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MG Midget and Sprite Technical - Rear suspension upgrade

I'm planning a Winter upgrade,and would appreciate any advice or comments.
The (72 RWA) car is putting out about 160bhp and 160lbf.ft.of torque.I already have a Tran X LSD,Peter May halfshafts,Spax dampers and polybushes in lowered Peter May springs.
I will fit 185/60 x 14 Toyo Proxi 888 tyres,nylatron spring pads,double bearing hubs,3/8 spacers and I plan to build traction bars using thick wall tube,a rose joint and a polybush.
The car is used for drag racing,so axle wind up on launch is a big concern.
steve cowling

Steve

Make sure your tramp bars are geometrically neutral - it's not a simple parallelogram as one side (the spring) changes length as the axle moves up and down. If you get the front eye of the tramp bar in the wrong place it will partially resist the vertical movement of the axle, effectively making the rear end stiffer and upsetting the front/rear balance.

We plotted the movement of the axle bracket for the tramp bar, worked out the centre of the arc and put the front eye at that point. Works a treat. If you have it right, you should be able to jack the axle up and down with after removing the bolt which secures the bar to the chassis bracket and the bracket and tramp bar holes should stay in alignment.
Paul Walbran

Hi Paul,
Thanks for this,I will try to measure the axle bracket arc of movement.The springs are pretty flat,and the polybush is there to take up some misalignment.
steve cowling

You might want to research a 1950's American drag car that was designed by a group of design engineers, they mucked around with the rear end & could lay down two rows of rubber off the start line, i can't remember the name of the car but it was the fore runner of the 'funny cars' with the odd looking stance; perhaps one of the Americans can jog my memory.
Brad (Sprite IV 1380)

Not this one ;-)
I cannot believe that there in the home of "left and right turn racing", someone is regressing back through the nascr*p "go fast, turn left" to the "try not to turn at all" forms of automotive competition and with a Spridget at that!
Shame on you ;-)
BTW, what engine and transmission are you running in there?
David "just kidding folks!" Lieb
David Lieb

Hi David,
Sorry I've disgraced the marque,but at my age you have to get your thrills anyway you can!The adrenaline rush is quite something.
steve cowling

The engine is a turbo chargecooled a series driving a s/c close ratio box.
steve cowling

Hey David, somewhere we have pictures of you participating in a spridget drag race.
Trevor Jessie

And doing quite well in it without 150hp, tc, or traction bars ;-) Nowhere close to Steve's times, I am sure...
David "At least I wasn't IN drag" Lieb
David Lieb

So you are running a spridget rear end...is that correct?


WOw...MMmmmm...Okay, Do you HAVE to use a spridget rearend?...160 hp is about 2.5 times to much for a stock spridget rearend, and almost pushing the top end for a mazda...granted yours is beefed up pretty good, but I remember Mark T doing a temp setup about a year ago and that set up was way lighter then yours and the pics where like Knarly, of P.M.s half shafts you should talk to bill young hes got a cool v-6 midget and nice beefy rearend (mechanically speaking of course) LOL. but I got a gut feel even with peter may half shafts...your going to be snapping a few of them

dana 40s, ford 9 bolts, and some of the other Drag names might be a better way to go...there isnt any thing those setup havent been thur before


just my humble opinion

Prop
Prop

rats photo didnt make it...try agian


Prop

Prop
stop with you exesive drive to swap everything midget for other parts!!
you should have bought a mx5 or som other crap box!!!!!!

if th midget parts are properly taken care of and maintained they can take a hell of a lot of punishment!!!!

the figures you always state for ribcases and axles are complete rubish an based on nothing more than guess work

Onno Könemann

Your correct onno, what was I thinking....

Steve, you got nothing to worry about, the spridget will work without a hint. the rearend was orginally designed for cars running around 50hp so It should easely handle 160hp and 165ftlbs of torque with no problem....I wouldnt even bring extra halfshats to the race track


My bad...Im sorry, thanks onno

Prop
Prop

Remember he is going in a straight line. So there are not a lot of radial (or would that be axial) forces exerted on the shafts.
Trevor Jessie

HA ha hahahahahahahhahahahahhah, prop and Onno, stop, my tummy hurts from laughing. My son wants a midget like that now....
Alex G Matla

That is a vary valid point treavor...Still Id think steve is pushing the rearend to its full modifed potential I think it will all come down to the tires and wieght of the car a to weather he hears a pop or not.

one thing he has going for him is he is running 14s instead of 13s so the wheels wont be spinning as fast off the line


Well I got to get to the shop.

Onno you know my advise is always free to you...LOL

Prop
Prop

Prop
you are insane!!!!
for onece in your life don't over react when someone is putting more hp through a midget component than it was made for!

there are boat loads of racers putting over 100 bhp throug a midget back axle
okay the use lsd's, special halfshafts and double bearings but it works!

you first reaction is bla bla bla midget bad put in this super high tech hijabusa vx352 part on it than you can take a gazillion torques and it has a nice cupholder!

you and most of us have a midget and if you do not like it buy a nother car don't make a midget into something it is not!


what the hell am i doing here arguing with prop
might as well try to learn pigs how to fly....

Onno Könemann

Hi prop,
The car weighs around 700kg/1450lb now but I plan to shave some more off that this Winter.The traction control is in my right foot,and I don't just sidestep the clutch pedal,but I am concerned about the stress from those big sticky tyres.
steve cowling

We've been running 185bhp in our K-series Midget through a "standard" rear axle for 7 years now. During that time we've done a lot of vigorous autotesting (including national championships) using road legal race tyres as well as a full range of other speed/race events. It's the autotests that load it the most though - lots of big 1st gear clutch dumps and wheelspinning - and despite all this nothing has broken since we fitted the LSD and uprated finespline halfshafts. (Having said that, it will probably now break at tomorrow's event!)

