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KevinH
United Kingdom
156 Posts |
 Posted - 03/06/2008 : 19:13:06
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PA1602 now has its supercharger fitted and seems to be running quite well with an RA needle as a starting point. However, I want to get the mixture set up properly, which may well involve trying different needles.
Does anyone know of a rolling road within a reasonable distance of Guildford, who keep a good enough selection of needles in stock to make a visit worthwhile?
When I last had my GTV8 with a modified 3.9 engine on a rolling road that were supposed to be good with SUs, they were unable to try different needles as they didn't have any suitable so I didn't achieve what I set out to do.
Kevin |
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tholden
United Kingdom
1638 Posts |
Posted - 03/06/2008 : 23:10:23
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Hi Kevin
There is the Mini Centre in Byfleet who have a rolling road, another company called SAS in Aldershot who have some very top of the range high tech gear and there is Janspeed in Salisbury. There is another very experienced man near Winchester. Quite possibly your best bet would be Janspeed who are situated adjacent to Burlen who can of course supply any needle you may need. I have experience with some of these people if you want to give me a call to discuss.
TH |
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KevinH
United Kingdom
156 Posts |
Posted - 04/06/2008 : 13:19:39
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Terry,
Many thanks, that would be useful. Could you please email me your number, and I'll give you a call
Regards, Kevin |
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Gordon
United Kingdom
691 Posts |
Posted - 04/06/2008 : 17:33:59
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You don't actually need a firm with a whole range of needles!
If you start with slightly too weak a needle then a competent operator should be able to dress the needle in the appropriate area by filing a flat to richen the mixture at that point. The critical first step is to ensure that the dashpot and spring combination allows the dashpot to rise fully at the maximum demand condition. Then working from the tickover slowly file a taper, section by section, till you are using full power (ie adjust rolling road/throttle conditions so dashpot rises up a bit, determine mixture, file a bit off and recheck. When mixture correct move on to the next condition). It doesn't matter that you have a flat now running down the needle as it is the cross sectional difference between jet and needle that controls the amount of fuel flowing.
Once you have the mixture set you could always have the cross sectional area accurately measured and get a needle manufactured to the resulting profile.
This is the way it was done on my car and when all was done we lowered the jet a couple of flats to richen it up over the whole range.
I would consult the tables (www.triumphshop.co.uk/Quiller/Downloads/suneedlechart.xls
and select a needle that was weaker than the RA so having the rolling road check out mixture of the RA you can find out if it is too rich anywhere and then proceed to work with the weaker needle as above to get the mixture right.
Gordon |
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KevinH
United Kingdom
156 Posts |
Posted - 04/06/2008 : 23:41:18
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Gordon,
Thanks. I totally agree that it isn't necessary to have a whole range of needles provided the operator is competent enough to modify a needle. The problem is finding a rolling road with an operator who has the expertise necessary to do it, or who has a good range of needles to hand. I'm hoping that this post might turn up someone not too far away.
As you say, the first step is to check that the piston/spring combination allows the dashpot to rise fully at max demand. I'm going to use a bowden cable in the top of the dashpot leading back to a guage in the cockpit to measure lift (Paul Duncombe described this method in the Bulletin a couple of years ago).
Once the dashpot lift is OK, then it's worth taking to a rolling road.
Another thought is that for the price of a rolling road session I might instead invest in an air/fuel meter with a wideband lambda sensor to get the mixture exactly where I want it over the whole range. Fit the sensor in a temporary adaptor at the manifold/pipe junction, measure needle position with the bowden cable, and then richen a needle that is initially weaker than my RA until the air/fuel ratio is right (I think 12:1 over the whole range would be a good target). An interesting idea that needs more research. If it is viable, then I could also use it on the blown L special that I'm building.
Kevin
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KevinH
United Kingdom
156 Posts |
Posted - 05/06/2008 : 18:05:22
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Hi Paul,
A lambda sensor compares the amount of oxygen in the exhaust to that in the air, and it seems that even very rich mixtures contain some unburnt oxygen for the sensor to work with. The original sensors were extremely non-linear and useful only for sensing lean/rich around the stoichiometric point. There are now wideband lambda sensors which were originally developed for dyno tuning, and are supposed to give reliable air/fuel readings from very lean to very rich. There are some kits available, for little more than the price of a rolling road session, that will give reliable air/fuel mixture readings on just about any car, with or without an ECU.
Installing one of these on a temporary basis together with your idea of the bowden cable in the dashpot, should allow accurate air/fuel ratio vs needle position measurements to be made on the road, and the needle gradually modified to get the desired mixture. One of the products I've looked at is from Innovate in the US (they have UK agents)http://www.innovatemotorsports.com/products/db.php Their kit includes logging software, so you can go for a drive with the PC in the PA and analyze the results later!
I need to look at this some more to see if it is going to work, but it may deliver more than an unsatisfactory rolling road session like you had, for more or less the same cost.
As for the best mixture to go for, the diagram I looked at showed max power at a ratio of 12:1 which equated to 7% CO and just seemed a good target (rich but not too rich). This was from my Gunson Gas Analyzer (deceased) booklet. I'm certainly open to plenty of advice on the right mixture for a mildly blown engine.
Kevin |
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KevinH
United Kingdom
156 Posts |
Posted - 05/06/2008 : 20:51:07
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Hi Paul,
I hope we get lots of feedback on this. The sensor route appeals because I will doubtless learn a lot, and there is always the possibility that others will benefit if it works.
