Well... I hate to rain on our parade here, but things may not be quite so rosy.
I just dyno'd my truck on Saturday, made 227HP - slightly lower, but right in the same range as what I've made before. This is with my Banks TE06H turbo, not my better one.
So, I managed to get the timing issued worked out; it runs decently, though the smoking when cold is really a concern of mine.... but that's just the nature of decompression, I guess.

What really worries me, though... For the last couple of weeks, after hauling a trailer with my truck, I'd shut the engine off and hear lots of air bubbling into the radiator reservoir(overflow).
At idle, no bubbles, so I figured it was just boiling or something.

However, after driving it /unloaded/ Monday, I came home(after a good hour of driving), shut it off... Lots of air escaping, lots of pressure in the radiator. And this was with taking it easy, no high revs, no high EGTs or water temps.

I've never seen this before, so it concerns me greatly. I'm wondering if I'm getting combustion gasses leaking by the gaskets somewhere. I don't know what else it could be.

 

Rob,


Concerning the gaskets, they work on Marks truck, however using them need perfect flat mating surfaces,cause they use steel shims on the outer surfaces. did u check that? I have a feeling you used one old head without any work done to it. Right? I wonder what the back pressure of the banks is at 20psi when it is out of efficiency being too small. The decompression gaskets are not made from Reinz extreme, so they withstand temperatures as regular gasket.
Yes smoke upon start up is the price for decompression plus IDI technology, it is normal. It is the compromise u have to make to be able to boost more without overstresing the engine. The 6.9 will throw gaskets at 30ish boost levels with stock compression.

 

Correct. And I'm not saying that the design is bad, just that I am having issues with it.
My old head I had on the truck with a stock-type gasket and no issues for a couple of weeks, so I figured it was probably just fine.
I guess I'll see when I take it apart.

I'm wondering whether these gaskets would work better with the two outer layers of shim removed, leaving just a single layer of steel in the middle, with the 'sealing' reinz material touching all surfaces. The fire ring might not be as well supported, but would still get some decent support from the middle layer.
Quite high... but I'll bet lower than what you'll get from a normal turbo hitting 45+ PSI.
I watch my EGTs, and haven't had any issues with standard FelPro/Victor Reins gaskets.

This is something I would have liked to know before installation, but that's the deal with being a beta tester. It is an important 'feature' to know when installing these gaskets.
Or, perhaps the solution is to ream out and install bigger bolts...

I'm thinking that there ought to be a good compromise in compression between stock and low enough that we are getting smoking when cold. It might be worth experimenting with slightly thinner gaskets instead. These just seem to be a /big/ jump. Perhaps removing the outer layers would be good enough?

 

Macrobb what bolts are you using, studs or stock?

 

Rob I do not say it is all the benefits this gasket, yes there are the other ways, shaving pistons. But the goal was to get a good gasket, capable of good performance without altering the engine components. Once u shave the pistons, it is ireversible, here you just replace the gaskets and you have stock engine. Imagine shaving pistons and not liking the cold smoke. Nothing to do about it. Yes here you change very expensive gaskets, but day later you are back to stock.
I talk with Mark Strock a lot and ask about the gaskets all the time how they perform, he claims to haul heavy all the time with no issues.
I am open to comments and critics, I would test the gaskets in my engine, but I do not have time, nor part if something goes wrong. However I can test vw, bmw and mercedes. The junk yards are full of those.


Sorry for the marked replies, I am useless with computers, comented to the quote so wanted to highlight the answer, otherwise nobody would notice, nothing behind it at all.

 

Macrobb, the additional smoke associated with decompression should not be that bad at 18:1 CR. Mark Strock's truck (with the same decompression gaskets) and Justin's 18:1-ish 6.9 Smogie engine did not smoke excessively. Think of it this way, the heat of compression is slightly less, so the amount of smoke would be similar to what you would expect during cooler weather than what your outdoor thermometer is reading. Once the engine is up to temperature there should not be any additional smoke. It should burn clean. Keeping the stock glow plug control system in place will help, as it is designed to cycle on and off to reduce smoke on a stock engine until the temperature comes up. If you have a lot of smoke, I suspect you have a timing advance issue. 18:1 is still quite high, unlike a 12:1 ether-start diesel race engine that is going to be flat out dirty no matter what.

For others considering decompression, I encourage you to do some homework to decide if decompression is right for your build, and if so, how much to decompress. I don't have specific answers for what is best on our engines. We are learning from anecdotal evidence one build at a time. Learn how to calculate your static compression ratio and compare your build to what others have done.

