Lotus Elan

SF Bay Area Fuel Quality

PostPost by: type26owner » Fri Sep 02, 2005 1:58 pm

Sarto,
I along with Tom Robard's help got http://www.baumtools.com to make us a socket that fits on the 3-eared KO nuts. It's 3/4" drive which I believe you'll need to get to the torque values the nut requires. Only problem is mine broke one of the tangs off that makes the socket cling to the nut. Had to recut the pockets and make the tangs wider and remove the sharp corners which were stress risers and machine in a radius instead. The socket is not heat-treated and modifying it fixed the problem of it breaking off the tang.

I'm almost ready to tune your Webers. Just need to finish building the power supply for the TPS.

BTW, filled it up with Valero 91 yesterday and even though it was chilly the engine ran ok. So far Citgo & Valero are the only two gasohols which my Webers don't have a problem vaporizing in the chilly mornings.
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PostPost by: mac5777 » Fri Sep 02, 2005 5:08 pm

Keith,
I did buy a socket from Baum tools and about to return it. The only size that they carried was the larger one for Jaguars etc., and it will hit the panasport/minlite type wheels if it is not held just right. I only got two nicks learning this.
Jim Boone got his from Baum when they still carried the smaller version and his tips also bent and he had to remake one. The design we have in mind does not use the little tips to hold it on. It will also costs much less.
You may be right about the 1/2 to a 3/4 socket. I thought that the 1/2 would be easier for the public to get and I assumed that it would take the torque. I had been looking for info on the required torque on the wheels before changing back to the 3/4 version. But better safe than sorry.
How far have you gotten with Baum tools and at what price?

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PostPost by: type26owner » Fri Sep 02, 2005 10:10 pm

Sarto,
Carry the socket and breakerbar in the boot all the time. I'll show you the modifications I did on the KO socket when I tuneup your Webers as a demonstration at Mike Ostrov's techday. You'd be smart to copy it if it fits the alloy wheels.

Tried to inform the Baumtool folks their socket was defective and never got a reply back. They've lost my patronage forever. At 240 ft/lbs torque that sudden lack of resistance sent me flying towards the ground. I came close to getting seriously injured when that damn tang broke off.

The price Baumtools charged several years ago was about $125.
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PostPost by: mac5777 » Sat Sep 03, 2005 12:20 am

Keith, thanks for the info etc. Is 240 lbs of torque correct for the KO nuts? Your problem with Baum KO nuts is probably why it is not available now. Their larger KO nut for the jaguars seems to be beefier.
We have kind of got off the fuel subject with the KO nuts. I've been using premium chevron gas, from Northern Calif, have you use or tested it yet??
Thanks
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PostPost by: type26owner » Sat Sep 03, 2005 1:26 am

Sarto,
I was using exclusively Chervon gasohol when I first started tuning with the AFM. I thought I was a failure and could never get the Webers running worth a damn. Until one day I tried to replicate some earlier work and could not repeat the results. Their fuel would make my car run like crap just about every other tankful and that was driving me nuts with inconsistant results. As soon as I switched over to Shell the tuning process improved enormously. Then it started happening again about seven weeks ago with the Shell brand of fuel. That's why I'm testing every brand of fuel that's available here in the Bay Area. The expensive to refine summer fuel will be replaced with the cheaper winter fuel now that the hot weather is soon to be over. Hopefully that winter stuff will not cause vapoization problems too. At least in theory I know how to correct the problem. I'm just happy to have pinned the problem down. :D

Please don't waste my time when I goto tune your car by filling it up with crapola fuel. No amount of tuning will make up for fuel that will not burn efficiently.
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PostPost by: bill308 » Mon Sep 05, 2005 12:31 am

Hi Keith,

I wanted to respond to your comments regarding when the mains come in, but first a question, are you using 30 mm chokes?

Originally, my engine was an S2 SE so it was fitted with the 32 mm chokes and the SE cams. I have not changed the jetting from stock but I have spent a good amout of time setting the balance and idle mixture. I have since upgraded to sprint cams, big valves, and mild porting to match intake and exhaust manifolds and accomodate the larger valves and valve seats, but settled for a minimal compression ratio increase of about 9.9:1 verses the Sprint's 10.3:1 to better accomodate todays pump fuels. Smaller chokes (30 mm vs. 32 mm) will develope increased vacuum and cause the mains to come in sooner though 1800 rpm is astonishingly early in my opinion. On my car, the pump stroke lasts several seconds so depending on which gear you are in, the engine may be running on the pump shot until it gets to a substantially higher rpm, say 2500+ rpm. Also, I'm not sure what removal of the emulsion tube/main jet/air corrector does. Fluid flow is not particularly intuitive. I never heard of anyone doing this before but it is possible this is a valid test, but I have my doubts. It may be that under this condition, the fuel will be drawn out of the auxiliary venturies sooner than when fitted with the jet/emusion tube/air corrector as the emulsion tube does act as a restriction to fuel flow and the ari corrector acts as a restriction for air flow.

