Don't put a single point system on that engine, put a sequential system on it and be careful how you do it.
Whether or not an engine is suitable for a single point mixer system isn't just about the material it's inlet manifold is made from, it's also about it's cam timing, ignition system, engine management system, etc. You might get away with a single point system (or maybe not), if so only by employing some additional trickery (closed loop lambda emulation). I haven't tried it and would only try it as an experiment which I'd expect to fail. But a properly worked out (by such as myself, as opposed to someone who fits the same parts on every vehicle they convert) sequential system can give great results on this engine. In my opinion a mixer system wouldn't be worth the attempt.
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I have to say I agree with Simon on this I do like single point systems for their simplicity but on a more modern engine a multipoint is lots better and generally more economical on my older vehicles I use single point blos mixers and they are great but all my injection cars I use multipoint
So the problem is the V-tec system (not working with single point)?
Apparently under light loads it opens one inlet valve fully and the other slightly -b to create "swirl" - under higher demands (or high rpm - I'm not sure...) both inlets are fully open.
My 16v EFI daihatsu has done over 12 years on a single point with lambda control and it has been flawless - but the engine isn't vtec - just normal valves**
**It has the Landi Renzo LCS2 - the one with two steppers -one in the dry gas hose and one on the vap controling the idle. IMO the best single point system but very old now
The VTec system won't be directly affected, though it could directly create some problems such as misfires/backfires if running on a mixer system (Vtec creates a problem for running with a mixer rather than the mixer creates a problem for Vtec). Or if the engine runs in rpm limited limp mode because of a different (fuel trims etc) related error code then Vtec will be almost irrelevant but only because it will never run in full valve lift/duration (Vtec) mode because rpms won't be allowed to get high enough for the engine to run in that mode. A chicken/egg situation.
We can fit a mixer system on engines that (1) won't backfire due to the mixer system and (2) where the petrol engine management system won't generate error codes that lead to it limiting functionality of the engine (rpm/electronic throttle limiting, etc). Even if the Vtec didn't cause driveability problems if a mixer was fitted I'd still expect a need to address other issues such as fuel trim drift causing error codes that would lead to the petrol ECU limiting engine functionality... at least unless something like an OBD interfacing, fuel trim steering lambda emulation device such as an AEB426 were fitted.
Even if you avoid drilling holes in the manifold to fit LPG injectors for a sequential system (by fitting a mixer instead) you'd still need to drill holes in it to fit a 4 branched valve lube system spider on this engine.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62, http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240