crazy headers

[shadow run]

hi guys, im just wondering what are peoples thoughts on those awesome long runner spaghetti manifolds that you see from time to time. Are there really benifits to be made from this type of design, or is it more for looks? Does anybody make these style of manifolds for purchase off the shelf for mx5's like you can for ae86's, or are they generaly custom made?

this is what im talking about

[plohl]

longer length headers produce resonance at lower to mid range rpm. They're not just for looks.

I have seen a few gary stewart engines with faily long 4-1 headers.

[NitroDann]

Its all about n/a power.

They will be tuned equal length, and designed to come on HARD at a certain rpm.

Im considering making a set tuned to match my next set of cams (some much bigger ones).

Dann

[wozzah1975]

Unless you have an all out circuit racing engine in a light car that can utilise a narrower power band you are far better off with a decent 4-2-1 designed header/extractor.

A well designed 4-2-1 produces a far better power curve for most applications, in particular road/club car use where a broad curve is required, and the mid range torque is far more useful than peak power. I use 4-2-1 headers on almost all the engines I build, and we've proved time and time again that they produce more useful power than 4-1 systems on the dyno, and on the track (in almost all instances)

Woz

[shadow run]

thanks for all the useful info guys! so, if you were to make a header like the ones pictured, but had them as a 4-2-1 style as opposed to the 4-1 would that creat the best of both worlds? i have seen a set up similar to this (on an ae86) where the "-2-" part goes as far back as about mid way up the passenger footwell.

Im planning on running quad throttle boddies and at the moment just some poncams, maybe slightely more agressive, with stock compression in an NA8. Maybe some headwork down the track. Its a street car that see's the track and im not really concerned about making it a little on the grumpy side for the comute to work, until recently it was turbocharged and has a very agressive 1.5 way mechanical lsd.

[shadow run]

Its all about n/a power.

They will be tuned equal length, and designed to come on HARD at a certain rpm.

Im considering making a set tuned to match my next set of cams (some much bigger ones).

Dann

this may be a dumb question, but how exactly do you "tune" the headers to match the cams? is it just trial and error on a dyno, or is there some sort of mathematical way of calculating the best design?

[NitroDann]

To wazza,

Graham Bell agrees with you and says exactly the same thing.

4-2-1s are 95% of the time better.

ive been doing a lot of measuring aftermarket headers, wherever I can. What Ive noticed is that all are 4-2-1s, and most have different length paired primaries.

To shadow run,

Basically, the idea is that the exhaust pulse from one cylinder bangs through the collector (the point where all 4 pipes join together in a 4-1 system) at the exact same time as the other paired cylinder (this is the cylinder exactly 180 degrees out of sync with it, on an mx5 the pairs are 1-4 and 2-3) is in its overlap period.

Long story short, with big cams, the intake valve and the exhaust valve is open at the exact same time, for a moment, and this is when you want the pulse to hit the collector, this creates a venturi which sucks the exhaust out of the paired cylinder and sucks extra fuel and air in.

You can calculate, using the approximate known exhaust speed, how long it will take for the pulse to get to the collector, then you work out when the overlap is(based on cam specs), how long it takes the engine to go from exhaust pulse on say, cylinder one, until the paired cylinger, 4, is in its overlap period.
Then you calculate how far the collector needs to be away for the exhaust pulse to take the same amount of time.

Anyways, you then build a set of headers with this configuration, that have a slightly adjustable length. Then you dyno it, changing the length by 5 or 10mm at a time until you get the right length for the cams.

If you have kept up, you will have noticed that it doesnt really help if you dont have big cams with quite a bit of overlap.

4-1 systems concentrate the powerband at one point.

4-2-1s give a wider spread.

Every set of aftermaket off the shelf headers Ive measured has been 4-2-1. And the primary pipes (the first pipes before they hit the first collector and become 2 pipes) have all had a different length matching pairs.
So one pair (say 1-4) has been say, 37cm long, tuned for one rpm, and 2-3 has been 41cm long, tuned for a lower rpm.

This gives a very wide powerband (in fact its not really a powerband).

90% of the performance improvement of headers on a stock engine, or mild mods (lets say intake exhaust ecu and little street cams, like poncams) is better flow, not tuned length.
The stock headers are poor flowing, no mandrel bends, big ridge at the flange due to huge welding dags, and the pipes go down to about 1'' at the collector.
Id bet that the best tubular headers on a stock engine wouldnt make 3 more hp than well made headers using the 100% stock design (length, pipe size etc)

Ok wazzah, jump on and tell me where I stuffed the explanation :p

Dann

[wozzah1975]

Hi Dann,

The Graham Bell book, although "old school" is excellent for anyone wanting to learn

Ok, this is how I calculate a starting point:

I'll use my old engine as an example. BP, 1840cc, cams, mild headwork, twin webers and high comp pistons. Estimated power around the 160hp mark.

