So I already advanced my timing to approx. 16* (1/8&quot Just curious if I can go farther than it, and what the side effects might be of this. Thanks,
Brian

 

Yes, you can go a little further. Maybe 1.7mm lift. You are around 1.5 right now. That is, if your stock timing was right on. The non intercooled ran around 1.35 and the intercooled ran around 1.25 stock. To much timing will cause detonation.

 

Detonation? As in engine go boom? Is there a way for me to know if ive gone too far without doing something harmful?
Brian

 

I know there is a thread archive with complete instructions how to check or advance the pump timing somewhere. I'm new to the game.

Could somebody tell me where or how to advance my timing. I don't know how to do it.

I think it really would help my truck and my dad's 90 w250 4x4 AT.

Thanks a bunch!!!

 

The biggest down side to advancing your timing too much is rapid increase in cylinder pressures...
That will lead (eventually) to head gasket problems.... If your timing is too advanced it'll start to sound like the old Mecedes.... rattle rattle sorta of thing...

Keep in mind that when you advance the timing it is based on your engine at idle, while warm (no KSB function).... As you throttle up, the internal pump pressure increases an so does your timing.
The first gen trucks ranged from 1.25mm plunger lift to as high as 1.40mm.
Going with 15-16* advance is right in the range for decent response, less smoke, improved idle etc.

Pastor Bob.

 

Mine has been set at 1.7mm for 50K now. Everyone that's heard mine at idle says it's one of the sweetest sounding Cummins engines they've heard. I run only 24lbs of boost with a 16cm housing. This setup will allow me to stand on it and light up the back end with no problem. It will take my buddies big block gasser out of the gate. I think the super bottom end and mild boost pressures make a plenty fast truck. I thought about the detonation answer for a second. I think thats what make our trucks run? Spontaneous combustion is another word for detonation? Bushy? Anyway, I've seen them run 2.0mm in other Cummins application so the 1.7mm seems safe.

 

I believe that the only time we are afflicted with "detonation" as it was used on gas engines, is if you shoot in some ether.... then, detonation is what you'll get...in more ways than one...
The diesel does not suffer from that as far as I'm aware.
The big issue is huge jumps in cylinder pressures.... that makes it hard for head gaskets, and of course, rings.

With too much advance on a gas pot and poor grade (octane) gas detonation happens with the resulting damage above.

Running less boost pressure will help minumize the cylinder pressures to some degree, just as a thicker head gasket would.

Bob.

 

Spontaneous combustion <> detonation, nor does the diesel engine operate on either one. The diesel cycle is based on compression igniton, whereby the air temperature created by compression is used to ignite the fuel. Diesel engines can also experience detonation, which is as I remember it, uncontrolled burning of the fuel ahead of the flame front. This situation makes for extremely high localized pressure spikes that will hammer the crap out of the headgasket, piston, rods, etc. The use of ether doesn't directly cause detonation, rather it ignites much sooner in the compression stroke creating very high pressure and temperature and causing the injected diesel fuel to be burned more rapidly, which compounds the effect. Also, the knocking associated with too much timing advance is not necessarily detonation. Poor grade gasoline will cause detonation because of unstable burning and lower ignition temp. Carbon deposits in the cylinders can also cause detonation from random ignition of the air/fuel charge.

Cheers,
Sean

 

If used improperly, propane injection can also cause detonation i/e knocking. This is due in part to the propane acutally advancing the timing somewhat.

 

About how far would the measurement be then from the original timing mark to where it is set now to be at 1.7mm lift? Or is there another way of checking this without buying an expensive cummins tool.

 

Ya...... what formula said... that's it......

It's also pretty tough if not impossible to tell EXACTLY were your pump timing is without at least the bare min. set up.
You need to know TDC, and you need to know current spec. Since our pumps can have an error of as much as 2.5* + or - or more, due to timing pin slop, the 1/8" method is getting us into the ballpark with accuracy fine tuning needed using proper tools.
Keep in mind that the 1/8" method is applicable to the 92.5-93 model year. Earlier than that and the stock "spec" was different on the pumps. Some were set at 1.40mm, some at 1.35mm and others at 1.25mm. In my case the 1.25mm is applicable. So, if you are using the 1/8" method and that takes a 1.25 spec to roughly 1.5mm or 15.5*advance then using that 1/8" on a truck spec'd out at 1.40mm will push your timing higher than 1.5* advance or the 1.5mm setting.
Does that make sense??? or is it just late and it looks good only to me...

bob.

 

I think that makes sense. Plus the pump on my 89 Doesnt actually go much farther than 1/8", so I guess I'm maxed out as far as that goes...Thanks for all the input
Brian

 

Aw heck, just bump it up till it runs backwards then forwards till it idles.
I used to drive an old Mack "B" cab that if you weren't paying attention it would start and run backwards. Downright freaky. No oil pressure though, and the exhaust would puff out the air cleaner. The boss said drinking wasn't allowed on this job. HAH, don't need it with this truck!

Dave

 

[quote author=Bushy link=board=9;threadid=19311;start=0#msg182341 date=1063087385]
Keep in mind that the 1/8" method is applicable to the 92.5-93 model year. Earlier than that and the stock "spec" was different on the pumps.
[/quote]

Bob,
Should that really be 91.5 to 93? ???

Carl

 

To be honest the only way to know for sure is to actually look at the CPL and check that referrence. For example I never knew that some were actually set for 1.40mm ..... I always thought it was 1.35mm or 1.25mm, one or the other....then someone caught me up and added the 1.40mm.

I guess what I'm saying is the 1/8" method is usually pretty close to what we find is acceptable. In fact I wasn't overly concerned about the 1.35mm spec because that would still have in the 1.55-1.60 "or so" range.
Man, I tell ya, these things just keep giving up secrets with the help of the whole team workin on em and adding their findings as we go.. Of course, the reason its a secret is cause I was too lazy to go look at a bunch of CPL's or a referrence book till now.

bob.