Only issue we ever had was the one event we did after commisioning the car while we were waiting for the LSD to arrive. Ran with a completely standard back end, and everything broke comprehensively!
Paul Walbran

Steve Im certianly not th person to take advice from...(But dont tell onno I said that) Im purly just a hobbiest and read alot of tech articals, it would appear that Paulhas a much better grasph of the topic.

Onno, friend, buddy,

I dont think Ive ever trashed midget componets (well thats not entirely true) I am just fasenated by how to make something better, stronger,and faster...for me its not even about racing and winning, its Art, the form and funtion of modification pure and simple, about making the ultimate midget for the street...not to race it it, but to just build it...for me autosports even as a child was never about the driver...I couldnt tell you the names of many drivers, but I loved the idea that you can make a machine go faster then it was supposed to.


If I had to choose to drive a F1 on the circuit, or work the pit creww in a local track in the jalopy bomber class...its a no brainer...I want to have my arms deep in the bowls of a greasy engine trying to figure out how to make it go faster.

So If I Poo Poo midget compontes its nothing agiants the parts or even MG, its just I see a better idea, and I want (or driven, to be more exact) to make that element better, faster, and stronger....The Six Million dollar midget!

In all fairness Onno...there really is NO other car as cool as the midget with the 1275...it feeds my need to express creativity and inspire the imagination...there is no other car (nor woman) that does that for me.

Prop. The Midget Artist, and his next project...Prop



Prop

Hi Paul,
What tyres are you running please?
steve cowling

Prop
you ar a realy nice funny crazy guy
and if you ever come to the old country's we will have to have a beer!

But some times you are just a bit to enthousiastic for me about pushing others to modifing midgets

mine is modified verry mutch but (apart form the FL kit)these are all with "original" or period components.
For me this is essential otherwise it would not feel like a midget to me
but luckly we can all do with our own car as we please!
(i mean look at that crazy dude Arie he has put a Kengine in there! ;) )
Onno Könemann

Most of the time it's been 175-60x14 Dunlop formula R medium compound, however these seem to have been discontinued so we've now fitted 185-60x14
Paul Walbran

Thanks Paul,that's encouraging.
Regarding original components,I try to stick with it,but accept some upgrades.So original block,5 port head,ribcase box,original axle.BUT turbo,megajolt,lsd.
steve cowling

Steve,

When you do the megajolt mod, I want to see that....besure to inform us and post some Pic. Its not something I want to do on the midget, maybe the work truck, but that is a cool website with alot of imagination involved...are you going to do the ford edis disturbutor-LESS ignition system also?

I think that will be a fun project.

Prop
Prop

Onno,

Its a deal, I hope to meet up with you one day,

the K-series, thats a tough call, looking back I wish I could have gone the 1.8 ford kentworth with a crossflow head..3rd th cost 3 timmes the power and looks exactly like the A-series

only came to the USA for 2 years via the ford pinto


Prop
Prop

Prop
look at this:
http://www.canems.co.uk/siameseports.php

This is a mod that is on my wish list
Mainly to be able to cope with the modern bio fuel's
Since i do not expect to be able to buy proper fuel anny more in 15 to 20 years, and ethanol has some trouble with aluminum parts and has some diffrent burn characteristics as petrol.
And the little added power an economy from an EFI setum are a nice bonus
Onno Könemann

Hey Onno,

Heres an artical you might like,,, I think you could adapt it to the midget by simply massaging the intake manifold a bit....there is a realy nice kit that was on ebay a couple weeks ago, But cant find it right now...But its going hand in hand with what the guys in your artical are doing.

Prop

http://www.7builder.com/MGB/mgbfi.html
Prop

Prop

if he is running his be like that he is ruining it
he is talking about 80% dutycycle of his injectors while canems have determind that 60% is the max because of the carge robbing.
He also mentiones one lambda so he is not checking for it and he mentions several hickups when an EFI car should run as sweet as pees

as for TB's
http://www.jenvey.co.uk/
they have a direct replacement for the weber witch looks good!
making the under bonnet presentation look a bit "normal"
Onno Könemann

Hi Prop,
Been running Megajolt for 3 years now.I bought the unit ready built,got an edis kit from a scrapyard and bolted the trigger wheel to the front of the crank pulley-a bit tight to the crossmember!You can see the edis unit and coil pack on the left of the bay.


steve cowling

Hey Steve,

Is it next to the baby bird, or the loose wire?....LOL.

Im guessing you had some fun, putting that togather, definatly a cool system. Are you ?

That megajolt with the edis ignition is definatly the way to go for anything with even a warm modifed engine...for the modern era, Im seriuosly considering it if I rebuild my toyota 22RE 4 banger truck engine and beef it up a little. It maybe a simple system but is so customisable and easy to tune from what I have seen, and read about

Onno,

Im going to have to defer to you, My head knowledge of EFI is basic at best and comes from reading the megajolt system website, and spending 2 weeks in blinding cold tracing down a broken wire in the efi system that crippled my truck....the 2nd time a super small 26 gauge wire brought my truck to its kness....BTW 26 gauge is about the size of the paper clip wire. guess thats why I like carbs

Prop
Prop

Hi Prop,
Megajolt is a good system,although it's quite difficult to set up 'on the fly'on a rolling road,so some RR operators are reluctant to work with it. An A series at 15psi boost needs proper RR setting,otherwise the result is ugly.Detonation is the silent killer,takes out ring lands,then the whole piston.
steve cowling

This thread was discussed between 25/09/2009 and 27/09/2009

MG Midget and Sprite Technical index

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