I think halfcent is thinking fluid statics not dynamics.

I'm having trouble understanding how a full return system would be immune to fuel supply problems caused by injector fireing order where a partial return system is not. Same amount of components just piped differently.

Pierre

 

yeah but still if the engine is running lean in the 4th cylinder than how is cooling an issue? can we find out for sure if the fuel pressure is the same from cylinder 1 and 4? and if cylinder 4 is suffering from loss of fuel

 

The pressure regulator will allow for the sudden and abrupt changes in pressure at the rail without any variables such as fuel line flow restrictions as well as holding fuel pressure above manifold pressure which our systems won't do. They simply make up for the pressure drop in pulse width with no regards to firing order.

I think the coolant issue is definetly the nail in the coffin for stock pistons that are over stressed but any large temperature delta over the head/block and we would be permanantly restricted to a certain horsepower level, which we know isn't true. It wouldn't matter what pistons are installed, aluminum still melts at the same temperature. I wouldn't call a temp. delta a problem really but I would say the fuel system needs upgraded on a more urgent level. Stock returnless fuel systems are not 100% and do have limits.

I wonder if thats why the IFR table is restricted to 63.49 lb/hr of flow, could that be the physical limit of the stock fueling system?

How do you know its running lean? It seems heat is the issue which can be caused by intake charge temps, a/f ratio, coolant temp, exhaust restrictions, and oil temp. Problem is, nobody has any data to support any of these.

 

The only true way to know if its running lean it to use a scanning EGT. You have EGT probes in each exhaust port that get displayed on a single gauge, allowing the user to compare. Larger piston aircraft engines use them. In fact, they are combination EGT/CHT gauges (cylinder head temp). With such a system, you could see a lot. For instance, if the EGT's are consistent, but the single CHT shows high, it's a cooling issue.

 

A diaphram fuel pressure regulator isn't going to follow pressure irregularities in the millesecond range. It's got a spring a diaphram and a valve section. All that has mass and will slow response. It will adjust the pressure over a longer peroid of time but it's not that fast. We have a pulsation dampner on the end of the rail that can compensate for some pulsation. It's fairly low mass but I doubt it's that fast either. The pump has some pressure pulsation also due to it's design. They are all pretty much the same though one pump to another.

Unfortunatly no one has taken pressure measurements at full load so we don't know what the situation is with pump capacity.

My impression is the pistons cracked rather than melted. I can't get anyone to send Me some pics though :-(

From your reports of a little pop @ 6800 that's repeatable was very interesting. severe preignition comes to mind. No one has ever reported knock on these events.

Dosn't anyone look at spark plugs any more?

Pierre

 

my piston melted it did not crack, i can 100% guarantee you that, ill try and get good pictures

 

Witt didn't say the fuel pump is modulated. It isn't. It runs full all the time. The pressure is regulated by a pressure regulator that is in the tank itself.

 

Whoops, nevermind I'm sorry. He said the ECU makes up for it with pulse width and I thought he was talking about the pump when he was referring to the injectors. Sorry about that.

 

so if the heat is an issue can we get hp tuners to make our fans to turn on a little earlier than what they do already?

 

Ok typing on a phone stuck in the middle of nowhere on a locomotive so bear with my grammar.

The pulses due to firing order are only part of a theoretical situation I dreamed up. Lets say the fuel pump is maxxed and rail pressure drops to 50psi at 7k rpm with 20psi manifold pressure. Now effective fuel pressure becomes only 30psi which amplifies these pulses by nearly the percentage change in the numer of fuel injectors open per each cylinders 4 stroke cycle. Switch to a return style and hold 3 bar pressure over manifold and the pulses wont have nearly the same effect.

I havent nuked any pistons but local guys have. They are melted and not cracked. The peculiar thing is they melt at one of the cooler areas of the piston which leads to an oil or coolant issue.

I have no data other than logs showing no knock and slightly rich fuel when these things nuke. I truely believe its simply over stressed pistons coupled by a very minor temperature difference in the bore causing number 4 to go. But it doesnt explain why i can replicate a lean fuel cut with a burn richer than rich best torque.

 

Ok I follow you now. I can see how the example you gave would be worst case.

My point was modify the stock short return system to supply 60 psi at the rail with a net pressure drop to 40 psi @ say at 20# boost. Still well within the injector rating.

Your suggestion is use a rising rate regulator to increase rail pressure as boost goes up.

Either system has to have a pump capable of enough pressure and flow.



I hope someone shows me some pics pleassssssse. Melting to me is a totaly different failure than cracking.

Grammar's fine..People who live in glass houses don't throw stones.

Pierre

 

is the pump to small? possibly, no one knows the answer for sure.
is it running lean? most likely, heat kills ring lands, so does detonation.

egt? GET ONE

 

Not a rising rate, a 1:1 compensation which is what I think you meant anyway.

I'll dig up a pic of WSFrazier's piston when I get home. Basically it melted above the wrist pin from the area of the oil rings to the area between the top and bottom compression rings iirc. My stockers were fairly scorched in that same area as well as underneath but only where the oil squirter shoots.

 

Interesting.... I've seen poor pics of the damage above the pin. They looked cracked but I realy couldn't tell given the resolution. I attributed it to a weak spot where there was very little material to support the rings. I'd like to see the melting. I would have guessed the scorching was due to ring failure thereby causing blowby in that area. I wasn't aware that the underneath had burnt oil on it from coking. Do you think the squirters can put a stream of oil in just that one spot or the piston has a hot spot that causes the oil to coke in that spot.

Thanks for your observations

Pierre