Tractorsport Flowbench Forum Archive

Posted: **Sun Mar 02, 2008 11:17 am**

Bruce you may have an idea about this since you have done alot of work on your Kohler Flat heads. I must say that my bench built from Bruce's plans is working great. What I'm looking for input on is trying to increase flow on my 12hp briggs motor above .350 lift. I've worked on the intake, intake port, and head, but my flow from .350 to .450 lift does not change. It holds at 92cfm. Would a larger intake valve help or have I reached the limit of my flat head?

Edited By larrycavan on 1204511258

Posted: **Sun Mar 02, 2008 10:27 pm**

Posted: **Mon Mar 03, 2008 7:07 am**

Boy do I look dumb. Looks like I have some things to do yet and learn with this flow bench. What is MCSA and Dead down the middle FPS? How do I find out what my valve coefficient is and cfm/sq in.? I can answer one question. My test depression is 28in. I'll do a test with the valve removed.

Let me give a little history on the motor and why I'm asking about flow in this range. The motor ran good last year with a cam that has .395 lift. and would turn up to 6600rpm down the long staits. This was with the manufacture recommendations on rpm. The motor displaces 31cu in. This year I'm trying a bigger cam with .450 lift that will probably go 7500rpm.

When I started using the flow bench, I was able to gain flow in the low and mid lift ranges by working on the intake manifold and grinding the head away near the edges of the valve. With this work, the lifts above .350 have not changed much. I don't want to go bigger with the port because I want to keep my torque off the corners. I do understand that I may have reach my limit and this cam may be to big, but you don't know until you try.

Posted: **Mon Mar 03, 2008 8:13 am**

Posted: **Mon Mar 03, 2008 11:21 am**

In trying to understand where the limitations of the head I was working on were, I made a 1" thick template of the port. I put my inlet plate on it and found that it flowed about 150 cfm at 28". My thinking is that this gives me an idea of what the max theoretical is for the port. Until I get the port close to that, and 90% is probably as close as I will get given flow losses through a 4-5" port vs. a 1" section, I still need to work on the transition, bowl, valve throat, shrouding, valve size etc.

Does this make sense? Am I on the right path? Sorry for looking like a hijack, but this seemed like the questions you were asking.

Mike

Posted: **Mon Mar 03, 2008 12:00 pm**

Have you done anything with the seats and valve faces? Seat width and angle plays a big part in how a flathead flows.

The air has to make the turn into the chamber not shoot straight up into the head.

Posted: **Mon Mar 03, 2008 1:02 pm**

Ken,

I am assuming you are testing via sucking through the crankcase with the head installed, Am I Correct here?

If so before you make any changes and during your testing no valve and with valve, take 3 to 5 head gaskets and retest adding one at a time (Stacking), compare the data.

My thinking here is you are adding lift and in a flat head at the same time you are equally shrouding the flow over the top of the valve by the increase in lift. You will need to think of the cylinder head as an extension of the port. In OHV engines we are fortunate to have the valve in the middle of the combustion chamber, but in side valve motors the Head, Deck and valves are all part of the flow path.

Just some things to think about.

Rick

Posted: **Mon Mar 03, 2008 1:33 pm**

Geez Rick, you're giving Ken all the hints!!

Edited By bruce on 1204565638

Posted: **Mon Mar 03, 2008 1:51 pm**

Posted: **Mon Mar 03, 2008 2:05 pm**

Posted: **Mon Mar 03, 2008 3:40 pm**

Bruce,

Sorry just talking about trying to make more power gets me going even if it is a Kohler or BS, cut my teeth on a Clinton 2.5HP :-)

40 plus years ago.

In your projects, not sure if you are cast iron or Aluminum block but have you looked at changing the valve angle off 90Degs? Tilting toward the piston.

Rick

Posted: **Mon Mar 03, 2008 8:37 pm**

Now this is great. I have a whole lot to look at with some intellegence. I didn't want to go grinding blindly. Larrycavan don't worry about me taking what you said the wrong way. I was just feeling a little overwelmed. 1960fl I did try adding a couple of head gaskets and it didn't make much difference, but that was before I relieved the head around the valve. I going to look at it again with also relieving the head gaskets the same as the head and adding more head gaskets. Larrycavan, 1960fl, MMack and Bruce thanks for the ideas and info. Its time run some more test with the bench.

Posted: **Mon Mar 03, 2008 10:05 pm**

Yes "grasshopper" get flowing those flatheads . . . and to think 3 months ago you had no idea what a flowbench could even do!!

Posted: **Sun Mar 09, 2008 7:56 pm**

Thanks for the help guys. I was able to gain an adverage 10% in flow accross the range of lifts with your help. I might add that this was done without increasing the diameter of the port or intake manifold, just working on the seat, short turn radius and turns in the intake manifold, so my port velocity should be maintained. I'll know more when I purchase a pitot from Bruce. Thanks again.

Ken

Ken

Posted: **Mon Mar 10, 2008 9:21 am**

Get youself ready for real eye opener when you get the pitot.

Tractorsport Flowbench Forum Archive

Flow above .350 lift on flat head