Wow! Thanks John so much for that valuable input. Certainly some real clarity and food for thought.
Cheers
Dave

My electric fan is 80W if that's any help and only switches on when the coolant outlet from the radiator is over 70 deg C.

I"m just thinking out loud here, I am absolutely not criticising anyone or anything here.

5hp from the fan? That's pretty high - if an electric motor was driving it 3000w divided byy 14 (since most cars run around 13.8 volts give or take) is over 200 amps It's more than possible to get belt slip from a single v belt and an 80 amp alternator without more attention to the belt tension (compared to how you can get away with murder with a 35 amp or so. alternator. Ignoring for the moment any losses from converting energy from one form to another, that'd be more than double the 'resistance' to spinning than an 80 amp alternator at full output. I think in fairness, it's more likely going to be around 1-2 bhp tops

Which isn't to be sneezed at mind you! I'm just saying that 5kw is likely more down to the general variance from one dyno run to the next.

With mechanical fuel pumps - here's an interesting thing. When the cam lobe (for the fuel pump) engages the arm on most mechanical pumps, it doesn't actually 'pump' - it compresses a spring, and fills the other side of the pump diaphragm with fuel (from the tank/main line). Then the cam spins around, and the lever arm can move, but the pump diaphragm doesn't (or might not) it is actually driven by that spring pressure. So if there's no pressure in the line from the fuel pump to the carb, the spring will push and pump the fuel forward. If there is enough (to overcome the spring pressure) then it'll just sit compressed and 'ready' to pump more fuel. Now if fuel isn't needed, when the cam lobe spins around again, it won't cost any power to act on that lever, as the spring/diaphragm is already compressed. Or if the pump only pushes a little bit of fuel, it only needs to be 're' compressed that little bit of travel, so again it costs (relatively) next to zero bhp.

That's a wonderful self regulating setup, and that spring tension basically sets what the fuel pressure will be in the fuel line going to the carb.

Going to an eletric fuel pump, you have to create the energy in the alternator (or from the battery, which the alternator then replenishes, whichever way you prefer to look at it) to spin the fuel pump. So it'd only be in cases where the mech fuel pump is tremendously in-efficient that you'd see more power from switching to an electric fuel pump.

This is hardly a new idea (afaik it started with Smokey Yunick did it in nascar decades and decades ago and, naturally enough, it was outlawed as soon as anyone else discovered it) but you could theoretically find a place where there's enough airflow and rig up a propellor driven alternator, Then the electrical power/battery replenishment would be 'free' and you would see gains from an electric fuel pump (however small)

Once a cam (for the valves themselves this time, not the fuel pump)lobe has passed max lifted, 'theoretically' the valve springs pushing on the rocker/pushrod/lifter etc would try and push the cam to spin forwards, so you'd gain back 'some' of the power that it costs to spin the cam and open the valves (with heavy race valve spring pressures) in the first place. But you always lose some (if not most) of it to friction. So what I'm getting at here is that you can also find power by determining the valve spring pressure/loads that are effectively just heavy enough to be safe for the rpm range and cam you are running, but no heavier. The problem there, of course, is finding where that sweet spot is might legitimately cost a decent head/valve or even engine or two, till you find it. So I likely wouldn't put that on top of any 'things to try' list, but I'm bringing it up more out of trivial interest.

you can also experiment with thermal sensors, perhaps sourced from light aircraft suppliers or the like, there are some you can find that are like a copper washer of sorts and fit sandwiched in under each spark plug. then you take temp readings (remember they are often air cooled and/or can adjust a/f mixture on the fly, so they monitor head temps and use that info as part of the process to where they need to set them for any given condition)

Anyway - what I'm getting at is you'll tend to find on a lot of engines (not necessarily the datsuns, but it's certainly possible) that due to position in the pecking order vs coolant passage flow paths etc, that some (or even one) cylinder runs hotter than others. You can't always correct that temp, but it does open doors for experimentation. For one thing, you could run that cylinder richer (if running webers or similar) or alternatively (and this is a trick I read about from David Vizard discussing minis) - if one is hotter, then that cylinder will be the one that detonates first. So if that happens, we 'usually' have to run less timing or compression (or both) to keep them all safe. Since the 'other 3' can handle more timing or compression, the idea is that you could carefully use a die grinder and make the chamber for the 'hot' cylinder a few cc's bigger in volume (without reducing quench areas to any significant extent, i.e. take material from the 'right' locations) - and then you have the other 3 cylinders with slightly higher compression ratios, and the 'hot' one with a slightly lower one. All end up then liking about the same timing, so you pick up maybe 2% power (or maybe a touch more, but 2% is probably around the mark) without increasing the risk of detonation/damage.

