Homebrew Head Porting: Attempting the dark art .....

[911st]

[kenikh]

Originally Posted by Steve@Rennsport

Hi Sherwood,

A few observations, if I might.

Thanks for jumping in and clarifying, Steve. Steve has been the master architect of my motor and specced and sourced the head work.

GOD, I wish I could assemble this motor soon - the flow bench numbers on these ehads are just rotten good. Too many irons in the fire.

Great work on the flow bench - this thread, along with Mark Jung's MFI dyno thread and Jeff Higgins MFI pump threads are why I come to Pelican every day.

[Gertvr]

Its been a while since i updated on my progress. I, like Kenikh above, have way too many irons in the fire

I have not changed much on the inlet port since the last update, only port matching to the inlet manifold. I had to open the port face to 42mm to match the PMO manifold and blended it back to the port original size in 1/2". This increased te flow to 275 CFM and the velocities as indicated in the port map below. I am satisfied with the flow and velocities and will go with what i have for now. Next step would be to test these in real life.

I found another interesting formula for calculating port velocity based on engine size, port area and RPM indicating that the current flow is sufficient. Here goes:

LPV= 0.00353*RPM*S*B2 divided by CA

LPV= limiting port velocity
S = stroke (2.771)
B = bore (3.74)
CA= min port cross section @ 40.3mm (1.97sq-in)

LPV @ 7525 RPM = 278 FPS




Below is the Entire inlet flow map without air filter




I am not making any more changes to the port until i have the final valve job completed. I have in the mean time decided to not use the SI stainless steel valves and will go another route with 8mm valve stems. There is still some flow to be gained especially in the SSR as the velocity in this area is pretty high. I will work on laying the SSR back some after the heads come back from the valve job.

I am copying the design to the other ports using cross sectional templates to get things as close as possible between the ports.

This is what the port looks like currently ( I'm not giving up my day job just yet )







Cheers

Gert

[Gertvr]

I started on the exhaust a while back and the main goal was not to make the port too big and from the above program output used the recommended Port CSA of 1.82sq-in (D of 38.6mm) was about 3mm bigger than stock. I also used the public domain flow numbers for a ported exhaust port as a bogie to chase with Max flow of 201 CFM @.5" lift @ 28" of H2O. (from Kenikh's post in the S registry)

When I started flow testing the first thing I noticed is that the ex port is extremely turbulent and the flow on the floor of the is almost non existent until almost max lift. I placed a short string in the port floor and it pointed anywhere but out of the port the most of the lift range. All the flow happened on the long radius of the port (roof) and the velocities were quite high +300 FPS range and it flowed no more than 162CFM at max lift.

I opened the port to the 38.6 mm diameter and didn’t gain anything at all. This baffled me. I changed valve head shape to a smaller angle i.e. the smaller radius between stem and valve head, lost another bunch of flow and the port still stayed very turbulent.

I did some more research and in Graham A Bell’s book on tuning 4 stroke engines he suggests the inlet port size to be the same as valve head in this case 41.5mm, this is very close to the inlet port size. This is quite a substantial amount of material to remove and was a little hesitant to do it. In Bruce Anderson’s book all the factory 3.0L racing engines had 43mm/43mm port sizes for inlet and exhaust which gave me some sense of comfort.

After opening the port to 41.5mm the flow went up to 191CFM with around 330FPS on the roof of the port the floor flowed about 150FPS. Still very turbulent. I started probing the port and discovered that the flow increases if I put an obstruction on the floor. I played around with that and got the optimum shape and the flow increased to 203CFM. This was with the stock valve shape. Changing the valve shape to anything but the stock shape also lost flow, up to 10CFM. The valve shape and seat configuration seems to be critical for good flow on the exhaust port and i will do the final shaping after the valve job is completed.










I am considering to have the port floor welded up and shaped as the ones from Extreme Cylinder Heads which should have the added benefit of reducing reversion.

[jpnovak]

this thread has already answered so many questions. I can't wait to read more.

