Author Topic: Which head to modify?(Opinions) Late model Alloy heads. (Dual carby conversion)  (Read 1124 times)

Offline Sluggo

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Looking for input.  Here is the basics:  On my early rigid frame project (The one with the Super flash style dogleg) I am going to run a late model alloy head on it and after many years of study of factory and modified dual carb heads will be doing one myself. 

First order of business-  Which head to use?  I have several alloy late model heads and checking casting numbers i have 2 types to choose from.  57-1126 or 67-1549   The 1126 heads I have appear to be late 50s Super rocket heads and the 1549 heads were of the early 60s version, SR & RGS,

I have not flowed them or done any port modeling to see if there is significant differences but soliciting opinions on which one would be best suited to a dual carb modification.

(Not interested in a dual carb vs single carb discussion, that is not what this is about and well versed in that topic)

This is for a mild performance hot rod BSA built as a tribute to the BSA Daytona racers but street legal.  So the topic is, which head would be the BEST candidate for this modification.
Bigger is not always better, velocity wins on the street but these 1950s castings could probably be improved on so,,,,,,,,,,,,

#2) I have access to a few guys who are well versed in vintage cyl head mods and considering having it reworked somewhat for improvements as well.  Any insights or topics I should look at for alloy BSA head mods?  Not looking to reinvent the wheel here but if someone documented stupendous improvements I would be very interested in hearing about it and analyze what was done.

(One source might be Baisley performance,  Back in the day their cyl head work was transformative on even a basic rework,, I rode Sportsters, Triumphs, BSAs and Nortons they did the heads on and it was night & day difference.  And,,,, trivia tidbit.  Baisley had a lot of input on the design of the modern Norton cyl heads. See: http://www.baisley.com/services.htm   )

#3) I will be looking at several options for the carb intakes and type, and will be happy to update with pictures and what I end up with.  Machined flanges with bolt on intakes or welded on stubs and race style spigot and hose coupling.

#4) carb type,,  There is a lot of options for carbs and this is likely to come up but while I am huge fan of some of the modern Mikuni and Keihin flat slide and round slide carbs I want it to look period correct so at this point will likely run some reworked Amal Monoblocs as I have some Handed (L&R) sets I have stashed.  Not the best carb in the world but that could still change.

Will update with pictures and details over time but again, first order of business is WHICH head to start with??  (I would like to narrow down what I am keeping and sell off the excess to help fund the project)

The motor at this point is not revolutionary.  Early 50s A10 with late model crank, upgraded rods, higher compression pistons, 356/357 cam and a few other tweaks but nothing earth shattering.  Basic 50s hot rod is the goal
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Offline rocker21

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Online Black Sheep

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On my shelf I have a bizarre modification. A twin carb alloy head which has had a single carb manifold rather badly welded onto it. An odd thing to do...
2 twins, 2 singles, lots of sheep

Offline Sluggo

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Thanks guys,  The antlantic green site is Dyno Dave, a great source of knowledge and expertise. He also does some great stuff with Nortons.  I make a point of reading anything he writes whenever i can find it.  He also sells manifolds for people who want to do these conversions as well.  So, yep, I knew about that site but what I was hoping for is some feedback from anyone who had done any testing on flow, or performance. 

In the end, I dont think there is any great difference that is discernable or will matter that much, but its one thing to think it and another to KNOW.  I am all about learning from others.

 Intuitively the slightly larger valves would seem the way to go, but in the real world that is not always the case. (especially from Idle to 4000 rpm-   A cam or head that only shows a big difference above 4000 RPM is not really relevant here)  So, it might seem odd that I am going twin carb because the reality is a single carb is better for torque and low rpm but this is a project that is about how it looks as well.

Black sheep,, do you already have pictures posted of that weird cyl head?  If not post it here!
Would be cool to see,, I bet Dyno Dave would like a copy for reference.

