hillbilly deluxe
Professional Pile-It
Any reason a guy couldn't just tap and thread a hole in the exhaust manifold for a pyrometer? I've been reading the closer to the engine the better for accurate EGTs.
CK5
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Tap the manifold
- Thread starter hillbilly deluxe
- Start date
DEMON44
Low-Tech Redneck
thats exactly where it should be. pre turbo.
Just remember, the thicker the better for the location you choose.
hillbilly deluxe
Professional Pile-It
I went to a shop in town and they said it would be fine to tap the manifold. The guy showed me where his is tapped in on his Cummins manifold. The easiest place looks to be the end of the driver's side manifold. EGTs should be the same each side. It'll be at the end of the manifold so it reads all the cylinders.
hillbilly deluxe
Professional Pile-It
There it is. At the end of the driver's side manifold. Also put in boost and fuel pressure. Interesting to drive now. These gauges are much more responsive than I thought they would be. I thought the EGTs would rise and fall slowly, more like the temp of the manifold. Not so, they are all over the place depending how I'm driving. With a little test drive I was able to get the EGTs to 1250 deg. going uphill empty with WFO throttle(boost showing 7 psi max). That suprised me, I have read that 1250 is danger temp and I didn't think I would be able to get there without a load on. I didn't sustain that though, I was not on a long/steep enough hill. I think of all the times I have driven it over tall steep mountain passes either empty going 75 or fully loaded with the throttle mashed and wonder how high I ever got that temp.
hillbilly deluxe
Professional Pile-It
I hit 1500 deg running WFO (empty) over Vail (10,554 ft) and Eisenhower (11,112 ft) passes this past Fri & Sat. Went to Banks website and they say 1250 to 1300 is okay sustained.
Whadayall runnin?
Also, I saw the boost gauge jump to 10 psi a couple times at the top of Eisenhower pass coming back from Denver. Figured the wastegate must have been hot and stuck closed a bit. I have never seen it go above 7 psi other than that. I was thinking about jamming the wastegate shut just for fun.....lol
Whadayall runnin?
Also, I saw the boost gauge jump to 10 psi a couple times at the top of Eisenhower pass coming back from Denver. Figured the wastegate must have been hot and stuck closed a bit. I have never seen it go above 7 psi other than that. I was thinking about jamming the wastegate shut just for fun.....lol
DEMON44
Low-Tech Redneck
if you pull up high like that often, be wary of the turbo. you can overspeed it very easily at those altitudes. overspeed and the compressor wheel will come apart fast.
hillbilly deluxe
Professional Pile-It
Thin air? I don't understand how it could overspeed. Shouldn't it be limited by how much exhast comes out? I ran over those passes again last week and drove by the pyrometer. Had to down shift where I hadn't been before. I probably ran 5-10 mph slower watching EGTs.
MaxPF
1/2 ton status
As you gain altitude the air gets thinner. In order to generate the same amount of boost (in absolute pressure terms) you have to spin the turbo faster. If you're already running near the edge of the turbo's capabilities you can end up overspeeding. I doubt you are that close to the limit on a GM series turbo at only 7-10 PSI though.
There are three ways to lower your EGT's that don't involve defueling: Put on a more efficient turbo, increase boost (this one is maybe - it only works if you're underboosted, and assuming doing so doesn't put the turbo's compressor in a less efficient area of its map and the drive pressure doesn't get excessive - both are problems with a GM series turbo), and perhaps most importantly is charge air cooling, either with an intercooler or water/alky injection. None of these 3 methods are mutually exclusive. They will all affect other parameters. For example, a more efficient turbo lowers both charge air temps and reduces exhaust drive pressure (backpressure). Increasing boost generally raises charge air temps and increases drive pressure, but the extra air can help moderate cylinder temps and EGT's to a point (until the charge air temp gets too high) There is usually an optimum level of boost for any given turbo and engine combo that gives the lowest EGT's, while boost above or below that amount will raise EGT's. Intercooling or water/meth injection (chemical intercooling) is always a win-win. You get a cooler, denser intake charge, and EGT's always go down as charge air temp goes down.
hillbilly deluxe
Professional Pile-It
7 psi seems under-boosted to me. The new Fords I drive at work run up to 40 psi stock. I drove semis for a couple years, too, and they all ran 30 or 40 psi. I understand the 6.5 has higher compression though and that has something to do with how much boost can be applied. Not to mention all those vehicles had intercoolers. Intercooling makes alot of sense to me. I was thinking about an adjustable wastegate. I wonder how much intake temps have to rise to see a difference in EGT. Makes me want to monitor intake air temp!