I'm off to the bike shop tomorrow for a long bowden cable, then to our local long steep hill for a test once the MOT is hopefully obtained on Satrday
Kevin |
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Drolshagen
Germany
669 Posts |
Posted - 06/06/2008 : 10:26:47
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Hello All,
here are a much cheaper device to measure the fuel/air ratio.
You need only a voltmeter with a high inner resistance,a digital is ok.Also you need a lambda sensor,prefer a heated one,ypu will find this on every VW on scrap yard for few pounds.
Every lambda sensor generates when the engine is running up to
1,5 Volts without any battery.
What you have to do is, connect the voltmeter with the lambda sensor
and measure the generated voltage.
A rugh rule:
Lambda 1 = 0,5 Volt
Lambda 1,05 = 0,3 Volt weak mixture
Lambda 0,95 = 0,75 Volt rich mixture
All Lambda sensors have M 18 x 1,5 thread,
I think with few pounds you can make your own fuel/air ratio
meter.
Carl
L2 2036
J2 4362
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David Allison
United Kingdom
665 Posts |
Posted - 06/06/2008 : 13:56:33
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Gents
I think you are making things a bit complicated for yourselves.
The information on set up is all freely available and although the advice is all rather dated it is a good starting point.
Paul - 10% CO does sound rather excessive.
The NA is running rather over rich at the moment (mainly because the needle is worn out and I have got to get around to replacing it) and that is running at around 6.5% according to my MOT tester man.
I dont tend to use rolling roads - prefer to use the tried and tested benchmark in combination with plug cuts and suck it and see road driving.
The NA has always used the same needle and never had any trouble although it does seem to prefer running over rich on the unleaded fuels at the lower end of the rev range.
Interestingly though the 1100 cc engine in the NB special runs much richer - odd seeing as the NA has a larger engine!
What you are looking for is a dark grey colour on the tip of the exhaust tailpipe - a little paler after hard driving.
If the tail pipe is a light grey or even white - then you are too weak - dark charcoal or black and its too rich.
I tend to the darker shade of charcoal for an engine which is driven hard - cos fuel is cheaper than pistons!
Regards David |
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KevinH
United Kingdom
156 Posts |
Posted - 06/06/2008 : 14:47:31
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David,
The only info that I've been able to find on carb setup on a blown engine is to start with an RA needle and take it from there. Is there something available that is more specific?
Maybe I'm too concerned about getting the mixture right, but as you say, pistons are very expensive. What would you say is the ideal percentage CO for a mildly blown engine? Is it necessary to get the mixture right for all needle positions, or just get it so that the exhaust is the right colour after a good drive?
Also, is it likely to be detrimental to the engine to run it at stoichiometric at 6-7 pounds boost at 5k rpm on the road for brief intervals when getting the needle/mixture right?
Kevin |
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KevinH
United Kingdom
156 Posts |
Posted - 06/06/2008 : 14:55:35
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Carl,
It's a good idea - I looked at it when I first thought of using a lambda sensor but discounted it as almost all the sensors found in cars today are the narrowband type which are only accurate around stoichiometric and I wanted to set the engine to run at a certain degree of richness.
However, maybe a simpler and cheaper approach would be to use your idea to find or modify a needle to run at stoichiometric, then simply wind down the jet by a couple of flats or so to get it running slightly rich.
Kevin |
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David Allison
United Kingdom
665 Posts |
Posted - 06/06/2008 : 15:48:31
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Kevin
The men from the ministry allow us to run up to 10% - but my experience is this is too rich.
I prefer to keep the CO to between 6 and 8% dependant on the time of year - hot dry days the engine will accept running richer than cold wet days.
My NA runs at around 6.5% at idle rising to 7% at 3000 rpm - I prefer to run a little richer on mixture than a lot of the rolling road people would though.
I do know of cars set up in the 4.5 - 6 % range but in my opinion this is too weak.
My Dad always taught me to tune the engine to run on a smooth idle - as long as it does not "Hunt" then the mixture is probably ok!
Hope this helps
Regards David |
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KevinH
United Kingdom
156 Posts |
Posted - 06/06/2008 : 16:41:41
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David,
Thanks. It ties up nicely with what I've heard from others ie CO in the region of 6-8%. perfectpower.com tells me that is an air/fuel ratio of 12.25-11.54 (12:1) which I think is just about the mixture that provides maximum power. I guess there is no point in adding a blower and then not running close to the max power mixture.
Kevin |
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KevinH
United Kingdom
156 Posts |
Posted - 06/06/2008 : 18:05:46
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Hi Paul,
Good point - I was thinking on the fly earlier about lambda sensors and not about needle profiles!
Just had the colourtune plugged in, and it looks good at idle now, but gets much richer at higher revs. There must have been something wrong with the jet not seating correctly a few days ago 'cause I couldn't get it right up to the bridge, but now it's OK.
Fingers crossed for the MOT in the morning
Kevin |
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ht1962
Netherlands
114 Posts |
Posted - 08/06/2008 : 10:12:04
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Hello,
I had 2 magneto failures using a colourtune to set up the carbs on my pre war italien designed Aston!
Nobody know's why.
Better be carefull using colourtune on magneto engines!!!
Halbe |
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George Eagle
United Kingdom
3238 Posts |
Posted - 08/06/2008 : 20:50:02
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Some of this is a bit deep for us amateur mechanics! What does stoichiometic mean?
Sounds like a good topic for discussion/debate at Silverstone.
George
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