| Slant Six Forum https://slantsix.org/forum/ |
|
| Camspeculation https://slantsix.org/forum/viewtopic.php?t=21822 |
Page 1 of 3 |
| Author: | gearhead [ Sun Feb 11, 2007 7:47 pm ] |
| Post subject: | Camspeculation |
| Author: | gearhead [ Sun Feb 11, 2007 7:58 pm ] |
| Post subject: | |
Ok...I finally posted it, but now I have to go the hospital to visit a freind for a couple hours...enjoy! Karl |
|
| Author: | emsvitil [ Sun Feb 11, 2007 10:14 pm ] |
| Post subject: | |
I understand effective compression ratio, but where did you come up with wanting 7.28:1? BTW, the first cam sounded familiar and I did some digging Toyota 22R engine (carb version) Intake 272 Exhaust 248 lobe seperation 110 intake centerline 112 Although thats a 4 cylinder engine...... 
|
|
| Author: | Doctor Dodge [ Sun Feb 11, 2007 11:33 pm ] |
| Post subject: | |
Good review, I do think the "reverse dual pattern" (RDP) design has some advantages, especailly for long stroke inline engines that are intake limited. Here is a design I did a while back, a little milder RDP cam design then the one you came-up with but it uses the same thinking as far as using later exhaust opening and shorter total exhaust event. As you already noted, the main problem is the lack of "fast" lobe designs that have decent lash ramps, good lift but are short on total duration. DD |
|
| Author: | gearhead [ Sun Feb 11, 2007 11:34 pm ] |
| Post subject: | |
7-8:1 effective compression is typically what the automakers shoot for to allow for engines to run on pump gas, depending on application. And in my own experience with my various engine builds of my own and friends engines, 7.5:1 is on the ragged edge of detonation with a full tune up on 92 octane premium. What I mean, is that your engine will run with your best tuneup, without fear of detonation, on 92 octane Pacific NW premium, assuming all normal parameters are in place. Any changes, such as extra engine temperature, or extra weight or load on the engine, you will probably start to see detonation. This has been the case in my Pontiacs. I can run around "gettin on it" no problem, until I get stuck in traffic on a hot day, then on the freeway onramp with 185 or more degrees engine temp instead of a typical 165-170, it would ping a little in high gear at full throttle. This general rule has played out in about 8 engine builds so far, not all Pontiacs. Now I realize this may not hold true for a Slant, but I've got to start somewhere and have no previous experience to guide me. Also, I want to run 87 octane in this car because it is a daily driver, and I'm willing to trade a couple HP for that ability. Also, I don't plan on running lower gears than the 3.23's I already have... So I have chosen 7.28 because it was convienently close to 7.25 when working the numbers. There are some other factors I could consider, such as Slants seem to run best with less timing, which means I might be able to up the compression a little without it causing a problem...something I might be forced to do based on dish size vs squish on a zero deck 238" engine. Also, since my cooling system is excellent, I run even lower temps than my GTO. However, those decisions are in my future and wouldn't affect my cam choice. I would simply up the mechanical (static) compression, and would see an equivilent rise in effective compression, with the same intake valve closing point. I would be more than happy to do the calculations for some known combinations, and then we might be able to find a consensus on a reasonable number for a street engine. If running race gas it doesn't matter as much. More compression is almost always better. The issue is finding true, known combinations. They would have to come from people who have a degreed cam, and still have the figures, run there engines at lower temps like I do, have carefully tuned the combination and are certain of its charactaristics. And most important, are on the edge to some extent, so that either they have to detune to run well without detonation, or overtune(extra timing or lean conditions bring on detonation) to get detonation. Not someone who is struggling with thier combination. I also discuss my reasoning in the cams--sanitized post. Karl |
|
| Author: | Dart270 [ Mon Feb 12, 2007 2:31 am ] |
| Post subject: | |
What is the bore/stroke of the Toyota 22R? I believe the bore/stroke ratio is a bigger factor in cam specs and power production than 120 deg vs. 90 deg comparison. Slants should have very efficient burn since they have small chambers and long stroke. I see huge falloff in power on my hipo motor going much over 30 deg timing advance, which you might not see with low comp and weak cyl filling. Lou |
|
| Author: | emsvitil [ Mon Feb 12, 2007 2:43 am ] |
| Post subject: | |
Quote: What is the bore/stroke of the Toyota 22R?
