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Yeah it's a two stage 32/36 like the pinto engines had. TBH, I had quite a bit of hassle getting the holley to work properly. But it dod give me more room to mount the nozzle.

A bigger cam will reduce detonation as it will reduce the resistance in the intake tract of the incoming charge, and actually reduce the boost figure. Since it's being compressed less, less heat is generated-Hence less chance of detonation. Plus The blower should use less power to drive.
I found my car was bloody thirsty with the weber on it. I think because or the powervalve set up on the holley, it uses less fuel when I'm only cruising.

That's spot on about bigger cam potentially equalling less prone to detonation. On ww2 military aircraft they experimented with it. It wasn't just the extra intake duration. The extra intake/exhaust overlap meant less chance of the tail end of the exhaust gases staying in the cylinder, heating the charge more, as well as contaminating it (taking up space where fresh air/fuel could otherwise fit). Additionally, extra air going through meant extra fuel (even if some of it was blown straight out the exhaust) and this fuel (as long as we are talking about a fuel introduced as a liquid which will pull some heat out as it changes to a gas) will essentially act purely as a charge coolant, not combustable material (since it passes through and out the exhaust.

Obviously there are real limits to this, and as you gop bigger and bigger with the cam (just like an NA engine) the powerband is shifted higher. All well and good for optimal competition output, but less and less street practical, or as long lasting (which is imho the BIG win with forced induction - you can keep the rpms sensible and get close to stock engine longevity with them) Keeping in mind that boosted setups (unless they are really way too small for the engine combination) will tend to extend (and by extend I mean you still retain the lower rpm output, it doesn't just shift the powerband higher) the useful upper rpm output to the point you might well be shifting gears as much as 1000rpm higher than you would with the same cam in an NA engine. Aside from flow at good valve lifts, with enough pressure behind the valve, it'll start flowing to a useful extent at a low valve lift whereas it wouldn't (as much) on a NA engine.

Last but not least - this info above mostly concerns supercharged engines. With a turbo, you have massive exhaust backpressure (at full boost) between the exhaust valve and the turbo. It's normal, and even an efficient setup (with very few exceptions and none likely ever achieved on many setups without a massive budget, i.e. not street cars or even most street/strip cars) will have 1.5-2 times as much pressure in the exhaust as in the intake at full boost/rpm. This means keeping the exhaust open longer, or having too much overlap is actually more likely to lead to some tangible amount of exhaust being pushed back into the cylinder.

As such it's why you typically see intake/exhaust lobe separation being increased on supercharged engines, but even more on turbocharged engines. Things like equal length exhaust runners (and assuming all are actually all equally 'right' not just equal but all the same wrong dimensions) and careful i.d. selection, will tend to mean you can run relatively slightly tigher lobe separation on a turbo. On a tight budget, just run a modified factory or steam pipe manifold and a wider lobe separation on the cam and don't worry).

A few years back there was a big thread on another forum about cam choice for a turbo setup, and mostly the recommended specs were something akin to a 'mild street' kind of a lobe with just a little wider lobe sep. It went into a tangent about a particular (very very very quick) drag car, and they mentioned running cams of close to 300 degrees seat to seat duration, which is huge, and it worked exceptionally well, no question about it. Worked very harmoniously with this spare no expense buildup (and for the record, I doub't I'd ever get a car to run even a second or two shy of it without wining a lottery)

But the thing that must be kept in mind was that this car launched and saw upshifts around (and I believe above it as it underwent optimising/testing) 10,000rpm. And it didn't have massive output (well not compared to its output at higher rpms/boost) down below perhaps 5000rpm. horses for courses so to speak. It also ran sophisticated engine management, and that's (relatively) easy to setup for a wide range of operating conditions. I love carbs, but getting them to support peak boost and 10,000rpm would make it hard to get acceptable drivability for even the occasional midnight street drive.

