Puckering a velocity stack to lower cfm.

[J.A.W.]

Dunno 'bout rare, you'd be hard put to find either a Holden boy-racer ever trying
to emulate Brock/Grice et al, & compete with the big bad locally-built Boss-type
4V Ford Cleveland 351s, (let alone a 'yellow maggot' highway patrol cop) - in mere 253,
hell, 'bout any old 245 Hemi Valiant hammered hard, would humiliate a bloody 'baby 8'!

Funnily enough, I fitted a reconditioned Q-jet 4 barrel I bought from 'The 308 Shop', on a
a Cain manifold with a set of extractors to a high-mileage (with sloppy cam-chain), never
pulled apart $900- Charger 265, (& I only bought it, 'cause even dead stock, it'd lay rubber).

Damn, with the 2.92 diff ratio, & that retarded cam, it would rev to 60mph in 1st (& reverse!).

[coaster]

The 265 was a beast, 2.9 diff 1.5 tonne car thats impressive. Most guys used to over carb the 253 and complain it was slow, Quadrajets were designed for smallblock chev size motor in the 6 litre range.
351's were dangerous, with an Lsd and inexperience, the cars were so nose heavy with an iron lump like a large boulder, a live axle with sloppy leaf springs and a mechanical lsd with lousy torque sensing. Fords were deathtraps in my opinion, except for the windsor models with a set of sway bars.
Glad to see a fellow dinosaur, times do change.

[J.A.W.]

Back in the day, GM put Quadrajet 4-barrel carbs on heaps of different-sized
engines from mid '60s inline 6 OHC Pontiacs, to huge displacement Cadillac V8s.

AFAIR, the last of the Holden 253's got 'em too, & with that small primary
plus large air-demand secondary, the Q-jet system worked well, good enough
for Grice to win at Bathurst in the 1986 homologation Group A Commodore VK.

Hemi 265's could shift a fair bit of air, with true 12 port/big canted-valve heads.

Weber carbs had replaceable venturi-throat 'chokes' to adapt to CFM requirements,
of different internal diameters within the size-range of the basic carb body type.

[coaster]

I agree with the quadrajet on the 308, its the 253 with a quadrajet that made no sense, the 4.2 litre simply could not get those big vacuum secondries to flow. The 465 holley 4 barrell was the correct carb but so expensive, most went for the 600 holley with double pump/ double float chamber for better value, but again, too big for the 4.2 litre.

[J.A.W.]

I agree with the quadrajet on the 308, its the 253 with a quadrajet that made no sense, the 4.2 litre simply could not get those big vacuum secondries to flow. The 465 holley 4 barrell was the correct carb but so expensive, most went for the 600 holley with double pump/ double float chamber for better value, but again, too big for the 4.2 litre.

The Quadrajet has mechanical secondaries, but 'air-doors' above, that open only wide enough
to accommodate the suction requirements of the engine via the inlet manifold, (on a 265 Hemi,
it was a whoompf! then growl/rush - or 'like V-tec yo!' , as the kids would say - these days).

So it seems a bit strange that GMH would go to the expense of a Q-jet, if it didn't work,
or fit it to the sporty VH SS 4.2, while rating it as worth 20hp (~15%) more than the base 2-barrel.


The Pontiac OHC six was close kin to the Holden 179, albeit a 230, (& despite the OHC,
it was still lumbered with the siamese-port heads), yet seemingly handled the Q-jet...

[Tommy Cookers]

(yes I do write this stuff for my own gratification ....)

when McLaren c.1966 destroked for 3 litre F1 the Indy Ford (already over-valved and over-ported) it was useless ...
till they 'puckered their velocity stack'/reduced the intake size using iirc Charger bits - making it only semi-useless

and .....
for about 40 years I was unaware of any canted-valve 6
(though c.1970 asked about Hemis when as a 'temp' handling orders at Chrysler International)

British motorcycles were pushrod-hemi for 70+ years .... but ....
rocker/pushrod geometry (for commonality with side-valve relatives) loaded and wore valve guides and then valves
as did 700cc ('motorcycle-engined') BMW cars and 300cc BMW Isetta 'bubble-cars'
(the 250 BSA and the Vincent had proper pushrod layouts)

the canted-valve presumably avoided this .....
as presumably did for the 50ish years the British also made 'true' pushrod hemi-head cars ......
Riley, Lea-Francis, Bristol (BMW design), Armstrong-Siddeley, and Daimler 'Jaguar' V8s ..... and .....

'forgotten' but quite numerous ...the Humber Super Snipe of 1958-1967 (also assembled in Australia and NZ)
mostly an 87.3 x 82.5 3 litre of 130-140ish hp related to the 3.4/4 litre Armstrong-Siddeley but lighter etc block
(the 6 cyl Armstrong-Siddeley was 90 x 90 and beefier 4 litre 97 x 90)

but Chrysler took over the Rootes Group (including Humber) in 1964
(and inherited the Sunbeam Tiger using the Ford Detroit smallblock V8 !!)
the Humber was a heavier car than the Chrysler Valiant derivatives

the Humber brand was applied to smaller Rootes cars of non-Humber origin - and outlived the above 'true' Humber

[Bandit1216]

Hi

I have rather big (46mm) ITB on a 1587 cc engine with mild cam. It does work. Only challenge is 1% to 2% throttle is already the threshold between engine braking and pulling. You can smoothen It out though, by setting ignition at around that point intentionally late, to make it less jerky. And I have longggggg runners, 350 mm.

