Stapleton - The MG Midget & Austin-Healey Sprite High Performance Manual

THE

MG MIDGET

A-H SPRITE

HIGH PERFORMANCE

MANUAL

Daniel Stapleton

First printed in paperback format in 2005.

First published in ebook format October 2013 by Veloce Publishing Limited, Veloce House, Parkway Farm Business Park, Middle Farm Way, Poundbury, Dorchester, Dorset, DT1 3AR, England Fax 01305 250479 e-mail info@veloce.co.uk web www.veloce.co.uk or digital.veloce.co.uk .

Ebook edition ISBN: 978-1-845846-41-1

Paperback edition ISBN: 978-1-845841-42-3

Daniel Stapleton and Veloce Publishing 2013. All rights reserved. With the exception of quoting brief passages for the purpose of review, no part of this publication may be recorded, reproduced or transmitted by any means, including photocopying, without the written permission of Veloce Publishing Ltd. Throughout this book logos, model names and designations, etc, have been used for the purposes of identification, illustration and decoration. Such names are the property of the trademark holder as this is not an official publication.

Readers with ideas for automotive books, or books on other transport or related hobby subjects, are invited to write to the editorial director of Veloce Publishing at the above address.

All Ebook design and code produced in-house by Veloce Publishing.

DEDICATION

To Rick Moses, aka Mr Sprite, for publishing my early work in the Sprite newsletter, which was an encouragement and inspiration to me and led to my writing the first and subsequent Sprite & Midget books. Thanks too for his work in the five yearly Sprite meets, which have been a rich source of information, friendship and modified cars.

Also, to my wife Isobel and my daughters Faye and Miranda, who are future Sprite/Midget owners.

Veloce Publishing Ltd

digital.veloce.co.uk

Contents

Foreword

A WORD FROM DAVID VIZARD

All too often practical books on performance tuning are written by those with little or no personal experience of actually doing the jobs described: when the reader tries to do the work, the writers shortcomings soon become obvious!

Fortunately, Daniel Stapleton can put himself into the shoes of his readers so well it seems as though he is turning the screwdrivers and pulling on the spanners and doing the very jobs he describes. His hands-on experience has taught him about the many small and unexpected problems and, of course, the real pitfalls that the reader without such information could easily fall foul of.

For all Sprite/Midget owners this book represents good solid how to step-by-step instructions, plus details of the results you are likely to get-all achievable with only what I would call a typical enthusiasts toolbox.

If you have a Sprite/Midget and are relatively inexperienced at modifying for high performance, then I can almost guarantee that this book will pay for itself from the first significant job you tackle.

David Vizard

California

ADDITIONAL foreword by John Sprinzel

I met Daniel recently at one of the Sprites 40th birthday parties in Pennsylvania, and enjoyed reading his very comprehensive Spridget tuning book. It reminded me that when the Sprite first appeared, my own modest how to tune it book on the A series was published. In those times, tuning was a rarity and virtually anything you did to your car invalidated the warranty. From very small beginnings in what we called the conversion business, tuning became more and more widespread, the range of available equipment vast, and the technology mind-boggling! Forty years later, with the cars long since out of production, one would hardly have imagined the demand for Spridget tuning parts and information. Yet, now there is so large a following for Donald and Geoffreys little sports cars, many businesses exist for the sole purpose of satisfying the demands of those who crave that extra performance or appearance. Daniels book covers very many of these products and hey he even lists some of the Speedwell and Sebring parts which were my companys contribution those many years ago. I still run a Mark One myself and often find myself looking up his Power Tune for data and addresses of suppliers for my own use. I am sure you will find it as useful as I have, and enjoy the enthusiasm with which it is written.

John Sprinzel

Hawaii, USA

Introduction & Acknowledgments

Introduction

This new revised edition about power tuning the Austin-Healey Sprite and MG Midget is concerned with improving every aspect of your Sprite/Midget to enhance its performance; not just the engine, but also the brakes, suspension and everything else the whole car.

Readers may be aware that there are several books dedicated to tuning the A series engine. Since those books are very comprehensive, e.g. cylinder heads tuning and swapping, this book does not seek to duplicate data. However, those same books, although comprehensive, often have a strong bias towards the transverse A- and A+ series engines. This revised edition, then, now includes new information and photos specific to the in-line A- and A+ series engines which, to the authors knowledge, cannot be found in any other book.

With the 1500 Midget now more likely to be modified than at the time of the previous edition of this book (though still much less likely to be used in motorsport), the content applicable to it has been increased. However, it remains the case that availability of tuning parts for this engine is much lower.

This book will show you how to go from this ...

... to this.

Before getting into the serious work and cost involved in modifying a Sprite/Midget, its worth thinking about what end result is desired, what sort of performance can be expected and exactly what is meant by performance. Performance can be split into four categories: acceleration, deceleration (braking), straight line top speed and, not least, cornering speed. Each category can be defined as follows

Acceleration = Engine torque to vehicle weight ratio. Increasing torque or reducing weight (or both), assuming a reasonable level of grip, will improve acceleration.

Deceleration (braking) stopping (braking) distances.

Straight line top speed = ratio of engine horsepower (or brake horse power) to the coefficient of drag of the vehicle. Strictly speaking, rolling friction and other factors should also be taken into consideration, but can be largely ignored because at speeds over 100mph the drag is the limiting factor. Improving horsepower or reducing drag (or both) will raise the straight line top speed. For the Sprite/Midget looking to achieve speeds higher than 110mph, it can be more beneficial to reduce drag rather than increase horsepower because the aerodynamics of the car are poor. For a non-frogeye car its estimated that the following power outputs equate to the following speeds: 100bhp = 113mph, 105bhp = 115mph, 110bhp = 116mph, 115bhp = 118mph, 120bhp = 120mph, 150bhp = 129mph.

Cornering speed = Grip to weight ratio. Increasing grip (tyre size or type) or reducing weight (or both) will allow greater cornering speeds but, to a large extent, its also important how the grip is used a function of suspension.