FireBirdKnight

ive been having mixed opinions about adding headers to this engine some people claim that the cam and ecm set up on this car will cause the engine to lose power on this particular engine and some others claim that the 305 is very touchy to exhaust mods specially headers will i truely lose HP if i add shortys and a cat back system?

Guest

who ever told you that is a complete fool, thats not even possible....put headers on motor...make motor faster....ooogggaaaboooggaaa.

LMAO!
; P

cIaRmOaCrZo

back when i had my 305 tpi, i put headers, y pipe, and flowmaster on it and it picked up a bit. that was also without a tune. if you actually get a tune, there is more power to unlock..the stock manifolds on those are the WORST design i think i have EVER seen. its not that bad to put headers on, but its kind of a pain to take off the manifolds lol.

when i had the 305, i was still a just a novice mechanic so i didnt do very much to that engine at all. just cold air, and headers, tb airfoil, and coolant bypass. but then i got it dyno tuned just for A/F ratio only (it was cheap) and it picked up even more. then after that, i went ahead and ported the plenum, and it picked up a TON lol. the funny thing is, i felt the most (seat to pants) differance from porting the plenum. then again, it may have felt the most because of the combination of the rest of the little bolts on's.

but im totally in a whole other league now, so i wouldnt be able to answer the little details with my old set up

Greg '85 T/A

I had my car for about ten years before I decided to finally pull the trigger and add an Edlebrock TES. Truthfully, I didn't notice much of a torque gain at all. You can tell it helped the higher end HP, though.

Is it worth the dollar/labor to performance gain ratio? Probably not. But you won't reap as much reward from other changes if you don't have them. Here's an article that lists the measured HP gain on a Firebird at 7 HP:

http://www.gmhightechperformance.com...all/index.html

A couple notes about the install:
1. The pass. side AIR valve will probably point the wrong way unless you get headers with the AIR fittings pointing straight up.
2. The car will run just fine. No PROM changes, no further tuning.

(By the way, the GMPP 350 HO conversion retained the stock manifiolds and yielded 305 HP - so what does that tell you?)

QUICKCHICKEN

iTrader: (12)

headers on a TPI is the single largest mod you can do. i sugguest the hooker 2055 headers and get the Y that goes with, and if you can spring the extra funds, get the headers coated.

a high flo cat and cat back will compliment the headers greatly and when you do this, save the hanger that mounts the cat to the trans, you will need it. that is the only stock part on my exhaust.

i have the hooker 2055 headers and Y and love em. i do sugguest getting a special spark plug socket like the one powerhouse tools sells from COMP cams.

keep this in mind, a motor is an air pump, the more you can put in, the more you can put out.

FireBirdKnight

well the debate got heated today as i brought up this .. they said its all about back pressure , claiming freeing up the back pressure on a stock 305 will result in a slower engine

torque_is_good

then don't do it. You don't need an excuse to not spend money on the vehicle.

I have headers on both Camaros, why is that?

I suggest that you research "volumetric efficiency" within internal combustion engines if you want to get the real story.

Then, after doing that, go outside, hold one nostril closed and shut your mouth tight and try and run a mile that way.

How much air are you able to inhale/exhale and how well were you able to run?

1MeanZ

iTrader: (9)

I've suspected this for a long time now but so many people go into convulsions when anyone suggests the stock log manifolds that I rarely comment. For engines 325hp and below, I really don't think the stock manifolds hurt that badly. The REAL problem is the factory "T" pipe aka Y pipe. The intersection where the head pipes come together couldn't possibly be any worse. This could be why the G92 dual cat cars seem to run so much better. Even more terrible is the small diameter exhaust used on the TBI 305s and the 305TPI engines in 91-92. My '91 TA not only had the horrible T pipe, but it only had a single 2.25" exhaust. That is terrible. I've since put a 3" cat back on it and a custom made Y pipe similar to the dual cat setups and it woke the car up nicely.

Again, the problem is the y-pipe, NOT the manifolds below 325hp. Just my $.02

Greg '85 T/A

The very first aftermarket exhaust products for TPI cars were y-pipes. Turbo City and Gale Banks both made them. SLP eventually went on to sell their version through GM dealers.

After headers came out, I never again read an article in a car magazine (sponsored by the header manufacturers, of course) that didn't zero in on the manifolds as the bottleneck.

paul_huryk

The problem with stock exhaust parts is the fact that the flow is impeded by bad intersections, like the forementioned y-pipe example. Not to mention that for some cars (LG4 and TBI) the pipes were just too damn small no matter how well the intersections were made.

That said, when you look at the stock manifolds on any 5rd gen, only about 2" outside each exhaust port, the escaping gasses need to make a 90 degree turn and then hit into the other exhaust from the other 3 ports, not so good. Even shorty header allow at least a foot of pipe before merging into a collector, much better...

I'm not sure if anyone realizes this, but when SLP started out, they only made Tri-Y headers (4 into 2 into 1), which really helped out TQ. I'm guessing that their headers morphed into shorties later as cost and install had to suck with all those tubes and connections. Arizona Speed also sold Tri-Y headers for race applications, FYI.

Headers are worth it - in an old magazine article, SLP headers (shorties with Y-pipe) were dyno proven to give 12hp more than stock L98 manifolds with a stock cat-back.

