What effect does fitting ITBs have on fuel map?
RazMan - 3/12/10 at 03:21 PM
As I'm 'working from home' 
this week due to the weather I've been playing in the garage.
Having fitted my ITBs sans trumpets (still waiting for post office to deliver) and I've got a nice stable idle now 
Obviously I can't
start mapping yet but I was wondering what sort of effect the ITBs will have on the fuel map (MBE 970).
I noticed that while revving gently the AFR seems to be quite lean (18-20) - is this the effect of getting lots more air into the engine?
Which brings me onto a second question - Can I increase the MBE's fuel gain to give me more headroom in the map? It is presently set at 110 and
with the standard (single) throttle body the fuel map it is almost maxed out at WOT, so it looks like I need to add more fuel. AFAIK the fuel gain
simply multiplies the fuel figures right across the map, so if I increase it to say 120 will that increase the injector duty cycle and give me an
extra 10% of fuel to the whole map?
stevebubs - 3/12/10 at 03:35 PM
quote:
Originally posted by RazMan
I noticed that while revving gently the AFR seems to be quite lean (18-20) - is this the effect of getting lots more air into the engine?
Its sure is...
quote:
Which brings me onto a second question - Can I increase the MBE's fuel gain to give me more headroom in the map? It is presently set at 110 and
with the standard (single) throttle body the fuel map it is almost maxed out at WOT, so it looks like I need to add more fuel. AFAIK the fuel gain
simply multiplies the fuel figures right across the map, so if I increase it to say 120 will that increase the injector duty cycle and give me an
extra 10% of fuel to the whole map?
Can't confirm on the MBE side, but if you're close to maxing out the values on a map, you're probably close to running the injectors at
capacity? Before tinkering with the map, I would first perhaps look at increasing the fuel pressure by 10-15%?
[Edited on 3/12/10 by stevebubs]
RazMan - 3/12/10 at 03:57 PM
That was my first thought but I'm already running them at 3 bar and I don't think my Landy pump will go much higher. The current injector
duty cycle appears to be quite low so I thought that the software was a better option - and I don't really want to get larger injectors unless I
have to. The fuel gain will apparently go up to 255 which makes me think a small tweak here might give me enough to play with until I get the car
properly mapped on a Dyno.
[Edited on 3-12-10 by RazMan]
MikeRJ - 3/12/10 at 04:26 PM
quote:
Originally posted by RazMan
As I'm 'working from home' this week due to the weather I've been playing in the garage.
Having fitted my ITBs sans trumpets (still waiting for post office to deliver) and I've got a nice stable idle now Obviously I can't
start mapping yet but I was wondering what sort of effect the ITBs will have on the fuel map (MBE 970).
I noticed that while revving gently the AFR seems to be quite lean (18-20) - is this the effect of getting lots more air into the engine?
Presumably you are running an "Alpha-N" fuelling strategy, i.e. fuel is determined by throttle angle and engine RPM? If you have moved from
a plenum with a single throttle to multiple throttle bodies, then there will be a very large difference in airflow in the first few degrees of of
throttle opening. This is precisely what makes ITB's more difficult to map - you need plenty of resolution on the throttle position sensor and
enough fuel "bins" in the map in this position to get good, progressive fuelling.
If individual bins within your map are approaching the limit of what they can be set to then you need to increase the base fuelling level, this would
be "REQ_FUEL" on a Megasquirt but I'm not familiar with the MBE. "Fuel gain" certainly sounds like a promising parameter to
adjust.
RazMan - 3/12/10 at 11:32 PM
It is indeed Alpha-N - sorry I should have said that.
As an experiment I tried increasing the fuel gain to 120 and straight away the AFR came down and the engine revved more freely and without all the
pops and bangs it had previously. It looks like I'm on the right track but I can't really take it any further until I fit the trumpets and
get it on the road for some readings under load. I'll get it fairly close and then take it to AT Speed for a proper setup - it will be
interesting to see how much extra power my homebrew ITBs give me
The MBE is certainly a complex ecu to tweak as it has soooo many options compared to most others. The TPS has 15 sites and the mapping resolution is
250rpm so I think it will play nicely. The MBE can control just about any add-on like turbo / supercharger, Nitrous, intercooler spray, water pump,
rad fan etc etc. Great fun for nerdy types like me - I'm learning loads recently and having great fun 
[Edited on 3-12-10 by RazMan]
atspeed racing - 7/12/10 at 11:31 AM
on the main mbe screen you will have injector duty %
make sure this is not maxxing out. you do not ideally want to see any more than 80% total duty.
or you will require either more fuel pressure, or larger injectors
dont forget we are not too far from you, and i am an approved MBE mapping agent with recent championship success
"SEMSEC 1st in class. Sports Racing and Kitcar Class B6 (Up to 1850cc Car engine and 1500cc Bike engine)
14 races for the championship 11 wins, 3 second places.
SEMSEC Overall Club Champion 2010
Thanks to Alan, Colin and Ian at Atspeed for there part in making 2010 such a successful season. After setting up the MBE engine management on my
Hayabusa engine on their rolling road, the car didn’t miss a beat all season.
Colin in particular showed real enthusiasm at the challenge to have a play with a new system and bike engine. A prospect some tuners would shy away
from.
Over the winter I am upgrading the car with a TD05 16G turbo, Carrillo rods, low compression JE pistons, uprated injectors and custom built
intercooler.
As the car stands it is producing 165bhp at the wheels with 74 l/b ft of torque, I am aiming at somewhere around 330bhp and 170 lb/ft after the
modifications.
I will again be entrusting Atspeed to set the car up for next season.
Thanks again lads!
Steve Garner."
- colin.