Fitting an exhaust manifold

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Fitting an exhaust manifold

Post by 350matt » Wed Jul 11, 2018 10:19 pm

So Gents
having had my thermostat become a bit reluctant to open I'd went through the rigmarole of fitting a new one only to find on fire up the exhaust manifold is blowing like a good one.... probably been doing it a while as my fuel economy has been worse than usual of late and its been quite stinky under the bonnet for while

So I've been eyeing up the Toyosport items on the bay for while anyway so thought 'sod it' and have purchased

any tips for getting the old manifold off? bear in mind all the fasteners were copperslipped and two studs were replaced when I rebuilt the thing so there should (hopefully) be no seized fasteners etc to worry about

just all looks a bit tight. Obviously the RH mount will have to come off but do I have to disconnect the steering column too?

I realise there's probably little power benefit to these things but I was wondering as I have ported the exhaust who knows? Maybe I'll pick up a smidge extra

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Re: Fitting an exhaust manifold

Post by 13Black » Wed Jul 11, 2018 10:22 pm

Have a think about machining the manifold flange flat as they can be warped from factory.

Also use an OEM gasket, not the Toyo one.

But yes RH engine mount undone and jostled out of the way.
Front underbody brace off.

No need to touch the steering or other major parts.
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Re: Fitting an exhaust manifold

Post by 350matt » Wed Jul 11, 2018 10:39 pm

Cheers

top tips there
is it worth using a smear of white exhaust assy paste too?

any power benefit in your experience?
does the exhaust note change?
Last edited by 350matt on Wed Jul 11, 2018 10:41 pm, edited 1 time in total.

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Re: Fitting an exhaust manifold

Post by Neilparry » Wed Jul 11, 2018 10:41 pm

Just make sure your sockets and spanner’s are six sided , gives you more chance of not rounding the nuts if they are stubborn to undo.

Hope you have bought a genuine Toyo from Toyo as any thing else in that price category is crap

Otherwise it’s as above and straight forward


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Re: Fitting an exhaust manifold

Post by 13Black » Wed Jul 11, 2018 10:45 pm

No exhaust paste usually - I only use it as a quick bodge if the gasket is no good and I don't have a new one to hand but that's usually further back. Never used it on the engine itself. Whether this would 'fix' it if it's not flat enough, I don't know.

Power benefit, no idea. Too small to reliably measure or be worth measuring.
Last edited by 13Black on Thu Jul 12, 2018 11:39 am, edited 1 time in total.
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Re: Fitting an exhaust manifold

Post by Neilparry » Thu Jul 12, 2018 9:43 am

Use the original metal manifold gasket and Don’t use the triangle gasket supplied between the manifold and the cat. As it will blow out in no time. Use an OEM sealing ring it’ll last last a lifetime


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Re: Fitting an exhaust manifold

Post by Scartlead » Thu Jul 12, 2018 10:28 am

When I fitted the racing beat manifold , it was pretty straightforward, having access , in my case a ramp, made the biggest difference. Also the 200hp it gave me also helped :lol: sorry I mean 2hp #-o. Looks awesome though and the weight difference must help in some way :thumright:

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Re: Fitting an exhaust manifold

Post by Harrizone » Thu Jul 12, 2018 4:46 pm

Scartlead wrote:
Thu Jul 12, 2018 10:28 am
the weight difference must help in some way :thumright:
Like me it is just the weight from your wallet that has made most difference. :lol: :lol:
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Re: Fitting an exhaust manifold

Post by warpc0il » Thu Jul 12, 2018 9:06 pm

I even went to the trouble of double-wrapping my Toyo manifold, as I was concerned with the lack of heat shield and the impact on the steering uj and o/s engine mount.

Wrapping is also meant to help with power output and getting the heat down to the cat - though I'm not convinced on either case.

However, when I worked-out what was involved in actually changing the manifold, I decided to leave it until/if the engine's out for a rebuild.
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Re: Fitting an exhaust manifold

Post by Bigblueknight3k » Fri Jul 13, 2018 8:38 am

What fo you do about the air pump for Mainfold delete it or put it back on ?

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Re: Fitting an exhaust manifold

Post by Essex2Visuvesi » Fri Jul 13, 2018 9:17 am

Exhaust wrap...
I have always been against it because it causes the pipe material to cycle repeatedly thru extremely elevated temperatures as the radiant and convective heat transfer to atmosphere is blocked. Since pipe contains stresses from manufacture and welding and since it is often made from steel or stainless with relatively low strength at high temperature the metal can degrade very badly. This is the effect of thermal stress as it's called. No need to go into the metallurgy.

The only possible benefit - if you are prepared to accept severe deterioration of the pipes themselves is reduced under-bonnet temperatures. The massive flow of heat coming off the exhaust - especially in highly tuned front-wheel-drive installations when not moving at reasonable forward speed - can cause the fuel in the carb to boil, the oil and engine to overheat. The underbonnet temperature can be easily surveyed with an inexpensive hand-held probe from Halfords or other auto shop and will shock anyone who has never done it. Certainly cold air ducting is great when your vehicle is moving but not so effective when it's not. If you must use wrap to reduce underbonnet heat - give the insulating material some stand-off from the pipe to avoid those high metal temperatures.

