The New Sherman type head 8 to 1 compression is now available from Kevin Prus. See you at Chickasaw
Your profile tells us nothing.
Who is Kevin Prus, and what credibility does he have to successfully make an 8:1 head?
Ralph,
A lot of us know Morris, he is a Model T guy from Arkansas.
Here's the previous thread where Morris posted pics of the Prus Hi Compression head:
http://www.mtfca.com/discus/messages/179374/244933.html?1323235112
Kevin rebuilds Model T engines and has been around for a long time. I expect it will be a good product.
I sent a proto type with Brent Mize of the iron one to Chickasha so if any of the western T guy's want to take a look at it. I would like some thoughts back on it good or bad. It is not going to be for every one but just trying some thing different for the speedster guys.
Just to clarify, both Kevin Prus and Joe Bell are now making high-compression heads. In talking with some T folks, some thought there was only one new one and had them confused. Kevin's is aluminum and Joe's is iron; Kevin's looks like a stock Ford head and Joe's looks similar to a Sherman Super-Fire. Pics of both are on the link that Royce posted above. I think it's great that these two guys are giving us T folks more options.
Has anybody ever been successful with 8:1 side valve head on a T? It should have a lot of power, and give much better fuel economy. Edelbrock has an 8:1 head for the late V8 24 stud flathead. They offer only 6.8:1 for 24 stud 1938-48 blocks. They don't have a head for 1932-37 blocks. Can a T with only 15 bolts hold 8:1?
http://www.edelbrock.com/zmags/automotive.shtml page 148
Morris has a gorgeous 11? that was on display along with two or three ladies in period costume at the 2008 Centennial event. I'd post a picture, as I took several, but those are some of the pics I lost on this computer. Pretty much everybody knows Morris. Pretty much everybody knows Kevin Prus, too.
I have ordered one of Kevin Prus new heads. Today I got pictures of the finished product by mail:
Kevin describes the project: "This has been a long process since early last year when I started this project. Pattern process went great. Foundry experiences were stressfull. Writing the CNC program to machine heads was hours to many to recall but somewhere around 100 till the fine adjustments were made. Finally a quality product. I tested 10 heads last night and they were all good. (---) I'm pressure testing the rest of them today. We did thirty in the first run. Leaving for Chickasha, Oklahoma tonight. I will send you head when I return at the end of the week."
Can't wait to get mine
Nice to see somebody making quality heads. I got stuck on a couple of the "Yapp Crapp" Lizard heads a few years ago that leaked water and didn't runn worthh aa crapp!!!
What kind of performance improvement do you think this head will provide?
What the asking price going to be? I might want one for my T
I could certainly use a new head. Might get one for my T, too.
Look in the thread Royce posted above.
Is the Prus head only available in 14mm plug holes? I like std 1/2 pipe.
Anyone done the calculations to study what extra punch will do to a 90 year old stock ford crankshaft?
Erich, I understand they went with 14mm to get a better heat range for the higher compression.
OOOOOOOHHHH, that sounds good. What are the recommended plugs then?
At the risk of being a voice in the wilderness, I am skeptical.
That is a very nice looking new head, BUT I suggest everyone who is considering buying one, step back and ask yourself how YOUR Model T engine will respond to more than doubling the stock compression ratio?
If you have a highly modified Model T engine that will withstand the higher compression ratio, fine.
If you have a stock Model T with original crankshaft, rods and babbitt bearings you might want to think again.
In my opinion the stock Model T engine will withstand a 6 to 1 compression ratio and even that will result in excessive wear.
Higher compression ratio and your (worn??) original engine bottom end may well be splattered onto the tarmac.
Consider buying a package consisting of the 8 to 1 compression head, a new Skat crankshaft and Skat rods plus some dinero to properly finish it.
