The cam Scott brown said that would work in my application works really good. He made it seem like it was his favorite grind for street and street/strip 350's and 455's.
While I certainly understand the reasoning that power is improved all throughout the RPM range, I can't accept a .7 sec 1/4 mile improvement from the addition of headers alone. I've put headers on too many cars and raced them afterwards to believe that much gain.
Could have been specific to one car that the combo was choked by exhaust system that was on previously.
In Denver ,on a ALL STOCK low comp 350 with re curved distributor, 3.73 gears, headers were worth 7 tenths over manifolds added to a current 2-1/4 dual system. Real results,not internet BS Carry on Don't care what anyone believes. Im not selling anything so nothing to gain by lying . 350 manifolds are VERY RESTRICTIVE and the reason I will not spend money on a 350 as I want a stock appearing type car.
Can't help but question how much of that 7 tenths was due to the distributor recurve. If headers alone we're worth 7 tenths they couldn't sell them fast enough. Maybe there were dead mice in the stock manifolds. Something else was going on with that car to get 7 tenths and attribute it to headers alone? Buick Eric / Oregon
Stock manifolds aren't nearly as restrictive on a 350 as they are for the 455. They even share the same exit port size of 2" diameter. There's always a tradeoff. Headers will always gain over manifolds, but to some the difference is negligible, particularly when you weigh in the initial headache, long-term headache, and extra cost, not to mention the actual need for them in the first place. If you want to maximize power and don't care, headers all the way. If you plan to actually drive the car for any length of time, a properly polished set of manifolds will serve you well on stock-moderate engines. BTW... a .7 gain sounds pretty incredible for a simple header swap, especially for a 100% stock engine...there had to be something else that attributed. Not saying you're trying to intentionally deceive, but it just doesn't make sense. :TU: ...although...I do recall a small writeup I did concerning stock cam lobe asymmetry and air flow dynamics regarding the way the cam responds very well to engine mods...but .7 sounds like a lot even considering that. o No: Gary
Nick, What brand /type headers are they? Spec? Does seem to be an incredible gain. I'm running iron manifodls and nobody with headers is .7 faster. Most are slower.
They were a A body header. 1-3/4 ". Pass side needed a arm touched up and 2 tubes remade on driver side as noone makes Apollo headers. Again i have nothing to gain lying about a 16second car . Lol Also think of this. A mid 10 sec car will pick up over 1 sec on 150 hp of nitrous up here . Way more than youd see at sea level. A little bit more power goes a long way when ur down on it as we are . There was a 9 month period where i sold car and then bought it back. Co worker who bought it sold/liquidated some stuff so i have to look for slips/ header pics. Car still has scarred up a arm .Mph i believe almost hit a mind numbing 82-83 or so . Hahahha Ran low 16s after headers. This was in mid summer where the da gets up on average 8500- 9000 ft.
I have gone 13.31 as a best in my car ran a 13.40 and 45 on the same day. The next week it went back to where it normally ran and that was 13.50-60. Some days I went 13.80. I never changed much when going to the track since most of it was bracket racing and how it ran that day is how it ran. So my change is with in a .5 sec area. It could be possible to go a .7 with the headers with more tuning on carb and timing curve. It all depends on the air on that day. If everyone would go to the track with a car each week you would see what we are talking about good luck with that and then try and retune it for the air that day to make it run the same time ET.
I know that the inlet sizes are smaller for the 350 of course, and then the internal structure varies some, with the driver's side leaving much to be desired in terms of flow quality for the 350 manifold. I'm going off the same size outlet and 105 more cubes trying to breathe through it. I know there's more meat to the big block manifolds, which can be ported to 2 3/8 safely (2 1/2 with some risk), which you can't do with a 350 manifold. Is there more I'm missing? I welcome all the information I can get my 'hands' on. I love to learn new things. Educate me. :Smarty: If you mean ported vs ported, then yes, the 455 manifold will outflow the 350 manifold. Comparing apples to apples though, I'm not convinced (though as I said, I'm more than willing to be convinced). Raw flow numbers may be a bit better even for untouched vs untouched, but how well the 350 breathes through its 2" exit port seems like it would have an easier time of it than 455 cubes through a 2" exit port. This is what I meant, and maybe should have worded it better. If the 350 manifolds flow that bad, a set of shorty headers with similar exit port locations and similar engine compartment dimensions would be in order. I have thought about making some, but didn't feel there was a large enough demand for it and figured they wouldn't be a day/night difference between a set of polished manifolds. If it turns out I'm wrong, I'll consider revisiting my Buick 350 shorty header notes and continue where I left off... :TU: Gary
You make a very good point here. I should have considered atmospheric conditions and commented thusly. Many more dynamics involved than what meets the eye. Thanks for pointing it out. Gary
If you place 350 manifolds next to 455 manifolds they look the same only 7/8 scale. Just like the rest of the engine. I have not tested them on a flow bench but doubt they are any worse.
If you couple headers with a X-Pipe exhaust system you should gain some appreciable power. It will also help balance the exhaust system. which, in the end should add power across the board.