Pulsing in secondaries MUST be even, firing order on most 4 cyl engines 1-3-4-2, so 1 and 4 collect, and so do 2 and 3.

Size:
1 1/2" OD tube flows around 25-40hp
1 5/8" OD tube flows around 35-50hp
1 3/4" OD tube flows around 45-65hp
There is an overlap. GOLDEN RULE: a pipe that is slightly SMALLER works BETTER than one that is slightly too BIG!!!
I picked 1 1/2" tube (40hp x 4 cyl = 160hp)

The secondary pipe should expand by around 2 sizes (1 3/4")

Outlet another 2 sizes (2 1/8")

Length
Far more technical. Once again, the Graham Bell book is excellent, but still only a guide. The only way to truly get the ideal length is on a dyno.

The recommended overall length is around 29" with my cam specs. As a starting point the primaries should be 15" long So with a required overall of 29", secondaries should be 14" long. There is my starting point for length.

The overall length of the header and the secondary length is the most critical. As long as the primaries are within 2-3 inches of one another in length, it will make very little difference. However adjustments to secondaries and overall length makes massive amounts of difference. Due to differences in porting, cam timing and intake length the only real way to do it properly is on a dyno. I use a slip joint on the secondaries on the extractors to play around with the length until I find a spot where I'm happy with the cam timing, trumpet length (intake) and exhaust length combination.

Obviously this is not for everyone, so here is a guide for buying off the shelf units.

-Pick a size that suits, and looks about right in the way the pipe size steps.
-If the primary pipes dont match perfectly don't stress too much, BUT if the seconday length of the pipes varies by alot steer clear. Pick an overall length that is about right for the tune of your engine.
-pay attention to the joins, make sure the pipes overlap the correct way (check out the Pacemaker website)
-avoid pipes with sharp bends and joins, and pick units with mandrel bends, not pressed bends.

Woz

[sailaholic]

Dann,

My headers are off the shelf 4 into 1 from apexi, so there are some around.

Sent from my GT-I9100 using Tapatalk

[ralt]

Hi.
Interesting topic and to read peoples ideas on pipe sizing lengths etc. Im interested to read how you handle the rest of the exhaust system from the end of the secondary to the exhaust pipe tip and how this effects power/torque.

[wozzah1975]

Hi.
Interesting topic and to read peoples ideas on pipe sizing lengths etc. Im interested to read how you handle the rest of the exhaust system from the end of the secondary to the exhaust pipe tip and how this effects power/torque.

As far as sizing goes I have a bit of a guide. Sometimes ideal sizes are hard to get as some exhaust places don't stock the sizes.

Engines making around 100-140hp 2" pipe
135-175hp 2 1/8" pipe (sometimes hard to get)
170-205hp 2 1/4" pipe
200-250+hp 2 1/2" pipe
Once again, a system slightly on the small side works better than one on the large side. Mandrel bends are nice, or if not possible and you need to make sharp bends (eg: in tailpipe) use the next size up on the bits that require the bends.

People spend lots on wanky big mufflers etc and in most cases they are a waste of time. I use a straight through fibreglass packed muffler, and if its a road car put a straight through fibreglass packed resonator at the back to take the edge of it. Avoid mufflers with lots of bends and baffles inside, and stay well clear on anything that has a expension chamber in it.

On small road/club cars I always run the system right to the back where possible (providing it doesn't involve silly bends) and this usually ends up being about the right length, on race cars depending on what it is I have ran them off to the side and made them a little shorter (eg: exit in front of the back wheels).

You don't have to spend a fortune to get excellent results

Cheers
Woz

[shadow run]

That's quite a bit of info to take in! Thanks for all your input guys. I'll be getting some headers custom made, so I'll show all this info to the guy doing the fabrication and go from there.

This thread kind of makes me want to go with some bigger cams now to justify a tuned manifold!

[dave2221]

That's quite a bit of info to take in! Thanks for all your input guys. I'll be getting some headers custom made, so I'll show all this info to the guy doing the fabrication and go from there.

This thread kind of makes me want to go with some bigger cams now to justify a tuned manifold!

DO IT

[ralt]

Hi.
Be sure the person you get to fabricate knows what they are about. It is an art.

[wozzah1975]

That's quite a bit of info to take in! Thanks for all your input guys. I'll be getting some headers custom made, so I'll show all this info to the guy doing the fabrication and go from there.

This thread kind of makes me want to go with some bigger cams now to justify a tuned manifold!

To be honest, unless you're building a race car I would just stick to off the shelf items and choose carefully. It's just not worth the expense, as the difference on your engine will be minimal between a fully custom set and an off the shelf set. Even on club race car and some race car applications I still use a decent off the shelf extractor. It's only on the full race cars that I bother with custom made ones.

I will dig up some images for you of what I think will work for your application,

What are your engine specs?

Cheers
Woz