PTS Flowbench Forum

I joined this forum about a month ago and I am now making my first post, so please bear with me. I have a highly modified 200cc single cylinder kart motor (Chinese copy of the Honda GX200) and I have gotten to the point where I am sure my cylinder heads are restricting air supply and potential horsepower that this engine could produce. So, I would like to port and polish my cylinder head but I want to be able to measure flow before, during and after I start working on it to insure I am making positive gains. I have attached an image of a mini bench (shop vac powered) that I was planning on constructing and was wondering if this would suffice for only needing to flow 150-200 CFM. Most ported and polished cylinder heads like the one I have max out at 100 CFM. The diagram I have provided shows some dimension and what the interior looks like. There are obviously some things missing like where I would put the cylinder bore opening (3" is all I need but may go to 4"), Pressure Port Pickups, back panel to mount Magnehelic Gauges, etc... Please let me know your thoughts on where to place the cylinder bore opening, whether the orifice plate location is okay, whether the partition would be better shifted to the right, how many pressure pickups to install and where to install them, whether this design even work, etc...

Hi there,

I am sure the more advanced guys can help more but your orifice should be mounted in the center of the divider plate/wall. The way you have it shown in your drawing can cause possible flow issues since one side of the orifice will be so close to the chamber wall. Basically about a 1/3rd of the orifice will try to act like an orifice in a tube and the rest will not. Could cause all kinds of calibration issues.

Do a search on here for these terms:

Settling Chamber
Baffle or Baffles

You should get LOTS of good info on those searches. Things like a formula to determine the correct size of the settling chamber compared to the maximum orifice diameter.

As for bore adapter placement. I am a sucker for details so mine is dead center in the chamber as well. A lot of guys mount them closer to the front of the box (by a few inches) to make mounting the head and possibly the Intake or Exhaust system easier.

For your pressure taps they need mounted away from moving air. Over in a corner or near and edge is good. My inclined taps are mounts in the front corner of the box right near the divider plate. The vertical tap is in the upper front corner. The only time I get any pressure issues is when the head is turbulent. You can hear this though so I know it ISN'T the bench. The port gets all kinds of noisy as it goes turbulent. If it's real bad the vertical and inclined manometers will jumps all around. Typically they move WITH the sound changes. Of course that's also when I know I may have my work cut out for me... Oh, speaking of taps Bruce sells some really nice ones in the online store. They make the process of hooking up the manometers super easy. Drill a hole smear some sealer on the edge and tighten the nut... DONE!

Anyway, I hope this helps.

The best advice I have is use the search feature and READ! These guys are really smart, know their stuff and aren't afraid to help point you in the right direction.

ccm399, thank you for the help. I will start searching those keywords and absolutely try to find that formul for orafice size too.

Welcome to the forum, get yourself some of Bruce's PTS plans, the design may not suit you 100% but you could possibly build half the cabinet as others have done and the plans will give a great understanding of flowbench operation.

Jim

Ebowski wrote:ccm399, thank you for the help. I will start searching those keywords and absolutely try to find that formul for orafice size too.

Beta ratio

Plans are purchased. Starting to research Beta Ratio now. Hopefully I will be purchasing plates and pickups soon!

I bought the plans to convert a pitot bench (car craft mid 80's article) to bruces orfice plate design. It was originally used on car and british bike heads but now I do the Clone heads and needed a greater differential pressure so low lifts and low flow of these little heads would have better granularity on my inclined manometer. It has worked very well for me. much easier to get accurate low lift flow. I just made the orfice chamber in a rectangular settling chamber approx 2ft by 1 ft and plumbed it into the original motor box and head settling box. There are some pics in the plans section you can look at once you get the plans.

Brucepts wrote:

Ebowski wrote:ccm399, thank you for the help. I will start searching those keywords and absolutely try to find that formul for orafice size too.

Beta ratio

Yep, that's the one I couldn't think of last night.