mrl said:
I realize this question has been asked many times before (I did use "search") in different shapes and forms but my application is somewhat specific. I am swapping a sbc into a tight engine bay, and I have to decide between exhaust manifolds or block hugger style headers. Long tubes are definately not an option. The headers I am interested in are part # H8052 from Patriot Exhaust. They are quite short, measuring only 6" from top of exhaust port to bottom of flange, and have 1-5/8" tubes. The ram horns would be the 2-1/2" version. The application is strickly for the street, in a 3100 lbs car with regular gears and a T5 trans. The engine is a 350, nothing special, 10:1, iron heads with a cam and Holley 750 DP one a single plane manifold. I kind of like the advantages of the ram horns (flow quite well, quiet and long lasting) compared to headers. Since I wont be revving this engine to the moon probably 5500-6000 rpm max, would I really get that much more power with block hugger style headers? Any comments or advise would be greatly appreciated.
In my experience there isn't any signifcant power difference between rams horns and shorty headers. Both give up power to tuned full length headers, but that doesn't sound like an option for you. Besides you stated it's a street machine which I'm sure will spend more time at a 2000 RPM cruise in 5th than it will at red line at WOT. So the argument about 15-20 hp at 6000 RPM for long tubes is rather moot.
These will put your engine somewhere in the middle of best max power, not as bad as OEM under the sparkplug manifolds and not as good as long equal length headers. The SBC will show a 15-20 hp gain for a equal lengths over the OEM drop manifold, but against the rams horn or shorties its more like 10 at red-line and WOT. Often equal lengths will show considerable droops in power output when the engine RPM isn't in an area compatible with the resonant frequencies of the pipes. So on the street just puttin' around it doesn't matter a whole lot.
An aside, I think for how you intend to use this that your compression is too high, you're over carbed, and the manifold choice would be better with a dual plane. This drives questions about the cam timing, final gearing, piston and head selection? 10 to 1 is a lot of compression unless you've got a long winded cam, some choice combustion chambers, and the proper contour pistons in there.
I think the choice of a cast iron exhaust manifold provides greater stability and less maintenance than headers. What-ever the selection, I recommend stainless fasteners from the connection to the head thru every nut and bolt to the tail pipe. Their resistance to rusting makes maintenance a much more pleasant chore, especially where headers are concerned since you know going in that you'll have to tighten things up from time to time.
While on headers to the head fastening, let me recommend that you mock this up and select different types of fasteners for different locations such that you can actually get some form of a wrench on the fasteners after the engine is installed. Typically I choose between ARP stainless 12 points, studs with a nut, or Allen heads depending on what can be gotten at specific locations with a wrench of some sort after the engine is installed. While doing the mock-up correct any header or manifold mounting holes that don't align with the threaded holes in the head, this eliminates fastener alignment, installation, and cross threading problems. This will save you sooo much pain later on. Check the spark plug clearance while doing this, it's a lot simpler to dimple offending tubes now than after the engine's installed.
I always use aluminum or copper gaskets between the header and the head and between the the header flange and the head pipe. These will resist blowing out or burning up for quite a while if a fastener loosens and you can't get to it right away. I also use a flex joint somewhere along the transmission area in the head pipe to decouple the headers with engine movements from the rest of the exhaust system that sees chassis movements. This really reduces tube fractures and bolt loosening in the headers. These can be stainless over-braided joints if you've got big bucks, a doughnut and outside clamp joint, or simply a short length of flex pipe with stainless band style motorcycle muffler clamps. Use either a H or X pipe somewhere ahead of the mufflers. These provide an overpressure escape when you're whipping the throttle so when running dual exhaust any one side of the engine can see the flow provided by both mufflers and tail pipes. It also mellows the sound, helping to keep the noise police off your back, but still lets the world know there's a V8 under the hood.
Bogie