mx5 vs sierra

[jay395]

hi guys, im sorta stuck which route to go down, mx5 or sierra , i suppose both have pro and cons and would appreciate your thoughts and what made anyone decide to go down a specific route for a reason.

I know sierra are hard to come by and a couple ive seen are the same price as a cheap mx5.

would like your opinions as im at a crossroad with no tomtom

[robo]

I dont think its a Vs as much as what turns up. You may read the sierra is in decline but that is not the case , there are still plenty about with spares etc and that will go on for years. The Sierra running gear can take more abuse if you are planning upgrades, the mx5 running gear makes for a very complete package but might have a question mark over the rear diff arrangement. Only time will tell.

bob ( getting ready to be shot down in flames)

[vmax1974]

My choice was to go with the mx5 purely due to the engine I once had one and it threw a con rod and even though it had a leg through the block I was still able to drive it home loved that car really revey engine (7000rpm redline) and pulled well for the size of the engine that coupled with a warehouse of tuning options made my mind up easily

Hope this helps

[PorkChop]

If you're not bothered about getting a complete donor car, then either way will do you just fine, there's plenty of both Ford and MX5 diffs, gearboxes, engines etc available and aren't prohibitively expensive. There were a million or so Sierras made, so there's truth in what Robo says.

If you want a full donor (e.g. for age related plate) then you will find more suitable MX5s than you will Sierra (don't forget the youngest Sierra you'll find is still nearly 20 years old). You can negate (or significantly reduce) the purchase cost by selling off unwanted parts but the MX5 market in particular is full of these and it's more difficult now to achieve the prices of a year or two ago. There are still some parts that command strong money (e.g. decent condition front wings, JDM tuning parts) though.

The MX5 bits are a little lighter than the Sierra ones, you will need 15" wheels to clear the Sierra based Roadster rear uprights, the front Sierra uprights will need modification and mushrooms to fit.

You do have a much greater engine choice with Ford running gear though (depends on what you want from the Roadster). The MX5 running gear can handle approx 250bhp from what I've read (if a Torsen diff is fitted, which is apparently rated to 300bhp). A Sierra diff, I've been told, can take a similar amount of power/torque.

There's plenty of options and knowledge on upgrades for both Ford and Mazda, although there is a greater choice of options for Ford IMO.

I went the MX5 route. The reasons why are...

1 - I wanted a complete donor car
2 - an ideal donor car (scruffy but decent condition running gear) was for sale at a fair price less than 10 miles from home
3 - market prices for the unwanted parts were very good
4 - the MX5 gearbox is widely recognised as having one of the best actions ever
5 - OEM Mazda wheels are generally very light and are very cheap
6 - the MX5 is a sports car, so the components were designed and built with that in mind. The Sierra was designed as a repmobile/family car, so may have had a slightly different design brief to Mazda's. Some people have the opinion that it's more satisfying taking a repmobile and turning into a sports car, rather than starting with sports car stuff in the first place. Fair enough.

WRT Robo's comment about possible issues with the MX5 diff. I don't think it's an issue per se, the front of the diff needs a custom mounting to replicate the PPF frame which links the diff and the gearbox together.

HTH

[jay395]

thanks for all the replys, not long after posting this i was offered engine,gearbox diff drive shafts for a little over a ton so took it so guess im heading sierra route and a q plate, which dont really matter to me what plate its on.

thanks again for the replys all

[The V8 Files]

There's not much I can add which hasn't been said above, almost a year ago I was trying to find a logical conclusion to the same question, I don't think there is one.

Mine was answered in the same way as yours seems to have been answered, pure chance by what becomes available.

If your looking for an age related plate then a whole donor is probably the best way to go but at the end of the day are you building the car for the car or the plate.

I believe the MX5 gear is more obtainable and a little lighter but there are less completed builds so possibly not quite as much support as for the ford running gear.

I'm not sure on how many diff ratio options are available on the MX5.

I know all these questions rattled round my head for a while, and it can be a daunting aspect when in the first stages of thought/planning etc.

In the end for me, I somehow fell in love with the BMW V8, I stumbled on some Scorpio Cosworth running gear on the bay, I've still got to sort a gearbox and decide on whether to use the ford/BMW diff, but gradually its getting there.

At the end of the day this is your build, your creation, your going to invest a lot of hours/money/stress in it so see what comes up and if it fits with what your dream is (within reason) then go for it.

Good luck

[jay395]

thanks, i best not mention "hours/money/stress" to the wife lol

[robo]

bump bump

bob

[Not Anumber]

I see your donor parts are for sale? Have you decided to quit or change over to a to Sierra donor instead

[Big Vern]

Originally Posted by robo

I dont think its a Vs as much as what turns up. You may read the sierra is in decline but that is not the case , there are still plenty about with spares etc and that will go on for years. The Sierra running gear can take more abuse if you are planning upgrades, the mx5 running gear makes for a very complete package but might have a question mark over the rear diff arrangement. Only time will tell.

bob ( getting ready to be shot down in flames)

Here come the flames
MX5 running gear can take a 250+bhp turbo motor without problems - there are enough of these conversions about.

The engine and the gear ratios in the MX5 are much more sporty than the sierra which was intended as a mid sized family car. For me its a no brainer, the MX5 wins every time and with plenty still about they are much easier to find with the running gear in good order than Sierra's
As for the rear diff so long as its properly constrained as I have stated elsewhere then there is no problem!

BV