I was just wondering because I'm ordering some tommorrow, and I was thinking since the LO3 exhaust is so restrictive, I'm thinking 40 horse, I also have a cat back. Thanks

 

um, not close to 40, but around maybe 25. reason being is cause we started off with manifolds, ****ty ones. same with 305 TPI, they gain a lot from headers, now a 350 TPI will gain about 10-15hp. I calculate my hp ratings as so. (i have some races to prove my hp rating )
1. TES Headers 20hp
2. RPM Series Catback 3" 20hp
3. Underdrive Pulleys 10hp
4. Open Element with K&N 3" 10hp
5. 8.8mm Spark Plug wires 5hp
Now believe it or not, i believe this is true. i run awesome with 305 TPI's all the time and i can beat my friends stang so i figure thats about right. as for the spark plug wires, i felt a lot better throttle response over the 7mm stock ones. these are just estimates and i think im gonna dyno my car soon so ill post the specs. btw, Edelbrock TES headers ownz

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K&N Air Filter 14x3' Open Element, Edelbrock Catback 3", TES Edelbrock Headers, 3" Dynomax Hi-Flow Cat, 8.8mm Accel Spark Plugs, Underdrive Pulleys, JET Chip (Thurs of this week)
My 88 RS

 

bah im stupid

1. TES Headers 20hp
2. RPM Series Catback 3" 20hp
3. Underdrive Pulleys 5hp
4. Open Element with K&N 3" 5hp
5. 8.8mm Spark Plug wires 5hp

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K&N Air Filter 14x3' Open Element, Edelbrock Catback 3", TES Edelbrock Headers, 3" Dynomax Hi-Flow Cat, 8.8mm Accel Spark Plugs, Underdrive Pulleys, JET Chip (Thurs of this week)
My 88 RS

 

But doesn't the TPI 305 have bigger exhaust manifolds than the TBI 305.

 

You will get about 20 horsepower from headers. The TPI exhaust mans are higher flow than are the TBI ones. And why on earth do you say the 350 gets less from headers, that is quite wrong buddy.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission

Current Mods: Edelbrock TES Headers, Hooker Cat-Back System, Performance Resource Chip, 160* Thermostat, Accel 8.8mm Ignition Wires, K&N high flow air filters, gutted air box, gutted MAF sensor, Throttle Body Coolant By-Pass, Homemade Ram-Air, Falken ZIEX Z-Rated Tires.

1/4 mile times without chip:
Best ET: 15.7 @ 89MPH
Best Corrected ET: 14.5 @ 96MPH

 

My guess would be 20-25 HP at most if the engine is still stock. The reason is the cam: it is so incredibly weenie, it will become the new bottleneck to the motor's flow, thereby preventing the headers from doing all that they could.

Cam & headers together could be worth as much as 50 HP with little or no other modification. I would recommend a cam about like this:

COMPETITION CAMS CAMSHAFT SPECIFICATION SHEET

PART # 08-302-8
GRIND NUMBER: CS 264H-R12
ENGINE: CHEVY SM BLK 305-350
INTAKE EXHAUST
VALVE ADJUSTMENT HYD HYD
GROSS VALVE LIFT .480 .480
.006 TAPPET LIFT 264 274
VALVE TIMING OPEN CLOSE
AT .050 INT 3-BTDC 33 ABDC
EXH 46 BBDC 6-ATDC
THESE SPECS ARE FOR CAM INSTALLED
AT 108 INTAKE CENTER LINE
INTAKE EXHAUST
DURATION AT .050 210 220
LOBE LIFT .3200 .3200
LOBE SEPARATION 112
THIS CAM SHOULD USE SPRING # 981-16

You are doing the right thing by replacing the exhaust first, it just won't completely give you its full impact until you uncork that one other restriction.

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"So many Mustangs, so little time..."

 

the 350 TPI gets less hp from headers because they already come with headers. You will notice more of gain in a L03 car then you will in a L98. They come stock with headers so its already got a little bit bigger advantage

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K&N Air Filter 14x3' Open Element, Edelbrock Catback 3", TES Edelbrock Headers, 3" Dynomax Hi-Flow Cat, 8.8mm Accel Spark Plugs, Underdrive Pulleys, JET Chip (Thurs of this week)
My 88 RS

 

Maybe i'm just way off or something, but slow rs, i don't believe ANY third gens came stock w/ headers except the firehawks. The only difference would be the L03 manifolds are like 1.75" and the TPI manifolds are 2.25".

