Any Pictures Mowog? I thought it could be done. Are you going to put up a full post on it explaining how it works in detail? I'm very interested. I tried (am trying) to have a go, but lets just say I've put that little hot cake on the back burner (also called the "to hard basket,, not too good at electriconicaly stuff).. Interested to hear more on how yours works,, and maybe pinching it in exchange for finanical re embusment

Yes, it can be used for selecting the correct spring. The spring should be selected such that the SU piston will only fully rise at maximum air demand (peak torque). By checking the Piston lift curve, if it is fould that the piston does not rise completely, it is likely the spring is too heavy (or the piston is sticking - these things should be checked first) and if the curve tops out for a period, it is likely the spring is too light.

It maybe possible to detect if the throttle shaft is worn, it would take a carful eye and some experience though. It would probably be better to check these things the old fashoned way - check for play.

I've spent the past couple of days adapting it to a HIF however it could not be done in the same way as for a HS type. I had to modify a bell, but this will now work with both HIF and HS types. I have done 1 run to check the instrument as a tuning aid and the results are GOOD, so I am looking forward to being able to sort this customers car in detail over the next day or so now.

This afternoons run log with a HIF 44;-

[img][img]http://img694.imageshack.us/img694/3293/session3a20091130.jpg[/img]
By gtmowog[/img]

This one includes the manifold vacuum (green), Revs (black), Piston Lift (red) and A / F ratio (pink).

it looks like you are getting the basics of the carby operation, but if you can now incorporate air flow[ie velocity] into carby it will be more important than vacuume. as the butterfly closes partially after increase of rpm the velocity will decrease more than variation of vacuume.
air flow across the piston will determin the rate and dist the piston lifts. There must be a differential air pressure to get the piston to lift.
the other thing to look at is cylinder firing temp and pressure as a air/fuel ratio will again change as the load changes .
air temp before carby is important as for every 1 deg in there is 6deg increase in exhaust temp

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Thanks for your feed back Dave. I'll chew it all over and I welcome anything you might have to add.

OK, this is how I see it, and correct me if you think I'm wrong;-

Airflow - If you think about how the SU works and the Piston, it is an Airflow Meter in itself, so we are already measuring 'Airflow' but not in CFM. I am measuring it by Piston Lift (in inches) so we can (eventually) directly correlate that to needle profile - after the spring rate is sorted.

Vacuum - I measure the Manifold Vacuum to determine Engine Load (as seen by the Carbie), we can see acceleration (High Load), Cruze, and Over-run and check this against A/F Ratio. We would like to see 13.7:1 under acceleration as about 15-18:1 on cruze. Yes, there must be a pressure drop across the Piston to make it rise (atmosphereic preasure is actually pushing it up), but this is not what I am measuring with the manifold vacuum, the two are not really related. Years ago when I did have access to a Dyno and while I used a Vacuum Gauge back then the owner of it thought it unconventional, however I was always able to achieve the same results he did but quicker.

Cylinder firing temp and ambient air temp - I have not measured these although I do appriciate there significance. Regretably the SU is unable to measure these and compensate for them. Ignition Timing will have a large effect on Firing Temperature.

when I use the bike tune-up programme set-up with the honda CV carbys I found that there are a few interesting things that occur.
the honda carbys work basically the same as a SU, and the air flow measurement is important. the computer will give a readout at the same engine rpm either under accel.or steady rpm. this will them tell you how much air is getting into the engine and a air/fuel ratio and the position of the needle. the ideal gas law- Pressure,volume,temp
I found that under certain conditions the mixture leaned off and this increased the cylinder temp.
the piston is lifting due to differential air pressure and you can have same diff in pressure ,but a big difference in volume of air into the engine.IE piston height and butterfly position. One of the tricks that steve showed me was how to modify the piston to get better lift as the air flow increased when the butterfly was fully open.
With this mod the engine can be accel from any steady rpm and it will go to excess fuel[piston lifts to max] then as air flow increases settle back to required position. every time the throttle is snapped open the engine has a puff of black smoke then settles down.

With exhaust temp this is critical as a variation in air/fuel may be slight but due to load the temp will increase rapidly. the alumin pistons do not have a big lee way before they reach deformation temp.
I found that with inlet v/v timing was critical as the extra air flow helped to drop cylinder temp and cool the pistons.
One of my early test engines had the extractors glowing red hot under full load and the piston crowns were badly deformed after I stripped it down. I know that the exhaust temps were around 575-600 deg C at head out-let but increased to over 700 into the extractors. By adjusting the inlet cam timing the cylinder temp dropped and the extra air dropped the extractor temp considerably.

this set-up has a ring with a internal groove and a outlet fitting to a pressure guage that fits under the spark plug . so as the engine is running the cylinder pressure can be measured[effective mean pressure] and this is what HP calcs are worked out from.with 4 seperate carbys/cylinders/exhaust this is easy.


What you are doing with this programme is good to see what is happening with the carby,but more info is a helpful thing to see exactly what is happening to the whole engine package. I am lucky I just borrow steve's expensive toy

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

I can easily add exhaust temp in to this set up. I have (presently) 2 spare inputs. And it could be useful, yes, I agree with that, but just to not loose sight of what it is that I have set out to do here is to have some meaningful instrumentation to assist in the selection of a needle profile and spring for an SU(s), it was not intended to be a full computer engine analyser (though THAT would be good ). Basically I'm using the same principal of needle and spring selection as recommended by SU back in about 1984 (yeah, yeah, times change) except I'm using A/F measurment instead of Colourtune (which has serious limitations) and actually measuring the SU piston lift instead of estimating it (I think Vizard also published a similar method).

I see that your friend 'Steve' has a you-beaut gizmo tester that can measure both cylinder firing temperature and BMEP. That sounds like a nice bit of kit. When I did my studies (a long while ago now) this was always a theoretical calculation (the BMEP) based on dyno results. Supposedly (except in research type engines) it was not possible to actually measure it (I really don't see why it cannot be measured).

If we could measure the BMEP we can easily calculate the power developed at the piston crown (PLAN / 33 000)

Do you have some details on Steve's 'expensive toy'?

stevegot the whole set-up from RB racing in USA. They have a guy there who is a genius at making electronic gismos. I think that it has cost him over $3000 for all the bits and soft ware. He uses it for tune up on the race bikes, set up on a solid stand, fire it up, into gear and let rip. Then you just apply the rear brake to put load onto the engine.
I basically do the same with the mini engines/gear boxes. setup in subframe with old drum brakes and watch them glow red hot. handy when you can not find your cigarette lighter.

To measure firing pressure of each cylinder on the big marine engines they have a indicator cock in the head. just connect a mechanical type pressure indicator and run the engine. With the info from fuel rack position, exhaust temp,and cylinder pressure each cylinder can be tuned up the same.
The set-up to measure cyl pressure is a ring with internal groove that replaces the washer under the plug with a out let pipe to a fluid filled pressure guage. the plugs have a groove cut down the thread for gas flow.
The cylinder pressure will vary due to air/fuel ratio.
Once you have that reading then HP and torque are a simple calc.
I have found it very usefull when I have had problems with either rings or valves not sealing properly as the engine is running. The A/F is right but the pressure is down.
The problem with trying to do all the measurements on a mini engine is the cross connection of cylinders, but a few basic measurements will give you a lot of info to work with.

_________________
Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com