Semi-sequential vs. Batch fire..
Discussion
GreenV8S said:
Jhonno said:
is it worth changing
That depends why you want to do it. Changing to a new ECU is expensive. If fuel economy is your reason for doing it, you need to work out how long your predicted mileage improvement will take to pay back the cost of doing it.Not worth it for fuel economy, and may not be worth it for the other benefits you list. But well worth it to learn new skills if you have the time and patience.
Out of interest why go for a "half way house" of semi-sequential? It will look like batch to the engine at moderate to high loads. Go full sequential and get the (even smaller) benefit of injection angle tuning and individual cylinder trim (if your ECU choice supports such things). Or is getting a cam sync on your engine annoyingly difficult?
Out of interest why go for a "half way house" of semi-sequential? It will look like batch to the engine at moderate to high loads. Go full sequential and get the (even smaller) benefit of injection angle tuning and individual cylinder trim (if your ECU choice supports such things). Or is getting a cam sync on your engine annoyingly difficult?
dnb said:
Not worth it for fuel economy, and may not be worth it for the other benefits you list. But well worth it to learn new skills if you have the time and patience.
Out of interest why go for a "half way house" of semi-sequential? It will look like batch to the engine at moderate to high loads. Go full sequential and get the (even smaller) benefit of injection angle tuning and individual cylinder trim (if your ECU choice supports such things). Or is getting a cam sync on your engine annoyingly difficult?
Because yes, sadly fully sequential will involve machining of timing cases etc, which involves engine out, and I've only just put it back in! Out of interest why go for a "half way house" of semi-sequential? It will look like batch to the engine at moderate to high loads. Go full sequential and get the (even smaller) benefit of injection angle tuning and individual cylinder trim (if your ECU choice supports such things). Or is getting a cam sync on your engine annoyingly difficult?
Playing with new software etc would be part of it too though I guess..What about the wideband lambdas? Or once it is mapped properly they are irrelevant too?
I see you have a Cerbera. I don't know how many ECUs support it because its unusual V-angle makes for the cylinders to fire in a sort of heartbeat - 1, 2... 1, 2... 1, 2...
I had an Emerald on mine. At the time I understood that to be the only other ECU (than the original one) that would work (because of the heartbeat). I sought out one of the (then) few Cerbs with an Emerald because I was familiar with one on my previous car, a Caterham.
Software is simple. Self mapping a PoP with a wideband lambda. Definite improvement in drivability over the original. Despite it making a shade under 410 on the rollers, it was as docile as a shopping trolley around town. No pops and bangs though - a properly mapped engine won't give you that.
I had an Emerald on mine. At the time I understood that to be the only other ECU (than the original one) that would work (because of the heartbeat). I sought out one of the (then) few Cerbs with an Emerald because I was familiar with one on my previous car, a Caterham.
Software is simple. Self mapping a PoP with a wideband lambda. Definite improvement in drivability over the original. Despite it making a shade under 410 on the rollers, it was as docile as a shopping trolley around town. No pops and bangs though - a properly mapped engine won't give you that.
Watchman said:
I see you have a Cerbera. I don't know how many ECUs support it because its unusual V-angle makes for the cylinders to fire in a sort of heartbeat - 1, 2... 1, 2... 1, 2...
I had an Emerald on mine. At the time I understood that to be the only other ECU (than the original one) that would work (because of the heartbeat). I sought out one of the (then) few Cerbs with an Emerald because I was familiar with one on my previous car, a Caterham.
Software is simple. Self mapping a PoP with a wideband lambda. Definite improvement in drivability over the original. Despite it making a shade under 410 on the rollers, it was as docile as a shopping trolley around town. No pops and bangs though - a properly mapped engine won't give you that.
Hi, yes I have a Cerbera, but both DTA S80 Pro and MBE 9A8 can run it fine with the specs I am interested in.. Pops and bangs will have to be retained or it isn't a Cerbera anymore.. I had an Emerald on mine. At the time I understood that to be the only other ECU (than the original one) that would work (because of the heartbeat). I sought out one of the (then) few Cerbs with an Emerald because I was familiar with one on my previous car, a Caterham.
Software is simple. Self mapping a PoP with a wideband lambda. Definite improvement in drivability over the original. Despite it making a shade under 410 on the rollers, it was as docile as a shopping trolley around town. No pops and bangs though - a properly mapped engine won't give you that.
I don't know how goods or bad your existing tune is, but it seems to me that getting a good tune is probably going to make more difference than changing the injection timing. I tried sequential on my RV8 (with a plenum, not throttle bodies). While I could hear the difference that phasing adjustments made, it really didn't make any difference to the behaviour as far as I could tell. What little difference I got could probably be got just as well by increasing the number of batch fire events.
I run wideband lambda sensors all the time because I use every opportunity to log and tweak the tune, but I think that's unusual. Wideband sensors are consumable items (and not cheap) so perhaps that's why people usually seem to use them just for tuning sessions.
I run wideband lambda sensors all the time because I use every opportunity to log and tweak the tune, but I think that's unusual. Wideband sensors are consumable items (and not cheap) so perhaps that's why people usually seem to use them just for tuning sessions.
Well it isn't to do with current tune, I have rebuilt the the engine to a whole new spec, so I either need a remap or new ECU and mapping.. Hence why I am debating if it is worth going to semi-sequential and wideband lambdas at the same time. Semi-sequential would be running paired injectors 180 degrees out, so not massively the timing exercise as fully sequential would be..
spitfire4v8 said:
Jhonno said:
Semi-sequential would be running paired injectors 180 degrees out, so not massively the timing exercise as fully sequential would be..
I think I've spotted your first problem then ...Edited by Jhonno on Tuesday 19th February 10:17
taking it as 2 4 cyl engines, If you were running full sequential you would inject each cyl once every 720 deg, for semi seq each pair every 360deg. If you inject both pairs every 180 deg as you've put then you've just recreated batch fired that's all, ie 4 squirts every 720deg, 3 fuel pooling squirts per cycle, and the extra injector dead times also.
Having said all that, the internet is rife with which cylinders to pair anyway. I've always done my semi seq in wasted spark coil order, but others disagree.
Having said all that, the internet is rife with which cylinders to pair anyway. I've always done my semi seq in wasted spark coil order, but others disagree.
Edited by spitfire4v8 on Tuesday 19th February 10:12
spitfire4v8 said:
taking it as 2 4 cyl engines, If you were running full sequential you would inject each cyl once every 720 deg, for semi seq each pair every 360deg. If you inject both pairs every 180 deg as you've put then you've just recreated batch fired that's all, ie 4 squirts every 720deg, 3 fuel pooling squirts per cycle, and the extra injector dead times also.
Having said all that, the internet is rife with which cylinders to pair anyway. I've always done my semi seq in wasted spark coil order, but others disagree.
Doh! Yep.. 360 degrees.. I keep brushing over the fact the bottom end turns twice to every once for the cam! I knew what I meant anyway.. Having said all that, the internet is rife with which cylinders to pair anyway. I've always done my semi seq in wasted spark coil order, but others disagree.
Edited by spitfire4v8 on Tuesday 19th February 10:11
Jhonno said:
For what reason? 
The way I look at it, you have a mass of fuel in the intake runner and settling on the valves while closed. Once per engine cycle the air is drawn through, carrying some of the fuel with it. The fuel mass is topped up by batch fire injection events a few times per engine cycle. With sequential injection you have better control over when the puddle is topped up relative to the air movement. That might mean that under some conditions you are altering how much fuel enters the engine as vapour rather than droplets, although probably not by much. Does the engine care?It makes more sense IMO when you're considering upstream fueling for maximum power where you want to optimise for charge cooling.
GreenV8S said:
Jhonno said:
For what reason?
The way I look at it, you have a mass of fuel in the intake runner and settling on the valves while closed. Once per engine cycle the air is drawn through, carrying some of the fuel with it. The fuel mass is topped up by batch fire injection events a few times per engine cycle. With sequential injection you have better control over when the puddle is topped up relative to the air movement. That might mean that under some conditions you are altering how much fuel enters the engine as vapour rather than droplets, although probably not by much. Does the engine care?It makes more sense IMO when you're considering upstream fueling for maximum power where you want to optimise for charge cooling.
At lower revs with batch fire you end up with some fuel sitting about resulting in worse emissions, and less smooth low end running/response. HOWEVER.. The big question and the point of the post I guess, is it it worth 1k extra (arbitrary rough figure), for the benefits I would see going semi and wideband.. I mean it would be nice to not have to "worry" come MOT time about emissions, a bit better MPG on a run would be good, flexibility is always good.. OBDII ECU reading good too. However, as Joolz attests to, the standard system can do a decent job on the AJP, especially when Wizards like him map it!
Sadly I have not had experience swapping between systems/setups, hence asking on here and trying to broaden my understanding a little.
Jhonno said:
From reading around, mid range to top end is unaffected by batch/sequential.. Although you need larger injectors to supply the same fuel for a sequential setup.
You only need big injectors if you want to squirt most of the fuel in during the intake suck period on large loads.If you are only interested in sucking all the squirted fuel in during intake valve opening on light duties (ide quality, MPG, light throttle drivability) , you can in fact get away with a smaller injector than running batch fired. On batch you have 4 injector dead times per cycle, sequential only one dead time. Less dead time = more fuel for a given injector..
spitfire4v8 said:
Jhonno said:
From reading around, mid range to top end is unaffected by batch/sequential.. Although you need larger injectors to supply the same fuel for a sequential setup.
You only need big injectors if you want to squirt most of the fuel in during the intake suck period on large loads.If you are only interested in sucking all the squirted fuel in during intake valve opening on light duties (ide quality, MPG, light throttle drivability) , you can in fact get away with a smaller injector than running batch fired. On batch you have 4 injector dead times per cycle, sequential only one dead time. Less dead time = more fuel for a given injector..
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff