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Home > 998cc > 998cc moke (1979) plan for full elec engine management and Turbo

Rod S

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5988 Posts
Member #: 2024
Formally Retired

Rural Suffolk

25th Dec, 2016 at 08:44:17am

On 25th Dec, 2016 s900t8v said:
Is the need for huge injectors because at higher rpm if the injectors are not big enough they will overlap pulses which will result in loss of fuelling? or is it purely because they need to be big so to be able to inject enough fuel in the short period of inlet valve open.

It's both.
They need to be large to get all the fuel out in a much shorter time period than a normal engine so as to go through the correct valve (rather than sit behind a closed valve like a normal engine) and, as RPM/load rises, that means the pulse width has to increase but rising RPM shortens the available time so they have to be really large...
Then, if the pulses overlap (un-intentionally, just because they get too big) then yes, in the overlap period you will not be getting the fuel the ECU calculated. That is assuming one injector (per runner) doing the two pulses. If you did your original suggestion of four physical injectors from your 4 chanel ECU you would still get all the calculated fuel but could you be sure where it's going.

The issue is the outer cylinder valves, inject too early and it will go in the inner anyway and if you are still injecting too late (outer cylinder valve now closed) it will sit in the runner and get sucked/blown into the inner 1 1/2 revolutions later.

This is all assuming you are considering two discrete pulses. As mentioned earlier in the thread, the other way is to have a deliberately "merged" pulse, that is inject once per cycle while both inlet valves are open but at a time precise enough to know how much goes through each valve.

Rover's MPI MEMS ECU did a mixture of both (at different RPMs/loads). On this forum, those very few who are actually doing port injection, are split between which is best (partly determined by choice of ECU).

It may be going massive on injectors (ie, without the complication of staging) is workable. My staged manifold isn't finished yet so I'm running 2 x 1000cc/min and it still idles better than a carb.


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

s900t8v

18 Posts
Member #: 11485
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25th Dec, 2016 at 02:29:47pm

thanks rod thats reassuring that it idles better than the carb! haha

thanks again, it's interesting,

while you're hanging around, what size extractors are you using pre turbo.

the thing is I see for better performance people are going up to 1.875" ID extractors, but a T2 or GT15 manifold is tiny! whats the balance, too restricted exhaust means higher exhaust valve temps, completely unrestricted means velocity and turbo spool suffers, did you guys experiment with extractor sizing pre turbo or is there a general rule.

I have a volvo TD04-15g turbo I am wondering if it would spool up in time on a 998cc mini

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