ZephTheChef

I apologize in advance as this is likely to get very lengthy.

So the intercooling discussions and such have really got me thinking/debating with myself about what direction I want to go with the car next so I wanted to talk about what is going through my head and get some input/thoughts on it. What I really want to discuss is what really matters at the end of the day for producing power, and to what extent we end up chasing very small gains with expensive and complicated changes to the car.

I mean we're enthusiasts, we're going to chase the "best" setup to no end regardless of whether or not good enough is good enough. But within that mindset, I still try to prioritize as much as possible. I have a very limited budget compared to most of this platform in general...if cars weren't my only hobby and if I didn't pretty much build my own stuff I couldn't afford to play this game at all, so I really need to try and pin down what the best/really important things to focus on are. I am going to be on stock turbos for the foreseeable future, if not forever and I am starting to wonder if intercooling is really where I should be spending my time and money.

Don't get me wrong, I understand the importance and function of intercooling more than most and I don't underestimate the dramatic increases in air density that can be achieved...otherwise, why would I be considering two-stage, ambient then refrigerated intercooling in the first place? But I'm just wondering how far it really makes sense to go with it. Is good enough good enough? The question boils down to: If I have intake temperatures well enough controlled, and a high enough octane primary fuel that I'm not at risk of detonation and the computer is not pulling timing or boost, is there any significant benefit to further charge cooling? The obvious answer at first seems like yes, but when you think about it in-depth may well be no. The key word being significant.

If you pull up an air pressure, temperature, density chart (link at bottom of post), it's easy to see that at 20psi and 120 degrees F air is .160 lb/cubic ft. Say you have an A/C or ice box setup and you can get that air down to 40 degrees F, it's .188 lb/cubic ft at the same 20psi. 17.5% density increase, which would yield the same increase in mass air flow through your intake valves...so you'd go from say 600hp to 705hp, right? Well given a compressor that's not maxxed out, yes.

With that said, it is my understanding that these turbos are definitely the limitation on these cars. By that, I mean if you were to run them all out, boost pressure would spike nice and high and then fall off in the upper RPMs to a much lower pressure, indicating that the engine is already eating more air than the turbo can deliver at the target/peak pressure, so anything that we do to improve the breathing of the engine, including but not limited to increasing air density at the intake manifold by charge cooling would require more air mass from the turbo if the boost pressure remains constant.

Now, that would be great if it was like an intercooler pump and the turbo could deliver more air mass at lower pressures...but I'm almost positive that it can't. Most turbo compressor maps have peak airflow about 1/2 to 3/4 of the way up the pressure curve, and that falls off, sometimes rather steeply as pressure drops. How does that make sense that an air pump would deliver less flow at lower pressure than higher pressure? Well the reason is because just like anywhere else in the system the flow through an orifice is dependent on density (in this case mostly a factor of pressure), so choke flow at the turbo's discharge pipe changes with pressure...they are limited on the top end by the flow limitations at pressure of the compressor wheel (just like an intercooler pump would be) and on the lower pressure side by the greater relative pressure loss caused by restriction in the housing, with peak air mass delivery capability happening somewhere in between.

So the point is, I really am kind of thinking further charge cooling post-turbo (refrigerated/ice box setup) is *nearly* pointless for peak horsepower purposes (we'd have to see a compressor map to be sure, but most turbos don't deliver any more peak airmass at lower pressures vs the middle of their operating map), provided you are at the limits of the turbo, and that we are already on a fuel and at a temperature that prevents us from being knock-limited, thereby preventing the computer from pulling timing or reducing boost. Improving the volumetric efficiency of the engine by having good density at the intake valves, and a nice flowy exhaust (as much as you can with a turbo in the way) may put a bit more power to the ground due to lower pumping losses, but does not change the air mass that the system as a whole is capable of digesting.

So why do people see such big gains from cooler charge temps? Probably because they are generally on pump gas and close to knock-limited so the computer is pulling timing or reducing boost to compensate, and thus they were losing power as a result. It's not that there was any gained power capability, it's that you're simply able to actually utilize/maximize what was already there. But what if I'm already able to do that with E85 and water/meth, then does further charge cooling offer any significant benefit?

