Carb swap

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i fitted the bigger Amals on small port standard head w/o an issue but the cosmetics of the lip of the head meeting the manifold which seemed to help lower rpm response and gave plenty of top end over 100 mph. Would be interesting to try it first w/o blending then later grind to match and see what ya notice.
 
You will need the correct manifolds, 32mm at the carb end tapering down to 30 mm at the head.
 
Bernhard said:
You will need the correct manifolds, 32mm at the carb end tapering down to 30 mm at the head.
Click to expand...
Hi,
do you think this measurement are very exhactily?
It seem a little more at the head (28,9).
Ciao
Piero
 
My Ms Peel used a 32 mm x 32 mm manifold just fine with good response and torque though may of cut down top end above 120 mph some. If ya get a chance to compare the tapered or straight + lip manifold and tell us if ya can even tell and if so which was nicer.
 
pierodn said:
Bernhard said:
You will need the correct manifolds, 32mm at the carb end tapering down to 30 mm at the head.
Click to expand...
Hi,
do you think this measurement are very exhactily?
It seem a little more at the head (28,9).
Ciao
Piero
Click to expand...

Obviously, the ports /manifold should blend into one another with no steps.
You do not get a blueprinted engine when it is mass produced.
 
Unless you are trying to get every ounce of top end power it doesnt make much difference which manifolds you use with what carb or head combination. Although usually referred to as 30mm heads most I've seen are around 28 - 29 mm on 750s anyway.
 
Small Commando port heads are usually officially listed as 28.5 mm but we know the factory tolerances not so accurate to .5 mm nit pick. Heck I've measured a pair of brand new out the box 939 Amals with that much off in bores and flange flatness. You may find the extra response [turbulence] below 100 mph is more pleasant and enjoyed than hanging on for over 1/2 mile to let the top end power differences show up. But if you let on that you have not optimized for max performance for dyno and road power contests you will loose points of respect here, so don't admit if ya land a foot in hobot camp. Do note the comnoz showed us the slowing down of port flow by funneled down tube so your call. I'd sure like to hear from someone [privately] if they have tried the experiment of both ways to do the 32mm carbs to 28 mm port manifold. We see how many on this forum reacted reflexly negatively to put down an active fella here that stated by far his best performance mod was gotten for a big single car, yuK. Could fill the manifold with JBW and hog it out before more serious permanent grinding on head lip.
 
hobot said:
Small Commando port heads are usually officially listed as 28.5 mm but we know the factory tolerances not so accurate to .5 mm nit pick. Heck I've measured a pair of brand new out the box 939 Amals with that much off in bores and flange flatness. You may find the extra response [turbulence] below 100 mph is more pleasant and enjoyed than hanging on for over 1/2 mile to let the top end power differences show up. But if you let on that you have not optimized for max performance for dyno and road power contests you will loose points of respect here, so don't admit if ya land a foot in hobot camp. Do note the comnoz showed us the slowing down of port flow by funneled down tube so your call. I'd sure like to hear from someone [privately] if they have tried the experiment of both ways to do the 32mm carbs to 28 mm port manifold. We see how many on this forum reacted reflexly negatively to put down an active fella here that stated by far his best performance mod was gotten for a big single car, yuK. Could fill the manifold with JBW and hog it out before more serious permanent grinding on head lip.
Click to expand...

Mike you may find out (possibly) That small port story comes my dyno story about the 92 INOA/NNENO rally dyno session on my combat 32mm carbs/manifolds... on a temporary 28.5mm RH1 head. I think this is the actual head...cleaned up and now on the shelf.
http://atlanticgreen.com/images/nhd70slg.jpg
It is a 1970 head, not a 71.
 
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