1st the specs: L69 not cat and gutted out muffler but other than that complete exhuast

ok so i finished my hedman header install last night and took her out, i must say i finally have a sound and sound level i want, but....yes,there's a but... it's slower, i have a little test i do on my street and from my mail box to the end of the straight, i normally hit 60-63 mph, last night i barley hit 55 and i could barley smoke the tires (unless i brake trq it). is this all bcuz i have next to no backpressure??? would a catco cat with the gutted flowmaster do the trick to get my trq back??? the only thing i was thinking was that i had super 94 gas in it and it's been sitting for about 6 weeks since last started and not moved for about 3 months, could stale gas be y it's slower????

 

backpressure is bad no matter what, the old myth that having no back pressure is hoopla. from what ive read a gutted cat is bad its better to either have a cat or have a straight pipe thru the cat, what it does is create a turbulence within the area where the monoblock used to be and creates a restriction which impedes airflow. youve relieved the engine of the stock restrictive manifolds, so now you have more free flowing exhaust unless you do more mods theres little chance of feeling it in the seat of the pants, it might show up better on a dyno.

6 weeks is not very long, my car sat for 3 1/2 years (while it was being built) with 3/4 of a tank of gas, it started rite up and ran the best that it ever has.

the 305 isnt noted for having gobs of power at the low end it runs better at mid-range to hi-end, but doesnt pull much after 7000 rpms. not when compared to a 5.3L ls1-

 

This is just a guess, but recheck the spark plug wires to make sure none got burned, all are seated well and that none got accidentally crossed when you put the headers on.

Other than that I have no idea why you would have had a power loss.

 

i do have a pipe inplace of the cat. and i have 3.73 gears and b4 i did the headers it pulled real hard off the line. it was the best part of the powerband on my car

Corbi_85-IROC, i let the car run on and off for a few hours to make sure everything was ok. and i did have 2 wires swapped but that was fixed after the first start up. other than that everything was fine.

 

you could be running lean now that you have better exhaust flow.

 

never thought about that, one how would i check and two how would i fix it?

 

you'd have to be able to read the O2 sensor to get an idea. A heated O2 may help also.

Do you have an exhaust leak? I installed hedman headers too, dyno'd it and I picked up 25hp and 25ft-lbs of torque at peak, and more power and torque throughout the curve.

 

i had to extend the O2 wire (harness side not O2) and i'm thinking that might be it, i do have a CEL on and am not sure what it is.

and yes i do have a leak where i put the pipe in to replace the cat, the conncetion to the I-pipe, so could that cause the loose is power? i'm getting them both fixed tomorrow i hope.


(i extended the O2 by about 10-12in if that matters)


u have a 350 so i doubt i'll pick up 25 and 25

 

any other ideas???

 

You shouldn't have lost any power. Did you try disconnecting the battery to reset the ecm?

Also, your fuel lines aren't too close to the headers are they?

 

Check the check engine light code before you change anything.

 

i disconnected the + & - & ECM power harness connector over night and as soon as i started the car the CEL was on, also i can't get the self diagnose to work.

i can recheck but the only line i had a prob with were the brake lines on the drivers side. how far away should the fule lines b from the headers.

 

any more ideas?

 

What diameter are the primary tubes? If the primaries are too big, you will lose low end torque, which 305's do not have a lot of anyway.

 

hedman 1 5/8's 3"collector. i had quite a bit of trq b4, so idunno

 

i;m wondering if 3' inch collectors are to big for a 305 , i bought some dynomax headers for my 86 305 tpi and they come with 2.5 '' collectors ,

just wondering

 

I was told a vehicle needs aprox 1 lbs of back preasure to function properly.

Another question...your intake. is it stock. I mean are you running an open element or something to allow more air in. If you open up the exhaust without opening up your intake then your engine is probably sucking some exhaust back into the valve. Something to think of there.

