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3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.

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#1 (permalink) Old 03-11-2004, 10:48 PM
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Ok, lets try this one. What gains could one expect from a good set of headers for a 325. M3 headers vs. after market. More torque? Hp?
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#2 (permalink) Old 03-11-2004, 11:05 PM
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Exhaust manifolds (headers) won't do much unless you enlarge and match the diammeter to the exhaust system. Plus, it's still restricted by the cats. If you hollow out the cats or remove them completely, you will notice more gains with the headers.

You will generally loose low end torque and gain high end HP.

4-2-1 (4 cyl) 3-2-1 (6 cyl) style header produces some high end HP while keeping your mid-ranged torque there

4-1 (4 cyl) 3-1 (6cyl) style header produces significantly more HP while loosing most of your low-mid ranged torque

Everything has to match, you can't just expect gains by slapping one bolt-on modification. I tell everyone the same thing, before you upgrade anything, understand why you think you need to upgrade it. Bigger isn't always better.

Lastly, make sure if you upgrade your headers that you get the very best quality. Poor welds or cheap materials could make the header leak. That way, you would loose power.

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#3 (permalink) Old 03-11-2004, 11:12 PM
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#4 (permalink) Old 03-12-2004, 12:08 AM
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Quote:
Originally posted by bimmerfan620@Mar 11 2004, 11:52 PM
for headers the only gains youll see is if they are equal length and have long tubes. otherwise you wont see any real gains.

those pipes look like gennie headers without the extend tubes which you should get to get your gains heres a dyno graph for them

first pic is the headers with the tubes.
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File Type: headers1 (46.1 KB, 71 views)

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#5 (permalink) Old 03-12-2004, 12:12 AM
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and this is the dyno graph
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File Type: dynoheaders (336.1 KB, 63 views)

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#6 (permalink) Old 03-12-2004, 12:26 AM
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a significant amount picked up midrange it seems... nice charts..



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#7 (permalink) Old 03-12-2004, 11:23 AM
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hey ! are thoes the "HIGH PERFORMANCE" headers listed on E Bay for 99.00
I was wondering about how legit they were. Lemme know if you mount them and if you get any gains.
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#8 (permalink) Old 03-12-2004, 11:25 AM
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Quote:
Originally posted by Doogle325@Mar 12 2004, 12:03 PM
hey ! are thoes the "HIGH PERFORMANCE" headers listed on E Bay for 99.00
I was wondering about how legit they were. Lemme know if you mount them and if you get any gains.
my post is not ebay stuff , i think they are gennie headers.

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#9 (permalink) Old 03-12-2004, 05:25 PM
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Yea, those headers were on ebay. They started at $99 but ended usually in the $400 range. I was keeping an eye on them. Can't find them now though.

What I was wandering was if anybody here have headers on their Bimmer. What gains do you feel.
I know all the tech. rubbish on headers. On V8's there is a huge diff. 15-25% gains in hp. I know. I built a couple of Mustangs. Is there just as big a diff. on a 325i? Or not?

Would a `95 325i pass emissions without the cat.?
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#10 (permalink) Old 03-12-2004, 08:02 PM
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Quote:
Originally posted by Mattitjah@Mar 12 2004, 06:05 PM
Yea, those headers were on ebay. They started at $99 but ended usually in the $400 range. I was keeping an eye on them. Can't find them now though.

What I was wandering was if anybody here have headers on their Bimmer. What gains do you feel.
I know all the tech. rubbish on headers. On V8's there is a huge diff. 15-25% gains in hp. I know. I built a couple of Mustangs. Is there just as big a diff. on a 325i? Or not?

Would a `95 325i pass emissions without the cat.?
yeah you are right i just checked. hmmm ,good price.

they arent supersprint headers mind you , usually youd be looking at around 1600 for a set of good headers.

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#11 (permalink) Old 03-12-2004, 08:38 PM
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Well, according to the graph that Furious posted, I should get pretty good gains with headers and down pipes alone. Ad my chip, CAI and M3 exhaust to that and I would probably be close to satisfied. I would estimate that it would put me in 220-230hp range. Maybe more?
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#12 (permalink) Old 03-12-2004, 08:55 PM
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Do you want to hear the truth or only what you want to hear? First of all your M3 exhaust isn't an improvement over your stock one. You need to properly match the exhaust pipe size of your exhaust to the headers, otherwise it's useless. And like I mentioned before, having the stock cats on restricts the airflow, without removing the cats or using a hollowed out racing cat, the larger headers are useless.

I have a friend with a 325is 5 speed who has Supersprint headers, Supersprint cat back exhaust, hollowed out cat and a Supersprint performance chip. Guess what? His car is slower than my 318. The reason behind it is you loose a lot of back pressure, you push all your power to high end at WOT (Wide Open Throttle) and you loose a crap load of low end torque.

You can ignore the facts and just believe what the manufacturers tell you. 15HP gain! Think again. Even if you somehow manage to gain 15HP, it would undoubtedly be at 5000-6000RPM. The most important thing you should think about when tuning your motor. Torque is easily traded off for Horsepower, but Horsepower is not so easily traded off for torque. You'll end up with a motor that you have to rev up high everytime to get power. Honda is the perfect example of a no torque lots of high end HP motor. Good for track, very poor for city driving. If that's what you want, then by all means.

Why do you think you need larger exhaust manifolds? Is that a restriction in your motor? What "other" modifications have you done in your car to require you to upgrade your manifolds? Put some serious thought into it. At $800USD for those headers there's definitely something else more worthit you could buy. Plus, buying no name brand headers or incorrect diammeters would ultimately make your car slower. If German engineers could increase your motor by 15HP just by adding a larger header, they would have done it already.

Not trying to put you down, but in real life it's not that easy. intake (5HP) + exhaust (10HP) + headers (15HP) + chip (10HP), wow I've already got a total of 40HP, who needs a turbo!? :wink

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#13 (permalink) Old 03-12-2004, 09:51 PM
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Bry, since you know so much( :wink )tell me this... How do you ad torque?
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#14 (permalink) Old 03-12-2004, 10:35 PM
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Quote:
Originally posted by Mattitjah@Mar 12 2004, 11:31 PM
Bry, since you know so much( :wink )tell me this... How do you ad torque?
Make everything smaller and more restrictive to create back pressure. That will make your car slower as well. I was just pointing out that it's easy to make HP at high end with the expense of low end torque, but it sacrafices your low end toque which would make your car slower on the streets. Without more mods (headwork), adding a larger exhaust manifold would only slow your car down. You're not sucking in enough air into the engine to need larger headers.

You give and take. That's why trucks have so much low end torque, but totally blow on the highway, the truck's peak out at low RPM's and at highend they barely make any power at all.

If you don't want any give and take, go FI. The only way to get more torque and make your car faster is to increase the displacement (bore out the heads).

Remember, you only go bigger if you determine the limiting factor is the restrictive size. If not, increasing the size will only kill your cars performance. Usually cams will require more air/fuel so that is when you do exhaust/intake mods. Otherwise the intake, chip and exhaust is the furthest you should go in terms of bolt-ons for a stock car.

Bry

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#15 (permalink) Old 03-12-2004, 10:40 PM
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so in theory to add HP and torque into the car you would have to indeed change the whole system to harmonize as well as the stock one.

ie - equal intake to equal exhaust to get an even increase in both .



hmmmmmmmmm does that make sense or am i wacked?

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