Myles Raymond (From Scotland) used to have a great website up, it crashed and some great material was lost, he has another page up now. Is he on here?   Many years ago I exchanged emails with him for a while.
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Online Klaus

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Hi Sluggo,
I had some twin carb heads but only one is tested. At the racer, the last 3 years, I had a 1549 big valve converted to one spring with alloy collars. Cam is a slightly regrind 357, Carb was Mikuni. This engine was tested at the dyno with 44 PS/ 6000 a the clutch and 47,11 nm/5500 torque.
With a little luck I could bought an 1106 with two Concentrics 28mm ready to fit. I aimed to get more revs with the twin carb head, but non, the same as with the single carb, deadline at 6500. No test at the dyno.
 By  concidene I could get another 1106 with the manifold to single carb. I was surprised that the ports are only one inch. The only two differences to the 1102 (A7SS) twincarb are  the smaller valveseats, and 68mm combustion chamber, this head has  allso the 1 inch ports.
These heads are ready to fit but not testet.
A new build up engine with a Megacycle cam, 10.5 compression ratio pistons, a ported 1106 with 389 copped monoblocks is ready for some test after ending the race season.

A cracked valve punched one chamber of an 1571 very hard, so I decided to weld squishing edges for a better combustion and more compression. This head is on an engine with a regrind 356 cam. Hard to kick down but a realy fine touringengine. Carb is 389 Monoblock with pancake. Test at the dyno 48PS/ 6500 at clutch and nearly 50nm/ 3600 torque.
It depends on so many factors, what you get at the end. But I gues twin carbs only get a little more performance at high revs.If you want to have a sporty and special locking engine twin carbs are a good choice but overrated.

Converting a single carb to twin is a lot of work and welding. I have done this with a wracked 1126, big valve 1.5 inch ported to 36 mm
squishing edges, but no engine for this head.

cheers Klaus


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Offline Sluggo

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Thank you very much Klaus, that is very helpful information.   
Sometime later this month I will take some of the heads in and see what a local cyl head shop have to say.  Mostly these days they just do Harley stuff, but they used to do a LOT of British bike heads back in the day.

I have not yet resolved whether to weld it up, or just machine it and use manifolds but the Dyno Dave manifolds look like an attractive easy solution.

I am NOT looking to get as involved or intensive surgery as this head, but thought you folks might find it of interest.  Sadly,, I dont think it will be used in the future as the new people on the project feel the design and changes were incorrect.  (I Disagree) 
A LOT of work, design, research and thought was put into this head, the ports extensively reworked, intakes modified, combustion chambers modified and a lot of custom valve work went into this.  The gentleman locally who did some of this (Group effort) is well known for his racing engines with the local road racing community and has many years of experience.

If you are wondering, Research SINGH Grooves for combustion chambers.

(BTW< this is the head for the worlds fastest vintage 500cc pushrod twin, holds 2 records.)
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Online Black Sheep

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Sluggo, here's the modified head. An engineering triumph. Or something. Still, not an impossible task to undo the botchery.
2 twins, 2 singles, lots of sheep

Offline duTch

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Sluggo,......................... An engineering triumph.......................................
  *eek*


 Not quite sure how to take that *conf2*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline Sluggo

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Sluggo, here's the modified head. An engineering triumph. Or something. Still, not an impossible task to undo the botchery.

Oh good lord that is so ugly it is almost beautiful!  Thanks for posting that.  Now that you set the bar it will effortless to surpass it.  I bet if you set it up in a milling machine it would clean up,, the issue is the rest of the casting.

I have some other heads that are mystery custom jobs, some might have had a sensible goal in mind and just never completed, others were on a par with your head.  They came in parts piles and the bodgers are long gone, dead or lost in mystery and can only speculate what their intent was.
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Offline Listerjag

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I have been modifying my Super Rocket head for squish and port/filling velocity. I have used an A7 head because it has smaller ports, chambers and valves.
 From what we could see on the flow bench the 500 head flows more air than the bike could use unless you are going to rev it higher than the motor could possibly stand.
 I will try posting pic's of my chamber and piston crown.
The pistons protrude slightly up above the barrel and have the area below the squish bands machined to give me 0.028" squish and 9.2:1 compression ratio.
 I will let you know how it goes.
Good luck with your project!

