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#1
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Hey guys...I've put headers and a hefty cam (.458 lift, 284 degree duration) on a '84 318. The collectors which came with the Hedman headers reduce to 2-1/4". Has anyone ever heard of the necessity of dropping the pipe somewhere in-line to 2" for backpressure reasons? Just asking before I have the Pipes bent! Thanks a lot!
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#2
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Use 2 1/4 pipe all the way back.
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#3
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Use 2 1/4 pipe all the way back.
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#4
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I would also put a "x" pipe in the middle instead of trditional "H" pipe. If your local muffler shop can't make one then get one from"dr gas" in utah. It's worth the money. I run one on my race truck and it works well.
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#5
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Hey Guys, thanks a lot. If any of you know what the tags on my rear end mean, please tell me. I'm trying to find the ratio and type of rear end I have. I have two tags...one says "1844", and the other says "2.2" any help would be greatly appriciated!
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#6
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What they said on the exhaust thing.2 1/4 duals with x-pipe if possible although an h-pipe would be okay too.
Diff thing. 2.2 is the gear ratio that is in the case. This is a really good gear to have with a 318 as long as you plan to run at the Bonneville salt flats with 4 stages of nitrous, a 6-71 blower and a tailwind. Should be good for about 250 mph at 4100 rpm LOL |
#7
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Christopher, so here we are again! Dave, I like your humor! All good advice, however I have a different opinion on 2 1/4 " all the way back. On a 318, I'd go with downsizing to 2" for these reasons. 1. A 318 doesn't move a lot of air like a big block with sewer cover size valves. 2. Just as in the tubing headers you don't want to go too big or you'll loose velocity. The smaller 2" pipe will be more than adaquate and the exhaust gasses will move faster too. 3. This fast moving exhaust gas mass also forms a suction on your cylinders and will "scavenge" (or pull by means of a vacuum, which follows anything that moves through air, the exhaust gasses moving through air present inside the pipes, @ speed, hence "drafting", as in Nascar racing ) the gases from the cylinders because of this higher speed of the exiting gasses. The "X" or "H" crossover pipe trick is a must for performance. This is my opinion, how do you other guys feel about it?
Richard Richard |
#8
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Everything Richard has said is true,however and this is just my personal opinion,I'd still use 2 1/4 " pipe at least to the mufflers.This is based on personal experience with a 72 Duster 318 I had as my first car.I put headers on it and went to NAPA and got a set of Walker mufflers for a '70 Hemi Road Runner.They were 2 1/4 in diameter.I put the mufflers in the stock area under the car and ran no tailpipes.(The Jacksonville Sherrifs Office later changed my mind on no tailpipes!!!)Anyway,I took the car to Gainesville to race and made some baseline passes with full exhaust,and then pulled the pipes off and ran open headers.Guess what?? The car ran the same ET and MPH (within 3/100ths)So that's the reason for my answer.I later did put tailpipes on the car,and these were 2.0" in diameter.Richard I feel like I've been chasing you today,and I like your answers.Dave,did you ever build that car you've described??? Oh,and by the way,the car was dead quiet with those Hemi mufflers too!!!
[This message has been edited by Christopher (edited April 22, 1999).] |
#9
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Everything Richard has said is true,however and this is just my personal opinion,I'd still use 2 1/4 " pipe at least to the mufflers.This is based on personal experience with a 72 Duster 318 I had as my first car.I put headers on it and went to NAPA and got a set of Walker mufflers for a '70 Hemi Road Runner.They were 2 1/4 in diameter.I put the mufflers in the stock area under the car and ran no tailpipes.(The Jacksonville Sherrifs Office later changed my mind on no tailpipes!!!)Anyway,I took the car to Gainesville to race and made some baseline passes with full exhaust,and then pulled the pipes off and ran open headers.Guess what?? The car ran the same ET and MPH (within 3/100ths)So that's the reason for my answer.I later did put tailpipes on the car,and these were 2.0" in diameter.Richard I feel like I've been chasing you today,and I like your answers.Dave,did you ever build that car you've described???
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#10
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Christopher, open headers are alright for racing, but back pressure should not be neglected in street use. Bone stock to mild performance 318 with headers and dual exhaust, my best luck was with 17/8 dia tail pipes. For a sleeper, go to 21/4 in a single exhaust version, 318 likes that as well.
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#11
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I'd still use the 2 1/4" pipe and at least till the mufflers. If it only had a stock cam I'd only use the 1 7/8" pipe,but with a .458 cam you will need to let it breathe.I am running a 360 with the dual pattern .455 mopar cam and I have a 2 1/2" pipe till the mufflers and then a 2 1/4" tailpipe with an h-pipe. Works GREAT and sounds INCREDIBLE. Not loud and Blatty, just smooth and rumbly.