Just for the sake of general understanding, here are a few talking points about decompressing a diesel engine... why it is done and what the benefits and drawbacks are:

1. The bottom line- it is done to reduce cylinder pressures that are high enough to cause damage. When you add fuel, you need to add air to burn it (boost). The more air you add, the higher the peak cylinder pressures will be. At some point the pressure becomes high enough to lift the cylinder head and blow head gaskets, bend connecting rods, and shorten the life of the rings, bearings, wrist pin bushings etc., Increasing the volume of the combustion space reduces the peak pressure spikes.

2. Decompression does not give you more power. It gives you less. If the head gaskets and engine internals can withstand the pressure, a higher compression ratio will give you more power than if you decompress. Decompression only becomes an advantage when it allows you to run higher boost (more air) to burn more fuel than you otherwise could without exceeding the limitations of your head gaskets and/or engine internals. That is how decompression gets you more power out of a given engine. Decompression does lower the torque. The high CR of the IDI is why it has such a high torque to horsepower ratio.

3. Static compression ratio is only one variable that impacts critical peak cylinder pressure. Valve timing (cam), ignition timing, burn rate (if methanol, propane or nitrous are involved) and air density (~=boost psi) are all very important factors. Lowering CR provides some latitude with the other variables but it carries a price. Peak cylinder pressure is a dynamic combination of variables, but in most cases decompression by one ratio point allows you to run 2-3psi additional boost while maintaining equivalent peak pressures. So a 18:1 IDI (decompressed 3.5 points) can run 7-10.5 more psi than a stock compression engine can handle.

On the user end of things, the loss of compression is felt the most under conditions where boost is not replacing the lost cylinder pressure (i.e., low rpm's). Low rpm's in a tall overdrive gear can feel particularly weak. Lowering compression will lower cylinder temperatures (thermodynamics of compressing a gas). This can result in hard starting and more smoke when cold, but it also means lower EGT's.

 

Once the truck is at operating temperature, it burns fine. It's cold starting that's smokey.
Either way, I understand why... I just want to make sure that anyone else getting these gaskets(or decompressing their engine, for that matter) understands that you will get smoke when cold.
For me, it won't burn fully cleanly until it's somewhere near 160F coolant temps - I can do a 'warm start' after sitting for a couple of hours and while I won't see too much smoke, I can definitely smell the non-clean-burn in the exhaust.

To me, anything beyond a quick puff on first cold start at 32F is excessive. So going forward, I will end up keeping a higher compression on my motor.

Also, yes, I've done all sorts of things with the timing. The lower compression on this motor has required quite a bit more advance compared to where it was, especially high in the revs. It probably also has something to do with the RD2-110 pump's limited hydraulic advance.

The real problem I have is headgasket leaks.
First, remember that these gaskets have been on this truck for a good month and a half now. I took my first real trip with them on the second of August(1,000 miles round trip), and I've got 2500 trouble-free miles on the engine.
So... Why now? I'm going to try to pull the valve covers off this weekend, see if the headstuds need to be retorqued. I put them at 120ft-lbs, per spec, but that might not be enough.

 

Keep in mind that the compression on Strock's truck is reduced less than on Rob's Truck. Strock is still probably around 19:1. a 7.3 with a .040" decompression is around 17.5-18:1 depending on piston protrusion.

I think decompressing a 7.3 isnt necessary until you are really going to throw some fuel at it... I bent 4 N/A rods and threw one from too much cylinder pressure, and I had no issue with the gaskets. The decompression gaskets are mainly for those guys running 6.9's and for 7.3 guys really pushing the envelope.

My bronco with a fresh 7.3 and .040" shaved pistons does the exact same thing as Rob's truck, its a bit smokey until its warm, then it cleans up, thats the nature of low compression and low injection pressure, get the precup hot, and it cleans up. My 7.3 needs lower compression, my original goal was 500whp, and now its going back together with a goal of 600whp.

