I am trying to design a Tri Y style Header for a hopped up Willys 134L flat head. And I am having hard time trying to figure out primary tube etc. lenght. The couple on line calculators i have run through end up with a primary lenght longer then the vehicle. I have almost all the specs it should take if someone experianced with this could help me this I would appreciate some guidance. ex. Open 47' BBC Closed 12' ATC Duration 239' Overlap 21' Lift .351" Cylinder displacement 35 cu in or 573.5 cc bore 3.185" Stroke 4.375" max torque 2000rpm compression ratio has been raised to 7.2-1 Thanks
Your over thinking it, while I admire your attention to detail, I think your looking at fractional horsepower gains with a perfectly designed header vs one that is designed for easy installation and good clearance around various obstacles in the engine bay. Personally I'd make a header that's easy to install and doesn't get in the way of the steering, clutch linkage, transmission, etc.. It's the intake manifold or lack there of that kinda sucks on that engine.
Check out post #37 in this thread for some inspiration http://www.jalopyjournal.com/forum/threads/f-head-flathead-conversions-photos.732281/page-2
given your input parameters, the calculators are probably showing >100" primaries w/ bore/stroke and torque rpm. I agree w/ above..... so you'll be 5% off of ideal....I don't think you will miss 2 or 3 HP.
The intake manifold is now a customized Pierce aluminum designed for the Weber DGV 32/36 that will be on it. I do see your points. As I have never designed or built a header before I was just trying to do it as close as possible to ideal. When you are trying to take 60bhp engine and pull 90 out of it you reach for anything that might add to the pile.
I have friends with the same basic engine in both L And F head. Just not a fan of the Clifford header which really does nothing at the less then 4500 rpm these 134's run. So I wanted build my own.
Tri Y design is not for max effort max HP- it's for building torque and power under the curve or broadening the curve. I'd venture that your averages will be higher with a tri Y but the peaks would be lower. If you'll be driving it, higher averages will make you happier than a higher peak. If you're racing it then higher peaks but make sure you're geared to get there and watch shift recovery too.
The mid range torque advantage is exactly what I am looking for out of a Tri Y design. The Willys will have a 5.38 final drive with a 30% OD so 12 forward gears and 4 in reverse. 60mph on the Hwy will be at 2550 to 2600 rpm in OD. As you can see from my Avatar the vehicle is a Jeep (lets call it a 48 CJ-2A as that is what it looks like even if it has a later CJ-3A windshield on it and a shaved tub. To give you an idea of where the drive train is headed heres a couple shots of the 134 L (now 140 cu in)
You want to let your firing order work for you. 1st and 3rd.. 2nd and 4th in the firing order. Then Y them together into another pipe. It's really a double merge. For torque your first merge will be near 25-28" the second close ending near 36" total. The order out the pipe should be expanding pulling out the next pulse. Burns Stainless can do a design but it's not free. Other here on the site are excellent also. Your engine is a long stroke and will like a long first pipe. Good luck
What shape and size are the exhaust ports? A smooth transition to the round tube really helps. I also like to size my tube to have the same cross sectional area as the exhaust ports.
Exhaust ports are 1.375" D perfectly round. Firing order is 1-4-3-2 so pairing is geometrically easy. 1-4 & 2-3 I do have the oil pump in the middle of everything to make things fun. Only other thing in the area will be the 3/4" D steering shaft and possibly one of the steering U-joints.
Sounds like a reasonable starting point. You could make the secondary Y where you could add 6" extensions in there, and try that. I doubt you will be dyno-ing it. It will be seat of the pants feel anyway, right?
1-1/2" primaries would work quite well then, nice and convenient. I would be tempted to use 1-3/4 or 1-7/8 for the secondaries, but I have no scientific evidence to back this up. I usually buy mandrel bend tubing from speedway.
1.5" primaries was the plan. I like the idea of adjustable secondarys. Actually I do plan on running it on a chassis dyno once the thing is on the road.
There's lots and lots of science about headers and gas flow out there. You want velocity, and you want negative pressure behind the pulse. Too big of a pipe and your velocity goes down dragging the torque with it. Here's one of many out there. http://www.impulsengine.com/how/header.shtml
Go the easy route build a little short header and drop a small turbocharger on it and double your horsepower . Easy to do and will make all the torque you need. Corvair did it. back in the 60's so it would still look era correct. They went from 102 h.p. to 180 h.p. boost limited.
Ya a turbo is not in the plans not really suited to the low rpm off road stuff. Now if I could find a McCullochSuper charger at a garage sale that would be different lol.
You are way overthinking it. What you need is the primaries to be long enough that you don't get reversion. most try ys, other than the ones built for balls to the walls dragsters, that I have seen have the primaries built in the 12-16 inch range. Some of the old guys told me when I was young that primaries are important and that you can let the secondaries run wild. That is not the case but that is what the old guys used to say. This would be a good question to direct toward @hotroddon he is really sharp with headers.
I just kinda guessed, now you got me thinkin' I left some critical HP on the table.....In retrospect I was going after a look as well as clearance. Will be following what you came up with.
It will be a while before I get anything actually done on the Headers. I have a bunch of Body work to do before it gets to be over 80 degrees here and I have to buy different activator for my paint. I plan on using 1.5" T Blue foam and tooth picks to design the header with I can use my bandsaw to cut the foam to match available tubing and the tooth picks to hold it together. Kind of like a super cheap lego set for headers. My hope as I am doing a 4 cyl with a 1-4-3-2 firing order is to bring the 1-4 together as close to the Oil pump as reasonable and then into the first Y. Then take the 3-2 pair straight out as far as I can from the Flange as possible without getting into the Intake manifold and angling them so the Y for that pair is just outside the 1-4 Y trying to keep all 4 tubes the same length. Then a Pair of Secondaries side by side down to where the collector Y will be at a point I can run a basically straight 2.25" Pipe from the back of the Jeep to. Once I get the drive train in the chassis I will start working on the design. Since I have a little leeway with the Steering I will leave that to do at the same time.
Yes as stated here prior, your firing order is what makes a tri y work. Length is not so much the factor. What you are looking for is as one cyclinder exhausts it pushes the prior gases and the prior gases pull the next. Its pretty simple. As the first pist suggests almost any length will work...the longer the better but servicing should take priority. Also stated, your finished flange fab and port transition is a huge power benifactor at any rpm. Sent from my SM-G920P using The H.A.M.B. mobile app
If you can check out a single side of a NASCAR header. You can see them on eBay. They now called a double merge instead of a TriY. It gives you an idea how long the primaries can be and how the second one slides on. Their primaries maybe a little long for your application. I have a set on my stock head GMC6 which has 4 exhaust ports. They are 3 step on two of the ports ans 2 steps on the other two. I guarantee they work. Good luck.
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