I wasnt getting offended or anything, its just I was getting 'advice' from people with clearly no experience of it, and that gets a little frustrating when I've been owning and tuning forced induction engines day in day out for over a decade, lol.
Anyhow, I got the car running properly with the bypass throttle removed from the loop, at last.
As mentioned previously blanking it off seemed to cause a boost spike that popped the bung out every time so was useless, but using a boost pipe from (I think) one of my old Volvo turbos I replaced the bypass throttle with the twin dump valves that are fitted as standard to Skyline GT-Rs, which just happen to fit perfectly.
If you unplug the secondary throttle, although it doesnt bring up any dash lights, it DOES disengage the supercharger clutch, so you cant do that. For the purpose of the test I left it plugged in but not connected to any of the cars pipework.
I connected up the vac pipes etc to operate the dump valves and started the car, and all was well, the dump valves are held open by the vac when off throttle, just like the electronic bypass one does anyhow, and the car ran fine.
One thing you do notice is you have the supercharger blowing right from under 1000rpm as unlike the electronic bypass throttle that stays open until 1500rpm, the dump valves close the minute you use any throttle. To be honest though, this does little, just a tiny bit more punch around idle speed.
On throttle unfortunately (or fortunately, depends how you look at it) the boost curve is exactly the same, so there is no leakage or partial opening of the throttle bypass.
When you let off the throttle the Skyline dump valves are MUCH quieter though, removing the sometimes annoying chuff the electronic throttle does when you let off, probably as they are reacting far faster so the boost doesnt spike as much. You see that on the boost gauge, with almost no spike as you shut the throttle with the dump valves fitted, but over 15psi spike on the standard electronic throttle.
I'm a little confused to know when the supercharger is disengaged too? I was 'told' (woo, more Merc forum mis-infortmation, lol) it was disengaged under 1500rpm, but thats not strictly true, as the stock electronic throttle stays open until 1500rpm, wasting all the superchargers boost, but you could clearly hear (and see on occasion on the boost gauge) the supercharter is running even at 1000rpm. I couldnt be sure if it disengaged at all, but sounded like all but possibly total idle speed (about 750rpm it seems) it is running.
It certainly CAN be disengaged as pulling the bypass throttle plug out does it, but when, who knows? It even stays engaged on the over-run, which is pointless but I guess if fuel-cut is activated then its not affecting economy.
I drove it about 6 miles with the supercharger disengaged, and to be fair, its not that slow feeling, quicker than a C180, enough to happily cruise at 80 on the motorway without needing much throttle.
IF I can work out which of the wires to the bypass (maybe any of them) affects if the supercharger is engaged, I reckon it could seriously improve fuel economy if I can engage and disengage the supercharger on a switch...
And thats it really. Only way left to try that can increase boost without a different sized pulley is pre-compressor water injection, which I guess I'll have to knock up to give it a go when I can be bothered...
Leads to lots of confusion.
