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is this still about the original twin turbo engine build or the second engine build….???
This is the second engine and third turbo system iteration in this chassis. The original turbo system and the stock '87 engine run just fine up to about 700 rwhp but after that everything run out of capacity at the same time (as it should in a well-designed system).
Later this year, we'll be taking apart the still perfectly well functioning '87 stock engine that took hundreds of dyno pulls and a lot of miles with the turbos. Then we'll learn more about how close to the limits the stock engine is.
One of the interesting things that we'll learn from the new engine is how the turbo system responds to different (bigger) cams.
The earlier dyno results were with the S4 cams that gave pretty good results, all things considered.
The new engine intake cam has the intake valve opening (@ 0.008") at 16.4 degrees BTDC and closing (@ 0.008") 73.0 degrees ABDC. It'll have about 0.0275" lift at TDC, 0.352" lift at 75 degrees ATDC (maximum piston speed crank angle), and 0.251" lift at BDC. Both the intake and exhaust valve are open by about 1mm or so a couple of degrees ADTC, and the intake flows about 50 CFM@28" and exhaust about 60 CFM@28" at that lift. So there's meaningful overlap in these cams even with the wider LSA (these cams have 114 LSA, S4 has 106.5 LSA). The S4 cams have no point at which both the intake and exhaust are open by 1mm.
We know these new cams rock at mid range rpm and run great everywhere with N/A engine that has headers. The question we're interested in is how the greater overlap works with the exhaust manifolds (instead of headers) and with higher exhaust back pressure at high rpms. At low rpms, the risk is 180-degree exhaust blowdown interference hurting cylinders 3, 7, 5, and 4. At high rpms, the risk is 90-degree exhaust interference hurting cylinders 1 and 6. We know it'll run great in the mid-range rpms, but since it's a turbo engine it of course did run great in the mid-range rpms with S4 cams also. It would run great in the mid-range rpms with pretty much any cams for that matter, getting the low and high rpms to both work is the trick.
The overall advance and retard of the cams also matters here. For an odd-fire V8 with twin turbos, the main issue there is that advancing the cams will make more torque at low rpms before the turbine has spooled, but will hurt the evacuation of cylinders 1 and 6 during the overlap at high rpms. The cams are currently installed at a position in which we believe there are meaningful benefit at low rpms and the negative effects at high rpms are minor. The negative effects at high rpms really accelerate after the overall cam positioning is advanced relative to "straight up" or 114 LCA on both intake and exhaust.
The intake manifold relates to this as well. Specifically, we'd want to get the intake and cams to produce as much torque as possible before the turbine spools and then we want the turbine to spool rapidly as the first torque peak of the intake manifold is about to fade. Camshaft overlap hurts idle and emissions, but really helps the torque from a surprisingly low rpm. (968 Variocam goes to 105 LSA and a significant overlap at 1500rpm.) Better cylinder filling, more torque, earlier turbine spool up leading to earlier boost, earlier boost allowing us to increase the intake manifold plenum volume and bring down the resonant point or increasing the turbine side, it's a virtuous circle...
Nitpicking is the act of removing nits (the eggs of lice, generally head lice) from the host's hair. As the nits are cemented to individual hairs, they cannot be removed with most lice combs and, before modern chemical methods were invented, the only options were to shave all the host's hair or to pick them free one by one.
This is a slow and laborious process, as the root of each individual hair must be examined for infestation. It was largely abandoned as modern chemical methods became available; however, as lice populations can and do develop resistance, manual nitpicking is still often necessary.
As nitpicking inherently requires fastidious, meticulous attention to detail, the term has become appropriated to describe the practice of meticulously searching for minor, even trivial errors in detail (often referred to as "nits" as well), and then criticising them (see hypercriticism).
Mounting fuel system related parts on to vibrating engine without some form of measures to prevent them becoming loose is nitpicking? Loctite might have been used and that would be perfectly ok. Not using anything calls for nitpicking.
Mounting fuel system related parts on to vibrating engine without some form of measures to prevent them becoming loose is nitpicking? Loctite might have been used and that would be perfectly ok. Not using anything calls for nitpicking.
I agree on the substance of this. It's going to get loctite when it's actually going together to be run. This is still being mocked up.
This particular bracket and hose would not cause anything catastrophic if they'd come loose. This is because both ends of the hose are reasonably well secured. However, the SS braided hose would rub some components near it and ruin them.
I'm not particularly worried about this one specific car since engine is going to be looked over, taken apart, modified etc. almost daily. If same setup is used on other cars which get less attention it could eventually lead into problems.
If I were nitpicking I would have pointed out one clamp has too long bolt in it in last picture. Totally unacceptable even for mockup purposes.
05-17-2016, 12:01 AM
