Here's a clever thing (???)

[JohnD]

Anyone come across this?  "ShackTune Vac Dump Kit Lucas Pi Fuel Injection" 

The description alleges that "for engines running Lucas Pi Mechanical Fuel Injection, cams with big overlaps and scavenging branch manifolds.  When you have a large overlap on your cam of 75 degrees + and you hit circa 4000rpm the Vacuum metering unit is fed a false high vacuum. This is caused by the branch manifold doing its job of scavenging and presenting a very high vacuum to the cylinder, this in turn causes the vac to be transferred to the inlet tract as the inlet valve is already open.  As the metering unit is getting its instructions from the inlet via vacuum, it is then fed a false instruction of high vacuum... This high vac instruction translates to "less fuel", when you actually want more fuel."

AT a settable  revs, the device disconnects the metering unit from inlet and opens it to atmosphere.   No vacuum >> maximum fuelling.

This does match what I've been told, that PI goes lean at full revs, so that it is always set rich at idle, hence the poor fuel consumption, even in road use.   SofS really can't do m ore than  98mph, even on a long straight, and it really should be able to do more than that, so I'm tempted.   Anyone used it, or dealt with ShackTune?

John

 

Edited November 23 by JohnD

[thebrookster]

Shacktune = James Shackford, who is pretty well known in the saloon world. He was also TR Enterprises gearbox specialist for many years.

Almost the entirety of the suspension setup I have for my 2000 has come from James, and I have driven his MK1 and can happily confirm it works!

He is also one of the sources of the bearing spacer kits for the small chassis front bearings.

I'd be strongly tempted to give it a shot, if you wish John I have a number and email for him I can send (via PM)?

Phil

[JohnD]

Thank you, Phil!   He's not a trader I've used before, so good =to have your comments.

John 

[egret]

Are you able to check this with a wideband, or a couple of pulls on a rolling road should be able to determine this as they will have a lambda?  Seems odd you're unable to hit 100mph, even with what I assume is a short ratio diff.

 

[JohnD]

Yes, it puzzled me last season, when my diff is 3.89:1.     I'm going to install (re-install) a lambda sensor.     Trying that will show.

John

[Nick Jones]

Hmmm….

James is one of the good guys. Knows his stuff, but I’m really not following his arguments here.

Yes, if you have a decent extractor manifold doing it’s job, it’ll be scavenging well and pulling a good inlet flow….. but PI has 6x46mm TBs….. what is the obstruction causing excess vacuum?!  Possibly it’s a workaround for an unsuitable mechanical “map” in the metering unit, though they are quite adjustable.

Your intention to fit (refit?) the O2 sensor (wideband I assume?) is a good one as this is the best way to discover what it actually going on.  It might be going rich not lean. Lean tends to bring hitching, misfires and melt things. Rich just goes flat, unless drowning rich.

PI can actually give decent fuel economy when properly setup to the actual engine it’s on rather than calibrated to a notional factory map on  a Hartridge rig.