200x 83'-85' head flow numbers.

[Mickey Dunlap]

Todays flow numbers for the 200x 83'-85'

When people talk about porting their heads it is very important to flow the heads before and after each mod. As you can see the (Up-Front Racing, my Dads business) Powroll head off my Team Honda 200x at one point my Dad must have replace the valves, but he didn't have a flow bench at the time and he didn't put a 30 degree back cut on the new valve and he missed out on a good amount of flow. This is why if you send your heads out to be ported ask if they have a flow bench, and if you can have the before and after flow numbers.

[Dave8338]

GREAT info, Mickey ! Just looking at the data, depending on where your lift numbers are at, you can gain about as much as going to the 2mm over sized valve, with a 2-step drop on the cam.

[Mickey Dunlap]

GREAT info, Mickey ! Just looking at the data, depending on where your lift numbers are at, you can gain about as much as going to the 2mm over sized valve, with a 2-step drop on the cam.

It depends on what the cam is. Most members don't even know what they get from a cam grinders off the shelf cams. And most off the shelf cams are so mild you really don't get what you pay for. I have a few of Webs off the shelf cams to degree in Friday to see how they come out against my old Powroll race cam. Then I'll start building a cam for my 253cc motor kit.

[Dave8338]

Looking forward to what you find out. All eyes and ears. Are you going all out or putting something together for an all-rounder ?

[Mickey Dunlap]

[QUOTE=Dave8338;1351616]Looking forward to what you find out. All eyes and ears. Are you going all out or putting something together for an all-rounder ?[/QUO

I have a good 20hp all around good kit already, but I want to build a monster for my self and maybe the project 200x for ATV on Demand.

[aramid]

.
Your chart is xlnt.

The 30 degree back cut intake is a very old school racing trick and it helps most at the lower lift numbers . . Once the valve is opened a certain distance, the effectiveness of the back cut is almost nill . . I was doing that on car engines back in the 70’s . . The flow increase at around .150 lift and below in the intake is not very important due to the physics involved but more is still better than less . . The increase with the big valve and back cut is xlnt and I'm guessing that you kinda wish you had that flow back when you were racing . . I would have liked to anyway.

It has been found that back cutting a stock type automotive exhaust valve can actually reduce overall flow in some cases . . I have test results from a stock exhaust valve and Ferrea valve, and the stock one flowed more overall . . I was a bit surprised but it seems to be that the longer face of a stock valve directs the exhaust gas in a more upward direction [which is of course more directly towards exhaust port] than a back cut one in some cases.

As you may know, you can also pick up a little flow by doing at least a 3 angle cut on the valve seat and preferably a 4 angle one with the 4th being in the throat of the port.

You can also pick up a hair by locating the contact area on the valve on the stem side . . This provides the least amount of obstruction by the valve upon its initial opening.

Have you done any testing with back cut exhaust valves?

[Scootertrash]

This is why I love this site. While I may not be able to use (or want to) the type of mods here, I can pick and choose my level of improvements. YOU GUYS ROCK!!!!!

As I explained to a buddy who likes to give me grief about the time I spend modding trikes: "It's not that I necessarily need it, it's there if I want it"

[Scootertrash]

Just so I have something for reference, what is stock 200X hp?

[Mickey Dunlap]

Just so I have something for reference, what is stock 200X hp?

I'll let mike, I mean aramid answer that.

[yaegerb]

Just so I have something for reference, what is stock 200X hp?

13 if I remember correctly.

[Dave8338]

Thinking around the 16hp @~ 8,000RPM mark.

Could be wrong...

[Ol Deuce]

Mickey: is the CC of the 200x head the same as the 185s head?? Ol Deuce

[Dave8338]

Mickey: is the CC of the 200x head the same as the 185s head?? Ol Deuce

Build it... BUILD it... BUILD IT ! ! ! ! ! ! Yes.................................................. .................................................. .................................................. .....................

[Mickey Dunlap]

Well on the Powroll dyno it's 11hp at 4000 feet in Bend OR.

Yes the cc's are the same, the only thing different is the casting numbers, and some casting flow better or are better to work with because of the placement of the seats is just a little different.

[oscarmayer]

under testing and flow bench usage the shop i use for doign all my porting has spent years doing cnc valve seat cutting work as well as valve itself cuts. they have found some of the best angles by doing multiple different shapes and cuts testing to see what works best. cutting the surface of the valve alone is yea an olf school trick that does help some. BUT working the seat as it should be is a totally different animal. You can increase nearly 25-25% of flow over stock by just working the seats and valve face itself. Then with porting we have seen as much as upwards of 35-40% increse on Honda race motors. (these are car motors but the principle still stands).

the 30* angle does help, as mentioned more so for the lower end, but every but helps. I do not agree that that doe not help in the upper RPM ranges. a angle cut to make the air flow better into the chamber is always going to be better than a flat 75* angle like most stucks are. the 30* helps round the corner some and thus promotes better flow.

also what works on 1 head does not always work on another exactly the same. castings shift, porting by hand is not 100% consistant and this there will always be tiny bit of differences. over all as Mickey mentioned, always make srue your porter has a flow bench to back up his claims and proves before and after flow numbers. if he does not or will not, FIND a new porter...

Good luck out there and awesome info Mickey.