Ron the Coilman
Ron is right, this doesn't seem like a bolt on accessory to the average T - it's a speedster item that may require modified ignition for a fuller range of ignition advance than what std magneto and coils can give. Tolerance to knocking will be reduced with higher compression. Unfortunately other available heads like the Z head only gives about 5.3:1 in compression, so there's still a small niche for a true 6:1 head
Kevin gave this answer when I asked what 14mm spark plug that worked best with his head: "The Champion spark plug #120 seams to work best"
Would it be N5C, then? http://www.ebay.com/itm/Champion-Spark-Plug-Stock-120-N5C-/230643342306
Roger, something you posted puzzles me, "Tolerance to knocking will be reduced with higher compression" can you elaborate on that??
G'day,
An old mechanic I did my training with told me that the harder and faster you make an engine work, the faster you will wear it out. So true, look at how many times a race engine is rebuilt.
It's good we have people who are making parts for our cars, I congratulate them and thank them for their efforts, just remember that not everything is an "Improvement" for all applications. Remember that for all actions there is an equal and opposite, often terminal reaction.
Peter
Forgive me for hijacking this thread, but it seems to fit: what Model T engine would have an 8-spark plug head?
http://cgi.ebay.com/ebaymotors/?cmd=ViewItem&_trksid=p3984.m1423.l2649&item=1306 63610773&sspagename=STRK%3AMEWAX%3AIT
Kerry, it was just a general statement - raise the compression ratio and you have a higher risk for knocking. Modern engines has a higher compression ratio than 8:1, so modern fuel will prevent knocking - if the ignition is timed right. A std Ford with 3.8:1 compression will tolerate a lot more misadjustment of the ignition lever without knocking than it would have if equipped with a 8:1 head.
The Yapp Lizard head was harder to drive as it needs constant adjustments of the ignition with only 6:1 compression (I think) - but there was a serious design problem with that head as the spark plugs were placed over the pistons instead of over the valves, as Prus and most other flathead designers has done - for a reason. See this thread: http://www.mtfca.com/discus/messages/50893/70987.html
I've just received my new Prus head a few days ago - (The long time in shipping was my choice to save some $$)
I tried to measure the combustion chamber volume and got about 210-215 cc or about 13 cu inches. According to the Tulsa club's calculations that's about 5:1 compression. http://mtfctulsa.com/Tech/head_design.htm
They measured a Z head to 203 cc or 12.4 cu in, giving 5.3:1 in compression. Unfortunately I haven't got access to one, but mr Prus has claimed his head has better compression than the Z head - perhaps the Z head the Tulsa club measured about ten years ago had higher compression than current production?
The water capacity is about 2.2 liters or 4.7 pints. The aluminum seems thick enough to withstand some milling. I may try milling some after more careful measuring. If 0.100 is possible, I would probably get 188cc or 5.7:1
Roger - you would have to know the volume of that portion on the piston that occupies the combustion chamber when on TDC, and include that in your calculations
A 5:1 compression ratio is quite a bit different from the 8:1 the head was reputed to have. Did you account for the space occupied by the part of the piston which extends above the block?
Looks as if John and I had the same idea.
The Tulsa club did include all that in their calculations.
"The compression ratios can be determined from the measured volume. A stock high head has a volume of about 294 cc or 17.9 cu in. The volume is reduced by 2.8 cu in because the piston rises 5/16 inch above the deck. The volume is increased about 0.8 cu in due to the head gasket. For a stock head, the combustion chamber volume is 17.9 - 2.8 + 0.8 = 15.9 cu in. An engine with stock bore and stroke has 44.2 cu in displacement per cylinder, so the total volume when the piston is at the bottom of its stroke is 44.2 + 15.9, and the compression ratio is (44.2 + 15.9)/15.9 = 3.8."
There should be an option for a 6:1 compression ratio.
That has proven to be acceptable on rebuilt model T engines.
One of our club members put a 6:1 ratio head on a tired engine and went almost 5 miles before all the rods started loudly complaining.
It looks like everybody took Mr. Prus' word on the 8:1, and did not ask for cc measurement. You must be real disappointed, Roger. If you mill the head, it's no doubt yours forever. If the seller gets advertised CR wrong, then will he know how much it can be milled?
There was a thread here a few years ago about promoting higher CR on used cars in the 1930s. They found it increased fuel economy dramatically, unless the driver changed his habits and regularly used the higher power available.
