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Reading your post on altitude effects with interest. So if you live at altitude and stay with normal gaskets / compression, doesn't it follow that your "normal" compression ratio of 21.5:1 acts differently as well?
You in essence have lower compression already and so at altitude could theoretically afford to run slightly higher boost?
When you travel to lower altitude it would be an issue.... not sure if boost controllers are a possibility
Reading your post on altitude effects with interest. So if you live at altitude and stay with normal gaskets / compression, doesn't it follow that your "normal" compression ratio of 21.5:1 acts differently as well?
You in essence have lower compression already and so at altitude could theoretically afford to run slightly higher boost?
When you travel to lower altitude it would be an issue.... not sure if boost controllers are a possibility
That is absolutely correct Ken. The compression ratio never changes (volume is volume) but because of the air density they cylinder pressures are lower. At 7,000' they are ~81% of what they are at sea level, and the engine will behave like 19:1 at sea level. If I always drove at altitude I could indeed get away with higher compression and not worry. But an hour and a half drive down the hill to Phoenix and I could potentially damage something.
Since the air is less dense at altitude, it follows that the boost pressure generated by the turbo will also be less. It is, but not by such a predictable amount. The efficiency of the turbo is affected by the drive to boost pressure ratio and air temperature. Turbos help even more at altitude than they do at sea level because the pressures are lower. The higher the pressures get, the less efficient the turbo system is.
Boost control is definitely a possibility and is done in a couple of different ways. The oldest and most simple way is turbine housing size. The specification is called the A/R, or area ratio. The larger the number, the less restrictive the housing is. Restriction is what drives the turbine, so a small A/R (say .76 on an IDI) will spool quickly and provide good boost at low rpm's. However, at high rpm's the exhaust volume increases and has to pass through the same restriction. The exhaust back pressure (aka drive pressure) becomes higher than the boost pressure and can be equally damaging to the engine as high boost. If you pick a larger A/R (say 1.10 on an IDI) it won't spool as fast low down, but will be less restrictive at the top end. It will be able to flow more volume, provide more oxygen, and will be capable of more peak horsepower.
The normal compromise if you want a turbo that spools fast at low rpm's but won't be overly restrictive higher up is to use a waste gate. Basically, you use a small A/R turbine for fast spool, but once a certain boost pressure is reached, a port will open up on the turbine housing to bypass the excessive drive pressure. You don't get quite as much top end performance as a larger turbine, but it prevents overboosting and high drive pressures. A wastegate is usually part of the turbine housing itself, but you can drill and tap in an external wastegate.
Internal wastegate design
External wastegate design
The more modern solution is known as a VGT turbo (variable geometry turbine). These have metal blades like a camera lens iris to change the A/R of the turbine itself. These are slick, but as you can imagine, something has to control the veins. On mondern diesels input from the mass air flow sensor, boost pressure sensor engine rpm etc., feed into the engine control module to regulate the turbine geometry. A few guys have used Dodge Holset VGT's on their IDI's and devised mechanical ways to control it such as spring pressure, manual choke cable, and some stand alone computers. The results for us IDI'ers have been sub par. We get better results from newer turbos with improved wheel and housing designs.
So.... back to my build. I'm keeping stock compression. Mark Strock on the Facebook group uses the decompression gaskets and confirmed that his truck did run a little smokey when driving in the mountains. He said the power was good, but it was smokey (=power left on the table). The turbo rods and pistons should be able to handle anything my pump and turbo can throw at it. However, if I see boost numbers trying to exceed 40psi I will not be comfortable with it. I will have to see if my set up generates more than that. If I really have to lay into it for a long period of time to build 40psi I won't worry about it. I can just watch my boost and control it with my right foot. If I find that it hits 40psi easily, I can try advancing the timing a little. This will build less boost. If I still have problems, or don't like how it acts with more advance then I it will be wastegate time. I would have a lot more to worry about with NA rods. I know the turbo stuff if good to over 40psi, but you start to see valve issues, and general longevity concerns. I want to be able to use the power, but getting too greedy will result in a short road to the auto graveyard. 250 wheel horsepower is about all you want to employ while towing. I know I've said this already, but my goal with the bigger pump and turbo is to raise the whole curve more than raising the peak number. i.e. Higher hp and higher torque at lower rpm's.
I finally have an update to share on this project. My block sat at my machinist’s shop for around 10 months. I won’t get into it too much, but let’s just say at the end of the day I have a superb block minus the rain water pitting which cleaned up at .020” over. My machinist has it rough bored, and as soon as he gave me confirmation on the piston size I placed an order with R&D. Justin is now a Mahle dealer, so I was able to get a good price on the turbo pistons, and I ordered the ceramic coating, and the Total Seal 2nd ring set. Once these arrive, my machinist will mic them and make the final bore at the correct clearance.
I dropped off the cylinder heads and I will be sourcing some valves and stem seals next week. Originally I wanted a full set of stainless valves, but my source for them is not getting back to me. My heads look nearly perfect, so I think I will just upgrade the exhaust valves to the OEM factory turbo type and call it a day. It has been a long wait, but some progress is now happening toward the engine build.
