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Hello everyone, I'm working on my first build i've gathered up some parts to use, but they are of slightly different dimensions that what is called for in the plans that i've been going off of and i have not been able to find any information as to how i could accurately adjust the dimensions. I've read a lot of posts in this forum with people having problems with this same build and members have told them they're dimensions are off in one way or another, but i haven't been able to find a way to tell how... The plan i've been going off of is attached below.

I think i've managed to figure out some of these rules of thumb but i wanted to run them by someone who has a clue (because I certainly do not)

1 - Combustion chamber length should be 1.5 times the diameter
2 - Intake pipe should be 4 times the length diameter
3 - The volume of the combustion chamber should be 5 times the volume of the intake pipe
4 - The volume of the exhaust piping should be roughly 4.5 times the volume of the combustion chamber
5 - The last i'm not very sure of but i believe there is some kind of relationship with the length of the exhaust pipe and its average diameter.

I'm taking a long shot at #5 but i can't see how they came to this 92.3mm, and the average diameter seems to be the most likely, i just don't know how to calculate that figure.

I've managed to find a piece of schedule 10 304 stainless pipe approx 15" long for the combustion chamber. If rule 1 is actually somewhat correct ill need to add an extra half inch onto it.

I've also found two 3" 90's (haven't taken an exact ID measurement)
The 90's have been grooved for victaulic piping so there is a slight indentation on the insides that runs the inner circumference. From what i have read on the forum this would make them no good for my exhaust piping, but i figured i'd double check before i chopped the grooves out of them. For all i know they are the wrong diameter for my combustion chamber.

Am i on the right track with any of the parts that i've found or should i just throw it back in the scrap bin and just fabricate everything from scratch? Or would pyrojoes Caliber scaling method work for this type of engine? It appeared that the method was for valved models with a linear flow, but i just have no idea.

Thanks for any help you can provide! I'll be sure to update you guys on how my build goes and post a video of it running!

Hi!

It might be a good idea to use Pyro's recipe for beginners for your first engine (it's for valveless engines). That lockwood engine is pretty crappy. For your first attempt, try making a linear engine. They are the most easy to do and easy to start. When you get bored of it, you can have it cut up in 5 minutes to make something different.

If you really want to go with that lockwood, make the bends smooth. Don't worry about the .5" of combustion chamber length. I think it will work fine for this engine. If you still have the option, go for this lockwood, it's much better download/file.php?id=11410&mode=view

So I've abandoned the Lockwood plan and went with pyrojoe's caliber method to scale my dimensions, just wondering if my rough, no to scale drawing looks like something that will run. All dimensions in inches, and not too scale obviously...

I guess I'm mostly concerned with the scaling method because I've gone so much larger then what most designs show and, the larger you go the further out the volumes will become. Double the pipe diameter, quadruple the volume right? Looking at my numbers I think my exhaust cone is a tad large and I'm worried about the pneumatic valving not working.

Holy Canoli. 26" tailpipe exit? Might I suggest you start with a smaller, known to run motor to get yer feet wet? There's a lot to it before jumping into something so dangerous.
Scaling is definitely screwy up in this range.

I built the suggested engine and tried starting it today, it sounded like it wanted to go but I think my tank got too cold before I could get it running. I had 3 half full or less 20lb propane bottles which I think was my biggest problem with it not starting today, I'll try again tomorrow with a full bottle.

My fuel injector is a piece of 1/2" tubing with 9, 1/8" holes drilled through and positioned perpendicular to the air flow. I think I might not be getting proper fuel mixing though just from looking at where the hot spots were

I got it running today! I'm guessing I think I need a bigger bottle to keep it running, thr 20lb bottle was pretty cold when I shut it down right after this video https://youtu.be/K6P7LQcQUN8

Good job! Try flaring the intake and don't use a gas regulator

I've got it coming right off the top of the standard propane tank valve through 3/8 hose and a ball valve, is there something different I can do to get more flow off the tank? I'm considering running another tank in parallel with it turned upside down and controlled through a needle valve for liquid flow.

Definitely read that a flared intake creates better mixing and intake air flow, planning to do that on my next week off as well as putting it in a proper frame so I can clamp it down properly! The few seconds of light thrust I got out of it was enough to free it from the c clamp I was using

Maybe the ball valve is restricting flow? Just running it from the tank should be enough to really get it going.

A ball valve is one of the least restrictive types of valves as the flow can pass directly through with no direction changes and it causes relatively little turbulence in flow... i feel like my issues in getting my engine to run lie in some deficiencies in my build quality.

I forgot to trim some of the excess length from my 3" u-bend, making my exhaust section about an extra 6" longer than the blueprints called for. I read somewhere else on this forum that lengthening the straight pipe section of the exhaust pipe before it begins to expand can actually lower the input required for the engine to idle, but I am sure that this is adding way to much extra length.

I also found another copy of the blueprint i was using and some of the dimensions have been edited to be more easily read. It looks like the only major deviations that i've made would be that the inlet of my CC is 5.5", whereas the clear blueprint calls for 6.5". Still the same total length and end dimension into the exhaust section of the CC at 7". Seems fairly minor by itself, but coupled with my extra straight pipe on my exhaust section i probably have too much resistance in my exhaust flow for my smaller CC.

I was looking to find more information on intake cone, but I don't seem to know where to look. I can't find much information on the geometry, other than why it's so helpful. I can only guess that making a cone coming off the intake at an aprox 45 degree angle for about 1.5-2" in added length would be sufficient but if someone could point me towards a more technical description on the design that would be greatly appreciated. Otherwise, the blueprint does seem to refer to this dimension as "R.25" is this just refering to a cone 1/4" in added length at a 45? I can only go off of what i've seen in other peoples videos and pictures but these cones generally appear to be much longer in length...

Pretty sure R.25 refers to "radius 0.25" which would mean that your radius is 3.52/2=1.72
1.76*0.25=0.44
1.76+0.44=2.2

That means the intake measures 2.2" across from your flare. I suggest also cutting the engine down to size and using the correct diameters

Fully planned on cutting the engine down to size, just read somewhere else someone was recommending extending the length a bit to aid with getting the engine to idle. I'll get to chopping!

Also, why did you multiply the .25 to the radius and not just add it? 1.76 + .25 = 2.01 seems to make more sense to me unless there's something I don't understand. And is the correct geometry for this flare a 45?

Yes you are correct, I was thinking way too complicated. I made a drawing to clarify things. The flare should be a bell mouth, not just a 45 degree cone. Also, do not just start adding lengths of pipe; stick to the plans.

Fixed up my manufacturing errors and omissions and it works great! Thanks for the help!

https://youtube.com/shorts/xv62KnXxLus?feature=share

Good job!