C20NE custom exhaust

[James McGrath]

Hello everybody,

I'm currently trying to get the fuel economy up on my C20NE equipped Diplomat. I've been through all the usual stuff; thorough service, tracking, tyre pressures, fuel injector cleaning, various ignition parts renewed.
All that has made a difference, now I'm getting about 38mpg on average compared to about 32mpg before.

I think I've gone as far as I can go while keeping her standard. My next target is the exhaust.
It's well known that the original 20NE, without a catalytic converter, is a fair bit more economical than the C20NE.
So I was planning on fitting a decat pipe (for track day purposes only you understand ) and I'm also considering a custom manifold. I know a couple of you on here have fitted one to these engines with positive results.
I've read varying accounts about what type to get some people say 4-1 is best and others say 4-2-1.

Before I start forking out money, I though I'd ask what everyone on here thought bearing in mind I'm after low to mid range power and maximum fuel economy.

[Mk3alan]

James, can't comment on the virtues of the 4:2:1 against the 4:1 but I fitted the former about 3 years ago.
Made by Sportex, fitted well enough but had a useless paint finish, had it shot blasted and finished it in Frost's manifold paint (which is not ageing particularly well)
I think it definitely allows the engine to breath better but as I use the car infrequently and not on a regular journey I cannot give any meaningful figures. I usually achieve 40+ to the gallon and have managed 52, not driving like a granny, but being careful!
Would I change it again? Not sure, but if I did I would try and source a stainless unit.

My car isn't fitted with a cat but I have replaced the front silencer with a straight through section (the original is still fine!)
Gives a slightly beefier exhaust note but don't believe it is any more efficient.
This unit was supposedly a 'direct replacement' can't remember the make but was about an inch or so too short! Made an aluminium spacer to compensate.
Would I change it again? No, no noticeable benefit.

My CD has always been economical which I put a lot down to the fairly high hearing and the fact that it is quite a light vehicle for its size.

Let us know what you get up to!

Alan

[iangsi]

All I can say is that the 4 -1 tubular manifold looks so much better then the standard cast iron one.

[Robsey]

I would love to get above 30 mpg....

I average 26.1 mpg, because of the horrendous traffic congestion on the main roads and motorways in and around Manchester.

I think one thing that would release a few extra mpg would be to remove the air-con belt during the winter months.
(If a multi-belt set up).
Or fit a shorter belt if your car has a single serpentine multi-vee belt.

[James McGrath]

I think one thing that would release a few extra mpg would be to remove the air-con belt during the winter months.
(If a multi-belt set up).
Or fit a shorter belt if your car has a single serpentine multi-vee belt.

Thanks Rob, I hadn't thought of that. Great idea

[Mk3alan]

In reality unless the air con compressor is being driven (Air Con On) the pulley is just a pulley as in an additional idler and can't be responsible for vast wastage surely?
Although I agree every little helps.

Alan

[Robsey]

As such, every pulley / bearing assembly will add to the drag / drawing effect on engine power.
Especially if any of the pulleys are old, and so not running as smoothly as they should.

[iangsi]

I tend to agree with Alan unless the air-con is on the pulley is just free wheeling as the electric clutch is not engaged, when you switch it on you can hear the engine note change with the drag of the air-con compressor.

[ilovedmymantas]

Just over a year ago I resurrected my air con, it didn't work when I bought the car, so even If I didn't use it I was stuck with added weight & fuel consumption.
I thought, why not, I'll only notice the difference if I turn It on.

I did a fair bit of researching at the time and found other benefits.

This page covers almost everything, better than I could
https://www.rac.co.uk/drive/advice/car- ... hs-busted/

I haven't been able to try aircon for demisting, It only lasted 7 weeks

Thought 1
I imagine it would temporarily help with dampness problems too, at least until the 'fixing' weather comes back

thought2
If It's icy will aircon draw less power/fuel than usual?

Last one
I wonder If there's a reason no-one seems to mod a cold pipe into the air system for summer use, or Is It just me being daft?

[Robsey]

Thought 1 
I imagine it would temporarily help with dampness problems too, at least until the 'fixing' weather comes back  

A working air-con system helps draw moisture out of the air, via the receiver-drier. So it would indeed help with moisture whilst it is engaged in the winter months.

thought2 
If It's icy will aircon draw less power/fuel than usual?

Nope, it will draw the same amount, as it is unregulated. So it is either off or on.
But the engine management fuel enrichment will be on longer as it will take a bit longer for the engine to get up to running temperature.

Last one 
I wonder If there's a reason no-one seems to mod a cold pipe into the air system for summer use, or Is It just me being daft?

There is no need to, as there is already a cold source of air in any car.

Although it could be said that ambient air in the gulley under the scuttle panel my be warmed by it's proximity to the engine bay.

It would be interesting to see where you would plumb in a cold air intake pipe, and I would recommend some form of filter to extract any dirt or insects sucked into the cold air intake hose.

Depending upon spec, the engine bay on most cavaliers, especially later ones can be quite full.
Especially if you have ABS, Power steering, alarm head and the standard wing mounted windscreen washer bottle in there.

The hose would probably need to be routed over the near-side arch-liner, and then a hole drilled into the scuttle area for it to pass through to supply cool air to the blower motor.

Potentially a lot of faff for minimal gain.
And the introduction of a hole into the scuttle could provide a weak spot in the body.