Last but not least, on a supercharger (and doubly so on a turbocharged setup) there's more air/fuel being burnt, so even if it's burnt very efficiently and completely, there's more heat/volume/energy being shoved through the exhaust valve whilst it is open. It heats up then, and cools when seated, transferring heat to the seat and the head and on to the coolant. So a really big cam, though it might work for a drag car, will have the exhaust valve open longer and the exhaust valve closed (and able to cool) shorter. So it might survive a drag setup, but it will run hot on a circuit or the street and lead to the exh valve being the 'trigger' (i.e. the hot spot) that leads to detonation or pre-ignition. So too much ex duration can become a double edged sword. Likewise since it cools through the seat, less duration (than a full race cam) but also - simply cut the exhaust valves/seats so that their contact face is wider. This will have a minor reduction in exhaust flow esp at lower ranges, but is more than made up for due to the extra potential output/ (and being able to run more boost safely). Obviously enough, the seats on a supercharged engine's exhaust wouldn't have to be as wide as those on a turbocharged engine, since it has less back pressure, unlike the turbo which traps a lot more of the heat in the exhaust tract close to the valve). don't get me wrong, one doesn't need seats 1 inch wide, probabaly considerably short of double what is effective on an NA engine - probably around or just shy 1.5 times the width for a turbocharged engine and around 1-1.25 times the NA seat width when for a supercharged engine.. Essentially, choose the cam to suit the specific form of forced induction, and when getting any headwork done, specify if it is to be supercharged or turbocharged.

Now back to the original query - I'd personally suggest that a bigger blower turning slower will mean less heat (unless the large one was a terrible design and the smaller was incredible). Longevity is always discussed, it is no doubt a relative term. I've heard of rpm limits of the sc12 and 14 to be around the 11,000rpm mark (so potentially close to a 2:1 drive ratio would be do able, But like everything, the longer you run at or near that max safe limit, the quicker it'll fail. One could use the analogy of engine longevity in general. An engine that is drag raced, only sees peak rpms for a few seconds. A circuit race engine, spends more time in the higher rpm range (since it doesn't complete the race in just 1/4 of a mile). So a safe drag racing occasional rpm limit would break the same engine in a circuit car. Then you move to the 'big daddy' of engine abuse - speedway. An engine that would last a race season on a circuit racer (just) would be lucky to last one or two race meetings in the higher levels of speedway racing, they are on the throttle a hell of a lot. And then there is finally the two things that will even challenged a speedway engine =- tractor pulling, and top speed attempts. Both are at full throttle for up to and often over a full minute. Tractor pulling is also low speed, so harder to get air through the radiator to keep it cool. Those are important considerations, because the same boost/rpm/compression ratio/timing of an engine that would never have a problem on a dyno run or a drag race and show zero signs of detonation or pre-ignition, they'll have a shorter lifespan than the roofing insulation government program

Great points there!
But a few things,
With a bigger cam suited to force feeding, (Which has a wider lode sepration angle) the exhaust event begins sooner. So although there is greater duration and the exhaust valve is off the seat longer, the EX event ends sooner than it would on an N/A performance cam with the same duration, but a narrower lobe seperation angle. This is where having a fit-for-purpose cam pays off. (Also having the EX event beginning earlier helps to evacuate the extra volumes of spent charge generated by having the charge artifiically forced into the engine.

The second point I wanted to raise, (Althtough getting a little off topic) was regarding what you were saying about the back pressure from between the EX valve and the turbine wheel causing greater exhaust gas reversion back into the chamber. the Other drawback of too narrow of a lobe seperation angle is that the gas flow (albeit still thermally expanding) form the EX port is tryng to spool the turbo, whilest the exhaust gas reversion from the aforementioned back pressure is corrupting the vaccuum signal in the intake tract. This is both impeading a strong intake charge siganl, and pressurising (somewhat)the intake which when you think about it is the other side of the turbo. So you're going to have pressure on both halves of the turbo, which hampers it spooling.
Of course this pressure will be overcome as the flow out the exhuast is greater (by far) that the reversion. But i'd say that drag engine Jmac mentioned with 300 degree duration would have to have had antilag to get the turbo spooling and overcome the reversion.