Christopher. I almost had that car I described before. Stock 318(125 hp!), 4000 lb. Mirada, 2.2:1 rear gears. I'd like to say that it started slow but really flew out the top end, but....it started slow and then plodded after that. To say that the car was slow to react would be an understatement. I once got sideswiped by a pet turtle. LOL! now that's a slow reacting car!! Later Dave |
#12
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Dave,I know what you mean!!! That Duster I described in the post had 2.76 gears in it.It wouldn't come out of the hole at all,but great top end!!!A couple of 455 Oldsmobiles found this out the hard way.
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#13
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O.K. guys, I like what you are saying about exhaust and cams, but I'll put my last 2 cents and side with Richard on scavenging. My last 74 318 duster build had 17/8 dual with headers, 9.5 compression, 340 heads and rods, 202 valves and a host of goodies, but the cam was M.P. P4120233, 292-292-76 degrees, .508'' lift intake and exhaust. the top end performance with the 17/8 pipe was really nice. I remember wanting bigger pipe at the time, and being talked out of it by the muffler guy. You choose your own, but I will stand beside this as a proved combination.
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#14
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Man I love this, I just wrote the other and now I have to eat crow. I went to the speed book, and they do say 17/8 is good for high rev or 4 speed app. which is what I had. But for max efficiency, 21/4 all the way back, with a minimum 2'' connecter any where between the collector and the muffler. My hat is off gentlemen.
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#15
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Brian: I also agree with Richard on the principals on the exhaust but I would rather err slightly on the side of a bit of excess. Keep in mind that we are not talking about primary header tube size but what to do with the exhaust gasses 34" later. The effects of oversizing the system that far down stream I feel would be neglible. Scavenging at that point is also quite minor. Keep in mind we are not talking about a 3 1/2" exhaust oversize but a 2 1/2" pipe.
P.S. to Brian. 1 7/8" exhaust on a .508" lift cam motor even if it is a 318 in my opinion is WAY under piped. I'm not saying that it wouldn't run. I'm not saying it wouldn't run fairly well. But it wouldn't run anywhere near to it's full potential. What comes in must go out and I think that would be like farting through an empty Bic pen On the lighter side I think you could sell tickets to watch it blow out candles at 30 paces V-E-L-O-C-I-T-Y |
#16
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You guys are making me laugh. How do you make those smiley faces anyway?
P.S. I guess an engine backfire would be equated to a burp. |
#17
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OK guys, here is my nickel's worth on the subject. Use whatever pipe you want. It is your vehicle. From my experience, anything from 2 1/2" to 1 7/8" should work fine. The big pipe = high lift cam support, louder, and high rpm potential. Small pipe = more torque, less cam lift, quieter, less rpm potential, probably better economy due to scavenging effect (altho minimal). I have used all sizes between the two ranges I mentioned above, and I prefer the 2 1/2" pipe between the muffler and the engine, and 2 1/4" for the tailpipes on a 318. One my 360's, I am currently running 2 1/2" pipes to dual cats to dual tailpipes and out the back, no mufflers on my big truck (360 hp). It does get a little "blatty" if you put your foot in it and leave it, but otherwise, it sounds awesome. On my little truck (185 hp stock 79 vintage police special 360) I am running 2 1/2" pipes to dual cats to dual hemi mufflers to 2 1/2" tailpipes and out the back. It also sounds awesome, but with the mufflers, it doesn't get anywhere near as loud. There is also a small issue of a sizeable difference in cam lift between the 2 engines, (360 hp has .494/.485 lift, and small engine has probably .385/.385 lift), but that doesn't mean much since the duration is so close to stock on both motors. Bottom line----2 1/2" pipes with dual cats and mufflers will provide plenty of flow & performance, meet all legal requirements, and still sound very good to any gearhead. One last thing, if it is at all possible, run the exhaust out the rear of the vehicle. If it exits anywhere on the sides, it will sound louder to the cops.
[This message has been edited by Ramcharger 4x4 (edited April 24, 1999).] |
#18
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All I can say is that my 70 Road Runner has the factory exhaust system on it and the pipes are 2 1/4".And my 86 Ramcharger is going to get the same exhaust(2 1/4 and street Hemi mufflers)
[This message has been edited by Christopher (edited April 24, 1999).] |
#19
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Man Dave your cutting me right to the bone, I gotta go get a bandaid, sell tickets? To watch a car blow out candles from 30 feet. Hey I ran this combo in 1977, maybe I better read a little more current stuff. A 318 with what 9-1 compression, if you figure it needs pipes like a 360 or 340, what ever floats your boat. I wish I still had my old duster, I'd like to go over and race you.