As far as the advance goes, Rob, I think you are putting far too much weight into advanced timing, and thats half the issue you are having with the variation in your setups. These pumps advance with fuel, or the start of injection advances in otherwords. The 110 pump has a lot of roller to roller to get the fuel from a 2 plunger pump, and more roller to roller means it has a broad injection duration built in when WOT. The reason the dynamic timing is limited is not only to account the excess timing when WOT, but when the range is extended, port over port duration is reduced and it kills fuel volume. The 110 has always been a very temperamental pump on the stand (More so than something like a 150) because it has to be set up just right. Couple that with the fact that I have Never seen advanced timing make more power than retarded timing on the dyno, ever. In fact, this last run where I blew the Reinz gaskets, I did 424whp/725wtq, torque peak was at 3000rpm, and hp peak at 3200rpm, because my timing was locked out at 0/0 (far more advanced than a normal pump at WOT) with base timing at 11*. I have enough fuel for 575whp on fuel only, and it only did 424 because the timing was so far out of whack, the turbo didnt spool till it was too late and my numbers suffered. Timing is key in these engines with the way our pumps work, and less is always more on a turbo engine. The reason your setup may like more timing, is because you have significant volume, and a turbo that pinches exhaust flow like crazy...More timing will make a setup like that feel better, but your numbers will still suffer. Id bet a trimmer screw adjustment (turn it in almost all the way), timing at 6* pulse, and the turbo you got from Jonathan will make 50 more whp than your current setup.

 

Wait a second... Wouldn't that be the other way around??? If the gaskets add a given fixed volume to the combustion space, that volume would change the ratio less on the larger displacement 7.3, not more... No?

 

No, because the offset in prechamber size. The extra volume relative to the compressed volume is more on a 6.9 than a 7.3.

 

I'm not going to argue with you on peak numbers. You may be correct on all counts.

However... I am not going for peak, but usable HP. I drive around at 1700RPM unloaded, 2200 RPM ish loaded. If I have to sacrifice peak HP(which I will never use) for more usable low-end(which, I might add, is right at the bottom end of my current turbo, let alone Jonathans), well, that may be OK. This may be one of the reasons I haven't really appreciated Jonathan's turbo... So far, I was only able to get it to spool decently above 2200... and I won't be using the truck much there.

edit:
That being said, I will end up messing with Jonathan's turbo again once I get a set of turbo piping and an intercooler. ABS just won't hold up to the heat.

--------------------------------
Back to the original topic, today I pulled the valve covers. I found nothing obviously wrong.
I re-torqued the head studs to 120ft-lbs... all of them moved. Most like 1/8 of a turn, some more than 3/8. I'm guessing the gaskets compressed over time.
Either way, they will need to come off. After driving it a couple of miles, I was getting lots of bubbles in the radiator at idle, and I could actually feel it by squeezing the upper radiator hose, as a hard "pulse".

 

Justin, can you please help me understand this math? I'm still not getting it... both engines have a stock CR of 21.5:1 because the 6.9 precup chamber is proportionately smaller (18.34cc vs. 20.42cc on the 7.3).

So we know:

7.3 swept volume = 908.76cc
7.3 combustion space = 42.26cc
(908.76 / 42.26 = 21.5)

6.9 swept volume = 860.77cc
6.9 combustion space = 40.03
(860.77 / 40.03 = 21.5)

FelPro gaskets are 0.073" thick
Decompression gaskets are 0.110" thick

Assuming a fire ring ID of 4.22":
FelPro volume = 16.73cc
Decompression volume = 25.21cc

Combustion space ADDED by decompression gaskets: 8.48cc's

Now...

7.3 swept volume = 908.76
7.3 combustion space = 42.26 + 8.48 = 50.74cc's
908.76 / 50.74 = 17.90 CR

6.9 swept volume = 860.77
6.9 combustion space = 40.03 + 8.48 = 48.51cc's
860.77 / 48.51 = 17.74 CR

They are only slightly different, but I am still arriving at the conclusion that the 6.9 is decompressed slightly more than the 7.3 when the gaskets are used. What am I missing? How are you getting a CR of 19:1 on a 6.9?

 

Been a member or over two years, thought I would make a second post.

First combustion space is my new favorite term.

Second You are correct that the 6.9 ratio will lower more when the same volume of combustion space is added to both engine. 8.48cc in proportion to the swept volume in the 6.9 is larger then the 7.3 if starting out with identical compression ratios.

third your formulas are not quit right
compression ratio=(swept volume+combustion space)/combustion space.

so combustion space=swept volume/(compresion ratio-1) If I remembered enough of algebra correctly.

7.3 swept volume = 908.76
combustion space=908.76/(21.5-1)=44.33
lowered compression ratio= (908.76+44.33+8.48)/(44.33+8.48)=18.21 cr

6.9 swept volume 860.77
combustion space=860.77/(25.5-1)=41.98
lowered compression ratio=(860.77+41.98+8.48)/(41.98+8.48)=18.05 cr

 

^^^Thanks!!!^^^

Right you are... stupid mistake on my part...