So if I was after 10psi up to 6500rpm engine speed I would need
the amr500 to spin at 2:1 (13,000 rpm) peak is 16,000rpm
the sc12 to spin at 0.83:1 (5400 rpm) peak is 11,000rpm
the sc14 to spin at 0.9:1 (4637 rpm) " " " "

So the bigger ones are spun to 50% of their peak rating
little ones are spun to 75% of their peak rating.
Meaning the little amr500 would be still mainly working
at around 80% of the time at around 50% peak rating and
the big ones at only 30%.
How does this affect efficiency and response?
eg. most driving is done under 4000rpm so which
superchargers will be doing their job better?

Could it be like 500cc bikes going around the tract
which more zest than 1000cc bikes due to the smaller
engines hitting the ideal rpm range more often?

here is a picture of a 108kw atw 5k motor using a 1.75 stromberg
like topgear used for his 98kw atw a12. It was supposedly burning
9L/100klm compared to the NA version which ate 10L/100km.

Attach file:

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  5ksc14.jpg (188.51 KB)

at cruise throttle, manifold pressure is no different to an N/A engine.
Say you take off from the lights, and squeeze the the go pedal to around 1/3 throttle. The motor will instantly boost up to say 4psi. (Give or take) Once you have reached the speed you want to be doing, you'll lift off to hold said speed, and your manifold gauge will drop back into vaccuum.
Since there is a diect link between the the crankshaft and the blower, the boost changes little. As the engine revs rise, and the amount of air it consumes increases. At the same time so does the blower speed, and the amount of air it is supplying to the engine. So your boost is petty much unchanged through the rev range.
A word of warning also, regarding your theoretical boost figures for a given blower drive ratio. Don't assume that the blower is going to move it's advertised dispacement of air per revolution in the real world. Unless I cocked it up, I plugged my s/c14 on an A14 numbers into a formula Feral posted here years ago. And I came up with much a much higher boost figure than what I got with this set up in the real world. There are of course numorous other variables in the real world. such as the condition of my blower. But it hasn't skipped a beat in the time I've been using it. (unlike the three engines it laid waste to. lol) It did make a hell of whine when it was pumping 1 bar though.
also on the topic of blower ratios, a mate of mine bolted an S/C12 onto a mazda UC13 in a rwd 323 wagon. I think it made about 5.5psi with a 1:1 drive. So based on that we calcualted a bigger pulley size. Only it made 14psi with that one. It went like a raped ape, but it rattled it's nuts off. (I couldnt talk him into locking the dizzy)

Will have to re-calculate everything as there are so many
variables that its not a perfect science.
I will have to consider the short rod a12/a14 cranked hybrid
for this build as it will as after lifting Simons and one of
my engines the other day its amazing how much lighter the a12
are compared to the A14/15 engines.
Id love an a15 but the diff ratios are impossible to get for
freeway cruising without developing tinnitus.

The picture I put of the K series Rolla was to show that a
cheap stromberg could be alright for response and not cramp
anyones style. I also have a 2 incher that might be better
but love the size of the stromberg in terms of height although
the SU as its been pointed to me is a better carb.

That picture of the 5 K setup. . .

The pulley is changed on the SC1x.

How has this been done?

I have an SC14, 2"SU and a welder. The drive has been the only thing stopping me. . .

Twin belt front pulleys are fairly easy to find but you would have to change the SC pulley as above.

I'd ideally like to go with a setup similar to the green ute (extended snout).

I've been told that the shaft coming out of the 'charger has a tapered spline. . anyone confirm or deny this? Pictures stripped?

Depends on the setup but some go the sc12 pulley on the sc14 for more boost.
Someone in the earlier datsun1200 days extended the snout of an sc14 by
removing all the clutch and pulley setup and you are left with a tapered
housing which makes it easy to weld a tube with length required to match
up to the crank pulley (a15 dual crank pulley with stepped pulley welded
over the top or tapped once drilled and threaded, the stepped pulley can
come from a diesel pump for cheap or some power steering pumps) then you
must have a bearing installed in the tube with a female shaft machined
to slide over the splined shaft sticking from the supercharger that has
a provision for a cogged pulley and also secured with a bracket for support
and strength. The female splining of a shaft to match the supercharger
output shaft is the expensive part of running the SCxx directly over a
factory modified inlet manifold.

double post