260ZRED Posted December 14, 2002 Share Posted December 14, 2002 Can somebody please explain what exactly 'air horns' do? I got a 260Z with 2 72 SU's and was wondering if it is worth buying the aftermarket airhorns.... Anybody got the ones from motorsport? Do they help at all? How are they supposed to flow more air and has anybody tried making their own? Thanks for any info. Also, how can I test the efficiency of my intake system? Quote Link to comment Share on other sites More sharing options...
Guest Zpeed Posted December 14, 2002 Share Posted December 14, 2002 they are supposed to suck in more air... but i see it as they are sucking in hot engine air... and you want cold air... my cheapo recomendation is... use the original 240z airbox... get some cheap flexible 3-5inch garden water hose, its the black stuff they use to put in the ground for pipes etc, also like ur home hoover (vacuum cleaner) hose... and put it thou the hole in the front next to the radiator, and put it in a spot that will get most air... when goin straight... and either put a POD air filter on that, with no filter in the 240z airbox, or no pod at the end, and use a k&N filter inside the 240z airbox.. and ur getting some cold air... and alota air... Quote Link to comment Share on other sites More sharing options...
Guest Zpeed Posted December 14, 2002 Share Posted December 14, 2002 alllllsssooo the air horns, in race cars etc, have no filters just straight horns picking up air.. but people who use them on the street put filter form around them... i actaully have individual k&N's on mine, and see them have a good performance improvement,i originally had individual form filter.. didn't like them... Quote Link to comment Share on other sites More sharing options...
Bob_H Posted December 14, 2002 Share Posted December 14, 2002 For my senior design project, I tested SU's from Z therapy,(with the help of Scott). In the end, for the airflow the motors are capable of, the stock mounting plate,(i.e. the stock filter plate), vs. the aftermarket horns,(I tested TWM horns, and some cast ones), are the same. The stock horns work great and you gain nothing from the fancy aftermarket horns unless you are talking a full blown race motor, such as GT-2. -Bob Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 14, 2002 Share Posted December 14, 2002 Running without any kind of air horns is pretty much similar to having a reduced-diameter restriction in the inlet flow path. Think of the air trying to make a hard 90 degree turn around the face of the carb or filter backing plate. Any kind of radius there will help, and full-radius horns would be desireable. The stock air horns should be adequate for most applications, though. People (some racers, some idiots) who don't care about engine longevity may run air horns without filters. I've always used filters with mine. It can be really tricky because the strut tower and brake MC are in the way, so be sure you size the air filter and air horns to ensure they fit. I've got a big oval ITG filter over 6 45mm air horns, and it's kind of a bitch to get the filter on. Better than before, when I had dual ITG filters over 2" full-radius air horns. I had to mount the filters upside down, and couldn't utilize the dzus-type fasteners to remove the filters, I had to unbolt the backing plates (whew). I should've used shorter air horns, full radius or not. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 14, 2002 Share Posted December 14, 2002 But Bob, the full-radius ones look so bad-ass! Seriously, that sounds like good evidence that regular (not full-radius) horns are adequate. Probably a lot cheaper than the $45 EACH I paid for the TWM full radius ones for my old 2" Jag carbs. If you've got stock carbs, then the stock air filter backing plate air horns are the way to go. Running no horns at all will likely significantly reduce high-rpm breathing ability. Quote Link to comment Share on other sites More sharing options...
260ZRED Posted December 14, 2002 Author Share Posted December 14, 2002 Thanks guys! I like Zpeed's "cheepo" idea the best, going to try it and post some results... I was wondering what those holes were for anyway! One more thing - would it help to have the stock orange airbox chromed or polished? Polished metal is supposed to reflect the heat away??? Off topic: Will I have to adjust my carbs after I do this? And can anybody hook me up with a K&N filter for the stock orange airbox? Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted December 14, 2002 Share Posted December 14, 2002 I've got the TWM air horns on my 240. I didn't notice any substantial improvement, but they sure do look bitchen. And they sound sweet too. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted December 15, 2002 Share Posted December 15, 2002 Bob, have you any data/personal experience at achieving 150% VE on a naturally aspirated setup? Seems REALLY high to me, and it surprises me a great deal to hear that number associated with a 30 year old design. (for example the jaguar D-type with extra long intake runners was in the 105%-108% area) From all I know, VE is a comparison between the air burnt during combusion, to the displacement of the cylinder itself. ie: if a 467cc cylinder consumes 450cc of air from the atmosphere (drawn at atmospheric pressure) that would be a VE of 450/466 or 96.4%. A 150% VE would mean 700cc of 101KPa air, compressed and crammed into a 467cc cylinder in the case of a L28... without the aid of forced induction. Someone please tell me if my concept of volumetric efficiency is incorrect! Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted December 15, 2002 Share Posted December 15, 2002 I've tested the stock air horns at the track on my 2.8L and my 2.9L and on both engines my ET and mph were quicker WITHOUT any airhorns. However this summer I made some stub stacks from a child's plastic play toss ring by cutting it in half and then gluing it to the base of my K&N air filter plate and I did start averaging around a .5 mph increase in my drag times so there is a benefit from a properly radiused entry way into the carb throat. later,norm Quote Link to comment Share on other sites More sharing options...
