SPR1NK
Full Access Member
So another question then, does the engine that I'm hopefully getting being bored over .030 change the compression?
compression question for possible 6.9 build
- Thread starter SPR1NK
- Start date
IDIoit
MachinistFabricator
PwrSmoke
Full Access Member
Boring will increase the compression ratio slightly but the piston manufacturers compensate by moving the piston pin a slosh closer to the crown.
PwrSmoke
Full Access Member
Please explain this? First I've heard. My engine has had a turbocharger since 7K miles.
FordGuy100
Registered User
Why is this such a complex issue?
10 years ago, lowering compression was a horrible idea. We had one sound clip of a DPS truck trying to start, and is scarred everybody away from it. Now there are at least a few lower compression IDI's running around, and they all seem to start fine. If your going to drop compression considerably, and you live in a cold climate, you should address this by running a block heater.
We have come a long way since I first started reading about these trucks.
Before even considering lowering compression, you need to figure out what you are going to do for forced induction. Thats the only reason to lower it.
10 years ago, lowering compression was a horrible idea. We had one sound clip of a DPS truck trying to start, and is scarred everybody away from it. Now there are at least a few lower compression IDI's running around, and they all seem to start fine. If your going to drop compression considerably, and you live in a cold climate, you should address this by running a block heater.
We have come a long way since I first started reading about these trucks.
Before even considering lowering compression, you need to figure out what you are going to do for forced induction. Thats the only reason to lower it.
PwrSmoke
Full Access Member
You're talking like this is a new thing. It isn't. People have been playing with IDI diesel like this for decades. It's one thing to start a low compression IDI in a Phoenix winter and quite another to start one in Boston tonite. Or one at 10,000 feet in Leadville, CO. Lowering the compression allows you to increase the boost some.. but you pay a price. How big that is depends on where you live and how you use the truck. That's what people need to understand, the cost vs benefit aspects. I've seen the results of starting low-comp IDIs in cold climates, namely Missoula, MT. They get very cranky and you BETTER have a bulletproof glow plug system that you can glow for 30 seconds at a time, or more. Or have a can of ether handy.
FordGuy100
Registered User
No, it isn't new. But since the forums came around the talk of lower the compression on an IDI was thought of as being crazy. We had that one sound clip of Kens truck starting, and nobody even thought about lower compression. Now, we have more people doing it, for higher boost.
As in, a decade ago we knew of one low compression truck. Now I know of at least a couple, if not more. And those seem to start perfectly fine. I'm going to find the one video of Justin's truck starting with a single group 31 battery.
IDIoit
MachinistFabricator
Sir AxleRod
Full Access Member
What did Justin drop his compression too?
IIRC, he had the ultimate high hp build, his numbers were neck and neck with the numbers of the new Cummins' I sell, but his were at the tires, not the flywheel.
If by Justin, you mean bigbadbII or whatever his screen name was, Justin Wheeler was the full name. His ostracism, tainted my opinion of the forum ... seemed like if you speak ill of King Agnem and the knoghts of the IDI round table, off to the gallows...
While I respect the opinion, and like many of them I lumped in that category, Dog Catcher, Old Bull, icanfixall, etc, have been around these engines for a long long long f***ing time, so, while their opinions need respected, there is also room, to a certain degree for new thoughts.
As the final caveat, he ended up going 12v in that truck, so..... who ultimately, was right? the nay sayers, or the I'm doing it my way guy?
I'm sure things are different now, and there will be Moose under my hood, but that was the impression i got back in the day....
IIRC, he had the ultimate high hp build, his numbers were neck and neck with the numbers of the new Cummins' I sell, but his were at the tires, not the flywheel.
If by Justin, you mean bigbadbII or whatever his screen name was, Justin Wheeler was the full name. His ostracism, tainted my opinion of the forum ... seemed like if you speak ill of King Agnem and the knoghts of the IDI round table, off to the gallows...
While I respect the opinion, and like many of them I lumped in that category, Dog Catcher, Old Bull, icanfixall, etc, have been around these engines for a long long long f***ing time, so, while their opinions need respected, there is also room, to a certain degree for new thoughts.
As the final caveat, he ended up going 12v in that truck, so..... who ultimately, was right? the nay sayers, or the I'm doing it my way guy?
I'm sure things are different now, and there will be Moose under my hood, but that was the impression i got back in the day....
