4.6EFI tips

[paul c]

Hi. I thought I had joined a few years ago but couldnt find myself on here.

I am starting a new project, a 110 landy 4.6. My original goal was to use one of my P76s but have found a cheap 4.6 shortblock, although it may need re sleeving so may not be cheap. The advantage though that it is a rover and everything will bolt on.

From reading other threads I think the 4.6 with 4.0 pistons and tophats will be the most reliable, with the 3.9 heads and composite gaskets. I have a 3.9 EFI cam from Autopost which I had been considering to use.

Which brings me to the question of which EFI to use. I have a couple of flapper systems and also a 3.9 of 94 vintage with an intermediate cover, and hotwire.

I tend to feel the flapper is more reliable, and according to some (eg RPI website) is satisfactory and possibly easier to set up. I also have a spare system so will have all parts as backups. I am anticipating a lot of travel possibly world tour.

So any opinions would be welcomed. Cheers.

[ChrisJC]

If you use the 3.9 heads, they were most likely from a tin-head-gasket engine, so will need skimming if you use composite gaskets.

The problem with the flapper system is it's age. The most recent vehicles are now 20 years old! It's also pretty crude. The Hotwire system is much more sophisticated.

Chris.

[CastleMGBV8]

Paul,

I would second what Chris said and use the Hotwire system, if you intend using 4.0 pistons then you should not need to skim the heads, even with composite gaskets the compression ratio may be too high.

This subject comes up from time to time and I have not seen accurate information as to the cc's of the bowls in the 4.0 and 4.6 pistons, does anyone have the relevent information?
The swept volume of a 4.6 cylinder is 569cc. the 3.9 heads gave 36cc chambers, the comp gasket adds 8.5cc the deck height probably adds another 3.5cc. which = 48cc. the piston recess is ? guess at 10cc. and the compression ratio will be 10.8/1

569 + 58 = 627 divided by 58 = 10.8/1 still too high for general road use.

If the vehicle is intended for general road use and some off roading I would have thought no higher than 9.8/1 would be ok so you may need to stay with the 4.6 pistons.

Kevin

[katanaman]

Getting a flapper system to run on a 4.6 is going to need some serious reworking. They are also really old and pretty unreliable now in the greater scheme of thing. Personally I would use the hotwire hardware but use a mappable ecu which will probably work out about the same cost as reworking a standard ecu but is much more flexible.

[paul c]

Thanks.

I wouldnt want to be too high in CR, about 9.5 would be more than enough, possibly around 9.0 even better as fuel quality may be an issue in some countries. I will have to start measuring things when I get them all apart.

My experiences with flappers have been good, I have two working systems, and have been led to believe they would work fairly easily, but you dont think so? My intention is to keep the vehicle as basic as possible, and reliable, but if I need to do repairs not too didficult to troubleshoot. Maybe I should stick to carbs? I feel there is too much to go wrong with a hotwire, even though it is a more sophisticated system. The hotwire has much less components to fault. And I already have a full system for spares.
There is always a possibility of things getting wet and vibration, etc, which is why I would prefer to be able to carry spares, especially ECU, and as stock as possible.

[ChrisJC]

After 20+ years, contacts are corroding, rubber boots have split, the resistive track in the AFM has worn a bit. It just gets prone to dodgy connections, a particular problem if it's in a Landie or something where it gets wet regularly.

Chris.