zx beast Posted January 8, 2009 Share Posted January 8, 2009 So, I have a 1981 280zx with k&n cold air intake, pacesetter monza header, and a flowmaster muffler... How much backpressure do I need? Would I gain power and or torque with straight pipes? I think I have about 2 inch tubing... Quote Link to comment Share on other sites More sharing options...
Drax240z Posted January 8, 2009 Share Posted January 8, 2009 Get a 2.5" crush bent or 2.25" mandrel bent system made, with a muffler and you'll be happy. Straight pipes are not ideal at all on any car, street or race. (most tracks have noise restrictions) Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted January 8, 2009 Share Posted January 8, 2009 ... How much backpressure do I need? ... None. any Backpressure is evil. Quote Link to comment Share on other sites More sharing options...
zx beast Posted January 9, 2009 Author Share Posted January 9, 2009 So, do I want backpresure? Or not? I don't care about how loud, purely performance. I have the flowmasters, and if they have to much backpressure, I will hack it off. lol I mean, how would 2 inch exhaust compair to 2.25 manderel bent with a muffler? About the same? Or would I not have enough power and loose low end torque? Quote Link to comment Share on other sites More sharing options...
jc052685 Posted January 10, 2009 Share Posted January 10, 2009 stock 280zx is slow and does not make much power. Doubt you would notice the differance in a stock and a full exhaust if your motor has not had some work done to it. Might see ??10hp?? up top maybe a tad more. That being said, the exhaust is a good place to start your modifications. A 2 1/2 inch system from any local muffler shop should be plenty of flow for most n/a L28s out there. If you are in search of anything over 200whp then IMO you should be looking at either a v8 swap or my preferance an l28 turbo swap. Quote Link to comment Share on other sites More sharing options...
280zxmike Posted March 24, 2009 Share Posted March 24, 2009 strait exhaust is no fun. lol if your z is like mine you have rust on your lower quarter panels? the exhaust fumes come right up through there and that stuff burns yours eyes and throat. on a second note, its annoyingly loud and doesnt exactly sound great lol Quote Link to comment Share on other sites More sharing options...
Challenger Posted March 24, 2009 Share Posted March 24, 2009 I wouldnt throw around numbers like 10hp. Quote Link to comment Share on other sites More sharing options...
zx beast Posted March 24, 2009 Author Share Posted March 24, 2009 I am now running straight headers... lol and the fumes kinda suck, but I like the sound lol I feel a differance when I get past four thousand rpm, but I feel a power slump between two thousand five hundred, and three thousand... So I think it is no good for top end. But when I really get on it, I do notice a differance in how long I do not have traction (I can't hear myself burn rubber now though... exhaust is too loud) Quote Link to comment Share on other sites More sharing options...
jc052685 Posted March 26, 2009 Share Posted March 26, 2009 I wouldnt throw around numbers like 10hp. Why not? I think it is a good guess on a 100% 280zx going to full exhaust. I would suspect your milage may vairy but and untunned upgrade like that on an l28e might show 10hp MAYBE 15hp on a dyno in the upper rpm. The OP is talking about hacking off his already modified exhaust in search of more hp. I gave the recomendation of a larger pipe diameter. But still on a factory L28e that has a high flowing muffler on it already a larger pipe might not even be noticed. Quote Link to comment Share on other sites More sharing options...
zx beast Posted March 26, 2009 Author Share Posted March 26, 2009 Your z is beautifull by the way mr jc 05... But anyways, I have been told repeatedly from kids at school (never a good source) but they say running a straight header is bad for your car, because I backfire sometimes, and that is bad for the valves. Is that true? Will running a straight header kill my car? And do you think I could fix alittle of the back fire problem with new high performance sparkplugs, and or wires, and or coil? To reduce the amount of unburnt fuel by burning more is what I was thinking... Quote Link to comment Share on other sites More sharing options...
