Agreed. There's also Nailhead, BBB, stroker, shorties, cams that add in to the package to over scavenge or not enough, situations where collectors are sized according to the muffler shop's doing or following the collector dimension and despite how the overall package might add up...a single part is attributed for the hit or miss scenario. If it's close, not much will improve it.
:3gears: Yee Haaa BooHoo out Your front window. Maybe not the fastest but ALL will get tore up in the twisties, It is called "The Complete Package" LOLOL. Proves you know nothing about my car. Break out the pipe. and some more popcorn please. Owned since 77.
I'm with ya, It take a lot of reading and research to figure some of this stuff out. Us 350's are very limited we have to work with what we have. But I am not getting much info.
I'll pass on the popcorn, but I'll take a rip off that pipe! lol You need to pay more attention to my posts then, Guy. I'm always the one going on and on about the entire package and how there's way more to any car than simply its 1/4 mile performance. Kinda goes along with what I've been talking about using an ST300, eh?... Anyways, my point was made. Why are you insistent on busting my balls? You bored?
This thread has become too quite and I need a reason to make another batch of popcorn. First this thread is entitled "Loss of torque with larger exhaust myth" and was based on a video of a long tube header exhaust. Is the discussion restricted to header exhaust system only? As pointed out earlier the header is doing most of the work of scavenging. This means that as long as the remaining exhaust system does not screw that up there will be good scavenging. Does this hold true for some cast iron common log manifold? Probably not. I suspect the exhaust system pipe size, length and any crossovers has a large contribution to the system's scavenging ability as a whole. So now someone cuts the exhaust system short and the engine power falls on it's face and we get "The engine needs back pressure to run". What a stupid conclusion. Kinda reminds me of the Scientist and the Frog joke. 8ad-f85 pointed this out several times and I think he was trying to be nice about it. Backpressure does not help an engine make power. If you need a smaller diameter pipe to increase flow velocity there naturally is an increase in pressure but to put that in terms of "backpressure" is just plain incorrect. On the first video after the comparison of the two different pipe sizes they showed a richer A/F ratio with the 2 1/2" pipes. Why not go back and retune for max power in each case to get the real difference in torque and HP between Open, 3" and 2 1/2" pipes? Whatever setup a person might use they are certainly going to tune it the best they can. They didn't even bring the tune-up difference into the small block comparison in the second video. The imformation was very good but like so many other videos they fall short of doing a complete job IMO.
I know it's a risk, but effit...I'll repeat something I've said in the past here, albeit briefly. If you want good scavenging on your exhaust (talking about v8s), a couple of factors need to exist: Either use headers to achieve this, or manifolds with a merge pipe. As long as the headers have a sufficient collector/reducer and some pipe length (as well as primary tube length/diameter), the rest of the exhaust really doesn't matter as much as long as it's sufficient to evacuate the system. With manifolds, it's a little more involved, since the exhaust system itself has to do the scavenging work, and still will never be as good as headers, but is better than using huge divorced pipes. Any kind of pulse drawing that can go on is better than relying on the engine to push it all out. As with anything involving performance cars, tuning is crucial to achieving the most out of it, as well as using the right combination of parts that work well together. I'll refrain from posting any more than this, omitting preference and controversial topics as best I can muster.
I'd be curious of a how a well placed merge does with any contoured, branched style manifold. The header and collector calcs often put a primary pipe some 70" from the valve (peak torque, as in some well developed motorhome chassis headers), presenting an opportunity within a car's chassis. It could be placed further away, such as closer to a cruise rpm or lower. Even more to the topic of not-too-far-off fantasy is the notion that just inside the manifold collector might be a cast merge that could be used to split the engine's bank to a dual pipe after each manifold in 180* firing intervals, allowing more merges timed to rpm ranges. I don't have any Buick manifolds here to look at but some Pontiacs I've tossed recently would allow this.
I have experimented with different setups on a Buick 350 with manifolds before swapping to headers. There is for sure a huge lack of power when using open manifolds. I tried different lengths of 2.5" tubing after the factory Y and found that anything shorter than 2 feet caused a lack of low RPM torque. I then switched to dual downpipes and 2.5 pipes and found the same applied again and it needed about the same length of pipe to give the best seat of the pants power gain. Adding extra pipe did not hurt the performance but less did. Swapping to headers I noticed little difference between open headers and adding pipe, was loud!
