Compression at diff

I have a 123 engines, it has been decked, it's got a 170 lbs of compression at 1420 feet elevation, Janichson you good at this, so what's my compression ratio? The only time it pings just a tad, if i cant put the clutch in on time, with the Woods on it, in tall grass! But it runs fine on 91 fuel!

1 to 12.17
13.961 is an approximate atmospheric pressure at 1420 feet altitude. 170 is your approximate measurement at altitude. dividing 13.961 into 170 gives us the approximation of 12.17 This seems high, but remember we are not adjusting for any real world variables, nor is there assurance that the gauge has been calibrated for "gauge pressure at altitude" This is the adjusting of zero to account for local atmospheric pressure. So compressing lower pressure air to 170 is pretty radical. Calculating real ratio is best done with sizes of the bore and stroke (swept volume) and the Volume of the combustion chamber. Jim

Check total advance timing at high idle and curb timing . Then drop down a little on heat rage of the plugs . Check jet size and also fatten up the fuel mixture , Run the intake valves a shade tighter . Don't let her lug down to far . Make sure the dist centrif. advance is working and the springs are not stretched , you can squeeze the spring ends closed around the post a bit to add a slight amount of spring presure to hold back the advance qand help bring it down as the engine RPM's start to drop and they helps as your not fighting advance timing . Now as figuring out the fancy math work i always left that up to my accountant . But if you have 170 PSI cranking and running 91 octane i would think you could get by . Just keep in mind here the OLD reg. gas from back in my day was 95 as a norm and the CHEAP reg. was 93
. Back in 75 was when this gas started to change along with everything else . 1972 was the end of the performance engines with the drop in compression ratios and a huge drop in getty up and go . We were still getting good gas up into the early 80's and you could still build a 10 to 1 engine and run it BUT you have to lay off the timing , then it dropped down to 9 to 1 with layed back timing for street use on 93 . Gas tractors started having fuel related problems back in the mid 80's not because of the no lead but octane and the way it is blended to burn HOTTER for emission reasons . I peronally ran gas tractors for my HOBBY farming as they were CHEAP to buy , i can not put a number on the 706 gasser i have bought out of dead rows and put them back in the fields , some needed new T/A's and all needed the charging system repaired and that was the reason they were in the dead rows because they would stop running in line headed into the ring at the auctions i went to and if a tractor quiet running in line for what ever reason they would not mess with it and would be plucked out of line by one of the big loaders and carried back to the dead row and dropped in a spot and be sold the next day for what ever it brought . Before the tractor sale i would go down and watch them start tractors and you would see them when first started gassers with dead batterys would only run a short time and just up and die . You also had a chance to drive them a little and check them out Some times they would die while you were playing and they would maybe try and restart or it many get the hook and off to the back of the lot for the next day . You could buy qa nice 706 dead gasser for 650 bucks and up to maybe 900 if you were bidding against a salvage buyer and he was in need of a parts tractor . I ran the 93 in my pick up and whle getting gas for the pick up i would fill the 55 gallon drum with what was going into the pick up when i found a deal on a 110 gallon in the bed tank with pump for 5 bucks at a sale then the drum when to become a fire barrel . I was NOT having the problems with my gasser like other were , i bought a super nice Massey 300 combine at a sale in a driving rain storm for 600 bucks thinking i should be able to make a grand on it , that did not go well as after five different sales and never having a bid on it and not looking like anyone wanted it i decided i would use it and bought a 7.50 corn head and a friend gave me the corn sprocket for it i put it to use and started shelling corn. This is when i saw problems of running hot on the 87 as i got cheap and was tryen to cut cost by not spending that extra dime a gallon . To get this thing to run under 220-230 first it was pull the rad. and have it cleaned a flowed , nothing wrong there , next it was the Tee stat and water pump and i changed it to the water pump used on a car with A/C they move more water . Next checked timing . Everything i did had no affect . Till one day coming back from a sale i stopped to fill the truck and i had bought two 110 gallon fuel tanks at the sale for chump change and while filling the truck i noticed the pump next to me that said FARM GAS and out there there gas was like 30 cents a gallon less then at home and this farm gas was fifty cents a gallon less So i fill both of them with Farm gas and the running temp on the combine went down to 180-90 . It was oh guess what 93 octane . When that was all used up i just used what the pick up ran . I feed my 88 Ford F 350 dually 4X4 with the 460 93 . and never complained about gas mileage on it as empty truck i got on the road 15 to 15.5 with trailer i would drop down to 13 empty and fully loaded i would avg 10-10.5 , . Ya might try stepping up to the 93 even though it is NOT working on the gassers around here , i should say on the 460-560 and the 706 and 806 gassers . One guy i know had someone else do a total rebuild on and 806 gasser for him and he had less then 10 hours on it and it is setting NOW with several pistons trashed and scored cylinders .

Well if his compression ratio is that high then NOPE ain't no way he can run and work that engine on 91 . On the engine i built with my accountant we had a 5.560 bore on 6 and a half inch stroke with flat top pistons and god don't ask me what the C C's of the heads were i forget as they were smal chamber M M4210 heads that i did some work on and did C C them and had to cut 50 thow off the one to get it to come into play then they went down to a guy south of me for port and runner work to increase flow and when done we had right at 250 cranking . we ran C12 VP in it . Ing timing curve was held at 28 degrees at high idle ad that was like 1850 max and would set in at around 1650 1750 depending on class and hang and at that rpm she was about 26 degrees .

I don't know how much they had to take off the block,i guess i never asked,but i got the carburetor pretty rich,it will handle that wood's mower until i get into some 30 inch tall grass for just a little bit, then the weather cap goes up, straight up. Thanks guys!

170 is pretty high, but If it runs fine, then don't worry or change any timing.

(quoted from post at 01:16:38 07/13/20) I don't know how much they had to take off the block,i guess i never asked,but i got the carburetor pretty rich,it will handle that wood's mower until i get into some 30 inch tall grass for just a little bit, then the weather cap goes up, straight up. Thanks guys!

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If the pistons are not hitting the head and nothing else was reconfigured they probably took off less than 0.005", which would have a minimal affect on the compression ratio. If they milled the head a lot per your request that is a different story. If they did this I would guess if the machine shop was legitimate at all they would have on the bill or job papers."Milled head x--" per customer no guarantee"

It was a stationary engine, used in Nebraska to pump water, and they used the water from the well to run threw the engine,[it's got the dipstick, running on one side abs stopped on the other] instead of Ethylene Glycol, so there was some pretty good cavitaion on top of the block, i seen that, but how much they had to remove,i dont know,it all happen during spring works, it was hired done, but it run like a dream now!!

8.5 to 1

OK, so may i ask how did u figure that ??

Tractor math. 1-1=20 psi, 5-1=100, 10-1=200

I agree. That engine couldnt have been more than 8:1 stock. Youd have to deck it like a quarter of an inch to get to 12:1. You would have had to install custom length shorter pushrods or the valves would never close.
I would check to see what the timing is at full advance. It may just be advancing a little too far or the initial timing may be a little too advanced.