First up: I refuse to read 20 pages of replies to see if what I am about to state has already been noted.
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Originally Posted by Phoenix'97
So, as a starting point for my build goals with my LT1 motor, I am very set on modifying a Tuned Port Injection intake manifold to fit on my LT1 heads, to use AS&M big runners and to have the plenum, runners, and manifold bottom port matched, gasket matched, and extrude honed. I plan on using 180cc DART heads since they emphasize port velocity, which is great for low end torque production and in my mind, helps in overall fuel economy. I also plan to use long tube headers designed to emphasize low end torque which are customized to work with my emissions devices and will use catalytic converters.
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I'm unfamiliar with the numbers and brands you are working with, but it sounds like 'big runners' are, well, big. If they are large diameter, they will lose port energy at low rpm, and this will adversely affect cylinder filling, which adversely affects torque. Whether this is bad for fuel economy depends largely on your cam and whether you are going for a semi-atkinson cycle. More on that one later.
If you get them professionally ported via extrude honing, make sure they focus on matching the flows, not just increasing. Matching flows is important when you don't have (or wish to pay for) cylinder to cylinder tuning, more on that later too. Matching flows still leads to overall average flow increases, because that's the only way they can do it.
Gasket matching is *not* a thing to do. The chances of your particular gasket being manufactured with optimum port sizing in mind is almost zero, it's much more likely to be there purely to stop leaks. Grinding out the head and manifold to suit the gasket will increase port volume much more than *port* matching (same thing, but you don't use a gasket, or you make your own paper gasket which directly matches one of the ports to do the cutting on the other one). An increase in the size of the port the length of the compressed thickness of a gasket (say, 20" / 0.5mm) isn't going to affect your port flow in any measurable way.
Long tube headers for low-rpm are unfeasibly long. 60" 4-1 headers are good for a 2500-5500rpm band on a 302-HO. If you intend to try tune lower than that they might not fit. Don't forget that cat converters mess with tuning lengths. If you can (and the length is appropriate) you want to fit a pressure wave termination box immediately before the cat. It simulates open headers for correct collector length tuning but allows connection to the rest of your exhaust. Also, if you're concerned about emissions, make sure your exhaust stays hot til the cat. This might involve wrapping, but heat shields and/or a coating are probably enough.
Quote:
Originally Posted by Phoenix'97
Also, for the sake of better efficiency, using Iso-butanol fuel to allow for a higher compression ratio of up to 12, equipping my motor with smaller low friction bearings, piston skirt/bearing/valve stem/valve spring/crankshaft low friction coating, low friction crankshaft seals, and a true roller timing chain.
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Non-standard fuel sounds complicated. Compression is nice though, provided you have the combustion chamber design and preparation for it. Run minimum quench clearance if your head is such a design (there is no optimum, optimum is just minimum before rod stretch means clearance is less than zero at your rpm limit), and make sure there are no sharp edges in your combustion chamber.
Bearing coatings are a crock for friction, the crank and rods float on oil, a coating can only affect oil-bearing friction and you *want* oil to stick to them. Piston coatings are a known thing though, I'm not sure about the valve related stuff though (I'm not saying those are crap, I've just never heard of them). Low friction seals are also a thing, as are low friction *rings*. Roller timing chains are also not a term I've heard (more later).
Quote:
Originally Posted by Phoenix'97
The last modification deals with the camshaft. After some research I found that the widest lobe separation is the most optimal for fuel economy, and such a lobe separation at 117 is what I have for my stock camshaft. I am left wondering if there is anything I can possibly do to improve upon the stock camshaft profile, increasing the lift for any marginal performance gain without sacrificing fuel economy. I do think the stock camshaft should be advanced to help improve the lower end torque that my car really needs, but again, I only have so much help using other forums that don't specialize in what I wish to achieve with my muscle car and daily driver.
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Cam timing is a tricky one, but also a magic one. If your headers and cam are tuned correctly for some particular rpm, the scavenge effect (negative exhaust pressure at tdc during overlap) can pull your entire combustion chamber clear of exhaust gasses, upping your volumetric efficiency. With correct inlet tuning as well, you can see 115%ve. Which means your perfectly designed 350 can produce peak torque numbers associated with a standard 400. It's difficult to do though and without computer simulation (or hundreds of other people going for the same thing who may have stumbled across the perfect combination) you aren't going to get to even 100%ve.
However if you are prepared to sacrifice low-rpm torque in favour of reduced pumping losses you can close your intake valve later, run higher compression, and have the same effect a Prius does, simulated atkinson cycle. At high rpm this cam timing can increase power (over stock, but not over high rpm specific cams) because air has inertia, and the late closing is actually optimal when you have very high port speeds. The Prius engine is gutless because of this, combined with 'weight, space, and cost reducing' (read: useless for performance) and a redline too low to make use of it with the comparatively massive ports.
Quote:
Originally Posted by Phoenix'97
So, what do you any of you think about these ideas to modify my second-generation LT1 motor for better fuel economy and a good enough increase in the "seat of the pants" performance.
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A few more additions:
Valvetrain:
$ spent here on lightweight rockers, valves, and pushrods, will reduce power consumed on cam opening thanks to reduced inertia. You will also be able to go lighter than stock in valve springs if that takes your fancy. I don't know if the LT-1 is a roller cam, but if you have the option, do it. That reduces friction even further, as well as allowing more kickass cam designs. Increased rigidity in the valvetrain is also a very good thing.
Injectors:
Get new ones, and make sure they are dynamically matched. I've seen graphs of brand new bosch injectors from the same batch vary by something like 13% at low delivery rates while they are perfectly matched at high rates. 13% is a wide margin. If you're tuning for 14.7:1 cruise that means cylinder to cylinder mixtures can vary from 13.75-15.65:1. I say get new ones, when I really mean get new *designs*. New designs almost invariably have better atomisation than old ones.
Cylinder to cylinder tuning:
Even if your computer *does* have the capability of individual cylinder tuning, does it have the option of separate map/rpm tables for each cylinder for both fuel and ignition? Are you willing to spend the time tuning it? I would say no, no, and no. So you really need to make sure the air and fuel flow are the same instead. This is easy to do while you are building the engine.
Transmission tuning: (Just read that you have a manual, I'll leave this here anyway though)
Time spent here (assuming you have an auto) will pay off fantastically. If you can modify the valve body to get lockup in all forward gears, so much the better. Make sure you tune it to allow high loads in high gear at low-medium speeds. Most autos I drive will never allow the engine to hit peak efficiency because they downshift too early and upshift too late, when in fact there's no good reason that a 4spd auto with lockup should use more fuel than a manual. It's not technically as efficient, but it can change gears at all the right times reliably.
I'll be very interested to see how this turns out, there's a lot of potential, and a lot of the mods you plan to do are conducive to bulk torque, and torque is fun.
Also, seeing as you're aiming for such high compression AND low rpm cylinder filling, water injection seems like a thing you want. Octane on demand. Given that a combo tuned almost exclusively for low rpm will have poor cylinder filling at high rpm (and you won't need the water injection), a single stage system aught to do. High, high, high pressure low-flow pump & nozzle for best atomisation, triggered above 75% load.
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