[Gary and Matt]

We FINALLY ([email protected]&%#!*[email protected]#$!!) have the new 350 close to running the way it should. Now it is getting close to the time to start thinking about headers and exhaust.

We're currently running factory headers from the old 307 with 2" pipe on our 3 year old dual exhaust. I know, we're really pumping/pusing air here and need to let this puppy breath like a big dog.

So is exhaust pipe size driven by the type/brand of headers or is there a 'standard' everyone uses?

Also, any recommendations on what headers that will work on a 3 Gen WITH power steering?

And I don't mean it will 'work' after you beat it to death with a 5 lb hammer.

Thanks

 

[Mike Goble]

Exhaust system tubing size is driven by horsepower. For a typical 350" SBC of 330 hp you might start with a 1-1/2" primary about 40" long with a 2-1/4" collector.

 

[TDWZ28]

When I was searching for an exhaust system, I used the chart on this site.http://www.torquetechexh.com/

 

[NovatoriusRex]

When I was searching for an exhaust system, I used the chart on this site.http://www.torquetechexh.com/

I'm sure there's good info hidden in there somewhere, but gawd what an awful website. :beat:

Here's their commentary on picking the right size exhaust:
http://www.torquetechexh.com/whichsize.htm

Here's the sizing chart you spoke of:
http://www.torquetechexh.com/Web Photos/Which 26.gif

 

[Real McCoy]

Novatorius, Are you asking about the header tube/collector size or the exhaust pipe and muffler size. I read it and thought you wanted exhaust pipe size but rereading it I think you want header tube and collector size. If you want header tube/collector size we need the motor info. RM

 

[Denis the Menace]

I bought a 3 inch exhaust from Torque Tech. It was very well priced compaired to what any of the shops around would/could compare too. Nice bends and a good fit. The guy's I spoke with really seemed to know what they were talking about. The reducers off the collectors are very long with a very slight taper. I originally saw a magizine article on there exhaust years ago, I think it's on there web site some where. I would buy from them again!

 

[Gary and Matt]

WE were wanting info on exhaust pipe diameters.

Also looking for header suggestions for 3rd Gen with PS.
I recall alot of headers will NOT work/fit with the PS in the way, without some kind of nudging (banging of the pipes).
I won't spend that kind of money and then beat it with a hammer.

 

[Real McCoy]

If you want header suggestions people need to know some engine info and what you plan to do with the car. Street car or street/strip or race only?

 

[CDJr]

Personally, I think the 2" pipes youre using now are probably close to ideal, unless you have some serious mods done to that 350. 2 1/4" would probably be as big as I would go with it. However, there are a lotta things that will affect what size would allow you to produce peak horsepower and maintain proper back pressure, but unless its really juiced up, youre probably pretty close.

 

[Gary and Matt]

Thanks

Our 350 was a fully prepared drag race engine with the 'largest hydraulic cam' you can get (was the seller's words). That cam has been the death of us for the last 9 months while we tried other things to make it streetable. Finally threw in the towel and put a new cam in it last week. I don't have the Comp Cams spec sheet with me right at the moment, but it has some lope (sp?) to it. It's a good thing we had this done, since there were some other little things they had done that ultimately would have ended the engine's life shortly anyway. (i.e. triple coil valve springs that were literally grinding two of the lobes off the cam, no O rings on the valves, etc.) It was definitely meant to run at above 5000 RPM for short distances!

Why we bought this engine (??) was a matter of price and timing when the 307 died.

Anyway, intended purpose is just a weekly cruiser (like today for me) with Matt using it as daily transportation for his summer jobs when the weather permits. It would be nice to be able to smoke the tires once in a while, but not a major issue if we don't. We are running a 600 CFM Holley and a 2400-2800 rpm torque converter. Rear end is still the stock 10 bolt for now since we burned the $$ intended for the rear end on the new cam swap.

Sounds like we have enough pipe for now. Maybe I can pick up a set of better flowing factory exhaust manifolds since I imagine the stock 307 exhaust manifolds aren't tuned for this engine. That way, I won't have such a fit issue with tubular headers.

Any suggestions on alternative factory exhaust headers?

 

[Real McCoy]

Big cams with small heads is not the ticket IMO. Big cams are needed for motors that are capable of alot of air movement. You should be happier with a smaller cam. Not sure what fully prepped drag motor means but I'll guess it means blueprinted properly. You don't mention what heads, intake or carb you have or the compression ratio so if you do go with headers stay small tube like Mike suggests. If you stay with factory manifolds the 2 inch exhaust system should work fine. Just my opinion. RM

 

[69NovaSS]

that site sems to contradict itself in a few spots on the same page

Basically, as a rule of thumb, if your intended use is strictly street, for cruising and maybe as an everyday driver, then 2.5" will be adequate,,,,,,,,,, unless you have 500 HP or more! For the strip, if you have a power plant rated around 425 or more realistic horsepower, then the 3" system would be the way to go. Powerplants with few horses just will not benefit from the larger 3" exhaust although 3" tailpipes showing from behind the rear wheel or under the bumper will make quite an impression.

