Bike Carbs or Fuel Injection ?

[billjackson54]

I saw a Berli at Stoneleigh in 2019 with a Pinto and bike carbs and I've seen quite a few Zetecs with Bike carbs / twin webers / Jenvey Throttle bodies etc etc. As an old school kindaguy to whom Fuel Injection is something of a dark art (despite having owned two EFi cars with LPG conversions) I'd really like to know the answer to this question. In the interests of Fuel Economy as opposed to out and out performance, what is the best option if considering an engine conversion. With a Sierra based Cabrio, the standard DOHC 8 valve engine has either carb , carbs, or EFi on the drivers side of the vehicle....as does the Zetec, only the Pinto is the other way round, where Mr Ford's excellent Servo limits the available space (I can't see how a twin Weber setup would fit on a Zetec is the car)...but a Bike Carb set up (with a short manifold) probably would if the brake pipes exiting the master cylinder could be moved (ie replaced and re-routed). The Bike Carb route is also the cheapest and least radical, avoiding the need for swirlpots and full electronic management. SO is there anyone out there with experience of the economics of running a Bike Carb setup? My 2 litre Pinto with w Nikki Carb gave about 32 mpg. My 8 valve DOHC i4 returns more or less exactly the same. Could I expect a significant improvement in economy running a 1800 Zetec with Bike carbs (or EFi / Throttle bodies )

[A_Hogg]

Bike carbs will I believe result in less manifold vacuum being produced, thereby servo less efficient and may requiring the addition of a vacuum pump to restore . Personally i think you'd be hard pushed to beat EFI for economy

[TVRFan]

Quote from one of the old time tuning books which I remember "Compared to a modern EFI system, any carb is nothing more than a calibrated fuel leak" . Even a DIY system should outperform any carb for both power and economy. Trouble is that like choosing the right needles/jets, the system has to be calibrated to get the best 'profile' to fit your engine. If it's an engine which has EFI already, I would do as much as reasonably possible to keep it , as the manufacturer has spent lots of time and money to get the system reliable and economical.

An example - My old Triumph 2500 engine with twin carbs vs. my Toyota today is astonishing difference. (Yes I know, that's not just EFi, but engine design too) In mpg - Triumph engine averaged in mid-upper 20's, and 30/31 on a decent motorway run. About the same in Marlin as in original saloon. A little bit less when tuned, for about 135bhp?? My Toyota V6 (2GR-FE same as used in Lotus) is 3.5 litre V6, develops 280bhp, but driven reasonably gives an amazing 33mpg AVERAGE, and even in town it gives upper 20's. Car is bigger and heavier than Triumph Saloon (A Camry bodyshell). On 'A' road equivalents around 60mph (New Zealand does not have many motorways) it often returns 40 mpg !! I don't think you will ever get close to that with carbs..... How good was the Rover 3.5 for same engine size ?

Even the old mechanical 'K' injection on Ford 2.8 v6 gave a little more mpg than the carb equivalent, and EFI more still, all for same engine.

[TVRFan]

Second Thoughts - But then I wouldn't be fiddling with My Toyota's EFI system. It's got so many sensors it's scary. I would say that if I still had my Marlin with the 2500 engine, I would seriously consider changing it to a DIY EFi system (there are several out there) mounted on the original PI manifolds, as seen on web, and taking away the dizzy as well. Something like the Rover V8 or Ford 2.8V6 (and the Pinto 2.0) was made with both carbs and EFI, so those stats should give you a feel for how much the economy improved.

[milliemarlin]

Having bike throttle bodies, with fuel injection, was a quite attractive option when I fitted my Zetec. Just to add a third way to go.

In the end I fitted a Griffin Intake Manifold.
Paul

[HairyDave]

There is an interesting article in TKC May/June 23 about Danst Eng. I do like the definition of a carb being a calibrated fuel leak, I suppose fuel injection is a power assisted calibrated fuel leak? What was wrong with the early wick carburettor anyway?