Let's talk headers.

[ForcedFirebird]

Has anyone calculated the tuning lengths on m20 headers? Collector length? Timed pulses on any? I have a design in mind and the materials will be here tomorrow, just wondering if any one else has put any serious thought into them - not talking about "buy these, they made xxhp" I'm talking about discussing the dynamics of exhaust flow on an m20.

[Sagaris]

I do not know the exact method and formula for calculating pulse timing but a few weeks ago I had somewhat of an epiphany and thought of a way that the calculation might work (I was thinking about intake manifolds but the same rules should apply). Someone chime in and let me know if this is reasonable:

-Use an approximate exhaust gas temperature to calculate the density of the exhaust gas (assume it is air)
-Use that density value to calculate the speed of sound through that air
-Determine the RPM you want to take advantage of pulse timing
-Based on the cam duration you have, determine the length of time that exhaust valve is open at your chosen RPM
-Determine the distance that soundwaves can travel using your calculated speed of sound within the time that the exhaust valve is open
-If the distance is 50 feet obviously you cant create a header with a bend 50 feet downstream, so take a fraction of that. Divide it by 50. So perhaps you could have a bend 1 foot away and the pulse would bounce off that bend and still arrive back at the exhaust valve right as it closes in order so that the pressure wave creates negative pressure in the cylinder while there is valve overlap (intake and exhaust valve open simultaneously).

That is how I imagine it working. I have been analyzing the design of the intake manifold to determine if pressure waves were taken into consideration with its design. I have some theories about how they might have designed the intake manifold although I am not certain on anything. The log style M50 intake manifold is a much better design for taking advantage of pulses if my observations have any merit. ... sorry about my blurb about the manifold on the other side of the head that you didnt ask about :P

[ForcedFirebird]

It's all good. Yes, your theory is correct, but instead of saying 1/50th the length to a bend, you have to calculate the time from the back of the valve to the end of the primary where it will collide with the other pulses and be directed in return to the back of the exhaust valve just as it closes to help evacuate the next pulse.

On the header we manufacture for another platform, we designed them very specifically to capture a pulse (close to it, perfect equal length in most vehicles is nearly impossible), and actually came out to approx 1/2 of the 4th pulse of 32".

Exact equal length headers are difficult to build, even to measure them accurately for length equality, you have to fill them with a measured amount of fluid. Tape measures don't work here, folks lol.

As far a tuning the length and size of the intake manifolds, BMW definitely tuned the runners, how do you think the eta had so much more tq than the 2.5, and hp was vice-versa?

I am using 1.625" 16ga primaries, length TBD depending on space limitations and possibility capturing a tuning pulse. Some think length is everything, but I have seen well-designed "shorties" out perform long headers with poor design both in the length and most importantly, the collector. Collectors are actually just (if not more) important in header design than primary length.

Check out Burns headers for their ever so popular merge collectors ;)

[StereoInstaller1]

The collector needs to be about 14" past the rear bumper.

Or, my math is wrong, maybe.

[ForcedFirebird]

The collector needs to be about 14" past the rear bumper.

Or, my math is wrong, maybe.

You always manage to put a smile on my face with your antics...


Did you use ricer math? :p

[Sagaris]

I think his calculation applies to this style of collector

[Easily Distracted]

Are they going to be 6 into 2? Anyone considered 6 into 3 into 1. Basically pair up different complimentary exhaust ports? No science here. The final merge may negate any gains anyway. Just talking out my @ss.

Most headers I've seen have several bends in the firewall side tubes graduating to very few bends toward the front in order to acheve as close to equal length as possible. Are the bends taken into cosideration in the length calculation? I'm not sure if head loss from bends is a factor with exhaust gas like it is with liquids in plumbing.

BTW - Interested in these. Willing to be a guinnea pig for pre-production.

[StereoInstaller1]

Did you use ricer math? :p

oh man, didn't even figure on stickers...what color are the stickers?

[ForcedFirebird]

The collector needs to be about 14" past the rear bumper.

Or, my math is wrong, maybe.

oh man, didn't even figure on stickers...what color are the stickers?

Silver, the only color to have them!



Eye candy...

The box all this came in didn't fit in the e30 lol



Separated the mild steel from the stainless...



and what's going to be used on the m20...




Made a boo-boo, though, accidentally got 2.25" bends for the final merge collector, should have been 2.13" so that the 2" merges slip inside for easy welding and to make them real step headers ;) the 2" is wayyy too small for the 2.25" :( oh well, they will be used on something, just sucks that $60 was spent when it wasn't needed to be...

[balooshinakus]

I think the most effective header route is to use s50 headers, but bolt them up to an s50 instead of an m20 :P

[ForcedFirebird]

I think the most effective header route is to use s50 headers, but bolt them up to an s50 instead of an m20 :P

Did an m50 nv swap in my friend/customer's car. Too much work for that plastic "fantastic", really wasn't totally impressed by the power gain vs work/time/parts involved.

I will be making m50 headers with a similar design, but the m50 won't be going in mine anytime soon, you guys just keep swapping and I'll keep collecting your old m20's and parts :D

Why does everyone with an m50 come in the m20 forum and preach the m50? lol

[jasonsnoddy]

I think the most effective header route is to use s50 headers, but bolt them up to an s50 instead of an m20 :P

Did an m50 nv swap in my friend/customer's car. Too much work for that plastic "fantastic", really wasn't totally impressed by the power gain vs work/time/parts involved.

I will be making m50 headers with a similar design, but the m50 won't be going in mine anytime soon, you guys just keep swapping and I'll keep collecting your old m20's and parts :D

Why does everyone with an m50 come in the m20 forum and preach the m50? lol

s50 =/= m50

[ForcedFirebird]

s50 =/= m50

Ooops lol. Either way, I want to play with the m20 ;) Boost will come later, but N/A fun first. I have a custom cam I designed on the way and am making these headers, got the Moates tuning setup for it etc. This isn't my "be bad-ass" car, it's a daily that is going to get as much power drawn from the engine as possible (the one that's in it haha)...

[nando]

S50 = m50b30

[MonkeyMadness]

Hey Forcedfirebird, when are you going to ditch that 60* stuff...
i sold all my crap awhile ago.. and don't plan on looking back..