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#20
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WHOA there Brian, IT"S just A JOKE!! HA HA! You admitted yourself that you had too small of a pipe. I'm just here to have some fun. RELAX! And besides there is ONLY a 13% differance in the cubic inches between a 318 and a 360 and you were running practically the biggest hydraulic cam that exists.
If I inadvertantly offended you I apologise. I'm just here to have some fun and to get and give advise. After all we are not talking about bow ties and ovals vs the mighty MOPAR. I wouldn't race you if we were ever to meet but I sure as heck would buy you a beer! Keep smilin' |
#21
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No sweat Dave, I will guarentee you that I rolled on the floor laughing when I read your comment about the candles. You definately tickled my funny bone.And I would take you up on that beer any time. Where I work, there is 100 of us running heavy equipment, we have 2 way radios to communicate, we have 2 business channels we use, and 1 chat or bushwhack channel. I'm quite used to comments coming suddenly out of the bushes directed towards the unsusspecting passerby. I've been on both sides of this game. On a serious note, even though I backtracked earlier, I did a little more homework on the 318, and found some points to ponder. page 89 of the 9th speed secrets talks about the ported 318 head. They admit most development has been done on the 340 and 360, very little on the 318. They say that since the 318 is 40 cubes smaller than the 360, it doesn't always respond the same way. Proof being the use of the ported 318 head vs the ported 360 head vs the stock 360 head, the results were surprising. The ported 360 was 25 hp over the stock 360 head. Gains like this are not usually seen with 9-1 compression and a piddly 450 lift camshaft. Big surprise, the 87 318 head with 360 valves and porting shows a 55 hp gain over stock 360 heads. How can this be, this head has small, doglegged ports. 318 seems to like that. I also dug up an old scrap of info I had stashed wher some fellow in the mid 80's proved that the H and X pipe configurations do nothing to enhance acceleration performance, but show gains only at high speed endurance levels. But my info was incomplete. I'm not trying to bore you or change your car, just let you know that all performance principals don't apply equally through the product line. A well matched system will beat an over built one every time. Don't always rely on the factory, experiences count in this game too. And I just do this to see more quality mopars on the road. Take it easy man.
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#22
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When you start comparing things you have to compare apples and apples. Flow and horsepower are 2 different things. Ever look at the exhaust side one of those goofy BB Ford? They get huge flow #'s but they are too big. They are so HUGE in fact that in race motors they put in an exhaust gasket with a flap to constrict the port.
That deal with the ported 318 head also has one differance that is often not brought up and that is that those heads were also the newer high swirl style. It's kind of a closed chamber design with a heart shaped chamber. It wasn't the flow that made the differance in horsepower, it is in the combustion chamber. |
#23
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Yeah, I hear what you are saying Dave, but bear in mind that this is a 9-1 compression ratio. I have one of these, it is a 1991, 160 horses and thats all it has. You add a .450 lift cam, 4 barrel and performance ignition, valves from a 360 and some porting to stock heads. Did you see the chart on page 89 of the 9th edition speed secrets, 335 at 5000 and climbing, thats 340 territory. The base line is this engine with stock 360 heads, not even 275 horsies. I'll grant you some compression difference, 1 full point. As far as I know this 318 is just the same old flat top 8.5 to 1 job from the early days, and they get 9-1 by using the heart shaped combustion chamber. You run what you want for exhaust, I ran this, it worked good. There was some fuss at my local muffler shop when I came to pick up my car, i wanted a big 2 inch system, but there was a real set of corvair turbo mufflers under there, they were the thing to have in those days, we all raced on the street, through the mufflers, and my engine made power above 4800 rpm, I'd go the way of a little back pressure again. Have fun! Briguy.
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#24
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Corvair mufflers?.....c'mon it's 1999. Talk to Flowmaster.
The size of an exhaust have little to do with the size of the engine when the sizes that are as close as we are talking about. The deal here is flow or horsepower. 300 hp from a 318 is going to need as much flow capability as 300hp from a 360. But if you want to run a sprint race with your shoelaces tied together....... And dat's all I's a gonna say....probably |
#25
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Well, thanks for all the great support! Anyway, I ended up using 2-1/4 all the way back, going through Thrush California series glasspacks. It sounds decently mean under idle, and really opens up and gets throaty under heavy acceleration. I come to find that I have a 7-1/4" rear end. I'm thinking of changing to an 8-1/4" or 8-3/4". does anyone know what kind of mods will have to be done to fit either one under this '84 f-body? Also, with 2.2 gears, ol' Bessy is a little slow off the line, but after about 5 miles an hour, she gets real mean real quick. it actually gets out of hand on the highway. if you so much as crack the throttle plates, you're running 65 m.p.h. But I would like it to be faster off the line. I'm also thinking about replacing the stock 318 heads with 360 heads. What do you guys think? would this really make any noticeable difference? Thanks for all the help!
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