Theres so much more to headers than primary tubing diameter. My 1-3/4 MAC longtubes work just fine on my street driven 408 in the 550-ish crank hp range. I would run larger primaries if it was a track car to shift the power band up higher, but of course that depends on so many other factors equating to a complete engine/drivetrain package. The SBF platform is inherently exhaust restricted and one would make up for that with more exhaust duration and valve events via the cam. Things like a tight radius right off the head and poorly built collectors will hurt power everywhere, not just in a specific rpm band. You can do quite a bit of primary tube bashing and not notably hurt power.

Exhaust gas velocity and laminar flow is what matters more than anything and the primary diameter needs to be small enough for good velocity, but large enough for high rpm breathing requirements. In some cases you can have lower backpressure and consequently better exhaust scavenging with smaller primaries and that helps low end power into the midrange. Backpressure is never good for power and just sticking bigger headers on a small street engine, thinking you're reducing backpressure, will just hurt performance all over compared to properly sized primaries. It just all depends on a whole bunch of factors, not just primary size.

 

Some of this is also based on the fact that the exhaust gas cools the further it travels away from the exhaust valve. It's why stepped headers are a thing. It's why port area tappers to a larger size at the exit than at the valve. The cooler the exhaust gas is, the more dense it is. The denser it is, the more area you need to maintain the same velocity. Otherwise, you increase velocity at the expense of pressure drop (back pressure). 1/2*rho*V^2, Mr. Bernoulli at work. So using the exhaust valve size as a deciding factor is really not good. While it could be used crudely, better would be exhaust gas temperature and actual exhaust port flow rates. Gas is the hottest at the valve, therefore, sizing would naturally be smaller at this point.

 

To me headers are all about scavenging (along with the valve events) to help pull the intake charge in as effectively possible for the application. There is some kind of voodoo magic scavenging with stepped tr-y merge collector headers that I leave to others to science out. Too bad the price is hard to talk myself into. Need to pull the kids out of private school and take them out of sports! LOL

 

Sound advice, it's not always just the individual parts, it's the combination. My wife likes to tell me that she is going shopping for a new dress, to which I would say, "go for it, use the American Express card". This is followed by her reminding me, "Of course, you can't just buy a new dress without considering new shoes to match, or a belt, or a scarf, and in some cases, a new hat (or worse, a necklace). This is known in wife talk as an "ensemble", which is defined as "A unit or group of complementary parts that contribute to a single effect, especially as in a coordinated outfit."

Married guys on this forum will know what I'm talking about. BUT, a group of "complementary parts" only works if we know where this "outfit" will be worn. A group of "complementary parts" to go on a fishing boat looking to catch deep sea sword fish are not the same parts fit to go to a Christmas party. The same applies to headers. Headers for a 1,200 horsepower, 430 cubic inch Ford powered race car, with a 250 shot of nitrous, are not the headers that will work well on a 450 horsepower street/strip Mustang...

 

That’s hilarious! 😂

 

As both bassman97 and and 65fastack mention, smaller diameter primaries speed up the exhaust flow to the collectors, and larger diameter primaries can allow for more volume. In most situations, we are dealing with having to make compromises. We need to spec the headers to work with the customers combination and how he uses the vehicle. Also, the weight of the vehicle and the transmission come into play. On a 5-speed manual trans street/strip car, I can usually go bigger on the primaries than I can with an automatic transmission Mustang, which, with less gear gear ratios (the C-4 has 3 ratios) compared to a car with 5 speed manual trans. It's a case of everything is dependent on everything else...

 

But if your wife asks “do these headers make my butt look big” - just run away.

 

I love my wife and I love being married, especially since my wife is 26 years younger than me. Marriage has taught me many things, and some of those things were very expensive lessons (this is my third marriage) if you catch my drift. Any discussion about my wife's butt is always entered into with the utmost of care. In fact, when I was in the Army, guys assigned to the bomb disposal team were not even as cautious as I am when the question "how do I look?"ever comes up...

My wife...

 

 

An interesting chart, Ed. I don't know when that list was created, but I think is very conservative. I think that technology on all levels has evolved since then. I think we can do things today that we could only dream about 30 years ago, in pretty much every aspect of higher performance. This is especially true with the Mod Motor engine. Think of this question: How much horsepower can a 289 Ford pushrod engine make, on methanol and turbochargers? A 1,000 maybe, or 1,200. I don't know. Now, look at the 4.6L Mod Motor engine (almost the same displacement, 281 cubic inches). John Mihovetz at Accufab has made just a tick under 3,400 horsepower, with a stock OEM block and the Ford GT heads (also stock), at 10,000 RPM and 62 lbs of boost, on Westech's engine dyno. The mechanical compression ratio is 11.25:1, and there is zero detonation (MoTeC computer). We have run that engine on the engine dyno numerous times, and it blows every ones mind. It's beyond comprehension. We are talking 12 HP per cubic inch. In the 1960's, the Top Fuel 392 Hemi Chryslers were putting out about 1,600 horsepower on 85% nitro methane. Look where we are now...

Hey Ed, I need an email address for you, please.

 

GK - that chart is from the man who built the headers for a lot of NASCAR and NHRA Championship winning and record holding race cars.

Here's a set he recently did up for a record holding Super Stocker...

