Twin Spark Twin Weber Conversion

[njh1964]

Hi All,

As some of you may recall, I originally wanted to install a complete Twin Spark with Bosch EFI gear into my 105 step-nose, but, for a variety of reasons, I've instead decided to go down the twin Weber conversion path. As it happens, I do prefer the old-school look of carbies.

As I needed clearance for the clutch master cylinder attached to the Alfetta hanging pedal box that I've already installed, I needed to fabricate an "up-swept" intake manifold to accommodate the master cylinder. I ended up cutting the runners off the underside of the stock Twin Spark plenum chamber. A mate of mine then TIG welded the runners (turned upside down to provide the required clearance) onto the stock Twin Spark intake manifold (ie where the rubber couplings used to be). He then welded laser-cut 40mm DCOE flanges onto the other end of the runners in order to mount the twin Webers.

The three forward injector ports in the intake manifold have been threaded to take screw-in plugs to seal them off. The rear port has been threaded to take the stock one-way valve for the vacuum feed to the brake booster.

I've also fitted a Nissan/Alfa 8-pole twin spark distributor from Vin Sharp. As usual, Vin did a very neat job of it, and has been great with follow-up information.

Regards,


Nick

[pancho]

Wow, looks like a fair amount of work to get the right result Nick! good stuff.

So would the AHM type manifold not fit after you put the different pedal setup in ?

[njh1964]

Wow, looks like a fair amount of work to get the right result Nick! good stuff.

So would the AHM type manifold not fit after you put the different pedal setup in ?

Hi Pancho,

I did look at the AHM type manifold, but they come straight out (ie perpendicular) from the head. In my case, due to the location of the Alfetta pedal box and its clutch master cylinder (I know...who's fault is that), the rear most intake runner and rear carb would have hit the clutch master cylinder. Also, the AHM manifold is the best part of $500 to buy.

As you can probably just see in my photo above, using the curved runners from the Twin Spark plenum chamber (ie turned upside down) gives me a gently curved sweep up from the head, which allows the intake and rear carb to easily clear the clutch master cylinder.

The end product looks like a photo is have seen elsewhere of another Twin Spark conversion (ie with an upswept intake manifold). The carbs now sit higher in the engine bay than would be the case with a straight manifold, and this gives me a little extra room in the narrower (ie narrower than later 105s) step-nose engine bay. In fact, I think I should be able to fit a Pipercross 600 series airbox and cold air intake.

But the best part... the intake cost me less that $150 to put together, including a case of beer for my mate with the TIG welder.

Regards,


Nick

[pancho]

Ah, I see now, it looks to be a good result!

I've got a pipercross air filter (elongated dome type) hat I can take some measurements of to see if it clears the side guard if you like.



Here is the image of the 600 airbox with dimensions if it helps

[Tristan Atkins]

Hi Nick,

Nice setup!

If you find you need additional clearance a TS pedalbox housing has a slight wedge that angles the clutch master cylinder downwards so as to clear the EFI manifold on the 75.

When I swapped in the TS on my 116 I used welding wire to trace the route for the coolant hoses. I then took them down to the local REPCO and they matched the wire to what hoses they had in stock. Make sure you measure the OD of all the connecting pipes so that you get the correct size. Hope that helps

Best of luck with the conversion,

Tristan

[njh1964]

Ah, I see now, it looks to be a good result!

I've got a pipercross air filter (elongated dome type) hat I can take some measurements of to see if it clears the side guard if you like.

Here is the image of the 600 airbox with dimensions if it helps

Hi Pancho,

The Pipercross dome type filter would be good, if I can't fit the Pipercross airbox in, but at only 78mm high, I'm pretty sure the airbox will fit with about 10-15mm to spare. I like the airbox because I should be able to fix a flexible pipe to the airbox intake in order to get lots of nice cool air into the carbies... whereas the dome filter would be drawing in warmer air from inside the engine bay.

I understand that the Pipercross airbox uses an inverted cone shaped filter mounted into the mouth of the airbox intake (ie you don't install the dome type filter inside the airbox). Is that your understanding as well?

Regards,


Nick

[njh1964]

Hi Nick,

Nice setup!

If you find you need additional clearance a TS pedalbox housing has a slight wedge that angles the clutch master cylinder downwards so as to clear the EFI manifold on the 75.

When I swapped in the TS on my 116 I used welding wire to trace the route for the coolant hoses. I then took them down to the local REPCO and they matched the wire to what hoses they had in stock. Make sure you measure the OD of all the connecting pipes so that you get the correct size. Hope that helps

Best of luck with the conversion,

Tristan

Hi Tristan,

Thanks for that... the Alfetta pedal box also slants the clutch master cylinder down towards the front of the engine bay, so clearance is good... so far.