And I believe I can in fact maximize the stock turbos on this setup. E85 has 3.29x the latent cooling potential of gasoline, or 164 degrees F of charge cooling (if all of that went to charge cooling) at a typical air fuel ratio. Compared to 50 degrees F for gasoline. Water/meth injection at the rate I am using is going to offer an additional 60 degrees F or so. Between the two, I have enough cooling energy to reduce the final charge air temp to below ambient even with no intercooling, IF all of that vaporization energy were used for that purpose (it's not, and it's not realistic that it ever would be...would have to be a completely cold engine, more time allowed for complete vaporization, etc). The liquid that doesn't vaporize for charge cooling is still extremely useful for cooling/pressure reduction during the compression stroke and will result in lower pumping losses.

The point is, I have already built-in more cooling capability than the intercooler system is even required to do, so I would come pretty close to being able to run them all out even without any intercooling (have done this before on other cars with slightly higher quantities of water/meth injection). Beyond just the raw cooling capacity, E85 is also very high octane. I've heard the exact figure stated so many different ways that I'm not going to get into it, but suffice it to say the *effective* octane is around 110. This obviously includes the charge cooling effect because the actual R+M/2 rating is something like 99 octane. Either way, I am definitely not going to be anywhere near knock-limited with ambient intercooling and E85.

I would argue that the ultimate limitation of power production once you've gotten knock/detonation concerns eliminated, is mass air flow. The limit of mass air flow in our powertrain basically boils down to one thing, and that's air density at and within the turbo compressor inlet. Some turbo flow charts list mass flow, but if they do, it is at some standard temperature and pressure. Otherwise they list volume flow, which changes based strictly on density at the inlet. Absolutely anything else that we focus on with these cars is a power preservation mod, not a power production mod. So as long as I've got intake temps under whatever value it is the computer starts having a problem with, say 120 degrees F (the water/meth injection and E85 will still bring that down just fine), is it really worth my while to fuss with an A/C setup or ice box? I am thinking not. Here's the cost-benefit analysis:

Quad intercoolers for two-stage intercooling would absolutely necessitate deleting the stock airboxes...simply no way around that. Not to mention an extreme amount of fabrication, and complexity, and altered underhood appearance. While I *might* have had room for pipes attached to the stock radiator ducting and filters in front of all the heat exchangers with a custom grille, I most certainly will not with the BMW x3 radiator as a heat exchanger. That means I would need intake pipes off the turbos with exposed filters in the engine bay drawing somewhat warmer air than the cold air scoops up front. This affects the air temps going into my turbos, which not only affects the air density at the compressor inlet (the ultimate limitation on max power), but also becomes subject to an efficiency penalty when it is compressed in the turbo. 20 degrees difference pre-turbo becomes something like 26 degrees difference in outlet temps...so that extra 26 degrees puts thermal stress right back into my intercooling system as well (almost 10% more, in fact). As well as a 4.22% decrease in mass air flow through the turbo (assuming 20 degree F higher underhood temps vs fresh air).

Now, what are the benefits? I would have two-stages of intercooling, nearly guaranteeing that the charge air temps in the intake manifold would be consistently near freezing. It results in more consistency and guarantees the computer will be running optimal ignition timing, but at the end of the day is actually going to reduce the mass air flow my turbos are capable of for a 4.22% peak power loss.

Now that's a huge amount to expect to recover from just the lower pumping losses one would expect from 50 degree F lower air temps. And that's the only gain assuming I wasn't sacrificing power due to ignition timing in the first place...and I shouldn't be, on the race gas tune with very close to ambient charge temps from just the x3 radiator as a heat exchanger and a pump upgrade).

I am honestly thinking it's going to cost me power, and lead to a much busier and harder to work on engine bay at the end of the day in order to do this. I think that as long as I want to remain on stock turbos, my best course of action after the heat exchanger/pump upgrade will be to focus my efforts on improving air density at the inlet of, and within the compressor of the turbos. Sure, I could do refrigerated intercooling pre-turbo, but the space just isn't available, it's the same problem as before...where do I put the extra intercoolers and more importantly, the air filters? So pre-turbo latent heat of vaporization cooling is the only practical means of doing this.

