The first obstacle to power in 36hp engines

[swanlakers]

I have a question about 36hp motors and I hope someone can answer. In a stock 36hp engine what is the first obstacle to power? Is the first restriction the size of the venturi, size of the manifold, size/shape of the intake port on the head, size of the intake valve, size of exhaust valve, lift/duration, or restriction from muffler, or the pea shooters.

The reason I ask is that I intend to build a 1300 - 69 stroke x 77mm with a compression ratio of about 8.3 to 1. I am trying to figure if it’s worth using larger valves, or to use ratio rockers 1:1.15, or a mild cam. I intend to use the 40hp manifold as I think it would bolt on to the now wider engine. (64 to 69) I will also probably use a stock stale air 40hp muffler.

I do not wish to use dual port heads, or dual single port carbs. I am only looking to get a lift in the low end power. I’m sure that if I only increase displacement I will see some sort of gain, but I might as well use a few of the other mods as well. I guess I will end up with sort of a 40hp version of a 36hp.

The heart of my question involves heads, I don’t want to open them up too much and loose gas velocity. I’m kind of leaning towards the ratio rockers on either intake, exhaust, or both.

I have both 36hp and 40hp tin I can mix an modify to keep cooling without leaks.

The point of this engine is to do what I can within the stock look.

Kind of a long question, but I wanted to get it all out at once.
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[slalombuggy]

Rule number 1...power is in the heads. An engine is a glorified air pump. The more efficient it can get air in and out the more power it makes. An increase in displacement and compression will help but you still need to make it breathe.

brad

[swanlakers]

Yes, thank you
I am looking for an opinion on what is the first obstruction, is it the carb, intake, valves, etc
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[EVfun]

Displacement?
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[henry roberts]

note. this is opinion only, based off zero experimentation.

i would start with TDE (theo decker) tailpipes. they are supposed to give a, "seat of the pants" noticable, increase.

from there i would look at the venturi and aircleaner.

i put a fair bit of thought into how i would build a more powerful "stock looking" motor. my thoughts to were to focus on the incremental increases everywhere to get every last fraction of a hp and let them add up... some of the ideas were as follows:

case. oil gallery added to generator side of the case for no4 main. deburred. possibly oil galleries opened up to a larger id. (most likely not needed for this spec.)
clearence top of case over center main to increase airflow between front and back of case.

most likely a 1600 offset oil cooler.

prob a 40hp oil pump.

crank knife edged (if possible), balanced, 8 doweled etc etc. if i was rich there is a oil shedding coating i would add.

flywheel maybe a pound or two off for a beetle but by no means light.

clutch, either a 9 spring bus or a 356 diaphram. the springs in the bus could be upped if nessecary.

rods, deburred (basically sandpaper finished to slightly reduce weight and shed oil) checked, rebushed etc with 40hp ARP bolts.

everything tested, shot peened, nitrided blah blah, blue printed then all rotational bits balanced together. ALL reciprocating bits matched as close as i could get them.

stock cylinders bored to 78mm with (from memory) mazda capella 1600 pistons. they might need domes removed. 20mm pin, nearly identical pin height.slightly lighter than stock with thinner rings for a good reduction in friction losses. i was looking for slipper skirts but never found any suitable. the dream would be niscals with custom pistons.

stock 36hp cam gears grooved as per the how to hotrod book.

the gear from memory it is rivited to the cam so drilled and tapped for bolts. grind undecided.

lifters/pushrods. uncertain as the rockers and grind undecided. i wasn't sure if the denzel type seperate pushrod/lifters would be nessecary. the desire was to reduce the weight as much as possible. i couldn't come up with a feasable way to lighten the lifters though. at the very least 1600 pushrod ends as lighter than the early style.

distributor drive thinned and lightened. possibly rifle drill the fuelpump pushrod then weld up the tip and reharden.

late pre filter high exit fuel pump or filter version depending on the year of the car (the exit was raised to improve flow). i once cleaned up around the inlet and exit ports of a 36hp fuel pump. nfi if it is worth the hassle though i just did it to see if it could be done.

