We all know that on an overhead valve motor with it's short exhaust ports, tube length and size and collector size and design can have dramatic effects on the power curve. How about on a big power blown Ford flathead? Getting the exhaust out of course is essential, but with the long torturous path of the exhaust ports through the block, and the Siamese centerport, does header tuning make any difference? Thanks, Joel
Good question Joel. I built the headers for the 8BA in my avatar, and it was 10yrs ago but I had done some reading on this subject and I believe some pretty knowledgeable flathead guys said it hardly mattered. So I stayed with a basic block-hugger shorty-style header design. But you're moving much more air than me, so it sure might make a difference in your case? Love this stuff. Let us know what you find.
LOL big power blown flathead is an oxy-moron. header tuning is always advantageous your port length only means that your primaries do not need to be as long. you tune from the valve to the end of the tube. Many men on the flaties put a divider in the center port. There has been a lot of discussion over the years as to weather that made any real difference in the performance. The thing to remember is that zoomies work well at higher RPM and the shorter they are the higher the RPM that they start to scavenge properly. A flathead is normally not a high RPM motor and would fare better with longer primaries and a collector. You want to avoid short primaries with a collector to avoid reversion. As far as actual tuning is concerned I cannot really help you. There is a formula or several that are used. That is just an area where my expertise is lacking. I have a tendency to copy headers that i know work and go from there.
To me there are two sides to this coin. On one hand, I think header tuning would be advantageous if and only if you can get the exhaust ports to flow enough so they are no longer a significant restriction. But on the other, if the exhaust ports remain a significant restriction, you essentially have a converging / diverging nozzle setup. And in that case, the portion past the throat of the nozzle becomes critical in determining how the pressure pulses are passed back through the nozzle and into the chamber (reversion and scavenging). Either way, someone needs to post some dyno data.....
This is very interesting. Could you explain how to apply it to the actual situation that exists with a flathead? From what I understand so far, the "converging/diverging nozzle" effect occurs within the block. Since "the portion past the throat of the nozzle becomes critical", it would seem to concern the pipe from the exhaust port out. It sounds like something could be done here, but what?
Think about a power valve on a 2 stroke. The down stream expansion chamber and exhaust pipe is a defined shape. This shape generates very good scavenging ( very critical in a 2 stroke) within a relatively narrow rpm band. At other rpms, the expansion chamber shape is not optimal, the pressure waves do not rebound ideally, and engine performance suffers and people complain about a 2 stroke not having any "bottom end grunt". This is where the power valve comes in. It effectively changes the throat size so the expansion chamber is effective across a much wider range of rpms. In a flathead, the throat is the internal exhaust port and can't be changed on the fly. The only option is play with header pipe shapes, diameters, lengths, etc to optimize performance across the intended operating rpm range. In the end though, the question may come down to is the juice worth the squeeze. There are a metric shit ton of less then optimal design choices in a flathead, and you might be spending alot of time dyno testing, flow benching, and analyzing headers for only a nominal gain.
Every time I see a question on header tuning it reminds me of the guys on Youtube who ran a small block chevy and essentially beat the hell out of one of their header tubes to test its effect on performance. They about beat it flat with no discernible difference in power on the dyno. Considering that a flathead isn't a high revving high horsepower engine to start out with my feeling is while it might make us feel good about using headers and such, there probably isn't a lot of difference power wise to be had in that area.
I saw that episode. It wasn't much of an engine, so it didn't need a lot of breathing. I'm talking about on a high power, high rpm, built to the hilt racing engine. On street engines, I agree it doesn't matter.
Unless you have the engine on a dyno and flog all the possibilities there is no true answer that theory and math can come up with as a RACE car would need. Street is all about packaging and hooking it up to mufflers
It was a 560hp 400cid SBC. Pretty stout if you ask me, i doubt there is a Flathead out there that makes 560hp on Gasoline.
That is a pretty stout street small block in the video, more so than I remembered. But those dents aren't big enuff, only 1/2 deep or so. Regardless, it is well known that tube diameter and length, as well as collector design, length and diameter will have an effect on the power curve of most engines.
What is your application? Model A Ford, or slingshot dragster? Either way, my advice is build the best header you can within your space and packaging limitations and don’t lose any sleep over it. Good luck and don’t forget to post pics. -Abone.
Joe Abbin's books have blown flathead dyno pulls, you might refer to those publications for a starting point. On a balls out blown flathead, (exhaust ports would be heavily modified) I'd have no problem just running a pair of zoomies
Finnegan's header bashing test was a bit of a joke too. They only showed peak power in the video. Show the entire curve, from just off idle to the top end. Then integrate and determine the area under the curve. They have a dyno with a proper data logger at their disposal, use it. Show more info, EGT's, combustion pressure vs crank position, manifold air density and pressure, etc. I bet there was more going on then meets the eye.