The partial miss I reported is not really a flat spot. I never had one. What I was referring to was a slight miss fire, or perhaps a lean roll, at very small throttle openings. This typically occurs when gradually slowing down, without breaking for a stop sign, or a low rpm steady state cruise, in say 4th gear around town. I believe under these conditions, I am running on the progression circuit and I believe DCOE's have a limitation in this respect. This is also where I believe the Dellortos will be a little bit better. Dellortos are claimed to have better fuel automization under all conditions, but I shall see.

In my opinion, driving style has much to do with what one expects and demands from an induction system. For several years, the Elan was the only car I had, so I tended to drive it very conservatively for much of the time, with occasional visits to Lime Rock race track to compete in time trials. In general, my driving style put a premium on every day driveablility. An Elan driven on the track, is almost always driven at large throttle openings. One is either on or off the throttle. Under these conditions, progression and balance are not really very important. It is under around town, in traffic driving conditions where carb balance and idle/progression response is most important. To me, the ability to acclerate from a standing start with minimum throttle is important. If one is running the snot out the car most of the time, these refined characteristics are probably not important.

On balance, I think Weber did a pretty good job on the DCOE's and Lotus did a pretty good job in specifiying settings on at least the DCOE 18's that I have on my car. One can argue around the edges that adjustments need to be made to accomodate local fuels or driving style, but in my reality, DCOE's are quite good. I am hopeful that the Dellortos I have on order will be a little bit better for my driving style.

Bill
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PostPost by: type26owner » Mon Sep 05, 2005 3:38 pm

Hi Bill,
I'm using the stock 30mm chokes. Measured the vacuum signal from the auxiliary venturi best I could at about 3mm of water. Now that I have a rev limiter I can do that same test at WOT. Betting the signal won't grow in strength by much though.

Both tests requires the expenditure of a combined total of twenty minutes of effort. If you're unwilling to spend that amount of time doing the testing and determining whether I'm correct or not then why should I spend my time discussing these issues with you. If you don't have any running DCOEs to test then you'll notice there's over 2000 people on this list now and no one is claiming I'm wrong. Those two tests I DEVISED are my way of establishing my creditability that I know exactly what I'm doing. Instead of being baffled like everyone else I've chosen to do the work necessary to understand the workings of the carbies so tuning them is NOT a black art. If you choose not to believe it, that's your right. I can backup all that I say with reproducable results though.

As far as Lotus goes choosing the settings for the DCOE_18s, it's my firm belief they actually screwed everyone by having Weber install 79 degree 30 minute butterflies. That required them to do minimal tuning but virtually guarantees a stumble coming off idle unless the idling rpm is set high enough. Only 1100 rpms if you're lucky but that might have to be even higher if you're not. Only by installing 78 degree butterflies and tuning the damn things can you get the idle speed down to 800-900 rpms and still eliminate the stumble. Unless you drive like an egg is underfoot you'll never suffer from this tiny stumble though. Opening the pedal by more than about 1/4" and you're already on the mainjet circuit.

As far as I know all carbies behave like that on overruns to some extent. Since the DCOEs don't share a common plenum it's just more pronounced. My Webers do the same thing. One of the shortcomings of the carbies is the flow from the idle mixture screws always is there on overruns. The fact that the engine acts as an air pump and the airflow past the progessive holes is higher than if accelerating leads to a mixture which is excessively lean at partial small throttle openings. You can't have it both ways with static jets.

It's definitely harder to tune for the road. Racing folks think they're hot stuff but in reality it's easy to get the mixture right at WOT only and have it run well enough so it doesn't foul the spark plugs at part throttle. It's about 10 times harder to get the mixture steady under ALL conditions like you need it to be when driving in stop and go commute traffic.
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PostPost by: type26owner » Thu Sep 15, 2005 3:09 pm

Tested the Mobil 91 the other day and it made my twinkcam run ok. Could be because the Reid Vapor Pressure requirement was relaxed in the last week due to Katrina from 7psi to 9psi.

My brother Alan tells me we're getting E15 only here in California soon. Going to be a real technical challenge to compensate for it's negative affect fully.
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