Help with Mid Engine Design

[V8turbo4me]

Hello Everyone,

I have always dreamed of designing and building my very own car since I was a little boy. I have decided to sell my VR-4 to begin to pursue that dream. Only I am going to need a little help in one of the design areas. That area is Mid Engine setup. I have never owned or worked on a mid engine car and frankly I have no idea how they work or need to be set up. My list of questions is humongous as you might have guessed. Most importantly though, I need to see some kind of diagram of a successful mid engined car so I can see and understand what all is comprised in the system. Secondly are a special transmission and rear end need because I was planning to use a 700R or 1200R transmission and a 9 inch rear end but if that won't work I am going to need to seriously need to rethink the whole drivetrain of this project, which I am willing to do! So if you can help me out in this department, please lend me your knowledge and enlightend me.

[Matra et Alpine]

I need to see some kind of diagram of a successful mid engined car so I can see and understand what all is comprised in the system.

A goo dplace to start woul dbe to review the various kit cars usign mid-engine.

Most of these transplant a transverese front engine front wheel drive into the rear. Newer ones use newer longtitudonal engines from front wheel drive cars. ( Suka ? Can you scan and post the build diagrams for the Libra ? )

Look for Mini-based cars from the 70-80s. They were very common.
Lotus have published a few articles on the Elise design. It's a custom design from ground up but will likely answer a lot of the detail questions. Thought I had a ref but I don't

Lots of experience here of stock, kit and modified mid-engined cars. Maybe if you give a bit more detail on what you expect to do? Complete car design, purpose, road or track, size and we can help more.

[V8turbo4me]

More details huh? well I plan to build a roughly 14 foot long mid engined small block V8 turbo charged car. The emphasis of the project will be on keeping the auto as light as possible to allow for maximum cornering power and great acceleration and braking response. The car would be used for road racing and driving very similar to this. My biggest problem is that I want to develope a lot of horsepower on this car and at this point I don't even understand how the transmission and rear end fit into the car! As you can image I am a little concerned about all of this and am in desperate need of some answers, any help will be greatly appreciated.

[Matra et Alpine]

More details huh? well I plan to build a roughly 14 foot long mid engined small block V8 turbo charged car.

OK, first MAJOR problem is you're talking about putting a lot of power down.
14 feet long doesn't leav a ot of space for a driver and engine
These bring issues in building a safe chassis that a scrutineer will pass for competition.
You'll have problems if the pedals are forward of the wheels as the tub would have to be shown to be strong enough to prevent suspension in gress in the event of an incident.
What are you planning for suspension ? Are you going to take it all from a donor or build-your-own like the Locost ??

The emphasis of the project will be on keeping the auto as light as possible to allow for maximum cornering power and great acceleration and braking response.

To race it competitively you will ahve to make it strong enough to handle the speeds and stresses of the power you're proposing.
You're heading along an expensive route, but we'll see if we can assist

at this point I don't even understand how the transmission and rear end fit into the car!

Do you plan to lift engine and transmission from a donor or can you do engineering to mate engines and transaxles ?
How much money do you plan to spend ?

As you can image I am a little concerned about all of this and am in desperate need of some answers, any help will be greatly appreciated.

OK, if I'm going to take 'standard' layouts you would want to put the engine mid-ship front to back and mate it with a transaxle - gearbox and diff combined. Your choices are a full race-spec unit from companies like ZF - expensive - or to seek simialr layouts and 'borrow' transaxles. Sounds like you're US so I cna't help. One of the cheapest/strongest in Europe is the Renault as used in my A610.
An alternative layout would be to take the transmission from a fwd car using the engine you plan to use. Then plant the whole thing in the middle. The disadvantage of this solution is usually the height. BUT depends on the donor. Again you need to source US parts.
Suspension.. do you have a car in mind to take working suspension from ? If so then as with the engine, you've all the measuremnets to design the chassis to. If you plan to do something 'special' then you're not going to get it to work. Chassis and suspension design is not easy. There are too many variables to get anywhere near right, sadly. So I'd recommend sourcing a decent donor. In Eureop the Ford parts bin is used for many kits
Now once you've chosen a reasonable set of possible donor or new parts you then need to sit down with a calculator and work out the weight of all the parts and calculate the corner weights to determine the suspension needs for springs/dampers and the front/rear bias. If you don't get enough weight forward then you'll have a car that will go off backwards every time you lift off the throttle Get too much and you'll have a car that will do the same eery time you turn in Once you have designed the chassis to meet a reasonable weight split ( between 40:60 and 50:50 ) THEN you need to look at the polar centre of momentum. This is the point that a car rotates around. To be competitive as a race car you want that to be as close to the centre driver position as possible. If you don't the car will be hard to 'feel' during cornering.
Now to do all those calculations you are best to have an engineering degree to know how to do it for scratch designs. Alternatively you can ask here and it will take us a couple of years to teach you the calculations
SO far we've not even covered the complex suspension settings, camber, castor, wishbone lengths etc etc. Get these wrong and you will get bump steer effects at front, back or both
Sorry but designing a race car from scratch stopped being a back-street-garage task about 50 years ago.

