The only testing that I know that’s been done .....there was some done by Carl McQuillan ........ GM (881) 2 x 4 versus his own beautiful 2x4 on a stock build ........ and quite sometime ago there was another member here who did some of his own testing on the speed port 6000 or 7000 versus the 2 x 4 881 manifold versus the Edelbrock you would have to check the archives
I would think that the new Edelbrock 2x4 would out perform the Offy by around 20-30hp.......That’s just a guesstimate
As of lately,the 5408 is no longer available.They may be waiting for enough orders to run another batch? The later test with the Speed-Sport was done comparing single 4 bbl.intakes.I'd suspect the Eddie would be up by 15-20 hp due to their more modern design,but know of no dyno tests to prove or disprove this.
Ok, I have both intakes, the one I select will be on a 10:1 compression ratio 427 CID 409 with 817 heads with minor porting and 2:19/1:72 valves. I like the look of the Offy but dont want to sacrifice performance thanks for now!
Comparisons of intake manifolds purely based on peak power production can be deceptive and that typically is what a lot of people look at when they compare dyno sheets.Its tough to extrapolate part throttle or mid-range performance from dyno charts,there have been many cases where a manifold has proven superior in dyno testing but when installed in a relatively heavy car and driven on the street it was perceived as inferior to another manifold.There are obviously instances where some are head and shoulders above their competitors,but in other instances where they are within a few horses of each other it becomes more a matter of which 1 feels better on the street(driveability).A good specific example of this is when comparing a Wieand Stealth intake for a Ford 429-460 to an Edelbrock Performer RPM,the stealth shines when in a lighter car with WOT only operation(strip)but the RPM is widely regarded as a much better intake when in a heavier car with lots of part throttle operation(street/strip).If you can't find someone who has done an on car comparison with your combination,you'll have to do your own to know for sure.
The basic difference between the edelbrock and Offy is the edelbrock is a dual plane design where as the Offy is a single plane. Offys short straight runners with a single large plenum generally flow well and make good top end power, where as the edelbrock has long curved runners and smaller dual plenums which creates good mid range torque with maybe lesser top end power. Note this may be generalizing a bit.
The beauty of spacers is they're easy to try,if they work leave em on and if not they're easy to take off.If you race a lot or have a big stroker it may love them,if your still around 409" and do a lot of street driving you may hate them.The particular example I referenced above with the 460 strokers was generally the more you got above ~520" the more attractive the stealth gets due to the larger plenum and runner volume.Of course that's not necessarily comparing apples to apples but the basic concept does still apply somewhat.Good luck on your experiment.
I wasn't too impressed with the interior of the "tall" Offy I have, it needed a lot of help. At the time, Eddy had not released any 409 stuff so I had no option. If I had both to choose from today, I would assume the Eddy had more thought put into the design and would be a better option for a small port engine.