There are some significant limitations and drawbacks to doing this with water/meth...primarily the fact that it takes a certain temperature for them to readily vaporize in air...so it's difficult to actually cool the charge air much before it enters the compressor unless you've got yourself a really hot day. And if you've got a really hot day, it's most likely pretty darn humid (in my part of the world) so the water still doesn't like to vaporize. There are still gains to be had just from the wet compression, which should improve the turbo efficiency and move the choke flow further to the right of the map, but I really think the gains to be had are in density at the inlet pipe. This means a less restrictive air filter/intake, or cooler air, or both.

Since the vaporization of water really isn't ideal at the temperatures I need, and methanol is only slightly better, I need something that boils a lot colder for when I really want to increase performance. I'm having to take a very hard look at a combination I considered a long time ago on another vehicle but never got around to putting into practice. Nitrous oxide (-127 degrees F boiling point) with propane (-44 degrees F boiling point) for the enrichment fuel. The trouble with using gasoline, or methanol, or anything else in a pre-turbo wet shot is that with the extreme cooling from the nitrous, the fuel is much more likely to fall out of suspension/puddle if it contacts any surface before things become heated in the compressor, since those fuels are definitely liquid at 20-80 degrees F below ambient (the approximate amount of charge cooling the nitrous provides at full load on a 600hp car from a 50 to 200 shot, respectively).

Propane should not have an issue with puddling due to the low boiling point, and also provides additional vaporization cooling down to much colder temperatures (albeit not very much cooling energy, it brings the earlier figures up to 24 degrees and 95 degrees...still net temps above the boiling point of propane unless it's an extremely cold day out and you're spraying 200 shot+ so no vaporization/puddling worries whatsoever). The big issue with propane is the same issue that can cause consistency problems with nitrous as well. The bottle pressure, and therefore delivery rate changes with bottle temperature...and as liquid boils in the bottle to restore pressure, the latent cooling occurs there and drops the temp even more. Propane in nitrous systems is typically run ridiculous rich to combat these changing pressure conditions and ensure that a dangerously lean condition is never encountered. This is why bottle heaters are used. I have something very different (and better) in mind.

If I do this, I will be utilizing two nitrous bottles...one filled with nitrous, and the other with propane. Both bottles will be fed either high pressure air, or nitrogen, or argon from a third bottle into the vapor space. This is typically called a "pusher" setup. I have not found anyone that has ever done a push delivery of both the fuel and the oxidizer from the same pressure feed source. The advantage of doing that is that with the same regulated pressure, delivery of the two will be at a consistent ratio regardless of ambient conditions.

A secondary advantage is that with a bottle pressure over the boiling point of the nitrous at whatever the ambient temp is that day, not only is the delivery rate consistent for both, but there will be no boiling within the bottles to replace pressure since that pressure requirement will be met by the push bottle. This guarantees both are delivered into the intake tract as liquid and that all the cooling takes place there, as opposed to in the lines. There will be no need for purging before each run (assuming the lines are routed away from high heat sources and insulated such that they don't get significantly above ambient), only after the very first time the bottle valve is opened.

So what's the math on it? I am going to do it as conservatively and with as much pessimism as I can so they will be kind of worst-case numbers. A 200-shot of nitrous is roughly 1.6 lbs of mass flow in 10 seconds. At proper ratios, the vaporization BTU/lb of nitrous and propane comes out to around 192 per pound of nitrous, or 307.2 BTUs total. Assuming humid air we'll use my more conservative/worst-case figure of .33 btu/lb/degree F figure to cool air (since this isn't a net heating/cooling operation as relating to humidity as it is with intercooling, it's strictly a cooling one). Along those same lines we will figure on the most airmass possible during the same 10 seconds. If the stock turbos are around 700 crank HP at their limit, we'll call it 750 to keep the figure pessimistic, that's right around 75 lb/min of airflow, or 12.5 lbs of air we are moving during the 10-second period we're using to calculate the nitrous BTUs. 12.5 lbs of air divided by 3 (since .33 btu/lb to cool) yields 4.17 BTUs required to cool the charge air 1 degree F. 307.2. So the math on that works out to 73.67 degrees F. At this point it becomes somewhat recursive because that cooling will increase the density and resulting mass flow through the compressor, which means there will actually be more than the 12.5 lbs of air moving through now. The actual temp is off the chart if we're assuming 80 degrees minus 73 and change, so we'll just figure it based on the closest point I can find data on that has that much swing. 14.8% density increase. So that then drops us to 64 degrees change, which changes that density increase to 13.2%, which in turn changes the temperature swing calculation again, but only by like another degree to the positive so I'm confident in saying that 65 degrees F and 13.2% density change are as close as I can approximate the worst-case improvement being.