I was pleased with the result. Pulls from 1500 to 7500. Also street car.

Would advice to get a computer that can run Alpha -N though.

And you can probably use a diesel vacuum pump for your brake servo. Vacuum will be half gone.

I think the duratec 2 liter is 90 mm cylinder spacing, correct? Perhaps you can look out for kawa zx12 IBT's like mine. They are 46mm and 92 mm apart, but I got them to fit 84mm cylinder spacing. Surely 90mm is easy.

[coaster]

Duratec and most 2 litres are a 96mm spacing, the bmw s85 V10 is 98mm spacing and was to be the source of the throttles, all i had to do was delete one and make a shorter thottle shaft. The bellmouths i were to create in cad and 3d print, these were to fit inside a pair or dcoe style air filters which i planned to protude from the bonnet.
I paid all up 270 pounds and was promised a full refund, it was not a full refund as they got me for the fedex half used to reach the airport.

Apparently car parts are now banned items for export from uk, maybe brexits the cause? Or 2030 fuelled car eradication? Beats me, i lost some dough and probably now will only purchase exotic bits from countries other than the uk.

[J.A.W.]

(yes I do write this stuff for my own gratification ....)

when McLaren c.1966 destroked for 3 litre F1 the Indy Ford (already over-valved and over-ported) it was useless ...
till they 'puckered their velocity stack'/reduced the intake size using iirc Charger bits - making it only semi-useless

and .....
for about 40 years I was unaware of any canted-valve 6
(though c.1970 asked about Hemis when as a 'temp' handling orders at Chrysler International)

British motorcycles were pushrod-hemi for 70+ years .... but ....
rocker/pushrod geometry (for commonality with side-valve relatives) loaded and wore valve guides and then valves
as did 700cc ('motorcycle-engined') BMW cars and 300cc BMW Isetta 'bubble-cars'
(the 250 BSA and the Vincent had proper pushrod layouts)

the canted-valve presumably avoided this .....
as presumably did for the 50ish years the British also made 'true' pushrod hemi-head cars ......
Riley, Lea-Francis, Bristol (BMW design), Armstrong-Siddeley, and Daimler 'Jaguar' V8s ..... and .....

'forgotten' but quite numerous ...the Humber Super Snipe of 1958-1967 (also assembled in Australia and NZ)
mostly an 87.3 x 82.5 3 litre of 130-140ish hp related to the 3.4/4 litre Armstrong-Siddeley but lighter etc block
(the 6 cyl Armstrong-Siddeley was 90 x 90 and beefier 4 litre 97 x 90)

but Chrysler took over the Rootes Group (including Humber) in 1964
(and inherited the Sunbeam Tiger using the Ford Detroit smallblock V8 !!)
the Humber was a heavier car than the Chrysler Valiant derivatives

the Humber brand was applied to smaller Rootes cars of non-Humber origin - and outlived the above 'true' Humber

The Humber Super Snipe 6 earned a good reputation downunder, esp' in NZ, once wrested from
executives & farmers - & to be head-skimmed to run on hi-test petrol - plus carb/exhaust mod's.

I recall reading a late 1980s mass road-test presentation of BMW cars being run in the alpine roads
of NZ's South Island, & the foreign journalists being amazed how hard an ancient Brit could be
punted up & out of tight, twisting climbs & how the latest luxury BMW's were so ah, humbled...




I always thought it was a shame that Peugeot never doubled their slant-block 404 hemi into a V8 to
match the British Daimler,(just as M-B later 'double sixed' their Cosworth DOHC 4V head 6, into a V12).

AFAIR, Edward Turner saw the twin-cam short-pushrod hemi-head Riley as 'inspiration' for his Triumph
twin motorcycle engines, & later, as part of the BSA organisation, then pushed Jaguar into buying
Daimler, since their hemi pushrod V8s could show-up the pukka DOHC 6 Jaguar engines - albeit Jag
durst not fit/sell the big one - & typically, put inordinate effort into their big OHC V12, instead.

[PlatinumZealot]

Hello, i picked up a set of 50mm itb's for a duratec 2 litre for a good price, i want to put them on a street car (locost) but dont want the huge cam to make them flow.

Could i 3d print a set of puckered velocity stacks and get the performance to match a mid range camshaft?

50mm?!!!
That is big! For ITB's.

I have a crazy idea....

Make new smaller valve disks at the size you need for your application..
Then make sleeve inserts into the ITBs to reduce the internal diameter... (these sleeves go either side of disk and spindle).
In this way the ITB will have the restriction and at the same time the volume between the throttle and the back of the intake valves will be reduced.

[gruntguru]

OK as long as the ITB's are fully machined internally - not cast.

[coaster]

I will take the advice for the zx12r itbs and respace them from 90 to 96, one bank of a s85 v10 bmw seemed tantalising now that most of the honda k24 guys are using one bank of the bmw s65 v8 which sell for double the price and both are the same specs, s85 gives you a spare being a bank of 5.

From now on overseas purchases from the uk will be avoided, i lost $120aud on fedex for the "banned auto parts" export gotcha.

Will be focussing on shortening the steering rack for now, local purchases.