rockers. ratio to be decided. there is some weight to be lost on the stock rockers so that would be done. if they needed rebushing i would cut an oil channel from the existing gallery to the bottom centre of the rocker and put the oil hole there.
12mm nuts and shortened adjusters.

shafts prob stock with a solid centre instead of a spring and the spring washers replaced with shims.

heads. my thoughts were to weld up the chambers top and bottom to increase the squish area. the dream was to fluke into a fast burn chamber design.
i was wondering if filling the top and bottom of the pocket area of the intake port would reduce port volume to keep airspeed up.
i also wondered about filling the outside corner of the turn from the manifold into the port.
i would love to know if rounding off the corners on the valve stem would be beneficial. i had wondered about fillet behind the valve stem to help the halves of the flow rejoin would be an improvement.

stock valve sizes but i was looking for suitable modern valves with thinner stems (for flow and weight) intended for 4 valve, turbo exhaust valve applications (to make sure they could handle the extra heat of an aircooled motor). matching lightweight collets and keepers.

valve springs as close to stock weight as possible. with a long stroke single carb set up it won't be a rev monster and with a lightened valve train why waste hp on heavy springs.

i was thinking of running a tight deck. below .040". while the increases stroke/ piston speed will increase the stretch of the rods, the lighter pistons and low rpm should keep things on check. it is not as if it is a 94mm piston on a 82mm stroke at 8000 rpm.

the intake would need the calculations done to work out whick 40hp intake diameter would be best... or if a modified 1300sp would be better. the final choice would have the aluminium shroud cut bact to better represent a 36hp manifold.

the best carb would need to be calculated but i would probably go with the body of a 32PCI1 ex vw industrial motor and the top off an ex Lloyd Alexander 32PCI with the 36hp like threaded fuel line. the 40hp manifolds would need modifications to work with the bore and stud spacing. these carbs have a 6 screw squirter pump caver so do look different to a 28PCI.

either a stock 36hp exhaust or a custom made one with 2 chambers only joined with a small area of connection, that looks the part with the front cyl from one side paired with the rear from the other.

as i said this was all pipedreaming and i never tried any of it. i hope this gives you food for thought.

[TomSimon]

The short answer is 'there's no silver bullet'. It's an engine system, with everything working together. A low performer at that, by today's standards.

As with any air pump (engine), to get more power you need to make it more efficient, increase the number of bangs per minute, slide the power band where it makes torque up higher in the rpm band, make it spin faster, and make each power stroke more powerful than it was before.

That all takes good parts, more cylinder pressure, more rpms. SInce you don't want more rpms, that leaves more cylinder pressure, a bigger bang with every hit. Increasing static compression ratio and higher octane gasoline jumps to mind. A larger duration camshaft will reduce dynamic compression ratio, so you can add even more static if you widen the valve opening and closing event, it'll breath better, too.

The high leverage items to more efficiency are better heads, then all of the components to take advantage of better breathing. The 85yr old combustion chamber design isn't doing that engine any favors, either. There's no quench pad, to speak of. There's lots of good information on that.

I have a friend that has been able to increase intake flow from a stock 36hp single port head to where it rivals an Okrasa dual port head. He has a flow bench, a basement, and lots of time on his hands.

The economics should drive one to building a new engine with increased displacement with a stoker crankshaft, adding dual port Okrasa replica heads, bump the compression up and add dual carbs, bigger cam, a header, 12v ignition. The usual formula.

But you don't want to do all that, I get it.

I'd talk to Ronnie Chuck or someone known for building championship winning 40hp based Formula Vee engines. The class rules, single carb, single port heads, etc, had guys really needing to innovate. But we are talking tiny gains in power over a narrower rpm range.

my 2cents worth
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2-time NASA Pro Racing Champion, Bonneville 130 Club and 150 Club Memeber, BRS Pro Gas racer