De catt and fuelling

[wycoller]

I installed De cat Y piece on SC500 Griff before installing my fuel map was good on Rolling Road fuelling was good.
I have just again RR and fuelling is weakening off above 4k and gets dangerously lean co 2.8%.at5120rpm Is this due to installing De Catt?

[spend]

Sounds like your cat maybe wasn't flowing very well, bit like defeating the SC IYSWIM.

[chris52]

You may have low fuel pressure, mine was running lean at higher rpm, an adjustable fuel pressure regulator sorted it out for me.

Chris

[HarryW]

If the map hasn't changed and the only difference is the Y piece then its fair to assume it flowing/breathing better and when back on the right AFR it will make shed loads .
Although it always surprises me that the AFM if still lucas type should detect the increase airmass and compensate the fuelling accordingly, thats unless it hasn't had the map extended beyond the base values seen on the original mapping session toa llow for future growth, tvr original maps were a bit like this in NA form.
The other possible reason, if you are looking for other reasons, could be the fuel pump is not holding pressure at high flow, I assume as a SC car you probably already have a pump more than capable for the increased power levels, worth a check if you are struggling.

[blitzracing]

My now car runs the catalyst fuel map without problems on a non cat system (less juicy at low throttle openings this way) but I did have problems with it running lean at full power, I changed the fuel pump, filter, and increased the diameter of the fuel line (Its not a TVR however), and it still ran lean, and eventully traced to the throttle pot not reaching the required value at full throttle, so 5 minuites with a needle file to elogate the adjustment holes it was sorted. This makes a big difference. Id aim for 4.6 v or above at WOT. The 5ltr fuel map can run a bit lean, and you also loose resolution from the AFM as it peaks at 5 volts before full power is reached, so you can only map against TP sensor and RPM at the upper limits, but as suggested a few extra PSI on the fuel rail may well sort it (assuming there is not a fuel delivery problem to start with).

[wycoller]

Thanks all i was looking at fuel pressure as the main starting point.
I will work on that
Could someone enlighten me on the fuel timing also how is the fuel timed?
Also fuel consumption is poor but that may be down to how i drive
I wasn,t reaching expected 400bhp (351) before with Catt in and fuelling was okay at that point people in the know where pointing to my cam being the problem i.e too much overlap for SC.
Could the leaning of also be due to a combination of wrong cam, and De Catt less exh back pressure at overlap like i said i would have to know more about how the fueling takes place before looking at this end.
But i,ll start on the basics and check fuel pressure.
MA and Colin say that standard fuel pump etc should be okay so its down to checking the fuel filter, fuel pressure piping etc and Fuel Regulator and Plenum Preesure feed back to Fuel reg and Vac advance.

[blitzracing]

The fueling is not timed as such, its not that advanced, all 4 injectors are simply batch fired on each side of the V8 at a time. The fuel vapour simply hangs around until its drawn into the engine.

[wycoller]

blitzracing said:

The fueling is not timed as such, its not that advanced, all 4 injectors are simply batch fired on each side of the V8 at a time. The fuel vapour simply hangs around until its drawn into the engine.

Thanks Mark so there is a possibility that the cam and cam timing can affect the fueling and i could be pushing fuel out on valve overlap.

[blitzracing]

wycoller said:

blitzracing said:

The fueling is not timed as such, its not that advanced, all 4 injectors are simply batch fired on each side of the V8 at a time. The fuel vapour simply hangs around until its drawn into the engine.

Thanks Mark so there is a possibility that the cam and cam timing can affect the fueling and i could be pushing fuel out on valve overlap.

It does happen in some cases, its called reversion or fuel stand off. There is a difference between the two, but I cant remember exactly what, but its also due to shock waves in the inlet bouncing the fuel back up the inlet tract. Ive seen it on carb'ed engines, but I dont know if its a problem on the RV8.

[spend]

His is a boosted engine, SC stands for Super Charger

Timing of the injection just really affects the quality of the mix with air, and its a very pedantic phenomenum you shouldn;t really worry about it too much. Some of the very best NA engines (350bhp) only use a single injection event for all 8 cylinders, never mind banked or batched.