Prus 8:1 High Compression Head

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Model T Ford Forum: Forum 2016: Prus 8:1 High Compression Head
Top of pagePrevious messageNext messageBottom of page Link to this message  By Simon Neubert on Wednesday, March 02, 2016 - 08:21 am:

I have recently acquired a Prus high performance aluminum head with 14mm spark plugs and I LOVE IT. By far the biggest single improvement you could make to any T to get you up the hills and faster down the road. The 14mm spark plug addition is huge for me because I have a huge variety of hot and clean burning spark plugs that the old T spark plugs cant deliver on. I have installed the head on a 1924 touring car that has coil ignition, aluminum pistons, reground camshaft..... however pretty tired after years of use. After putting the Prus head on this car it has totally transformed the performance giving the car much more low end torque that has greatly helped the performance in the hills of Pennsylvania. I also have acquired roughly eight more miles an hour over the original speed. I can now easily go well over 50 mph in my car without hesitation. Very impressed with a quality american made head that really delivers in all aspects of T performance!!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Carlton on Wednesday, March 02, 2016 - 08:29 am:

I'm definitely getting one since not wanting to go to an overhead on my build. Seems like the way to go.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Whelihan Danbury, WI on Wednesday, March 02, 2016 - 11:00 am:

I've had both: the Z head, and Prus head on the same engine (at different times, of course!) The Z head is a definite improvement over stock. The Prus head takes it the next step. Slightly more acceleration and fuel economy than the Z head. Either option is good, but for about the same money, I would go with the Prus head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, March 02, 2016 - 11:11 am:

Indeed, it's great. Just a pity the advertising is misleading - the compression ratio isn't much different from a Z head or about 5:1, but the combustion chambers are better shaped than in a Z head, so it's more efficient. About 2 hp more at top end than the Z according to a dyno test. (28 hp with the Prus and 26 hp with a Z head on the same engine)

The machined squish area and a better fit to the head gasket are a couple of other selling points for the Prus head that makes it worth the slightly higher price compared the Z head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Simon Neubert on Wednesday, March 02, 2016 - 02:33 pm:

Also dont forget that the Prus head is pressure treated with the same resin that is used on modern aluminum engine blocks. This will cause the aluminum to never corrode so you never have to worry unlike the Z heads which have a reputation to corrode.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Pat Kelly Montana on Wednesday, March 02, 2016 - 03:37 pm:

I just bought a new Prus head for my motor rebuild. Should be a big help on the mountain roads I run on. Did any of you notice a mileage increase? Regarding the 14mm plugs, what heat range did you settle on? PK


Top of pagePrevious messageNext messageBottom of page Link to this message  By Derek Kiefer - Mantorville, MN on Wednesday, March 02, 2016 - 03:48 pm:

I wish they were available with the Ford script.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ed Baudoux Grayling Michigan on Wednesday, March 02, 2016 - 03:58 pm:

I have the cast iron Prus head in our Fordor. The fit and finish are incredible.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Wednesday, March 02, 2016 - 04:14 pm:

I have run a Z head for about 29 years now. Hasn't corroded away yet...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, March 02, 2016 - 05:00 pm:

Just use fresh antifreeze mix and there shouldn't be any corrosion problems with an alu head on a cast iron engine (there are so many moderns that have had that combination for umpteen years without much trouble)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Will Copeland - West Melbourne Florida on Wednesday, March 02, 2016 - 05:38 pm:

If its getting about two more ponies over a Z head is there more stress on the crankshaft? I have a spare block that I would like to redo and am thinking of maybe going this route.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, March 02, 2016 - 06:34 pm:

Well, the stress on the crankshaft depends on how much you use out of the new available power..

Though, I don't subscribe to the theory that running too slow in high always is the main crank killer - I think there are certain rpm areas, "thum speed", we should avoid as much as possible where the twist in the weak crank gets amplified by resonance, thus hastening the inevitable fatigue failure that'll come some day even on a standard T.. But crawling up a hill in low to save the crank from lugging is a more immediate danger, increasing the risk of getting rear ended :-(


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Wednesday, March 02, 2016 - 11:17 pm:

Raising the compression adds stress to the bottom end wonder how bearings hold up


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Thursday, March 03, 2016 - 01:24 am:

The raising of the compression only adds stress to the bottom end if you open up the throttle just as much as you did before - if you open less, the stress should be about the same.
But indeed, if the bearings were loose and about to start knocking when the head is swapped, then it's definitely time to tighten them up afterwards ;-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon, Grass Valley, CA on Thursday, March 03, 2016 - 06:16 pm:

I have been in this hobby for more than 45 years now. For the very reasons of stressing the bottom end, I have never been a big fan of raising compression.
I have always had some mixed feelings about it. But since gasoline today only delivers about 75 percent as much power as gasoline did twenty years ago, raising compression today may not be so bad and give back some of the lost performance. Twenty-five years ago, the '16 center-door sedan I had would do 55 mph on the level almost anytime I asked it to. And that with a nearly as stock engine as you can put together. Most Ts would do that then. Now most Ts struggle to do 45 mph.
Drive carefully, and enjoy, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kevin Prus Sr on Thursday, March 03, 2016 - 10:10 pm:

I will have heads and high volume outside oil line kits at Marietta Ohio Swap meet this weekend and at Chickasha meet space NE5 if any body is interested.


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