Last edited:
Sir AxleRod
Full Access Member
[hi-jack]Ultimately, I'd runa pump with a 4500 rpm spring, find valve springs to support that, and then a triple set up, stopping at 20-30 psi, whatever the Grand Poobah's thought was max with studs it could handlewas.
The beauty to the triple, is the two itty bitty fawkers, that lit off idle, and pissed out at 10-12 psi, fed the larger one, so the rig acted more like it was super charged.
I'd ideally have a relaible 350/700 at the crank, just drove a 6.7 Cummins back from Ogden, factory tune is 350/650, that was ***.... and drive happily ever after, tearing it down every 100-150,000 miles.
Whether that is a realistic goal or not, I don't know, and don't even comprehend tubo logic enough to accurately predict or build that, so it remains a pipe dream.[/hi-jack]
re-edit for an addendum:
The compression ratio would be left stock at best, head work, and a decking would ensue, and furthering out the wet dream, if there were a nautical 6.9 ever made, I would change every bearing, etc. to the nautical parts for the rebuild. At least in a gasser, the nautical stuff is full roller, and designed to run WOT 24/7.. seemingly, that would make a holocaust proof IDIt.
The beauty to the triple, is the two itty bitty fawkers, that lit off idle, and pissed out at 10-12 psi, fed the larger one, so the rig acted more like it was super charged.
I'd ideally have a relaible 350/700 at the crank, just drove a 6.7 Cummins back from Ogden, factory tune is 350/650, that was ***.... and drive happily ever after, tearing it down every 100-150,000 miles.
Whether that is a realistic goal or not, I don't know, and don't even comprehend tubo logic enough to accurately predict or build that, so it remains a pipe dream.[/hi-jack]
re-edit for an addendum:
The compression ratio would be left stock at best, head work, and a decking would ensue, and furthering out the wet dream, if there were a nautical 6.9 ever made, I would change every bearing, etc. to the nautical parts for the rebuild. At least in a gasser, the nautical stuff is full roller, and designed to run WOT 24/7.. seemingly, that would make a holocaust proof IDIt.
Last edited:
Sir AxleRod
Full Access Member
but for that money, one could doa DT360/Ford401/6BT/6bd1t instal, and have a much simpler recipe to 4 figure power, if they so chose.
Black dawg
Registered User
No. The FACTORY turbo engine used a heavier rod, so possibly a different balance.
Sir AxleRod
Full Access Member
Hey.. ^ my name sake... (I was BlackDog once... I miss that Lab)
79jasper
Chickenhawk
Correct on Justin wheeler/NMB2
And actually he didn't swap the cummins in. Was going to, then sold it and bought a mustang.
But Justin anderson/RacinNdrummin is still doing all the idi stuff, along with selling performance parts.
Sent from my SM-T537R4 using Tapatalk
icanfixall
Official GMM hand model
King Agnem.....
I think your the one putting him on a pedestal. Not the rest of us. Back in the day seems a vague term. As time flows on we come to opinions that differs from the main stream. But the truth never changes. For the most park we correct whats not exactly correct here. This is a family forum. I have nearly 22,000 posts helping others. I rarely ask questions. I don't know it all. I do look at a postes count too when I try to help them. Making fun of a member with less than 50 or 100 posts is not something I will not stoop to either. Had Mel been able to keep all the posts he lost over on the "other site" he would be up near 45,000 posts. I have learned so much from Mel and many others on this forum. There was a great guy on the other site named CDSAIRGUY. and another named Fred Hemer. They really knew what they were talking about. I looked up to them and still do. those of us mentioned here by this new member are not heros. We are simple owners of what pleases us. We are not experts. Remember experts built the Tiananic and an amature carpenter built the ARK.
I think your the one putting him on a pedestal. Not the rest of us. Back in the day seems a vague term. As time flows on we come to opinions that differs from the main stream. But the truth never changes. For the most park we correct whats not exactly correct here. This is a family forum. I have nearly 22,000 posts helping others. I rarely ask questions. I don't know it all. I do look at a postes count too when I try to help them. Making fun of a member with less than 50 or 100 posts is not something I will not stoop to either. Had Mel been able to keep all the posts he lost over on the "other site" he would be up near 45,000 posts. I have learned so much from Mel and many others on this forum. There was a great guy on the other site named CDSAIRGUY. and another named Fred Hemer. They really knew what they were talking about. I looked up to them and still do. those of us mentioned here by this new member are not heros. We are simple owners of what pleases us. We are not experts. Remember experts built the Tiananic and an amature carpenter built the ARK.
Last edited:
