Dump Pipe Or Front Pipe

[mrsr32]

I've got a 3" exhaust off the factory dump pipe and would like to replace the stock dump pipe with one that seperates the w/g gases.

Should I go for something like this that looks like it would bolt in and replace just the stock dump pipe

http://www.drivenperformance.co.nz/scripts/prodView.asp?idproduct=329

or go with a whole front pipe which seperates the wastegate for much longer (this just means I need to get my existing exhaust modified to suit)

[DVS JEZ]

Go for a bellmouth front and dump in one

[mrsr32]

doesn't that create more turbulence then?

[Birds]

Doesn't create anything but a simple, efficient setup. Split dumps are a waste of time IMO. Bellmouth ftw.

[Moodles2]

All a split does is create more problems, cheap ones almost always have the internal wastegate flap getting jammed against the splittter you can see in the photo that seperates the 2 streams of gases

[GTSBoy]

Except for when you install them carefully and properly (like mine) and then you get no such problems.

[jjman]

Except for when you install them carefully and properly (like mine) and then you get no such problems.

and so when it is done properly like this what does it truly do?

create a more stable flow/boost pressure?

iv got this setup too that works perfectly but iv always wondered what it truly does over a big bellmouth...

[gtsttrk]

If you were looking at a split dump I'd say look into the CES split dumps. Apparently these utilise a a longer split pipe, unlike the JJ ones etc and are supposed to effectively reduce back pressure on the waste gate flap (iirc).

So therefore I'd say the full split front, and not the just replace the stock dump.

Edited September 30, 2012 by gtsttrk

[GTSBoy]

and so when it is done properly like this what does it truly do?

create a more stable flow/boost pressure?

iv got this setup too that works perfectly but iv always wondered what it truly does over a big bellmouth...

The point is to stop the wastegate exit gas flow from splashing horribly across the turbine exit gas flow. If you can keep them separate, the idea is that the turbine exit gas gets a much more efficient expansion out into the dump, resulting in lower overall backpressure, or more to the point, more pressure drop across the turbine (meaning better power available to drive the turbine). The wastegate gases are then dropped in much further down where they don't interfere so badly.

If you were looking at a split dump I'd say look into the CES split dumps. Apparently these utilise a a longer split pipe, unlike the JJ ones etc and are supposed to effectively reduce back pressure on the waste gate flap (iirc).

So therefore I'd say the full split front, and not the just replace the stock dump.

The CES dump is possibly a bit nicer in the conical expansion of the turbine exit region than the cheapy is, but as far as I can tell, the return point for the wastegate flow is about the same distance down the dump. This is for the case of the split cheapy shown above. Any of the really short split cheapies, where they are intended to only replace the factory cast dump and mate to the original front pipe, are the ones that are not worth considering.

When I changed to my cheap split (JJR I think - many years ago now) I gained a good improvement in boost threshold, more stable boost control, and an increase in max boost that I then had to adjust out. That shows me that the wastegate flow was better (boost control improvement from less intereference between wastegate and turbine flows), that the overall pressure drop was lower (better boost threshold) and that the flow at high flow rates was better (increase in boost). Overall, it has been good.

The only open question is whether those changes would have been the same, less, or greater if I'd gone with a bellmouth dump. I don't have a comparison.

Most of these guys around here just write off the concept of the split dump though. I can't understand how they refuse to accept the idea of them, yet all agree that an external gate on a bigger turbo is a better idea. The ideas are related.

[gtsttrk]

Does anyone have an example of a split that brings the WG flow back in basically where the the dump joins up with the cat? I've had a look around but haven't been able to find any that are produced like this.

[jjman]

never heard of such a design. N also could imagine why it would not exist as trying to merge the gas flow as it is also dealing with another change (going into a cat) could reduce efficiency of the design as opposed to merging it a bit further up the dump pipe- just like in the pic by the OP

[gtsttrk]

never heard of such a design. N also could imagine why it would not exist as trying to merge the gas flow as it is also dealing with another change (going into a cat) could reduce efficiency of the design as opposed to merging it a bit further up the dump pipe- just like in the pic by the OP

Yeah I worded what I was asking very poorly, too much excitement from the granny lol

Basically I was asking if anyone knew of a split like the one in the OP posted a pic of. Virtually all the ones I've seen either just replace the stock dump, or utilise the shorter split such as the JJ, CES etc.

[GTSBoy]

The OP pic is a JJR type. This is the normal sort. I have never seen a commercially available split dump that drops the wastegate flow in any further downstream than that.

[Old Booster]

is there any benefit in cutting the end off an aftermarket dump pipe, and fitting a flexible joint before the cat?

[GTSBoy]

Not really. In FWD/AWD transverse engined cars yes. In longitudinal engine layouts, much less so. If the exhaust is decently supported at the gearbox, then it will move with the engine anyway.

[Dose Pipe Sutututu]

If you're not making loads of power and using the stock turbo especially, you're not really going to notice any real gains with the split, not to mention there's room for it to jam and give you headaches down the track.

Save the coin for a slab of beer and just get the bell mouth.

[mrsr32]

Ok, so it looks like the latter is the better one of the 2. Had a hunt around for belmouths and there aren't any readily available. either way, its gotta be better than the stock dump. i'm interested in the gain i get vs my stock dump into 3"

[Got a Pulsar]

Just Jap Bellmouth. <---------((( Click it !!! Edited October 1, 2012 by Not a Pulsar

[gtsttrk]

I've used a JJ split before and didn't think that it was a bad little piece. Had it installed correctly and I definitely felt an increase at the RPM's that boost came on. The spool definitely seemed to come on earlier than when I was using a belmouth. Mind you, this could have just been a placebo. But the JJ split isn't bad for what you pay.

Just out of interest, has anyone used any of the CES products that I mentioned earlier? If you look at their website some of their products boat huge KW gains for what they are.

[wolverine]

If you're not making loads of power and using the stock turbo especially, you're not really going to notice any real gains with the split, not to mention there's room for it to jam and give you headaches down the track.

Save the coin for a slab of beer and just get the bell mouth.

This^^