Offline Sluggo

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Aha!  there we go! Ding ding ding! *beer*, Real world testing!  You are entirely correct that often times smaller IS better, seen it a ton of times with car engines.  On the street its off idle to 4k most of the time and where to tune to.
I most certainly would welcome any and all input you may have.  And by the way, your oval combustion chambers resemble to some degree that heavily modified Norton head above.

What pistons are you running may I ask?  I have some Norton ones like that with slightly domed tops.  I am wondering where you might source some like that for a BSA Twin.  Piston offerings are rather sparse it seems. 

In your quest for speed read up on Singh,,  We found exceptional results by following this path.
Sadly, the current tuners of that engine dont know or dont care and last I heard are going in another direction....  (Oh well!)  There was 15 years of development into that motor so it was not by accident.

See: https://www.popsci.com/cars/article/2004-09/obsession-mr-singhs-search-holy-grail
(A bit wordy but the meat of the matter is buried within)

See: https://somender-singh.com/

See: http://www.herningg.com/singh/  (See all the pages, but its well documented)

See: Some negatives, some positives. I CAN say theres a bunch of race engines in the NW here running these grooves, but I dont have any feedback or experience with a street bike.  But it should be of interest to you.

I found on a number of Triumph 650 builds that a single carb head, smaller valves, and certain cams made a nice torque monster.  Compared to big valves, dual carbs and bigger ports.  On a Triumph unit 650 and head post 1971 on average flows 30% better than earlier heads, but an early small valve head was faster.  This replicates my experience with some of my V8 car engines.  In my young days I was convinced I had to run the biggest valves, ports and cams to match.  Went like stink at high rpms but was a dog around town and truthfully ran like crap at anything below full throttle.   In comparison I had a 283 SBC with cast iron 2 barrel manifold, small ports, small valves power pack heads and a lumpy but conservative cam,
That thing ran circles around the other motor off the line and up to 70 mph.  It also got outstanding MPG and was very smooth and responsive.  Somewhere in between is a sweet spot.
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Offline duTch

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Aha!  there we go! Ding ding ding! *beer*, Real world testing! .......

 Is that something along the lines of venturi effect ?

 With regard to the tri..spit cough heads, I haven't had much to do with them apart from my '69 Daytona, and a very bitza pre-unit trike..., but was told that the trophy *?* heads had better flow than the Bonnies because the flow is more straight across whereas the Bonnies are in and radically change direction for outflow...??
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Listerjag

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Aha!  there we go! Ding ding ding! *beer*, Real world testing!  You are entirely correct that often times smaller IS better, seen it a ton of times with car engines.  On the street its off idle to 4k most of the time and where to tune to.
I most certainly would welcome any and all input you may have.  And by the way, your oval combustion chambers resemble to some degree that heavily modified Norton head above.

What pistons are you running may I ask?  I have some Norton ones like that with slightly domed tops.  I am wondering where you might source some like that for a BSA Twin.  Piston offerings are rather sparse it seems. 

In your quest for speed read up on Singh,,  We found exceptional results by following this path.
Sadly, the current tuners of that engine dont know or dont care and last I heard are going in another direction....  (Oh well!)  There was 15 years of development into that motor so it was not by accident.

See: https://www.popsci.com/cars/article/2004-09/obsession-mr-singhs-search-holy-grail
(A bit wordy but the meat of the matter is buried within)

See: https://somender-singh.com/

See: http://www.herningg.com/singh/  (See all the pages, but its well documented)

See: Some negatives, some positives. I CAN say theres a bunch of race engines in the NW here running these grooves, but I dont have any feedback or experience with a street bike.  But it should be of interest to you.

