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Nov 22, 2005 14:05:47 GMT
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I was going to mention the Vtec system, there's a whole new world of complication! In fact after a few attempts I can't word an explanation of how it works. Far from it, Its a surprisingly simple solution I`ll see if I can find some links to it...... Now Desmodromic Valvetrain is really what you want Mechanical opening and closing of valves..... very very simple, works well, no springs so no silly harmonics ;D Just got to get your material specs right ;D
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MWF
Posted a lot
Posts: 2,945
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Nov 22, 2005 14:20:25 GMT
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Oh right, I always thought Vtec engines just use double the number of lobes not a whole third cam - interesting.
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Nov 22, 2005 14:24:44 GMT
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Can someone explain hydraulic self-adjusting tappets to me please.... in particular how I can get the ones in my BMW to SHUT THE F*CK UP when the engine is cold.... it's quite embarassing when folk assume your engine is fooked when you start it up in the morning - it settles down after 2 mins.
And the people at 'Wynn's' must love me....
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MWF
Posted a lot
Posts: 2,945
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Nov 22, 2005 14:34:35 GMT
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Nov 22, 2005 14:34:50 GMT
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I think the oil pressure does this, so on an older engine, it can take awhile to build up the required pressure at the top of the engine.
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ImpManiac
Part of things
Imps... Imps... Imps...
Posts: 868
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Nov 22, 2005 14:50:42 GMT
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Yeah. Hydraulic tappets. My V6 Omega has 24 of them and they started rattling last summer. Put new ones in. Rattling again! As they wear, they bleed oil down from the cylinder heads too quickly. On an older engine at start up, they can be quite "dry" of oil. As oil reaches the cylinder head, it does not replenish the oil being bled down from the tappets quickly enough, so they continue to rattle. On mine, they are that worn out that they cannot retain enough oil to be hydraulic any more, so they always rattle! New engine time... Cheaper and easier than chasing my tail trying to fix the problems. Plus it comes with a VX warranty. Hydraulic "bucket" tappets (i.e. not finger, or rocker-type tappets) operate at much larger clearances (to the camshaft) than "solid" tappets. They contain a spring to take up the slack and an oil reservoir and metering valve. They fill with engine oil and bleed it out under the control of the valve to take up the slack between tappet and camshaft. Thus they should never need adjustment (in fact they cannot be adjusted) and should be maintenance free for years and years. Until they wear out! Solid tappets can be made lighter, reducing inertia. They need to be adjusted from time to time, though, which on many cars (especially V6 Omegas! : this can be a lenghty job. I would not mind trying a high-performance solid tappet camshaft on the Omega. Said to be worth 15 bhp increase on an already not bad 210 bhp or so. Ome day... ;D I'm EDIT: I tried Wynns too. It worked for a while but within 24 hours, the rattling returned. It is quiet sometimes, though.
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Last Edit: Nov 22, 2005 14:52:12 GMT by ImpManiac
1966 Singer Chamois sprint/hillclimb car in white over blue two tone 1975 Triumph Stag long term project (over 20 years so far) in colour TBA 2003 Vauxhall Vectra GSi 3.2 in black sapphire
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Nov 22, 2005 16:19:18 GMT
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lads, to see a twink fuel injected engine being built and running, along with the valve gear, etc, you want to download this screeensaver here40meg, so put the kettle on broadband users! BB
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Yesterday at 7:54, pogweasel wrote:
Nothing wrong with creature comforts. If I want masochism, I'll just go and slam my knackers in the fridge door for a bit.
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Nov 22, 2005 17:11:52 GMT
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The VTEC has one or two cams but three lobes per set of valves, at a certain RPM hydraulic pressure is applied to a pin that engages the third lobe and changes the valve opening time and lift. There are different systems, on called the VTEC-e is the economy model that only opens one valve at low RPM to increase swirl in the chamber and promote better combustion. The Hemi head works on the squish principle, where the charge is effectivly forced onto the plug under compression, this increses the burn speed and total burn amount. This is what causes the increased swirl in the chamber. J
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MWF
Posted a lot
Posts: 2,945
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Nov 22, 2005 17:15:26 GMT
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This is what causes the increased swirl in the chamber J Is that what's known as 'quench'?
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ImpManiac
Part of things
Imps... Imps... Imps...
Posts: 868
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Nov 22, 2005 17:37:19 GMT
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Quench is where the faces of the cylinder head and the piston CROWN come close together (a few thou!) at TDC and literally squish the mixture out, creating turbulence and enhancing mixing. A side effect is that a tiny portion of the mixture is trapped in the space and does not react due to the proximity of the relatively cool metal surfaces, leading to incomplete combustion and unburned hydrocarbon emissions (UHC). Catalytic converters oxidise this to water vapour and CO2. Quench is sometimes used around sections of the edge of the combustion chamber. V-TEC is interesting and very clever! I'm
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1966 Singer Chamois sprint/hillclimb car in white over blue two tone 1975 Triumph Stag long term project (over 20 years so far) in colour TBA 2003 Vauxhall Vectra GSi 3.2 in black sapphire
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Nov 22, 2005 17:46:52 GMT
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The japanese always come up with the simple answer to a complicated question!
Were doing a lot on combustion at university this year, some really very interesting stuff. Todays subject was exhaust gas recirculation, reduction of NOx emissions, and auto ignition time and how mixture affects this.
J
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Shortcut
Posted a lot
I won't be there when you cross the road, so always use the Green Cross Code.
Posts: 3,037
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Nov 22, 2005 17:54:58 GMT
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{{grokking}}
You sci-fi nerd you!!
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This space available to rent. Reach literally dozens of people. Cheap rates!
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ImpManiac
Part of things
Imps... Imps... Imps...
Posts: 868
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Nov 22, 2005 17:58:42 GMT
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Hey! I am a sci-fi nerd too! ;D My PhD was in mechanical engineering but specialising on combustion! Cool! Er, I mean hot! Mind you, I studied large gas oil, coal and biomass flames... IC engine combustion too! Worked with a right pair of petrolheads! One was into Land Rovers, the other Austin Sevens and other assorted exotica. I'm
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Last Edit: Nov 22, 2005 17:59:27 GMT by ImpManiac
1966 Singer Chamois sprint/hillclimb car in white over blue two tone 1975 Triumph Stag long term project (over 20 years so far) in colour TBA 2003 Vauxhall Vectra GSi 3.2 in black sapphire
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Nov 22, 2005 18:14:48 GMT
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Nice one J ;D I have the same V-tec pic somewhere ;D Very very simple and effective system You would like the EGR and SAI set ups on the S2000 All integrated into the exhaust face..... not an add on system like most manufacturers
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Have any of you tried that link that I posted up? Due to the lack of accolades I shall guess not. It is COOL, try it!!!
BB
PS It is a CAD sim, not some poxy stills or grainy video. And it goes into x-ray mode and you can see all the combustion cycle and valve movements, etc, as if you could see through the block whilst it is running.... Go-on, go-on, go-on, etc, etc....
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Yesterday at 7:54, pogweasel wrote:
Nothing wrong with creature comforts. If I want masochism, I'll just go and slam my knackers in the fridge door for a bit.
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Nov 23, 2005 20:18:04 GMT
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Have any of you tried that link that I posted up? Due to the lack of accolades I shall guess not. It is COOL, try it!!! BB PS It is a CAD sim, not some poxy stills or grainy video. And it goes into x-ray mode and you can see all the combustion cycle and valve movements, etc, as if you could see through the block whilst it is running.... Go-on, go-on, go-on, etc, etc.... Its pretty good I have had it as a screensaver for a couple of months
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Mr K
Posted a lot
Posts: 2,993
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Nov 24, 2005 22:27:39 GMT
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twin plugs / spark? why and what do you gain? noticed alot of dragsters seem to use it as do alfa and that NSU in RCmag.
water injection? why? i realise it makes the charge more dense but why is this so good?
LSDs? how do they work?
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Last Edit: Nov 24, 2005 22:28:01 GMT by Mr K
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ferrari camshafts move along inside the head, this means they can have quite a few different cam profiles to suit different rev ranges, and it simply slides the cam along when you rev the engine, for a better suited profile of the cam.
dunno if that made sense
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Shortcut
Posted a lot
I won't be there when you cross the road, so always use the Green Cross Code.
Posts: 3,037
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meanwhile at the othe rend of the engine...
tuned exhaust mainifolds, how, why and true or false?
free flow exhausts, loud and effective or just plain loud?
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This space available to rent. Reach literally dozens of people. Cheap rates!
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Mr K
Posted a lot
Posts: 2,993
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meanwhile at the othe rend of the engine... tuned exhaust mainifolds, how, why and true or false? free flow exhausts, loud and effective or just plain loud? for my college project I'm making a tubular manifold - heres what ive found out: the exhaust gases leave the head in a pulse, the pulse is differnt pressures all the way down, the front of the pulse is a higher pressure, the middle ambient, and the end is almost a vacuum. the basic idea is that where the pipes join it should be at a point when two pulses are right behind each other. e.g. on a 4-2-1 you should pair together oposites pipes in the firing order. say the fireing order is 1-3-4-2 u would pair together 1 and 4, 2 and 3. this is because when piston number one fires it will release the pulse, if the primary (1st section of pipe) is the correct length it should be at the bottom with its tail at the end of number 4s pipe for when number 4 fires, this will cause the higher pressure nose and middle of number 4s pulse to be attracted to the lower pressure tail of number one. and so on. this means that the gases literally suck them selves along. hope that make scence. a big pipe isnt best - it will cause the gases to have to much room and slow down how ever a small pipe is a restriction. a big tail pipe - despite what barry and his nova has told you, does not increase the power in the slightest - its just resinates more. a free flow exhaust box will not decrease your power, but will make you car quieter. a good system doesnt need to be loud. De cat pipes are also abit of a waste of time as most cats are free flowing and the power is not a noticable gain. thats the idea of it all. probably a few small errors. if that makes scence i have some diagrams. there are some more complicated things like cross linking V engine exhuasts to make each banddraw on the other and vairious other things.
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