I have a W.I. page on my site, based on the LET.
I haven't added any RR graphs yet, but I'll get to that eventually.
Different engines and different states of tune may call for totally different W.I. activation levels. (varying from 4psi all the way up to 20psi)
It's very easy to bog the engine down with too much water. Those who sell W.I. kits tend to over-emphasise the amount of water you need, because they want to make you think how badly you need their product. Try to read between the lines, if you want a glimpse of (their) truth.
cheers johnA i used your site a few times when i was doing the conversion and found it very helpful so it looks like i might need it again but can you say if its better set on a rr or could i do it through trial and error
Either way, you can do it by feel.
When the WI kicks in it should feel like it's running smoother and quieter.
If it doesn't, then it's probably kicking in too early, or it's not working (check the level of the washer bottle, after 10-15 seconds of WI the level should be a bit lower)
It's nice to stick a LED in the dash, hooked across the spades of the pressure switch. That way you can see when the switch gives the go-ahead, and can fine-tune the boost activation point.
There are gotchas with WI, don't underestimate it.
Also be careful with methanol, avoid it if you can.