I'm thinking about a full exhaust setup for my car. I'm thinking ceramic coated Hooker Supercomps into a 3 inch catback (I know it'll need some fab. work). My budget is kinda tight right now being in college so I want to make sure the power gain will be worth the thinning of my bank account. My current exhaust is totally stock, and the cat back is smaller then 3 in. (2.5 possibly??) with a midas type muffler. What power gains could I expect on an otherwise stock car?
What kinds of power gains have you guys seen with long tubes?

Edit: I am planning a stroker motor in the future so I'm trying to plan ahead a little bit with these headers. I'm just curious about power gains since the stoker won't be done by this summer.

 

Unless you plan on swapping those LTs onto a very well built 350, I'd just use some Hooker shorty headers.

 

Im gonna say what I always say....

On a 305 the 1 3/4'' hooker LTs would be alittle overkill IMO plus the coated ones are damn near 500$..not very economical IMO either.

On the other hand hedman sells a longtube header with 1 5/8'' primaries that is only 109$. That would be much cheaper and flow more than enough for a 305. and would still be enough for a pretty built 350 in the future.

 

Sorry I should've clarified, there will be a stroker motor in the future so yes, I am trying to plan ahead a bit.

 

I think that unless you've modded the 305, you may actually lose performance with the new exhaust your going to install. In the big picture I would'nt hesitate a bit with your plans, but the new exhaust will flow "too good" for a stock 305 and you'll lose the back pressure that those little huffers like to help produce torque.

 

Anyone else hear that dreaded word in there????


Yeah, you may lose some low end TQ till later on.

 

you MIGHT lose a SMALL amount of VERY low end torque

 

you can setup the entire exhaust with the hedman longtubes for about 300$...

You said you were on a budget and it doesnt get much cheaper than that.

 

heh now we are gonna get a lecture on how back pressure kills horsepower and how it is the enemy and how straight pipe is the best exhaust system out there

heh i just remembered this let me dig it up.

thought i would dig this up from the dumbass archives i keep in my head this was posted by momar. we all know the air pump is what causes straight pipe motors to back fire :


Originally posted by unknown_host
straight pipe sounds ghetto and nasty, you like the fact that when you let off it backfires and pops? or do built motors not do that
--------------------------------------------------------------------------------



Actually, I believe a lot of that comes from the air pump(emissions). I really couldnt tell you for sure but I think that that will still be there some even without the emissions, but I got rid of my cat and air pump when I had the 305 and it really cleared up that sound. I havent heard my car in nearing on 11 months though. It has turned into a major project. I will not exactly have straight pipes but almost might as well. I have hooker sc long tubes and am going to be running an x-pipe w/ hooker bullet mufflers. Maybe someone can answer better what that poping noise comes from, but I know my friend used to scare the **** out of people with it because he has an rs w/ 305 tbi and 5 spd. He would accelerate up into the rpms pretty good and let off real quick just as he got next to someone walking down the road. He did have a cat but no muffler. This caused quite a poping.

Ben

 

actually, backpressure does kill HP, it is something the engine has to struggle against.

please search for five7kid's explanation of it.

u want zero backpressure.

 

Well Ben is my brother, and i bought that car from his friend, and now it is sitting in our driveway right know. See..........

 

Unknown, I dont know what you are trying to say, but I was just stating the results I have seen from my experiences. My car never "backfired" but it did do that poping noise on the down rev when I had the air pump hooked up. That is all I know. I understand that straight pipes can sound bad, but the way that mine was set up I thought sounded good, and so did most other people I knew. I had several people that thought it was something better than that lg4 and no, I am not refering to those kids that dont know anything about cars that drive front wheel drive 4 and 6's. I am in the process of putting a 350 and some other stuff in my car and decided to upgrade the exhaust. We put that exhaust on my brothers car, which also had open exhaust when he bought it but didnt sound as good and it sounded a lot better. It has that popping on the down rev real bad though which I tend to think might be from the emissions. I dont know, maybe we will be able to see what it sounds like without the emissions(A.I.R.) sometime. Anyway, regardless of how hick you may think that it would sound it doesnt matter because its not yours nor will you likely ever see it. I dont think this is the real point to this thread anyway. No one said that straight pipes was the best sounding exhaust out there. If you are arguing that backpressure is good you are on the loosing side of an arguement.

Ben

 

Before everyone thinks I was "saying" back pressure is good, I'll take it back-somewhat. Mark says back pressure kills hp-but what makes hp?-torque they work hand in hand. Think I'm crazy, take a 305 in a camero/firebird all stock form from the factory, run a 1/4 and mark the time. Now, let take the same car in factory form install open full tube headers for no back pressure at all-not getting into the ECM system B.S. either, that car will run slower. Torque makes a fast street light to street light/strip car, for all out top speed you need hp, hp power will not win a straight up race if it does'nt have the grunt aka torque to get it there. Going back to the original post, I'll still stick to my guns and say that the his car, as is right now, might not see the "expected" seat of the pants or E.T. gains that one might think. Those little motors like a little back pressure plain and simple, you won't start seeing gains until you start "complimenting" the package so to speak. Heck, why do you think they make different size header tubes, if no back pressure is what u want, get a set of 2 1/8" primary tubes on your headers run a 4", heck even 5" straight pipe with no mufflers and you'll be the king of the street with a 305. Right?

