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anesthes | Primary tube math | ||
Master Guru
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I was going to post this on CF, but I don't want to get 12 responses from guys who said "xxx brand worked for me" yet did no research before their purchase.
Heads are trickflow 23. They flow 177cfm at .500 lift, and 183cfm at .550 lift (exhaust). I'm running a .528 exhaust lift cam, so say around 180cfm at my running lift. Exhaust ports are "D" shape, and use a Felpro 1404 gasket. (1.5 x 1.5") Looking at headers, options are Hedman 1 5/8 coated for $411 to my door or Hooker 1 3/4" coated for $710 to my door. Hedmans are 14 gauge and have an inside diameter of 1.459" Hookers are 18 gauge and have an inside diameter of 1.642" Both headers are coated on the outside only, not on the inside. The Hedman headers, considering the following formula of 80CFM per square inch, and 15 gauge will flow 133.74 CFM. 1 5/8" - .166 = 1.459 ID Area = 1.6718621478590436 * 80 cfm = 133.74 CFM. The hooker headers using the same formula flow 171.47 CFM. 1 3/4" - .098 = 1.652 ID. Area = 2.1434332693206293 * 80 cfm = 171.47 CFM. I made a math error previously, so this post is corrected. It appears from these numbers that, a 1 5/8" header will support a stock application. However pretty much any aftermarket head flows 160+ CFM.. It seems as if, for good aftermarket heads you really want at least a 1 13/16" header. I'm not sure such a thing is available for C4's, but it makes sense why a lot of C5 guys are running 1 7/8" headers. Now the wrench thrown into this mix is forced induction. I'm running between 6-8psi of boost. My camshaft has 2* of overlap at .050". So I think we can throw out any sort of scavaging since the intake is pressurized. The question is, will the spent charge exceed the 183cfm of the cylinder head thus requiring a larger primary tube? Pretty much all primary sizing math appears to be based on naturally aspirated setups, especially setups with larger camshafts with increased duration. Thoughts? -- Joe |
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Posted on: 2008/8/6 16:40
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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Matching up the flow bench numbers implies you care about having the same amount of pressure drop across the valves as across the primary tubes.
I don't see any reason to try matching those values. Maybe it'd be more worthwhile to match velocity. None of your parts are going to flow that cfm on the car anyways. Personally I'll take the least restrictive part available anywhere I can get it on the system until there is a penalty in torque loss or something. |
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Posted on: 2008/8/6 17:51
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1985 Z51, ZF6 |
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LT4BUD | Re: Primary tube math | ||
Guru
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The main point in selecting headers isn't really flow.....in fact it is scavaging....this is the basis of long tubes being more effective than shortys....I think you are focusing on the wrong parameter regarding your headers ....having said that, I agree with CC that for the most part bigger is better as far as basic flow restriction goes.... |
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Posted on: 2008/8/6 18:27
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
Well, the main point of selecting tuned primary pipes, I agree. However again with forced induction scavaging is not possible as the intake is pressurized. -- Joe |
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Posted on: 2008/8/6 18:52
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
Well on a naturally aspirated motor you want them as close as possible to maintain exhaust velocity, or you will suffer torque loss. (in theory). The question really is, with forced induction do you throw the velocity argument out the window along with the scavaging, and just go with the larger primary. That seems to be your logic? -- Joe |
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Posted on: 2008/8/6 18:54
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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Leaning towards it.
But even with forced induction, you still have pressure waves bouncing back and forth through the primaries, so it seems like they could still provide scavenging. Scavenging doesn't care about the static pressure, it just depends on a pressure differential and how long it takes that wave to get to one end of the pipe and back. But maybe the smaller pipes required to accomplish that do more harm than good on a blown motor, I don't know. |
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Posted on: 2008/8/6 19:01
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1985 Z51, ZF6 |
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tequilaboy | Re: Primary tube math | ||
Guru Newb
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With forced induction, the only concern is to minimize backpressure at acceptable sound levels, and to keep the flames from setting things on fire.
