I don’t have the Engineering specs for anything past HZ. WB definitely had a bigger exhaust, my dad bought a 3.3 4spd van new and the tail pipe was a lot larger than a HZ. Probably close to 2”.

.. I would think that the XT5 engines in WB would have gotten better/improved exhausts
as part of the engine upgrade (over XT4)

There is a significant power difference between the 6cyl and 4.2L XT4 and XT5 engines looking at figures between VB and VC. Bugger all difference between XT4 and XT5 5.0L though. Given the 4.2L and 5.0L engines shared the same heads and exhaust manifolds it mostly has to be in the induction. Very similar in the 6cyl engines too, although the heads are different they are the same basic engines. Very hard to tell exactly what is going on though as they are not SAE Gross but DIN figures, so they are not directly comparable as you don't know exactly what is going on, for example if there is a slight difference in the exhaust between tests it will show up in the figures.

Red 4.2 XT4: 87kW@4000rpm 271Nm@2000rpm (single). 96kW@4400 275Nm@2400 (dual).
Blue 4.2 XT5: 100kW@4200rpm 269Nm@2000rpm (single). 115kW@4400 289Nm@3200 (dual).

Red 5.0 XT4: 114kW@4000rpm 344Nm@2200rpm (single). 125kW@4200 352Nm@2600 (dual).
Blue 5.0 XT5: 117kW@4000rpm 336Nm@2400rpm (single). 126kW@4400 361Nm@2800 (dual).

SPOT ON !!

Dr Terry

HK1837 wrote:

..................... The 4.2 XT5 engine did also get a revised camshaft and timing gear but you don’t get to see the full effects of it as there is so many other changes. The cam and cam timing will almost certainly to take advantage of the 4BBL intake and Quadrajet. I remember reading that they originally had problems with the 253 in development with fuel distribution, and they did fart around with different camshafts during ADR27A, and then again for XT5. However the 308/304 kept the same cam all along except for that early HT to HQ period when they compromised and used a retarded 253 cam.

ugghh ... did not want to bring that up as it slightly muddies the waters of this part of the topic
but you are correct. GMH did change the camshaft, camshaft timing via different cam gear on 4.2 XT5s
and
I have no confirmation, only guesses.. its to do with extra output in compliance with ADR/EPA numbers
with XT5 4.2 litre engines

Overall ....
What GMH did was unusual... yes, new 4BBL Quaddie to suit the XT5 blue 253 which has leaner primaries (needles and jets) than
the 308 which is understandable...BUT richer (very much) secondary jetting. The secondary rod hanger is the same for both 253 and
308 XT5 Quaddies but the rods differ... a lot. The 253 uses CX rods* ( a finer so richer rod when they lift) and 308 used DP rods.

The 253 4BBL Quaddie is therefore richer at higher revs (both use the same secondary jets) or WOT compared to a 308 . Strange..!
and also remember back then, the Quaddie for both used the same core, same fuel bowl body and was a 750cfm casting...
(late 308s used the desirable 800cfm casting)

but
back to the camshaft... HK1837 is correct, 4.2 XT5 engines got a revised camshaft... which curiously was more aggressive than previous
with the longer duration, marginally higher lift (.005") and tighter LSA BUT ... and here is the weird bit. The new cam gear when installed
RETARDS the cam timing (which is why you NEVER use this cam gear on any other Holden V8)

More aggressive cam .. but installed 'retarded' means an engine with that setup is more responsive at high revs which suits the 253 Quaddie
jetting but for a street engine that has to comply with driveability and pollution standards???

In a word... weird ! (...for a car company like GM/GMH) And interesting!



*CX rods these days are the desired ones for Holden V8s... street, strip or track, they are the ones to get. You cannot buy them here
but Summit, JEGS and other USA parts places - Quadrajet Parts sell them. I have a number of sets of CX rods and run them in the race
Quaddies I put together for the racecar.

The yank carb builders seem to prefer AY secondary rods for Quaddies going on SBC ... look at their carb build parts lists and AY (or CE)
seem to be a favourites. AY is just about the same as CX except leaner on secondary valve initial opening...

Edited by user Friday, 9 April 2021 7:54:33 PM(UTC)  | Reason: Not specified

When using Gross HP figures not all Gross figures are measured in the same way you know, their is advertised Gross and other Gross curves they call them A curve and a B curve etc etc can be in the game.

And also we have Net figures that differ using what they called different curves and then DIN and ECE that Holden used 2005 on. ford kept the DIN.

So I think you will find that 227hp is real gross and 240hp is the gross advertised, they are not made up our of the blue it's the same engine.
Ford has the same thing with XB 250 advertised gross HP at 155 and another figure stating the XB 250 at 123hp I think it was about that, but in gross C curve and then another with Net 108hp B curve.
I have displayed the rating on this forum. or maybe not the C curve, if you want I will look to find it for you.

I would not say that the 253 had a horrid small carby at all. this carby feeds ford 302 V8's and I bigger than what the stock 250 Falcon 6 had back in the day.
A mate had such a carby on his HQ 308 and surprised me at how well it performed, it would float along at 180KM/H with ease and I think it could still do 200KM/H not as much grunt as with the big 4V.

I think the 4V is too big CFM for the stock 253.
Lets look at the VB-VC
VB 4.2L 86kw 4000 271nm 2000 single.
VB 4,2L 98kw 4000 271nm 2400 dual.

VC 4.2L 100KW 4200 269NM 2000 single.
VC 4.2L 115KW 4400 289NM 3200 dual.

look at that be good if we had a Holden graph we may see the VB making more torque down low and mid range with single stock exhaust that most had.

look at the VB VC 5.0L
VB 5.0L 107KW 4000 321NM 2200 S
VB 5.0L 126KW 4250 336NM 2500 D

VC 5.0L 117KW 4000 336NM 2400 S
VC 5.0L 126KW 4400 361NM 2800 D
only spark and better tuned timing is truly in this difference between both the 5.0L, so looking at the gains if the VC 4.2L was only a 2V, the gains in torque of the 5.0L = 4.5% with single and 7% with dual. we have lost with the 4.2L single.

Blue 253 was light years better than the red 253. All due to the carb and ignition.

I believe as to a stock 253 the best value for performance is single 2 1/4 free flow exhaust and that's about it.

I had heaps of drags with my HG 253 auto Premier 2.78 diff. it went well people thought I had a 327 chev in it, someone was claiming that crap, I think it was Kenny, his mums XC GXL 5.8L auto with dual exhaust it was always neck and neck all the way from start to 115MPH and that was it top speed for both of us.

I bought (GMH employee purchase) my missus this.... VH Vacationer wagon
with blue 253, N10, other xtras and M20 4 speed ( + HD axle and 4 wheel disc brakes)



and after a couple of years... chucked the exhaust system, added a set of
extractors (Lukey) and also a 2 1/4" into 2 1/2" y pipe system also from Lukey ...
(similar to what Lukey provided for the VK Grp A SS)

Why Lukey? my brother was Holden car line product manager there at Lukey Moorabbin
he was the one in a moment of madness who arranged this...



ps... that VH wagon sure got up and went after the exhaust mod

Edited by user Monday, 12 April 2021 12:43:46 PM(UTC)  | Reason: Not specified