ram-it

Great explaination Bill! I like it when you take the time to detail out a response. The way I understand merge collectors is that they help accelerate the exhaust flow. Your right but on a stock cube engine the flow just isn't going to change that much unless you do heads and radical cam. Air in to air out. No H/C or increase in cubes this air in part will not change a whole lot. I still believe that the merge collectors are not worth the expense unless you have other goals with high hp in them. Hot rodding was originally about going fast as cheaply as possible. Too small of a gain (if any) on a basically stock car. So I did not get them.

Now a case in point. I have been looking at LG headers for my car. The are the best on the market and made by Borla for him. They include his racing merge collectors. Headers only with a tune is putting these Z's in the 390rwhp range. Lou attributes this to his merge collectors. Dynatech has a exact copy of the LG's except no merge collectors plus they use cats. These cars are seeing within 2-5rwhp of LG's. Why so close if they are using cats and LG wasn't? Goes back to a relatively stock car can only produce X amount of exhaust gases no matter what. You can run open headers and it will not change.

Ryan K

iTrader: (11)

"Dynatech doesn't claim its merge collectors to be a magic, out-of-the-box bolt-on. In fact, if a combination has been optimized with standard collectors, Dynatech cautions that it's possible to "overscavenge" the exhaust when switching to merge collectors. This is why the company suggests additional camshaft testing may be necessary to get the best results from a merge-type collector. While 20-plus-horsepower gains are common, it's also not unheard of for a merge collector to initially lose horsepower or torque if it upsets the balance between the camshaft timing and engine airflow. Stepping up to a merge collector is a process best carried out on an engine dyno."

This is from Car Craft, the point that this paragraph makes is the camshaft statement. Professionals that run these merge collectors have exacting programs that use things like: header runner length, length of the exhaust after the collector engine rpm, Displacement, and the like. ALSO, and this is a big also, these guys have camshafts that have different specs for each cylender based on the above variables. There is no way that you can have a one merge collector for all applications.

Ryan

Ryan K

iTrader: (11)

Here is another good bit of info:

http://www.dalhems.com/engine/ssheader.html

Rokko

iTrader: (2)

Cams ground for each cylinders exhaust dynamics.... holy ****. Big boys games.

That's a great link Ryan. Explains a lot. I remember the older open wheeled indy style cars with the crossover headers. I think the original GT40 had those too. Now I know why.

Oh yeah, it also made my decision a no brainer. I was still wondering if I made the right decision based on my goals.

ram-it

I have always thought of merge collectors in the same way as head porting. The goal is not the maximize airflow, it is to fine tune the airflow's characteristics. The pursuit of 1/4mi times are different than road racing. Smart builders start off with the idea of their goals and tailor their mods to suit. Matching your airflow characteristics to your goals means being able to measure the air flow. That means that a merge collector will not give you any measureable increase if the engine cannot flow the air. Therefore, on a stock displacement engine with minimal head work and a emissions friendly cam the merge collectors are a waste of money.

WAHUSKER

iTrader: (4)

Very nice link Ryan! I should bookmark that one. Thanks!!!

Yeah Rick, having 'tuned length' headers is probably more important to you that the merge collectors for your application. Long tubes will dramatically increase the scavanging affect over the stock manifolds. And having the tube lengths all the same will 'tune' the timing of such events, so that each cyl gets a balanced service (for lack of a better term).

Which brings me back to the Groty design headers...so you made the right choice IMO.