[James McGrath]

I've come across a few different manifolds now.
I'm currently eyeing up this one, mainly because it's £50 cheaper than anything else I've seen!

https://www.ebay.co.uk/itm/Header-Stain ... 1438.l2649

But anyway, they all seem to have an oddly located lambda sensor hole.
The all seem to have it located before the 2 pipes join into 1.
Would this make a difference to the sensor readings?
Considering that it will only be sensing from 2 of the cylinders and only half the amount of gas will pass over it.


Just for reference, this is the standard lambda sensor location:




Here is a manifold made by Direnza:

[iangsi]

It looks like the sensor hole is close enough to where the 2 pipes join together to get a decent enough reading, looking at that site the GSI manifold is cheaper I may have to invest in one I think !

[Mk3alan]

Nice looking bit of pipework and good price!
There looks like more is available now, when I was looking manifolds seemed quite thin on the ground, and mine isn't sensor equipped.
Seems more logical to mount the sensor in the single pipe as in the worst case you could have a leaky injector on a cylinder and the sensor is measuring the other pipe so it wouldn't get picked up?
Is it simply because the cable isn't long enough?

Alan

[Robsey]

My sensor is on the exhaust manifold just below where all 4 pipes meet.
(I have a C20NE engine, but C18NZ exhaust and manifolds).

Worked perfectly fine for 3 or 4 years, up until my restoration in 2015.
I did have emissions problems last year 2017 / 18, but hopefully, things are fine now.

(EDITED POST - I did think originally that the sensor was adjacent to exhaust port one, but it is not)

[ilovedmymantas]

I've come across a few different manifolds now...
…But anyway, they all seem to have an oddly located lambda sensor hole.
The all seem to have it located before the 2 pipes join into 1.
Would this make a difference to the sensor readings?
Considering that it will only be sensing from 2 of the cylinders and only half the amount of gas will pass over it.

I'm pretty sure your right, It will affect the sensor readings. The standard setup seems to run slightly lean to improve emissions.
Can't cut & paste (copyright) but here's the page https://www.goodfabs.com/single-post/Ho ... nsors-work

It looks to me like the sensor placement is designed to increase performance by running rich , so more performance but less mpg.

The listing, performance exhaust, basically states for export only and not legal in Germany.
I'm guessing because It screws up your emissions by over-fuelling?

Having said that...
It does look like a bargain!

The listing shows it with a blanking bolt in the lambda hole.
I would seriously consider sourcing a local engineers that could drill & weld a new nut to help economy & emissions, if that's still what you're aiming for - has to be worth it at that price?

[ilovedmymantas]

My apologies James,
I re-read my first post and now realise It looks like a random hijack. Hopefully I can explain.

Hello everybody,
…So I was planning on fitting a decat pipe (for track day purposes only you understand ) and I'm also considering a custom manifold....
... I'm after low to mid range power and maximum fuel economy.

Reading this, I wasn't really sure If you were after performance or economy (my focus usually veers to performance) so I looked at both, and got overloaded

What I was trying to say with the link was that it may be a false economy to disconnect the aircon belt.
The seals etc. are likely to dry out with no lubricant being pumped around.
Considering the cost of aircon parts, If mine was working It would be worth a couple of mpg to me. Quicker de-misting in winter is a bonus for me too. - Sunny Scotland

Thought 1
I imagine it would temporarily help with dampness problems too, at least until the 'fixing' weather comes back
A working air-con system helps draw moisture out of the air, via the receiver-drier. So it would indeed help with moisture whilst it is engaged in the winter months.
[/b]thought2
If It's icy will aircon draw less power/fuel than usual?[/b]
Nope, it will draw the same amount, as it is unregulated. So it is either off or on.
But the engine management fuel enrichment will be on longer as it will take a bit longer for the engine to get up to running temperature.

Thanks for clarifying Robsey. that will be useful to other a/c cav owners.
I tried Haynes but no joy.
Aircon in a cav is classified as the 'dark arts'

As for the last one (at this point I was back on performance-it doesn't hurt to know ) I totally ars*d up explaining myself - sorry Robsey.

My primitive thought was a gated metal pipe plumbed in for summer use to increase performance, fed through the air-filter box to cool the intake air.

I found this later
https://www.quora.com/Do-cars-run-bette ... summer-hot

It looks like my sensors will negate that so I've given up. I've got more important thing to focus on (two weeks to mot )

[James McGrath]

Right, minor update.
I've bought one of those manifolds, it was too good a deal to resist.

I've done some research on the o2 sensor placement and it seems that it shouldn't really matter as long as all 4 cylinders are healthy and consistent. The o2 sensor on;y senses whether or not the exhaust gasses are rich or lean, the amount of gas that passes over it is immaterial. So as long as all the cylinders are performing the same (as they should be on a healthy car anyway), it should make no difference.

So I've decided to go ahead with it with the o2 sensor placed as it is and see what happens. If I find it stats running rich then I'll get it moved.

On a different note, I've just achieved a new record for fuel economy in this car.
On a trip to Aldeburgh and back I managed to get 46.5MPG out of her. Not bad considering I was doing a constant 70mph along the motorway. Very pleased with how she's running at the moment, hoping to squeeze a few more MPG out of her though.

[Robsey]

Such mpg has got to be sorcery.
I never see an average mpg above 28 mpg.

Motorways are like car parks up here in Manc-land.

You will have to see what your emissions are like after you fit the manifold.
It would be interesting to get a true image of the effect of mis-location of the sensor has.

[James McGrath]

A few weeks ago i would have agreed with you.
I'd not had more than 42mpg before now and that was a one off a few years ago.
Now this weeks average was 41.82
That included a week of commuting along country lanes. Covering just over 500 miles to 55 litres (£65)

Yeah, I'm going to ask for an emissions test when I get it fitted.