Hello, I have an 83 Grand Prix with a GM 305 LG4. I was made to understand that the LG4, doesnt breathe that well, so I am considering getting headers (acutally, mostly for more meaner sound, but power too ). I have been told however, that adding headers will make the car sound alot better, but that I would lose some power, because the enigine doesnt breathe well to begin with. Only power adders I have are a K&N air cleaner, dual high flow cats and dual Flowmaster 40 series, everything else is bone stock. Does this sound right to you techies? Do you feel I would lose low end power? Thanx in advance.....

 

I dont feel the you would lose power. Your engine doesn't breathe well to begin
with, and isnt the concept behind headers making the engine breathe better??
So therefore, wouldn't you gain power?? Seems to make sense to me, the only
argument that I could see is you may lose some back pressure. Right now your
engine is taking in enough air to run well in the stcok trim, but when you add
headers it will flow the air out better, but still be taking in the "factory" amount
of air, causing you too lose back pressure and therefore losing horsepower??
Does that seem right to anyone else??

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88 GTA
L98 350
700R4
3:27 axle
MODS,
Edelbrock TES headers, 3" straight pipe, Flowmaster 80 series, K&N filter, Accel 8.8mm wires, Bosch Platinum plugs, Wells cap and rotor button, Wells ignition module, MAF screens removed, Hypertech TB air foil, Thermomaster stage II chip, 180* Powerstat, Hypertech cool fan switch, B&M shift kit, B&M power clutch pack, B&M servo, GM fuel filter

 

less backpressure= more power. since your car is mostly stock I dont think the headers will add much power. If you have a 2 bar carb lose it, and put a 4 bar. on

 

The engine is a big air pump. Think of everything as a big garden hose that's 1 inch in diameter. If you cut it and splice in a 2 inch diameter section, the flow out the 1 inch hose will still be the same as the flow going in the 1 inch hose. That 2 inch section will have more water in it but the flow is still restricted by the rest of the hose.

The engine is the same way but the hose is intake, heads, exhaust system. Increasing the size of one but not the others won't increase the total flow. You can start by adding headers but larger isn't always better. 1 1/2" or 1 5/8" primary tubes is usually the best for a street engine. You can change the carb and do some head work later to improve the exhaust changes you do now.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas

Best results before the engine blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

 

the hose analogy doesn't work for me for 2 reasons:

1. flow through the engine varies at several critical points, and improving flow at one point can have a positive effect at other points. think of the intake as a 1 1/4" hose, the heads as 1 1/2" hose, the cam as a 1" hose, and the exhaust manifolds as a 3/4" hose. ultimately, the system can only flow as well as the smallest section of hose. however, if you increase the size of the smallest hose, then the system will flow as well as the next to smallest piece of hose. adding a better exhaust(small-tube headers and cat back) will make that section of hose perform as if it were 1 1/4" in diameter. that means the 1" section of hose(the cam) will now be your greatest restriction, but overall the system will perform better because the 1" hose presents less restriction than the 3/4" hose(the stock exhaust).

2. flow through a garden hose occurs in only one direction at a time. this is definitely not the case in an engine, especially in the exhaust system. in the exhaust you have the positive pressure of the exiting exhaust pulse, but you also have the negative pressure of the scavenging pulse. the scavenging pulse helps draw gases out of the cylinder as the exhaust valve opens, and also helps draw the exiting gases towards the collector - where they create a new scavenging pulse. this is analogous to applying suction to our imaginary hose, to help draw more flow through the entire length of the hose.

- get headers with as long a primary pipe as possible and keep the tube diameter conservative(1 3/8" - 1 1/2") to maintain the velocity of the exiting gases - which creates the strongest scavenging pulse.

in the end a good exhaust system will help remove more of the combusted mixture before the exhaust valve closes, which means there is more room in the cylinder for the fresh incoming air/fuel mixture. the more air and fuel you stuff in the cylinder, the more power you make.

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He who hesitates,... is lost!