The intake pressure and overlap will scavenge the cylinder just fine once your into boost. My guess is that you're into boost before the headers would have any effect. I suspect its what's downstream that has more effect on the back-pressure than the primary tube diameter, but I agree that bigger should be better. |
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Posted on: 2008/8/6 19:06
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anesthes | Re: Primary tube math | ||
Master Guru
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Neither do I (know). I was hoping someone would have some solid data.. All my books, and all the Vizard crap I read is all based on naturally aspirated motors. One book I have makes a mention "Size and length are meaningless on a forced induction engine, however blowers do not like back pressure therefor larger pipes are better." Larger than what? My finger? Ugg. I wouldn't mind but the difference really is nearly double the cost. The other option is I can buy some used 1 3/4" hookers off a forum member for about $250, and have them ceramic coated locally for another $200, and another $50 or so for reduces and I'm around $500. Or I can buy 'painted' 1 3/4" hookers for $430, and have them coated locally, reducers, etc for about $675 or so. -- Joe |
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Posted on: 2008/8/6 19:06
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tequilaboy | Re: Primary tube math | ||
Guru Newb
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Not directly on topic, but here's an interesting read on overlap and scavenging with inlet pressure greater than exhaust pressure. (I love these old NACA reports):
http://www.not2fast.com/NACA/naca-tn-405.pdf and another (more interesting): http://www.not2fast.com/NACA/naca-tn-2025.pdf |
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Posted on: 2008/8/6 19:27
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LT4BUD | Re: Primary tube math | ||
Guru
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You might consider contacting Burns with your question..
http://www.burnsstainless.com/Xdesign/xdesign.html They seem to at least acknowledge the effect of supercharging.. |
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Posted on: 2008/8/6 20:25
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
1932? Making figher planes outrun the Japs definately helped boost our automotive technology! Thanks for the links! How do you feel about ceramic coating the inside of the volute? For the simple purpose of keeping the air temp from heat socking the case and keeping the case from soaking the air. -- Joe |
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Posted on: 2008/8/6 21:08
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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I don't think ceramic coating is going to do squat to effect the air temperature inside. It's so thin to begin with.
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Posted on: 2008/8/6 22:32
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1985 Z51, ZF6 |
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tequilaboy | Re: Primary tube math | ||
Guru Newb
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I know there are some ceramic coated impellers intended to improve efficiency mostly used for turbos. I don't know how effective they really are for centrifugal superchargers, though. Less friction with the air maybe, I think the Raptor uses one.
Coating the volute/diffuser may keep the components themselves cooler, but I think that would just tend to increase the charge air temperature. I'd really like to see somebody do a fully shrouded impeller like the old DVL design. That's supposed to be the most efficient impeller style. Basically an impeller with a cover on top of the vanes which avoids any leakage between the vanes and the case. Would be expensive. |
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Posted on: 2008/8/6 22:52
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
With the Powerdyne I'm more concerned about overheating the bearings than I am the outlet temp. Outlet temp can be cured with alky injection or an intercooler, but I was thinking if the volute was ceramic coated inside it would keep the head unit from getting head soaked. Now, would the aluminum volute warp in the 550f oven while the ceramic is baking on? that is another question. Another thing, the ceramic would decrease the clearance between the impeller and the volute by a very small percentage which should aid efficiency. In theory it should keep the volute from expanding when it gets hot, so you would always have the same clearance rather than more when cold, less when hot. But I guess this is off topic. I think I'm going to run the 1 3/4" long tubes and have 'em coated in + out locally. maybe if the coating is good it will help with some of the high inlet temps based on where our air cleaners are located. Jethot told me 400f reduction in underhood temps. I've yet to find someone with an IR that has published before + after results. -- Joe |
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Posted on: 2008/8/6 23:10
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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I bet the underhood heat is due to radiation, and that's what the outer ceramic coating is trying to reduce, not convection. You could paint everything in the engine compartment white too, that'd help keep them from absorbing as much heat...
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Posted on: 2008/8/6 23:18
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1985 Z51, ZF6 |
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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400f reduction?
Um, are they implying that it's 500 degrees in there right now? |
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Posted on: 2008/8/6 23:19
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_________________
1985 Z51, ZF6 |
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
I'm not sure. I'm guessing the surface temp of the headers is around 500-600f. I should have checked my stainless ones with the IR before I took the car apart. By any chance, do any of you guys know which headers these are? They are not Hedman or Hooker by the looks: http://members.cisdi.com/~anesthes/wtf/ Seller doesn't know the brand or primary size. If they are good I'll sand blast 'em and ceramic coat them. I've never seen anything like 'em though.. -- Joe |
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Posted on: 2008/8/7 1:04
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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Looks like some attempt at an equal length setup, which is overrated on the already imbalanced timing of each cylinder bank on a 90* V8.
