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Stainless Steel Exhaust Manifold, 4-1, MX5 Mk3/3.5/3.75

SKU: SI6866

I.L.Motorsport has launched a brand new line of Stainless steel headers. This is a fully stainless header with 4 into 1 pipes is designed so that it delivers maximum HP and a maximum high flow. They have tested numerous designs to get to this special looking finished header. This price for this header is only available as long we have this current stock. These are now supplied with an oxygen sensor relocation kit which is required to fool the ECU into thinking the first cat is still there and stopping the MIL light coming on. You will need to install a bung behind the second cat and using the supplied wiring harness, move the second O2 sensor down, after the secondary cat. Click here for fitting instructions.

Fits all Mk3, Mk3.5 & 3.75 models, 2005>2015

Please Note: As from January 1st 2012, the UK MOT laws changed regarding catalytic convertors. Any vehicle built after 1992, MUST have a catalytic convertor fitted regardless of whether or not it passes an emissions test. Any car presented without a cat fitted will fail. Effectively, these stainless manifolds remove one of the two convertors fitted to the Mk3, so we have no choice other than to recommend that they are for off road use only. As your car would still pass an emissions test wth one of these manifolds fitted, it is unclear as to whether or not the one remaining cat is sufficient, so we would advise checking with your MOT tester before fitting this manifold if the car is being used on the road.



