Sure I understand what you are doing as to he Holden point of reference.

So we have a HX 4.2L Cam and a HZ 4.2L Cam.

But were did the HT to the HQ V8 Cam profile come from, I don't think any Chev Cam is such at all.
Not to mention why did they time them differently as to 253 and 308 not to mention time the first LH 308 to the 253 spec.

I think that Holden were trying to limit some of the torque of the first LH 308 by retarding the timing to the 253 spec, because of the piss weak banjo diff.

Not to mention that I was looking at advertising of the HJ 308 and how many times they were rating the 308 at 240HP now why did they keep saying that, maybe it's only the GTS and later SLR 5000 that got he 250HP.

As for the HJ 5.0L Cam being that Holden just grabbed the Chev GP Cam profile well it's not the same truly at all, not to mention that both the 4.2L and 5.0L HX Cams have much longer exhaust durations and this is not done for any performance reason that I can see of, but for heating up the exhaust more, so as to burn more unburnt fuel up, so as to meat ADR Laws.

They developed the HK 253 (later released with HT) cam, and developed a 308 cam too but by retarding the 253's cam in the 308 they got the performance they were looking for and could use a common cam across both engines. All HT to HJ 253 including LH and early LX) are the same (except for the few trial ADR27A HJ's from Pagewood). All HT to the end of HQ and early LH are the same (except L34).

Up until HJ the figures were advertised. After that they appear to be proper GM20 gross bhp. The HT to HQ 308 is really 227bhp by GM20 test, the HJ engine is 250bhp. I recently got curves for HD and HR engines that show "advertised", GM20 (SAE gross) and GM1 (SAE net) figures, the GM20 figures are about 15-20hp lower than the advertised figures, which is basically what the HJ figures are compared to HQ (except for 308). There were a few edicts issued by GM in the early for all their brands to align to Corporate Standards, I bet this was one of them.

HX 5.0L cam is the same as the HJ one (and the same until VL), it is not an emissions cam, just a General Purpose Grind and will be the original 308 cam developed for HT but not used, the part number aligns with HK era. Only the HX 4.2L cam differs from the earlier two camshafts. GM used the same basic cam as the 308 one until about 1980 in all SBC's too.

They’ll probably be GM1 (SAE net) figures. They are simulated “as installed” tests. This was adopted by GM fully in 1972 and they published both SAE gross and SAE net for 1971. The SAE Standard for it is J1349. The test includes air cleaner, exhaust, belt driven accessories etc.
The SAE gross tests (GM20 to J245) don’t include accessories, air cleaner or exhaust, just exhaust manifolds. Fuel and air are carefully controlled so that the tests are repeatable and comparable. The 227bhp I have for the HQ 308 is to this test.

You can start to see already with the SAE net figures between SA HT and HQ how anything other than SAE gross start to be misleading, unless you know the engines intimately you start to wonder why they are rated differently.

There were only ever two camshafts used in the LC XU1. Both camshafts were retarded by 6 deg via the keyway in the LC XU1 timing gear.
The timing figures quoted in the LC XU1 Advance Service Bulletin were incorrect. A bulletin was issued to cancel/correct the incorrect timing figures in the Advance Service Bulletin however the corrected timing figures quoted still did not take into account the fact the camshaft was retarded by 6 degrees. A third Service Bulletin was released to cancel/correct the timing figures quoted in the second bulletin.

It is worthy to note the LC XU1 Recognition documents sent to The CAMS had the correct valve timing figures listed. Although the CAMS recognition date on the form is the 3rd Day of January 1972, 10 copies of the Recognition forms would have been sent to The CAMS at least 1 month before the XU1's competition debut in 1970.
So whilst the GMH LC XU1 Dealer Advanced Service Bulletin (June 1970) and a subsequent Service Bulletin (September 1970) were both issued listing incorrect valve timing figures the LC XU1 Recognition forms were always correct.

The XH cam used in the final evolutions of the LC XU1 is the same physical grind as the LJ XU1 std cam, but it was also retarded by 6 deg in the LC XU1 and installed straight up in the LJ 202 XU1. The only difference between the two XH shafts that necessitated the change in part number will have been the 6 annular clearance grooves ground into the shaft for the 202 big end bolts.

