CUSTOM EXHAUST MANIFOLD

ProZac · Post by **ProZac** » Fri May 21, 2004 10:43 am

That is indeed a sexy manifold, but im dubious as to it fitting in a starion engine bay. The actual welding is probably easier than designing the damn thing IMHO, I've done some basic welding and im pretty confident i could get a decent product making it myself. Designing it however... hmmm.

NXTIME · Post by **NXTIME** » Fri May 21, 2004 12:36 pm

I am not a fan of that particular equal length design. I am of the opnion that the runners need to be as short as possible and as close as possible to the port diameter. I would also prefer to use a split-pulse turbo and manifold. All three factors will aid in creating much better spool up. Wouldn't mind making a manifold up to test this out on my engine one day. However, I am quite pleased with the current set up I have.

toysrus · Post by **toysrus** » Fri May 21, 2004 12:45 pm

I also believe they should be as close as possible to the port diameter for torque purposes.

The length of the runner does not matter so much if you have it ceramic coated :D

And yes split pulse turbo is the way to go !

I only put the pic up for a general idea on 'equal length' not to copy ofcourse

NXTIME · Post by **NXTIME** » Fri May 21, 2004 1:02 pm

runner length is very important :D the shorter it is, the less spool up time ;) If designed carefully, the manifold can be both equal length and have very short runners. Despite what many people say, you can have your cake and eat it too when it comes to exhaust manifold design. You just have to know how :D

4g6beat · Post by **4g6beat** » Fri May 21, 2004 2:12 pm

i agree with nxtime,
runner length and pipe diameter are the biggest factor in manifold design the longer you make it the softer the "hit" you get out of your turbo but you'll also gain top end (at the expense of power lower down) I've found that equal length isn't a very important factor (to an extent of course) ,

next to that try and get your pipe diameter just a little larger than your ports to keep the exhaust speed up and not create backpressure and keep the pipe bends as smooth and flowing as possible ie: no sharp bends anywhere, also make sure the collectors merge as shallowly as possible where the turbo joins up.

manifolds are all about exhaust speed and volume, stock inlets are usually great for speed however most can do with a bit more volume which is in harmony with what the designers wanted.

toysrus · Post by **toysrus** » Fri May 21, 2004 4:07 pm

Spool up has more to do with the intercooler piping, length, width and intercooler itself depending on turbo size.

Just by making the manifold say 5-8 cm shorter but equal length won't have the same effect as shortening the intercooler piping by say 30cm or by downgrading from a big 600x300 to a smaller intercooler with the stock TC05, correct ?

4g6beat · Post by **4g6beat** » Fri May 21, 2004 5:46 pm

true shortening the intercooler piping has a dramatic effect on turbo response but exhaust manifold design will ultimately affect the power making characteristic and how fast the air will be pushed into the system by the turbine ie: longer manifold less lower-midrange therefore less turbine speed and less spool response. as with anything pipewise the aim is to keep it as cool as possible and as short as possible.

NXTIME · Post by **NXTIME** » Fri May 21, 2004 8:39 pm

Funnily enough, when I went from a custom 400 x 200 x 75 cooler to a custom 550 x 450 x 65 cooler I had less lag and better throttle response. Manifold design, pipe length and diameter are more important, IMHO. Having said that, I have endeavoured to keep my cooler piping as short as possible and believe that it is the shortest length for a front mont on a Starion.

mrb1 · Post by **mrb1** » Sat May 22, 2004 12:32 am

NXTIME,
you can run tuned length runners, short as possible is not the best for top end power. Short is best for response however. But it depends what RPM band you have targeted. Horses for courses.
Tuned length inlet and exhaust work just as well on a turbo engine as normally aspirated, no difference. It's just that not many people have room for a turbo sitting at the end of their extractors

NXTIME · Post by **NXTIME** » Sat May 22, 2004 12:40 am

Mark, I agree with that, but in order to have a large turbo and half-decent spool up, shorter runners and tuned length manifold can still be achieved if it is designed correctly. I like the idea of having a large turbo that can spool up without too much (relative) lag and still have excellent mid and top end power.

toysrus · Post by **toysrus** » Sun May 23, 2004 12:15 am

NXTIME wrote:Funnily enough, when I went from a custom 400 x 200 x 75 cooler to a custom 550 x 450 x 65 cooler I had less lag and better throttle response. Manifold design, pipe length and diameter are more important, IMHO. Having said that, I have endeavoured to keep my cooler piping as short as possible and believe that it is the shortest length for a front mont on a Starion.

Intercooler thickness relative to spool up does depend on turbo aswell, which is why you got better response from a 65 than 75, if their was more pressure/cfm ie bigger turbo, there wouldn't/shouldn't be a difference.

scum · Post by **scum** » Sun May 23, 2004 5:17 pm

he stole my manifold :(

i didnt think my welding was that bad, just not good... or something.

NXTIME · Post by **NXTIME** » Mon May 24, 2004 12:49 am

toysrus wrote:
NXTIME wrote:Funnily enough, when I went from a custom 400 x 200 x 75 cooler to a custom 550 x 450 x 65 cooler I had less lag and better throttle response. Manifold design, pipe length and diameter are more important, IMHO. Having said that, I have endeavoured to keep my cooler piping as short as possible and believe that it is the shortest length for a front mont on a Starion.
Intercooler thickness relative to spool up does depend on turbo aswell, which is why you got better response from a 65 than 75, if their was more pressure/cfm ie bigger turbo, there wouldn't/shouldn't be a difference.

Nope, completely same set up, just changed coolers. The volume of the cooler significantly increased but the lag and throttle response improved. I don't see a relationship between intercooler thickness to spool up and turbo size - it is the relative area to be filled that is important, not how thick the cooler is. The only reason for these results that I can see is that the cooler I had before wasn't compatible with the turbo set up I have.

NXTIME · Post by **NXTIME** » Mon May 24, 2004 12:57 am

Having a look at some of the stats from my previous cooler, I was achieving boost at about 2800rpm. With the new cooler (and nothing else done to the car) I am making boost at about 2,200 rpm. This is tested in 3rd or 4th gear at about 60kph. I haven't yet managed to see how soon boost comes up in 1st gear on take off yet (but this will vary with launch technique).

toysrus · Post by **toysrus** » Mon May 24, 2004 11:27 am

was it the same, eg bar n plate or tube n fin ?

It would also depend on the design but your quite lucky on your results, most of the time it goes backwards if you don't know what your doing

Austarion

CUSTOM EXHAUST MANIFOLD

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