Good tip on the coolant hoses... I'll be installing the stock Alfa 75 radiator into the 105 engine bay, so there will be some creative plumbing involved. I'm currently looking for a suitable expansion tank, given that the stock Alfa 75 tank is way too big for an already crowded 105 engine bay.

There seems to be a range of aftermarket aluminium expansion tanks that could do the job, but I need one with a pressure cap, a small (8mm) top mounted inlet to take the overflow line from the Alfa 75 radiator, and larger (20mm) outlet at the bottom to take the return line back to the water pump inlet. I then need to find a spot to mount the new expansion tank high enough up in the engine bay to allow the cooling system to bleed air pockets properly.

Regards,


Nick

[Tristan Atkins]

Hi Nick,

There are a number of aluminium fabricators in Moorabbin that could take a generic aluminium cylinder and weld on the required fittings. They can also attach any brackets that you might need for mounting.

[AikenDrum105]

That intake manifold is a thing of great beauty - Very nice (and you still have the option of bunging in the injectors / rail again and putting the butterfly on the mouth of your intake air box if you ever decide to head back down the injection path !

That's the first I've seen that 600 airbox - Very interested in one of those for the Super - there's a Pipercross dealer in Mitcham - will give them a bell and see what the availability is like I think.   

I think you're right about the filter inverted inside the mouth of the box - struggled to find a pic on the internet, but I think this is it: http://www.reverie.ltd.uk/product_detail.php?group=A%20FILT&subgroup=A%20FILT%20FOA&part_code=R01SE0474 

I think you can order an alloy bellmouth for it too.

Any idea what the best size velocity stacks / ram tubes / trumpets   might be for inside it ? 

Cheers,

[njh1964]

That intake manifold is a thing of great beauty - Very nice (and you still have the option of bunging in the injectors / rail again and putting the butterfly on the mouth of your intake air box if you ever decide to head back down the injection path !

My thoughts exactly... the Webers could be replaced with ITBs, and an aftermarket EFI system added. I would have liked to have retained the Twin Spark Motronic set-up, but there's just not enough room with the other stuff I want to install in the step-nose engine bay.

Any idea what the best size velocity stacks / ram tubes / trumpets   might be for inside it ?

That one has me puzzled as well. With an external width/depth of only 78mm for the Pipercross 600 airbox, and allowing at least 20mm clearance from the top of the velocity stacks to the inner wall of the airbox, I can't imagine you could go with much more than 50mm high velocity stacks. Mind you, the original GT1300 airbox didn't have any internal velocity stacks... so perhaps they aren't cricital inside a Pipercross airbox either???

Regards,


Nick

[AikenDrum105]

the Webers could be replaced with ITBs

You know,  with the fuel line disconnected  - the webers basically are ITBs with a minor venturi restriction in the pipe ....   but that's just silly ....  which means of course I'm likely to try it....

I'm not sure what size the pipercross ram tubes AH sell with the filters etc - they look to be only 20mm if that,  probably more about smoothing airflow over the sharp edges of the filter backplate / carb intakes,  than a particular length / torque peak relationship,  the air box is narrow, so the lowest height ram tubes are probably best.

[pancho]

I'll bring it all with me next time I come around Scott. I've got the ram pipes and the filter as well as the manifold.

[njh1964]

You know,  with the fuel line disconnected  - the webers basically are ITBs with a minor venturi restriction in the pipe ....   but that's just silly ....  which means of course I'm likely to try it....

Hi Scott,

Alternatively, you could go with the following Alfa Romeo Twin Spark ITB kit from Competition Systems here in Melbourne...

http://www.compsystems.com.au/catalogue/engine-control/jenvey-throttle-bodies/40-alfa-romeo-itb/alfa-twin-spark-twin-cam-itb-kit.html?vmcchk=1

The kit price is $1,475, but should be less if you don't need the intake manifold. Maybe one day, but for now, it's twin carbs for me.

Cheers,


Nick

[AikenDrum105]

That looks like a neat package !   I'd never heard of that crowd before - thanks for the link!

The airbox might be a bit meaty to fit the gap I have in the engine bay though ....    It's even tighter on your car I think

[njh1964]

That looks like a neat package !   I'd never heard of that crowd before - thanks for the link!

The airbox might be a bit meaty to fit the gap I have in the engine bay though ....    It's even tighter on your car I think

Hi Scott,

Yes... the airbox would be too tight, and in the photo, they've got it pointing the wrong way for an Alfa (ie towards the firewall). The throttle bodies and fuel rail look pretty good. By the way, they also advertise Nord cam shafts on their site. Not sure if that includes Twin Spark cams.

Cheers,


Nick