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MG Midget and Sprite General - An Exquisite Spridget Racecar!

I bet you've never seen a Midget quite like this one: a hybrid between SCCA-tech and vintage. One of my favorite things about this exquisite car is its unique "limited-prep" suspension. Attention to detail here is remarkable - both in original build and in how Chuck presents it at every race. Check it out:

Chuck Pitt's Spridget Racecar (59 photos!)
http://www.britishracecar.com/ChuckPitt-Spridget.htm
Curtis Jacobson

Nice site....!

A very comprehensive roll cage / body bracing set up...

Must study this more :-)

Mark.
M T Boldry

Very, very nice car with some interesting mods. Thanks for the link Curtis.
John Payne

Pretty, but the write up is atrocious!

"Pyrometer probe holes have been welded-up and the headers have recently been ceramic coated.
Besides lasting good looks, ceramic coatings help minimize heat transfer into the engine bay."

You'd be better off ensuring a throughput of air through the bay as we do on our racer. Ceramic coating the headers will mean:

1. You retain the heat in the Cylinder Head which is a BAD idea.

2. You will increase heat soak into the inlet namifold which is a BAD idea (I chromed our inlet manifold to help prevent this).

3. You will change the gas velocity through the exhaust manifold which will affect its inertial tuning, This may represent a DROP in power!


"MG Midget "banjo" rear axle, with an excellent Tran-X state-of-the-art limited slip differential inside.
In 2006 Craig raced with a welded rear instead, because limited slip diffs tend to promote oversteer
(which he was fighting)."

Err NO they don't, they just DON'T! Properly set up LSDs tend promote UNDERSTEER. If you are getting oversteer then it is snap oversteer because the ramping rate hasn't been set correctly and the diff is 'snatching'.


As to why you'd want a rear anti roll bar (sway bar) on a cart sprung live axle is beyond me! Having said that I do like the FG springs (now I'm having ideas about ours!).

Nicely made Watts link but I'd like to see how effective it is against a Panhard Rod vs the weight of the two set ups.

I notice he has anti-tramp bars fitted which will make the car bloody twitchy on a bumpy circuit! Terrible bloody things and totally a waste of time on a Midget.
Deborah Evans

If you ceramic coat the exhaust manifold (headers) the heat is moved further down the exhaust pipe. The heat is not retained in the cylinder head. So, if follows you don't heat soak the inlet manifold which would be a bad thing if it did heat soak.

Chroming the inlet manifold is a good thing but a thermal barrier coating will be more effective.

I do think a good throughput of air through the engine bay is a good thing and I long for the day when Karl will be bashing out a set of louvres for the wings.

I couldn't make much sense of what was said about the welded diff and the LSD. I did wander if what the writer meant was the welded diff promoted oversteer so he switched to an LSD?

I did think that having an anti roll bar on a live axle might have been the real cause of excessive oversteer whether on leaf springs or coil springs.

I have anti tramp bars on my car and on a bumpy road I don't find it that twitchy.
Daniel Thirteen-Twelve

"If you ceramic coat the exhaust manifold (headers) the heat is moved further down the exhaust pipe."

Sorry Daniel but that just doesn't stack up with either the research I have done, nor with a lot of published research.


"I have anti tramp bars on my car and on a bumpy road I don't find it that twitchy."

Anti-tramp bars by their very nature have a different swing length to that of the forward part of the spring and thus fight against the springing action.

I've lost count of the number of clients I've had who insisted their anti-tramp bars were a good thing, only to be amazed at the transformation in ride quality and road holding once I'd convinced them to remove the execrable things!

There are FAR better ways of controlling Tramp!
Deborah Evans

I do agree with Deborah about the springs!
Those are intresting with the quality spings we have(had?)recently.
And them being more narrow than usual...

Now i am having brain waves about fitting a wirewheel axle with steelwheel halfshafts and being able to fit 185 (or wider) tyre's on a SWA car!
Onno Könemann

Deborah,

I've seen the arguments for and against ARB on the rear of spridgets/live axle cars and in my opinion they can be beneficial if judged correctly. Maybe circuit racing is a bit different and I've not done it but I have honed the handling of my car to my liking at hill climbs and track test days. I was finding that my sprite was suffering from excessive understeer in tight corners such as those seen at Wiscombe and added a re-bent Vauxhall Chevette rear ARB which sorted the handling issues at Wiscombe nicely and improved the balance in high speed corners such as I saw at Castle Combe in test days as well. My MK1 sprite has a FG front and rear with standard front springs and a 5/8" front ARB IIRC and 15 leaf rears minus one leaf and telescopics all round.

Other than that opinion I wonder why they bothered with the cranked Watts linkages as they were fitted with rod ends so a straight bar would be just as good and less work.

I fitted a Watts linkage to my car and also made one for a mates Austin Sprite and both worked very well. The Watts maybe slightly heavier but will almost all be sprung weight with the body centred mounted centre link and won't have the assymetrical layout of a Panhard. For racing though as most tracks run the same way typically CW in the UK the assymetry won't be much of an issue as you're largely turning then same way all then time.
David Billington

Austin A35s had a rear ARB as standard. I removed the one from my race car as it just caused the inside rear wheel to lift in corners.
Dave O'Neill 2

The problem with ARBs is that the induce DIAGONAL load transfer when cornering and MAY upset the Transition Phase while the slip angles are building and whilst the load(s) are transferring.

Diagonal load transfer REDUCES overall grip and slows corner speed.

