Best Ecu for Turbo Conversion

[crazymonk]

Hi, I'm doing anew engine for my e30 convertible using a 24v 2.5L engine. It's coming on really well, but whats the best ecu to use. I've been thinking of using the emerald ecu, but I'm not sure if thats the best option. I want a fully sequential system, and one that controls fuel and spark, and preferably one that can control boost levels and water injection. Any ideas or recommendations would be great.
Just out of curiosity, I know theres a lot going around at the moment about rear turbo conversions and stuff for low boost applications, (can't see the point myself), but has anyone ever got a turbo conversion working using a standard ecu?

[Colonel Sanders]

autronic sm4 if you have the cash is a very nice option, but megasquirt and vems are very good, and cheap!!

[Ant]

and regardless of brandname and pricetag, the mapping is what netts the gains, not the label on the box.

[Turbo-Brown]

and regardless of brandname and pricetag, the mapping is what netts the gains, not the label on the box.

Absolutely right!

Not sure there's any real gain to be had from running sequential though.

Also, unless you can get your system to run sequential at low revs and batch at high, you'll need MASSIVE injectors to give enough top end fuel.

If you can run seq at low revs and batch at high, you get a gain in that you have better control over the low end fueling.

[ShakeyC]

Why do you say that Turbo-Brown?

[Turbo-Brown]

Which bit dude?

[midnight]

MS any day of the week

[ShakeyC]

Which bit dude?

Not really understanding your comment, could you clarify please?

"Also, unless you can get your system to run sequential at low revs and batch at high, you'll need MASSIVE injectors to give enough top end fuel"

Why would you need 'massive' injectors for either seq or batch or both blended?

"If you can run seq at low revs and batch at high, you get a gain in that you have better control over the low end fueling"

What do you mean by "better control" ?

[Turbo-Brown]

Aah, fair enough

If you run batch fired injection, you essentially put the fuel into the engine in two halves; one half when the inlet valve is shut and the other half when it opens. The first half just hangs around in the port until it gets sucked into the engine.

At very low loads though, where you only need a tiny amount of fuel going into the engine, halving the tiny amount means that the duty cycle on the injectors becomes extremely low and thereby makes your fueling less accurate.

If you can run sequential at low loads, the duty cycle isn't halved so the resolution on your injectors becomes better as they have more work to do.

However, the same is true at high revs/loads so either you need to run very long injection pulses which might take you over 100% (i.e. the injector is just open all the time) or you just have to fit bigger injectors so that you don't go over the idealish 80% duty cycle on the injectors.

Of course then the problem of low load fueling comes back as you've now got sequentially fired injectors which are twice the size of the ones you would need to run batch fired so your duty cycles dwindles away again and the fueling becomes inaccurate.

So tying all that together, if you can use small injectors and run sequential at low loads, you benefit from accurate fueling, and if you can run batch at high revs/loads you benefit from effectively doubling your injector capacity.

When I say better control, I mean that the injector follows more accurately the amount of fuel you're asking it to flow. The variation in what an injector will deliver when told to open for say 1ms is down to the time it takes to open and close the valve. This opening and closing is variable and not predictable from one cycle to the next so if you can reduce the number of times it needs to open and close per cycle (i.e. run sequentially) you can more accurately predict the amount of fuel the injector will deliver.

[ShakeyC]

Sorry I dont completely agree, maybe it will help if I explain my understanding as follows;

With batch mode its firing injectors once every crank revolution therefore firing twice for every cam revolution as it is injecting the fuel in 2 pulses of 50%. The fuel required is injected twice per single cam revolution (two crank revolution totalling 720 degrees for a 4 stroke engine) to give the cylinder 100% of the fuel required for a given AFR. With sequential the injector only injects once per cam revolution to deliver 100% of the fuel required in that cylinder for the same AFR, the actual total pulse width and resolutions with either mode is the same regardless of engine RPMS.

For example if we need in theory 2ms of fuel delivered in batch mode it will be delivered in 2 pulses of 1ms as per 1 cam revolution. With sequential the injector will pulse once per cam revolution for 2ms to give the same amount of fuel. Therefore injectors in batch mode will be seeing double the RPM to sequential mode due to them being paired and pulsing twice per cam revolution but the actual total pulse width is the same just delivered in 2 halves. So with sequential mode effectively the injector is unlikely to reach max injector duty same as its unlikely to max injector duty in batch mode for same amount of fuel required.

At low RPM sequential mode has the benefit of being able to inject 100% of the fuel required when the intake valve is open in theory giving best emissions and economy; however as revs rise its critical to re-phase the injector timing throughout sometimes the whole 720 degrees of crank rotations which is where the difference between sequential and batch is blurred as at certain phases the injectors will be firing before the intake valve has opened just like batch mode but still delivering 100% of fuel required once per cam revolution.

In reality there is little to no difference in injector duty between sequential and batch modes as long as the injectors are able to flow enough fuel for the target power level regardless of revs. The main issue regarding revs is more to do with the injector’s ability to function i.e. open, close and seat cleanly; if injectors and engine run well in batch mode there is no reason to change any of it for sequential mode.

ShakeyC

[crazymonk]

I'm really interested in the discussion going on about sequential and batch, I always thought that sequential was jsut a more up to date form of injection, and that it gave better economy for the same power as batch injection? is this wrong then? So when using forced induction which is best suited, batch or sequential injection?

[Turbo-Brown]

I can totally see the logic of what you're saying, and it does seem to make sense.

All I can offer in my weak defense is that my text books suggest that you need bigger sequential injectors to fuel a given engine than batch.

Re: which is better for FI, it really shouldn't make much difference to either economy or power.

If you had a big overlap cam (which you probably wouldn't with FI), you can time the injection of fuel with sequential to avoid blowing fuel straight out of the exhaust and so waste less fuel. With the low overlap cams of FI though, there's much less of a problem with blow-through.

[ShakeyC]

I see where your coming from now Turbo-Brown; The theory in text books is correct theoretically for only injecting fuel when the intake valve is open. However in the real world we just alter the injector phases back and forth regardless of wether the intake valve is open or not which is why there is little difference in results at high rpms on most road cars.

Regarding big overlap cams it makes little difference if fuel is delivered in sequential or batch mode with respect to fuel blowing straight through, re-phasing the injector timing and cam timing with either modes helps to reduce blow through wastage.

Which is better for FI, the answer is fairly application and engine specific but the advantage of sequential is ability to trim each cylinder, minimise pulsing in the fuel rail and vacuum feeds, longer injector rest times all becomes more evident the more cylinders an engine has.