As another example of the above sort of thing - on vw air cooled engines (at least the ones I know of) - due to their fan and engine bay arrangement, one cylinder (I think #3, but honestly don't know for sure) runs hotter than the others. The 'lobes' on the points type distributors are spaced 90 degrees apart on the other 3 cylinders, but the lobe that lines up with a spark event for the offending hotter cylinder is machined 'offset' so it has about 3-4 degrees (again I don't honestly know exactly how much) later opening (or 3-4 degrees less advance) than the other 3. Obviously this works in practice, and I suppose if nothing else, it means it'd be important to install/fit the dizzy right so that 'late' lobe on the dizzy is synced up to that cylinder (and I don't know if the vw dizzy can be put in 'the wrong way' or if they have a slot or something to help ensure it is aligned or whatever)

If allowable, thermal wrap and heat shielding on the exhaust (probably already done, so this comment is redundant) will liberate hp, both from improved intake charge density, from lower enginebay temps, and less loss of heat/kinetic energy getting the exhaust out of there

One of the guys on the old mini list mentioned back to back tests at racetracks, and found a consistent mph or two on the longer straights (to be fair, minis have less power, for any given level of modification, less frontal area, but horrible aerodynamics comparable to a house brick) with the deletion of 'original' external mirrors. It seems that their size and location meant that they acted more like the ears of an elephant and pulled along a lot more air 'for the ride' than their actual size would otherwise suggest. On a similar track, it may be possible to find reduced drag (thinking mostly of changes to front windscreeen angle and slight reduction in frontal area) by lowering the rear a little more than the front. The problem there, of course, being that this may well not be achieveable without compromising suspension geometry.


I just had another thought - it'd take a couple of relays, microswitch and some wire, but I reckon it is doable. They'd almost certainly 'find' a propeller driven alternator, but how about another 'sneaky' option. Whatever the alternator drains powerwise, it only becomes an 'issue' when you are trying to accelerate.

You basically run one of the 'old school' type of alternators with an external regulator. When the field isn't powered up (I don't know the right terminology sorry) the alternator is essentially free-wheeling.

So here's the idea - have a combination of switches, for one you use the existing brake light switch, run an extra wire off that, to a relay (so the switch itself isn't overloaded) and run that via wires to the regulator, and basically any time the brakes are applied, the alternator is activated, and recharges the battery. Not bad since this will do it whilst braking before each corner. But the rules might specify it needs a 'working' charging system. No problem at all. The 'second' switch is fitted to work off the accelerator pedal (or linkage somewhere), And when the pedal is at idle, or up to (for arguments sake) 50% or even 75% throttle) this switch is on and the alternator charges. but once you go past that 75% throttle, it cuts out the regulator (so the alternator is freewheeling again) and you have full power without the drain of the alternator.

Actually = now that I think of it, you wouldn't even need the brake light switch - the throttle activation would 'already' work under brakes since you'd be off the throttle.

And to anyone scrutineering it, it'd legitimately charge and so forth at idle, if they tested it, and even with 50% or 75% throttle (and there's no way in heck they'd want you to nail the throttle - as it'd scream up to the redline too quickly, they'd only want a minor rev up to check it was working. If they checked it at all. Doing the setup like that, not only would you get back the power from swapping to a electric fan and electric fuel pump, but you'd also not have the mechanical 'resistance' from the alternator trying to supply current to power them both, at least not under full throttle conditions.

So with that 'switched' alternator in place you would potentially get 'all' the gains possible.

Thanks for that. Gosh 3kws- thats around 5 hp for free! Definetly worthwhile chasing. Interesting the comment re the fuel pump, I would have thought that would drain a bit but if there is no need to change for the sake of change then all good.
Cheers
Dave

We got power differences of around 3kw when the standard fan is on or not, the belt driven pump mounted one that is. When replacing it with an electric fan and racing you are mostly moving fast enough to keep the motor cool enough that it will never need the electric fan, so you score a lot by doing that.

Fuel pump's going to be fairly minimal I'd reckon, such a small amount of fuel being pumped I doubt you could measure the difference with or without.

Guys, I am starting to get focussed on preparing the SSS for the forthcoming motor racing season and have been looking at my setup/ potential teaks and was wondering if anyone has any figures on exactly how much of a horse power drain running the standard fan and fuel pump are likely to make?
Cheers
Dave