Lowering compression,,,

[RabbitJockey]

so, your telling me that if the engine has 50psi drive pressure, its going to have the EXACT SAME PCP as a n/a with NO drive pressure?

i find that HARD to believe...

Off course PCP will not be the same, but you are dumping a lot more fuel into a TD to get 50psi EMP than what you are doing to an N/A with no EMP

im not disagreeing because excessive emp can be caused by a number of things, but wouldn't it be true that if you are running 30 psi boost and have an emp of 60psi (which is quite possible for people running too small of a turbo and way too much fuel)  then at tdc when the exhaust valve shuts it is leaving a very hot 60psi in the dead space of the cylinder. the piston will have to travel down 10-20 percent of the way before pressure equalizes and boosted fresh air begins to flow in.  but that is just quick math in my head  wouldn't that leave a bunch of hot and already burned air in there so on the next xompression stroke everything gets even hotter and the next injection will not have as much o2 so it will burn even hotter make pcp higher and higher.

[R.O.R-2.0]

Thats gotta be tough on the starter motor, almost 10 minutes to fire it up! I'm wondering if they have tried some pre-heating techniques. I wouldn't want to be breathing all of that smoke as it's a known carcinogen!

It was sort of running on its own most of that time, all the white smoke was from when he stopped spraying ether into it and wasn't warm enough to keep going on its own.

There is a video of a big pro stock tractor that takes about 3 cans of ether to get it on the track and backed up to the sled lol. They run really low compression in them to make them live.

usually around 14:1 compression..

[Blownoiler]

so, your telling me that if the engine has 50psi drive pressure, its going to have the EXACT SAME PCP as a n/a with NO drive pressure?

i find that HARD to believe...

Off course PCP will not be the same, but you are dumping a lot more fuel into a TD to get 50psi EMP than what you are doing to an N/A with no EMP

im not disagreeing because excessive emp can be caused by a number of things, but wouldn't it be true that if you are running 30 psi boost and have an emp of 60psi (which is quite possible for people running too small of a turbo and way too much fuel)  then at tdc when the exhaust valve shuts it is leaving a very hot 60psi in the dead space of the cylinder. the piston will have to travel down 10-20 percent of the way before pressure equalizes and boosted fresh air begins to flow in.  but that is just quick math in my head  wouldn't that leave a bunch of hot and already burned air in there so on the next xompression stroke everything gets even hotter and the next injection will not have as much o2 so it will burn even hotter make pcp higher and higher.

Good point Trevorbr, so an engineer would be able to work out what effect the residual exhaust gas would have on peak cylinder pressure, probably with the help of all operating parameters - in theory anyway. There are at least 2 ways to look at this scenario, I believe that the factory engineers use egr to lower peak cylinder pressure in order to avoid making too much N.O.X. (pollution), yet residual chamber exhaust gas is going to dilute and heat the charge! One of the newer pollution control devices is cooled egr, I think that the cooler egr allows more power to be made without causing an overheat condition in the engine, I believe that egr is only operated at part throttle conditions too, but I'm not up to speed on pollution control so am just thinking aloud!

[vanbcguy]

I believe that the factory engineers use egr to lower peak cylinder pressure in order to avoid making too much N.O.X. (pollution), yet residual chamber exhaust gas is going to dilute and heat the charge! One of the newer pollution control devices is cooled egr, I think that the cooler egr allows more power to be made without causing an overheat condition in the engine, I believe that egr is only operated at part throttle conditions too, but I'm not up to speed on pollution control so am just thinking aloud!

EGR reduces the amount of oxygen in the cylinder (exhaust gasses are very low in oxygen since it has mostly already been combusted), thereby reducing the amount of oxygen available to combine with the nitrogen naturally in the atmosphere.  It is only used at part "throttle" as during WOT you are trying to use all the displacement available to you, whereas you don't "need" the whole engine's displacement when you are cruising along at 15% max power.

Oxygen and Nitrogen will combine simply in the presence of heat, so yes the EGR cooler helps reduce the temperature and therefore the speed of that reaction.  Diesel exhaust also has more leftover oxygen than gassers do making the EGR cooler even more relevant.

On gassers EGR also helps reduce pumping losses since the EGR gasses don't have to be pulled through the throttle, reducing the "work" required to pull the piston down the bore.  That doesn't apply to diesels though since we don't have a throttle plate.

All this EGR theory though only applies at part throttle - at WOT you want to get all the spent gasses the hell out of the cylinder.  Partly because you need the cylinder to be full of oxygen-rich air for the next burn, but also because the exhaust gasses are HOT and the incoming cold air will cool things down.  So when we are talking about high drive pressures we are talking about peak operating power, where temperatures will be the highest and the risk of damage due to high EGTs will be the most prevalent.  An increase of 200° due to leftover hot exhaust can definitely make the difference!