Aftermarket exhaust manifold question

[delhusband]

Hi, idiot question - aftermarket manifolds Like Hamishes and Toyosport decat manifolds - seen it said these can release potentially around additional 15bhp - what characteristic of these manifolds is it that effectively releases this additional power - is it just the down to the fact that they're pre-catless, or is it another feature of the design (i.e. pipework diameter? (what I'm getting at is, I probably have the stock manifold, without precats - could I gain anything by fitting an aftermarket manifold?)

[Call the midlife!]

Hi, idiot question - aftermarket manifolds Like Hamishes and Toyosport decat manifolds - seen it said these can release potentially around additional 15bhp - what characteristic of these manifolds is it that effectively releases this additional power - is it just the down to the fact that they're pre-catless, or is it another feature of the design (i.e. pipework diameter? (what I'm getting at is, I probably have the stock manifold, without precats - could I gain anything by fitting an aftermarket manifold?)

Nope, not a sausage, not a single four legged creature of any description it's all just hokum...
Ok, maybe not all of it, just most of it.
They're usually a bit lighter and let the gasses out betterer than standard but bhp gains are going to be minimal.
I certainly didn't notice much in the way of a massive increase in performance when I fitted mine.


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[1979scotte]

Hi, idiot question - aftermarket manifolds Like Hamishes and Toyosport decat manifolds - seen it said these can release potentially around additional 15bhp - what characteristic of these manifolds is it that effectively releases this additional power - is it just the down to the fact that they're pre-catless, or is it another feature of the design (i.e. pipework diameter? (what I'm getting at is, I probably have the stock manifold, without precats - could I gain anything by fitting an aftermarket manifold?)

I almost choked on the sausage roll I was eating.
1.5 would be closer than 15.

[lamcote]

I think the idea of getting power gains from simple bolt on mods is a hangover from the time when standard cars were really pretty inefficient. I had a Cavalier Coupe in the 80s with the 1.9l engine.
I bought a Janspeed exhaust manifold for it, that's all I changed, I even kept the standard exhaust system, frankly I couldn't believe the difference it made, it really was noticeably faster and measurably more economical, I was amazed. It was definitely more than placebo effect.
Modern efficient engines (including the 1zz)  just don't have the kind of inefficiencies that can be improved on like that.
(The standard Vauxhall engine produced 47bhp/litre, the 1zz produces 76bhp/litre, that's over 60% more per litre.)

[8thumpers]

Zero difference with manifold or airfilter.... But they look so good when you pop the hood!

[delhusband]

Hi, idiot question - aftermarket manifolds Like Hamishes and Toyosport decat manifolds - seen it said these can release potentially around additional 15bhp - what characteristic of these manifolds is it that effectively releases this additional power - is it just the down to the fact that they're pre-catless, or is it another feature of the design (i.e. pipework diameter? (what I'm getting at is, I probably have the stock manifold, without precats - could I gain anything by fitting an aftermarket manifold?)

I almost choked on the sausage roll I was eating.
1.5 would be closer than 15.

I quote from the Toyosport website
"Increases horsepower by a minimum of 15BHP, Dependant upon engine mods"
Toyosport Linky

*EDIT* s'pose the "Dependant upon engine mods" is the get out clause...

[jonbill]

"Other mods"=replace the ECU with a standalone optimised for premium petrol etc then maybe. But you'd get most of that 15bhp with the standard exhaust too.

[Call the midlife!]

Of course there's the difference between horsepower and "performance" to take into account, if you're making changes that make it breathe better then you're going to make it perform differently. You might get a better throttle response, might make it feel a bit livelier at certain revs/gear combinations etc but don't expect your 0-60 times to come tumbling down, especially if you're adding weight like I keep doing with mine.
But then it's not all about greasy fast speed for me, "leanin to the side, I don't speed through".


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[delhusband]

But they look so good when you pop the hood!

Yes they do  Nice

[The Other Stu]

Zero difference with manifold or airfilter.... But they look so good when you pop the hood!

See, I'd argue that you've probably lost Bhp with that.

1. You'll get much more heat soak. The standard filtering is surprisingly good - particularly with a markiii pipe. It does sound nice though (although I'd argue a toyosport manifold and a TTE exhaust sounds better)
2. There's an argument that you want to keep your exhaust gases as hot as possible getting to the cat. Now the difference may be marginal, but you're certainly going to cause a lot more heat in the engine bay and see 1 - you're going to be putting more HOT air into the mushroom filter.

[Beachbum957]

Of course there's the difference between horsepower and "performance" to take into account, if you're making changes that make it breathe better then you're going to make it perform differently. You might get a better throttle response, might make it feel a bit livelier at certain revs/gear combinations etc but don't expect your 0-60 times to come tumbling down, especially if you're adding weight like I keep doing with mine.
But then it's not all about greasy fast speed for me, "leanin to the side, I don't speed through".


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Good analysis. 

We have run one of the cheap TRD clone headers for years and the only change seems to be a bit better midrange and throttle response, based on the Butt Dyno.  But a 15HP increase? Nope.

[8thumpers]

Zero difference with manifold or airfilter.... But they look so good when you pop the hood!

See, I'd argue that you've probably lost Bhp with that.

1. You'll get much more heat soak. The standard filtering is surprisingly good - particularly with a markiii pipe. It does sound nice though (although I'd argue a toyosport manifold and a TTE exhaust sounds better)
2. There's an argument that you want to keep your exhaust gases as hot as possible getting to the cat. Now the difference may be marginal, but you're certainly going to cause a lot more heat in the engine bay and see 1 - you're going to be putting more HOT air into the mushroom filter.

Do you know what... the measurability of road use bhp on exhaust and filter swaps is totally zero. You can't tell the slightest difference unless you are on a track against a clock - say at a hillclimb or sprint event - However, open the hood at a meet and see the difference then!
If you want bhp then turbo it, or swap the engine. Simples.
Don't get me wrong, I'm not  "all show and no go" otherwise I wouldn't be building the v8!

[shnazzle]

Relative.
If you went from stock with pre-cats removed to a Hamish, your probably gain up to 10-15...but only because you lost that when you took the pre-cats out

A Zero or PPE most certainly does offer bhp gains. This has been proven endlessly. But they are properly built and tuned manifolds designed specifically to get a certain performance out of the '2.

But all in all, no, if you went from stock to Hamish, you'd be unlikely gain much in the way of power but it would rev up to redline quicker and you're torque curve will have shifted.

[potge]

Another similar question. I was trying to source a "relatively" cheap de-cat exhaust manifold but with decent reviews. Though I love quality stuff, since most probably 1zz will end up either with forced induction or swapped, I really can`t justify spending for a zero or anything similar.
With that being said, unfortunately, it appears that most of the commonly used are out of stock (though I am still waiting a couple of replies for some of them).
Do you have any other suggestions/ideas?

[Dev]

Many of the breathing modifications are not that great in comparison to a much bigger restrictive engine that can benefit from simple bolt ons. However there is one bolt on modification that has proven at least 10hp and that is the downpipe.

The factory downpipe is the bottle neck for this car because the flex sections have restrictive  chokes in them probably for sound reduction. Also the factory cat is restrictive. If you get a downpipe that has larger flex sections and piping with a high flow cat you can get some solid gains you can feel.

 

[tony=m=]

Anybody have one of these or know someone that has? any good?

https://mr2-ben.co.uk/products/649

also sells the cobra cat back exhaust

https://mr2-ben.co.uk/categories/19

[jvanzyl]

I have the cobra twin pipe... I like it, it's a lot lighter than stock and you can feel the difference that makes.
It's not too loud to be honest...

[Call the midlife!]

The main body of it is VERY much like the "Hamish" ones and they've seen a lot of good service among members but the flange to head on this particular one looks pretty poor in the images. Doesn't even look to have a flat face?

Anybody have one of these or know someone that has? any good?

https://mr2-ben.co.uk/products/649

also sells the cobra cat back exhaust

https://mr2-ben.co.uk/categories/19

[Bernie]

Rob was the first to get a zero manifold it was an early mod and he had a dyno run after install clearly an improvement over stock

Also in the early days came with heatshield

[tony=m=]

Just out of interest has anyone took the precats out of the oem manifold and wrapped it and put it back on? any performance differences or is it pointless to wrap it etc due to what dev said about the factory downpipe and cat being restrictive ?

[Gaz mr-s]

If a metal other than a good quality stainless is wrapped, it'll likely crack. Mild steel should not be wrapped.

According to Exhaust maker Zero, removing the cats will be detrimental to performance (flow), but nobody's written they've noticed it.