seems to be a lot of talk about headers recently! lol! I cant help but wonder if most of this recently got started because of me! Anyway, with all this header talk going on i was wondering if someone could answer some questions for me. i know this sounds very elementry but hopefully someone will help me out. why are headers better than stock manifolds? are the stock manifolds THAT narrow? why are headers louder? do manifolds have baffling in them or something? what is the usual hp gain with headers on an LTx car? what is the normal quarter mile improvement with them on that same late model C4 car? any input is appreciated

 

Headers are better because their ports are much larger where the pipes meet the heads.
Changing port size affects sound on any engine, beit intake runners or exhaust pipes, so theyre much louder. Its just a property of engines in general, but the V8 produces more bass. No baffling or anything like that on stockers.
Headers on an LT1 should give between 10-15 hp, but there is some variance. That would translate into about a tenth.

 

Headers help the exhaust gases flow with less restriction. They also help scavenge the exhaust gases which in turn increases flow volume and flow velocity. The stock manifolds are restrictive because of the narrow bends and the way they all merge together at the flange. Headers has individual tubes for each exhaust port that is usually tuned to a certain length, they all merge to a outlet collector. Typical tube lengths vary per car and application. Tubes also vary in diameter, big HP and high RPM demands larger tube ID's, typical performance street applications will have tube ID's of 1 5/8 up to 1 3/4 for small blocks and up to 2 1/4 for big blocks.

Headers are not louder than stock manifolds. Well let me rephrase that. Headers can be a bit louder if you are measuring the noise right at the headers themselves. With quality headers using 16 gauge and thicker tubing you normally should not hear anything at the headers themselves, if really cheap headers are used, sometimes you hear a tinny ticking noise as the exhaust gas pulse hits the tube walls. Normally all the noise you hear is from the mufflers. Having said that if you bolt a set of headers on a car to the stock exhaust system, there should be no increase in noise level.

You can expect around 10 to 15 hp with a set of quality long tubes from a C4. Final Hp numbers are also dependant on other mods to the engine such as cams, heads. As for drag strip improvements it maybe worth a tenth or two.

 

Not to hijack your thread but I think my question is an extension of yours. 10-15 hp for several hundred dollars and lots of labor doesn't seem worth it for a daily driver. Having said that, I'm considering headers and the hot cam with 1.6 rollers for my stock 94 LT1 6spd. Used in conjunction with the hot cam, would the headers have more than 10-15 hp gain. In other words would it be 10-15 hp from the headers + 30 from the cam or would there be a higher cumulative hp gain. Will the cam and rollers give me enough w/o the expense and labor of headers also? I know, you can never have enough hp. If I choose to spend my limited funds on one or the other, I would think the hot cam would be the way to go.

 

OK - I understand the answer to 1996man's question - it all makes sense. I'm in the market for some headers for my 1994 Corvette Coupe with an automatic. I need to keep the emissions hooked up as Maryland has inspections and testing. I have a Power Effects exhuast system from the cats back on the Corvette now that I would like to maintain with the headers. I use the car for bracket racing and some limited street driving. The LT1 motor is stock for now with some bolt-ons and modified air intake system. I have changed the rear end from the OEM Dana 36 to the Dana 44 with a 3:43 ratio. I'm running BFG Drag Radials on 17X11" ZR1 wheels and have ordered Weld ProStar 15X3.5" wheels and Monroso (DS2 26X4.5-15") front drag tires. Headers, Hi-flow cats, shocks and ingition wires are my next scheduled purchases. What brand of headers should I be looking at to purchase for my application? Thanks for any recommendations and sorry to 1996man for cutting into his posting.

 

Yes.
You would get more from the headers+cam than you would with either alone. If I recall, Nathan Plemons has these results on his site, where he added the hotcam before doing headers+exhaust and gained 20-25Hp from that exhaust work. I hope he corrects me if i'm wrong.

Whether its 'enough' is up to you and your goals. I like the sound of headers, so I would do them. It'd be easier to put them in while everything is out for the cam install.

Brands, well there are several brands mentioned in other threads here on the main page and they should all show up in searches, Exotic Muscle, Hooker 2149, TPiS...etc.

 

Thanks. It makes sense - now to use this logic on my wife. I'm sure she'd understand.

 

Packages. That's how I think you should plan your upgrades. For instance, I'd start with heads and a cam with a good header. We all know that the GM Hotcam is a great compromise for street and strip. We also know that 1.6:1 roller rockers work well with the Hot cam on LTX motors. To get the maximum out of this a good clean header/exhaust system is needed. Oh, what to do with heads? There is a number of shops that port and polish to match this profile. This package is known as a "top end" package. Make sure you have a "tuner" reprogram you ECM to finish the job. I'm in the process of collecting pieces to do just this. So far, I have the headers (EMs) sitting and waiting. The cam is next along with the roller rockers. Money, that's my only roadblock.

 

All the stuff about flow is correct and contributes to the higher dyno numbers. However, it is only half the story. The stock cast iron manifold and cats are HEAVY. When I installed my headers, I dropped at least 50 lbs. Lower weight = greater acceleration even if there is no hp increase.

 

that is a tremendous weight savngs! i had no idea the cats weighed that much! i dont have them on my car anymore but i never lifted them once they were off to see how heavy they are! thats great to know! im about to have a full new exhaust system if you add it all up, im sure the weight i lost on mufflers cats and soon to be iron manifolds equals quite a bit of weight i have dropped since it was stock!

 

Here are my $.02. Picture the exhaust gas blasting though a single tube header as if it was water going through a hose. It has mass and momentum. Before the exhaust makes it to the collector, the exhaust valve opens to let out the next combustion charge. At this point there is a vaccuum behind the first charge just beginning to exit the header tube (this is the reason for specific length of tubes) simply because of the mass and momentum. This vaccuum helps evacuate the combustion chamber. It gets better! While the exhaust valve is still open, the intake valve starts to open. During this interval the exiting exhaust vaccuum is still there and so is the new exhaust pulse headed down the tube, so it actually "sucks" the new intake charge into the combustion chamber. Then the exhaust valve closes but the intake is still open. The intake charge also has mass and momentum, so it tends to cram even more mixture into the combustion chamber, then the intake valve closes. Then both valves close and the next firing occurs. Very efficient.

With cast iron headers, all the "suction and vaccuum" efficiencies are lost because the exhaust charge simply empties into a common chamber. No momentum or mass in the very short portion of the exhaust manifold that bolts to the head, say, a couple of inches only. Plus, figure the chaos inside the header as all 4 cylinders are firing rapidly and all the exhaust pulses are competing to get out the single exhaust pipe where it bolts to the cast iron header. The new combustion cycle actually has some contamination from the last charge that did not make it out the chamber, plus there was no momentum to help suck in the new charge of unfired air and gas. A bigger duration/lift cam without headers, simply exaggerates the inefficient combustion cycle because it is producing even more exhaust gasses. But the single header tube greatly enhances that process because both valves stay open longer for better scavenging and refilling. And each cylinder has its very own exhaust tube to help that process.

 

Money, that's my only roadblock. [/QUOTE]

I`d be rich, if it weren`t for my lack of money.