which engine should I go for.

[cezeta]

vapour speedos use a pickup ,this means that you set the speedo for circumfrence of tyre. as you go faster your tyre gets taller and the speedo reads wrong .
car speedos are notoriously wrong from the manufacturer.
gps systems are run by global positioning sattellites and are as close to true speed as you can hope for . if you run a garmin 101 and a tomtom together you get exactly the same speed showing .

what it does not take into account though is land gradiants and it also relies on sitings per second (for want of a better explanation) so where a signal is poor the average is taken from fewer "sightings" Our gps is not to the same quality as the US milatry (whos system we fund) which is why now and then a sat nav will take you somewhere strange like the driveway to the house that runs parelel to the cam lam workshop it only happens in heavy traffic where the line of site is obstructed and the city of london is a no no too:roll:

its a bugger because i dont carry maps anymore

Im not a satalite expert.......dont like heights.....but i was part of a team that built a satalite control station in london for Inmarsat so asked the obvious Joe Public questions and got to re possition a satalite and see it move :bouncing: which involved pressing the return key following some else entering the relative info but still it was a buzz

http://www.tbs-satellite.com/tse/online ... arsat.html

[nick jordan]

what we really need to know is at what temp is damage done/pistons holed etc---does anyone know this?

[mark]

i am aware of all that i just think its the most relable speed sensor out today. tyres grow in circumfrence an incredible amount at speed. i spose the answer is to go with what you feel is best .

[tony]

Going back to egt. Stuart is right in saying they are all different. I'm coming from an angle where an engine is designed around a temperature which is safe. Maybe this is too advanced at the moment as we are using mainly off shelf pipes and kits.Designing motors to run at certain temps is what Charlie does.
So yes motors are different BUT all pistons have a melt point. And we are measuring the temperature of this very gas than can melt the piston. A crude thing to do ,to just establish that is to take a piston and melt it with an oxy acet torch. At what temp does it start to show signs of distress? Forged pistons will take so much, a cast piston will take so much. But you get an idea of what is happening and it will all happen at a given temp. From this you can at least see that there is a temp that is tolerable and that temp is fairly consistant piston to piston (if you melt a few!). Of course the heat build up in the real world which rises with load etc is another thing and has to be understood. But pistons will melt at a certain temp. From this we know the ceiling figure. A good egt gauge will respond very quickly to changes in temp whilst a head temp sensor is way behind what is actually going on.

So to sum up..there is a working range for egt thats efficient and safe. And yes as stuart said we need to know what exactly this temp should be. When I was given my falc motor Charlie told me.."its designed for 'X' temp. If it does this then the motor is doing this. If its doing that then the motor is doing this. Keep an eye on it!" So maybe the tuners of today should be looking at little more into this and telling the buyer what temp their motor is designed to be safe at. I bet there arent many that can tell us.

[cezeta]

mark, i was just chewing the fat realy, within 5mph is fine for me as Im not trying to break any records just trying to not get a ticket from a speed camera.

just waffling realy.....its sunday....home alone

going back to egt, the egt is not necasarily telling you you engine is hot like the head or water tempriture does it telling you that your gasses are hot.

if you run an advance and retard ignition then at higher revs you will expect to see the gasses getting hotter but not necasarily the engine getting hotter. this is because the retarded ignition timing is igniting later so some of the burn exits into the exhaust where as the heat is absorbed into energy or the body of the engine at a more advanced setting.

there is nothing wrong with the egt system but unless we know what we are looking at/for we can be reading it totaly wrong.

im about to fit one and have to confess that its a bit confusing

[mark]

just waffling realy.....its sunday....home alone

i do it every day until i can walk (hopefully new year)

[nick jordan]

i had thought about seeing at what temp a piston melted with a blow tourch but thought this wouldnt be a realistic experiment as wouldnt the piston be under different conditions in normal use--ie under pressure etc? however we did heat up the egt sensor to 700 degrees ---it was glowing cherry red--scary

[tony]

i said that about melting pistons to state really that they will melt consistantly at a given temp. We then just need to relate that to what the gauge is given us and work from there. This new tech can save motors. So i say read up on it.Examine it ....but certainly dont dismiss it as some 'gadget'.

[sideout]

http://www.matweb.com/search/datasheet. ... 001&ckck=1
620-650 for aluminium alloy.

Things to take into account is the position of the probe from the exhaust port and the fact that not many egts are calibrated in situ. I know mine's not

Another aspect is how long you keep the exhaust gas temperature above 620 degrees. There has to be enough time for the piston crown to heat up to its melting point. The cold charge each cycle will help to take the heat away, up to a point

Personally, I'm much happier running an egt gauge on my Mugello 186 and have adjusted the jetting according to the results I've seen.

(apologies for the slight thread highjack )

Cheers,

Nigel

[cezeta]

is ceramic coating the crown worth while, i appreciate its best to get it right but I'm a belt and braces type......looks a bit odd when I'm wearing a suit