Can you compare the flow velocities? The initial results that show a stock head that has a flow velocity of 290 fps and a slightly ported head of 340 fps. At what location is that measured? I would like to compare it to the current map of the intake tract flow velocities.

The bump in the exhaust tract is quite interesting.

[jluetjen]

Originally Posted by Gertvr

Does this include the carb venturi?

[jluetjen]

The exhaust port work is interesting, but I'd be cautious. Compared to intakes, exhausts are very different animal. Specifically, the temperatures and pressures (and thus the energy level) are much higher, I believe that the density will also be dropping quickly as the charge leaves the cylinder. I don't have a clue about the level of turbulence, but suspect that it's also pretty high coming out of the cylinder. My observation is that exhaust gasses will do just about anything to get out of the cylinder -- including burn their way through gaskets. You most likely don't have to help them a whole lot to get out the exhaust pipe. Just don't put anything in their way.

My uneducated opinion is that acoustical tuning of exhausts is most likely far more important then the port shape. The overall volume of the exhaust port (combined with the volume of the exhaust primary) will -- I believe -- have a far larger impact on the acoustical tuning of the exhaust system then the port shape will. Personally I'd be afraid that your addition to the exhaust port will end up setting up an echo towards the valve which might break-up the overall system's tuning at the valve face.

[Gertvr]

Originally Posted by jluetjen

Does this include the carb venturi?

Yes the 41mm diameter is the venturi in the carb section, the drawing is a little crude but at least gives some view.

Originally Posted by jpnovak

this thread has already answered so many questions. I can't wait to read more.

Can you compare the flow velocities? The initial results that show a stock head that has a flow velocity of 290 fps and a slightly ported head of 340 fps. At what location is that measured? I would like to compare it to the current map of the intake tract flow velocities.

The bump in the exhaust tract is quite interesting.

It should be comparable except for the last modification at the port entry that was a big departure of from the stock and slightly modified port entry diameters. I measured that velocity 0.5" into the port right around where the blending of the manifold now ends. Most of the mods were in the bowl area and just some casting flash cleanup on the port leading up to the bowl.

Adding the carb and the inlet manifold reduced the overall flow by about 23CFM. I was a little surprised bu this as the carb manifold combination flowed over 300CFM.

[jluetjen]

BTW -- as you're considering the flow numbers, see if you can calculate the peak flow velocity at the smallest point in the track at your engine's peak HP engine speed. Then also look at the flow velocity at the carb venturi and the valve face at your peak torque engine speed.

Obviously you don't want your velocities at the peak HP engine speed to go too high. But it's also important that your velocities at the intended peak torque engine speed do not go too low, or else you're going to end up with driveability problems and a "peaky" engine as opposed to an engine that pulls strongly across it's rev range.

[Gertvr]

Originally Posted by jluetjen

The exhaust port work is interesting, but I'd be cautious. Compared to intakes, exhausts are very different animal. Specifically, the temperatures and pressures (and thus the energy level) are much higher, I believe that the density will also be dropping quickly as the charge leaves the cylinder. I don't have a clue about the level of turbulence, but suspect that it's also pretty high coming out of the cylinder. My observation is that exhaust gasses will do just about anything to get out of the cylinder -- including burn their way through gaskets. You most likely don't have to help them a whole lot to get out the exhaust pipe. Just don't put anything in their way.

My uneducated opinion is that acoustical tuning of exhausts is most likely far more important then the port shape. The overall volume of the exhaust port (combined with the volume of the exhaust primary) will -- I believe -- have a far larger impact on the acoustical tuning of the exhaust system then the port shape will. Personally I'd be afraid that your addition to the exhaust port will end up setting up an echo towards the valve which might break-up the overall system's tuning at the valve face.

You are right, there is a lot more to exhaust system than just the port and a completely different animal all together. The pressure delta, cylinder to port puts these ports on initial low lift close to sonic speeds and these ports are even more of a dark art than the intakes, even guys like Darren Morgan and gurrus from Speedtalk dont really have an idea as there is no real means of testing them.

