A Question of Timing

[db]

I like the 'it's so easy to install you'll think you're doing it wrong'
also liked the bit at the end about magazines and how they favour certain products that happen to have the biggest ads- so true
Gonna try and sound clever now.... .... could this sensor be rigged up to a water injection system and would there be any advantage ?
Just thinkin if it's retarding the ignition it must cost at least a teeny amount of power?
Water injection seems to do a similar job but i'm not sure how it's controlled. I understand water is normally injected earlier in the intake to help atomization. This would wet cylinders that aren't pinking so- if it was combined with maybe fuel injector or nitrous-type nozzles, this critter could, if wired up by someone clever, hit just the offending cylinder(s) with a measured squirt of H2O, just when needed. In race applications this would save on weight of water over a more primitive system and maybe save a couple of crucial HP at full noise over an ignition retard system. And on the road would be a really flash techy gizmo to boast about down the pub

[Dave-R]

Water injection does not wet the cylinders that are not pinking. It vapourises just the same no matter what so you don't need to just hit offending cylinders.
Many people swear by it. But bear in mind that anything that reduces the temprature of the burning gasses will also reduce the pressure in the cylinder and that will reduce torque.

I would imagine that this electronic system would not reduce torque to the same degree.

[Anonymous]

water injection is used to reduce intake charge temperature which resists pinking and allows greater charge density, apparently. Never used one, but since they are principally used on turbo charged cars to allow greater levels of boost without detonation I would have thought they could also be used to allow higher static compression ratios than are normally considered safe on pump fuel. Methanol has also been used for this as it burns off rather than turns to steam although theres some reason why the water vapour turning to steam is supposed to be good as well.

Theres a whole load of stuff I read, but probably didn't fully understand, on how you can run 12:1 on the street (some Hondas have static CR around 11.5:1 as stock) and reap the benefits. The thing is you only get detonation under certain circumstances (in my case it seems to be acceleration LOL) and if you can avoid that you can get the benefits of a high CR for the rest of the time.

David Vizzard once built a "super MPG" Mini running about 13:1 CR or something mad on regular 4 star. The idea was it was super efficient at part throttle and would only pink if you drove it in certain conditions. Certain stuff was done to limit these conditions but I recall the car would still pink if driven hard. He shrugged that off with "you don't build an ultra-economy car and then drive it hard". The cam timing made a big difference and I think it probably had some funky distributor with huge amounts of vacuum advance and retard. It was done before the days of ceramic coatings in aftermarket applications so gawd knows what CR he'd shoot for on 4 star with TBC coatings on valve heads and piston crowns...

I'm liking the idea of this device. Question is does a 12:1 motor running a few degrees of retard make more or less power than a fully advanced motor running 9.75:1 ???

Swings, roundabouts, all that sort of stuff.

[Blue]

Static compression is only part of the story, it is cylinder pressure that you need to watch. pressure can be bled off useing cam duration, that's how the Custom Car street eliminator cars manage to run pump gas at 12.1 compression without detonation, Rob loaring was explaining to me how they do it when we were discussing my engine combination. Aluminium heads also allow more compression than iron heads.

[Anonymous]

Aye, mostly it was cam timing, ignition timing and "heat management" (coatings and running special coolants etc.) so you could run huge streetable compression. The Honda engines do it all by ECU dynamically apparently. Not sure how streetable its really going to be if you are running funky cam timing like that... Anyone tried... Its free power, right?

There was a load of maths in there which kinda lost me though about cylinder pressure and "dynamic CR" in various stages of the cycle and how this relates to cam timing. This is the bit that I didn't really get, although I see the vague principal behind it. I'd end up with a valve through the top of the slug first turn if I tried it LOL

[Dave-R]

There it is again. "Aluminium heads also allow more compression than iron heads".

NOPE!

You NEED more compression with ally heads.

An ally head engine will make the same power at 11:1 compression as an identical iron head engine at 10:1. The cooling effect of the ally heads reduces cylinder pressure during combustion so you need more static compression to make up for it everything else being equal (same port runners, valves, etc).

The same may be true with water injection to a degree but that is more complicated. I still think although water injection is good you might loose less power controling detonation electronically. You would be better off using an intercooler in turbo/supercharger applications.

Someone should (maybe they have) do a comparrison. There's a degree project for you James!

[Dave-R]

You bleed off pressure on high duration cams because of valve overlap.

The longer the duration of a cam the more valve overlap you have (where the intake valve and exhaust valve are both open at TDC on the exhaust stroke) and therefore the more static compression you need to maintain cylinder pressure.

If I understand right this is why peak torque moves up the rpm scale with duration. It is because the more overlap you have the less cylinder pressure you have at lower rpms. As rpm goes up the pressure has less time to escape so torque goes up. That is just my simple understanding. I might be wrong because I have never read anything about how a cam works that explained that.

[Guy]

Ok so if my car had iron heads and 11.75 comp and pinked a little bit with the correct timing if I fitted ally heads they would allow me to raise the compression before pinking would occur.

[Blue]

Yes Dave, I should have added that you NEED more static compression when useing aluminium heads, the point I was cack handedly trying to make was that is why modern ally headed engines appear to have very high static compression.

[Dave-R]

That's Ok Blue just don't do it again!

Yup Guy you have got that right. But cylinder presssure (during combustion) would be lower until you rasied compression up one full point. Then you would be back where you started.

[Guy]

OK now i've got it------------just dont know what to with it

[Anonymous]

eh? This is something I've assbackwards somewhere then.

So if I have a generic V8 making 400BHP/450lbs @ 10:1 with factory heads which flow say 300 CFM, have say 75cc chambers 2" inlet and 1.8" exhaust and I replace them with a set of alloy heads which are stock style castings same flow rates, same valves & chamber shape & size my motor would then make what 380/420 until I bumped it to 11:1 at which point I'm back with 400/450.

So, apart from weight, whats the advantage of running ali heads? Do they (as I had previously been lead to believe) support higher compression and more power or not? IE in my example about I could go to say 11.5:1 or 12:1 on same fuel and make say 435bhp/470lbs or with no other changes is power output fixed by octane?

Will ali heads not make the motor run hotter as well as more heat will be passed to the water jacket?

[Dave-R]

The advantage of ally heads is;

a) They are lighter.

b) They usually come with better shaped ports/chambers and bigger valves as standard allowing more room for porting.

c) They are easier and cleaner to port.

d) They come with unleaded fuel compatible valve seats

Quite often an "out of the box" pair of ally heads like the Edelbrocks will flow as well as a pair of well ported and bigger valved original iron heads.

I opted for ported iron heads because I had a performance target that could be met easily with iron heads that looked exactly the same as the originals on my car. Plus the ported iron heads were a bit cheaper even when taking shipping into account.

If i was building a race car I would use ally heads for the weight reduction alone. Plus i might want to port them more than an iron pair would take without welding etc. But iron heads on an iron block will always seal better so for a street car I think iron wins for the most part.

[Blue]

If a everything else was equal you would need to raise compression by 1 point when going from an iron head to an ally head to retain the same power output, so yes they will stand more compression but that alone will not make any more power. The main benefit of an aftermarket aluminium head is flow, An out of the box edelbrock big block head will flow almost as much air as a fully ported 906 iron head, plus It will cost less money, will not crack due to port walls getting thin ( and can still be ported further if needed) and can be skimmed more if compression is an issue,They are basically a redesign of the iron head useing modern techniques to produce a superior head in all respects.

[Anonymous]

OK, I get that now, I'd just assumed a few things incorrectly on the basis of the heat transfer properties being different.