The exhaust side of the engine is possibly more complex than any other part of an internal combustion engine. You could probably spend your entire life studying it and still have more to learn. So it's no surprise that it often seems like witchcraft. We dumb it way, way down and even then have a hard time dealing with pulsations, response curves, and volume reduction from heat loss, which is rarely addressed except on production cars. (Ever wonder why the tailpipe is smaller than the header pipe? It's more than just the cost of the tubing.) You can say that a 4 cycle header is completely different than a 2 cycle exhaust and in a number of significant ways that is true but in a number of other equally significant ways they are very much alike and do very much the same thing. It's largely just a matter of degree. Both, when properly matched and at the correct engine speed, suck the exhaust out of the cylinder and suck the intake charge into it. A 4 cycle header tube is a straight tube because of packaging considerations primarily, not because an extractor would provide no additional benefit. Think of a multi-cylinder 2 stroke motorcycle. For me what comes to mind is a early 70's Kawa or Suzuki. Those bikes did not use extractors. Their exhausts were remarkably similar to 4 stroke exhausts like you saw on the 750 Hondas. Why? Packaging. There wasn't enough room for 3 extractors under the bike. Now, modern 4 stroke singles run extractor type exhausts. They just aren't as radical as the 2 stroke versions, but the designs are similar. So before getting too deep into header discussion it is always going to be a good idea to review exhaust pulse propagation through an extractor type exhaust to get some idea of what is actually going on inside the system, because it's more than just pulses traveling down a tube and helping each other along through the collector. That simplified analysis is very useful, but it leaves out a lot of other important stuff that is going on at the same time. Plenty of info is out there, including motion graphics of pressure waves inside the system. But in a nutshell, they all suck. Or at least the good ones do. Jim
my issue with all this is WHO is going to do the manufacturing of said buick products and do dyno and track time? WHO has the time and MONEY to do all this and report back? somebody please tell us all. if nobody, it kind of becomes "analysis paralysis". we will talk it to death, but not do anything about it. this is my complaint about a lot of these theory threads. YOU HAVE TO PROVE IT TO MAKE IT USEABLE. on paper is bathroom use.
How about this paradigm shift...prove any of these sciences not to work. I would challenge anyone to intentionally design something using reasonable methods and upon it's failure, have their peers scrutinize the efforts. People can ignore things and continue to see the same results or try things, take risks and push further. I don't think it's a matter of proving that any 50-100 year old sciences that are taught in engineering courses are worthy to consider for a niche market like Buicks where the products are geared for demographical or 'stage build' use. The typical clientele here isn't going to demand an unrealistic power goal that is limited to a pre-selected parts combination that's traditionally fallen considerably short other than the magic part that makes it all work better. That's just silly. I don't A-B-A anything I've designed and built for people. It's rare to even do it for myself, except at convenient times such as swaps and maybe when changing an engine to see if the attributes follow as predicted. If we are talking about street or drag, it simply has to meet expectations to be worthy. All you have to really do is make someone happy or take on a project that knocks them out of the park. Very little R&D was done with the head I brought to market. It hit all of it's goals with a tiny bit of dimensional revision. *Meaning...we are getting paid to do things and any engineering or sciences are simply tools in the toolbox used to reach the goals.* I can attest to everything I write about and could care less if people drink my kool-aid, as I have nothing to offer for sale. If I were to make a product that had enough projected sales and a fast enough turn, it would be handled appropriately. This is one of the truest subjects that could be explored because there isn't a major gain for anyone.
I had a 2012 5.0 Mustang that had a 2.9 whipple supercharger on it that made 736 HP to the rear wheels with the factory 2.5" exhaust no Cats but the factory resonators where still on the tail pipes. The car went a best of 9.97 @ 140 MPH weighing in at 3850 lbs.
Copied from elsewhere in reference to a Nascar and Prostock header designers discussion on engine development; The direction that Nascar and Prostock went was to increase scavenging until over scavenged, then decrease exh. valve and port size...especially when it's competing with space on the intake side. Then make the intake size more apt for the intended application, just like any other internal combustion engine. These motorsports examples were used as a reference. One of the top header builders had previously wrote about how they surpassed various plateaus. An important reason for these jumps was in getting a better working header and exhaust. Even Vizard published a very simplified version of accepted formulas 20 some years ago through magazines and books on the 'No Loss Exhaust System' I bet you can still Google it.
The exhaust needs help getting out to produce more power, and can be done with scavenging on N/A applications, or through forced induction. Forced induction engines tend to be less adversely affected by 'back pressure', and in cases with turbo chargers, more velocity on exhaust builds more power, which typically results in more back pressure under higher boost levels and RPMs in relation to the power being produced vs exhaust size. Back pressure will restrict how much power an N/A engine will produce because it reduces the draw on the intake side, but when it's being forced in there, the adverse effect of back pressure becomes moot, up to a threshold where it would start to overcome the full boosted effect (which can still be overcome again on the intake side with a wastegate or pressure valve forcing a certain PSI regardless of restrictions).
The science behind this reason is simply scavenging. Headers do it all on their own and need little if any (usually none) help in achieving optimal scavenging, and can be improved somewhat with header size/length tuning, but even a plain jane set of headers will provide plenty of benefit in terms of optimizing scavenging vs manifolds by themselves. Divorced pipes, when sized correctly on both length and diameter, can help scavenging some, I think mainly due to pipe temperatures and gas momentum (anyone who's used a wood burning stove understands that when the chimney/stove pipe gets hot, it draws harder), and this is accentuated when a merge pipe is introduced (whether it be a scavenging type "Y" pipe or a properly placed balance tube (H or X)) which aids in evacuation using the pulses from one cylinder bank to draw on the other. What people don't seem to realize is this isn't 'theory' in the sense that it hasn't been proven to work and is just some fantasy hypothesis--it actually works, and has been proven repeatedly to do so in various other areas of observation, including automotive industry.
