Question for MLPANKEY (and others)

Just for grins and giggles, I've got an engine build question for you. What would a 175 piston on a 4" crank do for a guy? When I built my first WC, the guy in the shop told me to do that. Tractor runs good, seems to have plenty of power, but I'm curious for those in the engine building know, what'd I gain or lose?
Aaron SEIA

I don't have the answer from experience but I can help calculate the effect.

First measure the distance of the piston from the top of the block to the top of the piston on the WC. Then measure the distance from the top of the piston to the top of the wrist pin on both pistons.

If the latter two measurements are the same, it will make no difference if the diameters are the same.

If the distance from the wrist pin to the top on the 175 piston is greater, subtract the difference from the first measurement and calculate the new compression ration.

Horsepower increases are directly related to the ratio of the compression ratios - 8:1 has more horsepower than 7:1. The efficiency of an internal combustion engine is directly related to the compression ration; that is, raise the compression by 10% and the efficiency increases by a percentage. My book suggests changing compression from 6:1 to 8:1 will result in about a 5% efficiency improvement. Since efficiency is the measure of energy in vs energy lost, the horsepower will increase by the same amount if the amount of energy being consumed is the same and the rate of rejection of heat is unchanged. Usually the rate of heat rejection (exhaust) goes up with compression ratio by a small amount so it is an approximation only. However, breathing will be significantly improved because of the smaller combustion chamber so fuel usage may increase providing a greater than theoretically expected horsepower increase.

well it will be lower compression on the four inch crank than it would be on the 4.5 crank providing they both had the same rod length and deck height . The 175 crank 4.5 inch parks the piston .250 higher at top dead center and .250 lower at bdc than a 4 inch does . thus the 1/2 inch gain in stroke. was this suppose to be a trick question ?

ps you gave up some cubes also by not using the 4.5 crank . no replacement for displacement and compression makes torque. I believe the wc pistons on the 4.5 crank would make more comp. and definitely 25 more cubes.

I hope I didn't miss something. I thought you were considering 175 pistons in a WC. MLPANKEY's response sounds like you are considering WC pistons in a 175. I assumed the WC tractor because of your statement of 4" crank.

might out to read my posts again . I was saying that a 175 piston on a wc crank would be lower than factory advertised the 175 compression ratio because they gave up 1/2 inch stroke . I also think the 4.5 crank with the wc piston would make more comp.than what he has and I know it would make 25 more cubes . sorry if I dont convey my thoughts well when posting

ok heres the technical . a wc had 5.5 to 1 compression with a 4 inch crank you add the 4.5 crank to the same piston you have 8 to 1 . a 175 piston was 8.1 to 1 comp. with the 4.5 crank reduce it to a 4 inch crank and you will have 6.1 to 1 . that is providing both pistons are flat tops. a 45 power crater piston on a 8 inch rod 4.5 stroke will go over 12.1 comp. ratio

So, you are saying that a WC with a 4" crank and 175 pistons is better than a 4" crank and stock pistions, but obviously not as good as 175 pistons on a 4.5" crank. This isn't a pulling engine, just a restoration. I built it almost 10 years ago and the shop guy at the AC place I was getting my parts from was a puller. He suggested the 175 pistions on the stock crank as a bump from stock. It's a 35 with no electric start. Just wondering if I went backwards from a stock kit or not.
Aaron SEIA

I think with the math you gained 1/2 a point in compression . Now the math could be off a little for I do not know the compression height on a 175 piston and would have to pull a wc piston out of a old block to measure it . I did however know the deck hieght and rod length along with stroke and advertised comp. ratio for each tractors in stock apperance to find the unknown. so with all that said and looking back at my data i wonder if allis used there over stock wc pistons to make the comp. ratio of the 175 also the cam shaft profile of a 175 would make the .1 difference.

Thanks for the info. I'd love to come watch you pull sometime, but SE Iowa is a lot of fuel away from where you run. You definatley know your orange pullers.
Aaron SEIA