D-port and shell wheel sizes

[Hudriwudri]

Hi,

It's been a lil while as I get been busy with family and projects.
Just did a exhaust D- port weld up with raised floor on a Sr/TT/Xt (I'm currently working on a couple Xt/TT/sr heads so I thought I'm gonna post it as you guys might hopefully appreciate pictures of that kind, despite that the port still needs some fine work.
As soon as I'm done with some of the backlog on custom cylinder heads, I will try to start redoing the heads on my own Xs and see where I will get with measuring and reasoning.

Btw: any of you guys know what the wheel sizes were of the original 70's shell xs Flattrackers? In particular I would need to know the rear rim size, as I would eventually like to have a rear wheel for recreational DT use.
Anybody ever try to use the hub of an early spoke wheel rd 250/350 to be able to use a disc brake?

Thanks and good weekend to all of ya!

Christian

 

[stinky78]

hi Christian, can’t help with wheel size sorry, when you do the XS head make sure you post some pics for us!

 

[Hudriwudri]

Hi stinky,don't worry I seem to have found already tire sizes and perhaps rim sizes of the xr750s which should also do.
Regarding pictures yup I'm definitely planning to do that as I have some wacky ideas that I would like to try and basically have currently almost two spare heads to play with.
First I have to get all the backlog worked off, for the rest I have to get a grip on my procrastinating habits.
But as said I'm curious myself, would love to do it with either the mc30 or mc40 cam but have to investigate first.

All the best and kind regards from italy

Christian

 

[Jack]

Christian........I don't know what method you're using to weld those ports but they look really good! Despite the crude ports on the XS head,they flow
exceptionally well with some work,there's no wrong way of porting them. The exhaust ports depending on the casting can flow around 140 upwards
to 180 CFMs,just depends on the flow ratio you're aiming for. The outer port bowl and wall of the exhaust port is lazy in terms of flow. I've found
that by canting the floor,raising it some by means of welding and turning the the whole port to the exit will enhance the flow ratio. It's a tricky
process as the whole port must be aligned to eliminate port turbulence and there has to be enough material in the short turn for a smooth radius.
If you have a few heads,viewing from the front,look at the left E/P,in most cases it has the most material in the outer portion of the short turn
transitioning up and over to the floor.

 

[Hudriwudri]

Hi Jack,

Thanks for your kind comment, which is really appreciated!
For welding I rely on my lincoln Tig inverter usually i weld all my ports and combustion chambers with my personally developed machine settings (super hard arc high frequency pedal pumping) and as for ports I usually use xxlong cups trying to minimize constant heat input quantity through ampere bursts and highly localized weld puddles (manual pulsing aka pedal pumping as I have already the age for such white beard long hair old schooler antics ahaha)
Thanks for your hints on what to look for as that was exactly what I had in mind as I will try to map the port with my pitot tubes.
For the exhaus ports I most likely will have to fi d some solution as I remember last time I saw them that they are a hint on the wide side.
I'm currently contemplating if I will go to sich lengths to install big valves in order to support the 850/880 ccm of my engine.
Cam I would like to use the mc30 in case I find a nice reasonably priced used one (although I'd love to use the 40 as I love, depending on engine and set up short duration high lift on cams)
Carburetors I will use my dellorto 38 pumpers as I have internal tuning parts in abbondance for the dellorto's.

Big Compliments to your work I have been reading some time ago your d Port post (among other stuff of yours) with very great
interest!

Kind regards and greetings from italy

Christian

 

[Jack]

Use to follow you over at the 500 forum and I have the utmost respect for you. Your workmanship is amazing and your knowledge will be most appreciated by the members of this forum. My opinion on oversized valves is they're not necessary once the short turn height is addressed, how it's moved back ,radius of short turn ,bowl work,guide and boss profiling and last valve choice. D porting taught me alot on how to shift flow and to increase it
without using oversize valves. You'll encounter no problems increasing flow with your talents.
Good Luck!

 

[Hudriwudri]

I have a personal (which not necessarily has to line up with other porting philosophies) porting philosophy in which I try to stuff the biggest valves that an engine "efficiently" can use in my heads.
I'm on my heads not overly worried about lowered port velocities as I regulate them elsewhere in the port where I also have easier command over them. (Sounds easier than it is sometimes in reality)
In accordance with my porting philosophy I usually try to use the shortest highest valve lift in order to not exaggerate on "total" timing area overlap area.
Knowing that in my engine should (haven't opened it yet for lack of time) be something like sr/Xt pistons I would be heavily tempted to see if one could mount valve sizes in the range of +43ish through reinclining the int and exh valves, and to say it in easy sloppy terms building a doubled up tt500 short stroke engine.
First I would have to see how thick the cast skull of the combustion chamber is as I'm at this point not willing to pull the cast skull and go to ramses like pharaonic efforts and destroy some nice sane cylinder heads.
Well however I'm very stoked and super curious on the project.

All the best thanks for the kind comments and attention and kind regards

Christian

 

[TwoManyXS1Bs]

Have a look in here.

http://www.xs650.com/threads/cylinder-head-cutaway.30559/

 

[Hudriwudri]

Late but not forgotten, finally I got my Xs head for some scrutinizing and comparing outta the other garage.
First impressions:
Short side radius on intake port almost not existent but similar to Triumphs and beezas the heavy valve inclination angle helps to cover those short comings somewhat up.
Exhaust port in my opinion a semi disaster, no short side so to speak of in exaggerated terms and the rest of the port way to big in diameter

So anyways @stinky78 :
I kept to promise and will slowly but surely do some analysing, unfortunately can't post pictures yet but I compared the stock port mold with race Sr intake port mold as well as race goldie intake port. I'm still inclined to think that for big bore race purposes it would be interesting to install 44-45mm intake valves in case needed reangled.

All the best and kind regards

Christian

 

[arcticXS]

I just wanna share a picture of a XT250 exhaust port, after just a light cleanup. This port is definitely a D- port from the factory. At 22 hp from 250 cc (i.e 88 hp/liter), the stock specific output is quite a bit higher than the XT500 32 hp (64 hp/ liter) as well as the XS650 (81.5 hp/ liter). Official Hp numbers, so not exactly real world hp. But all from approximately the same era. Maybe the exhaust port plays a part in that? Of course, the shorter stroke, and balance shaft will also allow the 250 to turn higher rpm without issues.