In this case the shape is pretty strait forward with almost no change in the shape after the guide. In my case i will be using venturie merege collectors from Burns SS and from what i read in Bell's book this type of collector reduces acoustic tuning effects and relies more on momenutm to perfom scavanging.

The port that i ended up with is also in the 2sq-in range and quite a bit bigger than the CNC port maps Bullet Bob posted where his ports peak out at 1.8sq-in if i read his plots correctly.

As far as the floor addition goes, when blended correctly could be viewd as D shape on its back, which is somewhat in line with what i have seen and read for other heads. (Vizard and Bill's port shape on the Extreme Heads) this rizer in the ports are also used by some of the Harley porters that has a hemi head configuration and should also have a negative effect on reversion as this is on the slow side of teh port. If it is not cost prohibitive then i will try it, good thing about it is that you can just grind it out if it does not work.

[Gertvr]

Originally Posted by jluetjen

BTW -- as you're considering the flow numbers, see if you can calculate the peak flow velocity at the smallest point in the track at your engine's peak HP engine speed. Then also look at the flow velocity at the carb venturi and the valve face at your peak torque engine speed.

Obviously you don't want your velocities at the peak HP engine speed to go too high. But it's also important that your velocities at the intended peak torque engine speed do not go too low, or else you're going to end up with drive-ability problems and a "peaky" engine as opposed to an engine that pulls strongly across it's rev range.

I have already done this with the LPV formula a couple of posts above, it uses the smallest CSA in the port, the RPM you are choosing and the engine size. At peak power (7525 RPM ) the velocity is 278 FPS.

If i use the same formula and assume 5525 as peak torque RPM ( i am not sure what that real RPM is at this point) the velocity goes down to 205 CFM which is a little on the low side and will have to see how this affects drive-ability. It can not be worse than the stock engine as the smallest port size has not changed much only the carb venturi has. The only item that i can change in this case again to have a smaller CSA is the carb venturi to get the torque peak velocity up.

I did this (changed ventuies) in my ITB miata and it was a trade-off between good top-end power and reasonable lower torque or great torque but quick drop-off the power curve at high RPMs. It probably will come down to the same thing here, evaluating the track and tuning according to the requirements. This is a pain but doable. One thing that will be necessary will be to change my driving style and gearing to make use of the power band that will be not as wide as it used to be.

[Gertvr]

The heads are done and here is the latest update. The head volume ended up to be 86cc with 52mm inlet and 42.5mm exhaust valves. Both inlet and exhaust flows quite well with the following numbers:

Lift Inlet CFM Exhaust CFM
0.050 29.9 13.7
0.100 70.5 48.5
0.150 103.0 81.2
0.200 138.1 104.3
0.250 178.8 126.6
0.300 212.2 151.4
0.350 241.9 173.8
0.400 265.7 191.5
0.450 276.8 202.2
0.500 288.7 209.4

Now for the final test.

[jluetjen]

Interesting. Keep us posted!

[PFM]

Gertvr,

Have you used a velocity prob in that port to measure port velocity rather than calculate it? I ask because the stock port has anything but a uniform velocity profile with the stock port shape.

The insert in the exhaust port floor, is it welded in place? It looks like a separate piece.

Regards,

PFM

[PFM]

Bullet Bob,

Check your PM please.

PFM

[Gertvr]

Originally Posted by PFM

Gertvr,

Have you used a velocity prob in that port to measure port velocity rather than calculate it? I ask because the stock port has anything but a uniform velocity profile with the stock port shape.

The insert in the exhaust port floor, is it welded in place? It looks like a separate piece.

Regards,

PFM

The ports are welded up and then machined down see pictures of the process below. I used a pitot tube to measure the port velocity.







Cheers Gert

[dshepp806]

Just read this thread....very educational. Thanks for sharing (teaching)........way cool stuff.


Doyle

[crummasel]

Any news here?

Very interesting research...

[Gertvr]

The combination made good power, the car is very drive-able even with a very radical cam and pulls strongly from 3.5K through 8K. I am more than happy with the outcome.

Below is the result of one of the dyno pulls.

[lvporschepilot]

That's really wonderful power there. Congrats. PMO 50s right?