Small Chevette Tuning
The text on this page appears to be originally from "Cars and Car Conversions" magazine. This web page has been created for convienence sake from scanned pages which were mentioned on the forum. If anyone knows the source for sure, please let us know so we can properly credit the article.
Don't think you have to go to the 2.3 litre engine. The 1300 Chevette is worth a look.
Pentti Airikalla's win on the Welsh Rally earlier this year was more than a well needed tonic for Dealer Team Vauxhall - it also put the Chevette firmly into the minds of people who had previously not given it as much as a second glance when considering a competition car.
The Chevette win was the result of six months hard development by the DTV crew at Bill Blydenstein's railway station workshops at Shepreth in Hertfordshire. Dealer Team Vauxhall's rally programme had passed to Blydenstein late in 1975 and by mid '76 he was called upon to switch from the Magnum to the smaller (but surprisingly not much lighter) Chevette. After a somewhat embarrassing debut on last year's RAC Rally the car started the year well, culminating with the fine win in Wales. Suddenly, it wasn't Escorts all the way: the Vauxhall Chevette was a force to be considered.
Currently only available in 1256cc form the Chevette is a good and solid car based on Opel Kadett running gear but using the four cylinder engine originally developed for the Viva. Obviously, it has most potential in 2.3litre form but Bill Blydenstein reckons the smaller engined version should not be dismissed lightly.
The 1256cc Vauxhall engine has a history dating right back to the HA Viva 1057cc engine of 1965 and therefore has undergone careful and consistent development over a long period of time. It's never been a spectacular engine in terms of competition performance but has now matured into an extremely strong and reliable unit that, despite its six port head design and pushrods, is capable of quite a reasonable power output. People seem to forget that Bill Blydenstein was racing the HB Viva with engines of this type (of varying capacity as development proceeded) as early as 1967 and by the time the unit was replaced by the two litre single overhead cam engine (the Viva GT) was achieving a measure of success. In fact the HB Viva engine had a capacity of 1159cc but Blydenstein raced on most occasions at 1258cc although engines nearer 1300cc were also built.
As installed in the Chevette the latest variant of this motor has a compression ration of 9.2:1 and with a single 1.50 CD Stromberg develops around 58bhp at the flywheel which is good for 40 to 42bhp at the wheels of a well sorted standard car. The standard camshaft is that which started life as the '90' engine pack grind in the old SL90 Viva and valve sizes are 34.5mm inlet, 30mm exhaust. The crank runs in three main bearings and has reasonable mains journal sizes of 53.3mm. A 184mm dia clutch is standard fitting.
The Viva/Chevette cylinder head is an interesting design. It's a cast iron, non-cross flow type with only six ports - four exhaust and a pair of siamesed inlets. Where it differs from most engines is the the inlets are vertical, the inlet manifold feeding down tho the top of the head. With a full downdraught carburation set up, this is an extremely good design but, of course, the restrictions of bonnet height mean that the production Viva and Chevette have to utilise a cast alloy inlet that curves through a full 90 degrees to place the side draught Stromberg at a relatively low level.
As I said, the small Vauxhall engine has undergone quite a lot of development during its long life and the net result is that Bill is quite happy to say the latest versions have no inherent weak points that need to be considered seriously until you get to virtually full race tune. Most of the Blydenstein parts of the 1256cc Vauxhall engine are in fact listed as DTV Sportsparts and therefore available through those Vauxhall dealers who are DTV representatives.
The best way to deal with the power side of the engine is to take the unit through what Bill regards as the logical tuning sequence. Although an initial carburettor swap is certainly a nice and easy way to get power. Bill rates a decent cylinder head as being the first stage of any well thought out conversion. His Stage III head which features 36.5mm inlet valves and a first class gas flowing job is likely to put about 8bhp onto the flywheel while the III H head will add a couple more brake horse to that. Blydenstein defends the rather illogical method of starting with Stage III by saying that in his company Stage One and Two heads have always had standard size valves, therefore their Chevette head... etc.
The III head has standard exhaust valves, standard compression ratio and (you guessed) standard valve springs. The III H version differs only in that the compression ratio is upped to around 10 to 1 by removing metal from the head face. The standard compression head is, in face, allowed within Vauxhall's standard manufacturer's warranty for new cars although the III H will put the engine out of bounds.
Next step is most definitely carburation. The 1.50 CD is replaced by a 1.75 CD which, gives about four brake horse power on top of the head. Fuel economy must, obviously, suffer slightly but having driven a Blydenstein car with head and carb mods and still managed 35mpg everywhere (including a very high speed run to visit another tuning establishment) I don't think there's too much to worry about on that score.
At this point the Blydenstein file (Bill has a file for everything) advises fitting Lumenition ignition. No, it doesn't add 25bhp or even keep the windscreen clean but it's considered worthwhile on grounds of total lack of maintenance and a much quicker warm up, resulting in improved fuel economy.
Logically, the next step is an exhaust manifold. The four into one tubular system with bore primary pipes gives around two bhp on top of the head and carb. This manifold mates to the standard system although a complete larger bore system is currently being worked on.
With head, carb, Lumenition and exhaust manifold any decent Chevette is giving a respectable 72bhp at the flywheel. Although it's hardly anything to shout about, this sort of power coupled to the excellent handling of the car (you can't keep a good Opel down y'know) makes the Chevette a useful 'shopping' car and weekend road rally machine.
It's after this that, inevitably, things start to get expensive. You need a better carb, but there's also a crying need for a camshaft change. Bill won't separate the two: the next step is a 45 DHLA Dellorto (or Weber if you have one lying around) along with the CHR-1 camshaft which increases the effective overlap of the old '90' profile by about 10 degrees and adds 0.020 in to the valve lift. Don't ask for more precise timing details because they hadn't been worked out at the time we went to press. What we can tell you, however, is that the Dellorto carb has these settings:
Now the 1256cc engine is giving around 80bhp at the flywheel, which is still not great stuff for a 1300 but is certainly respectable.
|Vauxhall Sportparts mentioned in the text||Part Number|
|Stage III Cylinder head||33/888|
|Stage III H Cylinder head||33/911|
|Stromberg 1.75 CD carburettor kit complete||22/844|
|Lumenition electronic ignition||66/877|
|4 into 1 exhaust manifold||35/322|
|Performance exhaust system||34/211|
|'Crossflow' Dellorto 45DHLA carb kit||22/899|
|Manifold only from kit 22/899||22/892|
|Rally type camshaft||33/902|
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