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Pre Cups

If you remember my response to one of your first posts here I said I thought it might partially be a factor. That's when I thought you were running more cc's at 120 I think gains would be negligible when you get up to the 180 + range is when I think your going to see more improvement. I base this on the changes GM made an others have observed when trying to run the older smaller precups with more fuel. I also did a fair amount of research on precups/swirlchambers. That by no means makes me an expert but better educated on the subject than alot of people. I don't mind strong debates as long as everyone remains civil. People can read alot into what is typed
 
I wouldnt say we have no experience, that is a generalization. I have been monitoring power impressions, how the larger turbos feel with different engine configs, some precup experiments that have been done already, and another 6.2 precup engine that wont run 70cc without black smoke and high EGTs under 17+ psi of boost under load, but runs just fine at 65cc of fuel, no issues at all. Whereas 12psi of boost would have cleared the smoke and EGTs on an otherwise stock 6.5 turbo engine. There are other projects with more tid bits of knowledge that is more than nothing to base the theories on. So you dont have to just believe that GM did it for no reason.
 
ak diesel driver said:
I don't believe it was done entirely for CR drop there seems to be a ratio of how much volume of the precup vs squish area. and when you turbocharge you need a bigger precup volume to keep the ratio in balance
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The squish area plus precup makes up the entire combustion chamber that is the 1 factor in the XX:1 compression ratio. So any change to the precup volume lowers the CR, which will lower cylinder temps as well. It could also be done to help burn more fuel volume, more precombustion.

On some level though, since they started the 6.5TD with high CR, almost same as the NA, and experienced so many engine failures, and blown head gaskets that I imagine they desired to lower the CR. Additionally the mouth ended up being so wide that they had to take material off the walls to make it fit right. So it is anyones guess what GM's primary intent was with the precup mods, but its no coincidence that the mouths increased in size with power rating increases, and with emissions exempt vehicles comparatively.
 
buddy said:
I wouldnt say we have no experience, that is a generalization. I have been monitoring power impressions, how the larger turbos feel with different engine configs, some precup experiments that have been done already, and another 6.2 precup engine that wont run 70cc without black smoke and high EGTs under 17+ psi of boost under load, but runs just fine at 65cc of fuel, no issues at all. Whereas 12psi of boost would have cleared the smoke and EGTs on an otherwise stock 6.5 turbo engine. There are other projects with more tid bits of knowledge that is more than nothing to base the theories on. So you dont have to just believe that GM did it for no reason.
Click to expand...

I'm not generalizing "you" as in the "gm IDI guys".... You guys are more innovative than the 6.9/7.3 crowd for the most part by far... which is why I find myself continuing to come over here.

Black smoke, and EGT's also are largely, and primarily controlled by your pump calibrations and timing. Turning the max fuel screw changes your WOT calibrations.

Example would be my truck right now with a stock maxed out DB2..... WOT 72cc's of fuel I can hit 23psi, and 1,000*.... black smoke and its slow as dog crap.

My DB4... 120cc's of fuel and 30psi boost... 1,150* and a light haze.
 
you can see in this picture exactly how the pre-cups fire, and how wide..... you can also look at the piston to the right, and see how clean and even the burn/combustion is across the piston.

IMG_3244.jpg
 
also interesting to note the clean edges of the pattern on the normal cyl must have more velocity or heat there
 
And why wouldnt you want the flame to be a little wider on the piston, the more area that you apply a pressure the greater the force it exerts. And the wider it is, it may mix with oxygen in the cylinder quicker, faster exposure.
 
nmb2 said:
Black smoke, and EGT's also are largely, and primarily controlled by your pump calibrations and timing. Turning the max fuel screw changes your WOT calibrations.

Example would be my truck right now with a stock maxed out DB2..... WOT 72cc's of fuel I can hit 23psi, and 1,000*.... black smoke and its slow as dog crap.

My DB4... 120cc's of fuel and 30psi boost... 1,150* and a light haze.
Click to expand...

Oh believe you me, the pump mapping and timing advance was tweaked every which way, and this would easily work on normal 6.5 turbo engine out to 100cc.

When I run loaded I get no haze at all, and I usually think of any haze as some inefficiency in the combustion. Might be surprised what a little larger precup may do to clear that up :hihi:
 
buddy said:
And why wouldnt you want the flame to be a little wider on the piston, the more area that you apply a pressure the greater the force it exerts. And the wider it is, it may mix with oxygen in the cylinder quicker, faster exposure.
Click to expand...

You would need to change the piston to match it. Also, you do not get your power from the flame front coming out of the pre-cup and hitting the piston. You get your power from the 'secondary' combustion that takes place in the main combustion chamber.
 
still under construction and those are lower compression pistons. they're sold by Kennedy diesel. I'm sure there's someone out there running them but don't know of anyone
 
ak diesel driver said:
still under construction and those are lower compression pistons. they're sold by Kennedy diesel. I'm sure there's someone out there running them but don't know of anyone
Click to expand...

Interesting. I find it depressing that the 6.2/6.5 market has such support, but the 6.9/7.3 market doesn't. My best guestimate is that the Powerstroke came out in mid 94 to replace the IDI whereas the 6.5 ran so much longer....I'm guessing that's when its performance base started, to help play catch up with the PSD and CTD.

We have the 1200hp hypermax 7.3 that was built.... other than that..... nothing.
 
ak diesel driver said:
your fixing to change that aren't you?
Click to expand...

Sort of. This is a hobby for me.... I'm actually going to work for a diesel company that doesn't support IDI's when I ETS, so it's not like I have much to gain.

There isn't a bunch of money to be had because IDI owners are usually cheap. I have to charge at least $3k to build someone a turbo kit, and that's hard for a lot of people to swallow, which is exactly why I haven't sold one, or spent the time building a jig to produce them. Its also why our engines have no aftermarket support... cheap ass owners.

I'm currently working with someone that has a bolt-on banks kit. I want to outfit a 6.9/7.3 with only head studs, a 120cc DB4, my cam, intercooler, and a bolt on turbo kit to see what would happen. If that worked out... getting 300/600 from a ford IDI would be a cake walk, and fairly cheap.
 
I wish we had the longer stroke like you guys so we could produce more low end torque for towing. It is nice to have that higher rpm punch tho too. LOL I want it all
 
The IDI Ford cups.. Did they see sort of an evolution through the years similar to our 6.2/5's? Any pics floating around?
 
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