Management: how to make boost come faster ?
Turbo Mini Forums

I'd like to make a thread about methods that make boost come up faster. As we are turboing small and low VE engines we use high (well not low) boost pressures with big turbos (compared to engine displacement), so the boost build up is slow.
Note that usual ALS systems work during gear shift and not during acceleration, but we could discuss that as well.

I'd be great to tell us if you tried, someone tried or you just know about a technique.

I think a usage of small turbines with huge external wastegates is a different subject.

Usually the methods are based on raising of the exhaust gas temperature to make turbine spin faster.
During acceleration (WOT):
- enrich the mixture to create post-combustion
- lean the mixture to increase combustion temperature and get hotter gases
- retard ignition
- make missfires to create post-combustion that does not overheat exhaust valves
- certainly something more ...
All these methods:
- increase chances to overheat exhaust valves
- lower power output because they lower
They can all be used every N cycles to preserve the engine and power output

During gear shift (usual ALS) the same methods can be used more aggressively because the required power output (mixture quantity) is much lower, so engine suffers less.

Edited by alpa on 7th Jul, 2010.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

I've got a ball bearing RHF4 IHI, internal WG, it spins all the time, I can hear it especially when engine is cold (I don't know whether it's due to a richer mixture or a cold compressor). So in theory it's the best case.
During acceleration is 2nd the pressure is at 1bar at 4500 rpm, most of the pressure at 4000 rpm. I'd like to shift all that down by 500 rpm to get more pressure at 3500.

I tried:
During WOT:
- retard ignition by 20-30 degrees every N cycles: no effect to build-up, power goes down

During gear shift:
- if RPM was above 4000rpm then maintain idle at 3000rpm, AFR 14:1 during 1 second with 5 degrees advance: this works fine to have a fast gear shift however does not help a lot to build the boost faster. If this idle is held long enough to read the pressure then I'm getting a very light boost pressure (I have a boost gauge ahead the throttle).

I'm going to try at WOT:
- enrich/lean mixture every N cycles with regular advance
- misfire every N cycles

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

There is a lot of overlap between terms like Launch Control, Flatshift, Anti-lag etc.

As far as I'm aware the more sophisticated systems use modifications to the basic design like plumbing compressed air into the exhaust manifold (rich mixture and retarded timing then causes burn in the manifold after the engine).

The simpler electronic only systems just alter timing and fuel.

Have a look at the Megasquirt Extra code - it provides a number of ways of doing it for Launch and Flatshift with just a single input of clutch position. I've wired mine up for it but haven't a clue how it will work in practice but there is probably a lot of info on the MS-Extra forums.

EDIT - typo

Edited by Rod S on 7th Jul, 2010.

Schrödinger's cat - so which one am I ???

Launch and Flatshift are difficult problems. The main problem is getting boost faster.

The probably best ALS is the one using EGR to recycle during the shift. But this does not work at WOT.

Edited by alpa on 7th Jul, 2010.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

If yur cr is low you can weaken a bit the mixture on the boost ramp you"ll find more 250 rpm than 500, but then you should have an exhaust gas temp yo know what you're doing, anyway, anything too rich on the boost ramp is slower boost curve, a bit lean it'll help by building heat , too much heat and pistons/turbine/valves kiss

If your cr is high you have to keep the mixture a bit stronger, but it'll also help the boost ramp, then will limit total boost /and a trade on ignition timing.

fab, did you try that on a A-series engine ?
Engines don't react the same to richness changes, it depends on many internal factors.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

Mine's all have been a bit of highish cr and a bit big turbine/compressor with the bov as a priority breather, as this, the compressor spin to ambiant first, then as soon as the manifold see a bit of boost closing the valve.

Then leanning the ramp boost with an blowed SU ,
I'm somewhat happy when I'm between 11 afr up to 13 , my last needle gave me 10.5 at partial throttle to have a strong mixture on ramp and full boost.
It was a pig to drive with leaning device, sort of on /off, so binned it.
Robert can attest that a KKK K16 was not any laggy on this set up, and that the boost building was good.

Then if you can, any turbine will like a bit of the hottest gas you'll give her, a bit Weak (ie above 12.5/1 not lean looking at stoïck, that's why I prefer talking weaker than leaner) and you have it, too much , then in the ass.

lean and more timing. Basically anything that will increase the torque output will help build boost.

Wastegate and boost control will also play a part too. If you can keep the w/g jammed totally shut for as long as possible, it will help too.
Anything that allows the w/g to creep open at a lower boost pressure than you wish to use, will slow spool up.

Of course if its really bad, you could squirt a little nos low down to help off boost performance.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will