It's been our experience that too big a system will not hurt performance (as long as the primary tubes on the headers are not too large -- Headers do the main 'tuning' of the exhaust), just cost a little more.

If you're not sure of the horsepower rating of your powerplant, but have raced at the dragstrip, then any 1/4 mile ET's in the 12.40 - 12.70 range or quicker would benefit from the larger 3" exhaust versus a good 2.5" mandrel bent system.

Now the info below is from the same page but they say their source is the Dynomax website.....did they not read it before they posted it cause it contridicts their postings above

Pipe Diameter
A common misconception is that the larger the diameter, the better the system. But bigger isn't always better. Systems that are too large in diameter can actually hurt performance. As a general rule, switching to a performance system that is 1/4" to 1/2" inch larger than stock will provide you with the best horsepower increases. To determine which pipe diameters will be best for your system, decide what RPM range your engine will operate at, most of the time. Smaller diameter pipes will produce low- to mid-RPM torque. Larger diameters produce mid- to high-RPM torque.

Horsepower Depends on Flow not Pipe Diameter Alone
Bigger isn't always better. Systems that are too large in diameter can actually hurt performance. Improved flow is what you need. Having large diameter pipes isn't what's cool. Going fast and making horsepower is.

Sooooo which is it???? Is it that too large a dia of pipe does not hurt performance and looks cool or is it that too large a dia of pipe hurts performance and performance is what is cool not pipe dia ....

 

[Mike Goble]

It's been our experience that too big a system will not hurt performance (as long as the primary tubes on the headers are not too large -- Headers do the main 'tuning' of the exhaust), just cost a little more.

You didn't highlight the disclaimer. If you have a properly designed header system, oversizing the exhaust pipe will not affect much as the tuning and reflected waves are already at work before the tertiary pipe comes into effect. The use of stock manifolds will bring the size of the size of the exhaust pipe more into play, as this system depends more on just the pressure gradient to move the gas.

 

[69NovaSS]

True enough Mike, but the second quote has no such disclaimer and is seemingly only talking about the pipes themselves not the headers...so again I ask which is it.....does too large a dia of exhaust pipes effect the performance of the vehicle or not???

 

[Mike Goble]

I'll need a complete description of your exhaust system to determine that.

 

[69NovaSS]

well I wasnt really talking about my exhaust system but I was talking about how the website of a company that wants to sell exhaust systems seemingly contradicts itself on the same page as to whether or not running too large a dia. of exhaust pipes will or will not effect performance of ANY given car.

Lets just say it was determined that my car would run the best with an exhaust pipe dia of 2.250" and I wanted to run 3.0" just cause it looked really cool......In one paragraph they say it would not effect performance of the car to do so but a few paragraphs farther down the page the say that it will effect the cars performace to do so....its a little confusing as to which it is

I mean both statements are somewhat mutually exclusive so you would think one of them must be wrong

 

[CDJr]

Yes that does seem somewhat contradictory. And yes, too large of a pipe WILL hurt performance, via the lack of back-pressure. How MUCH it affects it is dependent on the engine, etc, but there IS an optimum amount of back-pressure, and too large of a pipe can be almost as bad as too small of one.

 

[Mike Goble]

What does backpressure accomplish? It seems that there is a myth about backpressure being needed in an exhaust system to achieve some effect but I'm not really sure what it is. Are we talking about an average pressure? Peak pressure? Is it a backpressure wave?

 

[CDJr]

Well, Im sure I worded it wrong, and Im certainly no authority on this, not to mention that Im not very good at explaining things, but Ill try lol. Ideally, what you want is a fast-moving, steady stream of exhaust going through your pipes, mufflers, and exiting the vehicle. A smaller pipe will keep this flow moving at a steady pace to prevent any hiccups in the flow from occuring as the exhaust valves are opening to release the exhaust gases. In a way, it kinda creates a vacuum and sucks it out as opposed to the piston having to PUSH it out. However, a large pipe will have a slower flow and will not keep a strong enough flow travelling through the pipes. Most of the time, its not THAT critical, and unless you put it on the ol Dyno and tested it with different sized pipes, you ordinarily wouldnt even notice any difference, unless you were way oversized or way undersized. In other words, theres a pretty good range thats acceptable, and by the same token, theres always ONE optimum size.

TOLD ya I wasnt very good at explaining lol

 

[NovatoriusRex]

TOLD ya I wasnt very good at explaining lol

That's a very good explanation in layman's terms. Explaining it in terms everyone is pretty much guaranteed to understand is a good thing. Kudos to you.