 

i was talking to a guy at a car show and he sed he had adjustable exhaust and when he ran a 1/4 with open it was slower than when he adjusted it.

everything else is stock. stock intake ,stock air cleaner, OEM style filter (i think it's dirty) i was planing on getting the k&n extreme top & filter, i don't really want to change the air cleaner bcuz i still want to use my hood scoop.

 

well the stock intake, air cleaner, and the element dont help your situation very much.

 

So does that mean my buddy was right?

 

i guess i'l try and get that K&N Xtreme top

 

might be, idunno. i'm going by what he told me.

 

If your cel light wasn't on before, and it is now, somethings wrong. Fix that and then you'll get your power back.

 

Maybe not help, but they won't make it worse.

I think you're just running lean now. Improved exhaust flow like that will lean it out alot.

 

ok like i sed b4 i had to extend the O2 wire (harness side not O2) so the CEL could be on bcuz i running lean or the O2 is reading right. am i right? i make it rich by tunning the carb right? if i'm wrong let me know

 

SEL means a sensor is miss reporting something to the ECM. Pull your codes using either a GM code puller. I heard a few members mention something about using a paper clip to pull the codes however I am not completely sure how that works. GM Code pullers are 20$ CDN. Cheap and very much worth the coin.

 

I know this debate went for about 3 pages once, but I think the message got lost in the bickering. You must have backpressure to run a n/a car, IF you want to make top end power . Without backpressure, the lack of exhaust flow will kill low end torque.

A turbo car on the other hand, needs none at all. The more you uncap it, the more power you make throughout the rpms.

 

I'm not sure if checking your codes is the same in an '84, but this is what I use in my '86. https://www.thirdgen.org/newdesign/faq/thirdgen.shtml
Scroll down to the misc. section on that page and it will tell you how to display the trouble codes. I use a piece or wire or paperclip to jump two of the pins in the ALDL port in my car. Mine is pins 5 and 6. Then turn the ignition to start and read the flashing check engine light to decode them. It starts by flashing once, then twice (meaning code 12), it will do this 3 times, then flash any stored codes (it will repeat each one 3 times). Then it will just keep repeating them over and over again.

 

P.S. that first code 12 is not a trouble code..... it will always flash that one before going on.

 

If it is now throwing an EGR code and it wasn't before, don't worry about it. The reduction in backpressure can cause it to set off. The EGR valve opens as a result of backpressure and the addition of headers, removal of cat, or addition of a freeflowing muffler will affect it.

 

i tried it both ways, 6&12 & 6&5. nither one worked, and it looks like the connectors r only in 1 3 4 5 and 6. so i would think i would put the clip from 5&6. i've done it b4 and worked fine so idunno what's goin on.

 

You connected them with the key off, then turned the key forward to on (without starting) and nothing happened? Don't go buy a new ecm, but that was the problem with my car at one time. The code reader would not report contact with the ecm when plugged into the aldl port. Turned out to be a bad ecm. Sounds like you need a little more advice than what I can give.

 

yup i did what u sed and nothing. if it's the ECm how much will that cost me?

 

ok sooo i really really hope tomorrow that i'll be gettin ahold of a scanner to see what the CEL is. but does anybody have any other ideas?? or how much a new ECM would cost??

 

<b>Without backpressure, the lack of exhaust flow will kill low end torque. </b>

Without starting an entire new debate on the subject, im just going to point out one small detail.

According to David Vizard (not me, but Ive experienced this to be true so far...)

And exhaust system, when "tuned" properly (right diameter + right length) creates a suction inside the cylinder during overlap up to 10X times greater (in a race situation) than the suction generated by the piston moving down the bore on the intake stroke.

