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Message: [QUOTE="me2, post: 322017, member: 3825"] More waiting, so therefore more rambling. [B]Turbos[/B] Why are you building a 600 HP engine for towing ? You'll never need that much power ! I have 325/610 in my old truck right now. First off, 610 ftlbs isn't enough torque for towing our trailer at 1650 RPM, which is where it runs at 60 MPH in OD with 3.73 gears and 20 inch wheels. One can argue that is a gearing problem and there is some truth to that. However, I used to run stock 16" wheels on my old truck, which put the engine speed at about 1750 RPM at 60 MPH and it wasn't much better. Our trailer is 35 feet long, 11 feet high and weighs 14K. And it has a bunch of stuff on the roof. It takes about 75% of full throttle from my 325/610 to pull it in OD at 65 MPH in flat, still conditions. Throw in a 20 MPH headwind and/or a slight grade and the engine is maxed out, stuggling to maintain speed. It is easy enough to drop a gear into direct, but then the engine is reving 2500 RPM all day where its noisier and uses a lot more fuel. Its not very relaxing. And it still doesn't seem to have a lot of extra power. Even in direct, passing another vehicle on a 2 lane highway is a very slow, dangerous process. And even when gearing isn't an issue, there are mountain passes that have my old truck down in 2nd gear wound out at 2700 RPM doing 30 MPH. So I definitely need more power and torque than 325/610. The question then becomes "How much ?" The next step up in a stock Cummins engine is 350/800 from the new HO Dodge 6.7 engine. I like the 800 ftlbs part, but it doesn't seem like a huge improvement over 610 ftlbs and likewise 350HP over 325HP. It would tow better, but without better gearing, I don't think its enough of an improvement. So then I started looking at gearing. And the problem is that with most transmissions, when you juggle the rearend and transmission OD gear ratios so that they are good for towing, the engine speed is plain wrong for running emtpy. This is my biggest gripe with all the pickup truck transmissions except the 68RFE and the 6R140, which I think have excellent gear ratios. So the solution to my towing power issue is twofold. First, use a transmission with better gearing. By better gearing, I came to the conclusion it needs to be double overdrive with a towing OD gear in the 0.8x range and a cruising OD gear in the 0.6x range. Of all the available transmissions, only the 6R140 and the 68RFE have those ratios. All the others have OD ratios in the low 0.7x range. I chose the 6R140 because the 68RFE has trouble handling the sort of torque and power I want from my setup. The second part of the solution is to build a torque/power monster engine so that it pulls well even when the gearing isn't perfect. Mack used to do this with their highway trucks and still does to some extent. For a while, while everyone else was building trucks with 13 and 18 speed transmissions, Mack was building trucks with torque monster engines and 8 or 10 speed transmissions. Because I want an off the shelf pickup truck transmission and nothing exotic like a RTOO13, I need an engine that has a wide, torquey powerband like Mack did. I need an engine that pulls good at 1600 and 2600 RPM and everywhere in between. So I have 610 ftlbs right now. Something in the 1000-1200 ftlb range would probably be perfect. Instead of going over that pass at 30 MPH, wound out in 2nd gear, I could now go over at 45 or 50 MPH, at a reasonable engine speed. So that brings me to the Cummins 6.7, which can certainly be built for monster torque/power. But it needs more air to do so. That is where twin turbos come in. And it needs better fueling and engine control. That is where EFI Live comes in. To be continued. [/QUOTE]