The other update I have is a change of plans regarding the drive train. I was at the junkyard looking for a small block ZF for my https://www.ford-trucks.com/forums/1981-straight-six-manual-4x4-project, and I ended up stumbling on a Doug/Nash dual range auxiliary overdrive unit instead. So my new plan is to use my Gear Vendor overdrive unit behind the close ratio T19 in my 1981 F150, and use the Doug/Nash (DNE2) unit in my diesel behind a close ratio ZF-5 rather than the wide ratio 460 ZF-5 as previously planned.
The main reason I want to use the DNE2 with the diesel is that it is a direct gear drive unit and can be left in high range at all times in all gears. The GVOD uses conical clutches, and has a speed interlock to prevent it from staying engaged below 25 mph (excessive torque force on the clutches at low speeds). I wanted the wide ratio ZF for a better start out gear, but I think the close ratio gear set moved up a notch will be even better. I can leave the .80 ratio DNE2 engaged and my truck will act like the 4.10 gears were switched to 3.28’s. I also believe the DNE2 may be stronger. The folks at Gear Vendor told me over the phone that the clutches were good up to 1,200 horsepower, but they don't have it drop out of overdrive under low speed high torque conditions for no reason. On the other hand, Justin has the DNE2 in his truck making north of 600 ft lbs. torque at the wheels and has put it through several truck pulling competitions.
The other pragmatic factor in this is that the GVOD is ready to bolt on and go, and I need to get my 1981 in service asap. The DNE2 on the other hand came from behind a C6 auto transmission, and the adapter housing was specific to that use. I will have to make my own adapter to replace the tail shaft housing on my Borg Warner 1356. This will take some time. Justin has the flanges drawn in CAD, and is going to burn me a set on his plasma table. I will have to source my own tube, and weld it together once I mock up the two gear boxes. Here are pictures from Justin’s build:
CAD model
My DNE2 also needs some repair. The shift motor is bad, and one of the long screws that holds the motor together fell out inside the gear box. A piece of the shift linkage fell in while I was inspecting it, so I need to open the the case for cleaning and removal of any bits of the bad shift motor. One criticism of using the DNE2 is that the manufacturer is defunct, and there is no longer any support. However, all of the bearings and seals are GM TH400 transmission parts, so the major wear items are readily available. There are also issues with the shift motor and the shift motor limit switch. These items, however, are the same parts used in Eaton 2-speed differentials for heavy trucks. These are also still available…. sort of. Mine is a later model DNE2, and uses a solid state controller with a shift timer in place of the limit switch. The shift motor uses an external electrical connector instead of the pair of leads by the motor shaft that go to the limit switch inside the case on earlier models. I have not been able to find the later style motor, and I don't know the Eaton part number. If I can't find it, I have a couple of options. I can ditch the electronic controller and buy the old style motor and limit switch, and regulate it with a bi-directional 3-pole momentary switch (Bronco rear glass up/down switch?). Or, I can keep the electronics and try to devise a way to route the wires through the holes in the case cover where the limit switch mounts on the earlier units (mine just has bolts in the holes). Obviously finding the correct motor would be nice, but if not I have options.
Egads! And I thought I had looooong posts. But, in all fairness, it wouldn't be as long if there weren't duplication.
Anyway, I think I understand. And it looks like the DNE2 is one stout unit.
And, things are moving on the engine, finally. Sometimes having the patience to wait turns out to make for an excellent solution. Looks like it will in your case.
Egads! And I thought I had looooong posts. But, in all fairness, it wouldn't be as long if there weren't duplication.
Anyway, I think I understand. And it looks like the DNE2 is one stout unit.
And, things are moving on the engine, finally. Sometimes having the patience to wait turns out to make for an excellent solution. Looks like it will in your case.
Yes, Gary, I was hoping to get my post fixed before anyone tried to read it, but you caught me....
When I started the thread I was using Photobucket. I could write the post on a word processor, paste in the photo links and submit a perfect post. But something happened at Photobucket, the resolution of all my images has gone to pot, the phone app wants me to turn on "auto backup" to do anything, and it's so congested with ads that it's impossible to use. So I started using the "mountain" icon in the FTE task bar (way better resolution than uploading to FTE albums). Only problem is you can't do it all before you post. Today I go to do this and the uploader launches a google ad services box that won't go away. The box covers a lot of the task bar as well as the submit post button. To upload images in between text you must upload one at a time, so I would insert a photo, copy all, then refresh the page to get rid of the ad box, then paste the contents and repeat for each image... arrrrg. See the potential for duplication error? "They" (whoever that might be), are sure making it hard to post images...
Regarding the build, I hope the rest of the machining is a little more timely... but known quality work is getting hard to find, and worth waiting on. That was one of the main reasons behind getting the 1981 and working it in ahead of the diesel. I don't want to be rushed to get it done right.
The inability to control things, like photo albums, is part of the reason I created my web site. IB thoroughly broke the ability to manage multi-page albums, which kills the ability to tell stories via albums. I've brought it to their attention several times, but they don't care. So, I started my own web site. And today I was approached by someone wanting to advertise on it.
Anyway, Rome wasn't built in a day, and a killer old truck seems to be just about as hard to build as Rome. Hang in there, it will be worth it.
Thanks! That is just a stock photo from the R&D website showing his ceramic coating service. My actual pistons are probably still in the process of being shipped from Mahle to R&D.
10-26-2016, 10:20 PM