My engine builder made me sit in the car during the dyno tune partly due to the new leather interior and probably more so due to the fact I would be the one who blew it up. It made 308 HP on a chassis dyno before the inevitable occurred. No, it the flatty didn't grenade, I did. After the pull he yelled at me and said "you lifted!" I replied "I also shat myself!". I was still a ways off the rev limiter but the the test was basically flawed. You can't ask the guy that just spent $15,000 building a flathead to be the one to flog it! Moral of the story, you can make "big" (all things considered) numbers on a flathead with "off the rack" headers and full exhaust. Could I eke out some more horses by tuning the pipes? Why bother? It's fast enough and in the end... I would still lift.
Header tuning is done to a specific rpm on race cars. I doubt that you will gain or lose any noticeable power on a street engine by playing with the tube length.
it has been my understanding my whole life, that thru drag racing a proper header design all the tubes are equal length .FROM THE VALVE SEAT TO THE COLLECTOR, this lines up the exhaust pulses and causes a scavenging effect, or siphon effect . this way there is a vacuum in the pipe waiting when the exh valve opens and at really high rpm will draw the gasses out past tdc of piston on exh stroke leaving in somewhat of a vacuume for when the int valve opens .... all this makes free hp ,,,no tradeoffs no extra stress on anything period ,however cubic inches =tube diameter math and rpm range =header length ..yes heavy physics math to optimize.... , non equal length "headers " are tubular exhaust manifolds and horsepower gains are ONLY because they are not as restrictive as stock iron manifolds ,period,, now because flathead,,,, we have intresting problems that need worked out we need to figure port length and the outsides are pretty long and the Siamese center ports are short and a problem (however ive read of a crank and cam that changes the firing order and helps with this). a port wing would help for starts and your center tube is gonna have to be long enough to make up the length given to us by the outside fwd port to collector length (wherever that works best) as this will be your longest tube and will denote the length for the others , they will have to be a lil snakey to add length before the collector ,, like the rear tube on ALL hooker supercomp headers ,, all this being said is it worth it ? we fiddle with these things endlessly anyways and if you do your own fab work fab is free .. the bottom line is its "FREE HP" as in hp and no side effects , so imo its worth it ,, free hp is great.. example oil pans another freebie ,, example on a drag motor bb chev say making 700 or so a moroso or hamburger big buck oil pan is worth 50-75 hp because of how it manages the oil spray ,,pricey yes but 50-75 with no side effects ,ill take it ,,,,,, ok that my 9 cents fabricator john miss you dad
Wow those are huge numbers for a flathead, congrats. How much boost and what size crank? Considering how hard it was to make ~170 (max) on mine, I'm fascinated by these big HP flatheads.
Merc crank, .125 over bore, Ross pistons 8.5:1, 8 pounds of boost from a 471 on Navarro intake, Navarro blower heads that were re-machined a bit to dial in the CR. Aluminum fly wheel, 1.5" Chevy valves, every bit of block prep/grinding that Joe Abbin said to do. His recipe, not mine, I cant take credit. I added MSD distributor and 6-BTM timing box to control detonation. M-15 Melling pump, electric pump in tank, Holley regs feeding 3 97's from Clive. Dyno test was pulling all 3 carbs (progressive now). Crank is held in with H&H's CNC main caps. My machinist liked to joke that the block weighed half what it did after machining. In my little roadster it is scary quick...not 442 fast mind you. These flatheads don't have big torque numbers and you can feel the difference.
Wow I would love to ride in that thing! My machinist that did my block (balancing, boring, valve relief) was really trying to talk me into adding a blower, because basically everything is setup for it except compression, and naturally aspirated it just feels like the poor thing can't catch its breath. Fun engines though, I still love mine. Interesting that you run 8.5:1 CR along with 8lbs of boost. My machinist really worried about that CR, mine is also 8.5 IIRC, but he told me if I change my mind and add a blower later he wanted to change pistons out to lower the CR significantly. But obviously it's working for you really well. Now it's got me thinking......I really should just add a blower. Only thing I'm missing that yours has is the larger main caps. I'm running the Max1 cam, that maybe should be changed I suppose.
I've built 40-50 camaro and T/As and this flathead would run with any of them, of course it is a bit lighter than the F bodies. I have 29" tall drag slicks in back and it twists them up very well. That lower end makes my gut wrench once in a while. I left a light down the street form my house coming back from a night cruise accouple months back, had a car along side egging my on, I took the bait and dumped the clutch at the light at around 2500 RPM. What a ride off the line. QC Posi required some active steering and 1st gear didn't last long, made that shift a bit sideways. Stupid, that could have been ugly...and very expensive. But we don't build them to just look pretty do we?
HAHA no sir, they're made to run! Man that's so badass. Mine is in an F1, so it's heavy and will never be a fast truck but I'd love to see it breath and make more HP. I have a 3:73 posi and it will just barely do a burnout, haha. Goes down the highway at 70mph real nice though, so I guess I can't complain too much. Sure love these engines. Best sound in the world. My WWII vet grandfather bought this one brand new in '51, he and I used to work on it together. This little 8BA has become the family heirloom. Apologize for the thread hijack OP! Carry on.
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