wd 45 compression question

Glockhead thats a hard one . Most manufacturers for tractor pistons dont advertise the compression hieght or the ccs of the dish if its a dished piston. If you could find a flat top 4 1/8 bore with a compression height of 2.316  you would have a static compression ratio of 8.091. That is also dependent on where the first compression ring is located on the piston . If its a dished piston ring land placement and ccs of dish would make for a larger  compression height  number by needing the piston pin hole located farther down in the piston .

Edited by mlpankey - 14 Feb 2010 at 12:44pm

Hi Jeff

I would bet that a 170 kit (4 inch bore and 8.0 to 1 comp ratio) would peform as well as the SP-48 (4 1/8" bore and 7.4 to 1 comp ratio) and it will use less gas!!! In fact M&W used to claim 57 HP in a D17 with the SP-48 kit, which is a 4 hp increase. The 8.0 to 1 ratio with a 4 inch bore would yield an almost identical HP increase and be more fuel efficient. What would be nice is if the SP-46 (WC-WD) kit was now available and could be used with the 4 1/2" stroke for 10.5 to 1 in antique pullers.

My motive here on the SP-46 M&W kit was to have a realtively inexpensive way to raise HP using racing fuel....a drop-in set of 4 1/8" sleeves and pistons that have high (approx 10.5 to 1) compression. Not everyone wants to spend $3 to 4000 dollars on a big bore/ big stroke engine. This old SP-46 kit required machining off .150" or so off the top of each piston to work with the 4 1/2" stroke crank and worked very well for what it cost to be able to install it. When it wasn't available anymore, I still haven't found a "cheap" alternative yet to replace it.

DrAllis wrote: My motive here on the SP-46 M&W kit was to have a realtively inexpensive way to raise HP using racing fuel....a drop-in set of 4 1/8" sleeves and pistons that have high (approx 10.5 to 1) compression. Not everyone wants to spend $3 to 4000 dollars on a big bore/ big stroke engine. This old SP-46 kit required machining off .150" or so off the top of each piston to work with the 4 1/2" stroke crank and worked very well for what it cost to be able to install it. When it wasn't available anymore, I still haven't found a "cheap" alternative yet to replace it.

  use a 8 inch rod and the wd45 power crater piston and if you machine it the same you will be there. could use that chrysler rod thats just in under 8 inches long and probably not have to mill any from the piston. just  have the expense of turning the crank. I personally think that the 4.188 bore 413 chrysler piston with a rod length change to get the comp. ratio desireable would also be a cheap build just bore a set of used 4 1/8 sleeves .060 over.

The solution to your problem is a lot more simple than you are trying to make it. You are dealing with a flat head and if you use a stock head gasket you can assume they are 0.040 thick.  Measure the deck height of your block (distance from center of crank to top of the block (deck).  Do your calculations as to what compression ratio you desire to determine what the compression height of the piston should be.  The good part about your needs is that 4.125 is a very popular piston size that all piston makers stock.  You can call them, tell them the compression height and the pin size and all they have to do is pull 4 pistons and cut the pin hole and boss.  I personally tell them that I want standard small block chev ring grooves as these rings ready available and reasonable.  The price that will usually be much cheaper than you buy off shelve pistons and have a local machine shop modify them for.  In the past I've used J&E and Ross and were pleased with the quality and price from both companies.  Also don't forget to tell them to put lock ring grooves for the pins.  Also if you want a chambered piston, you just find a chev piston with the type / size chamber you want and figure accordingly.

 

You will probably be disappointed. What is the cost of the two kits??  If the 175 kit is cheaper than the 170, go for it !!! it used to be the other way around. How much is the kit with no compression????

MikeB (SD) wrote:  I agree Dr. Allis. One would think if your going to the drawing board they could have come with a little more compression and horsepower than that. I agree with your theory to Mitch your thinking about the dynamic compression ratio as opposed to simply the static compression ratio. I did a little checking with AGCO this past week also and they currently have the sleeve kit for the 8:00:1 compression (170) piston's marked 28% higher than the 8.25:1 compression (D17LP/175) pistons and I checked with (3) different local dealer's. Thats completely nuts it the exact same piston blank!

I always work with  the dynamic comp. ratio

It don't matter if you're pulling or farming, if you want a specific compression ratio you will probably won't find a kit for the same.  But I can tell you from experience the 241 cid with the right compression height and the right  timing setting will run long and hard in the field and will give you the performance of a 60 hp tractor with no problems.  The only thing you have to watch is the engine temp and an electric fan (on front in addition to standard fan) will solve that usually.