280zxmike Posted March 27, 2009 Share Posted March 27, 2009 backfire usually comes from either leaning out or running too rich, but yea open exhaust (meaning no back pressure) is bad for an N/A car, but if your turbo no problems Quote Link to comment Share on other sites More sharing options...
jc052685 Posted March 27, 2009 Share Posted March 27, 2009 Your z is beautifull by the way mr jc 05... But anyways, I have been told repeatedly from kids at school (never a good source) but they say running a straight header is bad for your car, because I backfire sometimes, and that is bad for the valves. Is that true? Will running a straight header kill my car? And do you think I could fix alittle of the back fire problem with new high performance sparkplugs, and or wires, and or coil? To reduce the amount of unburnt fuel by burning more is what I was thinking... Thanks, I suppose you could "burn" a valve. Though I have never seen one, but that does not say much. The Idea behind doing a performance mod is being able to tune for the change in airflow into the motor. There is a very good post on this kind of thing witch it below. I think the whole "burn a valve" thing is from very old thinking in the american muscle car world. Carbs and people that dont know any better doing mods and not tunning for them can damage things on a non turbo motor also. http://forums.hybridz.org/showthread.php?t=110185 Quote Link to comment Share on other sites More sharing options...
jc052685 Posted March 27, 2009 Share Posted March 27, 2009 but yea open exhaust (meaning no back pressure) is bad for an N/A car, but if your turbo no problems Not exactly true. With tune its fine........ see. lol Quote Link to comment Share on other sites More sharing options...
Challenger Posted March 28, 2009 Share Posted March 28, 2009 Are we comparing nitro fueled supercharged 8000hp v8's to a 30 year old strait 6..... I also lost low end by removing my exhaust. (exhaust manifold and about 4 ft of pipe) Quote Link to comment Share on other sites More sharing options...
S130Z Posted March 28, 2009 Share Posted March 28, 2009 stock 280zx is slow and does not make much power. Doubt you would notice the differance in a stock and a full exhaust if your motor has not had some work done to it. ...... I went with a 2.5 inch straight pipe with headers and I REALLY noticed a difference in low end, BIG lose. Every N/A motor needs some back pressure, and just like a SBC, there is a sweet spot to place the muffler for peak performace. Keep doing some research on back pressure before you make your decision. I wish I had put in a muffler, but I'm going turbo, so no need to change up now. Quote Link to comment Share on other sites More sharing options...
jc052685 Posted March 28, 2009 Share Posted March 28, 2009 Are we comparing nitro fueled supercharged 8000hp v8's to a 30 year old strait 6..... I also lost low end by removing my exhaust. (exhaust manifold and about 4 ft of pipe) Not really, just the first pick I found lol. Of course you lose low end. Your are trying to make horsepower! Not lowend torque. You gotta tune and match your mods. Cam, intake, header, port work, ect all have to work together. As in be designed to increase the power made in similar rpm ranges. Back pressure is not needed on a N/A motor to make power. You may be confusing back pressure with exhaust velocity, wich is used for port scavenging. Go down to your local 1320' and you will see most of the old schooler american v8s are racking long tube only. Small blocks and big blocks anywhere from 350hp on up. They want there motors making power WAY up high. My old boss was shifting his mild BBC at like 7500rpm. Quote Link to comment Share on other sites More sharing options...
PurePontiacKid Posted March 31, 2009 Share Posted March 31, 2009 My personal experience I found that my 2.5" crush bent system flowing into dual Cherry Bombs actually felt like it had more power all around, and pulled MUCH better towards the top end (I don't shift at redline anyways, but it gets to where I shift much faster) than running open head pipe (I don't have a header) or even the stock 2" exhaust with the muffler hacked off (even though it sounded damn good ) I noticed with the 2.5" system, it's a little throatier sounding, and the Cherry Bombs keep the same sound as the straight pipe, just a bit quieter Of course, I also "tuned" the AFM after I did all my mods (at least as well as you can tune the stock AFM, still running pig rich at WOT...) Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted March 31, 2009 Share Posted March 31, 2009 Backpressure in exhaust is ALWAYS bad. It just doesn't use simple rules like a bigger exhaust always reduces backpressure, so it's harder to visualize. Quote Link to comment Share on other sites More sharing options...
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