 

Umm... Hello..... As has been said a million times you need scavenging not backpressure. If you get too large of a pipe you loose scavenging. That is why you need different sizes of pipe for different motors, not because you want backpressure. Backpressure puts pressure against the piston in the exhaust stroke causeing it to slow and in turn lose power. This is not to say you cant loose power by choosing the wrong size exhuast, just to say that it is not back pressure that does it.

If you dont believe me.

DO A SEARCH

 

umm...to answer the question, i put open long tube headers on my 305 Tbi, and i have yet to find a good way of setting up the rest of the exhaust and its been over a year. i had the mufflex y pipe and didnt like it. but yes i did notice a DRAMATIC INCREASE in both SOUND AND PERFORMANCE, THROTTLE RESPONSE, AND ACCELERATION.

RICK

 

oh man, sorry to anyone but i'm drunker than hell, but if you tin backpressure is good do as eahc liek was me3ntioned, damn, this sucks.. lol

 

lol, to drunk to type but still tries anyway. Mark your a thirdgen addict.

 

no chit, i came home last nite, girl passed out in my bed, so i was like hmm, maybe a little tgo.

 

i am not gonna get into this anymore than it has already been into, having a straight through exhaust makes more horsepower on a car that is designed to run no exhaust and is designed to have no back pressure, but on a car like a TPI car which is all about low end torque, you lose tons of low end torque to pick up top end, which TPI cars dont have. Believe me, I know that in some applications (my friend's 383 powered S10), straight pipe will pick him up a few tenths in the 1/4, he doesnt run it on the street tho

 

yes, but you're not understanding backpressure correct still.

You odn't want backpressure to keep low end torque, it's about scavenging of the exhaust not backpressure.

 

To quote five7kid

 

but for exhaust to scavenge there has to be some back pressure thats the whole point. i think we are on the same page but just using different terminology. i am simply stating that the exhaust needs to become more efficient, not necessarily bigger to produce maximum flow, the same as cylinder heads.

 

Bzzt wrong answer. You DONT WANT BACKPRESSURE. You do need properly sized pipes though. The reason for that is that if they are too big, the exhaust spreads out too much and has too much of chance to slow down(preventing scavenging). If you have too small of a pipe the exhaust has to be compressed into the pipe(backpressure). The piston then has to waist some of its power AND TORQUE to force the air into the exhaust. If you have the proper sized pipe it travels down the pipe kind of leaving a vacume trail behind it to pull the following exhaust pulse out. This is what you want.

Ben

 

I live in Texas and just failed their new emissions test because i don't have enough backpressure. I have 92 rs 305 with eldebrock hearders and flows, anyone know what i can do other than take the headers off my nox reading was like 1900 way over the maximum

 

What makes you think that it is becuase of too little backpressure. Do you have a new cat? If not I would get a new high flow cat. Also what kind of tune is your car in? Do you have good spark plugs, wires and such.

Ben

 

LMAO, did you not read the above, you don't need backpressure, that isn't what caused you to fail.

 

im just relaying what the guy told me, he said there wasn't enough backpressure to open the egr valve and told me i need a new converter which i just put on last week or take the headers off. I dont know anything about emission, only that its a pain, But to answer the question the plugs and wires are only 1 year old, bosch plats plugs and wires with a k&n filer

 

Takin off the headers is BS , unless you don't have the AIR tubes then that may cause a problem.

 

the air tubes to the headers shouldnt even be a problem if the car is warmed up because it goes to the cat after it is warmed up. I would try some new non plat plugs. From what I hear normal plugs work better, plat just last longer. What kinds of tests do they do? If it is just idle, the egr doesnt work at idle, only at constant highway speeds and such. Do you mean that you put the converter on before or after you had the car tested? Does your cat have the air tube still running to it?

 

In Texas they just started this new test on cars older than 1995, if its older they test the emmissions at 15 mph about 1315 rpm's and they also test it at 25 mph about 1290 rpm's (im guessing thats when the nox reading is at its highest?)and the new test has a nox reading unlike the older tests. The mechanic was telling me that there wasn't enough back pressure to open the egr valve due to the new converter not having enough resriction, (they're telling me that its on the verge of opening but it doesn't and that i need just a little more restricton)so he told me to get a different one or take headers off. I passed all the HC,CO,and the dilution just failing the nox. When i failed the test the first time thats when i changed the converter and i've still failed when i took the test again.with the old test i passed every time for the past 6 years but now with the new test with nox reading i fail, oh he did say that i could probably achieve enough back pressure if i could somehow put a small kink or dent on the pipe that runs to the converter.But im not about to turn my good lookin car into a "almost passing smog"pos,So tomorrow ill go back to the place i got the converter and see if he has one with a little more restriction and again spend more money

 

Yes and I've seen you use it too