Use DCOEs as ghrottle body?

[itiejim]

I'm currently building an Alfa twin spark engine to go in my 1968 GT Junior - the older Nord based engine rather than the later FIAT based one.I would prefer to run it with an internally mounted ECU and with injection, but would like it to look reasonably authentic at first glance.

So, my question... The Alfa 75 used a very stubby little inlet manifold with injectors very close to the ports which then linked to a single plenum with throttle control. Is there any reason that I couldn't just use this original manifold, link them to the DCOEs and just let the carbs act as throttles? Clearly they'd need to be air tight and have a throttle pot fitted. Any thoughts?

[DVandrews]

You will need to blank the idle feeds, pump jet feeds, progression feeds and main jet feeds and perhaps remove the chokes and the aux venturis. One thing to bear in mind is that the shut angle of the butterfly on a carburettor is higher than on throttle bodies which can make mapping the area just off idle quite tricky as the granularity per degree of opening is initially much coarser.

Dave

[stevieturbo]

Although a long time ago now, pretty sure Dave Walker from CCC/Emerald did this quite a few times.

if you want to retain the carb visuals, mount the injector bosses and rails etc on the underside of the carbs where they'll be better hidden from view

[itiejim]

Thank you folks. Looks like something worth exploring then. Good call regarding the initial throttle opening. Perhaps this can be partially addressed by changing the linearity of the throttle pot if possible?

[itiejim]

Regarding mounting the injectors under the carbs, this was my initial intention. However, looking at the 75 manifold, it's so slim and innocuous and gives the injectors a lovely straight squirt down the inlet port that it seems a shame not to make use of it.

[stevieturbo]

Of course if there is room in the inlet manifold you could mount the injectors there too.

[itiejim]

Sorry, I wasn't clear - that's where they're already mounted, hence my thought to retain a known and successful location.

[stevieturbo]

itiejim said:

Sorry, I wasn't clear - that's where they're already mounted, hence my thought to retain a known and successful location.

Ah right, didnt get you at first.

It's already fuel injected. Yes strictly speaking you would need a throttle position sensor on the carb spindle shaft

Or...some modern cars use a linear pot mounted to the pedal for their DBW setups, so you could add that to tell the ecu throttle position and have the carb end looking like carbs

[DVandrews]

Mounting a pot on the end spindle isn't too hard, you just screw on an extension with a D piece to engage the TPS and make a small mou t for the pot. For best power you need the injectors as near to the trumpets as you can, for best transients you need them as close to the inlet valve as possible, with DCOE style throttle bodies which are designed to replace DCOEs the injector bosses are close to where the DCOE throttle plates would have been if you get my meaning.

Dave

[itiejim]

DVandrews said:

Mounting a pot on the end spindle isn't too hard, you just screw on an extension with a D piece to engage the TPS and make a small mou t for the pot. For best power you need the injectors as near to the trumpets as you can, for best transients you need them as close to the inlet valve as possible, with DCOE style throttle bodies which are designed to replace DCOEs the injector bosses are close to where the DCOE throttle plates would have been if you get my meaning.

Dave

I'm just after a lively, torquey, driveable engine really, rather than the last BHP. Based on that, is there any reason why the original location - very close to the inlet valve - wouldn't work with the DCOEs acting as throttle bodies? Injector location is very similar to the below.

http://www.berlinasportivo.com/forumpics/q4/inlet....

[stevieturbo]

itiejim said:

I'm just after a lively, torquey, driveable engine really, rather than the last BHP. Based on that, is there any reason why the original location - very close to the inlet valve - wouldn't work with the DCOEs acting as throttle bodies? Injector location is very similar to the below.

http://www.berlinasportivo.com/forumpics/q4/inlet....

it will work just fine.