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Flapper on a 4.0 v8 ?

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V8 gods required again, but with the backing of the megasquirt deities.

Currently in the throws of binning my 3.5ltr, its very tired, loud and knackered, in its place is going a very nice 3.9 blue print jobo.

Forumeer Mr. Fridge is building me a megasquirt as we speak - cheers John :D Going for edis.

You have the background, now the question!

Is the standard 3.5 inlet manifold and injector system going to cope with the better and bigger 3.9?

Will the megasquirt improve the usually undersized 3.5 injectors?

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Why not just bolt on the 3.9 injection system that is perfectly adequate and easily available?

Sorry, but I've never seen the point in megsquirting an engine where theres a perfectly serviceable off the shelf injection system available for it. Fit the hotwire system as its designed for the engine and will fuel to match it. Running the 3.5 system on a 3.9 will probably casue it to run lean. The 3.9 system IIRC uses lambda sensors so can run closed loop which is far superior to the flapper system.

It'll certainly run with the flapper system, but you can only really alter the idle mixture on it with the standard adjusters. you might get away with it, but its likely to always run lean......


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Hi Jon,

I dont have a hotwire system to hand, and replacing with megasquirt (for the same money) gives me the opportunity to tune/self diagnose at home, Im seeing too many mates now running standard rangie and when they get a fault, they seem to be into a massive circle of replace with a known good unit. It also allows the factory loom and associated off shoots to stay in place.

I think the emphasis of the question needs to be, can 3.5 injectors work with the 3.9, surely, it will only run lean on the top end?

(The main reason I wish to keep the 3.5 inlet manifold for now is to keep my current lpg install, as eventually I will be going to a 4.6, but cant afford the lpg parts just yet)

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3.5 or 4.6 the inlet hardware is basically the same, the only difference (ignoring the Thor setup) is the injectors went from barbed-hose fitting (most 3.5's) to the more traditional clamped-down by the fuel rail type, they used the same injectors (ERR722 - green stripe) from 3.5 to 4.6 so they have the flow.

The flapper is mass airflow (MAF) so should not run lean as it injects the fuel as a proportion of how much air flows past the flap. This is one benefit of that system. Bear in mind though that the 3.5 or ECU will not be programmed to see the flows that a bigger engine would generate at high RPM. I ran flapper on my 3.9 until I installed the MS and it worked fine (as fine as Lucas does anyway).

Even running MS I was running the early 3.5 barbed injectors and never maxed them out so you should survive - EFi is designed to never exceed 85% duty cycle (injectors open 85% of the time) for safety so you have 15% fuel flow allowance on top. The thing to do with MS is watch for the duty cycle exceeding this limit during tuning, if it gets close then back off and weigh up some 3.9 injectors. You should need just a set of injectors and a fuel rail, pennies at sodbury.

Edit: I think Hotwire injectors are high-impedance so you would need to lose (short out) the resistor pack from the flapper system.

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