Peter Jenkins Posted August 30, 2009 Share Posted August 30, 2009 Has anybody any experience of using the Just Engines spark ignition kit to convert a Saito (100 upwards) to run on petrol? Do you need to change the carb to the Saito pumped version? How difficult is is to install the magmet in the prop driver and what sort of shimming is needed to reduce compression? Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted August 31, 2009 Share Posted August 31, 2009 hello peter-there is an on going thread somewhere on here about the very subject-get searching before you spend your/her indoor's dosh......... ken anderson........ Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted August 31, 2009 Author Share Posted August 31, 2009 Ken, thanks for the steer but I have to say that having read all three threads I am none the wiser! An article by the WOO on doing a conversion would be great. Tantalisingly, his latest review of the Saito SG20 states that it is a standard Saito 120 glow engine but then doesn't go on to say what the changes are to compression ratio. I note that it has a new pumped carb although WOO says that the needle valve is standard Saito! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 6, 2009 Share Posted September 6, 2009 PeterI think you will find that most glow engines use a similar compression ratio to petrol so I suspect shimming the head may not be required.The air/fuel mixture is however very different. In a nitro glow it can be as low as 4:1 but for petrol it needs to be pretty close to 12.5:1. Such a difference may not be within the carbs capability to control the mixture accurately over the full throttle range. Quote Link to comment Share on other sites More sharing options...
Former Member Posted September 12, 2009 Share Posted September 12, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
thomas oliver 1 Posted September 17, 2009 Share Posted September 17, 2009 Simon, Are you sure you havent got those ratios the wrong way round? Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted September 17, 2009 Share Posted September 17, 2009 The chemically correct air/fuel mixture for complete combustion is just under 15:1 but because of uneven distribution within the cylinder Simon’s 12.5:1 is the practical ratio. Glow fuel carries its own Oxygen in the Nitro and therefore needs less air. Quote Link to comment Share on other sites More sharing options...
Bert Posted September 18, 2009 Share Posted September 18, 2009 Posted by Brian Parker on 17/09/2009 20:36:28: The chemically correct air/fuel mixture for complete combustion is just under 15:1 but because of uneven distribution within the cylinder Simon’s 12.5:1 is the practical ratio. Glow fuel carries its own Oxygen in the Nitro and therefore needs less air. Except there ain't no nitro in straight fuel Bert Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted September 18, 2009 Share Posted September 18, 2009 The reason for the different air/fuel ratios is that petrol has a much higher calorific value than methanol.....you get a bigger bang with less fuel...... For really high power engines methanol is often used as you can cram more of it into a cylinder & compress it more before pre-ignition. Many dragsters use methanol & have no cooling systems because a) the engines only run for a short time b) they are practically liquid cooled by the amount of (liquid) fuel being poured into them!!!!! Quote Link to comment Share on other sites More sharing options...
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