A few post updates from over the last couple weeks.
I heard from one of the NAPA guys that the Eureka airport where I ran the car last summer posted up they are having a run whatcha brung event on Friday May 6, so I may try and make that. I'm supposed to work that day but can likely get it off.
Drove the car and it really seems to have quite a bit more power from the seat of the pants feel. I had initially re-used the fiber gasket because I liked how thick it was, but it really hadn't come apart clean, so the vacuum leak at the manifold wasn't surprising at all. I replaced it with a new thin tin one from NAPA and it still has a little vacuum leak issue, which isn't surprising given I never had the intake flange surfaced, but it idles down to 600-700rpm in neutral so it's not too bad. So I pulled the intake again, it only takes about ten minutes since the bolts are easy to get to and it's only the intake, cleaned up the surface of the bit of copper RTV, which clearly showed some failings, and put a bead of Right Stuff around the port and then skimmed it off with a metal putty knife, leaving a coating of the Right Stuff in the low spots. I let that sit about an hour and then ran a bead of Right Stuff on the outer edge of the tin intake gasket's raised grooves. So the bead should contact the intake flange first and anywhere the gasket isn't enough the Right Stuff should play filler and shouldn't squeeze its way to the runner. Then let it sit for a couple hours even though Right Stuff says it should be able to go right back into service.
It seemed to have worked. Unfortunately after about a ten minutes of run time it started to leak fuel at two injectors. I the repeated removal and installation of the fuel rail had compromised a couple O-rings which I found upon inspection. Found two of them nicked, this one was the worse, but I replaced all of the upper o-rings just to be sure. The risk ran when removing the fuel rail a few times. The injectors usually stay with the rail, but sometimes they stay with the intake and I had to re-install them into the rail, that's how this happened. I just didn't take enough care installing it last time. [url="http://s42.photobucket.com/user/TheSilverBuick/media/Firebird%202/IMG_20160307_132143570_zpsopyyjw73.jpg.html"][/url]
It still has an audible vacuum leak, and it appears to be narrowed down to between the ports, where I wasn't able to effectively coat the welds in epoxy... I used a screw driver to attempt to paste in some Right Stuff between the ports, but only had marginal success. So the intake may yet come off again... Got to love R&D, if it was easy everyone would be doing it =P Prototype #1 is about done.
I tried using a high speed datalog to see if one cylinder has a greater leak than another, but no such luck. The only thing that came out of it was it "appears" cylinder three pulls the most vacuum, but is likely just a result of the vacuum port being right across from cylinder 3's runner entrance.
The for some reason log is read right to left (as determined by as time increased the logged value was to the left). ​
Just to compare numbers. I am still contending with some vacuum leaks, so the new intake having a higher manifold pressure isn't surprising, but the test is also ran at around 100rpm lower than the first test. So I may dial the target rpm up to 825rpm and run the test again to see how it compares. The extra rpm "should" pull a bit more vacuum and really compare the two charts.
The stock manifold, with the short runners and comparatively small plenum volume runs about 3kPa from low to high, and the new intake ran 1.5kPa from low to high, which I is expected from the much larger plenum volume** combined with the runner length. When I re-run the test at 825rpm I don't expect the variances to change, just shift the wave to a lower pressure range (higher manifold vacuum). The average shift is ~4.75kPa more pressure or 1.4inHg less vacuum.
**The new plenum volume is approximately the same as the engine size, not counting the runner volume.
Test 1 from January 2015. ~825rpm, ~34kPa - ~37kPa
Test 2 from March 2016. ~713rpm, ~39.5kPa - ~ 41kPa.
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