60 replies to this topic

[Dr Terry]

Hi Chopper.

Pre-ADR27A 308 engines had either 240 or 250 bhp, depending on the version.

HT/G/Q & early LH had 9.0:1 compression & 240 bhp.

HJ & LH (Nov 74 onwards) & early LX had 9.7:1 compression & 250 bhp.

GM-H didn't quote any different figures for the L34, even though they were more powerful, the book says 240 bhp.

The A9X was an ADR27A car & the engine was no different in spec to any other late LX (or HX/Z, VB) 308/5.0 Litre.

AFIAK an A9X engine was a bog stock L31, whereas the L34 had many items upgraded like heads, cam, rockers, exhaust, distributor, even on the standard (non-HO) engines.

Dr Terry

[REDA9X]

This has come up a lot in the past.
Quoted figures LH SLR5000 179kw, LX SLR5000 161kw.
The A9X engine wasn't the same as the HZ or late spec SLR5000 at all, it had an upgraded crank, cam, no engine fan etc.
A HO version (as in an L34 with the HO kit fitted straight from the dealer) would not have been close to 350HP when 350HP was the best HDT were getting out of their race L34 engines before moving onto the A9X.

[REDA9X]

I think if you have a look it says 350HP for race cars. Have a look at what actually came in the HO kit and you'll realise it needed more than that to really make it sing. Holden only had to homologate the bits they couldn't change on the race cars, so thats all they supplied in the kit.

[Dr Terry]

The A9X engine wasn't the same as the HZ or late spec SLR5000 at all, it had an upgraded crank, cam, no engine fan etc.

As I understood it the camshaft was just late HX 5.0 cam (pre-HZ upgrade) & the crankshaft was similar. The only 'real' change was the removal of the engine fan.

I remember in those days, guys with stock dual exhaust HX & HZ 5.0 V8s getting the same rwhp figures as the A9X once they had removed the engine fan.

Red have you got any factory literature as to what the actual differences were (I realise the listed part numbers were different).

GM-H didn't need any engine parts homologated, why build anything 'special'. If they went to the trouble of building special cranks & cams, why not do something with the dreadful inlet manifold & heads on the stock L31.

On the subject of L34s, I believe one of the Marque/Spotlight books quotes HDT as getting 270 bhp from an L34 fitted with the HO kit, with no others mods.

Dr Terry

[REDA9X]

Terry the changes made to the A9X engine were from the lessons learnt from the L34 problems. The crank was stronger and the cam was thicker at the front and had a different grind from the SLR5000. Again a lesson learnt from the ADR27A mods. It wasn't designed to give more power (why bother they only needed a smooth car not a race car) it was trying to cope with the rough running engines most of the magazines at the time complained about and a lack of urge.
I'm sue I have some GMH paperwork somewhere about some new parts being homologated and more as the race cars progressed along.

[yel327]

Cool stuff to learn if correct. I always thought what Terry states, ie A9X engine was standard HX as L34 engine was already homologated for Group C (I imagine it'd have been unlikely that production crank and cam were used in race cars). If crank was made stronger for A9X then it'd probably also have been used in all other 308's as well.

[REDA9X]

The rules of the day stated what you had to use from the production car, or what was homologated for use. You have to understand the homologation process of the day and how complicated it was.
The L34 was homologated for racing, but the car had certain freedoms, wheels and tyres were the most obvious, and for the engine the most obvious was exhaust was free after the first break. This is one of the reasons the L34 was no screamer off the showroom floor, combined with pain from the supercar scare.
The cam while you could use any grind you liked was always prone to breaking at the front, and the cranks broke too. You had to use the crank from the road version, obviously you could balance it.
To fix these problems, Holden had to homologate new items, and these came with the evolution of the A9X with a thicker cam front journal and stronger crank. Holden did the bare minimum they had to do, so while I have never checked it, I seriously doubt these stronger parts made their way into other engines at the time because of the costs involved otherwise every engine from L34 onwards would have been an upgraded version of the L34 rather than a stock 308.

[yel327]

I'm still not sure how a thicker cam journal helped though, as didn't they use Wade or some other aftermarket cam on the race cars anyway (whatever was homologated for L34)? Was the A9X change simply to allow the aftermarket cams to have a thicker journal?

Although I have no idea on what actually happened, I would have thought the opposite for changes though, if you changed the design of a cam or crank for one you'd do it for all. Like GMH did when they destroked the 308 for Group A. Didn't the re-designed 308 and 253 (late HQ, early HJ) blocks get many of the L34 design changes incorporated as well?

[REDA9X]

You could use whatever brand cam you liked in the race cars. As Chopper says, if it had a habit of breaking in a certain area, making it thicker in that area would stop it breaking. Whilst you could use any brand of cam and grind, it still had to be the same basic specs as the road car in that you couldn't suddenly make your cam thicker or bore out a journal to stop your cam breaking, you still had to work within the rules.
Yep the extra webbing from the L34 block did find it's way into later blocks , but not the other 308 blocks at the time the L34 was produced, i would imagine it was the same deal with the crank and cam in the A9X, it probably made it's way into later versions, again I'd have to check the numbers but i don't believe the crank made it's way into all of the 308's being produced at the time of the A9X. Again, why would Holden do more than they had to to homologate the parts, the stronger parts would have cost more to produce, and if the standard crank was good enough for road application in the average 308, why spend the money.
With the Group A the rules had changed again and you had to have 500 evolution models and 5000 of similar specs which meant 5000 of those 4987cc blocks/cranks rather than the old 5044cc.

[AbsynthHatch]

Sounded like Holden purposely hobbled the performance of the press cars on a number of models over the years

[REDA9X]

The only way to do a fair comparison is get a time machine, go back and buy a new L34, new SLR5000 and a new A9X. Blokes with great memories of over 30 years ago still go on today about how good the L34 was engine wise, and it was, but not off the factory floor. Take it home tune it fit a decent exhaust and aircleaner and it went better, certainly nothing close to the 350hp suggested by some people. Do the same thing to an A9X engine, the performance wouldn't be there, simple. Fact is it's a lot easier to modify an A9X engine up to make it go than it is to slot a 10 bolt diff and rear discs into an L34.

[Litre8]

LX SLR 5000's produced before the dreaded ADR27a were factory rated at 186kw, possibly courtesy of their 9.7:1 compression.

[Litre8]

There were a few pre July 1976, mine is a Feb 1976 build.