vintage Blown JAP 500cc in midjet speed car

[fitsracing]

G'day, want to set up WI between throttle and supercharger on vintage 500cc JAP hill climb cooper midjet speed car running on methanol.
the blower is a cabin pressure pump from a DC3. the problem with this set up over the last 50 years has been detonation,when changing gear. going from wide open throttle (WOT) max revs /pull and full boost to closed throttle for gear change,at this point high vacuum between closed throttle and blower, reopen throttle,still high vacuum and as surge of intake gas charge through open throttle until vacuum drops and the inertia of fast flowing intake charge momentarily gives a boost spike into and through blower, over boosting engine causing detonation.
too off set this previous safe tune obtained by retarding ignition and long intake runner.
wanting to WI so more ignition advance can be used .getting most performance safely.
this may be old school stuff with no electronics.
a waste gate or blow off valve would help.
but answer lays in WI, to get ignition advanced.without detonation.
can someone help?
regarding simple vacuum operated carby type WI,as the huge increase in manifold vacuum caused by closed throttle after full boost/revs.hoping to cure problem using the cause of problem.
the speed car has run almost continually since 1950s but no one has realised its full potential. I'm hoping
cheers tony

[Howerton Engineering]

This sounds like a fun one. Let me discuss a few options with Richard and one of us will get some recommendations to you shortly.

[Richard L]

G'day, want to set up WI between throttle and supercharger on vintage 500cc JAP hill climb cooper midjet speed car running on methanol.
the blower is a cabin pressure pump from a DC3. the problem with this set up over the last 50 years has been detonation,when changing gear. going from wide open throttle (WOT) max revs /pull and full boost to closed throttle for gear change,at this point high vacuum between closed throttle and blower, reopen throttle,still high vacuum and as surge of intake gas charge through open throttle until vacuum drops and the inertia of fast flowing intake charge momentarily gives a boost spike into and through blower, over boosting engine causing detonation.
too off set this previous safe tune obtained by retarding ignition and long intake runner.
wanting to WI so more ignition advance can be used .getting most performance safely.
this may be old school stuff with no electronics.
a waste gate or blow off valve would help.
but answer lays in WI, to get ignition advanced.without detonation.
can someone help?
regarding simple vacuum operated carby type WI,as the huge increase in manifold vacuum caused by closed throttle after full boost/revs.hoping to cure problem using the cause of problem.
the speed car has run almost continually since 1950s but no one has realised its full potential. I'm hoping
cheers tony

The only way you can to help you situation is by activating the water inejction with throttle linkage. It appeared that water must be already flowing before the ignition is advanced. How does the engine advance the ignition?

Richard

[fitsracing]

thanks for reply, the engine runs a magneto with centrifugal advance spring loaded.you are suggesting a constant flow vacuum operated WI? This was my first thought, trying too make it work on demand may be complex.which is why I contacted you
Using methanol for fuel what ratio of water to methanol should I start with? or other additive.
The water injection will have to be between the carby and the blower. the only place for vacuum operated constant flow WI.
cheers tony

[Richard L]

I am suggesting triggering the WI with throttle movement, it is by-far the quickest way to turn the water spray on. Knock is normally associated with high load - or lack of vacuum. using a vacuum sensor to trigger a spray is slow compared to a microswitch at the throttle plate. YPu can set the switch at 1/4 throttle etc. It is not difficult to fabrocate a bracket for a long lever micro switch by the throttle linkage.

http://www.aquamist.co.uk/forum/micro-switch.jpg
http://www.hobbyengineering.com/H1882.html


There is a danger of spraying before you crank the engine because the vacuum switch might mistaken the "absence" of manifold vacuum as "full" load.

A good starting point is 50:50 - no other additives.