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SPI being short of horses
https://www.ausmini.com/forums/viewtopic.php?f=2&t=30797		 Page 1 of 3
Author:  buztoy [ Fri Apr 20, 2007 7:34 pm ]
Post subject:  SPI being short of horses
hey
the demand for an injected induction is pretty big right, so many poeple have said to me "dont bother with the SPI injection setup(90's mini), its crap and couldn't pull a hat off my head".

no one has exsplained why :?
Author:  Harley [ Fri Apr 20, 2007 7:47 pm ]
Post subject: 
Simple.

Carb:
More fuel + more air = more power.

SPI:

Computer restricts fuel levels for emissions, + limited air = less power, but torquey and smooth. :D
Author:  drmini in aust [ Fri Apr 20, 2007 7:50 pm ]
Post subject: 
Well, the SPI was invented so the UK Mini 1275 could pass the emission rules of the day.
Power was 61 or 63 HP I think, about the same as an old single carb 1275.
Nothing special. By comparison, an MG Metro with carb was 72HP.... :wink:
<edit> when the MPI came out, it was not much better than SPI in stock form.
Author:  buztoy [ Fri Apr 20, 2007 8:30 pm ]
Post subject: 
in what way does it restrict the flow, is it the size of the injector, or the fact that there is regulator that sends the fuel back to the tank, if so whats stopping you from removing it completly or swapping it from another car,

what stops it, in alot of other cars its avoidable
Author:  Harley [ Fri Apr 20, 2007 8:36 pm ]
Post subject: 
Okay, so my answer is too simple......prolly even wrong. :D

The main restriction comes from the head design. There is one inlet for two cylinders. One cylinder will always get slightly more fuel than another, but with the carb there so much going everywhere it doesnt really matter. A lot is 'wasted' (is that the word?)

Other restrictions:
The single injector can only deliver so much fuel.
Air changes angle in manifold
Engine capacity
Cat exhaust
Compression ratio

Lots of things really. Just like any other car.
Author:  buztoy [ Fri Apr 20, 2007 8:41 pm ]
Post subject: 
when you say injector, do you mean it had 4 inj or 2 because that would make it a bit better,

and no one has stuck the set up on a another motor?
Author:  drmini in aust [ Fri Apr 20, 2007 8:44 pm ]
Post subject: 
It's bloody hard to make port injection work properly when you only have 2 intake ports. The breathing through each port is not symetrical.
The firing order is 1-3-4-2. Displace it 1 stroke > for clarity, it is 3-4-2-1. So 3 sucks then 4, then that port rests while 2 and then 1 suck on the other port.
Also, the inlet timing overlaps, at a point both cylinders are sucking on the same port together.

If you are serious about MPI, go buy an 8 port head for starters. :wink:
Author:  Harley [ Fri Apr 20, 2007 8:47 pm ]
Post subject: 
Simply put......the head is the restriction.
Check out what the miniman gets on a relatively 'stock' engine with a twin cam head on it.
:D
Author:  buztoy [ Fri Apr 20, 2007 8:58 pm ]
Post subject: 
drmini in aust wrote:
It's bloody hard to make port injection work properly when you only have 2 intake ports. The breathing through each port is not symetrical.
The firing order is 1-3-4-2. Displace it 1 stroke > for clarity, it is 3-4-2-1. So 3 sucks then 4, then that port rests while 2 and then 1 suck on the other port.
Also, the inlet timing overlaps, at a point both cylinders are sucking on the same port together.

If you are serious about MPI, go buy an 8 port head for starters. :wink:


i gathered that from the start, thats why ive gone a dual thoat carby at the moment, the reason why i was asking is with the turbo setup i am going to use i need a dual throat carby or inj, i hate SU and webber, dello or inj is the only other options, i was talking to a carby builder today and he said that webbers and dello don't really like being force fed, he said that i would have to put a valve in to make sure the carby does nt back fire through its self,

i haven't got $ for an 8 porta,
Author:  Joe [ Fri Apr 20, 2007 9:32 pm ]
Post subject: 
but even still with the twin port head, an injector should be able to flow as much as a carby with less restriction. A vacuum variable venturi carburettor (su) will always be a restriction. You could put bigger injectors, reg, pump, etc... But in England many smart men have been trying to make power out of the cpi/tpi minis and it seems they all hit a brick wall trying to make easy ECU upgrades (unichips etc...) to modify the fuel map. Its all about injector time and injector timing (there is a difference).

And at the end of the day, without forcing the air in there, you can only run at 100% volumetric efficiency and if a webber or SUs etc can provide that for you... why spend mid to high 4 figure numbers, when with carbys, low 4 figure numbers can get you the same result.
Author:  Joe [ Fri Apr 20, 2007 9:39 pm ]
Post subject: 
would a turbo fit into the end of a webber? they don't look like they have much room there in the webber box
Author:  mini-dunger [ Sat Apr 21, 2007 1:14 am ]
Post subject:  here we go again
did you say bimmer twinky? :roll: here we go again
Author:  KLAS [ Sat Apr 21, 2007 1:53 am ]
Post subject: 
if you say injection can not make more power you know only part of the story.

first of all the injection set up can make much more power by its own, the throttlebody is also found in Rover K engines with up to 90HP, only with a bigger injector.
the mini injection engine itself is build to give 63 HP, with a camshaft that delivers 60HP in carb version ( Rover Metro). if you change the cam and the head you can get more than 80HP without problems, and that is still with small valves.
if you fit bigger valves, like the MG Metro, you get even more, but will run out of fuel if you don't change the injector

and i know it, i'm driving this kind of engine :wink:
Author:  Spaceboy [ Sat Apr 21, 2007 1:54 am ]
Post subject: 
i think the injected minis have a bit more power vs the same engine with a carb, however they have limited tuning options.
Author:  buztoy [ Sat Apr 21, 2007 10:04 am ]
Post subject: 
Joe wrote:
would a turbo fit into the end of a webber? they don't look like they have much room there in the webber box


it either im going a suck through carby or a blow through, in which case if its going to be blow im going to stick where the oil breather is at about 11 oclock coming from the center
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