MaxPF
1/2 ton status
High compression IDI engines like the 6.2/6.5 and Ford 6.9/7.3IDI can't tolerate as much boost as a lower compression DI or IDI engine. This is due to the way adiabatic (isentropic) compression works. As the air is compressed, the energy expended is converted into heat, which causes the pressure to increase beyond what would be accounted for by the simple mathematic ratio of the engine's compression ratio.
[deep $hit physics mode]
As an example, I will use a cylinder with exactly 1 liter of volume (everything will be done in metric, but I will give Imperial conversions where necessary) and an 18:1 compression ratio. For simplicity, we will assume a standard pressure of 100kPa (14.5psi, near sea level) and a standard temp of 21C (70F). We will also assume the compression is truly isentropic. In a real system there is always losses, but since the compression in an engine happens rapidly it can be considered an approximately isentropic system. If you calculated the pressure as a simple 18:1 ratio you would assume the resulting pressure at TDC would be 1800kPA(261psi). If no energy was added (or the gas was cooled back down to it's 21C starting temp) you would be correct. However, remember that work is being done to the gas when you compress it, so energy is being added in the form of heat. When compressed adiabatically at a ratio of 18:1 (again, assuming no losses), the resulting pressure in the cylinder at TDC is 5669kPa (822psi). The temp is an impressive 658C (1216F).
Now lets assume our same cylinder has a compression ratio of 21:1, which is approximately what a 6.2 has. At TDC, the pressure will now be 7117kPa (1032psi), and the temp will be 721C (1330F).
The difference in compression between 18:1 and 21:1 is 16.6%. The difference in temperature at the end of compression between the two CR's is only 9.5%. The pressure increase, OTOH, is 25.5%.
If we add boost to the situation, it gets even more severe. Let's assume we add 100kPa (14.5psi) of boost to the 18:1 engine. Now, at TDC we will end up with a pressure of 11452kPa (1660psi) and a temp of 661C (1222F). In the 21:1 engine we would have 14235kPa (2064psi) and 721C (1330F). You notice that, as long as the charge air temp is the same there is no increase in temp between the unboosted and boosted versions (the small change in the 18:1 example is due to my rounding in the calculations), but there is a doubling in cylinder pressure, which is to be expected.
If we do a bit more math we find that we can increase the boost to 150kPa (22psi) on the 18:1 engine before we reach the same approximate TDC pressure as the 21:1 engine. In other words, a reduction in compression of only 14.3% lets us increase the boost by 50%, given the same peak pressure limitations.
[/deep $hit physics mode]
Keep in mind that the 6.2 is a light duty engine, so it can't handle as high peak firing pressures as, say, a Powerstroke or Cummins. That and differences in compression ratio (DI engines like the PS, Dmax, and Cummins have lower compression) is why you are limited to 10-15psi in the 6.2 and 6.5.
Whether 7psi is underboosted depends on different variables. If there is no smoke, then you aren't underboosted from an A/F ratio standpoint. However, as you saw above, assuming the inlet air temp remains the same (i.e. good intercooling), increasing boost will put more air into the cylinder without increasing it's compressed temperature. Since the injected fuel now has to heat a larger mass of gas the peak temps, and hence EGT's, will be lower. Hot boost, OTOH, will make cylinder temps go up. A 100C increase in charge air temp makes the TDC (pre combustion) cylinder temp increase 300C! So, yeah, intercooling helps a TON!
hillbilly deluxe
Professional Pile-It
Hey thanks alot for the great info, I eat that stuff up! It's a good post that everybody will find useful. The truck smokes alot but I have yet to replace the injectors and timing chain. I have to "normal up" the motor before I apply any expirimentation just so I can sleep right.
