Lotus Elan

Airlow box?

PostPost by: alexblack13 » Tue Jan 08, 2013 10:24 pm

Hi Guys,

Just a quick opinion seeker.

I have been toying with the idea of building an airflow box to check the butterflies on the Dellorto carbs. Just to check (and adjust if need be) the airflow through each choke. Mainly on tickover setting.

Any ideas? Worthwhile or overkill? I was thinking to power the device with an industrial vac' unit I have. Is there a nice simple method? Light?


Thanks guys..

Al'..... 8)
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PostPost by: garyeanderson » Tue Jan 08, 2013 10:44 pm

are you talking about something like these?

http://www.dellorto.co.uk/merchandise/p ... ctionID=17

Image

43 quid and a bit :D

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PostPost by: lotusfan » Wed Jan 09, 2013 7:43 am

Alex

I would strongly recommend http://www.carbtune.co.uk/index.html as a very good means of measuring individual choke airflows, it uses tappings which already exist on the Dellortos.
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PostPost by: alexblack13 » Wed Jan 09, 2013 8:17 am

No Guys. Thanks very much for the suggestions. I have the tools for measuring and setting up the carbs on the engine. Exactly the One you have pictured Gary. Many thanks..

When one has the Carbs on the bench and checking resetting after fitting say new bearings to the spindles and you suspect a slight twist (common) of the throttle spindle giving a different airflow through the two butterflies on the same Carb. I was just thinking about the best way to correct this and I understand the pro' carb shops attache the carb to a flow box, and put an airflow through the carb. Then its easy to see which butterflies are flowing what amount of air and helps when adjusting (untwisting perhaps?) the butterfly. It makes it easy to set the butterflies on the bench. Removes guesswork.

I know it's possible to do this with the engine running, but there are many factors to consider and one can never be sure what may be causing an imbalance on the same Carb..

Just a thought..... :roll:

Aahemm...

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PostPost by: jono » Wed Jan 09, 2013 8:29 am

....have you just retired by any chance, Alex? :lol:
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PostPost by: alexblack13 » Wed Jan 09, 2013 8:32 am

How did you guess!! :lol: :lol: :lol:

AB...
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PostPost by: garyeanderson » Wed Jan 09, 2013 9:19 am

Either sell the Elan you have and get another project or just get another project :) .

If you want and airflow bench for doing carbs then get a Superflow or some such. or look at what they offer and coble something together to suit your needs/wants.

http://www.superflow.com/flowbenches/index.php

Theses are just calibrated suck tools so that one can accurately measure and repeat that measurement.

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PostPost by: ElanSeries2 » Wed Jan 09, 2013 9:59 am

Alex

Whilst I haven't done a web search, I have a book on cylinder head modification that includes a good section on building a flowbench (I'm pretty sure this is the term to use). Its a Veloce title, called How to Build, Modify and Power-tune Cylinder Heads by Burgess and Gollan. You are welcome to borrow my copy (although I'm in Halifax) or perhaps you can pick one up easily.

That said, I think you may be using a sledgehammer to crack a nut on this one! On the bench, you can measure the lift of the butterflies with dial gauges. If you can't detect a difference, put them on the car and use the tappings provided. As you say, there are many things that can affect the airflow, but as long as the engine is seeing the same through each port, you should be ok.

One thing I used to do was have manometers set up at various different positions on the inlet tract, so you can see where you are getting losses. If you have a set of manometers before and after the butterfly, you can isolate changes due to the butterfly (without the hassle of building a flowbench).

Are you most interested in quality of idle or fuel economy, or merely the pursuit of perfection?! I assume its not outright power.
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PostPost by: Chancer » Wed Jan 09, 2013 10:49 am

I have a great tuning book called "Practical gas flow" which taught me an awfull lot about race engine building, its a very down to earth and practical approach to a complex subject, the book shows you how to flow test cylinder heads (and why not carbs) using a vacuum cleaner!

One of the things that has always stuck with me from the book was a calculation for effective compression ratio when using longer duration cams, using this I always managed to run a higher compression than most engine builders for a given cam yet avoid detonation.
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PostPost by: alexblack13 » Wed Jan 09, 2013 4:45 pm

Thanks Guys.. I fixed it I think. I hope..probably..

I know about the tapping's in the carbs and the tools for balancing. I have those.. That is how I detected the slight imbalance on the rear carb's chokes... Thanks though guys... :wink:

And... You are right! Just looking for a nice pleasant to drive car. Power is not an issue as long as it is running right I am happy. If I want to go fast it will be in something else with a lot more safety built in...

I had a slight difference choke to choke on the rear carb as I said (Now sorted)... I used a very low power setting on Mrs B's vac. basically limiting the sook and applied the hose to each choke in turn and sure enough there was a very slight difference, throttle closed on my flow-meter. Very very small but there just the same. The slightest of twists on the shaft sorted it out. Took three 'tweeks' but it is now bang on.. It was as I say, very little and I would have gotten away with it no bother as the car was running very well before I started, but I think it should be even better now after the carbs rebuild.

The said carb had a dip today for 30 Min's in the ultrasonic tank and it came out really nice. Soaked it in petrol for 5 Min's or so before a blow dry and it is now sitting on my bench awaiting blowing out carefully and then re assembly.. I have already re grease the bearings (which now feel very smooth!) on the spindles too. Before the tweek!!

The other carb will get the same check / treatment but I think it will be dead on. It balanced very nicely last time checked.

Thanks to all... & Gary!! Those flow-benches are great but... are just a bit more than I need... Being a bit of an anorak but I'll get over it. It was interesting to see the 'vac test' confirm the same slight imbalance that the carb did on the Car. I was surprised at that. As I say, as It was between very little and bugger all... :roll:

My next 'project' will be shooting off in a camper-van, hopefully with trailer & Lotus (or ?? ) on the back! and not coming back for about 3 months!! Roll on summer.

Cheers Guys.. Very interesting comments that I really appreciate.

Alex ......
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