D Slater-LPG head

Or someone else who is sure of the answer. I am putting a 281 cu in engine kit in my Super M. It will have the original the IH fire crater pistons in it with new sleeves and rings. I bought a 22 degree advance plate from Dave Slater. Getting ready to finally assemble the engine. I noticed today that it has an LPG head, cast 12-6-58, letter appears to be D, hard to read. Head number is 8574 DC. Webers Tractor Works says the LPG set up with firecraters has 197 psi compression. Is that correct or does the factory LPG have other modifications? My tractor did not come from the factory with LPG. I did little more with the tractor but drive it around with no load and on the road in 5th. I did not hear detonation in 5th, but I am 75% deaf. Tractor will not be used much, when it is it will be with a bush hog at considerably less than full load, since my bush hog is only 5'. Does this tractor require premium fuel?? Anyone have an idea what the drawbar HP is?

With a 197 PSi compression your darn tooten and even with a 22 degree plate look at the problems we have with a 706 and fresh we are only talking around 165 to 170 on cranking pressure and 18 degrees. And even the 93 octane may not be enough . as for hearing the PING on a tractor engine when ya hear it HUSTON YOU HAVE A PROBLEM . Now i have never run a compression test on Vernon's S/MTA as it has the high alt. 450 pistons in it with a 450 gas head and a 450 cam and manifold i can however tell ya that she will make five to six more ponys then the 706 will on the same dyno and hold it well . Like all our gasser they are fed 93 and as long as the fuel supplyer brings us the 93 we have not problems . BUT let them mess up and i am replacing pistons . Would i have this problem with a FORGED piston ????? don't know as all ya can get is CAST pistons and they will not take the heat.

I can tell you, from having a 450 LPG, that I just had rebuilt, that the factory pistons on a 450 LPG, are the same as what come in a comparable 450 gas. The extra compression in the LP motor comes from a smaller combustion chamber, and not from different pistons. I don"t know about the Fire Crater pistons, but if they have a taller deck height than the standard pistons, I would think about standard pistons. I have built a 351 Ford V-8, 4-barrel engine, that had about 200 psi cranking compression, and it would just barely get by on 92 octane unleaded. I ended up installing a thicker copper "head-saver" gasket made by Fel Pro, and had no problems from then on with just regular unleaded, 87 octane. My point is that 197 psi at cranking speed is going to be marginal on even 92 octane (premium) unleaded, but there are two ways to lower the cranking compression: Lower deck height pistons, or thicker head gaskets, which are offered by Fel Pro and some others. You can also have your Fire Crater pistons machined down a little, it will not affect your 281"s balance significantly, nor will it adversely affect the pistons" durability. Any questions, drop me a line, [email protected].

No worries 8574DC is a replacement gas head for a SM. Replaced 8574DB or 8060DC. If I remember correct the only difference from a DB was more metal added at the valve seats.

Thanks -- In my parts book LPG is listed as 8574 DCA or DCAX--not sure because my parts book is out in my shop, will check later tonight or in the morning. I thought when the numbers were the same, the suffix was a modification of some sort.

Thanks, I'm not planning on changing anything, I somehow think the 197 I read is wrong. I was expecting maybe 150, won't know until I get it together.

On a SM the gas and LP heads had the same casting number and combustion chamber size. LP head with a smaller combustion chamber didn't start until up in 400 tractor production.
Parts book should show the bare head casting number listed under the assembly numbers you posted.

The number I showed was listed under the assembly--so what is the difference between the gas and lp heads? If the chamber size is the same the 197 is definitely wrong. If no difference then the compression is 135, I think.

tractor vet what pistons in a 281 would you run with an lp head for a pulling tractor to make the most power ?
thanks!

CNKS,
450 l.p. head is shallower then gas.
Factory l.p. heads came with flat top pistons.
Stock gas got its extra compresson from fire craters. Stock l.p.s got there extra compresson from the head. If your cast date is 58 its off a 450.
Can you tell me what a 22% advance plate is?
Tony

Difference in heads was stellite faced exhaust seat in the one used on LP tractors and no valve rotorcaps. This following is for head numbers after the originals that would be a bare casting number of 8574DB or 8060DC used at factory on real late M through SMTA. 8574DCX was a head without valves for gasoline and LP. 356994R92 was a 8574DCX head with valves and rotocaps for gasoline. 8574DCY was a 8574DC head with valves and no rotocaps for LP. IH was still using that size combustion chamber head on some power units and industrial machines after farmall tractors stopped using them in production. 8574DC and 8060DD was just a upgrade from the previous castings used on SM tractors and became the replacement parts head in 1955.
Did you notice the number on the firecrater pistons. Going by memory but think the standard elevation one is 374457r1. If thats what you have. To be safe I would guess around 10 PSI on both sides of 130 PSI cranking after break in. H.E. 374471R1 used as S.E. in LP.
What most call a LP head from the middle fifties was cast # 364586.

It is not necessarily off a 450 as IH was still selling replacement heads in 1958, I have not looked up the 450 number as of yet--The SM number matches the one in my SM parts book, so it was an option, perhaps after SM's were built. My tractor has fire craters, which were not available when sold, head was also added later. It ran fine when I aquired it, except for differences in compression between cylinders, which is the main reason for the overhaul. 22 degree advance plate holds the springs and weights, when fire craters are used the full throttle advance is reduced to 22 degrees.

Yes, the piston number is 374457 R1. Valves have rotocaps. Thanks for the information, I wish I had your knowledge. Got a little more complicated than I expected, but it appears that eveything is ok. The head on it is a replacement head, and it has replacement pistons--I'll never know if the original owner was looking for more power and bought the so called LP head along with firecaters or if the original one cracked or something. Thanks again.

I have a Super M with hi alt firecraters, with a 8574 head, making 165psi, dynos at 63hp on 87. I know of a Super mta making 115+hp and runs on 93! Loves the stuff! I lock the advance in the distributors now n tune by base timing at work rpm. Much better torque curve on dyno. Chad

hey chad! trying to get ahold of you! need to talk to you over the phone! give us a call!