1MeanZ

iTrader: (9)

Here is where I need clarification. Was this a 12hp increase on a dual cat car, or on a single cat car? If that 12hp gain was on a single cat car, then I'd suggest that nearly all of that gain was due to the Y-pipe and not the manifolds.

Again, we're talking about sub 325hp apps here. If you're going to add any aftermarket intake parts, install a new cam, or do any cylinder head work, obviously the manifolds need to go. But for guys that do not intend to do any engine mods, I'm not sure the manifolds deserve the reputation they've gotten.

paul_huryk

Understandable...

Have the article in front of me - Car Craft April 1989 pg 30 to 35:

They tested an 1989 L98 TPI (Corvette motor with the Al heads) with stock F-body TPI manifolds and y-pipe. First they dyno ran to baseline the motor's power. They then changed the y-pipe to a turbo city one and dynoed again. Then they changed to the SLP headers (Tri-Y, my bad on that one) and dynoed again. This was a single cat application as shown in the pictures...


Results:


Stock exhaust:

RPM TQ HP
2000 295 112
2500 315 149
3000 336 191
3500 336 223
4000 317 240
4500 287 244
5000 236 224


With Turbo City Y-pipe:

RPM TQ HP
2000 297 112
2500 318 151
3000 341 194
3500 341 226
4000 321 243
4500 293 249
5000 242 229


With SLP Tri-Y Headers:

RPM TQ HP
2000 302 114
2500 323 153
3000 351 200
3500 352 233
4000 332 252
4500 301 256
5000 249 236

As you can see, the Turbo City Y-Pipe added 5hp at 4500 and 5000 rpm and an additional 5lbs of TQ at that peak. Not bad for just a y-pipe

The SLP headers added 12hp at both 4500 and 5000 rpm. And they also increased TQ by 16lbs at 3500 rpm.

So if we subtract the 5hp from the 12hp, we get 7 peak hp for the manifold change to headers. Keep in mind that the TQ increase is much more substantial at 16lbs for the headers vs. 5lbs for just the y-pipe.

1MeanZ

iTrader: (9)

EXCELLENT post Paul that is the kind of info we need more of around here. Actual data is so refreshing!

paul_huryk

Your welcome!

Too bad they don't make those headers anymore... Or the y-pipe for that matter...

1MeanZ

iTrader: (9)

The Y pipe is the easy part. I just made this a few weeks ago for my TA.





Headers would be much more difficult.

QUICKCHICKEN

iTrader: (12)

1mean, that is a NICE piece ya made there!

1MeanZ

iTrader: (9)

Thanks, it was a bit time consuming, but pretty straight forward. I just built what I think GM should have equipped the cars with from the factory. Sorry the pictures suck. I'm used to working on my dads 2 post lift, this job was done on my garage floor on jack stands. It's hard to get good pix when the car is 20" off the ground.

Sorry to hijack the thread, back to topic..

hairysox33

iTrader: (4)

Great info posted here! Just for a visual comparison, here are manifolds from a 1991 Z28 (5.7 TPI car), and the hew headers I have bought.

QUICKCHICKEN

iTrader: (12)

hey hairy, how does the Y pipe and the collector connect on those headers? is it a gasket style system or like the hooker 2055 headers where it uses a ball and socket connection?

hairysox33

iTrader: (4)

It uses a "ball and socket" flange. No gaskets.

paul_huryk

Those headers look like a winner for my next project - are they Hookers? Where did you get those puppies?

85_ZED28

Which headers are those? Do you have a y-pipe for them as well?

hairysox33

iTrader: (4)

I ordered them through Summit. I have to say, the coating looks 100X better in the photos than it is in real life. If I were to do it over, I would have bought the uncoated version IIRC almost $200 cheaper, and have them powder coated.

Headers:
http://www.summitracing.com/parts/HED-68478/
Y-Pipe:
http://www.summitracing.com/parts/HED-17478/


The uncoated version of the Headers:
http://www.summitracing.com/parts/HED-68470/

Bought both versions, and they are the exact same, just coated or not. they KICK *** though. Other than needing to weld in an O2 bung if needed.

paul_huryk

Sweet!

Is that y-pipe a 3" entry into the cat, or is it a 2.5" like the desription is stating?

hairysox33

iTrader: (4)

2.5" ID... I have a 3" Cat back... Trying to think of the best way to link the two. I would like to buy a cat because dammit, I love mother nature. Besides, a cat is not going to kill much power at the level my TPI motor is at lol.

85_ZED28

It's too bad hedman doesn't make a 3" outlet y-pipe for those headers!

paul_huryk

Only 2.5" - that is going to be a major choke point and a deal killer for those headers. I'm sure a good shop could replicate the y-pipe with a 3" pipe into the cat.

hairysox33

iTrader: (4)

Yes they fit, and look nice in a terrible picture. How well? That is another story... Not at all an easy thing to shoehorn in especially by yourself. Did not have to dent, break, or modify anything major to get them to fit. But you WILL NOT be retaining your factory coolant line routing. You WILL be lifting the engine up a few inches to get the drivers side in, and you WILL likely scratch the **** out of the flimsy coating Hedmen so graciously overcharged for.