You are thinking about undertaking a very complex task.
You might want to research kits that meet the goals you've set.
There will be one out there !!

Someone else has done all the calculations and even better have then modified their deisngs based on EXPERIENCE of driving it. You will find that you will ahve to redesign parts as the foibles of the car surface on the track. That is time consumming an dpotentially expensive.

Sorry if this sounds too negative, but if you plan to be serious about racing than you're biting off more than you can chew based on the question you've asked here. Realising that now will be healthier for your bank account and mental health

[V8turbo4me]

Well I don't think you realize how qualified I am to undertake in this endevour. I am an Engineering student and fully understand all the wonderful workings of the suspension. Also I am not really talking about building this car for club races because that is by no means what I wish to do with it. Yes I will drive it hard and fast on the backroads and hills but I won't be doing any endurance races anytime soon. So with the thought of competition out of the way my options are a little more open as you can see. Yes, I do plan on building the whole suspension and frame myself with the help of another engineer and a master mechanic with 27 years of racing experience.

I have a hard time believing that any front wheel drive set up or any renault short of full race is going to be able to handle much more than 300 horsepower, and that would be assuming that I could actually fit the unit to the engine.

[Matra et Alpine]

Well I don't think you realize how qualified I am to undertake in this endevour. I am an Engineering student and fully understand all the wonderful workings of the suspension.

Sorry V8, it was your initial quesiton and comments about not knowing mid-engine layout made it sound like you didn't know what you were bgetting in to.
There are lots of public descriptiosn of lots of alternative mid-engine layouts. If you were more experienced I would have expected you to have questioned alternatives rather than open-ended.
My apologies.

Also I am not really talking about building this car for club races because that is by no means what I wish to do with it. Yes I will drive it hard and fast on the backroads and hills but I won't be doing any endurance races anytime soon.

OK. What kind of roads. Do you plan to take it on unmade or off-road ?
Again a totally different proposition

So with the thought of competition out of the way my options are a little more open as you can see. Yes, I do plan on building the whole suspension and frame myself with the help of another engineer and a master mechanic with 27 years of racing experience.

So what are you planning for the rear ?
Double wishbone will make it tight for space in the rear if you want reasonable suspension travel.
Trailing arm would be the easiest but most difficult to fabricate.
WIshbone and Macpherson would likely be easiest but then you need to decide which donor as that's not the kind of layout you can fabricate from scratch cheaply.
You will need to go round the design options a few times to decide what is easiest, cheapest and meets your needs.

I have a hard time believing that any front wheel drive set up or any renault short of full race is going to be able to handle much more than 300 horsepower, and that would be assuming that I could actually fit the unit to the engine.

The Renaullt transaxle I was talking of has been used in many sports cars and outright race cars. It's capable of taking 500-600bhp.
Lots of modern transverse boxes are capable of taking 300bhp.
You just aren't intriduced to them as Euroepan cars are generally frowned on beyond the 'luxury' names
The TRANSVERSE boxes I discussed I pointed out needed to be thought of in conjunction with the engine. So maybe you're engine is smaller
The weight balance is important and equally so trying to get good traction.
It's easy to put an engine/box IN, getting one in that works effectively won't be so easy. So maybe a smaller lighter engine is a better all round choice for performance. Could you afford a K-series engine/box and Rover suspension ? A good starting point.

