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Old 02-19-2013, 11:50 PM
barry12345 barry12345 is offline
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Join Date: Oct 2012
Posts: 4,622
This gentleman is running close to the top end of the current recommended pressure range. That is known as certainly safe to do.

I think the fuel pressure is implict in the injection pumps profile of the sequential injection point of each element in relationship to each other. If not that then in the volume of fuel flow from each injector being equal.

Good fuel pressure equalises this and is to be expected as bosch the manufacturer of the injection pump always stated at what pressure they wanted the injection pumps calibrated.

Someday someone is going to do a milli volt examination of how much higher the fuel pressure can be taken without upsetting the power balance of the engine.

With low fuel pressure the power balance is off. Loading the first element of the injector pump better than the last one in the string especially is the effect I suspect. Of course the change is progressive right down the line.

Thirty pounds pressure makes a further major differance but without the testing may be tilting the power balance the other way or opposite to what low fuel pressure does.

If testing properly does not indicate this is a problem we should all use still higher pressure. Unfortunatly I feel bosh was well aware of this area but may have designed less than possible results for some reason. Or ran across objectional issues.

The test setup to prove this one way or another is not all that complex as I visualise it. Since these indirect injection engines are not as critical as direct injection engines. There may still be some safe headroom pressure wise.

I know there are people runing thirty pounds base fuel pressure out there for quite a time now but have performed no tests to see what engine effects might be there long term that I am aware of.

So currently unfortunatly I as an individual cannot recomend this practice even though the benifits of doing so are substantial and known to some.

The 616 four cylinder engine especially needs all the power we can safely make it deliver. So at some point hopefully I will do the comprehensive testing that should be done for elevated fuel pressures. Or a better statement is to establish if any risk factors are present by using it.

One of my viewpoints that has never changed since established. . If a person owns a 616 four cylinder engine and does not check their fuel pressure. It may ultimatly cost them the engine. This warning is worth repeating from time to time even if it just saves a few engines.

A good injection pump rebuilder with a variable fuel pressure supply could answer this issue in a very short order. Or if an injection pump is re calabrated at thirty pounds pressure should be totally safe. Testing would decide if the recalibration was a neccesary component of dealing with elevated fuel pressures.

My most recent thoughts are that bosch knew about this and they decided without a permanent fuel pressure gauge installed there would be serious issues down the road. If a injection pump is calabrated at thrty pounds supply presure for example. And an owner is negigent in maintaining a good operating pressure. As has already been proven the case with a lot of of these older models.

The results would have been more catastrophic than they have been. Also bosh had to supply a system at a price. A higher fuel pressure system cost more to produce. Part of the problem right now is the 616 uses a lower pressure output lift pump than the turbo 617 does. Making partial filter obstruction with use more detremental than on the turbo engines.

This leaving fuel filters in service till they really load up is just one of the serious causes of engine failures if the practice is of long standing in my opinion.

Some site members including myself like bargains. If you can get a fuel pressure gauge installed on your car for around twenty dollars. It is one g bargain that is hard to beat.

In one way or another it can pay its cost just in increased fuel milage benifits fairly short term. Many have reported years ago that they observed changing their fuel filter out increased their milage.

Superficially one would expect either higher or simular fuel milage with less available fuel pressure because of a restricting fuel filter. What was not generally realised then is that under low fuel pressure the engines power balance was being distorted. Reducing it's efficiency.

A gauge clearly informs you by dropping fuel pressure that either a filter change is required or something else is going wrong. One of it's real strengths is it's application as an early warning device. This area is worth rehashing in my opinion as it is somewhat signifigant.
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