XT5 Cam max lift = 8.9mm or .350"
EFI Cam max lift = 10.2mm or .401"

Edited by user Monday, 25 March 2019 6:27:53 AM(UTC)  | Reason: Not specified

Correct, the LC 3100X valve timing was 23-65, 268deg, 58-30, 268deg, 0.345", 0.345", 53deg overlap, from SOP for all 3100X prefix engines.
Advancing the camshafts would have resulted in better low/mid range torque in the 186 XU1.

Installing the XH camshaft straight up in the 202 XU1 would have resulted in better top end HP.

But you woudln't bother to retard the stock cam from it's original installed (straight up) position. GMH engineered it up to give the best compromise between torque, HP and fuel consumption..
Anyway, I don't see how retarding or advancing the cam is going to have any great bearing on when you want to ignite the A/F mixture.
At the moment the plug fires the inlet and exhaust valves are closed.

What a WB with a red intake and carby on it.

And a 30/70 Waggott Cam is about the same as a HX 3.3L what BS every 30/70 Cam I have driven be it 202 or 308 has very lumpy idle and f all power down low, ones grand mother could not take off the line with such without stalling it and they will rev to 7000RPM easy.
I don't see no ADR27A 3.3L doing that, not even a 3.3L EFI coming anywhere near it.

Well they did with the original LC XU-1 and the next, but as to stock Cams they do, as they did change the same Cam position in the HT-Q 253 to 308 and not to mention the first LH 308's.

I am quite sure that the Ford F100 250 log cam was advanced because of the grunt that my dads had, would kill a XB 250 for torque.
Look at the Valiant slant 6 Dodge trucks I drove as well had impressive performance to drive and they were low compression, I think that the Cam or the timing may of been different to the sedan and maybe the hemi 245 was low comp in them as well, look at all the Cam grinds that the 6 cyl Hemi had in sedans one for the 1V carby and 2 grinds for the 2V just for a start.


What happens is that when you change the Cam adv or retard it, well that is your reference point that is what is telling your timing light is coming from, it's not your reference point coming off the crank is it. it's coming from the cam as the spark is in regard to the Camshaft that it's connected to.

When you look at the spec of a Cam and in relation to the Intake, lets say 20/60 for example, now if you make it 15/65 then you loose dynamic compression, so their is a rule that for every deg more that your intake valve closes you have to up our static compression to counter the loss, that's why we see the compression increase with a hot Cam engine. as lets say you increase your stock 202 red from 9.4:1 to 10.5:1 on 97 octane what would be the point, as you could go backwards with power and fuel economy easy. but if you had a big Cam 10.5:1 would be a good thing, but 9.4:1 would be a stupid thing.
Remember the later the intake valve closes has the biggest effect of all.

Now what it we make it 25/55 well we may have to run a lower compression.
I think that the jetting may change for sure with any mod as that is all to too with volume efficiency.

Their was a mod that was done to the IT Yamaha that you cut 15mm out of the front of the pipe before the expansion chamber, now that is a 2 stroke but you had to change the jetting and if you did a little port work the same again so fact is anything that you do, to get the best out of it you will need to deal with the jetting.

The advance or retard of your camshaft is not the reference point for your timing light. Sure the camshaft drives the distributor but the distributor is timed in relation to TDC of the crankshaft/pistons not the camshaft.

Yes in the aftermarket cam world you tailor the grind to the compression, and the stall and the gearing and the weight and the intended use plus other factors. But not in GM (or GMH). They used as few camshafts as possible. GM used the same hydraulic cam for SBC engines ranging from advertised 8:1 right up to 10.25:1 on engines from 307ci up to 350ci possible on small and bigger too. GMH did the same with 6cyl cams in low and high compression 149 through to 202 which range from 7's to 9's in compression, and also did the same in 308 and later 304 ranging from 9.7:1 in HJ right through to low 8's in VL plus it was used in the low compression 308 in Bedford. They used a common camshaft too in low compression 253 starting in HT right through to the 9.8:1 L34. What GMH appear to have done wherever possible was to do was advance or retard camshafts to achieve "close enough" rather than Engineer a new camshaft

I would bet the ADR27A 6cyl auto cam is exactly the first LC XU1 cam but not advanced, I would even hedge that the lift is the same and that they didn't bother correcting for the 7 thou difference (less than 0.2mm). The only reason the part number would have changes is so the cam could be modified to fit the 202. Why they did it with the trimatic and not manuals? It can only be they wanted more power but in the manual it wouldn't pass ADR27A emissions.

Edited by user Monday, 18 March 2019 9:34:52 AM(UTC)  | Reason: Not specified