 

I suspected that the chart was for naturally aspirated engines. Engines using power adders (superchargers or even nitrous oxide) would have to be on another chart. One of the major differences I see between an all our race engine and a street/strip engine is the required power band. Again, we are dealing with the world of "compromise". A street/strip Mustang probably has a power band between lets say 2800 to 3000 RPM and up to 6200 to 6500 RPM, which means you need a reasonable amount of power (or torque) all through the mid-range of the power band. An all out drag car probably leaves the starting line at 5000 RPM (most 3500 RPM stall converters flash up to 5000 RPM at the initial hit on the starting line). And during the run, they probably shift above 7500 RPM, and never fall below 6000 RPM. The requirement for mid-range power is not needed, in essence, they are above the mid range all the way down the track. Engines like that can use much larger primaries and get away with it. The headers have to be tailored for what you are doing with the car. It's like shoes, if you are going to enter a dance contest, my advice is to not wear your golf shoes...

 

Ed just thru my golf shoes out the passenger side window in that regard Bad enough the little town cops in Groveport, Ohio decided to tag team me today to amuse themselves. Oh well, There is always the racetrack.

 

I have a question. How can the OEM 4.6 block take all that boost ? I've heard that the 4.6 can only be bored 0.020 over with out causing overheating issues and cylinder wall distortion? I DON'T know this for a fact or from personal experience. The 4.6 in our mercury grand marquis ran great. Again, I'm not saying that I know these as fact just asking a question.

 

4 bolt, cross bolted mains, some are 6 bolt mains I think. Unlike the Windsors, Ford realized that copying GM maybe wasn't the greatest, so they went back to the Y-Block/FE design inspiration with deep skirts which helps to improve strength/rigidity. At the levels quoted, more than likely, the block was also sleeved to 3.7" bores too, so keep that in mind. But end of the day, there is not doubting the fact that any late model block, from any brand, is leaps and bounds better than what they came up with in the 60's where 1 hp/cu in was amazing.

 

This is a header thread. Stop. Ask mod motor questions in the mod motor section.

 

OP brought up a 3,500hp stock block 4.6. That’s impressive! I’m not interested in the 4.6 but if I was I’d be asking questions. After all, he brought it into the thread.

I’d rather be schooled a little on the 4.6 than read you guys b!tch about where a question belongs.
$.02

 

I agree

 

Yes, it was brought up in relation to examples of exhaust sizing and the capabilities of modern technology, not building. I prefer to stay on topic with relevant information and saving 5 pages on how to build a mod motor in the 5.0/5.8L section that will turn into a crapfest.

 

 

That doesn't make any sense

 

Didn't you quit this website... 3 times???
[/QUOTE]
I did. Don't know why I came back, it wasn't because of your friendliness that's for sure.

 

Didn't you quit this website... 3 times???

I did. Don't know why I came back, it wasn't because of your friendliness that's for sure.
[/QUOTE]
Not meant just for you, there's others

 

Always entertaining, maybe not relevant to the subject at hand, but entertaining nonetheless.

 

Sure is. Sometimes I do say things that I shouldn't. Don't mean to hurt feelings.

 

Here’s a good example for y’all. Spoiler alert, it’s disheartening for the bolt-on buyer.

The reality of bolt ons. How much hp do they really...

Bolt-On Power! Super Ford, May 1996 Dynojetting the popular 5.0 Mustang performance mods to see how much power they really make text by Donald Farr "How much power does it make?" must be one of the all-time most asked questions when the talk turns to 5.0 Mustangs and the plethora of...

www.allfordmustangs.com

 

Here’s a good example for y’all. Spoiler alert, it’s disheartening for the bolt-on buyer.

The reality of bolt ons. How much hp do they really...

Bolt-On Power! Super Ford, May 1996 Dynojetting the popular 5.0 Mustang performance mods to see how much power they really make text by Donald Farr "How much power does it make?" must be one of the all-time most asked questions when the talk turns to 5.0 Mustangs and the plethora of...

www.allfordmustangs.com

Interesting post. Couple notes: 1) They didn't know at the time that Chokemaster mufflers weren't a good choice for power and 2) I feel redeemed for sticking with underdrives (10HP, 2nd largest power gain for those who don't read the post) whereas everybody says they do nothing power-wise.

 

Still would have been interesting even at that low power level to use a straight-through vs. chambered. Oh yeah, Engine Masters did that - what did it cost? 40 HP on a real motor . Kids, don't use Chokemasters!

 

Still would have been interesting even at that low power level to use a straight-through vs. chambered. Oh yeah, Engine Masters did that - what did it cost? 40 HP on a real motor . Kids, don't use Chokemasters!

40 horsepower!? C’mon. I once was on the dyno with a clogged cat and I didn’t lose forty horsepower. How many cubes did the “real motor” they were using have, 1000?

 

I made 900 thru Manaflows running tailpipes. They are pretty quiet. Borlas are similar in design, but neck down to 2 1/2" inside the muffler.

 

I made 332 with the stock exhaust minus two of the four cats while using the dreaded chambered mufflers.

 

It was an interesting episode. I want to say this was a mild 454, but I could be wrong.

The 3" single made more torque and horsepower than the dual 2.5" with either muffler.

 

Same deal on my Suburban.... replaced duals with a larger single system and it was better everywhere. Mileage, power and quiet!

 

Generally we can be sure those running "old school" Chokemasters weren't making any real power. They sounded like they were making a s-ton tho Based on the testing, I'd lose about 20-30 HP on my 428 using chambered mufflers.

 

which headers will help me get a trophy wife 20 to 26 years younger than me?