Exhaust design

[lamcote]

Yes, the reason my calculation is slightly different is because I used a different BBDC opening angle for the exhaust valve timing as the standard exhaust cam is very mild.

[lamcote]

I'd be surprised if the cylinder wall generated any significant shrouding in the 1zz. By the time the valve is open far enough to be protruding out of the combustion chamber bowl and into the cylinder bore itself, the angle of the valve will have moved the head of the valve away from the cylinder wall sufficiently that the extra 1.5mm of space created by the larger bore would have pretty minimal impact I would think?

[manos3003]

Right, an opportunity appeared out of nowhere to get a custom exhaust built for an absolute steal   s:bounce: :bounce: s:bounce:  

I won't make my own manifold for any other reason than pure fun and some practice (I've not TIG-welded in a while)  s:D s:D

If anyone is interested, I can provide all relevant info + CAD as I go along. If you want to make your own, that is.

[lamcote]

I was reading an article about tuning the 1zz in the Elise and someone was quoting a really good exhaust manifold with primary pipes at about 30-32 inch length. I can't find it again now though, I'll keep looking.

[manos3003]

Sounds kind of long though, considering you need to fit a cat pipe and a backbox with a silencer.

Plus, why would anyone want to tune a 1zz in the Elise when they can have a 2zz?   s:lol: :lol: s:lol:

[Nostromo]

Folks I have a question and this seems like the right place to ask.

I want to build my own exhaust which will most likely eliminate the rear silencer. I realise this will be noisy. The plan is to run a length of pipe with a larger bore (3/3.25 inch probably) from the cat with a couple of bends and out the back on the right hand side. There is very little science in what i'll be doing so I want to ask:

Could this result in a loss of power/torque?

Is there any point in running a larger bore pipe from the cat?

[lamcote]

Yes unfortunately our engine is the wrong way round really. Because the exhaust is right at the back there is very little scope to get much benefit from the manifold, the pipes are just too short. I wonder whether there is more to be gained from the cat pipe than the manifold?

[shnazzle]

As Nic said; the MR2 is very sensitive to the manifold. So I dont think that;s strictly true. Adding 1/4in diameter and/or 10cm length would probably change it quite a bit.
I reckon the cat pipe would just accentuate what's there.

[manos3003]

Echoing Patrick and Nic, yes. Our cars are very sensitive to any exhaust design parametres due to limited exhaust travel you have with the MR layout. A 4-2-1 for 1zz is good enough if you get the primaries any close to optimum, then use a 200cpi cat to help with the flow  s:) s:)

[MrT]

Hello folks
Interesting discussion, thanks. I've been thinking about this also. I have a PPE Header on my car, very happy with it, but I only have a stock car to compare with. I am wondering why nobody seems to consider the Elise/Toyota Avensis original header. Does it clash with the sub-frame or something? I realise it would require a custom cat link pipe but that is nothing complicated and it has equal length 4-1 collectors/headers of a length in between stock and PPE and is used on the same engine. Seems the obvious choice to my uninformed mind.

[shnazzle]

I think the Elise one did indeed hit the subframe. I'm sure this came up a while back. No clue about Avensis.
I guess you could hack the 2zz one. Same as for the 2zz conversion but then instead of welding it back onto the flange higher up, weld it to a 1zz flange higher up

[MrT]

This is the one I am referring to. Definitely doesn't look too long, but it needs a link pipe attached...

[attachment=0:nu2gfqg0] ia0 Elise-Avensis_OE_header.jpg ia0 [/attachment:nu2gfqg0]

[shnazzle]

Looks like the Celica manifold.

[MrT]

Probably the same one. Same engine... Have these been tried before? I'm considering chopping in PPE header for a more mid-range system for fast road rather than track performance.

[shnazzle]

Bit of an expensive header to chop  s:) s:)  

From what we could tell, the Zero exhaust manifold is the best all-rounder. Thats what I'd go for.

But I'd be very interested in what a chopped 2zz manifold (like the pics above) have to offer.

[ChrisGB]

Probably the same one. Same engine... Have these been tried before? I'm considering chopping in PPE header for a more mid-range system for fast road rather than track performance.

Having done dyno runs back to back comparing stock and PPE manifolds, the PPE gave gains across the whole rev range, particularly in the mid range.

[MrT]

Shnazzle, that pic is a 1zz manifold from Avensis 1.8i hence why I asked. A stock manifold that is cheap as from the breakers'. But I'm glad to hear the PPE is best all round, ill hang on to it then.

[MilesH]

Deleted my post.

Ignore me, I thought this was about 2zz exhaust design...oops!