Rear end woes
 

Right so I'm in process of buying a m60b40 for my mx5.. I'm reasonably confident with it, and I've got all the time in the world as it will have all test fitting and wiring in my spare miata
But.. I don't know what to do about the rear end :L what's a suitable diff, and drive shafts to use?
Any help would be greatly appreciated
Cheers Luke

What is a m60b40?

M60b40 is the 4l bmw v8

I'd go with the Ford 7.5 due to price, availability and that is plenty for the engine. Are you doing an auto or manual trans?

I don't mean to be nosey but could I ask why this engine? I only ask because there are guys over on LS1tech that swap them out of BMWs to put LS engines in.

Oh I just noticed you are in the UK. Why not the 5 series BMW diff that matches the engien and trans? Find a mid 90s car that has been wrecked and you would have all the parts you need. Any good drive shaft shop can make you custom axles with the Miata parts on the outside and BMW parts on the inside.

Well the choices I have here for a v8 are old rover v8s, bmw v8s that fall into a decent price range,
I was going to use the m60b40 because of a trader willing to sell me a complete engine and box including all ancillaries and ecu for a very good price
So I sorta figured that would be my best option as I'd have the whole front end and trans sorted all I needed to worry about was beefing up the back aha
I'd love an ls but they're few and far between and any you do get don't usually come complete and I don't want to spend time hording parts for the build ):

Makes sense. I would imagine there are not very many thunderbirds in salvage yards around your parts either.

The Miata rear end would probably hold together but the gearing is all wrong. No help from RX7s either but they are a stronger diff. It depends on your high gear in the trans and what you are going to do with the car but generally guys go with something between 3.25 to 3.50 to 1 for a 5 speed trans and maybe 3.40 to 3.65 for a 6 speed trans. Though there are plenty of t56 6 speeds with 3.27s, 3.73s and even 4.11 gears running around.

So what trans are you using and any idea what the high gear ratio in it is?

No I don't, when I finish work I'll find out.. I can only assume it's the trans that originally come with the engine?
It's intended to be a drift car ;) I've not had time to do a decent search at work about the rear end, do we weld to the rear subframe or fit a new one?

I know stated earlier have a machine shop make up some decent drive shafts that will fit the mx5,
But I think that may be the answer actually

So are you thinking dedicated drift car not running on the street? If so I'd just use the stock Miata torsen and be done with it. It's geared a little high for the street but would be great for the track and should hold he BMW power fine. If you wanted a bit stronger unit use an RX7 which is an easy swap but I really don't think you would need it.

No it will be used mainly for late night streeto, and track when I can :L
The m60b40 stock works out as.. 282bhp I believe? And the b30 is around 212bhp?!
If I used the three liter (b30) I guess a 1.8 back end will hold the power as a lot of the fi boys retain stock back end and push 250ish

It's the torque though, as what I'm worried about I could expect the drive shafts to twist and snap :l
Before settling on a v8 conversion I was going to fit a sr20det from a 200sx but a lot of people are doing that now..
But yeah straying away from the point!
One lad with a nissan powered miata was running 310 on a forged sr lump when one of his driveshafts snapped during a transition from ice to tarmac

Do many of you v8ers run stock back ends?

Thanks for all the replies so far! Your much nicer then some of the users on my usual forum! Haha

I know of one Ford conversion with the stock back end but pretty much no one uses them. Partly because the gears are not avaiable to work well with the V8 and partly because dumping the clutch on 400 ftlbs of torque would probably not end well for them. But I'm not sure the modified axles we use would hold up from ice to pavement either. That is quite a shock.

So how about RX7 stuff then? I believe it is a fairly direct swap and a stronger set up than the Miata.

My other thought is what's your budget? I bet for 200 bucks in shipping you could get an entire Ford 7.5 set up shipped form Martian over the pond.

My budget.. I don't really have one.. Not insinuating this is going to be a budget build haha but as stupid as it sounds I'd rather not set a budget them I don't exceed a budget ;)
The mrs is going mad as I'm £1300 into a car that doesn't drive haha..

I would like something like that.. But I've got to look at it in a way of if something where to go wrong, especially as a drift car and an some sort of ancillary was to brake or something internally in the engine how easy is it to source a new part!
I know there's got to be a couple of ford lumps round here but other v8s can be much easily sourced

For example said v8 conversion I mentioned, all in is just under £800.00
The engines alone can be picked up for around half that, I know it won't make mad power but again as stated I'm looking for the instant response and torque

I'm thinking.. If it really isn't enough maybe a supercharger, but ideally I'd like to keep it naturally aspirated

What engine do you run yourself?

Oh man my life just passed in front of me and I nearly fainted. If I could offer some unsolicited advice here I have to tell you planning is everything in a build. It’s critical to the build that you know what you are getting into and what it will take to complete the project before you start.

