Porting and polish 850 head

[Guest]

Hey guys, in the middle of cleaning up an 83 850 head with the 34mm cv carbs, Already cleaned everything up and "trued" / "milled" head surface, I'm using early vm29ss gsxr flatslide carbs so the intake boots already match the carbs, just have to re-space the throttle linkage for the 2 inner carbs to match.

I don't see a lot of casting flaws on the intake side of the head and it already has the larger ports for my carbs so I don't have to "port match" them.

Are their any advantages to polishing the exhaust ports or any tricks that I can do while I have it apart or should I just leave it alone?

The mild engine build is,

-850 top end with 850 cv head (going to use the 750 cams)
-Mikuni vm29ss flatslides from an early canadian gsxr
-APE K&N style pods
-4-1 Yoshimura with Aluminium Can

Bike already has Dyna ignition and 3 ohm coils, sonic front springs, Koni rear shocks, dual front disc from an 83 850G, Ferodo pads,

Any info or advice from our Racers is appreciated,

Cheers

[Nessism]

One thing I've noticed while working on my GS1000 head(s) (and my KZ750 head too) is that there is a sharp corner in the floor of the port (on the short side radius) where Suzuki cut the head for installation of the valve seats. Stick your finger in the port from the chamber side and you can feel the discontinuity. I took a long file and smoothed out this transition. I also ground away any similar edges and casting flash on the ports in the bowl area. I'm not sure how much effect this clean up work has but it made me feel good anyway. I don't think polishing the walls of the ports does anything so I didn't waste any time with that.

[one_civic]

I would only polish the exhaust ports as (at least my theory) would be that it would help lesson carbon build-up on the exhaust side of the head / valve's, but would have no gain in flow.

I don't really see any sharp corner's or casting flash on the intake side of the head. Cyl's. 1-4 are already look pretty good from the factory, cyl's. 2-3 have a little more of a sharper angle but not enough to really do anything with,

As far are re-shaping the intake ports, I would leave that to the Experts, just wondering if I should remove a little of the sharper angle's on 2-3 then scuff them up for proper fuel atomization,

Rapid Ray, do you have any advice?

[Nessism]

I would only polish the exhaust ports as (at least my theory) would be that it would help lesson carbon build-up on the exhaust side of the head / valve's, but would have no gain in flow.

I don't really see any sharp corner's or casting flash on the intake side of the head. Cyl's. 1-4 are already look pretty good from the factory, cyl's. 2-3 have a little more of a sharper angle but not enough to really do anything with,

As far are re-shaping the intake ports, I would leave that to the Experts, just wondering if I should remove a little of the sharper angle's on 2-3 then scuff them up for proper fuel atomization,

Rapid Ray, do you have any advice?

Did you put your finger in the port and feel the short side radius like I suggested?

[one_civic]

Yeah, I going to smooth that out, thanks for noting that,

[one_civic]

Any other recommendations?

[stetracer]

Any other recommendations?

Yea don't use 29mm carbs on a head that came with 34mm carbs. Or you will hurt the air flow.

[GregT]

Yea don't use 29mm carbs on a head that came with 34mm carbs. Or you will hurt the air flow.

The GSXR flatslides he's using are 33mm on the engine side of the slides. 29mm offset intake throats on the airbox side. They flow enough air stock to work well on a warm GSXR1100...And can be bored 33mm straight through if he wants. IMO they'll work very well - and they're very tunable too.

[boris.h]

could watch on my own project / rebuild thread... I'm currently porting my gs 650 head.... A lot of aluminium to remove to get a good ported head...
Moreover, polishing is a good thing to avoid deposits in the head....but: the best way in intake holes is not to polish because the "ganularity" of the surface can "help" air and fuel mixture together
You can follow my thread, I will take pictures of the avancement on my gs 650 head

[Steve]

Yea don't use 29mm carbs on a head that came with 34mm carbs. Or you will hurt the air flow.

The fun part there is that the 850 came with 32mm carbs, not 34.

Not sure where he got his info on the 34 measurement.

.

[one_civic]

Sorry steve, but GregT is right, the intake ports on the later CV 850 heads use 34mm carbs and intake boots, the carbs I'm using came on early 86-87 gsxr 750's around the world except for you guys in the US for emission purposes. here are some pics, I have 2 pairs of these carbs, one for mock up and the other that I'm rebuilding. The VM29SS carbs fit the stock CV 850 intake boots perfectly and cyl.2-3 line up no problem, just have to re-space the 2 outer ones. here are some pics,
would just like to mention that Agemax was a great help, he's in the middle of doing a similar project.
IMG_0365 (1).jpg

[one_civic]

here you can see that the intake boot lines up perfectly,

[one_civic]

IMG_0860.jpg

sorry, here's the pic I meant to upload instead, best thing is I only have $300 invested in the 2 sets of carbs, that includes 4x new OEM carb bowl gaskets, 4x new OEM cover gaskets and a set of Robert Barr's o-ring kit.

[one_civic]

and boris.h I only mentioned polishing the exhaust ports, not the intake for the same obvious reason,

more pics

[Steve]

Sorry steve, but GregT is right, the intake ports on the later CV 850 heads use 34mm carbs and intake boots, ...

OK, now you have my curiosity up.

I have an '83 engine under the bench, will have to check the diameter of the intake ports.

Maybe it's a "US vs the rest of the world" thing?

Your Canadian jetting was just a bit better than ours, maybe you got larger ports, too?

.