So let's apply that 13.2% to what we KNOW these cars are capable of on stock turbos (even though the percentage swing would be higher at lower airflow...remember, this is worst-case). 690hp is what speedriven claims from downpipes, a tune, and intercoolers (and some other stuff that has zero effect on power output). Essentially, that's what they are comfortable saying the stock turbos are good to. 690 * 1.132 comes out to 781 horsepower, plus the 200 from the nitrous yields 981 horsepower. Had this not been a worst-case calculation, I am certain that would put it over 1000 horsepower. Realistically, I'm not sure I'm comfortable with a 200 shot, so the math on the 50-shot results in a much less impressive 2.7% density improvement at the compressor inlet and a total of 758.63 horsepower.


Obviously, the nitrous would only be for track or very occasional use since it involves consummables. But really, if the stock setup with exhaust cutouts and a race gas tune with turbos all-out makes 700ish hp...how often will I really feel the need for more? I mean the car spins the tires if I hammer it at 50 mph anyway on the street...I think the only place that extra power would realistically be useable is at the drag strip.

Do I have other ideas for on the street? Obviously. I mean water/meth in the inlet tract will still help shift the turbo map some, just not to the extremes that nitrous/propane can. And it can do so at a lot lower consumption rate, not to mention how cheap water and methanol are relative to the other option. There are some other crazy ideas I have that *could* work and be cheaper than nitrous/propane as far as consummables go. But also would add significant complexity and cost to things probably for small gain.

So I am now thinking what I want to do is forget about chilled, mult-stage intercooling and just add a couple more water/meth nozzles pre-turbo to my existing system for street use, and spend money finishing the nitrous and propane setup for track use instead of on over-optimizing and complicating my intercooler setup and potentially ruining the car's cabin air conditioning capacity. I already have the bottles and pusher bottle valves, as well as the correct regulator and check valves/adapters to hook up to the bottles...I really would just need lines, solenoids, nozzles, various other little odds and ends, and to figure out the correct jetting (probably experiment with it on another sacrificial car equipped with a wideband...I have access to plenty of cars that are basically salvage/parts but still run and drive). All in all, the nitrous stuff I am missing would cost me less than a thousand dollars at most. So there you have it...I totaled it up and with another $1,000 into the nitrous, I would be approximately $4,000 total into performance upgrades on this car at that point and be at 981hp (conservatively, if I chose to run 100hp shot to each side...which really, compared to what some of the V8 or even Honda guys run is very small). Granted, that requires a consumable to get there, but like I said, how often outside of the track can someone put more than 750hp to use anyway?

I know having talked myself through all the math and considerations writing this, it may seem like I've made up my mind on my own, but I am still looking for input/opinions/corrections where I may be wrong about, or have missed something. If you stuck with this book til the end, thanks so much and I look forward to any feedback, positive or negative.