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Posted on: 2008/8/7 6:22
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_________________
1985 Z51, ZF6 |
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
True. Apparently they were Lingenfelter headers, which are now made (or copied) by Stainless Works. I think I'm gonna go with the Hooker 2151's and just have them ceramic coated inside and out. -- Joe |
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Posted on: 2008/8/7 12:05
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jhammons01 | Re: Primary tube math | ||
Senior Guru
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The reason that there is no data on FI over N/A is that forced induction will have no effect on CFM at all.
CFM will be dictated by the smallest orifice in the entire setup......once you've determined where the smallest orifice is.....and you calculate the flow of said orifice, no upstream pressure will change that flow. So you are looking for Data that does not exist and that is why you are asking it on this forum....what I mean by that is you are a very very capable researcher.....and you are failing to find what you are looking for, hence the need to ask here. "tuned" I am not an expert but the way Tuning of intakes and Exhaust were explained to me was the "Flow" or waves are tuned to move at the right time. Picture a wave in the ocean hitting a wall or a jetty. The wave "bounces" back creating a wave heading in the wrong direction.....you want that wave to hit the other side and be heading toward the inlet valve when the valve opens up again.....that is the reason for the "Length" of the plenum being so important. Headers are the same way, there is a restriction, somewhere down there, a valve opens up and exhaust comes flying out of a chamber in a large wave...you don't want that wave to hit the restriction and come flying back just at the time the valve opens up..... That was the explanation I got on flow and tuning. The CFM part I work with every day and I am sure of those facts. The Tuning part.....I'm just throwing things out there |
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Posted on: 2008/8/7 15:52
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anesthes | Re: Primary tube math | ||
Master Guru
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Quote:
True. I was more asking for opinions. I had 1 3/4" primaries. I think they were sized appropriately, but once I developed a flange leak (that ended up being the cats, but that's another story) I decided before spending $700 or so on headers I'd review my info, and gather up a few opinions. I appreciate the responses. Quote:
Oh I know the theory, at least in a naturally aspirated setup. On a boosted setup with overlap your intake pressure during the overlap pressure will exceed the vac negative pressure so it renders the scavenging effect useless. (at least that's my opinion based on my reading material). I've also read, as Kevin suggested, data showing on an odd fire V8 (sbc) that 'equal tuned / length' primaries are of no advantage. I was more looking for a few people to say "yeah, you want the 1 3/4 on your boosted setup, because you want the most flow possible". I think both Kevin and Patrick made those statements and I put a lot of weight in both of their opinions. Quote:
Agreed! -- Joe |
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Posted on: 2008/8/7 17:56
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jhammons01 | Re: Primary tube math | ||
Senior Guru
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Good, 'cause they know a lot more than I do. |
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Posted on: 2008/8/7 19:04
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CentralCoaster | Re: Primary tube math | ||
Senior Guru
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Quote:
CFM will be dictated by the smallest orifice in the entire setup......once you've determined where the smallest orifice is.....and you calculate the flow of said orifice, no upstream pressure will change that flow. Uhh.... The upstream and downstream pressures will always effect the flow through every part of the system. And every single part of the system has friction, causes pressure loss, and impacts the flow, not just the most restrictive part. So knowing the flow rating of just that part of the system is meaningless. |
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Posted on: 2008/8/7 19:50
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_________________
1985 Z51, ZF6 |
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jhammons01 | Re: Primary tube math | ||
Senior Guru
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No no....and don't make me go digging up Flow rules and all about conductance (that is the term you are struggling to find). Conductance is dictated by how many elbows and bends reductions etc.
Bernoulli's law is in contradiction with what you posted. Look it up. An entire systems flow rate is predicated by the CFM capability of the smallest orifice It doesn't matter how much pressure you have upstream the orifice will only allow a set amount of volume to flow threw it over a given period of time. |
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Posted on: 2008/8/8 4:09
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jhammons01 | Re: Primary tube math | ||
Senior Guru
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pre-emptive
Conductance - The actual capacity of a piping system in CFM. Conductance in a vacuum system can be limited by line size and configuration. Quote: Reprinted from page 99 of Scientific Foundations of Vacuum Technique by Saul Dushman 2nd edition (J.J. Laffery - editor) with permission from John Wiley & Sons. Copyright © 1962 by John Wiley & Sons. |
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Posted on: 2008/8/8 4:35
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