I have my 26 coupe totally apart, body wise to paint and I plan on installing a "Z" head. I have flat top aluminum pistons already and would like info and suggestions on which head might be the best choice. I'm looking for a little more power for the hills. I'm not ready for rear end change yet due to cost. My car is a driver and staying original is not my objective. I know the purist are going to have a field day with this thread so to give you a little more material on my car...I run an alternator, distributor, disc brakes but no water pump. Bob
I like my Z head and have it installed on 2 of my T's. I'm otherwise set up like you.
A friend has a P head and there is no way I can keep up with him! I do not remember if he upgraded his carb.
By the way Bob we have very few flat roads our here so I have the Z head for the same reason you sited.
You will like the quick bolt on improvement of the alum heads, just about the best way to increase power. Am using both, the original 'Z' by Zajicek family, and the newer 'P' by Kevin Prus.
For my motor combo, of cam, stock ignition, and .060 over flat top alum pistons, the 'P' head gives the smoother boost.
The 'Z' has Ford script and its hard to make out when painted that its not a real iron T high head.
The 'P' lacks the Ford script, but in 1927 Ford did away with the script on the high head, so it is perfect for my '27 touring
'Z' alum head compared to stock iron T head
'P' head, very similar to 'Z' but is CNC machined in the chamber, unlike the cast finish of the 'Z', then processed with a vacuum injected polymer to seal any porous portions of the alum die casting, rather neat special addition offered only on the Prus head. And the Prus head is also offered in iron for a bit more $.
Dan, Is the 8;1 compression ratio head Lang's offers the "P" Prus head?
If you look real close (with glasses for me ) you can make out that cast "P" on the water outlet neck on Lang's p/n 3001HP.
(jumping in for Dan here)
Yes, the Prus head is being advertised as 8:1 but is actually about the same 5:1 ratio as the Z head, so it's safe for splash lubed babbitt
A test with both heads on the same engine showed about the same low speed improvement, but two more horses at the top end for the Prus. (26 vs 28 hp)
Dan, do you use the Prus head that takes the original style plugs, or the 14mm type? I read that the 14mm type gives you more to choose from for a heat range, but i would prefer using the stock X plug.
I don't think the Prus is offered with anything else than modern 14mm plugs?
With the Z you have a choice.
I suppose a Prus head can be rethreaded for 1/2" plugs should anybody want to, but I'm very pleased with the modern plugs Kevin Prus suggests, Champion #120, haven't had to remove them at all since I started using my Prus head some 1500 miles ago, and with old style plug wire connectors they don't stick out as much
Roger, i didn't think so either because when i inquired about a cast iron head Prus said that there was enough material to drill and retap for a standard plug. But i did find this one at Lang's that says it takes a standard plug, go figure.
Yes, Prus makes both, std. 1/2 pipe or 14mm, your /choice. Lang's pn 3001HP and 3001HP-14
Just using regular Champion 25's, seems just fine for my set-up, stock ignition. But if need to change, have lots of X's and other 1/2" plugs...no metric in my Model T's
Ok, I had a mail conversation with Prus back when he started production a few years ago, he only had 14mm back then. Nice to know there are options now.
I run a Z head with ½" plug holes and adapters for 14 mm plugs. I suggest this for anyone not in need of original looking plugs. You get the advantage of the less costly, more readily available, modern plugs.
The other advantage is less apparent, but the real reason to go for ½" holes. I remove and install my engine using lifting bolts in two plug holes. On an iron head I am not concerned about thread failure (although I have had part of the thread chip out in a low head), but in the aluminum head I worry about tearing out one of those dinky 14 mm holes.
If the engine is on a hoist and one lifting bolt pulls out the other will likely follow. A complete long block falling from a hoist is unlikely to be a good thing.
Aluminum is soft and weaker than cast iron... So I try to improve my odds with the larger ½" holes. Of course if you lift with tongs or straps then you can discount the above argument.
If you've got a '26 like I do, you really don't want the "Made in USA" on it anyways (unless you feel the urge to). I ran a Z head on my engine originally, but pulled it and replaced it with a Prus head. About the same money, more power, smoother running engine. The old Z head will go on the spare engine. Both are running original type spark plugs.
I will start out by saying that I have no experience with the X-head. I purchased a Prus head last summer and installed it on a 23 engine with the only modifications being .010 over aluminum pistons on a stock re-build. The engine still has the stock cam, intake, carb and I am running Champion X plugs. All I can say is she runs and idles smooth as a cat and is really frisky! When I hit an uphill grade, all I do is pull down a tad on the throttle and she will walk right up the hill. When I crest a hill, I usually have to back off, because she will run faster than what I want to drive. I truly believe the Prus head is the best single performance investment that you can make. Just my two cents worth. AAA+++!
Thanks for the great feedback on the P head. The aluminum heads are available in T plug style and 14mm. These heads are impregnated. The cast iron heads are available in 14mm. I have several cast iron heads available from the last run.
Put the Z(?)-Head on the block without the head gasket. Put a few head bolts in to line it up. Then crank the engine over slowly, and watch the head. You are looking to see if it moves, particularly up and down. Pistons are hitting the head?
Mine did, but I fixed the problem. It's not too difficult.
Just to throw a monkey wrench in the works: a good aftermarket carburetor (like a Stromberg OF) will have as much or more noticeable impact on the performance of your T compared to any other change you can make. I would definitely get a new carb before getting a new head of you're running any kind of stock T carb. When I bolted on my Zenith S4BF (was running a very good Holley NH before) it was like I had doubled my acceleration and top end.
then what about both a new head and a good carb, Seth?
Lol well Roger, except for a lucky few on this board that I'm very jealous of, most of us are working with a limited budget and have to pick and choose where we make changes. I just wanted to throw out there that a period correct aftermarket carb is a better bang for your buck. Well, in my opinion anyway.
I personally have domed pistons and a low head, but that's because I was thinking of skipping the improved head stage and go straight to an OHV setup. The price jump is a little bigger there but I'll just save the $400 along the way.
That's good. I was just looking at the domed pistons online - thinking about the same idea. Lang's are $30 higher than Snyder's on their domed pistons, so they might lose that sale, always got to keep the budget limited..