here was actually worthwhile. He made the point most folks only care about two things; whether it will start and will I get home. I and few others on this forum like to take our cars onto the racetrack and therefore operate at a higher level than the will it start level stuff. Going 10/10s with a forty year old car that has issues is a lot of fun. To do it safely and eck out every little bit of performance out of it is a race engineer's delight. Doing the same thing on a Porche would be totally boring to me since their engineering refinements are top notch. The Lotus has always been rather crude and under-developed. Back in the day there were a few drivers which refused to drive for Chunky because they considered his cars to be unsafe. They were the really intelligent ones! :rolleyes: The potential of sorting those issues and having it all come right is what I relish. Come out on the track and see if your stock car is faster than mine. I find 104 hp is plenty of power for a performance road car. When it is tuned correctly it hauls ass. Got on the freeway last weekend following my son in his 70 RoadRunner with a hot 383. He really nailed it and was shocked to see me in his rearview mirror almost glued to his rear bumper with a huge shitty grin on my face.

I'm off to tweak a spare dizzy which will allow me to burn this 87 octane crud fuel (zero static timing) and still bump up the total advance so I can run at altitude at full power.

[Matt7c]

For me there are 2 aspects to owning a car: the pleasure obtained from driving and the pleasure obtained from tinkering. I like tinkering, and hate paying others to do what I can do myself. However, I have no plans to get too complicated and I know where sk178ta is coming from. Not least because I'm not smart enough! I am, however, in the (for me) fortunate position that after 14 years off the road, most thinsg on my Elan S2 need improving - but that's just to bring it up to bog standard! How I dream of attaining bog standard performance

[sk178ta]

Keith, please don`t stop posting your fascinating technical articles, even though I don`t even know what a 70 Roadrunner with a hot 348 is !!
Regarding minority track use; that`s not my impression here in the UK. Last October in France on the high speed bowl at Ceram and on the main straight(away) at Dijon-Prenois our S3 would easily pull max.revs. in top. We even got 10 laps at the Ferrari test circuit at Fiorano and the Elan was about the quickest thing there, so the old guy at Buxton must know a thing or two.
Next month we are off to Scandinavia for a week visiting 4 circuits, with unlimited laps. I think you`ll find lots of Elan owners here do track days, though in my case the squealing of tyres and wife, and the need to start the next day and get home, reduce effort to 9.9 tenths.
Regards,
Jim

[type26owner]

Hi Jim,
A 70 RoadRunner is a Detroit Iron muscle car. Also known as a linear accelerator. His car will cut a 13 second light in the quarter-mile. I can stay up with him till about 60 mph then he dusts me off. Only can do that since his tires will break traction at half throttle in the lower gears. Meanwhile I'm fully hooked up and at WOT.

Wish the GGLC trackdays had better attendence then just Dave Anderson and myself in our Elans. Pitiful! Running in a pack of Elans would be great!

I didn't answer our query about the thermostat so here goes with a nutshell explanation. Keeping your engine temperature between 90 to 100C provides more power, increases the fuel mileage, reduces the pollutants, increases the efficiency of the cooling system and makes the puny cabin heater put out enough heat to roast your legs. I'm sure there are more benefits but that will do for now.

If you are feeling overwhelmed by my postings then don't read them. I'm really pushing hard to complete these upgrades on my Elan so I turn my full time attention to restoring my 55 Aston Martin to race-prepped condition. It's in pieces in my garage at the moment.

[type36lotus]

Hi Keith,

While your posts are generally way over my head, I do find them very interesting. As apparently do others as your topics seem to have high view counts. So while you may get very little participation from us less technical types, the few who are at your level generate interesting responses. You are targeting 10/10 ths, me - will it start, run, and return home under it's own power. Thanx for posting.

[twincamman]

I heard it said 'the most successful Lotus driver was completely devoid of any engineering knowledge'-------------ed law :rolleyes:

[type26owner]

Hey Ed,
A couple years ago I purchased the four VHS tapes chronicling the Lotus racing history. It's sobering to see the carnage of those times. Those guys were truely fearless. I think your point is generally valid anyone with the engineering knowledge would suffer from it.

[type26owner]

Looks like no matter how much I retard the timing at idle I can't eliminate the detonation from burning the 87 octane California RFG when pulling away with moderate power at sea level. Bummer! Maybe it will go away with the 89 octane stuff.

[lotus026]

Gee, seem to have wandered quite a ways away from the original question! And I never saw an answer - so I'll give it a shot. As regards jetting for altitiude, I've been dealing with that for a couple of decades since I've been running hillclimbs for the last 23 years. So if you were jetted about right for sea level, as a rule of thumb I'd probably drop down one size main jet for use in Nevada - but if as you say you're running rich anyway, you might have to drop a couple of sizes. Or you can also go up a size or two on air correctors; I've never done the adjustment for altitude with them but know it can be done, I get the impression that it's way easier and more effective to switch main jets; might have to go up 2 sizes of air corrector to have the same effect as down one size main jet. So for example if I'm running a hillclimb that's up around 4,500 - 5,000 feet, I'd drop the jetting from a 150 to a 145 (these numbers are from my Datsun, since it's the one I've had the most experience with!); and the times I've done a hill at 6,500 - 8,000 feet I needed to drop down to a 140; and changing jets was the only change I made.
So I'd just take a couple set of jets with you, and once you're on the way up Donner stop and change down a size; only takes a couple of minutes, that's what I usually do on the way to a hill once I'm a ways up! If it acts like it's fouling the plugs, pull one and take a look; maybe go down another size.
Hope this helps.....
Dave
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