MTFCA Forum

Well i finally decided after much thought, and some inspiration by others i know, to install the Prus head i have had sitting on my shelf for a few years now. I still have a few questions that i hope some of the great minds here can answer. From what I've read, I'll need less advance for normal operation that i usually run V.S a stock head, and its better to drop the spark gap from .030 which my engine prefers now, to .025 for the H/C. Any thoughts and experiences would be greatly appreciated.

I left the spark gap alone and just advance the lever 1/3 to 1/2 down the quadrant. No problem with this method. John

You will climb steep hills better with the spark 1/2 advanced (just as it works with a stock head). On the highway level I run full advance

If I run full advanced with my Sherman head, I will get spark knock. John

With my Z head, I ran about half way down the quadrant for in town, but 2/3 down on the highway. I'm still playing with the Prus I put on the 20 but so far I've been doing the same and it seems to run well. I'm not sure that 60 degrees BTDC isn't too much for the higher compression head. BTW, I got about 70-75 psi with my Prus compared to 52-55 with the stock head.

Thanks for the input, i appreciate it. Got it done today without a hitch, and will run it tomorrow. Had the head off about 600 miles ago to replace the valves and add adjustable lifters and it looks like everything is working pretty well inside. Thanks Again.

Have a few sets of X plugs i can experiment with gaps today, will be interesting to see how the new head responds. Will make a video of how the engine runs with the new head if anyone is interested.

Had the Prus head on my car for going on 4 years. Had a z head before. Prus head is a noticeable difference. I run the timing advanced about half way through the quadrant in town or just putting down country roads. But if the speed builds up to around 25 mph, I advance fully to almost within a few clicks of the end of the quadrant. The engines just hums and is very happy there. On hills, depending on the grade, I will either back off to a little more than half way, or downshift to the Ruckstell direct and leave advanced or backed off depending on rpm. For plugs I am using F11 Motorcraft plugs gapped around .030-.032.

My only advice installing the head is to remember to re-torque. I do it four times. Aluminum heads are re-torqued when cold, cast are re-torqued when hot.

My advice for what it is worth.

Use a thicker washer than the one supplied with the head, available from McMaster Carr. The thin washer will cause the bolt holes to dish.

Run a bottom tap in the threaded holes in the block and blow them out with compressed air. Use a good copper anti-seize compound on the bolts.

Check for piston interference first by placing the head on the block with two loose bolts and cranking the engine over by hand. The bolts can be run down to make sure they will not bottom out in the block at the same time. Do this without the washers.

Use the correct length bolts which may not be the ones specified for the head by the suppliers. Run a couple bolts down without the head on and measure the distance to the underside of the bolt hex and compare with the thickness of the head. McMaster Carr has grade 5 bolts of different lengths.

Use a copper faced gasket and the copper gasket cement.

Not advice but a comment on the head design: The combustion chamber has a squish area above the piston which creates a lot of turbulence during ignition. This speeds up the burning of the air/fuel so less spark advance is needed. It also increases the efficiency of combustion which leads to more power.

Neil

Thanks for the tips Neil. Got it running today, sounds great. Still playing with the timing to find out what it likes best. I used to run it about a 1/2" inch from the bottom, but now it seems to like it a lot further up, like about 2/3rds down. Also still playing with the plugs and mixture as it seems it might like something different from before. I was always under the impression that you should reduce the gap to .025 with these heads, or maybe not. One thing i did notice is that the exhaust tone is definitely different, and it seems to run a little cooler. After fiddling with it today in the yard for a half hour in 85 degree temps, it didn't even gurgle after i shut it off. One final question if i may, Did you find after installing a H/C head you had to re-adjust your fuel mixture from where you had it set prior? Thanks Again, and short vid below.

https://www.youtube.com/watch?v=qsjHAAY ... e=youtu.be

I had to lean mine out about 1/4 turn.

Thanks John, still playing around with the mixture/timing/plug gap to see what it likes best.