This is why Race cars are set up using springing and ARBs are only used to FINE TUNE for a given circuit.

On a Road Car or even a Sprint/Hillclimb Car where ultimately corner speed never reaches that of a Racer this is of less concern and may well work well in the trade off against ride.
Deborah Evans


I'll just respond to the anti-tramp bar comments. (Debbie is particularly far off base.)

Are you folks all completely unfamiliar with 3-link rear suspensions?

The fiberglass leafsprings on this car are decoupled by means of spacers on the u-bolts which prevent clamping force. Skinny little fiberglass leafsprings are pretty floppy to begin with. For those two reasons, Chuck's Spridget might as well have coil springs at the rear. His leafsprings can't and don't locate his axle fore-aft or side-to-side. There's no question of them "fighting" anti-tramp bars. Radius rods locate the axle more precisely and predictably than leafsprings, and NO Chuck's car ISN'T twitchy.
Curtis Jacobson

They aren't strictly Radius Rods for a start.

I take your point about the decoupled spring however.

My point stands however, that with stock type springs they would fight the springing action.
Deborah Evans

I do not know squat about race cars, but I do know often engineers get locked in a paradigms and reject non conventional ideas despite obvious proof of their success ...I'm just saying ... as an ignorant hillbilly.
Trevor Jessie

Hi Deb,

If the exhaust manifold is ceramic coated the heat does not radiate out of the manifold. So where does the heat go? There will always be some heat transfer from the flange of the exhaust manifold to the cylinder head but if the exhaust manifold is cooler with a ceramic coating then less heat is being transferred to the cylinder head.

I think it's fundamental that the heat not being radiated out of the exhaust manifold goes into the cylinder head because were that the case the cylinder head would either melt or put a massively increased load into the car's cooling system.

The fact is that the heat is in the exhaust gas itself and if it cannot radiate as it passed through the manifold it simply radiates further down the system and ultimately leaves the tailpipe hotter than it might otherwise have done.

If you have done back to back testing with and without ceramic coated manifolds I'd be interested in seeing the data. For example does that data record the exhaust gas temperature (EGT) at or near the tailpipe on engines with and without ceramic coating?

Likewise I'd be interested in seeing published research on why ceramic coating's don't work. I have seen a great many race engines of all types and sizes that have successfully used ceramic coatings on the exhaust manifolds.
Daniel Thirteen-Twelve

Daniel

Are you referring to coating the header internally as well as externally? If so, would agree with you.

A
Anthony Cutler

Now I have a question, regarding suspension:

the stock rear springs are 75 lb / in ('64 ~ '66) or 80 lb/in, ('67 ~ '74) and the heavier rubber bumper cars used 86 lb / in.

The write up of this race car says that he used 120 ~ 130 lb/in for his rears.

Would that work, or am I missing something. It sounds like he's got the rear of his car so solid (3-bars + watts + 2x the spring rate + rear sway bar), maybe it just uses sidewall flex for compliance?

I've been following the suspension discussions here over the last several months and his setup seems to go in very much the opposite direction of "stiff front, soft rear".

So, I thought I'd ask about it...

Norm
Norm Kerr

Norm,

I would assume that he has upped the rear spring rate in proportion to the front to keep things balanced. I couldn't see any detail of the front spring rate but judging from the pics and the few coils it'll be pretty high compared to standard. The ARB diameters are given and are impressive considering he has one front and rear. A mate has an Austin Sprite road car with a 7/8" ARB courtesy of the former owner that worked at Stothert & Pitt and that used to rip out of the chassis legs with regularity until we reinforced it, and gave lots of terminal understeer

Deborah,

In my case the addition of the rear ARB was to reduce excessive weight transfer to the outer front wheel during cornering and had the desired effect so reducing what you refer to as diagonal load transfer.
David Billington

Curtis
That is certainly a novel way to decouple the rear springs.....never seen it before does it appear on any other vehicle? I would have thought the rear spring-front mounting could have been modified to slipper/sliding joint whilst retaining the original mounting point, given Chuck's obvious ingenuity.

I'm a bit confused about this part of the explanation:
"The second and third exhaust ports on a BMC A-series cylinder head are "siamesed". In other words,
they merge within the cylinder head to share a common outlet"
If thats corrct its bit unusual to siamese the 2nd & 3rd ports 'within the cyl head' is there any photos of that ? I guess it could be typo as the photos show a fairly conventioanl LCB exhaust.

Its good to see somebody testing rules by a new interpretation. Its great to see these detailed photos of a top car.
Ian
Ian Webb '73 GAN5

Ian
They describe exactley what you see, a siamese port and lcb.
To us A-series people that does not need explanation but to most it does
Onno Könemann

Ian, I don't know who invented the idea of putting spacers on u-bolts so they don't clamp the leafsprings... but the idea was certainly used to good effect on the National Championships dominating British Leyland sponsored Huffaker Engineering MGBs of the mid-70s. If you're curious, you can have a good look at original Huffaker three-link MGB rear suspensions (with leafsprings!) here:

http://www.britishracecar.com/DonDickey-MG-MGB.htm

and here:

http://www.britishracecar.com/EddieBeal-MG-MGB.htm

Curtis Jacobson

Curtis, thanks .... I havn't seen that before.

Onno; yes I read it incorrectly when I was scanning it quickly in my tea break at work !......I thought they were describing something special, not the common set-up (I do understand the standard head thankyou)
Ian
Ian Webb '73 GAN5

This thread was discussed between 20/05/2011 and 23/05/2011

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