If you are planning rough or off-road work, you need to look at narrow gearbox, long driveshafts.
Tarmac will involve less suspension travel and can handle a wide box/diff and short driveshafts.
You say you plan to build suspension.
What about driveshafts ? Are you also able weld and heat-strengthen components ? Again, if not - or cost-driven - then sourcing a complete engine/drivetrain AND suspension should be looked at.
This was VERY common in kit and mainstream manufacturers in the 70s. Studying their choices will help guide you.

[Coventrysucks]

Have you looked at the chassis of the Ultima?

It is a 14ft mid engined sports car, designed to take engines over 500hp

[Matra et Alpine]

here's some details of how small ( and fast ) it can be.
Versions of the ABS Frestyle do extremely well in the UK Autotest circuit.
http://www.funbuggies.co.uk/gallery.htm

[V8turbo4me]

well I am planning on taking the car on tarmac roads and DEFINATELY not offroad! lol. Yes I have looked at the Ultima and it was key in my inspiration to undertake this project. I was planning on (this of course was when I was thinking of using a ford 9 inch rear end) using a satchell four link rear suspension to provide adaquate support to the axle and allow myself to achieve the highest amount of anti-squat possible without getting brake hop. I am planning on using an Independent suspension on the front obviously and I was thinking that I would probably use a double A arm setup that would allow the car to pick up some negative camber as the suspension went through its travel. My thought was that this type of front suspension would significatly help to negate the effects of any body roll.

Matra, I have actually heard of a lot of those european auto companies unfortunately their components are not easily obtainable over here in the states so I tend to rule them out for practical reasons. My reasoning for the open ended questions is that nothing that I have designed is set in stone yet and this project is still very much so in its infancy, I havent even sold my other sports car yet, so I was looking for opinions. And you have been very helpful! I am not really going to consider a smaller engine because the whole idea for this car was that it would be a turbo V8, something I have always wanted to do.

This brings me to my next question. I am planning on developing in upwards of 800HP on this car, now do you think that a twin set of TO4 turbos or one GT-45 or T-88 or comprable turbo would produce better response? Obviously with proper sizing neither set up should have much in the way of lag time, even the T-88 will get going pretty fast considering the large amount of exhaust gas it will be barraged with from a V8 engine. Again this is just a theoretical question, so if anyone has some turbo knowledge and would care to lend your expertise, please give me some input.

[Matra et Alpine]

well I am planning on taking the car on tarmac roads and DEFINATELY not offroad! lol. Yes I have looked at the Ultima and it was key in my inspiration to undertake this project. I was planning on (this of course was when I was thinking of using a ford 9 inch rear end) using a satchell four link rear suspension to provide adaquate support to the axle and allow myself to achieve the highest amount of anti-squat possible without getting brake hop.

If I understand US terminaology, you are planning to use a rear diff ?
You won't have the space to fit a V8, then gearbox, then sperate diff.
Unless you are willing to push the driver well forward of the midship and legs between front suspension.
Normal mid layout is either
- transverse to shorten engine length - but often ends up taller.
- engine with transaxle - diff with gearbox behind cf a ZF race tran
- rear-engine is an alternative but makes the handling MUCH more difficult
Never seen a designer get the space to put seperate gearbox/diff with short prop. Is this what you are thinking ? ( Sorry but terminology makes me think it is )

My thought was that this type of front suspension would significatly help to negate the effects of any body roll.

With mid-engine you will have to spend much more effort on the rear geometry to prevent body roll as the main momentum force will be applied to the rears.

Matra, I have actually heard of a lot of those european auto companies unfortunately their components are not easily obtainable over here in the states so I tend to rule them out for practical reasons.

sounds a sensible idea

I am not really going to consider a smaller engine because the whole idea for this car was that it would be a turbo V8, something I have always wanted to do.

Good to know the aims and preferences. Understood.

This brings me to my next question. I am planning on developing in upwards of 800HP on this car, now do you think that a twin set of TO4 turbos or one GT-45 or T-88 or comprable turbo would produce better response?

The biggest challenge you are going to face with that amount of power is the heat dissipation. You may have to consider forced colling.
A single turbo will require you to route the exhaust gasses to one area and THIS will generate heat issues and the long pipes from header to turbo will make lag inevitable.
For a self-design ( rather than taking a 'stock' solution I'd recommend the twin JUST to get those hot spots low and to the outer edge of the engine where you can easily scavenge cool air flow.

