any ideas why i lost power after installing my hedman longtubes? right now i am running just the headers. the car feels like my old 2.8 now. i think i've seen this problem before on the boards so i figured someone can help me out cuz im lost.

 

you will lose bottom end performance with lts on a 5.0 but should run better on the top end,from the sound of your disappointment you have a relatively stock set up,add a cam,intake and some gear 3.42-3.73 you will feel way more.you definately did not waste any money!!!!!!

 

could be a tuning issue, but i doubt it, w/ just exhaust mods most people dont seem to need tuning to get better results.

It seems lots of people think they 'lose' power down low because they are used to having power down low and not up high. With the high flowing exhaust you gain power up high and it feels like you've lost it downlow, because you have it everywhere now instead of just downlow. You should get some numbers to see if you really have lost anything, or if you just 'feel' like you've lost something.

maybe its something differnt though, double check everything, sensors plugs/wires, makes sure its all plugged in.

-chuck

 

I had to make some pretty big adjustments in the chip to my friends Lo3 when he put on some shorty headers. My guess is you fuel curves are off a good bit now. That'll hurt some power, but not knock off 2 cylinders. Make sure your not getting any codes, you could have knocked a connector off of a sensor during the install.

 

You need to get into chip burning. Just like BMmonteSS said, even with shorty headers these cars can really use a custom tune to dial them back in. Dewey316 is another example of this and he picked up .5 or .6 sec with just a custom tune. When he added headers his tune was off again and needed attention. Long tubes on a stock 305 are over kill and I bet you do have a loss in power. You do not have the heads or cam to utilize the advantages of a long tube header. Those headers are to big and have caused a decrease in exhaust velocity out of your faint 305. Flow is good now but velocity is bad. You need a mix of both to make power with any header set-up.

 

1 5/8 inch right? certainly NOT 1 3/4 inch right?

 

1 5/8...does everybody have this problem when putting long tubes on a stock 305??? im probably going to take them back off.

 

Before you get real crazy and rip them back off, I would check to make sure its not something simple like plug wires mixed up or burned threw and grounding out. Most people get in a hurry and dont tie them up out of the way. You say you are running just headers now. Maybe open headers is causing a false spark knock. If so your timing would be sevearly retarded. Step back and look at the big picture, maybe you missed something.

 

Many people don't usualy go with long tubes for a stock 305. They are just a bit overkill. I would double check like JokerRS mentioned because it is easy to get wires crossed or burned up if they are resting on a primary.

 

I am gonna second everyone that is saying longtubes are overkill for a 305. Basically, to keep the torquey feel of the car, you need some form of back pressure to increase exhaust velocity. If you are just running straight headers, you're getting too much flow and causing it to slow down. Finish off your exhuast with a high flow cat and a decent muffler and you'll probably feel an increase. Regardless, you have gained power up high, so don't rip em off too soon.

 

I agree. If they were 1 3/4" I would tell you to take them off. Since they are a bit smaller you can still make them work. My car was slower when I ran my open flowtechs until I got it hooked up to the rest of my exhaust. Your car should feel better once you have cat and or muffler set-up on there.

 

You know If long tube headers weren't so hard to work with on thirdgen camaros ie... not much room for a good dual exhaust system, not much ground clearance, They would be the perfect header for our stock lo3's. They acually give you more low rpm torque than shorty's do and they will still be tons better in the higher rpms as well. Long tube headers are really the best all around header there is, expecially if has equal lenght primarys.

Steve

 

thanks for the advice..about how long do you think it would take to burn a wire? i made sure they weren't touching the primaries but they are pretty damn close, possibly touching while driving. is there a shorter 02 sensor i can use on my car? the stock one is now pressed up against the frame of the car(like an idiot, i welded the fitting slightly in the wrong location)

 

I got to go with Steve on the long tubes. Also, I read one time on a header site that the whole needing back pressure to run right is an old wives tale. The velocity thing is important but that is controlled by primary tube diameter not by adding a restriction down stream.

I think you need to install the rest of the exhaust.I would go with as low a restriction as possible. Now you have two choices.

1. You could detune you free flowing exhaust with restritions till you car runs right.

2. You could tune your car to run right with your free flowing exhaust.

I'd pick door number two, I'm sure you will find more power behind it.

Look at your wires where they come close to the tubes. If they are burned they will appear that way.

 

Steve and Joker have this one right. I'm guessing something else is wrong or your butt dyno is off. You should have gained a pretty good amount of power all around.