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85 Z28 (Soon to be GMPP 350 HO)
Headman Hedders and matching y-pipe, Edelbrock Performer, Ram Air, Accell cap and rotor, Accell Supercoil, 160 stat, highflow Catco converter, absolutely no other smog equipment, B&M shift kit, Rapidfires, numerous carb mods, and flex-a-light fan.

"If you think education is expensive, try ignorance."-Ben Franklin

 

I wish my 350 came with headers.

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88 IROC-Z,L98 350 TPI, 700R-4 Tranny 2.77, K&N Filters, 126K Miles runs great. http://www.j-body.org/library/humor-...arearicer.html

 

somebody's makin **** up again... mustangs came from the factory with headers. youll be hardpressed to find any camaros that came from the factory with headers except for dealership optioned cars such as yenko, baldwin motion, and dana/nickey.

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92 CAMARO RS 25TH ANNIVERSARY LO3
91 CAMARO RS V6
83 CAMARO Z28 (new project!) 700r4, 3.73 posi, 4 wheel discs, 454 in the works...

[This message has been edited by nichoulas91rs (edited July 21, 2000).]

 

The only mustangs that came with headers stock were the cobras.
Also, don't the new SS camaros and firehawks come with slp headers?

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White '92 Firebird w/ 305 TBI. Open element w/ non drop base, increased fuel pressure, TBI spacer, Hedman Hedders & y-pipe, no cat, cat-back exhaust

 

Instead of changing the cam couldn't I just put 1.6 rockers on and make a big difference or do I have to shell out the $259 for the roller cam.

 

You will get 40hp by changing the entire exhaust-not just headers. This means headers, a 3" cat, and a 3" cat-back exhuast. Gotta do the whole thing to maximize gains.

------------------
Paul Huryk, billionare in training.
Monkey Guy Racing
Almost part of the moderately infamous NJ in-your-face all goomba crew

Do it right the first time.

Paul's home page

1985 IROC LG4 POS Best: 15.20s at 92.1mph
1984 Camaro 350 LG4 Best: 12.21s at 121.7mph

The smart person pays for something today so that more is received tomorrow.
The ignorant person gets something today and hopes to have enough money to pay for it tomorrow.

 

I all ready have the 3" cat back, I just don't have the 3" cat

 

The 3" cat is what you need to give you max power gains-the stock 2-1/4" one will only support 150-175hp, a 3" one will give flow up to 325hp. No matter what anyone else says, it will hurt you-regardless if you have headers and a 3" cat-back or not.

------------------
Paul Huryk, billionare in training.
Monkey Guy Racing
Almost part of the moderately infamous NJ in-your-face all goomba crew

Do it right the first time.

Paul's home page

1985 IROC LG4 POS Best: 15.20s at 92.1mph
1984 Camaro 350 LG4 Best: 12.21s at 121.7mph

The smart person pays for something today so that more is received tomorrow.
The ignorant person gets something today and hopes to have enough money to pay for it tomorrow.

 

Wrong ,86 or 87 and up 5.0's came with headers .

 

In the July issue of GMHTP, they swapped to 1 3/4" headers for the stock manifolds on their 350 and had only 6 HP increase on the chassis dyno. They then went on to talk about "internet HP and HP increase claim for headers". I think they were bang on!

Headers by themselves don't give much of an increase on a stock motor because the engine itself is not really pushing much air; hence the exhaust system isn't as big of a bottleneck (inspite of your puny stock exhaust system). But combined with other mods (or intended mods), they do offer big dividends. That is when the stock exhaust manifolds turn your engine into a constipated pancake eater.

 

They are right, you must (to get the best gain) get you a good cam. I don't know witch one to recomend, but bigger cam and headers is a great upgrade.

PS No L98's came stock with headers, WE ONLY WISH

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1992 Z28 5.7 TPI 700R-4
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To many mods to list.

[This message has been edited by GOFASTER (edited July 22, 2000).]

 

I've been told by two local muffler shops that w/o a cat, there is no reason to upgrade to 2 1/2 pipe unless I'm pushing out a LOT more horsepower, is this true?

Also, I believe that the reason GMHP only got 6 hp was because the 350 TPI comes with better manifolds, a larger y-pipe, 2 cats and 2 1/2 inch exhaust. Therefore, headers on an LO3 will help much more than on an L98.

 

I'd like to add that There are L98's that came stock w/ headers!!!!

They just weren't F-bodies they were vettes.

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1987 Firebird Formula 350[*]Stock except...[*]Cragar Street Stars
My Car Website w/ Pics
fyrebird350@hotmail.com
AIM/AOL Screen Name: FIREBERD350