H power increase

what do i got to do to get more hp out of my 51 H and still keep same carb?

Scott: You can do all kinds of things, but going to a different carb would probably be one of the first things to consider. You can buy an overbore kit with stepped pistons. Would probably run better if you re-jetted the carb after doing that. Probably your best bet.
You can get into swapping cams and heads from a 300 or 350, but I don't know how much good that will do if you keep the stock carb.....
An engine is an "air-pump system". It can be difficult to get performance by only changing one thing - or by refusing to change something. It all has to work together. Good luck. mike

Scott: You can do all those things Mike mentioned, plus probably a few he missed, however I question how much it will improve hp.

When I was a teenager back in the 50s, my dad had an H and a 300. H with C-152 and 300 with C-169. Other than the advantage of TA and IPTO, we couldn't see a huge difference. PTO work was the most noticeable advantage to 300. On drawbar we pulled the same 2 bottom plow, same 28 blade disk and same 4 section spring tooth. At the end of the day, H covered almost as much ground as 300.

Today I tinker around with SA, 130 and 140. Even though 130 and 140 are 10 more cubic inches, the Super A will still give them a hard run on a drawbar pull. I've had those tractors a long time.

Couple that with the fact these tractors are now 50-70 years old, be happy with what you have. IH ain't building these anymore. If your tractor pulling, got a bit of advice for you, the smart operator always wins.

this H my grandad bought new in 51 for use on his hog farm that
was a sideline to his steel mill job, motor has never been touched inside,tractor is in nice shape but burns oil,aint no show piece and grandpap wouldnt want it to be, he wanted me to get another 60 years work out of it. I farm for a living and so did my dad we H back home that dad still has that i learned to drive on 35 years ago that H always ran perfect and had power for a H, ten years later dad and i overhauled and restored a 350 mainly cuz we liked that old H so much it had slightly more power but used so much more fuel, granted live PTO,TA,and espeically fast hitch was nice the old H still found it self working quite a bit. our "big" tractor back then was a 656 and assortment or other 60 to 75hp diesel come and go used things that never found favor like them farmalls, so after all that long story,bottom line is i want to make grandads H run like dads, all we ever did was change plugs on that old H,just for routine maint,it was the 152 block,gas head and manifold original carb but had
dome pistons

If you want to keep it simple just look for a set of Firecrater or high altitude (5000 ft)pistons (or similar type) and sleeves. Better think about freshening up the bearings and grind the valves while you are in there. If the bearings are a bit loose now they might start knocking with the extra jolt of the higher compression. I have a 51 H also with Firecraters and it delivers 150 lbs of compression on all 4 with those pistons. It makes plenty of power for pulling logs and what not, but haven't hooked it up to a plow yet but I have no doubt it will pull fine even in clay. It did pull a 16ft trailer with seats and full of people at idle in 5th gear and I hate to say it but the idle was so slow it sounded like a JD, but kept right on going and not once acted like it would die. There is a nice little "crack" to the exhaust with that compression. If I am pulling a good size log up a hill at full throttle it has never acted like the carb was too small. Just remember, a lot of carb engines run more efficient at a higher air flow through the venturi. Too big of carb will slow down the air flow and not mix the fuel all the way. it might act like it runs better, but that is just because some gas isn't getting vaporised and it is running lean at that point and lean can act more "snappy" but falls down with a load.

Thanks Bob,your description of your H sounds just like the one back home at dads,my 51 has the 7mph 4th which makes the worn engine even more obvious,got to get it to run with that snap and crack and lug down like a old john