Engine/Transmission (1994 - 1998) Fuel Timing

[MWyckoff]

I want to advance my fuel timing. Any ideas as to how far I can adjust it? Mine is set at 14 deg btdc from the factory.

 

[KingS]

you can adjust it as far as you want to depending on how cold it get where you live and ofcourse how much you like you head gasket.



I would go 15 maybe 15. 5 since don't know your setup plus remember when you turn it up you compression level goes up some to so that mixed with boost pressure can tend to mess with the head gasket but most guys I'm sure will agree that 15 is good and no more then 15. 5 depending on truck setup.

 

[Matthug]

What truck do you have and what mods? Since it's already 14 from the factory I'd say 16 is a good all around number even if it's stock.

Raising timing does nothing to your compression. Raising timing raises your cylinder pressures which in turn can pop your stock head gasket. Now, many factors come into play here. It all depends on what boost pressures you are running, how much power you are making, how many miles are already on the gasket, and many many others. But 16 is what most people say to run in a daily driver. You won't even notice a difference probably going from 14 to 15 degrees. I went from 12 to 15 and barely noticed anything. The exhaust note was slightly raspier and EGT's went down about 100 degrees. But thats 3 degrees, 1 degree isn't worth the time and effort.

 

[MWyckoff]

My truck is a stock 98 12 valve and only has 95,000 miles on it. I have only gotten about 20 pounds of boost so far. Will increasing my timing help my fuel economy? I live at 4600 ft. and have mild winters and warm summers.

 

[KingS]

if you add more pressure to the cylinder you in turn increase compression.



The compresion of the motor is governed by the stoke of the piston and clearance at the top the less clearance and longer stroke the more volume that is compressed into a smaller area which in turn increase compression.



If you increase pressure in the cylinder and add that extra pressure to the pressure from the piston sqeezing the normal volume in the cylinder in turn increases the compression do to the fact that there is now more volume in the same small area.

 

[Matthug]

MWyckoff- Yes increasing timing will increase your fuel economy.



KingS- By increasing the timing of when the injector sprays in does not give you more cylinder volume to increase the compression. And clearly you have no clue what cylinder pressure is.

 

[DESL PWR]

KingS... As you stated, the compression of the motor is governed by the stroke of the piston. That is true. Compression is purely the ratio of cylinder volume at Bottom dead center to Top dead center. Thats all compression is.

Now, cylinder pressure is a different animal and is affected in many ways. Here we are talking about the timing of the injection of fuel. If you inject fuel into the cylinder eariler (advancing the timing), you are giving the fuel more time to ignite and burn causing the air molecules to heat up and expand all while the piston is still on the upstroke. Hence your cylinder pressure is going to increase.

 

[KingS]

yes and if the pressure in the cylinder is higher it takes more pressure to squeeze it down which it takes compression to squeeze it down plain and simple if you put pressure in samething it take more pressure to sqeeze it down.

 

[Matthug]

yes and if the pressure in the cylinder is higher it takes more pressure to squeeze it down which it takes compression to squeeze it down plain and simple if you put pressure in samething it take more pressure to sqeeze it down.

Thats a pretty good definition of cylinder pressure you got there.

 

[zstroken]

As much as I hate to I have to agree with Matthug. TIMING HAS NOTHING TO DO WITH THE COMPRESSION RATIO. It does effect cylinder pressures though.

 

[Matthug]

:--)



Lol

 

[KingS]

ok guys I was just stating what I had heard from others when timing was turned up.

Going back an forth even if one is right and the other is wrong isn't helping this guy and since I some what started this I will be first to say sorry to MWyckoff for the inconvience of having to read through this to get the answer you wanted. And to the rest for the waste of time I cause you also.

Lastly I look back at my post and I should of use the word pressure instead of compression to convay the concern of needing to watch head gasket after timing was done.

Thanks for reading this and lets keep the information sharing going for all to learn even me.

 

[zstroken]

No harm no foul. We all mess up from time to time. I got hammered one day when I said TPS, instead of APPS or something like that. Some people get emotional about things, even me. At least you got the post rolling!!

 

[MWyckoff]

Thanks guys you answered alot of questions I had. hopefully this weekend I will have time to do the adjustment.