h vaccum?

I thought I would post this here first. Does anyone know how much vaccum there should in an H manifold at idle or WOT. This is for my tractor puller. You guys seem to be more helpful on these technical questions. Also which tractor had the smallest venturi that will fit a H carb. Was it the distilate H? Thanks guys.

We run a vacume gauge on my Super M puller.
We use the gauge to tell us if it needs more fuel.

At idel ? at wide open throttle it should read almost zero. If it has vacume at wide open throttle it is showing you need more fuel.

We put a vacume fitting in just above the carb on the intake.

We have also preformed this test on the dyno to see how load effect timing as well as vacume and fuel.

Good question , most don't think to do this.

Thanks. I have a hot little H that wont lug worth a darn. I think I hogged out the venturi to much. Makes good horse up top but get out lugged on the big end. I pull antique class 1st gear only pull.

CJ, Jim, Engines are gonna make a certain amount of power. It can be an engine thats fresh and new and got the latest puller tricks, or it can be an engine thats just got the plain jane rebuild kit. They are going to make a certain amount of power and torque.

If you have "freshened up" your engines, runs good, makes decent power, but your stalling the engine, your gonna spend alot of money on it, and do alot of complaining that something didnt work, snake oils, etc etc, and thats something you and we all hate.

You dont need more power. You need to know more about the tractor, and its adjustements to aide in assiting the actual balance, or weight transfer, the actual important chassis componets that transfers the engines power thru the transmission, thru the final drives, to the tires, is where most spend alot of money on. In fact, its from that point on is where you need to look at,,, there is more to it that whats under the hood.

See, there is a engine, then there is a chassis. A chassis is a long list of complicated specifications,, taken only from years of experience to obtain. So, here comes the "Club Rule Book" . A series of what you can do, what you cant do.

Safety equipment, weight bar distance specs, and also, you will see Hitch specs in the common standard pulling rule book.

X amount of HP will pull. It can be 20 hp it can be 30 hp, it can be 40 hp, so on and so on. Knowing the limits of the engines power and weight can be adjustable, and the adjustments are not found in the engine books. History can show you, survivors can tell the tales, winners are proud, second place sucks, and who ya gonna call when you have spent all the money in the world, and you have a fire breathing dragon, but only goes 50 feet and spins out. There are two spans of the pulling spectrum, the ones who want the biggest and the baddest engines, and the ones who want their tractors to pull better with what they have already.

A 25 hp H can pull just fine, and outpull other 25 hp H's that are there, sometimes, they outpull their 30 and 40 and sometimes 50 hp mutant conversions of a H, if, a little thought is put into the chassis, instead of the cubic dollar.

With that said, CJ, if you have your hitch set to rule book specs, and your powering out, the problem is not in your engine.

Its in your hitch. You are overloading the engine by the amount of "Hook" or bite" the hitch specs give your chassis takes alot of cubic dollars to pull competitvely if thats the path you choose to take,,,,,,,,

If you have the hitch at the 18/20 guidelines,,, and your powering out,,,,,,, I would like for you to raise your hand.


Now, the ones who got the power and spin 10 feet behind the leaders,,,, (top 5) raise your hand,,,,,,

I just rasied my hand to the second one. I got the power, but scratchin for traction,,,, so you see, your on one end of the scale, by having too much bite, not enough power, where im too much power, no bite.

So, back to basics,,,, my question for you, is where do you start and go from here. All the dyno time in the world wont help. All the cubic dollars are spent, and here we both are,, in the Farmall Forum. ChadS

My hand is up and waving! I have more than double the factory horse in my H. I recently pulled against an H that was set up the same way. I know for a fact that he is dynoed at 27 pto horse. We pulled off the drawbar, not the swinging part. Same size tires. Weight within 100 pounds. I got to the other end and my engine wouldnt lug. the other H kept going and was lugged way down it out pulled me by 30 feet. I think all my horse is up high at 540. I Think that it may not have enough vaccum to keep fuel going up the manifold. does this sound possible? I guess that is what I am asking. I will sacrifice 540 horse to get lugging torque. Is this making sense? Also if I pulled just as high but farther back on a swinging drawbar would that help? Any other suggestions other than running 18 up 20 back?

Rethink your hitch, as well as the carburator issue. If you run the H carb, they had two sizes of venturi options, small and a 1/4 inch bigger ID. M carb, you need a 25 or less. Venturi ID sizes are measured in 32nds of an inch, so when you see the two digit number, in the ID of the venturi, it means, (for example) 25, which is 25/32. Keeping the venturi size smaller than the biggest setup,,,
Will increase vacuum pressure, increase manifold air speed.
You need fast air speed to keep the air moving into the cyl when its lugging the hardest.
If the air speed is too low, it becomes dead air beacuse it pretty much loses its ability to draw, and mix the fuel that enters the cyl. It goes flat rpms drop faster.
Higher manifold vacuum pressure is associated with air speed, faster air speed, the higher the manifold pressure, faster, higher quality conditions inside the manifold and port create better conditions to enhance torque when the rpms are pulled way down, the carb butterfly is wide open, the air speed has to be matched up for the rpm ranges.

