ameristar1
The One Blue Thing
What are the structural weaknesses of the 6.9/7.3? I read the stickies about the block worm, but what breaks and why when turbocharging this engine beyond 15psi boost?
What are the Structural Weaknesses of the IDI
- Thread starter ameristar1
- Start date
icanfixall
Official GMM hand model
Really nothing if you have head studs and hard anadoised piston tops. Any boost above around 12 lbs is lost because the air charge going into the motor is around 300 degrees. The turbo baldes heat it up and anytime you compress a gas it heats up. So running an intercooler will get the job done. What boost are you thinking of running.. My motor makes 10 lbs of boost with a cranking compression of 530 lbs. Ken ran around 18 or 19 lbs without an intercooler on a street motor with very little piston damage over a long run. I forgot how many thousands of miles it went but it was impressive to say the least....
ameristar1
The One Blue Thing
Ok, here's what I am looking at. I saw the article on Heath Diesel's twin turbo 6.5 Chevy Bonneville truck that ran 153mph average speed across the flats. I called him up and asked him about what he did and was surprised at how much of the stock pieces he used to build the motor. Drives great, get's 30mpg, will go faster with an adjustment of shift points, 22psi boost on top of 22.5 to 1 compression.
Now the IH has a better block, decent heads and comparable compression, plus it's bigger. The fuel injection components are the same between the two motors. What would prevent the IDI from running 22-25psi of boost and live? If intercooling was used, along with a water/**** system, it should keep the egt's in check.
I noticed that most IDI's don't run a lot of boost even if they are built up, and I didn't know if it was because they scatter after a certain point or not.
Now the IH has a better block, decent heads and comparable compression, plus it's bigger. The fuel injection components are the same between the two motors. What would prevent the IDI from running 22-25psi of boost and live? If intercooling was used, along with a water/**** system, it should keep the egt's in check.
I noticed that most IDI's don't run a lot of boost even if they are built up, and I didn't know if it was because they scatter after a certain point or not.
Last edited:
Ironman03R
Full Access Member
Its because no one wants to push it... I have plans for a built 6.9 but I need to find the right turbo or turbos. Also, I dont care what everyone else says, but the stock IP cant push enough fuel for a high output engine. My pump has been maxed for years.
Running high compression with a lot of boost is not a good way to go. All we want is a lot of oxygen in there. If you can get it, without ungodly cylinder presure than that is the best. Unless you drop the compression in an IDI, you won't be able to get enough air volume in the cylinder to really make any HP. All you will get with high boost, is added strain during compression, and you'll probably squeeze a gasket out no matter how good the head studs hold. Piston wrist pins are the next problem area.
Ironman03R
Full Access Member
I agree, high comp and the IDI are 2 things we have against us. The Heath diesel truck is impressive that it runs 20+ boost with high compression, It can be done but I agree with Mel that it will put more strain on internals over time.
I eventually will be lowering the compression of that 6.9.
I eventually will be lowering the compression of that 6.9.
ameristar1
The One Blue Thing
Can the pump timing curve or camshaft timing be altered to compensate for higher boost? If the dynamic compression ratio (not static) were reduced, would that be enough to take the strain off the engine at the lower rpm levels? It doesn't make sense to me that with all the available displacement that an IDI has, even with a turbo that it can't break 300hp in a streetable, towable package without doing serious work to it. What is the missing part of the equation that is needed to get 300 or more hp plus the torque out of this engine?
icanfixall
Official GMM hand model
You really need to say "where" you want the 300 hp at.... Is it the crank or the rear wheels. Reason I ask this is because it makes a lot of differance. I dought there are any streetable 300 rwhp trucks on the daily driver roll. Banks "claims" that their sidewinder wastegated turbo will give you 264 hp at the crank. I really don't know if this is true. Remember they are selling sometimng. Lets say its true. Now add a Moose pump... Increase boost to maybe 16 lbs, drop the compression by running the Mahle low comp turbo pistons and run studs and an intercooler. Advance the timing to 9.5 degrees and of course heaveily port the intake and the heads. I bet you will have 325 to 350 at the crank. Now you still can run propane (grill gas) and water-methonel injection (window washer fluid). So if none of this gets your hp needs try some nox and someday the Moose mister injectors. I really don't know what all the above will get you but I'm sure it will get you going down the road quicker. We really don't have any aftermarket cams but some are trying a few with nice results and thats too bad. Maybe we could really gain some economy and hp from the cam industry. We just are not that big of a money draw....
ameristar1
The One Blue Thing
300hp at the wheels (360-375hp at the crank). Not quite 1hp/ci. Are the heads that restrictive? Any flow numbers available? If I am sounding quizzical it's only because I really want to get to the bottom of the problem about making this engine perform. Sizing up turbos and getting enough fuel doesn't seem to be the issue, nor rpm capability, because the injection pump can fuel to almost 5000rpms, it's just that it seems there's a bottleneck somewhere holding up the party.