One must also remember that the heat doesn't just flow outwards radially thru the pipe and down the pipe - it gets into the port, the valve and seat - even piston - region and can cause all sorts of dramas: seats cracking, detonation etc etc. General increases in head temperature are going to degrade the inlet charge density too. And, if, for argument sake, you have a very highly tuned motor and you wrap your exhaust tightly and you're running a cooling system with plain water and no water-wetter or antifreeze your cooling system on the ex side of the head is likely to be totally overloaded due to nucleate boiling = no heat transfer at all to the coolant system - and the first thing you'll know about could well be a blown head gasket, or worse.

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Re: Fitting an exhaust manifold

Post by Phil Bate » Fri Jul 13, 2018 11:47 am

Bigblueknight3k wrote:
Fri Jul 13, 2018 8:38 am
What fo you do about the air pump for Mainfold delete it or put it back on ?

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You can delete it (I have), but you will need someone with MazdaEdit to disable the CEL for it or you will be resetting your fault codes every other cold start
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Re: Fitting an exhaust manifold

Post by Bigblueknight3k » Fri Jul 13, 2018 11:51 am

I am having a 200cell power cat on it is it ok to do still and any good place near me who can do the it if i can delete it

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Re: Fitting an exhaust manifold

Post by warpc0il » Fri Jul 13, 2018 12:27 pm

An air pump delete is only a good idea if you have a decat.

Removing the pump doesn't stop the pcm adding the extra fuel fora cold start but there won't be the air to allow this to burn in the cat, it will just poison the cat instead.

The pcm tweak just blocks the CEL.

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Re: Fitting an exhaust manifold

Post by Phil Bate » Fri Jul 13, 2018 3:43 pm

The core will be saturated until the enrichment decay is over after cold start, but it does then recover. I deleted mine years ago and the original cat still aces the emissions test (approaching 90k miles now), but as ever it's an 'at your own risk' affair.

It's worth remembering the PCM does run the AFR extremely rich under other circumstances without running up the pump.
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Re: Fitting an exhaust manifold

Post by 350matt » Fri Jul 13, 2018 4:11 pm

Can't you lean off the start-up fuelling in Mazda edit?

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Re: Fitting an exhaust manifold

Post by PeteH » Fri Jul 13, 2018 4:23 pm

Why would you want to? It's not like the RX-8 is famed for its ease of starting :shock:

Cold enrichment is required because the cold surfaces of the intake, chamber and rotors cause a lot of the petrol to drop out of suspension, and condense on the surfaces, where it can't easily burn. Enrichment ensures you still have enough petrol in suspension to ignite. But the condensed fuel gets pushed into the exhaust as liquid. Leaning the mixture wouldn't change the condensation much, but it would ensure you had no petrol vapour left to burn.

Interestingly, this is the major reason rotaries have to run so rich when cold. The intake is long, the chambers are a very odd shape (spheres have the minimum "surface area per volume", and rotaries are a long way from spherical combustion chambers), and the mixture has to travel half way around the engine to reach the spark plugs. It's a wonder any of the fuel stay in suspension when the engine is cold.

On the plus side, all that neat petrol is great for flames. :twisted:
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Re: Fitting an exhaust manifold

Post by Phil Bate » Fri Jul 13, 2018 9:56 pm

:whathesaid: A table for enrichment decay was uncovered in ME ages ago but exactly as Pete says, it's function is not simply to warm up the cat so it's best left alone.

It's basically the equivalent of one of these:


s-l400~2.jpg
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Re: Fitting an exhaust manifold

Post by 13Black » Fri Jul 13, 2018 10:01 pm

Isn't that one of those claw things to pick up keys out of drains.
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Re: Fitting an exhaust manifold

Post by SeeJay » Fri Jul 13, 2018 10:13 pm

Oh for the days of carburetor's..and manual choke cables which you had to pull out an twist to lock 8)

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Re: Fitting an exhaust manifold

Post by warpc0il » Fri Jul 13, 2018 10:28 pm

I had a girlfriend in the '70s that thought that was "the handbag holder" #-o
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Re: Fitting an exhaust manifold

Post by 13Black » Fri Jul 13, 2018 10:44 pm

If the hat fits...
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Re: Fitting an exhaust manifold

Post by 350matt » Fri Jul 13, 2018 10:53 pm

thanks for the explanation of cold start fuelling chaps...... :roll:

I meant if the cold start has excess fuel in it over an above what would be required to get the engine to fire cleanly so the secondary air pump has something to go with it then reduce the excess once the pump is gone

but as Phil says cats generally survive fuel saturation quite well in any case


on another note the 200 cell cat I fitted about 4k miles ago is showing signs of distress, its not broken up but is slightly melty and distorted
so I've got another cat to try, a larger diameter (5" up from 3.5") but still 200 cell which should flow a bit better and I was thinking to try moving it back from the engine a bit

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Re: Fitting an exhaust manifold

Post by Phil Bate » Sat Jul 14, 2018 12:02 am

This is the problem with some aftermarket units. The standard cat is a beast - to go aftermarket you need something very chunky to cope with the output. Something that would be more at home behind a serious turbo four pot or a V8 perhaps. Let us know how the bigger one copes!
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Re: Fitting an exhaust manifold

Post by 350matt » Sat Jul 14, 2018 8:44 am

Agree that the stock cat is a very effective emissions device with 3 kinds of brick and a zeolite trap and was state of the art at the time

interestingly enough we were looking into using zeolite traps on the V12 at work but the industry has since moved away from them as they can shorten cat life

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