Good ID size for NA headers

[bcjammerx]

I'm thinking of getting a 4-2-1 header...and I'm not going to spend over $200 on one right now...so while I know it won't last long or be as good as bisi's $850-$1000 4-1 header, I still want to get the most for my money.

I plan on keeping my engine built mild, and n/a...so what about the size? Advice? PLEASE don't tell me to save up for bisi's...I'm not dropping 1k or nearly 1k on any one part for a LONG time. Even over 3-400 for one part is most likely a no no for me right now.

It seems all the no names on ebay are 1.75" collectors to 2" even tasauto's is like this.

I've seen a few that are 2" collectors and go to 2.25" ...since my catback is 2.25" I figure that is the smallest I should go.

What size are most GOOD headers? should I go with the larger size or is the first better? Or should I find one with an even larger ID

I've also noticed some of them have the #4 cyl cut down quit sharply to the right, and some have it curve more...either better? I would think the curved is better.

Given all this...is an aftermarket header under $200 going to give me ANY gains over the tubular style a4 or the cruddy a1's?

[cloudasc]

Find and modify an a4/a6 header, and have them weld a larger collector on it, say 2.5" all the way to the cat (flexpipe included), replace the cat with say a magnaflow 2.5" spun, then reduce the outlet to 2.25" to match up your catback. Probably give you more power then buying a dc, or megan racing header. Should be able to be done for less then $200. Sorry those are OD measurements.

[bcjammerx]

Find and modify an a4/a6 header, and have them weld a larger collector on it, say 2.5" all the way to the cat (flexpipe included), replace the cat with say a magnaflow 2.5" spun, then reduce the outlet to 2.25" to match up your catback. Probably give you more power then buying a dc, or megan racing header. Should be able to be done for less then $200. Sorry those are OD measurements.

I don't see how they would do that...could you go into a littler more detail on that? Seems like you are saying to modify to tubes coming from the flange (and the flange's ports) to make them larger...the only way I can see to do that is to cut them along their length, widen, and re-weld.



Another question, if I did get an aftermarket header, is all it's going to do is move my powerband up in the rpm's or will I see a significant increase in hp/torque...say...10% or so [around 10hp]

[cloudasc]

I don't see how they would do that...could you go into a littler more detail on that? Seems like you are saying to modify to tubes coming from the flange (and the flange's ports) to make them larger...the only way I can see to do that is to cut them along their length, widen, and re-weld.



Another question, if I did get an aftermarket header, is all it's going to do is move my powerband up in the rpm's or will I see a significant increase in hp/torque...say...10% or so [around 10hp]

I guess I mean increase the tubing size between the 2-1 merge, flexpipe, & the cat, on a a4/a6 lower manifold. Should see a gains in hp & tq throughout the entire stock power range, and the largest increases at higher rpms, when the largest volume of exhaust gasses is trying to escape your motor. Also the magnaflow cat i'm thinking of is meant to handle up to 5.2liters of displacement, which will lower your emission readings provided everything else is working right and will not be a restriction like the stock cat is. At this point the biggest restriction could be your 2.25 catback piping, resonator and/or muffler.

As for how aftermarket headers from different manufactures will affect your powerband, your best asking other users who have experience, or contacting the manufacturer themselves.

For my car I will be going 3" from the 2-1 merge to the spun cat (until i can afford a bisimoto), then reduced to 2.5 through 2 magnapacks & a dynomax super hemi turbo muffler.

[bcjammerx]

hmmm...yeah...I imagine not everyone's bends are quite the same...but they all look remotely similar.

Main difference is the inner diameter and whether the tube coming from cyl 1 goes straight to the tube for cyl 4 or whether it has more of a curve.

The inner diamters are 1.75 and then 2" to the cat vs 2" and 2.25" to the cat...wondering what if any difference there is there

and also if that straight to or curve has anyeffect...but mostly curious about the sizes

[cloudasc]

Size of combustion chamber & compression ratio will help you determine the volume of each cylinders exhaust pulse, from there your goal is with a good exhaust system to is to time the pulses so they merge smoothly together and out your the rest of your exhaust system. Keeping in mind all these things, while remembering the firing order while your looking at the headers will help you figure out which design is better. Smoother bends are always better then sharp ones if size is the same, and the distance the exhaust gasses will be traveling are the same Good Luck!

[fatboy1185]

You could save up another $200 and get a ESP header

[bcjammerx]

What makes the ESP better? I COULD get a dc header for more than bisi's...but they look just like these no name headers...if the bends are similar/same I can deal with cracking...I'll just weld it back if need be...why spend $600 more on something if all I have to do is weld a crack every now and then...really isn't that big of a deal to me...hell after I re-weld, it'll be better.

A crack developing doesn't have anything to do with bends and how well if flows really, just a weld quality issue...again...I don't see how that would effect flow while it's new and sealed.

If the bends are different then yes, if the angles are different the yes...but if the only issue is a crack developing...I'm not spending $600 more.

Eventually the way to go is bisi's f1 style header...but not until I put some real cash down on forged internals...for now...not worth it.

also having difficulty finding info on the ESP headers

[bcjammerx]

bump for another take on the question

What difference in power will I see with:

stock tubular steel 4-2-1 91 ex manifold
vs these two
aftermarket 4-2-1 non-f1 style 1.75" to 2"
aftermarket 4-2-1 non-f1 style 2" to 2.25"

Debating whether there is significant difference between the stock 4-2-1 over these other two. Please note I am not referencing bisi's header or one that is f1 style. I can't find any specs on dc headers...but they SEEM to look just like these other 4-2-1 headers I'm looking at but MUCH cheaper. A dc header is what...$600...brand new from majestic the OEM is like 350? but a jy is ?50-100...these aftermarkets are about $100

[d112crzy]

You could save up another $200 and get a ESP header

They don't make anything for f22's.


OP, I would just get the a4 stock header, and modify the downpipe. Get a REAL 2.5" collector, and possible cut the secondaries right after the flange and step it 1/8" ID piping.

[bcjammerx]

They don't make anything for f22's.


OP, I would just get the a4 stock header, and modify the downpipe. Get a REAL 2.5" collector, and possible cut the secondaries right after the flange and step it 1/8" ID piping.

I really don't think I'm going to gain any power by getting anything but the a4 header...the dc style may give a LITTLE over the stocker...but unless I get an f1 style I just don't see how I'm going to get much more power over the a4

[d112crzy]

Because most of the gains on normal size tri y headers come from the collector, not the 4 into 2 part.

[bcjammerx]

Because most of the gains on normal size tri y headers come from the collector, not the 4 into 2 part.

excellent...thank you much.