FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Qikbbstang on January 05, 2016, 12:49:23 PM
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I have a feeling nobody can answer this as well a Jay. I've noticed professional engine builders almost always use their tried and true "pet" dyno headers for dyno testing their customers motors regardless of motor combination. Beside the facts that shop dyno headers are optimum (high dollar) equal length, tri-y mege collectors etc. they are free of the confines of bends, different lengths etc required to stuff then in the typical unibody shock tower car.
What I'm wondering about is how valid will a "dyno room" tune be once the owner drops his dyno-room "tuned motor" into his street/strip Mustang Fairlane etc. with over the counter headers and a decent exhaust system?.....................I take it for granted the dyno test'd motor owner would supply his to be run Carb and Distributor.
Am I correct to presume the (a)timing would not change with different off the shelf FE headers and maybe an exhaust system and (b)jetting would only be a step or three?...........
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I think your conclusions are about right, BB. You might see a change in A/F going from a really optimal set of dyno headers to the headers you use in the car, but in my experience its only a few jet numbers. Same with timing, very minimal if any change.
Why not dyno the engine with the headers that are going to be used in the vehicle? Then you take the dyno headers out of the equation. Sometimes there are fitment issues, but not usually...
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I think the AF change is often due to adding a restrictive air-cleaner system to the engine and not having a wide open or tunnel fed air system like most dyno systems have.
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Jay, have you ever had a set of Super Comps or similar on the dyno? If so, any fitment issues? I would like to use my bundle of snakes when I dyno my next one so I can get a fairly accurate measurement.
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Can't speak for other installations - but my DTS will not "play nice" with many of the catalog FE headers. Especially the Hooker and similar race headers that dip in under the oil pan a bit on each side. The dyno cart gets in the way of those, and the absorber/driveshaft/mounting cabinet needs at least 17.5" between the collectors. Several headers are closer together than that and we end up not being able to connect the exhaust.
I have tried installing Hooker race headers upside down like a boat - they were about 12 horsepower less than my dyno headers that way FWIW. My dyno headers are actually kinda small for some of the "big" engines, with 1.750 primaries going to 2.000, and a 3.500" tri-Y collector.
Nice thing is that they fit easy, have all the EGT connections in place, and can stay mounted to the cell exhaust - makes life a lot easier...
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My dyno was modified, before I bought it, to make it narrower in the middle where the headers pass. It's only 10" wide at one point, and about 13" wide where most of the collectors are. It was probably about the same width as Barry's when Superflow manufactured it. And I have had the Hooker Super Comps and adjustable race headers on my dyno without fitment problems.
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Thanks for the feedback guys. Jay, I hope the dyno I use will be as accepting of headers as yours sounds.
The headers I currently have are an old set of Headers By Ed, that wrap around control arms, steering/clutch linkage, etc. Sorta like the adjustable race headers.
Didn't mean to hijack anything, just a "while we're on the subject".
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Same here.
We use what will fit the dyno cart. I use a Stuska and it usually takes a custom sprint-car style header to clear the cart and put the collectors in the right spot.
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My "dyno room score of the decade" back in the Miami-Vice days of Drug Running there was a St Augustine, Off-Shore Racing Boat facility KS&W Offshore Engineering that was second to none - so the "king-pins" could maintain fleets of go-fast boats. It was seized by the Fed's and is still used by US Customs, DEA, USCG etc to refurbish their own boats to this day. About five years after the seizure, when the gov't finally got around to having a three day auction: 1st Day-Inspection, 2nd &3rd day Auction, those that failed to get there day #1 inspection had not a clue what was being auctioned - no inspection allowed. I wanted a set of the fancy double jacketed stainless headers for my boat and bought two, four-foot tall palleted crates of headers for a few hundred dollars... When I started unpacking I was surprised to find (four) Super-Flow Velocity Stacks, Pyrometers, drive couplers and all sorts of marine and racing headers. Turned out I had bought the Dyno Room headers and dyno room goodies -- none of them had ever even been on a boat - no salt - dyno-run-only.
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We work on many engines for folks who actually race them competitively, where every little bit counts. My dyno headers are made to (a) fit and clear the cart or stand on any dyno I may visit, and (b) share the same step lengths, sizes, and collectors that will be used in the vehicles in which the engines get raced. When we dyno engines other than race-only engines, it probably helps the numbers, but they are in fact numbers generated by THAT engine. Generally speaking, most engines will need two or three less jet numbers when run through a full exhaust than the best tune when run "open headers" on a dyno. Most of my race engines come right off the dyno, go right in the race car, and require no additional tuning, so the dyno headers are very representative of the step headers we use in the cars. For me, it is about repeatability and accurate tuning in an environment that is as close to the real situation as possible for the racing engines. Numbers don't mean as much as the ET slip. Using dyno headers has never produced any ill effects for street engine customers. Lately, we have done more and more work with custom headers and collectors for the street/strip crowd. You can tell the difference in good header design by the butt-o-meter too, you don't have to have a race car to feel the benefits.
When scavenging is very efficient, it will require a richer mixture on the intake side. Better exhaust means less garbage is burped back into the cylinder and the intake manifold at overlap. More power will require more fuel.........physics. I have never seen a header or a collector pick up power that didn't show to be leaner in an A-B test, and when it is fattened up..........a little more power comes with it. When whatever you hang on it for exhaust hurts power, it has always richened it in the process on everything I have tested.
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Blair touched on a couple useful items to consider with that post.
First is the "THAT engine" reference. While testing with dyno headers might not provide exactly the same numbers as with the vehicle exhaust, it does allow very good comparative data between various similar combinations by eliminating a variable.
The other comment is the variance in optimal mixture between dyno and car. Due to room limitations and city neighbors, my cell exhaust uses a pair of 90 degree bends about 18" behind the dyno assembly, followed by 5 feet or so of straight pipe out the side wall, another pair of vertical 90 degree bends, a pair of big truck mufflers, and ten feet of vertical straight pipe. I have seen other cells where the exhaust simply goes straight out the back wall (to a field or whatever - some scared cows???) and is wide open. Neither version is "right or wrong" but they are different and will deliver different numbers as a result. You will need to tweak things once installed if you are chasing the absolute optimal tune.