http://www.engineeringtoolbox.com/ai...ity-d_771.html

ZephTheChef

What I forgot to account for in those figures is the air that the nitrous and propane would displace. That comes directly out of the volume flow through the compressor. That could be quite significant since we are injecting into atmospheric pressure, not boost. It is certainly going to offset some of the air density gains, but it's unclear to me how much. I am going to try to rough out the math. I think the total mass of nitrous and propane in the example is 1.6 lbs nitrous and around .24 lbs of propane over that 10 seconds. The nitrous will vaporize to a density of .117 lb/ft^3 at standard temp/pressure and has 1.735x the oxygen mass of air by volume, which weighs .0807 lb/ft^3 at standard temperature and pressure. So that nitrous would displace 13.675 ft^3 of air, or 1.1 lbs of air. The propane at .24lbs and a density of .125 lb/ft^3 is 1.92 cubic foot of air displacement, or .155 lbs of air. So the total displacement is 1.255lbs of air off of that 12.5 lb/10sec figure, or almost exactly 10% of the volume moving through the compressor. Which reduces the gains from density improvement significantly, but then to add to the recursive nature of the problem with less air mass, the temperature change expected goes up again, and that increases the mass flow again, which reduces the temperature change, which decreases the mass flow so you're chasing the answer just like before. I have realized I don't actually need to calculate the difference the higher oxygen content the nitrous displaces because we've already accounted for those gains in the shot size that we were adding to the total hp. So there again, we're back to just subtracting the air it displaces from the mass flow of the turbo. That 10% is then a hard penalty against the total, so I just need to work the math off the 11.245 lb/10sec airflow figure instead and compare the resulting % density increase to the -10% displacement penalty of the nitrous/propane. So the cooling then becomes around 14% after figuring out all the recursive stuff. So it's entirely possible this only represents a 4% gain in mass flow, not 13.2%. Which makes it 918 HP as a worst-case figure, not 981. Nothing's free, as it turns out, and that result kind of puts a damper on my enthusiasm about this setup. It's not quite as exciting if the side-effect gain is only a 4% improvement vs 13+%...although the 200hp shot yielding 227.6hp is really not much to complain about, I'd rather have the 291 I had gotten all excited about.

ZephTheChef

And of course, since that math is all done at standard temperature and pressure, the variables all change at lower temps. Given the higher starting density of nitrous and propane at standard temp and pressure, it's likely the density change is more significant than that of the air itself with temperature, which would cause it to displace somewhat less air than I calculated, even more so as it is being compressed. So as is usually the case, the truth/real-world number is probably somewhere between the two calculated extremes. Which cheers me back up a little since the worse-case one really isn't even THAT bad.

ZephTheChef

Nope, that's still messed up. The air density figure as it turns out is at "normal" temperature and pressure, whereas the propane (and I'm presuming) nitrous figures were at "standard" temperature and pressure. So the air weight displaced is lower. It should be 93% of what I figured. Which since that applies to only the 10% figure, is really less than a 1% change in air mass. No big deal...still only a 4.something % mass flow increase at 32 degrees F.

ZephTheChef

I was moderately worried about backfires with a perfectly vaporized fuel and oxidizer mixture traveling the entire length of the intake, so I ran the numbers on that as well. Propane at a 12:1 gasoline-equivalency AFR is about 1% of the charge volume at max load. The lean explosive limit is 2.1% by volume. So I've got a pretty wide margin even if it were to pop back, so long as I'm not spraying at low rpms. That's a good reason not to run overly rich on the fuel side though.

Speedriven1

Why all this fascination with the stock turbos, though? Even just modding the wheels and housings yields huge gains in power without pushing components to/past their max.

ZephTheChef

Multiple reasons, but primarily it's a cost thing. I'm basically poor so I have to maximize what I've got to the extent I can. It is my understanding that the entire engine has to come out to change turbos. If the compressor wheels can be upgraded in-car I would certainly look into that option but something about changing parts on a 100k+rpm assembly without having it rebalanced just sounds like a bad idea.

And then even if I do upgrade the compressor wheels, there are other drawbacks and it gets expensive in a hurry. I know there would be substantially more turbo lag. That kind of thing is muted in an automatic car anyway, but having done compressor upgrades before on stock TT cars (3000GT/Stealth), you can definitely tell the difference in response. I like having full boost at 2,000rpms. More than I can describe. I have driven/built plenty of big turbo cars and they have miserable street manners.

Beyond that, I am uncomfortable with the stock fueling. Jerry @ eurocharged told me on his tune the injector duty cycle is 76% @ 593 hp. That sounds too good to be true to me if the fuel pressure is in fact a fixed 55psi on these cars with no boost reference. That means even at only 15psi boost on the high end, the effective fuel pressure is 40psi. I flowed stock injectors @ around 350cc/min @43.5psi. These things must run pretty lean and mean under power. To get to 76% duty cycle at 593hp, that puts 100% at 780 crank HP, and to be at only 76% on that injector size and pressure the BSFC would have to be .49. That's pretty aggressive for a 93 octane turbo gasoline tune. 12.2:1 or something AFR under power...that's usually around where I shoot for (on a gasoline scale) on E85. I guess that's the beauty of air/water intecooling...I might want to get even more aggressive on my Buick since it's refrigerated, lol.