Even just an "X" pipe (a properly engineered one, otherwise it can work against the exhaust) with manifolds will help substantially with exhaust evacuation. Those Flowmaster "Y" scavenger series look pretty good too for large single exhausts, which by the way will flow just as good if not better than a pair of smaller duals, particularly when they're press bent. As a matter of fact, a single 2 1/2" mandrel bent pipe flows better than 2" duals that are press bent (but only if they're press bent; otherwise, mandrel 2" flows better). The reason is the larger pipes increase volume exponentially as the diameter increases, so there's more to it than simply an extra 1/2" (or whatever the increase). That extra 1/2" diameter increases the outermost part of the circumference and adds substantially more area. The larger you go, the more of an increase. Going from 2 1/2" to 3" is even greater than going from 2" to 2 1/2". Same principle with the larger valves. You don't have to max out lift to get more from a larger valve. They give more at any lift. Anyway, a pair of 2" mandrel pipes leading into the Flowmaster scavenger series "Y" pipe 2 1/2" collector and then 2 1/2" mandrel pipe constructed the rest of the way back into a good flowing 2 1/2" muffler will outflow your standard 2" press bent muffler shop generic dual exhaust system. Just an FYI for those who didn't know. Gary
Although the above statement in bold is probably true with my real world testing I had a 2" press bent dual ex. system no X or H pipes with Cherry Bomb mufflers all the way to the back over the axle exiting out behind the rear bumper and changed to a mandrel bent 2.5" X pipe system where track testing with both systems showed virtually zero gains, both systems with the same headers. To see or even need a better exhaust system than a press bent 2" no crossover system the engine needs a cam and heads that need to exit more exhaust than the 2" system can handle. So in other words there is no sense in spending the $$ on a fancy mandrel bent system unless the engine has the mods that call for a better system.IMO The cam in the example engine is very mild with a 202* in. and 212* ex. duration @ .050". I think there is a point of diminishing returns when the back pressure is removed from a certain point that would be the end of the gains and if to much back pressure is removed that could even slow the car down. Size accordingly. GL Derek
While you are correct with the bigger is not always better analysis, keep in mind I'm comparing 2" press bent duals to a 2 1/2" SINGLE mandrel exhaust. Some applications may have difficulties with space for room with duals; otherwise, it was just an FYI statement to show the differences between the two. A 2" muffler shop bent system (if space permits) is fine for most setups from stock-mild and even some lower-end moderate combinations. Press bending isn't as detrimental as the mandrel endorsers will claim, though it does of course restrict it some. The main restriction is tight bends, such as over the axle, and even then it's in the thickness perpendicular to the bend, not the part that's parallel to it. In other words, it doesn't restrict it much at the width of the bend, but at the thickness part of the curve, so only *about* half of the restriction is applied mathematically to the restriction, which comes out to about 1/4" difference on 2" pipes (not 1/2" as mandrel endorsers will claim). Pretty much all exhaust pipe is measured from the outside diameter, and with 16 gauge steel (which is 1/16" thick, x(times)2 for each side) is actually 1/8" thinner diameter on the inside, so a 2" pipe is actually 1 7/8" ID (inner diameter). Press bending this constricts total flow by about another 1/4" (2/8), so making it 1 5/8" flow at the most extreme bends. THIS is what flows worse than a SINGLE 2 1/2" mandrel bent pipe. Then you must consider gas expansion and contraction with temperature (the exhaust cools very quickly as it goes further away from the engine) and so requires less pipe to flow since contraction occurs with cooling. This, coupled with the fact that as the exhaust travels farther from the engine, it also slows down, requiring smaller pipe to maintain velocity to ensure efficient evacuation. This is why smaller tail pipes are desired over same size compared to head pipes... Velocity is what evacuates the exhaust, so larger can actually harm performance... Same principle as to why you want smaller diameter primaries on your headers for smaller CID/lower RPM engines. A single 2 1/2" mandrel bent system may or may not be cheaper than a 2" press bent system, but then there's the muffler cost offset of needing only 1 instead of 2. Then there's the ground clearance. A larger pipe will hang down farther than a smaller one, so that must be considered as well. Let's see...did I forget anything? Oh yeah, the math behind my statements. You said 'probably' as if I was just guessing at it. lol... Area = pi x r squared. Rounded pi is 3.14, times the radius, squared. Let's do this for a 2" diameter circle: 3.14 x 1x1, or 3.14 x 1 = 3.14 square inches in a 2" diameter pipe, times 2 for dual exhaust is 3.14 x2 = 6.28. Now do it for 1 5/8" (times two) and then for 2 3/8" and see where the numbers take you. I'm not pulling this out of my ass you know. Let me know if I made any errors in my typing or math. Edit: I'll do the math here so it'll be easier for everyone to see: 2" pipe is actually 1 7/8", or 1.875. Get this by dividing the fraction into itself, 7 divided by 8 = .875, then add the 1, getting 1.875. Divide this by two to get radius = .9375 times itself (squared) = 0.87890625 then multiply by pi (3.14) to get 2.76 (rounded for simplicity). Double this for dual pipes, and you get 5.52 square inches for dual 2" OD (1 7/8" ID) pipe. This would be mandrel bent. For 1 5/8" (1.625), it's 4.14 square inches (summarizing the math). This would be dual "2 inch pipe" that's press bent. For 2 3/8" (2.375) ID (inner diameter) for 2 1/2" OD (outer diameter) pipe, it's 4.43 square inches for mandrel bent pipe. 4.43 > 4.14 (2" press bent vs 2 1/2" mandrel) thus my statement is proven true. Then we see that 5.52 > 4.43 showing that mandrel 2" is better than single 2 1/2" mandrel. Gary
Yeah, way to early to do math. LOL Just wanted to share how I wasted $$ for zero gains, carry on......... Derek
It's ok, I did the math already in an edit to the previous post. lol Dammit Derek, making me do extra work. :laugh: Gary
Think of the future get headers with the X-Pipe and put flanges at the mufflers and you will be able to drop the system from the headers to the muffler to aid in removal of the transmission. because that will be next in line. Use Walker Dynomax mufflers for the most power gain.