I found on a number of Triumph 650 builds that a single carb head, smaller valves, and certain cams made a nice torque monster.  Compared to big valves, dual carbs and bigger ports.  On a Triumph unit 650 and head post 1971 on average flows 30% better than earlier heads, but an early small valve head was faster.  This replicates my experience with some of my V8 car engines.  In my young days I was convinced I had to run the biggest valves, ports and cams to match.  Went like stink at high rpms but was a dog around town and truthfully ran like crap at anything below full throttle.   In comparison I had a 283 SBC with cast iron 2 barrel manifold, small ports, small valves power pack heads and a lumpy but conservative cam,
That thing ran circles around the other motor off the line and up to 70 mph.  It also got outstanding MPG and was very smooth and responsive.  Somewhere in between is a sweet spot.

 Thanks for the links. I have not heard of this development, I would be keen to try it as it seems to give best of both worlds.
The pistons are standard flat top IMD 8.25:1, with 0.6mm machined off under the squish lands and a deeper intake valve pocket.
 The flow bench results are at work but from memory a super rocket head just about flows as much air as the motor can consume through just one port :-)
 What got me keen to try this mod was an article I read on the forums about an owner that had a 650 A10 that went a lot better than it should have, he stripped the head off to change the valves and found the Super rocket valves he bought were too big and the bike had flat top pistons, it was basically an unmodified A7 head on an A10, which would have given him a little squish.
 I have always run the bike on avgas which can be a pain if you are travelling.
 I am hoping I will get better combustion and it won't be so sensitive to fuel.
 If you are interested I can let you know the cfm's for the different heads.
Thanks again for the links :-)

Offline Sluggo

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Well, I cant say if the unit 100 heads,,,how exactly they compare to 650 unit

 (*Wait, on Triumphs Tiger & Trophy was used on a lot of 500 & 650 models interchangibly so its confusing to use those monikers)

BUT...... T100 unit 500s my understanding from source materials from Stan Shentons Triumph Speed tuning, some of David Gaylins "Triumph in America"  Mick Walkers "Triumph the racing story"  All seem to suggest from my takeaway that there is 3? variations in the 500 unit heads.  The early Hemi combustion chambers, later chambers were less domed/dished and then allegedly the valve sizes were increased in the later years with perf improvements to the Late Daytona heads.  What I have heard is that SOME builders prefer the early Hemi heads on a 70 and later Daytona 500 unit bottom end as well as later R type cams.  But not evryone shares that opinion. It comes down to your beliefs about tall domes versus small snow cone domes and how you set up the motor.   (Compression ratio plays a huge factor here as well as fuel quality and spark but in a race motor there seems to be consensus that the hemi chambers and hi- comp pistons are good for high rpm racing.

I dont know about the ports between a 500 and 650 unit. It would take me quite a few hours to go thru all my books,  Some of the guys who did a lot of that head stuff around here are no longer around and most died in the last 5 years or so, so my ready source of info is limited.

But there is an old racer who is pretty famous up in Spokane and he told me the BSA A65 heads are WAY superior to anything triumph ever built.  He said their cams are better factory stock from the factory and the heads are better and only fault is that the cam is a single cam and not a dual Int-exh like a Triumph.
He is known as Captain Dirt.  And a legend in racing circles.

But I have NO input on comparing them to a preunit BSA head,,  and not many people doing anything with them these days.  At some point I will take some heads in and just for grins see if I can get some flow work done for base measurements.   I dont know when yet, but I think it would be interesting to see.

So much flow and testing has been done with Nortons, and Triumphs but most BSA people just seem to run whatever they have available.  Hence, my asking about any real world testing of BSA heads.  If you guys know of any  material I would find it interesting and I think it would informative.