So basically, given that information, the stock computer isn't going to be able to provide fueling above 780hp or so. Neither is the pump probably...that mercedes training pdf says the pump is 245l/h. From the 16A max draw, I would venture a guess that rating is AT the 55psi pressure, not free flow like most aftermarket pumps are rated. So the pump is out of steam at 97% or so injector duty. Fortunately the pump is very easily replaceable since I don't have an SL. From what I've been told there's no way around the limit in the computer though because the injector size cannot be scaled, and the fuel pressure is fixed and doesn't rise with boost which exacerbates the problem. I also don't know at what point the computer decides you've hit max fueling and cuts fuel or spark or whatever. Is that 85%, is it 100%, who knows until you get there? Based on advertised HP figures with various upgrade packages, I think I should be able to get very close to that 780 figure on stock turbos with the cutouts open and an ice box, so from my perspective any turbo upgrade is a waste. Perhaps an S65 computer could be adapted for a little more headroom without spending $10-15k on a custom solution...but if not, then the turbo or compressor wheel upgrade turns into minimally:

Turbos or compressor wheel upgrade
Aftermarket ECU
Fuel pump upgrade
Fuel injectors upgrade

Easily a $20,000+ project based on the price of the ECU, even if I do most of the legwork myself and stick to just a wheel upgrade. And then the transmission blows up and there's another $3,000-20,000. I'm talking about spend an additional $1,000 maybe to do it my way.

If I do grenade a wheel from overspeed, I've got intercoolers to catch any debris and the turbos would obviously have to come off at that point anyway so that's when I would have them rebuilt. Am I taking a chance doing this? Sure. But it's a known and acceptable risk. The car in it's entirety plus all the mods and maintenance I have done so far cost less than the minimal investment it would take to overcome the limitations of the stock turbos and computer. And even if those things were upgraded there are countless other driveline parts that I would still have to worry about...it's not like "doing it right" with that nets me any extra reliability with the exception of the turbos spinning lower rpms for the same mass flow and less likely to grenade.Worst-case if **** hits the fan, I still am out less money total in this car than a turbo upgrade and ECU would cost me and still have a really nice parts car, or be in search of a not so nice one to fix whatever broke.

So basically, my options are either to leave the car alone and perform no further upgrades, or to provide additional standalone horsepower that the ECM doesn't even need to know or care about in the form of wet nitrous. I like propane with it to prevent puddling, since I'm shooting for such low charge air temps anyway, E85 or methanol would have more trouble staying vaporized.

ZephTheChef

Based on those fuel numbers, I am super curious how you guys get 850 on the stock computer with bigger turbos with just "fuel system upgrades". If your tune can scale injectors then I would definitely be potentially interested in buying one. I calculate that would take almost a 14:1 AFR on the stock injector limit. Perhaps just running bigger injectors and the computer is able to adapt a certain % to allow more headroom? Or changing the commanded AFR to an intentionally incorrect value and oversizing injectors to arrive at the actual desired AFR and a lower injector duty cycle?

Speedriven1

You're talking about a car that's on peak boost at 1800 rpm going to 2000 or 2100 rpm, and there's a big difference between the Stealth/3000GT 3.0 liter 6's lag and these. Like, a generational difference.

I get why you're saying what you're saying, I just think your information/assumptions are 15 years out of date. Like guys putting in lower compression pistons to run more boost- why!?? Is it 1985 again?

ZephTheChef

I had a rather lengthy response typed up with some further insight on why I hate lag so much but the computer crashed, lol. Don't really feel like typing it all up again, so I'll skip the backstory and keep it more brief. I completely understand where you're coming from as well...I'm like the noob that's trying to do things the incorrect/different/cheap way and you're the experienced platform guru trying to show me the path when I just don't want to listen, which is frustrating. In other places/platforms, I'm in your position and there are other people asking advice and then doing it wrong and ignoring my advice anyway.


Suffice it to say, while I may not know this specific platform intimately yet, I do pretty much know what I'm doing in general when it comes to performance mods, especially relating to forced induction. But the real answer to why I don't buy bigger turbos is I simply I can't afford to play this game the way a lot of people do. So it's equally as frustrating for me to be putting ideas out there and to get, "why don't you just buy bigger turbos" as a response as it is for you for me to be a downer with respect to that idea.