Bore 3.622 Stroke 3.504 144.4 cuin (216.6 if it had 6 cylinders) |
|
| Author: | emsvitil [ Mon Feb 12, 2007 3:45 am ] |
| Post subject: | |
Quote:
BTW, the first cam sounded familiar and I did some digging
Also the 22RE engine is the oppositeToyota 22R engine (carb version) Intake 272 Exhaust 248 lobe seperation 110 intake centerline 112 intake 248 Exhaust 280 lobe seperation 110 intake centerline 112 The EFI engine has long tuned port intake runners compared to the short single plane on the the carb engine. The exhaust manifold is the same and is actually a very short 4-2 system with the 2 going down to 1 in the header pipe. This brings up a question: What are your thoughts with if you have a hyperpak type manifold with the long runners (sort of tuned port) on the cam selection? |
|
| Author: | DusterIdiot [ Mon Feb 12, 2007 6:44 am ] |
| Post subject: | That's a good one... |
Quote: What are your thoughts with if you have a hyperpak type manifold with the long runners (sort of tuned port) on the cam selection?
This also will change things as the overlap has to be within a certain "window" reverb in the plenum and runners is really bad at certain times (and in a very narrow range it actually is "helpful").I would also question the use of "PAC NW Pump Gas" since you're in Portland we know that anything you get is mandated to be oxygenated and is not the best gas to be using on the planet (the good part about Salem is we don't get oxygenated pollution additive controlled gas-we get 10% ethanol in the cheap stuff like Arco). Quote: 7.5:1 is on the ragged edge of detonation with a full tune up on 92 octane premium.
I'm not sure where this goes, I have an 8.3:1 compression '67 that runs fine on 87 regular and runs fine with the stock bumpstick, Holley 1920, etc(a switch to EI makes tuning much nicer than the points distributor)...I also have the 9.2:1 CR slant I just built 6 years ago and it runs fine on 87 when tuned to do so (heavier springs in the distributor to take in the advance rate...I do run 92 when I can afford it and am running strictly "quickly advance springs" for time/tune purposes). Otherwise a nice article and good exercise of the brain. -D.idiot[/quote] |
|
| Author: | gearhead [ Mon Feb 12, 2007 9:29 am ] |
| Post subject: | |
Hi Ed: I would think this would benefit a long branch manifold, because the added momentum of the moving mixture mass that is in a longer manifold runner, would aid in cylinder filling with a longer intake duration. The lower overlap period allow that mass to have less counteracting exhaust reversion. And becuase that mass is greater than normal, the affects of exhaust scavenging would have less total cobined affect as well, so the tradeoff would be beneficial. I would think, maybe...who knows. Duster Idiot: We only have oxygenanated fuel from November through Feb., I just meant we typically seem to have greater issues with consistancy. Or at least I have, so I prefer to be conservative. The 7.5 figure is effective compression and not static compression. Your 8.3:1 engine is likely 7:1 or less if I new your cam specs and plugged them in. Its all based on when your intake valve closes. As stated in the article, I am building the engine to 9.25:1 static compression if possible. (edited/deleted by mod. I tried to leave the main part of this post alone, and just remove the derogatory parts) Also, as I stated in the article, there are many tradeoffs when building an engine combination, and that what helps in one place might hurt in another. In a four cylinder engine, there is not another cylinder firing until 180 dregrees of crank travel. And obviously, no useful work can be done at that point. All I am saying, is that there might be something to be said for having a later exhaust blowdown point. Maybe even for 4 cylinder engines. But certainly not past the tradeoff point in scavenging vs. useful work. Which, of course, I pointed out in the article multiple times. In fact the whole point is that all you have is inertia once the exhaust valve opens. Maybe a little later blowdown event relative to the usual choices might help make some more average power. Especially with longer relative intake durations. Added after editing post ------------------------ In fact, I pointed out in the article that this might not be the best way to improve peak power production, such as in a race engine. In a high rpm scenario, the benefits from tuning your overlap and scavenging affects for a narrow rpm range might very well negate any benefits discussed from a later blowdown event. If your exhaust is setup such that your overlap period creates the proper affect at the rpm your converter stalls at, then, if you keep your rpm within a narrow range around that peak, and allow the drivetrain (converter) to accelerate the car, the tradeoff might very well be in favor of longer durations. Also, as I said...I could be wrong altogether. Or maybe only partly, perhaps the tradeoff would be best incurred somewhere before 120 degrees of crank rotation, and that intertia can do the job after that...it would take experimentation to find out. ---------------------------------- Smith and Morrison...funny, I did read them, but I guess it depends on which article or what you get out of them. The one I read was about average power production and helped me come to the conclusions here. Do you have one that would help make your point...perhaps a link, or some other helpful input. Gearhead |