It's really tough to get above 6:1 with a side valve head. What flathead V8 is 8:1?
I stand by my post on the prior thread, which turned out to be the last one. It takes more than foundry and machining to build a good head.
rdr
Well - I was prepared by Dean Yoder's posts: http://www.mtfca.com/discus/messages/257047/276192.html?1332042419 http://www.mtfca.com/discus/messages/257047/281421.html?1334112289
Had some email discussion with Mr Prus and from that I think his 8:1 claim comes from a compression reading of 90-100 psi (if a std 3.8:1 head usually gives 45-50 PSI, then a 100 PSI reading must mean 8:1 he thinks)
I think the head will be pretty much OK since I've decided to build this engine with light weight in and low price in mind, including a 1915 alu hogshead w/o starter, std crank and splash oiling. Wouldn't have been able to hand start a true 8:1 anyway. And with no front brakes (yet) I should keep speed down
Quote: "What flathead V8 is 8:1?"
Don't know about stock, but there was a lot of aftermarket high compression heads available for The Ford flat head V-8s, up to at least 9.5-1.
How did they do it, Ken? There is only so much you can shave without the valves and piston hitting the head.
Ricks, if you look on ebay, speedway sells edelbrock and offenhauser heads in 8-1 and more for the 8BA engines. This one is 8:1 http://www.ebay.com/itm/200784153052?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m142 3.l2649
This one is 9:1 with a 4" stroke
http://www.ebay.com/itm/120945415899?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m142 3.l2649
Ron P, is that you out in my wilderness? I, too, am from the camp that feels uneasy about pumping up old engines much. A member of our local HCCA group has a beautiful 1909 (non-Ford) only restored surviving example. He has had a lot of trouble the past ten years keeping the engine together. Many castings including cylinders and crankcase have broken. I recently had a conversation with a very long time member of the club and one of my longest and best friends. He knew the fellow that had restored the car and told me that the engine had at that time been pumped up quite a bit. My longtime friend is also of the camp that bumping the compression and other power boosting things do have a major downside. He is convinced that that is the reason the car has a model A engine in it now. Sad.
Certainly, there are cars or restorations that warrant higher compression. Race cars, speedsters, and somewhat modified stock type cars may be built that way. Personally, I prefer to stay within era and do not like model A crankshafts in Ts. But that is my choice. You may do as you wish.
I do like era accessories. I love my auxiliary transmissions. They allow me better choices of speed and the ability to run the bent hairpin in an rpm range it likes (do not lug a T engine nor over-rev it). And I love my era added brakes. They make it better to stop if that beautiful transmission or I do something stupid. I love my coupe. It has twelve speeds forward, and brakes as good as two wheels get.
Most importantly;
drive carefully, and enjoy, W2
Thanks, James. I see a big part of how it can be done. The proportion of bore to stroke is smaller in the V8: 3 5/16" compared to 3.75" of the T with the same 4" stroke.
Pardon me if I missed it, but I didn't see any discussion about the squish area of the Prus head. In my opinion, the combustion chamber design is just as important than the compression ratio. The Prus head looks like it has a close clearance with the piston, causing high turbulence during combustion. This will cause a faster and more complete burn and higher efficiency. High compression ratio helps too.
The stock mag ignition may not give exact enough control of the spark advance for high compression heads, causing knocking. A distributor would probably work better for these heads.
If you keep your foot out of it, or should I say, your hand, then there is no more stress on the engine with a high compression head than a low compression one. The engine is developing the same torque at 40 mph regardless of which head you use. Of course, if you do open the throttle more, then the high compression head will put more stress on the engine.
Neil
I agree with Neil that the combustion chamber design is also very important.
I also agree with what everyone else was saying that perhaps 8:1 is just too much for a normal T. That's an awful lot of stress on the crank, babbitt, and just about everything else. However, if you have a racing engine with a new crank, fresh babbitt, new pistons, a hot cam, aftermarket carburetor and ignition, etc., then this might be a good choice.