10-03-2015, 10:30 AM
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#8
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Join Date: Oct 2002
Location: On a hilltop in Pa.
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Re: Merge collectors
Quote:
Originally Posted by Alan Roehrich
Ed,
Step headers and merge collectors are similar to 4-2-1 headers, you need to do a serious amount of tuning and probably cam testing. When you use either, or both, you significantly alter your exhaust tuning, with an exhaust lobe that is large enough for a set of single diameter headers and a merge collector, it is very likely that you can create a serious "over scavenge" condition. If that is the case, you can see what happened with the right dyno data. The solution most often is a smaller exhaust lobe, as much as 4-6 degrees. You may also need to spread the LSA a degree or two. But what you may gain from all of that is the ability to run a large(r) intake lobe.
The short version of that is: if you have a correctly matched and tuned set of basic headers and collectors and cam, it is likely you will find no power gain, or a power loss with a set of stepped headers and merge collectors.
So, when/if you buy a set of stepped headers and merge collectors, and you spend $1500+, expect to buy at least one cam, and maybe spend money on a couple of dyno sessions and a track rental, so another $2000 is easily possible. It's just another example of "HP cost money, how fast do you want to go?"
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Alan, I've been telling the same story for years but nobody seems to want to listen. There are advantages to being able to take exhaust lobe away from the engine though. If a conventional header is "properly" sized to a combination, the average Racer should be satisfied. IMHO, most Racers buying off-the-shelf headers are buying too large a primary tube for their application and then being sold the merge collectors as the fix.
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Billy Nees 1188 STK, SS
Reality, what a concept!
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