Horsepower increases.

[Frank Acampora]

For those of you who are interested, I have been corresponding with a fellow from The Chrysler Crew for the past month or so. He has given me what is supposed to be a proven formula for gaining horsepower on the four cylinder blocks.

1. Mill the head .0625 (1 1/6) to provide a .045 "squish" clearance and raise compression up to about 185-210. This will require premium fuel.

2. Raise the center exhaust ports .025 inches and square ports. Chamfer the edges to prevent catching rings.

3. Square the bypass ports and chamfer the edges.

4. Mill the bypass cover sealing surfaces .025 to increase crankcase compression.

Now, I have squared ports but never raised them and have never milled the head. I also have never milled the transfer sealing surfaces.

Supposedly, these modifications gained 10 MPH on a small light hull because the engine was able to swing a much higher pitched prop.

I am in the middle of a total house remodel and I simply do not have the time to try it. However, if any of you guys have an extra block laying around and want to try, it would make an interesting project.

 

[pnwboat]

Re: Horsepower increases.

My current motor has the squared by-pass ports, but nothing done to the exhaust side. I do have a head that has been milled .040 that I plan on installing this Spring. Hmmm, milling by-pass cover sealing surfaces.....interesting. What about adding material to the floor of the by-pass passage, or inside the crank case itself to increase crankcase compression? The possibilities are endless....LOL!

 

[Frank Acampora]

Re: Horsepower increases.

My 140 has the bypass and exhaust squared. If it is not set high and if the lower unit is not vented above the water line, it actually produces less horsepower than stock.

Adding material is called "Packing the crankcase." In the old days they used cork so that if it came loose during running it would not harm the engine. I have often looked at the crankshaft and thought that there was an area to be improved. Significant packing can be achieved by making the cheeks complete circles with hollow steel cups welded on and lead counterweights added to the solid parts of the cheeks to restore balance. BUT-- This takes cubic money and you are still left with a 50 year old crossflow design which will never equal current loop charged engines.

On the other hand, there are still people who soup-up old Ford flathead engines---just because. These engines have a certain Je Ne Sais Quoi.

I never measured the bypass cover clearance but I suspect that milling the sealing surface .025 will allow the inside to be flush while supplying a small amount of packing. You would not want to add material to the cylinder side as this would reduce the cross sectional area.

 

[Michael Lang]

Re: Horsepower increases.

Very curious on how one machines a round port hole into a perfect square, its been over fifty years sense I worked in a machine shop and would really like know how it is done, I guess one could use a broach or just use a small end mill but that would give a small corner radius. seems like a lot work to get fifteen HP.

 

[pnwboat]

Re: Horsepower increases.

I used a die grinder and a couple of different carbide burrs. Done by hand, nothing fancy. Idea is to increase the size of the openings.

 

[Frank Acampora]

Re: Horsepower increases.



Michael: I have seen on some of the older engines elongated ports to increase area. They were also milled into a roughly squared shape. From the size of the radius, it appears that the factory did use about a 1/4 diameter end mill. Now, on the 5 cylinder 150 Force, the center web was simply drilled out leaving a port with three overlapping circles. The factory did not move the end mill to remove the "points" left by the machining.

All the squaring port work I have done was done by hand with a dremel and 1/8 carbide bit. This does leave a desirable small radius in each corner. Other port work I have done on a drill press was done using a 1/4 inch end mill. The two center photos were done this way but the port work did not have the desired effect. I still need to try some other modifications to see if I can improve that particular engine.

 

[Michael Lang]

Re: Horsepower increases.

Wow, Thank you both for the response, after I sent the question I starting thinking (hard to do at my age 74), maybe they just grind and file, some times that's the only way to get the job done. Frank I really appreciate your detail explanations.

 

[fisheymikey]

Re: Horsepower increases.

would this work on 125 force? I have a seized block that I could play with?

 

[pnwboat]

Re: Horsepower increases.

would this work on 125 force? I have a seized block that I could play with?

Yes, this should work on your 125HP motor.