Based on 12 reviews

Rashid Aldossary
Sounds so good. definitely one of the best parts to swap.
09/05/2023 12:17:09
David Connell
Came supplied with manifold to head gasket and conical gasket to midpipe plus an extension for the secondary O2 sensor, not quite sure why as both O2 sensors need extending for this to be plug and play. I have extended my primary sensor myself and am going to leave the secondary one out as this can be 'turned off' with a remap.
01/12/2020 12:16:04
Martin Pike
I bought this header after I had the ecu on my 2007 2 litre engine remapped and had it fitted at my local garage. The remap vastly improved the responsiveness of the engine - even though increases in bhp and torque were modest (Dyno results showed a 3.5% and 4.5% increase respectively). However after the header was fitted the Dyno readout showed an increase in bhp from 163.5 to 175.1 - with the biggest improvement just where you need it for overtaking, at the mid to high rev range. I expected slightly less torque at the lower rev range - but the opposite was true. From 1800 revs torque increased - and peak power was at 6924 RPM with the engine continuing rev to 7033. This is significantly higher than standard. The rest of the exhaust system remained as standard but I did fit a Pipercross air filter to improve breathing. I also fitted an exhaust wrap (heat shield) around the pipe nearest to the alternator to avoid heat damage. Fabulous piece of kit with fabulous results.
05/10/2017 12:16:13
Jason Payne
Great quick delivery. I took it to Skuzzle Motorsport to get fitted and remapped, just as well as fitting these things are not as straight forward as I thought as there is not much space to manoeuvre it about.My only downside with it was the crappy spot welding of the bolts on the bracket at the bottom of the manifold which broke so the bolts span round when doing the nuts up. Back on the plus though, it sounds great and feels so much more responsive to drive. Highly recommended.
09/09/2017 12:16:13
Chris Lane
This arrived exactly on time (per normal with MX5 parts order / delivery service). It is a high quality piece of kit, very well made and finished. Am looking forward to seeing how it performs when fitted.
04/09/2015 12:16:19
Matt Bowden
A beautiful piece of stainless steel engineering. IL Motorsports don't state which of the bungs to use for the O2 sensor, and - when asked - simply suggested using whichever fitted best. We used the one furthest from the engine as that provided the best cable run for the sensor, and it should be measuring where the gases are better mixed. The stud holes in the flange aren't recessed, like the original, so once done up the ends of the studs are flush with the top of the nuts, which isn't optimal for strength. The head gasket doesn't have the cut out for the EGR system, so there's a risk that the gasket might be blocking the flow slightly. I bought an OEM gasket instead. The wires for the front O2 sensor have to be extended - I don't understand why the manifold only includes an extension for the rear sensor. A front extension can be purchased from I fitted the manifold with the IL Motorsports midpipe and the original backbox, and the increase in power and torque (after a dyno retune at Skuzzle Motorsports) is significant. The exhaust noise is very slightly louder and raspier, but nothing like as loud as I feared - it's fine roof-down or roof-up on main roads. Note that the weld-in bung provided with this kit isn't stainless steel, so it's not a perfect match if you're welding it into an IL Motorsports stainless midpipe. The alternator and the coolant line that runs above the manifold might need some additional heat protection since they're right next to the pipework.
11/04/2015 12:16:21
William Howell
Lovely bit kit, very impressed. Very nice design, welding and finish. Took me 2 hours 20 minutes to fit with a ramp and ample tools, once it was on I was quite disappointed to find that although there is a rear oxy sensor extension lead there is not one for the front sensor. This means you have to cut and solder in longer wires and tape it all up, not something I wanted to be doing to what I consider to be a fresh innocent low mileage car. The other issue is that the lower bracket which connects the pipe to the block doesn't line up great and needs a bit of bending to fit - not that impressive on such a well finished manifold. So it loses a star for the grief.A note on sound levels, I have this connected to the il Motorsport mid section race cat and factory backbox. I was worried about it being too loud as loud isn't what I want, I wanted a raspy escort type sound so didn't order a back box as yet. The sound is possibly marginally louder than standard, very little with a very nice rasp especially at low revs. It certainly won't offend anyone's ear drums! Wouldnt be scared to order a silencer now. Quality product lacking a couple of things but would definitely recommend.
22/11/2014 12:16:22
Adam Goodley
Yep, its good alright. Better than the racing beat im happy to say, and yes i have seen both in the flesh. First off i have a decat midpipe and the mx5 parts rear silencer and with this fitted its really loud, smelly too. I expected this, but actually after having it on for a couple of hundred miles it has quietened down a bit, its not as agressive sounding. Pops and bangs in almost every gear change and defiantly on overrun.... love it. This isnt for the faint hearted if you have a backbox fitted too, this will not go with the road or race backbox made by cobra because it will make you deaf in a minute. This isnt a DIY job really as you need a high rise ramp, its worth paying and getting it done properly and to just sit back as it looks a pig of a job. You will need to get the ecutek licence so that you are able to get rid of the error codes it will bring up, i have also had to extend and re route the o2 sensors as the extention plug it came with wasnt the right one. No idea why, bit annoying really.You will need to get a proper remap when you have fitted this to get full gains of the new power otherwise your doing it for the sound. But yeah i love it, sounds like a v6 and power gains are substantial with remap.
26/06/2014 12:16:23
Tom Wykes
I just wanted to add a note to say my MX5 passed its MoT fine with only the second cat futted. Emissiins were fine,so don't worry about it being non-compliant.
23/12/2013 12:16:26
Tom Wykes
What a lovely piece of kit. It's not often you shell out £300 on a bit for your car and you feel loathed to fit it because it's so well made! Fantastic service from MX5Parts, as this turned up less than 24 hours after ordering. It took about 7 hours to fit on axle stands, and the result is superb: much better response and power from 2500 rpm onwards. The sound volume increase is only barely noticable when fitted to a standard mid pipe and rear box. It sounds a bit more "sports car" though and my wife approves. It arrives in a posh box complete with gaskets and O2 sensor "Hoodup SIM". You will not need additional gaskets. You can find a useful step by step guide here: I must warn you not to attempt to fit this without ample tools. Don't expect to start this on a Sunday afternoon on the drive, armed with only an adjustable spanner and a blunt screwdriver! You will need:15mm swan neck ring spanner. Deep sockets and lots of wobble extensions. Ratchet spanners with swivels. 22mm O2 sensor socket. Multimeter and soldering iron. Wire wool and copper slip.Stilsons. I removed the old manifold (a pig!!!) without draining any coolant or touching the alternator. Take you time as the nuts are soft. A swan neck ring spanner is essential for this and access to the rear 2 is best from underneath. Wear gloves as you'll rip your hands to shreds when the nuts finally move - as i did. Take off the heatshields and remove the studs which bolt up the midpipe. You see what's in the way before waggling the manifold out. In contrast, the new one flies in. The new gasket supplied with the manifold is too thick - the stud threads won't poke though the nuts so I wire wooled the old tin gasket and reused that. To aid fitting, I left the studs and sensors off until it was in situ. Bolt up the head before fitting the engine bracket to the bottom. I had to open the bracket holes up a few mm to allow it to line up. There must be a stack up of tolerance but easy to overcome. Then the faff starts....You need to be handy with a soldering iron to modify the O2 sensor flyleads. They BOTH require lengthening!! I even removed the dish fitted to the upper sensor to facilitate tightening it up as access is compact under the car. Follow the wiring diagram and you shouldn't have any snags. Vrooom vroooom.
28/03/2013 12:16:29

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