Custom Exhaust Manifolds

[raddavey]

Has anyone had any experience with flow testing the stock manifold compared to a custom one? Or dyno test or seat of pants feel after swapping manifolds.

I'm currently building one but its going to take a lot of work and was wondering if it will be worth it. I'm trying to gain more power moreso down low and in the mid range. Looking at the stock manifold it does look like a custom one with mandrel bends and a merge collector will flow a sh*t load better.

I have a 'stage 3' camshaft 225/226 duration @ 0.050inch and was thinking a good designed manifold will reduce reversion and increase low end torque, economy and spool up time.

[Ben Hewitson]

i believe that the shorter the manifold runners the better. you also need to make the manifold get as hot as possible as hotter exhaust gas flows faster..

if you make a manifold with very long runners it will reduce response and increase the rush of boost forming and increase the top end (ie Bathurst EXA has massively long runners).


http://autospeed.drive.com.au/cms/A_2604/article.html

http://autospeed.drive.com.au/cms/A_2605/article.html

[raddavey]

I don't have a subscription care to send the article? Maybe email me.
daveyra@iinet.com.au

[tassuperkart]

Ive read a couple of articles and so-on and the consensus seems to be that going to the trouble of adding a merged collector is not worth the time and money.
You can create a decent "merge" at the flange anyway with yolur 4 pipes.

My on ly experience here was with my old turbo Capri 1600.
It originally had a "log" style manifold and the turbo place i dealt with at the time swore black and blue that would work as well and anything and leave it alone.

however, after the unpteenth time the fucking thing cracked (another story) I built a new one out of stam pipe bends and smoothly "merged" them together at the turbo flange.

To say there was an improvement is the understatement of the year.
Increased horsepower at given boost, greatly improved spool times and reduced lag.
I made no concessions to tuned length runners and the manifold was made as short as possible to fit a given setup. I kep the runner diameter to a minimum (same as the port exit) to maintain gas velocity.

L8tr
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[coidog]

just get some mandrel bent extractors they glow red and sound good too. might not work for you turbo lovers, .

New advertising campaign......"Turbos.... Its like Viagra for you engine"

lol.

[raddavey]

well i've already made the merge collector and going by '6boost' manifolds on performance forums the merge is the most important bit. I'm using 1 1/4inch steam pipe. The runners will be as short as possible but to fit the merge collector in they will probably end up around 20-30cm long.

[Ben Hewitson]

if your interested in runner length that is another thing you need to research. as with N/A cars different setups cause different effects. like old 4 into 1 extractors give good low end, whereas longer 4 into 2 into 1 gave good top end etc.. i hade a special extractor set made for my datto 1600 (2.2L L20B) and it was 4 into 2 then into 1large pipe. the 4 extractors merged about where the gearbox was and the 2 merged about where the back seats started.. tuned length aparently.. made a hell of a racket and from 4500rpm to 9200rpm it was an absolute monster. lit up 3rd and 4th at over 100km/h... nasty..

but back to turbo's.. if you want response shorten the runners..

you lot probably dont know this but the high mounted ET manifold give a fair bit more turbo spoolup and response than the lower mounted Aussie EXA or even the super low Japspec EXA manifold..

also dont forget that they have to be of equal length, cause you want the pulses (1, 3, 4, 2) to arrive as close behind each other as possibly. also you'll need to look at how the runners come together and you dont want any bends here. as has been mentioned before, the acumulator (merge collector) is very important indeed. you want to get this section as hot as possible to increase the pressure thus velocity of the exhaust gasses.. remember that PV=T.

you'llprobably notice that Rally cars have super short exhaust manifolds and short intake runners. this is to air response because outright power is not an issue because of the WRC imposed intake restrictors.

on touring cars, and i'll go back and mention the bathurst EXA again, the manifolds are longer to give increased mid to topend power from the turbo. as these cars spend most of their track time above 5000rpm you can see why.. *this is also why they break down with multiple pace car laps as the alternators on touring cars aren't efficient below 5000rpm because if they were they would simply blow up at the high revs of a race)


also note that this car made the 234kw's on the standard intake manifold, it used a dizzy and i believe it still used the standard computer... (although i doubt that as the AFM was swapped for a 0 to +5 map sensor..)





also about those articles, i dont have a subscription but i hunted them down on google with the "pages from website" function to overcome the registration requirements.. lol...

if anyone has pictures please post them up.

also a quick search through this forum shows a few of them.

this ones from Chris LUu's ET.. maybe ask him what design rules he followed for this..? if he's stilla memeber that is..



Here's another.. from Bjorn..

[raddavey]

It's going to be about the length of bjorns and chris's but with a merge collector where they join. Its just difficult making it all fit without the turbo hitting the bonnet. Then i need to re-route my intercooler piping and do the dump pipe. I might make new radiator pipes from stainless so i can make more room for the dump. The stock hoses get in the way.

I'll let you know how it goes.

[Ben Hewitson]

yeah please post up some images of your progress. that would be cool.