revving the motor while cold?

[6 Nebraska IDIs]

Cheaper, arent your compression numbers backwards? 6.9 is lower than 7.3? Atleast I know for a fact an 83 6.9 is.

 

[Cheaper Jeeper]

Cheaper, arent your compression numbers backwards? 6.9 is lower than 7.3? Atleast I know for a fact an 83 6.9 is.

Not according to what I have read by fairly authoritative sources. The 7.3 has slightly greater swept volume, but it also has less dome to the pistons, and more headspace - at least from what I have read. The 83 may be an exception to that - isn't that the first year for the Navstar in Fords? I've also read that the 83 IP is different and had the "index" pin for the drive gear in a different location.

 

[Diesel JD]

I've heard the 7.3 and maybe later 6.9s were 21.5:1 and the A model 6.9s were lower perhaps 20.7:1. The Haynes book says all 6.9s are 20.7:1 but we all know they have a good bit of sketchy information.

 

[subway]

Yes, there is a residual film of oil - I never said there wasn't. What isn't there is oil pressure which is actually what prevents metal to metal contact in the bearings. The oil being forced through the small amount of clearance between the journals and bearing inserts under high pressure actually "suspends" or "floats" the journals inside the bearing inserts.

That is why oil pressure is so critical - that and keeping the lifters pumped up. It doesn't take more than 1 or 2 PSI - if the flow is of sufficient volume - to push oil to the upper areas to lube the valve train. It takes significantly more pressure than that to keep the journals "floating" on a cushion of oil - including cam journals.

I agree with that, it just sounded to me at first that there WAS metal to metal contact until oil pressure picked up when you start an engine. i see now we are on the same page i just miss read some.

 

[sassyrel]

If your pyro probe is post-turbo (like mine) you have to adjust that number downwards about 100*F to allow for cooling of the gasses as they pass through the exhaust pipe and turbo impeller.

Just like a cutting torch, where the heat alone doesn't do the whole job of cutting through the metal, the extra O2 at high pressure aids the process. In the cylinder of these old motors at running at 22.5:1 compression (6.9) and 21.5:1 (7.3) the extreme pressure at TDC can help the heat to blow-torch a hole through the top of the piston if the temperature of the piston top is allowed to get too high.

Just my $0.02[/QUOTE]--///////////////your suppose to adjust the number 300 deg if its post turbo----and ya, thats the reason a turbo engine would take out pistons quicker--is because of way higher compression, and the pressure of the turbo---aluminum gets soft before it acually melts, and thats when the piston lets go-----------and this happens in about 150 degree range --from solid to melt

 

[Agnem]

...The 83 may be an exception to that - isn't that the first year for the Navstar in Fords? I've also read that the 83 IP is different and had the "index" pin for the drive gear in a different location.

Yes, first year in Fords, but not in Internationals. The 6.9 came out in 1982 in IH trucks and busses. Not true about the index pin. That's the same on all of them. 83 and 84 model A engines have the lowest compression of the family. This was increased in later models in an attempt to meet the emissions goals.

 

[Cheaper Jeeper]

your suppose to adjust the number 300 deg if its post turbo----and ya, thats the reason a turbo engine would take out pistons quicker--is because of way higher compression, and the pressure of the turbo---aluminum gets soft before it acually melts, and thats when the piston lets go-----------and this happens in about 150 degree range --from solid to melt

WOW, 300*? Really? Will it cool that much that fast? I may have been running mine in the "danger zone" a little bit.

EDIT: I just did a little more research and came across a couple of bits of info comparing temp drop (post turbo) to boost...

"The valves are of most concern and if they reach 1800ºF you can expect to be very concerned. This happens when the exhaust manifold temperature (pre-turbo) rises to ~1350ºF and most people will agree to a max limit of 1250ºF..."

"...At 2-5 psi there is a 50-100-degree drop. At 5-10 psi there is a 100-150 drop. At 15-20 psi it can drop up to 350...." This opinion has also been verified by testing done at Banks..."

So since my Banks won't make more than about 10-12 PSI max, it looks like my "safety factor" number should be about 150*-200*. That equals 1050*-1100* on the pyro.

BTW, I'm going to have to double-check, but I am 99% sure that the manual for my Banks said that 1150* was the safe number based on where the probe installs (in the inlet sid of the snail).

Of course that is the number for continuous running and can be exceeded a bit for short periods of time without doing catastrophic damage. Nevertheless, I think I'm going to have to start watching it more carefully. Even short periods of time excceding those numbers can't be good if it is done too often...

SECOND EDIT: I dug out the maintenance & installation manual for my Banks kit and looked it up. Per Banks EGTs up to 1150* are safe with the probe mounted in the snail. So the "agreed upon" safe limit of 1250* and the Banks spec of 1150* is where I got the idea that the adjustment is only 100*. Where the difference comes in is the fact that with the Banks setup the probe is in the inlet side of the snail housing, so technically it isn't really pre-turbo OR post-turbo. More like IN-turbo