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General Category => General Discussion => Topic started by: harrytief on December 15, 2016, 11:16:42 AM
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I want to install 36mm dellortos in place of the 30mm vhbs on my cx100. I know that the intake ports need widening and smoothing but l want to avoid pulling the heads for machining if possible. How concerned should l be about going at this in situ with a dremel? What to look for? Anyone with before/after pics?
TIY
Harry
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Harry,
I had this done by Ed M. on my super Lario (30 to 36). It appears he left the head side as is and used the original 30 tracts. What he modified was the outlet side from the carbs by having a guy add steel (welding), then ground the OD to fit the carb. I'm certain it's also tapered inside to meet the original dia. part way down. In other words it's all original at the cylinder side and most of the entire way through.
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I know very little about porting and polishing naturally aspirated engines. So I went a-googling, and decided that I know less than I thought and there's people out there that know less than I do.
I realize that what you're discussing is not head modification, but I caution against any work that risks leaving dust or chips in the passage. Repeat, caution.
I've heard conflicting opinions - it seems logical that modifying any abrupt transitions between inside diameters would be good, but beyond that I'd be uncertain. I saw evidence in my Eldo intakes that somebody had cut in a basic swirling pattern on the intake side, but I don't recall if that was in the head or the carb/head junction pipe. The logic appeared to have been that encouraging air to mix with fuel was a good thing.
Again, untutored, and I've only looked, not modified.
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I've heard conflicting opinions - it seems logical that modifying any abrupt transitions between inside diameters would be good, but beyond that I'd be uncertain. I saw evidence in my Eldo intakes that somebody had cut in a basic swirling pattern on the intake side, but I don't recall if that was in the head or the carb/head junction pipe. The logic appeared to have been that encouraging air to mix with fuel was a good thing.
I had the heads gasflowed on both my Ducatis. The job was done by a renowned engine tuner, backed up with years of experience and use of a flow bench, the results were very good; around 15% power hike (combined with other mods).
Anyway he left a 'rough' finish on the intake ports and manifolds, to create turbulence to help with flow & mix and a smooth finish on the exhaust side for a quick, unimpeded exit of gases - there is obviously more to it than just the finish but, hopefully of interest...
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Why would you want to port a head in situ?
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kevdog - how much of a change was there by adding the larger carbs? I've been thinking of going up in size from the 30s on the T3. I've got some 38 Dells I might try, or possibly watch for some 36mm flat slide Mikunis. I'm really curious just how much of a difference larger carbs make.
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Harry , that is a lot of metal to remove with a Dremel tool , it is gonna be hard to keep the shape right . Oh , and the heads will have to come off .
Dusty
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With projects stacked up as far as the eye can see...and now fresh snow to shovel that will help pass the evening...i was tempted to look for a shortcut. Thanks guys for reminding me that there are none.
;-)
Harry
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36mm porting from LeMans workshop manual. Click on pic. it should expand.
(http://thumb.ibb.co/gecJwF/36mm_port.jpg) (http://ibb.co/gecJwF)
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kevdog - how much of a change was there by adding the larger carbs? I've been thinking of going up in size from the 30s on the T3. I've got some 38 Dells I might try, or possibly watch for some 36mm flat slide Mikunis. I'm really curious just how much of a difference larger carbs make.
Well, I can't attest to the changes the carb swap alone made, as I had lots of head work done as well. Is there evidence of someone going to 38's on the T? Guzziology suggested that the Lario could handle 36's. That along with larger valves made it a no-brainer to try. It turned out brilliant, but I wouldn't have a clue about whether or not moving to larger carbs on the T will get you much or work as well as what you have. Let us know your findings.
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I want to install 36mm dellortos in place of the 30mm vhbs on my cx100. I know that the intake ports need widening and smoothing but l want to avoid pulling the heads for machining if possible. How concerned should l be about going at this in situ with a dremel? What to look for? Anyone with before/after pics?
TIY
Harry
I've done port matching on cars a couple times with heads in place. Your success has everything to do with your preparation. I use a piece of closed-cell foam cut approximately to port shape, give it a thin coat of grease and plug the port below where you are working. Be certain the intake valve is seated completely as well, of course. Poke a hole through the foam and pull a string through it so you can remove it when you're done. If the foam is shaped right and compressed enough, it will wipe the port walls and any debris away on the way out. Use a shop vac with the tip as near to your work area as possible to suck out chips as you go.
Personally, I'd just remove the heads-it's a good opportunity to check valve seats etc.
Given that you have no open areas elsewhere on the engine, should be easy enough. The shapes, tapers, etc. are entirely up to you and your research.
What valve sizes does that engine have?
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I ported and polished the Mille heads myself. The butt dyno tells me I have a smoother running engine, better fuel mileage and improved top end. The carbs are still 30's with jetting increased by 10% and Lafranconi Copetizeones. By far, the major grinding occurred at the valve seat to head junction. The alignment was horrid. More than half of the seat was proud of the inlet tract by 1/16 inch. I used a Dremel with a flex extension followed by a polishing of the exhaust ports to a mirror finish. That reduces carbon buildup. The intakes were hand/finger finished with 60 grit paper. This leaves a rough surface with more area for fuel to emulsify and a bit of turbulence. Put a drop of fuel on a piece of glass and nail file. Blow gently and see which one evaporates faster. As for shape, I used a very bright flexible inspection light to reveal shadows behind the peaks. Looking from both valve and port opening ends, I inserted the light from the other end and very slowly advanced it towards my viewing position. Time consuming but very rewarding.
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Thank you all for your replies.
The take away, as I am seeing it, is that for the job to be best done, the heads need to come off. Any less and I am not getting my money's worth in buying the carbs in the first place (guzzi content). Redrider, if you are in the neighbourhood, drop by and do mine as well...I admire your intensity.
Harry
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Good conclusion, imo. Aside from the danger of getting crud inside, it's darn inconvenient to get around the circle with the head in place. :thumb:
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PM sent
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I used a cnc machined inlet manifold from HMB-guzzi that lets you mount the 36mm dellortos on the small valve heads. It lines up with the head surprising well, but should only be seen as a temporary solution. The right thing to do is to port the cylinder head to match the bigger carbs. Oh, and the model I have is a straight manifold so you can't use the standard airbox.
And :1: to reriders comments. Taking the heads off allows you to fix the ports all the way up to the valve seat and if the work is being done already with the head and valves out, it should be considered to recut the valve seats to improve the flow as well.
I used the inlet manifolds because the main goal was just to get the bike running at that point. When I return home to Denmark I will start the work on porting and dual plugging an extra set of cylinder heads I sourced.
-Ulrik
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I have had the 36's on my CX for about 10 years? Anyway, I never did this modification and not because I don't won't to do it but it just never got done. The last time I had a valve job on the heads, the shop was suppose to modify the inlets but they didn't do it and I needed to get the bike running. Likely, it is not getting the full effects of the carbs, but I can live with that. Maybe next time I pull the heads......