Knock control questions

[Lizard]

Hello I am looking at the VEMS system but have a very secific question.

I have heard that the VEMS uses a staged knock control, (only listening within a few deg of actual ign), so as to not get alot of excess noise.

Is this true?

If it is true, when running a full COP setup (not wasted, v8), can VEMS do individual cylinder trimming for knocks etc.?

Or is something such as the J&S Vampire knock control unit required, http://www.jandssafeguard.com/VampirePage/J%26S_Vampire.html

TIA

[rob@vems.co.uk]

Yep we have a window where we listen for knock, and compare it to the rest of the signal.

No we dont trim each cylinder, and if you look at the dynamics of knock theres no reason that you'd want to.

Its better to limit the likelyhood of detonation in the first place, and we do this by retarding ignition once IAT rises above 40degC, and controlling fuel correctly to lessen the likelyhood of detonation occuring.

[rob@vems.co.uk]

Okay, I've got some back tracking to do here as I've had a few points corrected by a mate of mine who knows what he's talking about.

The statement "No we dont trim each cylinder, and if you look at the dynamics of knock theres no reason that you'd want to."

Is not correct, modern OEM systems can trim each and every cylinder individually, and do so to overcome variablity in detonation characteristics across the various cylinders (cylinders don't fill evenly, heat distribution etc can cause one cylinder to detonate before another).

The main reason we're not likely to implement this is due to the hugely complex task of correctly setting this feature up.

[Lizard]

lol,

thank you for the concise answer,

This is a feature I am really wanting, so I may just end up getting the J&S vampire unit in addition.

I have seen full well the benifits that individual cylinder trimming has.

the earliest production car I am aware of that had it was the 87 928S4 Porsche.

[rob@vems.co.uk]

You are absolutely free to experiment how ever you wish - as long as you paste the results here of course

What engine are you putting this onto?

Personally I'd start with just the VEMS and add complication once the initial installation is stable.

Rob

[Lizard]

Rob,

I have a 1986.5 Porsche 928 32V 5.0L V8 in a 1981 Euro 928 Chassis.
I currently have it running on MSII V3.0 W/ 2.881 code.
I cant seem to get any REAL answers on the MS system and parts of it are just downright haywire.
I have a spare engine that I am rebuilding and will have twin turbos, ITBs, dry sump etc.

I will really be looking for certain features coming with the VEMS (mainly dual EGTs, dual wideband, etc) but I really feel the need for a proper knock control system to be installed on the car for max power.
I will be running 1.0 bar boost on factory internals of 10:1 CR, so detonation control is critical. I will be tuning the engine on 94 octane and will need to have control to back off the boost and ign should I go somewhere I cannot get good grade gas.

So already have started with the basics, now I am just going to be getting serious.

thanks again.

[rob@vems.co.uk]

Porsche 928s are firmly in the domain of Peep Päädam:
http://www.vems.ee/projektid.html
vems@vems.ee

While we have dual EGTs we do not have dual wideband control.

[Lizard]

Yes, he goes by the name Racing on alot of forum boards, I am familiar with him, good fellow.

Yes I knew that, I just had a brain fart while posting before