Thanks for that - Its a job I have to do next winter :)
I started with the head - went round the ports and stud holes with a grubby finger on paper. marked a dimensioned horizontal and vertical line, scanned it and emailed to EMF in Henderson.
Called round the next day to pick up the plasma cut exhaust manifold flange. Perfect fit.
I like the idea of using plumbing fittings :)
sr2,
Dec 3, 9:35pm
Thanks for the link, I thought the pvc mockup was a great idea. Just be aware they are only building "free flow" exhaust systems not tuned extractors.
mals69,
Dec 4, 6:18am
Top engineer know used water to work out same internal volume for each tube. Mandrel bends.
tintop,
Dec 4, 6:38am
True - but using plumbing fittings allows ready experimentation in layout to arrive at correct lengths.
tintop,
Dec 4, 6:43am
Yes. That would be a good way to arrive at the same length for each one for pipes of a constant diameter - bearing in mind that it is the lengths that need to be tuned rather than the volume.
mals69,
Dec 4, 7:01am
Oh ok - thought good ones same length/volume ? Mate used piece of string for length. Longer they are better it is for torque ?
sr2,
Dec 4, 7:08am
Couldn't agree more; I think using plumbing fittings is a great idea, it could even be of use for mocking up tricky parts of exhaust systems. (I might even give it a go next set of headers I build).
tintop,
Dec 4, 7:12am
Here you go. There are a couple of typos in the article, but they dont interfere with the principle.
The idea is to have the primary pipes at the correct length terminating into the largest volume collector as can be fitted.
As an aside - the siamesed exhaust ports on cylinders 2 and 3 on the BMC engines, especially 'hot' Minis causes difficulties and is the reason behind the uneven 'brap brap' idle of these.
sr2,
Dec 4, 7:20am
"The proper handling of the pressure waves in the exhaust can help us to this end, and even help us ???supercharge??? the engine."
Interesting article/advertising blurb but I took that little pearl of wisdom with a grain of salt, it doesn't matter how hard you suck the atmosphere will only blow at atmospheric pressure.
tintop,
Dec 4, 7:21am
You will get close with a bit of string, but it tends to 'cut corners' .
I used a length of garden hose. :)
tintop,
Dec 4, 7:26am
True, but having a bit of 'suck' at the end of the exhaust stroke will help scavenge the last of the exhaust gases and start the inlet flow a wee bit earlier during valve overlap time.
mals69,
Dec 4, 7:34am
Interesting link thanks - will save that.
Bit more to it than most back-yardies think.
sr2,
Dec 4, 7:36am
Agreed, the ideal in a n/a engine is to be as close as possible to atmospheric pressure at the bottom of the inlet stroke.
mals69,
Dec 4, 7:37am
Well put - its where some dirt bike riders go wrong by whacking a dirty big muffler opening on and lose important back pressure, factory usually knows what is best anyway.
bjmh,
Dec 4, 7:42am
True, but having a bit of 'suck' at the end of the exhaust stroke will help scavenge the last of the exhaust gases and start the inlet flow a wee bit earlier during valve overlap time.
Quote
tintop . a lot of the headers in the early days ,had staggered pipe lengths in the collectors to achieve this. then eventually I guess it was a heck of a lot easier to just join them all flush inside the collector,i built some for a zephyr looked like a spaghetti factory. but had a sound of its own,who knows if it went different.
mals69,
Dec 4, 7:53am
Well put too cheers - makes sense - helping to pull air in and exhuast gases out, like in the article - supercharging in effect :)
tintop,
Dec 4, 8:02am
I think anything that was different from the punched pipe 'manifold' would go better. But to loose the sound of the chuff chuff from the No.1 cylinder connection would be a bit sad! lol
bjmh,
Dec 4, 3:15pm
I just watched that video,it jogged my memory . I remember joining 1.5.3 and 6.2.4 . where as Griffith etc had 123 and 456 then joined at the collector,i had read where the firing order helps scavenge . probably a load of bollocks. but it seemed to make sense. we had no dynos only sat night fever to test our mods.
2get1,
Dec 4, 3:18pm
merge collectors are the best to use, specially if you can buy them for what you are doing, They aren't cheap, but they are good.
sr2,
Dec 4, 3:20pm
Not quite right; supercharging is forced induction, whereas scavenging uses atmospheric pressure.
sr2,
Dec 4, 4:32pm
While we're on such an interesting subject (as opposed to left/right lane hogging on motorways) I??
lookoutas,
Dec 4, 4:42pm
I recon you need to make it go as good as possible, otherwise you'll be holding traffic up
sr2,
Dec 4, 4:43pm
LOL; would this be the left or right lane!
rotormotor7,
Dec 4, 4:47pm
bought a cheap set of homejob ones for 12a wankel. tight steel bends off the flange. after welding up holes that kept appearing got a set of coby headers with the cast iron 90° off the flange. seems the flames from the exhaust ports were rather too hot for mild steel
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