Starting my first build soon... looking for advice on which SDV car to get

[RizFizz]

Hi all!

 

I've got an SDV MX5 kit on order, which will be my first build 😬 So I'll need to get hold of a donor car soon! I'm a little bit confused about what the options are though. Westfield tell me I can have a 1.8 but only if it's a MK1. 

 

I've done a bit of searching on these forums though, and it seems that people do use Mk2 1.8 cars? So I'm wondering if Westfield only advise against this because of things like the manifold differences? 

 

Ideally I'd like to avoid a detuned 1.6, avoid a VVT (if it means loosing the clean look of the standard bonnet) and would like something with an LSD too, so otherwise it's just a case of finding what's compatible and ticks those boxes, 1.6 or 1.8... seems like it's much easier to find mk2 cars at the moment though.

 

Any advice would be great!

 

[TAFKARM]

My advice…don’t do a track day in the mx5, you’ll end up keeping it! 

[Dommo]

It might have something to do with the uprights on the mk2 being different, affecting steering geometry. I think the arms mount slightly higher on the mk2. I thought as long as you told Westfield what donor you were using they'd weld the steering rack brackets to suit. Mk1s don't tend to be so cheap anymore.

 

My thoughts on mk1/mk2 1.8s:

• VVT solenoid will be tricky to squeeze under the normal bonnet, but think some have. Might leave the sump rather low though, and they're low enough as it is
• Exhaust manifold. Ah this must be what they were referring to. The mk1 1.8 has a 4-1 manifold, so the Westfield supplied downpipe is a single pipe shaped to route through from the manifold to somewhere a silencer link pipe would be expected to start. The mk2 has a 4-2 manifold, so the Westfield downpipe wouldn't fit that. Easy solution though would be to bolt a mk1 1.8 manifold to the mk2, or spend the extra on the manifold that Westfield sell

 

If you're definitely not going to be looking for 160bhp+, try and find a 1.6. Might as well use a lighter donor after all, and no slower than a 1.8 in the real world. It would make an excellent road car!

[Mark (smokey mow)]

All very much as Dommo said, the Mk1 mx5 uprights are a slightly different geometry to the Mk2 but you can always swap these out cheaply enough for another pair.
 

the Mk2 1.8 exhaust manifold is also different to the Mk1 so you’d either need to spend the extra on the Westfield 4-1 manifold (well worth it) or alternatively find a Mk1 manifold so you can then fit the link pipe that comes in the kit. 
 

IMO the 1.6 is the better engine out of the box than the 1.8 as its lighter and more willing to rev and will build you a car 30kg lighter but theres better availability of the 1.8 engines and you can’t deny their tuning potential. 

[RizFizz]

Thanks very much for that! Great advice   So I'll probably go for a mk2 seeing as there's much better deals available on that car (who doesn't love pop up headlights).

1.6 sounds like a better option for me too (I only want this for road use and maybe the odd track day, so lots of power isn't required) But as you say, they don't seem to be in plentiful supply either! Maybe it's the wrong time of year to be looking, but there's not that much out there.

 

From what I can tell 1.8 is the only one with a torsen diff too though, and that does appeal to me.

 

Am I right in thinking that Mk2 1.8= 140 bhp, but fits under the bonnet just fine, Mk2.5 1.8 =146 bhp, but fitment issues with standard bonnet? There's a loads of speedbumps around here, so that's also a concern (I'm aware that getting the sump modified is also going to be a requirement no matter what)

 

 

[Dommo]

Those power levels sound about right. Did the mk2.5 also always have the 6 speed box? That will be an extra bit of weight. Some of the mk2s will too, but I'm unsure on which special editions did and didn't have it. 10th Anniversary rings a bell, and some of the imports? But then, they've been around long enough now anyone could have swapped one either way.

[TAFKARM]

Having had both, the 5 speed is a much nicer box than the 6, especially if you want to push the power 

[Mark (smokey mow)]

One advantage of the 1.6 is that it is shorter than the 1.8 so you can fit taller engine mounts rather than modifying the sump for ground clearance.

 

I wouldn’t worry about a 6-speed gearbox, the best combination in a Westfield would a 5-speed gearbox running with either a 3.6 or 3.9 ratio diff from a 6-speed car depending on the level of engine tuning.

[RizFizz]

Thanks again for the replies  I have to say, one of the big reasons for picking a Westfield over the other options was this forum and the people here willing to help out people like me, so it's really appreciated

[Gary Taylor]

Ive a Mazda sdv  1.6 , 5 spd box and Mazda open diff from a mk2, it’s nippy enough around the countryside and has been all over Scotland and from way up here to Switzerland and back

Good luck with the build

[Dommo]

Just for clarity, I was suggesting the 6 speed wasn't worth the extra weight. Hope the way I wrote it wasn't adding an extra layer of confusion!

[DavidMiller]

I have a MX5 SDV - mk1 1.8 block and 5 speed gearbox, but mk2.5 head. I have an FW bonnet though and it all fits easily under that. I made up my own exhaust manifold so no issue fitting that in. It does have the sump shortened about 30mm as it was far too low as stock.  

[RizFizz]

On 10/10/2021 at 20:53, Dommo said:

Just for clarity, I was suggesting the 6 speed wasn't worth the extra weight. Hope the way I wrote it wasn't adding an extra layer of confusion!

 

Nope it wasn't   I think that's exactly what I'll try and go for: 1.6 with it's 5 speed gearbox from a mk2, and a torsen diff from the 1.8

[BenD]

Didn't the mk2 1.6 only make 90bhp also just be mindful that the prop on the 1.6 is different to the 1.8. It has a smaller drive flange 

[Mark (smokey mow)]

24 minutes ago, BenD said:

Didn't the mk2 1.6 only make 90bhp also just be mindful that the prop on the 1.6 is different to the 1.8. It has a smaller drive flange 

 

109 because of the Cat. it’s only the post 1995 Mk1 that was detuned from 115 to 90 along with the auto.

 

the Mk2 1.6 should also use the same larger diff as found in the 1.8 so prop should likewise be the same.