To stage or not to stage
Turbo Mini Forums

Hello, I am new to the forum, I have a 1275 gt with blow through Eaton m45. Currently on a metro turbo carb but I am in the process of port injecting it.

I'm going down the sequential route but can't decide whether to use one injector per port, or two per port and stage them. My max power should be around 130-140 bhp. Using Paul Sturgess and Rod Sugden's injector size table from their pdf I'm looking at a total of 2300cc/min for that amount of power. So shall I put one large injector per port or two per port and stage them?

Would one per port be able to control flow at idle conditions?

Thanks,
Rob

You're on the borderline between using 2 large injectors and 4 smaller ones (2 primary and 2 staged secondaries).

The 2300 cc/min for 130/140hp was an early guide. We have seen some go higher with less so I would suggest having a go with 2 1000cc/min injectors as a starting point.

You should be able to get enough control at idle. I'm running 800cc primary injectors on my 998, that's pro-rata the same as 1000cc on a 1275, and it's fine.

Edited by Paul S on 14th Dec, 2017.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I would concur with Paul, try 2 x 1000cc and see.

My current setup is 2 x 1000 and idles absolutely fine. I still haven't finished welding my staged manifold (don't even ask how long it is since I started it...) so I don't have a direct comparison of my own but from a comparison Graham T (on here) did with his setup (staged with smaller primary injectors) then borrowing a pair of my 1000cc injectors, there appears to be a bit more to it than just the injector size when it comes to the idle characteristics.

The total size (single or staged) essentially determines the maximum power (although even that isn't entirely straightforward as it depends on how long you allow the pulse width to get before you start losing control of the mixture distribution between inners and outers) the idle quality - when the pulse widths are really small - seems to be affected by the choice of injector as well.

Everyone will have their own preferences and points of view on this but from what Graham told me, when he tried my injectors and ECU, the idle was better even though the injectors were larger. The main difference (apart from the size) being low-z vs. high-z (hence why he also borrowed my ECU as the drive circuitry is different) and completely different spray patterns. Whether it was low-z vs. high-z, or the spray pattern that made the difference, who knows....
Apart from those two fundamental differences, you can probably add manufacturer of the injector and manifold design (ie, where the injectors point) into the equation as well.....

But, the main thing with idle is getting the ECU settings to really match the actual injector performance especially with respect to the "dead" time correction (open/close/latency depending on who you believe) and voltage correction (which is more important than most people think as the battery won't be under charge voltage at idle). Those correction factors vary a lot between manufacturers.

EDIT - typos and a bit added.

Edited by Rod S on 14th Dec, 2017.

Schrödinger's cat - so which one am I ???

According to my datalog from my original dyno session, I hit 25% duty at 4847RPM and 209KPa (15.6 PSI).
That gave me an alleged 148HP and 162 Lbs/ft. This was with Siemens Deka 840cc/min injectors, non staged.



From that point on, there was overlap on the pulses, if you can understand the below graph.





I believe I am on what I thing is the edge of the injectors ability to properly open when on tick over.
With Rod’s low z injectors I was able to drop the Injector opening time down to 0.7ms, compared to the 1.2ms I am running the Siemens injectors at. With Rod’s injectors the tick over was much smoother and much more stable, with AFR’s around the 14.1 mark, with My Siemens injectors I need to be at around 13.4AFR to get a reasonable tickover, and then it is still not brilliant.

What RPM do you think you will be at to achieve your max power?

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675