Bob_H Posted December 15, 2002 Share Posted December 15, 2002 looks, shmooks. Until you got up into the 150% VE there wasn't a difference btw the stock backing plate, half radius horns and full radius horns. And I think it was a total of about 5-10 cfm total difference at 25 inches of water,(or 27, can't remember right now). But NO backing plate did make a rather significant difference, esp. as the airflow increased. Remember, on a a 2.4L, 100% VE was about 150 cfm per carb. The carbs maxed out somewhere just under 300 cfm. So even for a 3.1, it is well below the tolerance difference btw stock backing plate, short or long horns. -Bob Quote Link to comment Share on other sites More sharing options...
Bob_H Posted December 15, 2002 Share Posted December 15, 2002 Richard, Your concept is fine, but I think I wasn't clear in what I was saying. I was saying that to get the benefit of the fancy aftermarket horns, you needed a 150% VE. Something you just won't see on a NA motor. In otherwords, they aren't worth the money. The best a 2.8, mildly modifed motor might see is low-mid 90% range. 100% or more requires serious work on the cylinder head, esp. the the L6 non-cross flow head. A fully stock motor might only see 80% VE. -Bob edit-clarified the aftermarket vs. normal horns... Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 15, 2002 Share Posted December 15, 2002 Bob, are you saying you didn't see any difference between having air horns and having NOTHING until you got to 150% VE equivalent flow? That would be very surprising. It wouldn't surprise me if the stock backing plate air horns flow almost as well as aftermarket ones, but I wouldn't expect a setup without any horns at all to flow nearly as well at 100% VE equivalent flow. Norm's results are very surprising as well. It would be nice to have some comparitive dyno results. I wonder if not having anything, which should make the carbs act like they're smaller in diameter, might IMPROVE low-end to midrange torque to the point that ET and trap speed are better. Or if it's more an intake tract length relationship and the shorter length with no horns or with stub stacks improve midrange to high-rpm power. You ever go to the dyno, Norm? Who was it said "In theory, theoretical results are more important than practical results, but in practice..."? Quote Link to comment Share on other sites More sharing options...
Bob_H Posted December 15, 2002 Share Posted December 15, 2002 I know I often confuse even myself, but I did say: But NO backing plate did make a rather significant difference, esp. as the airflow increased. So, recap: no backing plate sucked. The stock backing plate,(or air cleaner assy), and aftermarket horns, however, are nearly the same, i.e. no difference gained from the fancy horns over the stock air cleaner assy. Clear as mud now? One more time. Nothing but carbs = bad... Stock air cleaner/backing plate = good Fancy aftermarket horns = good That should help. Also, we have no idea what the airflow in the engine compartment is like at 80-100 mph. For all we know, it is pressurized, and negates the benefit of the horns, hence Norm's improvement? or maybe he just drove better those days... -Bob Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted December 15, 2002 Share Posted December 15, 2002 Horns vs No horns. Think of a wing on an airplane and what exactly causes lift? Pressure differential. Same goes for adding airhorns. The gains are due to a pressure differential created and the velocity of the air is greatly increased as it enters the stack because of this. I used small stacks on my last intake manifold and have heard they work just as well in forced induction applications. This was during construction of my last intake manifold. Quote Link to comment Share on other sites More sharing options...
johnc Posted December 15, 2002 Share Posted December 15, 2002 You boys are forgetting about fuel metering. Air horns reduce turbulence at the needle and jet giving a more consistent pressure drop. Using a strobe on an engine dyno I've seen how fuel kind of puffs out without air horns and becomes more of a flow with air horns. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted December 15, 2002 Share Posted December 15, 2002 Now that sounds like a much better explanation of the benefits of air horns! On my 260z I have just the "flat plate" for a airbox back. I'll see if I can track down one with the stock air horns on there, and do a seat of my pants comparison. Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted December 16, 2002 Share Posted December 16, 2002 In real world track testing with air rushing over the engine compartment I ran faster track times without the stock airhorns. I tried it a number of times on the same day and it was consistently slower with the stock airhorns installed as opposed to just the carb body entrance. The sharp edges on the stock airhorns DISRUPT and hinder airflow. If the edges had a good 270 degree roll then there would be an increase in airflow. David Vizard has written a carb tuning book and it has a small section on SU carbs with Dyno graphs that SHOW a LOSS of HP with nonradiused airhorns. He showed a 4% increse in HP with a properly radiused 4" air horn. He showed a 5% increase in HP with a 1" stub stack. He made an 18" long air horn and showed an enormous increase in low end torque in the realm of 10% but the HP obviously dropped way down. Since installing my home made stub stacks my drag times have improved over just the bare carb body entrance.A consistent half mph increase would indicate an increase of about 4 HP through the better controlled air entryway. If you have time go by Barnes and Nobles and look at the David Vizard Carb book. later,norm Quote Link to comment Share on other sites More sharing options...
Drax240z Posted December 16, 2002 Share Posted December 16, 2002 Norm when you say "1" stub stack" what do you mean exactly? A 1" tall air horn, with full radius on the inlet? Drawings, pictures, etc. if you have them. Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted December 16, 2002 Share Posted December 16, 2002 Think of a donut cut in half and then placed at the carb throat entrance and you have yourself a stub stack. They don't help with low end torque production like a 4" air horn does, but they do make more HP. later,norm Quote Link to comment Share on other sites More sharing options...
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