custom/modified rear intake manifold

Post your 'Carburettor & Fuel System' FAQs, comments & questions regarding Ducati motorcycles here.
Post Reply
riccorman
Cucciolo - the Lil Pup
Posts: 20
Joined: Wed Dec 31, 2014 7:11 am
Location: Oklahoma City

custom/modified rear intake manifold

Post by riccorman » Sun May 28, 2017 12:45 am

I have a '78 SD which has intake manifolds with 52mm stud spacing. I would like to fit larger carbs than the 32 PHM but when I do (using rubber couplers from Malossi), the rear carb sticks out of the frame so I can't use the sidecover. I think I read somewhere where someone trimmed down the flange on the manifold for this purpose, but I have issue with destruction of an original part.

I discussed this problem with our gracious host Steve, and he mentioned using a front cylinder manifold on the rear to address this problem. Unfortunately, both my front and rear manifolds are identical. I referenced the parts manual and the part number for both the front and rear manifolds is the same. Steve also mentioned that his SSD has a spacer on the rear manifold that rotates the manifold 90deg CCW, pointing the carb rearward, but I don't think this would work with my bike because of the 52mm stud spacing.

Does anyone have any experience with regard to this? Is there perhaps a compatible manifold from another bike that can be used in place of the original? Surely I'm not the only one who has experienced this issue, so I am appealing to the knowledge of the community here for ideas.

Thanks in advance for any/all replies.
-ric
-----------------
1978 Ducati 900 SD Darmah
2001 Ducati ST2
2006 Ducati GT1000
2008 Ducati 1098
2015 Ducati Diavel Titanium #196/500

User avatar
Craig in France
Cagiva Gran Canyon
Posts: 873
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: custom/modified rear intake manifold

Post by Craig in France » Sun May 28, 2017 4:07 am

Hi Ric,

Ok first off, I've gotta ask: why do you want to fit bigger carbs? I assume you're thinking of 40mm, btw.

You won't see any difference in performance unless you also enlarge the inlet tracts of your heads. They are the determining factor here. And with the 52mm stud head, you can't re-work the ports to any appreciable amount without getting into some significant re-engineering.

(What you're proposing is in fact, similar to what the UK importer did in 1979: Imported a Darmah 'special' with 40mm carbs and Contis, but still using the 52mm stud head. Called it the "SD Sport". Contemporary accounts noted that there was no significant increase in performance).

When Ducati switched over to the 58mm stud head, it became possible to bolt on 40mm carbs by using two SS manifolds, part no. 0765.92.580. This is as detailed in the 'Tuning Kit' described in the 1980 parts book. In addition, the 'Tuning Kit' also lists a manifold for use with the 52mm stud head: part no. 0799.88.007.

But beware: the Tuning Kit also included Conti silencers, different cams (from the 900SS) and larger valves. So it was never simply a matter of bolting on bigger carbs.

And what will these bigger carbs do for you? Increase top end, a bit (but not much if you stick with Lafranconis). On the other hand, you risk losing tractability low down.

Also see here: viewtopic.php?t=4732

HTH

Craig

wdietz186
Cagiva Alazzura
Posts: 701
Joined: Sun Sep 10, 2006 5:40 pm

Re: custom/modified rear intake manifold

Post by wdietz186 » Mon May 29, 2017 9:49 am

Craig is on the money. The 40mm Dellorto carbs don't really add anything by themselves, you need cams, pistons, and port work for noticeable performance gains but doing so will affect the tractability. The 40mm carbs are pretty crude and don't atomize the fuel well at low air velocity and getting them to idle consistently is close to impossible. If you are seeking power gains a set of higher compression pistons is the cheapest/easiest route and as you'll have the heads off it will let you check the valves, seats,and guides for wear etc. The 32mm carbs are more than big enough for street use even with hi comp. pistons.

ducadini
750 Sport [BEVEL]
Posts: 248
Joined: Sat Jul 31, 2004 9:54 am
Location: Antwerpen

Re: custom/modified rear intake manifold

Post by ducadini » Mon May 29, 2017 12:33 pm

You could look for some Pantah 36's , best of both worlds.
You would have to modify the standard manifolds and heads a bit but not so much as the 40's.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

tassuperkart
Cucciolo - the Lil Pup
Posts: 2
Joined: Fri Sep 12, 2014 2:48 am

Re: custom/modified rear intake manifold

Post by tassuperkart » Fri Aug 25, 2017 9:01 pm

Agreed
I used 36's on my SSD. They woirked well and consistently.
E

Post Reply

Return to “Carburettor & Fuel System Shop”