## Here is what Capt Dirt told me about BSAs,, now this was MANY years ago, and sometime later he had no recollection of the conversation, Factor in some of these race guys tend to make up some wld fabrications or even deliberate MIS-Information so take it all with a grain of salt.##

I started with asking about Timing side bush vs bearing conversions.  He said they built a LOT of race motors and if the cases are blueprinted, all the specs are optimized and you ensure good flow of oil the bushes hold up just fine in racing.
#2) He said the A65 heads were better than any Triumph. The hot factory cams were good as anything in the aftermarket except for a long track miler.  He said modify the rods with a steel cap off a Norton, use new rod bolts and resize to tight tolerances.  & Polish the rods.  Measure the Lightest 650 unit Triumph crank (They played with the factory weights over the years) and lighten the BSA Crank to that same weight.  (The BSA is super heavy).  Then dynamic balance the whole thing.  (A little more about ignition and carbs too)  But he said that motor set up that way makes a very potent race engine for short tracks and loose dirt.  He said the heavy cranks on the BSA Is their only bad feature.  So,,, about 6 years back I setout to replicate what he told me.   I would not say its a good setup for a street bike you want to ride a lot.  The guy who ended up with it said it was scary fast and spun up like his 2 stroke dirt bike.  He really liked it.  But while that was fun,, getting the crank lightened was a very arduous journey and balancing was very challenging.    In the end,, for a hot rod it did exactly what Capt Dirt said it would.  But I would not recommend it for a road bike you want to plonk around on daily.

Sadly we lost another great mind some years back,

" December 11, 1939 - February 27, 2014 Jim (Capt Dirt) died on February 27,2014 from pneumonia, he was 74 years old. He was born December 11,1939 in Spokane Wa, a son of the late Theresa (Perry) Poffenroth and Manuel Poffenroth. Jim had many talents and trades working as a welder/fabricator, machinist, and glaser but, most will remember him for Captain Dirt's Racing. Jimmy had a passion for all things with wheels from the drag racing/car racing days to the motorcycle weekends. He especially loved building bikes with his much loved friend Matt James. He was an avid collector of almost anything"
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Offline Sluggo

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" Thanks for the links. I have not heard of this development, I would be keen to try it as it seems to give best of both worlds.
The pistons are standard flat top IMD 8.25:1, with 0.6mm machined off under the squish lands and a deeper intake valve pocket.
 The flow bench results are at work but from memory a super rocket head just about flows as much air as the motor can consume through just one port :-)
 What got me keen to try this mod was an article I read on the forums about an owner that had a 650 A10 that went a lot better than it should have, he stripped the head off to change the valves and found the Super rocket valves he bought were too big and the bike had flat top pistons, it was basically an unmodified A7 head on an A10, which would have given him a little squish.
 I have always run the bike on avgas which can be a pain if you are travelling.
 I am hoping I will get better combustion and it won't be so sensitive to fuel.
 If you are interested I can let you know the cfm's for the different heads.
Thanks again for the links :-)

I would very much appreciate any specs, measurements and insights you might already have or can do with heads for these BSAs...  In fact I cant speak for everyone here but I think it would be very useful if you posted it up as a separate topic, much like dyno daves page on BSA heads, with his info on what they look like, and your measurements that would be a great resource IMHO.

Are you in NZ or Australia? I apologize for not knowing but the little flag I cant quite tell with the small icon.
Shipping is prohibitive just for experimentation, But I have a friend in Christchurch who at one time offered to do some head mods for me.  At the time he had access at a Jet Engine test center to all kinds of tools and equipment.  But shipping over a crate of Triumph-BSA and Norton heads was not in the cards.
But, if you guys like gear head projects, he has a wide range of them to review.  Smart guy,, Good friend.
See: http://www.retrotech.co.nz/   

Cars and motorcycles (Not everything has been updated) but good work with blowers-Turbos, EFI, cyl head porting, engine builds and plain wackiness
Remember that any advice received on a free internet forum is generally worth about 1/2 of what you paid for it.
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