why to use a boost controller?

[QuickTD]

What about peak pressure during combustion? Wouldn't that be the limiting factor because it's that maximum pressure at tdc plus the increase in heat from combustion? For instance, on a NA, when the piston is at TDC at ~325psi, won't the pressure when the fuel is injected and combusts be much higher than that?

Ideally, the pressure should not greatly exceed the end of compression pressure for remainder of the combustion cycle, that's what engineers shoot for. The holy grail is to hold the combustion pressure constant near to end of compression pressure for the entire power stroke. The reality is, of course, somewhat different. There is a sharp rise in pressure when the cylinder fires, this is aggravated by excessively advanced timing.

In other words, isn't there some maximum safe level of boost w/o increasing fueling that can be achieved, because during combustion the peak pressure is much higher?

Running boost just for the sake of it isn't really productive. The only reason to increase boost would be to burn more fuel. Stock boost is fine for stock fueling, increasing the boost without increasing the fueling will do little in the way of performance. It may be possible to run 50psi of boost (with a small enough turbine A/R) if the fueling isn't increased but it won't increase power one bit.

 When you increase boost and fuel, naturally the combustion chamber pressures will rise, there is no avoiding that. Keeping it within reason (and preventing it from destroying engines) is what we're all trying to do.

[lyeinyoureye]

In terms of power I've heard there are minute differences, which are proportional to the supposed increase in efficiency, which I'm guessing is what someone running additional boost and just that would be concerned with. For instance, there's someone on the vwdieselparts forum claiming significant improvements to mpg can be had by retarding timing with a turbocharged vw diesel while running NA fueling. The downside is a big spike in NOx emissions, so CI combustion, especially in passenger cars, has to walk a fine line between power, economy, and emissions.

Otoh, large pickup truck manufacturers can put out diesels pickups that are 4 times bigger than diesel passenger cars, but can still get 15-20mpg, probably because they have NOx emissions regulations that allow roughly 4-5 times that of passenger cars. Supposedly, these can do even better with aftermarket chips... Which don't have the emissions limitations of the manufacturer, and can further lean out the engine.

Of course this is purely speculative since I haven't had time to tinker, but I'm hoping it's possible.

[macsdub]

i had a garrett from an 86 td
and it worked nicely with my shop air regulator for a boost controller
now the kkk im runnin from an 84 td,its wastegate doesnt really function the same
all the boost controller seems to control is how fast itll get to peak boost
to adjust peak boost ya gotta adjust the wastegate screw
i miss my garrett it was a way better turbo for these cars than the kkk junk :cry: and it gave more power too :cry:

[HarryMann]

So was that T2 or a T3 Garrett - I notice the wastegate design and aneroid design is quite different on my T2 than the equivalent KKK

[scopefrfd]

I use a boost controller..on my K14.  A glorified ball bearing and spring in a t fitting.   I works well though.  factory  wastegate is around 12 psi.  I mistakingly forgot to tighten the boost fittings when I added the boost controller and the k14 easily pinned my VDO 25 psi boost gauge.  With the controller it maxes out @ 22 psi.  So it's definitely a good way to run higher boost in order to burn the extra fuel, but still have some safety factor built in

[macsdub]

i dont know,,it was a stock garrett from an 86 td
not an eco either..........
there must be pics of the blown up one around here........

[myke_w]

I mistakingly forgot to tighten the boost fittings when I added the boost controller and the k14 easily pinned my VDO 25 psi boost gauge.  With the controller it maxes out @ 22 psi.  

I run the k14 too, are you saying you regularly hit 22 psi with no issues? I have always been afraid to go past 15psi for fear of wreaking havoc....

[macsdub]

lol turn in the screw all the way for some real fun,like 40 psi of fun
driven daily like this.......

[HarryMann]

Will you build me an engine that will stand 40 psi and send it over to good old Blightie please mate...

Promise to send the packing crate back full of real English beer - by return - a fair deal?  :roll:

[myke_w]

I created a topic that addresses max boost so that we arent thread jacking...

I don't want to be that guy..
here's the link..
http://vwdiesel.net/phpBB/viewtopic.php?p=41618#41618