Last edited:
Ironman03R
Full Access Member
In-Direct-Injection You lose power due to the design of the engine. These engines also use a rotory pump that has limited fuel metering capibility. The ports in the heads are huge on these engines, and you can port them. The whole problem is that these are old engines that were never meant to have a turbo or put out big power. I'm not saying it CANT be done, Tractor pullers worked with rotory pumps for years before the inlines came along but the mods that can be done for pulling kills your driveability.
Lower your compression, have a cam custom ground for your RPM limit, get a pump that can flow the fuel you need and a turbo to match it, then it should scream. Why hasnt anyone done it? COST. There is very little aftermarket for these engine and what is there is directed at the everyday driver that needs more A$$ to pull the 5ver, not the big HP junkies. Almost anything we need for these engines to make some power has to be custom made. You can thank Mel for his Pump he offers it seems to be what people are looking for, I'm looking forward to checking this thing out at the rally next weekend.
Lower your compression, have a cam custom ground for your RPM limit, get a pump that can flow the fuel you need and a turbo to match it, then it should scream. Why hasnt anyone done it? COST. There is very little aftermarket for these engine and what is there is directed at the everyday driver that needs more A$$ to pull the 5ver, not the big HP junkies. Almost anything we need for these engines to make some power has to be custom made. You can thank Mel for his Pump he offers it seems to be what people are looking for, I'm looking forward to checking this thing out at the rally next weekend.
ameristar1
The One Blue Thing
Thanx Steve, I looked at some of the previous posts on this site and there was a thread started about doing a hot IDI last year that airflo71 started.
Looking at IDI motors like the Mercedes Benz 5 cylinder modified by our European counterparts to produce 350hp and more and rev to 6000rpms on stock bottom ends shows that provided the necessary changes were done, the IDI does not have to be a limitation.
The fuel volume question: I was curious as to how much fuel it takes to make 1 hp, and it is something like 1.6-2cc's per hp. Can the rotory pump be modded to produce 200-250cc's of fuel?
Fuel curve and timing curve of the pump: The DB2 being all mechanical will have a problem with precise timing and fuel adjustments, unless someone knows how to curve the thing. The electronic DS4 with a custom program a possibility?
I am going to go to Garrett Turbo's site and make some calculations for airflow on the turbos.
The comment I often hear about tuning for power is that we have a tendency to overfuel our engines; good for the smoke show, bad thermally. Any thoughts?
Looking at IDI motors like the Mercedes Benz 5 cylinder modified by our European counterparts to produce 350hp and more and rev to 6000rpms on stock bottom ends shows that provided the necessary changes were done, the IDI does not have to be a limitation.
The fuel volume question: I was curious as to how much fuel it takes to make 1 hp, and it is something like 1.6-2cc's per hp. Can the rotory pump be modded to produce 200-250cc's of fuel?
Fuel curve and timing curve of the pump: The DB2 being all mechanical will have a problem with precise timing and fuel adjustments, unless someone knows how to curve the thing. The electronic DS4 with a custom program a possibility?
I am going to go to Garrett Turbo's site and make some calculations for airflow on the turbos.
The comment I often hear about tuning for power is that we have a tendency to overfuel our engines; good for the smoke show, bad thermally. Any thoughts?
Last edited:
Diesel JD
Full Access Member
No no, you want the mechanical DB4 pump not the POS DS4 pump. I'm going to if I eventaully get the time and money....build a 6.9, I invite anyone to steal my formulation... 18.5:1 custom made pistons to bolt to 7.3 IDI turbo rods and the bigger piston pin associated. Studs in the head and intake. Single non wastegated turbo and intercooler, straight through 4 or 5" exhaust. For the fuel, a DB2/DB4 hybrid pump with a smoke puff limiter to keep the thing streetable but able to be adjusted for max POWER. Moose Misters. All this will set me back 4-6K bucks. Gotta find the right truck to throw that at.
ameristar1
The One Blue Thing
Can you elaborate on the hybrid DB2/DB4 pump? What is it and what makes it better than going electronic?
Diesel JD
Full Access Member
Well, bear in mind its all about MY OPINION and Mel's Moose Pumps may even have as much potential. A DB4 is the mechanical pump that John Deere used on many of their off road tractors. It has 4 instead of two fuel delivery plungers( I think) and it has .0033" plungers as opposed to .0031" for a 7.3 DB2. If you have access to the hydraulic head from a DB4 for an 8 cyl application you can graft it onto at DB2 pump so it can easily be bolted onto a 6.9 or 7.3.
Ironman03R
Full Access Member
JD I believe the DS4 uses the same 4 plunger head, theres also different diameters of plunger avalible.
Similar threads
