sequential injection or not ?

[trond]

contemplating trying sequential injection vs batch. Worthwhile or not, what is the concencus?
Twin spark 3.2SS with mellow cams and ITBs. I have both crank trigger and cam position sensor

Against I see added complexity and fiddling with setup parameters also more cables required than I believe I have between engine and MS2 ECU.

[Jonny042]

It's probably going to depend mostly on your engine position sensors. If you have a crank sensor only you'll be stuck with batch. If you're triggering with a cam angle sensor or distributor with a 1 pulse per rev sensor then you might have the capacity for full sequential.

I think batch is probably almost as good and probably easier and more reliable.

[tirwin]

This is an interesting question. I am curious to see what responses you get.

I always thought sequential was superior but I read an analysis that basically said sequential is only useful at lower rpms. Once you get to higher rpms sequential and batch are essentially equivalent because of timing of injector pulses.

Is the main difference fuel economy? If it’s about power then how different are the two in reality? Makes me wonder what the cost/complexity is vs the benefit.

[r lane]

A system that I am using is sequential, phase or full. For full you need a cam sensor and I think it fires every 720 whereas phase is every 360. I was running full then switched to phase and I think I like it better. I think some of this is referred to as waste spark. What is Batch? Bob

[lvporschepilot]

If you're not running a very hot camshaft then batch injection is just fine. Hotter cams respond better when mated to a fully sequential arrangement. At low rpm is where full sequential is most noticed, above around 3000-3500rpm there really isn't any difference. Rasant's distributor wheel with cam trigger setup built in all as one unit is the best, easiest on the market.

[trond]

so with lazy cams no point ? I am currently on stock SC cams which suit my use of the car about perfect and I can not see hot cams in my future

[spuggy]

I think batch with modern injectors will have zero difference at higher RPM, as a lot of the duty cycle is against a closed valve anyway. Some motor types apparently idle better with injectors timed to fire when the valve is closed - but there's lots of room for experimentation there... My wrench says he tried a few values and never really noticed much change/difference with 911s.

Older injectors don't atomize as well - and old, large, injectors can make it difficult to get a decent idle. So depending on your choices, it could be useful to have more fuel kicking about in the intake (if they're firing all the time, you can use smaller).

But sequential is literally pinning up one sensor cable and clicking a few buttons in the ECU software as you already have the cam sensor. If it saves you 5% fuel below 3000 RPM, then why not? (and I can't see how it would only save that - you're only firing injectors on the combustion stroke, instead of all 6)...

After suffering the fuel consumption of CIS (which injects Continuously, hence the name) for years (a 930 in town gets 6-8 mpg, same as the track), I just couldn't bear the thought of injecting fuel on the exhaust stroke.

I went sequential. (twin-plugged/COP with SC cams and a 3.2 manifold); still amazed how crisp, clean, responsive and willing it runs up off-idle/boost.

[Peter M]

I'm surprised that no one has mentioned yet that it allows individual trimming of each cylinder.

OEM's have used sequential injection since the mid 90's to improve idle quality, fuel economy, emissions and probably peak power within the constraints they need to work within.

I'm continually surprised how many people are reluctant/too ignorant to adopt now affordable technology that the cheapest runabout cars have had for years and like Spuggy has said above, the benefits that modern technology brings to our old 911's

[stlrj]

Why not just pick up 996 that has all that tec already and for what they are going for today seems like quite a bargain. Meanwhile, you could still enjoy living in the past with the joys of old technology.

[targa72e]

Sequential has benefits at low rpm with cams with a lot of overlap. With batch fire multiple injectors fire at once with cylinder in different phases. Since you can not time the injection pulse some of the fuel injected at the wrong time gets blown away from intake valve on overlap. this results in poor ability to control mixture. Some cylinders will be lean some rich depending on phasing when injection pulse happens. With sequential you can time the injection pulse in time with the intake cycle. Once the engine speed gets over a certain RPM the reversion effect becomes less as the mass and speed of the air keeps it from being blown back up the intake tract. this is also why cams with large overlap do not work well with common plenum intakes at low RPM. ITB have a throttles at each cylinder that are close to the valve that and keeps revisions from going up the intake tract. Some injection systems allow you to batch fire in pairs and based on pair selection you can get sequential like effect. Sequential is generally more precise but In your case with SC cams which have little overlap you would probably not see much difference.

john

[trond]

i will try sequential then, with current CIS plenum and SC cams. Get it to work first, then install ITBs, then if not entirely happy install more lively cams possibly. If nothing else it should keep me occupied. How to time injection will be another never thought about issue to google and think about.

If I get bored I guess I will buy a 996 that just works out of the box, but what's the fun with that ?

[tirwin]

Trond,

Curious about your setup. What P&C are you using?

[trond]

10.5CR CP pistons. 98 mm
twin spark

[spuggy]

Originally Posted by trond

then if not entirely happy install more lively cams possibly

If you often potter about between 2500-3000 RPM, and like the car to respond instantly and jump forward when you apply throttle, SC cams have great low/mid range response; twin plugged with ignition control and a good advance map, you might be surprised just how sharp the response can feel. Lightweight rods/flywheel help. ITBs should be even better (heh, I still want those)...

SC cams are "game over" around 5500 RPM, so it all depends how much time you want to - or realistically think you can - spend over 5000 RPM. My logs almost never hit 6K, even trying to tune boost control. If short-shifted (say 5K), still in "full boost" territory in the next gear.

Personally, I'll trade theoretical horses @ WOT/6500 RPM that I'd almost never get to use against torque/part-throttle response lower down that I use every time I merge/change lanes etc. YMMV.

Also, boost being all-in by 3000-3500 RPM on my car (with enough load) does change the dynamics a bit...

Originally Posted by trond

How to time injection will be another never thought about issue to google and think about.

Experiment/test by all means. The motor likes what it likes. It'll let you know if you listen.

[trond]

thats exactly the case with SC cams. Significant response from around 2200 but all over before 5500. How often on the street is what happens north of 5500 even interesting ? I found just about never. I grew up with cars with small engines and feel ultimate horsepower is useless in itself. Throttle response and stealth is what counts, the ability to overtake immediately in 5th gear on small county road, rather than drop down 2 gears to get into a narrow power band. With my choice of pistons I believe I may have to either swap cams to reduce detonation, or swap pistons to get lower compression. Did not like light flywheel btw and swapped back to stock.
Hate to swap pistons really as they are newish and were expensive but this is what I am leaning towards. Gives me an opportunity to take a closer look at what surface finish the cylinders have and maybe get rid of the burnt oil smell