Forged or Cast pistons ?
Discussion
Mr2Mike said:
This is something I have been trying to find out about the ST170, AFAIK the other engines that use the Ford VCT system do have feedback from the cam sensors. An unreliable source insists they work purely in open loop, the ECU applying a certain PWM duty cycle to the solenoid to achieve the required timing, but without feedback I can't see how that could ever be remotely accurate or repeatable over the life of the engine.
From the work I have done on mine the inlet cam timing is controlled by oil pressure but it does have an electrical connection also but I believe this is for monitoring only? The other system prone to issues is the duel intake manifold, good idea but I do here of a lot of problems with the IMRC unit(although mine has been fine).lemonslap said:
From the work I have done on mine the inlet cam timing is controlled by oil pressure but it does have an electrical connection also but I believe this is for monitoring only? The other system prone to issues is the duel intake manifold, good idea but I do here of a lot of problems with the IMRC unit(although mine has been fine).
The cam dephaser is operated by pressurised oil which is directed into the advance/retard chambers via a solenoid valve. The actual oil pressure is not a controlling factor, though I've seen this myth repeated numerous times on various forums. Using absolute oil pressure straight from an oil gallery as a control variable would be completely unworkable as it would change with engine rpm, engine temperature, seasonal temperature, oil life and engine wear etc.The ECU controls the solenoid valve, and I strongly suspect it controls the cam timing on a closed loop basis by looking at the phase difference between the cam and crank sensors (as it is on many other Ford VCT engines). This is what I would like to confirm.
The VCT on the GJ engine is oil pressure actuated. As mentioned a "moog" valve proportions the oil pressure to either side of the vane tyre phasor. Because the system modulates oil pressure to either side of the phasor, the absolute pressure of the oil only affects the maximum rate of change of the phasor, rather than its ability to reach any particular angle. The system uses the cam sensor in relation to the crank sensor to determine current camshaft position. it then adjusts the valves pwm to correct the position to the current target. The system uses a feedforward value of pwm (an open loop term) that is read from look up tables based upon estimated oil temperature and engine rpm). The final value of pwm includes the closed loop correction value, which accounts for engine to engine tolerances and the value of the current cam position error. Typically a minimum oil pressure of approx 1bar would be required to ensure timely adjustment of the cam position.
More modern engines have moved to a "cam torque actuated" system, where the cam drive load reversals (as the cam passes MOP) are used to move the phasors. These systems use a lot less oil, they simply use the oil as a hydraulic medium, with the control valve opening and shutting multiple times per cam revolution. the timing of said openings therefore defines in which direction the cam phasor moves (depending on the direction of cam torque at that point)
More modern engines have moved to a "cam torque actuated" system, where the cam drive load reversals (as the cam passes MOP) are used to move the phasors. These systems use a lot less oil, they simply use the oil as a hydraulic medium, with the control valve opening and shutting multiple times per cam revolution. the timing of said openings therefore defines in which direction the cam phasor moves (depending on the direction of cam torque at that point)
I have been involved with various engines with forged pistons (namely ford) & have seen various differing ideas about them.
From my experience if the engine is using a lot of oil then there is a problem although some will use a little which is normally down to in efficient breathing (cosworth is one) on the other hand my focus rs has done 91000 miles is running 22psi boost for over 300 bhp & uses no oil & does not rattle
The one thing that does get me though is the amount of oil some stock modern engines are using. vag tdi's can be ridiculous as are the tsi (turbo & supercharged) also a lot of vauxhall engines can be horrendous.
From my experience if the engine is using a lot of oil then there is a problem although some will use a little which is normally down to in efficient breathing (cosworth is one) on the other hand my focus rs has done 91000 miles is running 22psi boost for over 300 bhp & uses no oil & does not rattle
The one thing that does get me though is the amount of oil some stock modern engines are using. vag tdi's can be ridiculous as are the tsi (turbo & supercharged) also a lot of vauxhall engines can be horrendous.
I drive late summer in this year Mobil 1 5w50 peak life (ex rally forumula). Last 2011 summer and early summer in this year i drvie Valvoline VR1 racing 20w50. I notice that i don´t have anymore oil consumption at all when i use Mobil.. Not sure is there any effect with non synthetic and synthetic oil?
Our race engine builder say that VR1 racing oil is designet to short race use only, not for street or many many miles..
I replace valve steam oil seal´s last winter, and not effect with 20w50 oil..
I will say, oil will make difference..
Our race engine builder say that VR1 racing oil is designet to short race use only, not for street or many many miles..
I replace valve steam oil seal´s last winter, and not effect with 20w50 oil..
I will say, oil will make difference..
Pumaracing said:
Lots of useful stuff about piston clearance.
I wonder if you could help me please? I'm building an engine with a friend, we're looking at getting a cast iron block bored for a nominal 84mm forged piston (Wossner 4032). OE cast clearance was .06, i'm thinking .08mm for the forged ones? It will be a turbocharged high power unit and wondered if you thought that would be ok?I'm also thinking of getting them hard anodised, but will maybe start another thread on that if there was any interest or info to be gained, I don't think it will make any difference to the clearance.
I have so we should be ok.
I'm not looking for more power, just greater reliability and less wear, so longer before rebuilds and new components are needed as the ringlands and other parts of the piston won't wear so much. As you know the melting point of pure ali is around 650'c, hard anodised is 2000'c. I am thinking of utilising high CR so we are edging into dangerous det' conditions and will need careful mapping. Hopefully the hard crown will resist det for much longer when mapping and/or if something else goes wrong or underperforms when running at full power on a trackday etc.
It doesn't cost much so I thought it an interesting and useful addition.
I'm not looking for more power, just greater reliability and less wear, so longer before rebuilds and new components are needed as the ringlands and other parts of the piston won't wear so much. As you know the melting point of pure ali is around 650'c, hard anodised is 2000'c. I am thinking of utilising high CR so we are edging into dangerous det' conditions and will need careful mapping. Hopefully the hard crown will resist det for much longer when mapping and/or if something else goes wrong or underperforms when running at full power on a trackday etc.
It doesn't cost much so I thought it an interesting and useful addition.
I would be cautious anodizing the entire crown. The anodized layer will act as a thermal barrier, greatly reducing the splash cooling effect from the oil beneath (or through the gallery wall if gallery cooled). The chamber will retain more heat, which will contribute to detonation and perhaps even pre-ignition in extreme circumstances.
Anodizing of the ring groove is commonly used to prevent microwelding and wear resistance from ring pounding.
Anodizing of the ring groove is commonly used to prevent microwelding and wear resistance from ring pounding.
Edited by HJG on Thursday 13th August 15:52
Pumaracing said:
How do you intend to obviate the dimensional growth of up to 1 thou per surface on things like ring grooves so the rings still fit in them?
The total depth of the process goes 50% into the aluminium and 50% (the growth) is outside of the aluminium, this is fact. What I believe is that the process (if it's anything like zinc plating) doesn't like to get into internal cavities as much so the growth there isn't as great anyhow, but i'm not sure on that.What I do know is the growth on such a small area such as a ring groove is negligible and can be eased by application of a piece of 250 grit paper and 2 minutes of time. The gudgeon pin hole can be masked off or maybe (not as good) be taken out after with a fine hone. Is the pin hole normally a part of a piston which wears? I don't believe so, but am open to correction.
I just dusted off one of my engineering books from the early 1800s and it appears '1 thou' is 0.0254 mm
From what I have observed aluminium doesn't grow that much when hard anodised by someone who knows what they are doing whilst using the correct equipment properly.Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff