Yet another VNT control idea...

[blackdogvan]

So this is just vaporware but i wanted to kick around another idea for mechanical VNT control.

Its pretty much accepted that VNT control via a wastegate actuator alone works (Chrysler gassers from the 80's), but really isn't optimal. For example you'd end up running on the highway at higher boost pressures all the time. So whats then required is a link to the throttle lever, however its setup, to allow the boost pressure to match the throttle position. WOT, full boost. Less than 1/2 throttle, less boost etc. Libbybapa, Tintin & others have pretty much perfected this but it requires an argueably complex mechanism to work. Please don't read that as in any way a negative comment about those systems.

So what i'm thinking about is a system that only has a wastgate actuator attached to the VNT lever but has a boost control valve installed on the actuator sense line with the boost controller actuated via the throttle position. Finding the right valve would require some tinkering, in my head its a small 1/4 turn ball valve which would be pretty easy to attach to the throttle lever. Attaching it so pressure bleed started after 1/2 throttle would be good to limit too low rpm boost. If it was setup with a 5psi gasser actuator you'd still be left with some pressure while on the highway but thats not entirely a bad thing, is it? Floor it, the sense line bleeds off & boost rises, foot off & the wastgate actuator on the vanes goes back to doing its thing.

The major pro as I see it would be a easier installation as all you'd be connectiing between the turbo & the IP would be some tubing & everything would be prettymuch off the shelf.

One con would be the lack of a positive vane actuation stroke meaning coking vanes would still be an issue. Libbybapa's latest design has that vane actuation, engine off & a few foot to the floor pedal pushes exercises the vanes & clears coke.

Another negative as I see it would be limiting full boost pressure. If it was setup to give high boost at lower rpm's, the whole point of a VNT as I see it, boost pressure would continue to rise with RPM. You'd control full boost with your foot to a certain extent I suppose. Another higher pressure actuator could push the boost valve closed but then its getting complicated...


Would that work? Am I on glue? Anyway, just looking for some discussion on the subject & maybe some ideas on how it could work.

Thanks!

[blackdogvan]

No comments from the peanut gallery??

[blackdogvan]

I'd really have to think about what you're presenting.  It sounds like it might have possibilities, but I really like the fact that with the latest mechanical vane control I made my foot is applying full pressure to closing the vanes.   

I agree 100% about exercising the vanes. I just want to kick around ideas.

[blackdogvan]

So putting aside coking issues & back to the OP and the idea of a boost controller based VNT control. Check out the cable operated boost controller in this link: (near the bottom)

http://www.addictiveperformance.com/Hallman-Differences.php

If the cable setup was attached to the IP lever you'd get your throttle position input & using a flipped vac can or a WG on the turbo vanes. Adjusting the travel of the cable would set your max boost as the WG would do its thing on the turbo.

All off the shelf bits too.

[blackdogvan]

Hmmm, good point on the idle vane position... needs more thought. Another problem is the adjustment on those controllers is a turn not linear. Those would be good for a WG vanagon setup tho if you could lengthen the cable.