Rule of thumb here, if your motor makes gobs of low end torque, but not horsepower (such as, a stock or nearly stock 2.0 liter, 305 / 350 / 400 / etc...) then creating a NO-BACKPRESSURE situation will DESTROY your low-end exhaust scavenging, and create issues with charge contamination (reversion due to slow moving exhaust during overlap) and "basically screw your motors low end over".

i have no doubt this is what happened in this particular situation. You can keep a free flowing exhaust on the motor, but size the pipe right and run mufflers. you will be loads happier.

 

I can't remember how much my ECM was, but it was under $100. Could've been half that. Sorry, just don't remember. Sounds that getting hooked up to that scanner is going to be your best bet. In my case, the ECM was working properly it turned out, but it just would not communicate with the ALDL port.... probably a bad connector in the ECM or something. So replacing the ECM did not cure the codes, it just got me getting back to reading them!

 

I know this may be obvious but if your o2 sensor is further downstream in the exhaust,which since you said you had to extend your o2 sensor wire then your o2 sensor might not be heating up enough to function.Most people have to go with a heated o2 sensor after installing headers for it to work right.Just a thought.They are also right if you do too good of a job with freeing up your exhaust system you will destroy your low end torque.

 

ok so the self diagnostic didn't work, i had a scanner and it didn't work (it was OBD I i'll try a OBD II or III at a dealership i used to work at) and anyone who has looked sed it most likely is a bad ECM. so i think i might just have to go with a new ECM but y would it be fine when i started my header install and as SOON as i started the car the first time the CEL was on, i guess it was just it's time to go.

 

hmm, i thought i posted here...

or perhaps it was another thread talking about backpressure.


anyhoo.

backpressure is bad. no matter what. it causes pumping losses.


the problem is, people see smaller header pipes and they think backpressure is why it helped with the low end tq.

its not backpressure its velocity. because the same volume of air is going thru the pipe, the velocity is faster when the pipe is smaller.

so directly after the exhaust port, you want whatever size gives the highest speed, so that the momentum (yes air has momentum.. it has mass) causes it to pull a lil extra out.

once out of the longtubes, or into the Y pipe on shorties, the velocity isnt important.. the air just has to get out.
so anything from a cutout to a full length exhaust would work.







just ask yourself this... if it was backpressure, couldnt you just buy 2" primary tube headers, 4" dual exhaust, and then stick a potato halfway in the tube? i mean, that would have the backpressure effect you want. does anyone here think a potato mod will help their motor?

 

HOLY CRAP...i don't think too many would of thought of this. i was messin around with the self diagnostic again and dropped the paper clip into the cig lighter (ya what were the odds of that) and blew a fuse bcuz of it. so i checked the fuses and found another fuse blown so i replace both of them and then thought about see what the other fuse was...CCC...computer comand control. and bam it works, CEL is off, self diagnostic works and no codes.....yet..i had just connected the bat back up, and i take her back out for my test and hit my 60mph mark. i'm happy right there. but then i come back to check my tranny fluid, so the engine is running and i look down and the # 6 wire is arching...as a matter of fact it wasn't even on the dam spark plug. so i hit my mark on my test and it was only on 7 cylinders so as soon as it cools down i'll fix the wire and try her again.

my ***..if that paper clip didn't fall from 2 ft down into a 1in hole and blow a fuse i would still be at stage one. i mean i never would have looked...and all IT WAS JUST A FUSE!!!!

 

Hey man that's funny as hell and awesome for you.

Guess sometimes its better to be lucky than good.

Keep us informed on how it feels after everything checks out.

Oh yes, one more thing "Thank ***" this kills the backpressure arguement.


hmmm that's really weird *** = G O D

 

Hey Chio, maybe you can come over and figure out my what's causing my CEL code now.... bring your paperclip.

 

well i fixed the plug wire and everything but i was driving to school today and the CEL came back on, something shorted out and blew the fuse again. i looked under the hood and saw 2 wires laying there and they look like they goto the AIR valve thingy, (what the air hoses off the headers goto) on the pass side of the engine. well i don't know what wire goes to what hole, there's a brown wire and 2 black wires that go into one connector