We're needing to find a forum to share drawings
Maybe you can do a few sketches of the componenets you WANT to incorporate and we can then discuss the issues. I'm not aware of "satchell" suspension, but as he IS a respected US race designer from NASCAR days ( we do get SOME US coverage over here ) it made me think of live rear axle which is't on either. So before going further maybe a sketch or a link to description of the components of choice can help us move forward

[Matra et Alpine]

got 15 mins to kill and did a seach.

Taking comments at http://www.427cobras.com/rear_suspension.html then I presume you are considering a live rear xle. Aint going to work for mid-engine.

Also that site is VERY dubious on it's suspension comments.
That a live axle is as good as IRS is just "BS"
On a theoretically smooth road and on cornering with NO body roll then it is possible to be equal. But in the real world. independant rear allows the designer ( and setup ) to dial-in the same live-axle characterstics AND to have thenm available over bumps and extreme cornering.
You can't make a live axle have compliant suspension AND corner well.
If it's stiff enough to keep the wheels planted then it will lift an inner wheel on cornering. If it's soft enough to keep the wheels down then it has horrendous body roll and the handling nightmare THAT introduces when driving real road twisties.

[V8turbo4me]

Matra, I know your right about the live rear axle not working, that was just my original thought when I was thinking about this project. Also I know that an IRS would be the ideal solution if road adhesion is the goal but it is literally impossible to develope more than 30% anti-squat with an IRS where numbers over 100% are available with the live rear axle. Yeah, there are many challenges and compromises that need to be made and overcome in designing a suspension and there are a lot of factors that influence each decision. I am not sure what I am going to do exactly at this point in time, but hey thats why I am here talking about it with you. Sometimes you need to bounce ideas off of someone and you have been pretty good to me in that department.

[V8turbo4me]

Well I guess my question now is does anyone know of any Transaxles that can handle around 800HP that can be made to fit a small block chevy V8? This where I am right now and I cant go forward at all until I have some answer to this question, lol it is kind of critical.

[Matra et Alpine]

...it is literally impossible to develope more than 30% anti-squat with an IRS where numbers over 100% are available with the live rear axle.

I'd like to explore this to see if I can help.
What do you mean by "30%" ? and can we check what YOU mean by squat..

An IRS only tries to squat (one definition) when the diff is located ABOVE the wheel centre line. The squat is as the power forces the driveshafts to straighten. Once they're straight the challenge becomes them being allowed to move up or down again for as long as power is pushed.
If you can afford the loss in ground clearange to get the diff as close to centre line as poss then it will not be significant.
CV ( of whatever type ) can get to be expensive and or bulky for the torque you're going to apply, so that may be the limiting factor.

If you mean whole car squat that's a function of mid-engine I'm afraid.
You need weight to the front of the car if you want to utilise the weight most effectively to keep the rear up/nose down. Of course you could go for Citroen pneumatic suspension and with race settings you can make the WHOLE car squat as one on acceleration But that's old technology.

How much money are you willing to put to theis project ?
You could clearly get a second hand race transaxle like a ZF fairly easily.
But they are V expensive to repleace/repair gears

FOr home builds with LOTS of power, it pays to go look oat light truck/large vans. They are built to take lots of torque due to the high weights carried so there might be a local solution. ( Can't think of a UK equivalent, but you may have more luck )

Suggest a wander down to local stock car meeting and wander in the pits and have a chat with the guys for some inspiration. They ususally know 'strong' solutions

[Matra et Alpine]

Well I guess my question now is does anyone know of any Transaxles that can handle around 800HP that can be made to fit a small block chevy V8? This where I am right now and I cant go forward at all until I have some answer to this question, lol it is kind of critical.

OK, thinking kits, I contacted a mate and he recommends talking to these guys about suitability of your proposals.
This is a GT40 kits using ZF transaxle - with prices
They sell kit with 400bhp, but should be able to advise what the trannie can take and options if it's too wek.
Good luck
http://www.erareplicas.com/gt/gt.htm

PS: Having a look at the site, I tihnk you can get MANY answers confirmed. The kit is described in detail including suspension, mounting etc.