CJ, in your case, your target rpm for tuning will be from 1000 rpm to 1800 rpm. If your tuning it to run 2500 rpm, and on the track its running 1800 and less, tuning it at 2500 doent do much good, if it never sees it while its working under a load.

The other H was tuned for low rpm operation, his air, fuel were dialed in to run low rpm, and thats what you need to duplicate in your tuning.

40 degree distributor will kill you!
(more on that later)

Chassis adjustments, If your hooking that well, to the point of stalling, you dont have to touch anything in the engine to gain distance. A chassis adjustment is meant to balance the chassis. 18/20 hitch spec setup takes power on a good track.

If your stalling, you need to drop the hitch height 2 inches, if it goes further down the track, but still stalls, drop it downm another inch, but dont move the hook point back further away from the center of the rear axle centerline,,,

Once you have the chassis loosened up to the point of tire slippage, its now time to start looking at proper weight placement to get your chassis to LIFT the front end when the slightest load to the drawbar is applied, what goes up, must come down,,,,, when the front end drops if your air pressure in your tires are good, the hitch will lift the sled pan off the ground releasing its grip from the soil and putting all the weight on your rear axle and carries it till, you either stall, spin out, or full pull.

I suffer most cases from the opposite with my Super H puller. I spin out bad. I idle it down, to try to let the tires grab a bite to gain lift, but either the track is loose, and the best cut tire in the world is useless against a brand new tire in this case, or when I get to a soft spot, it spins and the front just bobs.

The first thing I will tell you is, I have never ran weight behind the rear axle on this tractor. I lightened the nose up quite a bit,,, and relied on the engines power to acclerate and hope it sticks, but 5 out of 10 times, it will spin with the front end down.

On a good track, I get it figured out pretty quick,,, as do most drivers, on the loose sandy tracks,,, Im three weight classes heavier than usual, just to try and get a bite to harness the massive torque this litte Super H stroker makes,,,, but, Ive exhausted my search for tires, for fast gears, power is not a problem, its in my chassis adjustments I have seemed to have seen many times on others, but dont have on my puller. It tells me that my front is heavy, need to move weights behind the rear axle to create a better counter balance for the lifting leverage that the chassis creates during the act of pulling.

Other optins I have considered, is changing the angles of the drawbar to create lift off the chassis by making brackets that have attaching points above the rear axle centerline, then rebending the drawbar, so it drops lower in the front and at an upwards angle to the hook point. When the front is up, the drawbar should be level with the ground, and pulling off the high points above the rear axle, actually making the front seem lighter, without changing weight. I can see this in my head, but have not got that far to redesign.

Oliver pullers already know this about the hitches, oliver hitches are one of the best pulling hitch design in stock form, vs IH, and it comes down to how its attached to the rear end, and how it creates lift. Its why olivers are hard to beat, but if the same basics are used, it can increase the pulling effect off a tractor. NATPA banned any part of the hitch above the axle centerline to even the odds, so this is a reasoning for my belief, If I can adapt an Oliver 88 hitch on the back of my H, would it pull better........... ChadS

ChadS, you sir, are a wealth of knowledge. I sure do appreciate all the help you have provided. Now about the 40 degree distributor I have in my tractor. I know with the compression I it breaks up a bit wide open but what is the problem with it. I figured that while I have you here I better get all the Info I can. Plus we have exchanged info without criticisim from the rest on the tractor pulling forum.

With a base timing set at 20-25, (second notch on the pulley) then add 40 degrees advance, thats a total of 60+ degrees total timing when you combine the two. So your timing is advancing way too much and will LOSE power in the lugging rpm.

You want a total of 40, or around a total of 40, but not much more. On my Super H, I had a 40 degree dizzy, it fluttered under acceleration, it was very lazy under power. I went back to a 23 degree distributor, it was a totally different animal! It revved up quicker, it idled alot better.

I want my advance timing in, before I hit rated pto rpm, so when the load is applied,, everything is there, already waiting for the load to be applied, if its still searching for timing from too much advance, it will float the timing advance and the rotor will rock back n forth,,, hunting I call it,,,

With it locked into less than or around 40 total degrees, it will set itself faster and lock in ready for a better peak power range for a certain rpm range.

Now, if you have high compression, lets say you run a compression test,,, and its less than 200 psi,,, throw away the race fuel, its not helping to build torque. Only one fuel combination has worked to make power for what I have done in the past. A mix of E85 and 93 octane pump gas. Its also about 4 bucks cheaper a gallon. ChadS