Carbs or fuel injection???

[Nimrod70]

I'm thinking about switching from carbs to fuel injection on my Vauxhall 7. I've been quoted about £2k, is it worth it?

 

are the drive ability and BHP gains worth it????

[k.russell]

Yes just the gains in drivability, with no more power gain it will transform the car, I ran my 16v vx for years on carbs but the change was the best thing I did to the car.

[OliverSedlacek]

You can probably offset the cost by selling the carbs. My conversion project is going rather slowly, so I can't comment on the difference yet.

[Roger King]

There is one hugely important item that always gets ignored in the carburettor/fuel injection debate and that is the IGNITION system.

Just about any full engine management system will have 3D mapping of the ignition timing, whereas the vast majority of carburettored cars only have 2D mapping (if you can describe weights flying around on springs as "mapping").

This means that while carburettors and fuel injection are basically doing the same job as each other (albeit in different ways), there is an entire functional system missing from the ignition of most carburettored cars. 3D mapping isn't there for fun; it makes a huge difference to driveability and fuel consumption and a large amount of the perceived difference between injection and carburettors is actually down to this.

Now, no sane person would deny that a properly set up injection/ignition system provides better control of fueling, economy and emissions than carburettors, but in reality, properly set up carburettors with 3D ignition can get very, very close, to the extent that the differences are more noticeable in the measurements than in the driving.

Fundamentally, without 3D ignition, you are driving round with retarded ignition timing all of the time with the sole exception of the few moments when you use full throttle. Do the same to an injected car and see how much worse that feels too.

I'm not advocating that you should necessarily stay on carburettors, but merely pointing out that one of the major reasons for the differences between the two systems should be understood. It is also a lot cheaper to fit 3D ignition than a full management system.

One of my customers once stated that it felt like he had fitted a much bigger engine after going 3D.

 

[Paul Deslandes]

Like Kevin, I converted my Vx 2 litre to injection 15 years ago but had gone 3D ignition a couple of years before that.  The ignition change really was transformative, as Roger has described, but I liked the idea of mapability of the fuelling so eventually went injection as well when funds permitted (or, rather, when SWMBO wasn't looking).

I would have thought £2k was a bit optimistic by the time you've bought the ECU, loom, throttle bodies and injectors, plus a decent mapping session, although there are reasonable 'starter maps' out there.

Another option would be to start with 3D ignition but buy a fully populated ECU which will also drive injection if you decide to go the whole hog later.  Ignition only ECUs can't be upgraded to injection as a lot of the necessary bits are missing, although they are quite a bit cheaper for that reason.

If you physically remove the distributor you need to modify the exhaust cam by blocking the oil hole at the end to stop oil being pumped out.  A small ball bearing is hammered into the hole to achieve this.  You'll also need a blanking plate.

There are several options for throttle bodies including Jenvey 'Weber' type which fit the existing carb manifold, Weber type direct to head from QED and Jenvey individual TBs/manifold from SBD.  The original carb manifold is quite restrictive unless heavily worked on and will limit your ultimate power considerably.

As for ECUs - MBE, DTA, Omex, Emerald - take your pick or find a local ECU mapping expert who has his favourite that he can map for you.

 

[alan c]

Hi,

I converted mine in stages over a period of a few years. First I went to 3D mapping but did this with a full loom and ECU that could go to full injection. I subsequently went to full injection.

The move to 3D was the most dramatic in terms of change, no real gain in power but used a lot less fuel. Full injection is more driveable.

I think you could do the first stage for less than £2k, you need a loom, ECU and a mapping session plus you have to deal with the distributor. For full injection you add the cost of the injectors and you need to make changes to the tank/pump and another mapping session. The carbs would sell quickly but have a look at the Northampton Motorsport website they now convert them to run fuel injection. Not sure about cost difference v buying new TB's but you keep the look of having carbs.

If you plan on going to the Alps make sure you add the pressure sensor, it's not expensive. Without it my car would not run properly once I got higher up and it certainly wouldn't idle without my foot on the throttle.

alan

[The Bear]

I would have thought that after Monday night, you don't need any more bhp!!!!