|
| Author: | AnotherSix [ Mon Feb 12, 2007 10:22 am ] |
| Post subject: | |
AS far as ignition timing and pumping loss is concerned: The advance needed and the effect on power output has to do with the chamber design, the bore, stroke and even the rod ratio to a lesser degree. For a given family of engines, in this case the slants all with one of two chamber designs, the total timing is going to be the same or very close for all engines with the same chamber design. It has to do with the time of the burn and peak pressure. If an engine works better with timing advance that is unusual for what it is, something else, most likely the jetting, is way off and two wrongs don't make a right. When I started working on our slant I asked about what timing lead is proven to work, knowing I would end up very close to the same setting as optimum. The only real way to change the timing lead needed and have it work right is to change the chamber design first, and then the bore and stroke. The part throttle and mechanical curve need to go with the cam, but the total advance has little to nothing to do with the cam. It's not about the octane either. The octane needs to match the effective compression ratio through out the rpm range under load. The fuel needs to be ready to burn but stable enough to wait for the flame front from the spark plug. To much octane in a properly tuned setup will lower power. A range of a few degrees timing is about all there will be if things are right. Sure if the engine is a high rever it might be able to use a little high rpm retard, but that has to do with higher cylinder temps at that point. This is one of those base settings that needs to be right. Otherwise trying to compensate for it with other changes will just get you farther and farther from success. The affect timing has on power is all about the burn, not pumping loss in other cylinders. I think one of the big issues with finding the right cam is the industrial log style intake manifold we are more or less stuck with. It is more like a plumbing fixture than part of a tuned engine combination. |
|
| Author: | Bren67Cuda904 [ Mon Feb 12, 2007 6:37 pm ] |
| Post subject: | |
Humm- not sure what to think after reading so much and I only got about half way through it. One concept sticks out to me. Aside from cylinder scavenging I think that each cylinder should be thought of as one little engine, so our slants are basicly 6 little engines connected to a single shaft. If the power output can be maximized for each cylinder, than the total output is maximized. When you first talked about the difference between the firing angles of the 6 vs V8 and not overlap of power stroke I thought of exhaust manifold pressure being lower. This means less exhaust duration would be needed to get the same amount of exhaust out. You may have said this in your article. One thing I do know is my head hurts.  Some may disagree with your article, but all can agree it is thought provocing. Thanks for your time. Brennan |
|
| Author: | AnotherSix [ Mon Feb 12, 2007 9:11 pm ] |
| Post subject: | |
edited by mod In any event I would love to know what the best cam choices for a slant are, but am still looking and thinking. The crank degrees between power strokes don't have much to do with it on any engine. That would be something to adapt the intake manifold to. Engines have flywheels or torque converters and the time between power strokes and the number of them is what counts. Sure they are farther apart in degrees on a four cylinder, but most of them rev much higher so there is not much more time between the power strokes. Aside from the intake on our slants it is the small bore, long stroke that seems to make it hard to work out. To a lesser degree the rod ratio. We are playing with an engine that is designed for low rpm grunt and economy. Yes I still want more too, but we have to keep our feet on the ground with what is already proven about engine dynamics. Just the fact that we need intake heat to run good at low rpm should tell us something about this. |
|
| Author: | Charrlie_S [ Tue Feb 13, 2007 5:47 am ] |
| Post subject: | |
Waooo!!!!!!!! What happened here? This thread sure got out of hand in a hurry. I am going to delete much of this thread. Let's keep it on topic. Karl, I deleted your last post, because it was too hard to edit out the parts about your GTO. I did not think it was appropriate to leave it, since I had deleted/edited out others comments about it. Please feel free to keep posting, your knowlegde and theories. |
|
| Author: | Doc [ Tue Feb 13, 2007 8:20 am ] |
| Post subject: | |
   Here are the SL6 cam design issues I keep working are: - Matching the overlap and port velocity to the rest of the engine - Finding lobes that get to max lift and stay there at the time when piston movement is the greatest. - Using lobe profiles that have nice lash ramps so the cam operates with minimum noise and wear. I keep getting "closer and closer" but as we know, each engine is a little different so it is hard to really know if the results are "luck" or the based on sound data. DD |
|
| Page 1 of 3 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|