AMG-Driver

Nice to see some new thoughts in the discussion. From my experience it is not possible to get to 780 Crank-HP without touching the Turbos and no nitrous. 600 can use 65 Fuel Pump and its bigger injectors which are capable quite a lot more than the 600 parts.A good cold air intake and downpipes with100 cell Euro4 cats help a lot to let the the stock turbos work. But in my opinion for a further serious upgrade you need to adress the Turbos. Sorry that I dont have a cheap solution, but best bang for the buck is a good ECU- TcuTune with a good Intercooler pump IMHO. Also when you eventually one day you want to sell the car again.

ZephTheChef

The tunes and pump/heat exchanger are already checked off my list (or at least in progress). As well as injectors, E85, and catless downpipes with electronic cutouts.

Are you saying there is a tuner that has the capability to tune injector size in the computer, or are you running on an S65 computer/calibration, or were the bigger injectors just thrown in and are still within the computer's adapt range so it scales them itself? Most cars only use fuel trims at part load, but it wouldn't surprise me if these had WOT adaptations as well.

AMG-Driver

You might ask Speedriven for further information, I think they also change the 600 injectors at a certain power level.When I had my SL600 my tuner changed with the ECU Tune to the 65 fuel pump, to make it safe for high speed runs on the German Autobahn.Injectors remained stock for this power level.

ZephTheChef

I wouldn't think a bigger pump would take any changes in the ECU or tune. I haven't studied it in-depth to find out for sure, but I'm pretty sure the ECU has no input or control whatsoever over the fuel pump. The pump controller handles all that itself, its primary purpose is to monitor the fuel pressure sensor and adjust pump speed with PWM to maintain 55psi of fuel rail pressure at all times. It's essentially a closed-loop controller for the fuel pump.

A larger pump is just going to require slighly lower "effective voltage" through PWM to deliver the desired pressure. Assuming the pump control module can handle the higher amperage requirements of a bigger pump at higher fuel flows then any bigger pump should drop right in. The higher current shouldn't be an issue at all since it will only be for a brief time period. Unless of course the pump module has a hard current limit where it shuts down the pump altogether if it is exceeded.

Injectors however is another story. That would require tuning changes for sure. I wouldn't expect speedriven or any of the other vendors to let the cat out of the bag as far as how injector upgrades could be handled on the stock computer...so if I get to that point I will probably have to figure it out myself. I suspect an S65 calibration (or computer if the two calibrations cannot be cross-flashed), combined with the S65 injectors and pump. Or as I mentioned earlier, non-actual AFR target numbers in the tune, or simply letting the computer adapt (if these cars have long-term WOT fuel adaptation).

But we're talking about around 780HP before I would even have to cross that bridge. And from that point the simple/obvious answer is that any extra power and fuel enrichment needs to come from standalone enrichment of the available oxygen and fuel to the engine (wet nitrous) if I want it to be at all cost-effective.

ZephTheChef

So back on topic, after much additional research, an EPA study has confirmed my fears. Chemical injection into the intake tract for the purpose of charge cooling to improve volumetric efficiency has a detrimental effect to volumetric efficiency in most cases...due to a large portion of chemical vaporizing on surfaces within the intake tract, which increases the gas volume in the air stream without cooling the air to the degree the BTU math would predict.

Basically, what that means is in order for me to even stand a chance of hitting that 4% mass flow increase figure I ended up calculating, absolutely all of the injected nitrous/propane would have to vaporize in the air itself as opposed to on any of the surfaces it might come into contact with. I think that injecting it right at the compressor wheel would not be optimal because most likely the air filter is a bigger choke point than the compressor inlet itself, so in order to achieve the greatest effect I think it would need to be injected as soon as possible in the intake so that the density improvement is realized going through the air filter as well. Basically, centered right in the radiator scoops. With a boiling point of -44 for the propane, and a calculated cooling potential of around 65 degrees F, as long as it's over 21 degrees F out then everything should flash boil in the air and an insignificant amount of heat will be lost to the charge pipes (just the heat transfer from the then cold air to the pipe as opposed to the latent cooling actually taking place there). Obviously, further insulating the piping will help.