I suggest taking a month and reading build threads. All build threads but especially guys that start from scratch like you are doing rather than use a kit. Things like oil pans and exhaust are really big deals that guys struggle with a lot.

This would be a great build thread for you because it is all of the stuff you are going to be doing. The engine and body is different but the process he goes through is exactly what you are looking at.
BMW e34 Touring LS1 swap (BMW 5 series wagon) - LS1TECH

Honestly if you don’t have a budget, a plan and a very supportive wife you will die a slow painful death as your Miata rots in the garage....

Oh and you can check out my blog too. It's not super technical but will give you a good idea of the effort it takes. And share it with everyone over there to run the UK hit count up!! :la:

Jim and Jenna build diary, Miata LS1 Conversion

Aha sorry :p yeah as it stands.. I've got a vague idea of what I'm going to do.. But obviously not enough to be right this weekend we start aha

I did anticipate it to be a lot more work then first thought, but I still don't want to set a budget for it, I'd rather pay what it costs then at the end be like oh right it cost me this much to build.

Buh yeah at the mo I'm just gathering information, I don't plan to start it until next year

When I get home tonight I'll open the laptop and start having a proper look at engines, trans and diff
The sump didn't pop into my head at all /: that's the trouble haha maybe a case where I end up purchasing a custom sump

Would my life be made easier with this current situation?
The "Project durift" is the soon to be v8
My current miata "trusty rusty" is, dying a slow death of tin worm..
So once I have got round to pollybushing the front end (this weekend) I will be swapping over parts from trusty rusty to project durift which will leave me with a rolling rusty shell and memory of the best car of my life ):
Ideally I'd like to put trusty to good use, so.. My question is do I keep the shell to test fit the v8 until it's done? Because I don't expect it to be a case of I know all I need to know got all the pieces and throw her together..

Absolutely keep the old car until you are done. You will go to it over and over for brackets, lines, wire and who knows what else. I was amazed at how often I went to my shell to grab something.

The thing about the budget is it’s easy to figure out the expensive stuff. What nobody anticipates is the million 20 dollar parts you end up buying. Look at any build thread and you will see dropping 40 bucks 3 times a week at the parts store is not unusual in the thick of the build. There are some great real world parts lists in build threads out there. Mine is on the right side of the page under what is all this costing. Check it out that is the real deal you are looking at. (yeah still looking for the UK visiter count!:biggthumpup:) Jim and Jenna build diary, Miata LS1 Conversion

I’m looking forward to some other guys commenting on this thread!

I checked out your link pal (: I'm not sure if it's because I use my phone but couldn't find a build thread on it, I love you bonnet though! Looks excellent!

What would be a ball park figure to be looking at for a full conversion then?

Click me
https://skydrive.live.com/view.aspx?...EnMKcJ0CspHsIw

The thing about figuring cost is so much of it depends on your ability and resources. You read build threads and you see lots of guys are not able to weld and have the welding done. That adds cost both in buying parts that could have been made and in paying a welder. On the other hand you see lots of guys like the BMW link I sent you that have the fabrication skills and equipment to make parts rather than buy them and that reduces the cost considerably. Then there are guys like me that was not comfortable making the engine mount due to the complexity of getting the suspension geometry right but I had no fear in making the trans mount and frame supports. So I paid $1250 bucks for a frame I could have built for $50...

But again that stuff is easy to figure what gets people is the little stuff. The $15 harmonic balancer bolt you didn’t know you needed or the grade 8 diff bolts you didn’t put in the budget. But to answer your question about a guestimate I would think if you were really careful, made all the supports yourself and could get your engine trans and diff for less than $2000 you might be able to do it under $6500. But that is based on what I know about the US market and parts prices here it could be way off for where you are.

I think my experience was typical and a lot of guys will tell you the same thing I am about to say. I worked for many hours researching parts prices going over every thing that I would need to buy and do to the car and created a detailed estimate and plan to do the build. My estimate before I started was $7300 just the conversion cost not including the engine and trans. What I actually spent was just under $10,000 on direct conversion costs. Total into the car with engine and trans costs was closer to 16K.

If you read through the threads here you will see lots of guys say whatever you figure it will cost or how long it will take double them both. Look at some of the threads from last winter when guys told me that and it is easy to see I didn't believe a word they said!

Now just to be clear here I am not trying to scare you or dissuade you from doing the build at all. You want to do it and you will not be content until you do. I just want you to be aware of what it takes now rather than be discouraged when you have it all apart. You might ask if I thought my build was worth it now that it is done and I would probably say no. For the same money I could have made my donor car amazing with far less effort. But in the same breath I would tell you that I would absolutely do it all over again with no hesitation at all! I enjoyed every minute of the process and even now visiting with guys like you has made it all worthwhile.