 

i am 100% sure it lost power. before i was running just manifolds and y-pipe and the car ran and felt great but sounded like crap down low. i figured open headers wouldn't be that much of a difference but now i know i was wrong...those primary tubes must make a really big difference compared to manifolds.

 

Don't jump into it and rip the headers off. Something else is wrong if you lost power with them.

 

Do you plan on running open headers all the time or are you just doing it till you get a complete exsaust on it? Where did you mount the o2 sensor? If i were guessing and you didn't put the o2 on yet then thats a real problem that will give you all kinds of trouble. If you did mount the o2, then it's probably giving the ecm a bad signal due to too much air reaching the o2 during reversion at low rpm. Just a couple of thoughts to consider. If I were running open headers I would put some collector extentions on, this would also help build a little more torque as well as keep the outside air from reaching the o2 sensor.

Steve

 

Its most likely the fact that you dont have the rest of the exhaust hooked up yet. My friend ran open headers on his early 90's short bed pick up and went from running a 16.0 to a 16.3. Once he got the rest of his exhaust ( high flow cat and cat back) he ran a 15.5. So dont worry about it until you have the rest of the exhaust on there. If you still feel a like you have less power then you have a problem because adding headers and a full exhaust is one of the most noticeable mods you can do on our cars. Good Luck.

 

a heated 02 sensor may be a thought. mine are ceramic and i have the 02 in a reducer from 3 inch to 2.25 and worked well. no heated for me. goes closed loop at 157 deg. maybe 02 is the answer.

 

if you're going from those long tubes into a single cat back, you have more than enough back pressure.

mine are shorties, but i picked up hp and torque all through the power band with my big tube headers, dual 2 1/2" cats and 3" cat back. i have more bottom end torque and picked up 1.5 mph on the top end, too.

before you do anything else, i'd suggest you check your fuel pressure. stock it's supposed to be between 11 and 13 psi. just going from 11 to 13 will make a difference. if your pump is old and not performing well or the fuel filter is clogged, you could have significantly less than that, causing a lean condition. going to a more free flowing exhaust would just make that lean condition worse.

 

This is most likely what it is. Non cermaic coated headers do not keep enough heat in tot properly heat the O2. Ceramic coating can cure this but the main problem is that the O2 is so far downstream. Shorty's don't have this problem. Finishing the rest of your exhuast should help keep some heat in but you may have to coat those puppies. I would still look at your data logs to varify though.

 

if i understand it correctly, the 02 sensor wouldn't affect wot performance, would it?

since doing my exhaust, i've noticed a drop in gas mileage around town, yet i picked up 2 mpg on the highway. i believe it's because the 02 sensor never gets hot enough on the short drive to work to go into closed loop. i have a heated sensor kit i plan to install soon.

despite the sensor problems, however, i've picked up quite a bit of performance from the exhaust.

 

yes, i already have the o2 sensor hooked up. it is connected to the header collector. i have the hedman extentions, the ones that route the exhaust around the trans, but haven't been able to put them on yet. for the complete exhasut i wanted to go headers, extentions, h-pipe, straight pipe, then some sort of mufflers but ground clearance is a small problem. fuel pump and filter is less than a year old. i adjusted my FPR both ways and that didn't make a difference. what is a heated o2 sensor and where do i get one? i also need a shorter than stock sensor because the stock one is rubbing against the frame of the car. something is throwing on the SES light so when i get a min. to check it i'll let you guys know.

 

Yup you are right. His part throttle performance is horrid. I geuss he never mentioned how the car responded at WOT.

 

there really isn't a difference at WOT. feels about the same as before or maybe a little slower.

 

You greatly reduced the exhaust flow restriction, which means that the cylinders get scavenged much better than before.... which means they also intake proportionally more air.

Do you have the extra fuel to match that extra air?

Raising the fuel pressure will help, but it won't give you good driveability at all loads/speeds --- for that you need TUNING.

Finally, even with the above, if the headers are too large in diameter then the velocity of the exhaust as it leaves the head and enters the port will slow down because the headers MIGHT be oversized for the other mods you have on the engine. I don't have a problem with long tubes, but the tube diameter might not be optimum for the rest of the engine.

Don't take them off until after you've, ahem, exhausted the fuel issue..... and keep in mind that an exhaust mod is the best thing you can do for an Fcar, but if you haven't done something about extra fuel (via FPR or tuning or both), then you won't necessarily get good performance at WOT. HTH.