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MG MGB GT V8 Factory Originals Technical - fuel injection rev limiter

Hello, I just finished putting the Rover hot wire fuel injection under the hood of my '73 MGB-GT. The engine is a 4.2L with air conditioning. It runs great until 5500 rpm when the rev limiter kicks in. I know many of you have installed this fuel injection in the past, has anyone figured out a way around the rev limiter? 5500 rpm just spoils all the fun.

Thanks in advance.
------John '73B '73BGT
John Masters

Have you got a 'road speed' sensor in the circuit?

If so then not only will you have the indicated 5500 rpm cut, which I suggest is over optimistic reading of the tacho as it should be 5200 or ther abouts, but also when the actual speed reaches 110 or close to that (production tolerances) the speed limiter will also apply.

If you have no road speed input then the cut out your experiencing is somthing that does not apply to the systems I have experience with.

The systems I have experience with can be run without the road speed input as this is a 'correction factor' for the implimentation of 'idle speed control'. Running without does occasionally show up with some odd idle characteristics but I have not found these too difficulkt to live with.

Retaining the road speed input and removing the rev/speed limit involves alterations inside the ECU to which I have had done by Lucas before the axe fell on the automotive section. A company such as Superchips here in the UK can not only remove this but also provide a modified fuelling map that does really sharpen up the throttle response and add a few bhp.
Subject to checking I think that their webside is www.superchips.co.uk

Rog
Roger Parker

Roger, I do not have the road speed sensor in the car as of yet. I had heard that the engine will still run ok without it. I am planning on installing it without the cables hooked up to see if that will smooth out the idle a little bit. Anyway, the system came from a us spec 89 Range Rover 4X4 with a 4.2L engine. Since the engine is pretty much stock and I am very pleased with the increased power and fuel economy, I would rather not change from the factory chip if I can help it. I'll check the Superchips site tonite to see if they have any ideas.
Thanks for the help.
John
John Masters

Roger - I lived with an erratic idle but the engine would sometimes also stall so the outfit now includes the speed transducer - and runs perfectly.

John - you might put a switch on the
supply wiring to a speed transducer - to give
you control over the speed input (and the 110mph
limit).
My understanding is that you would still
be mimited by engine speed although you should get closer to the sensible top speed of the car (depending on drive train etc).
Roger

Gents,
just a question does a stock V8 reach max power at Revs greater than 5500 rpm ??? And if so why do you need to go greater than 5500rpm. (this comes from someone yet to get my V8 on the road I dare say I'll get the urge to go beyond the 5500 range when my is done).

Spriggsie
Clem Spriggs

The rev issue is one directly related to gearing. With appropriate long gearing (in ALL gears) the speed ranges will be adequately covered with a 5000 rpm band. However if it is lower, then the frequency in which the revs will rise to the cut off point (remember it should be at about 5200rpm not 5500) will be far greater since the ability of the engine to accelerate this lighter car will mean that inadvertant straying into this limit is likely to occur. If the engine is able to breath better then there will be a much sharper appetite for the engine to rev.

The fact that the larger displacement Rover spec V8s will give peak power at around 4700rpm is a little misleading. The power drop off after this peak is not severe enough in the following 800 rpm or so to see any reduction in the acceleration of the much lighter MG. This is why I mention 'straying' into the higher rev band will occur inadvertently.

Rog

Roger Parker

This thread was discussed between 28/03/2000 and 09/04/2000

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