During our last exciting episode of the multiple carb intake testing, the crossram intakes had provided interesting results, and the Dove tunnel wedge intake was on the engine being tested after a water leak problem had been fixed. Test results last time for the tunnel wedge were lower than expected, but the A/F was far from optimal, so the next steps were to richen up the jetting to an A/F of 12.5:1 or so, in a search for better power.
The other intakes tested so far with the 660 center squirter carbs had all liked the 63 jets Id been using, and had all shown good A/F numbers, but the tunnel wedge wanted more jetting, so on Wednesday this week I jetted up from 63s to 66/67 jets in each carb, and ran another test. HP jumped by more than 10 to over 400, and A/F was down to about 13.1:1, so I figured I was on the right track. On Friday evening, I went to 67/69 jets in an attempt to reach closer to 12.5:1 A/F. This seemed to hit the bulls eye; the manifold made 410HP, and the A/F was in the 12.5:1 to 12.7:1 range. Here is a photo of the tunnel wedge intake on the engine, and also a HP/Torque graph for this manifold:
I was pleasantly surprised by the torque production of this intake; although not as good as some of the dual planes, it nevertheless made over 450 ft-lbs. It is obviously not as good of a match to this engines requirements as the dual plane or small single plane intakes, but it didnt give too much away, either.
Next up were the tunnel rams, so I spent Friday night tearing down the engine and installing the first tunnel ram intake. This is a homemade unit, provided to me for testing courtesy of qikbbstang. It consists of some kind of low riser aluminum intake base, with the top cut off and the tunnel ram runners and plenum welded on. BB provided the intake and the linkage, which was pretty important, because I think I would have spent literally 4-5 hours making a linkage setup to work on this intake if BB hadnt sent the matching linkage along. Heres a photo of this intake:
Yes, it is as ugly in person as it is in the picture. Apparently the welding on the intake is porous, because whoever built this intake slathered all the welded areas with a putty type of epoxy, for sealing purposes I assume. (By the way, BB did NOT make this intake himself, someone else did). At the same time, its cool, because you can look into the plenum and see a straight shot down the intake runners and into the head ports, and the carb pads are rotated to aim a barrel at each port opening. The only thing I saw that I didnt really like is that the transition from the welded on runners to the manifold port openings; this area wasnt really smooth, and in fact the builder had also smeared a bunch of the putty epoxy on the insides of the ports, to try to smooth the transition out a little.
Unfortunately, all the epoxy on the intake showed signs of separating from the aluminum, and it was chipped and cracked in multiple areas. Heres a photo of the inside of one port, showing this issue:
I spent some time cleaning up this intake on Friday night before installation, and after inspecting the epoxied areas I gave serious consideration to not running the manifold. There were many spots inside the runners where the epoxy had separated from the aluminum, and it was entirely possible that a big hunk of epoxy could break off during the dyno test, and get ingested by the engine. Finally I decided that I was curious enough about the performance of this intake to take the risk, so I bolted on the intake, hoping the engine wouldnt become a sacrifice to the HP gods. I also used the 660 carbs, with the same 67/69 jetting that I had used on the Dove intake. After hooking up and adjusting the linkage, I called it a night.
Saturday morning I fired up the engine, hoping not to hear any unwanted noises. Joel H (tall69) from the forum had come by to help out. Everything sounded fine, so after the warmup we ran the first pull. The first pull showed the A/F to be a little rich, so we jetted down from 67/69 jets to 65/66 jets in the 660s, and ran again. The A/F improved to around 12.5:1, but the two pulls were pretty close despite the change. Heres a plot of the HP and torque numbers from this intake:
Peak HP from this intake was only around 393 HP, so it was definitely down a little from the top performing intakes. As a guess, I would attribute this to the aforementioned port exit areas, but I dont know for sure.
Next up was another tunnel ram, courtesy of RWJ. This is not a homemade unit, but instead appears to be cast specifically for the FE. Im not sure who the manufacturer of this tunnel ram is, but one forum member thought it was a Dove, so were going to call it the Dove tunnel ram. This manifold features a nice smooth radius on the runners going into the ports, so it appears to be superior to the homemade tunnel ram intake in this respect.
Joel and I got the intake installed in about an hour and a half. I didnt have linkage for this intake, but the carbs were positioned the same as the other 2X4 intakes that I had tested previously, so we were able to adapt the linkage from those intakes to work on this one. Here are a couple of pictures of this intake on the engine:
With the same 65/66 jets in the 660 carbs as for the previous test, we warmed up the engine and made a couple of pulls. This tunnel ram was very impressive, hitting the 410 HP peak seen with the other top intakes, and also providing excellent torque all across the curve. Here is the HP/Torque plot:
Next up was the Blue Thunder version of the Medium Riser 2X4 intake. This was a brand new intake I had purchased for these tests, and removing it from the plastic I was struck again by what a beautiful casting it was. All the Blue Thunder stuff that Ive had has been just top notch in this regard. Joel and I had it installed on the engine by late afternoon. The carb linkage was no trick, because the carb positions were identical to the factory low riser and medium riser intakes, so I had the linkage set up already. Prior to installing the carbs, we jetted back to the same 63 jets that we had used on the factory MR intake. I expected this intake to behave nearly the same as the factory unit.
By this time Joel had to leave, and Shoe had arrived, so Shoe and I finished up getting the engine ready to run. Here is a photo of this intake on the engine:
After warmup, we made two pulls on the engine which gave nearly identical results. Here is a HP and torque plot for one of the pulls:
A/F was right on at about 12.6:1 with this intake and the 63 jets. For some reason, this intake was down a very small amount on HP from the factory intake; it peaked at 407 HP, whereas the factory intake peaked at 410 HP. However, this kind of variation is in the noise, and for all practical purposes the results from the BT intake and the factory MR intake are the same.
Finally, I was down to testing the last multiple carb intake. This was the Edelbrock F262 2X4 manifold. I had originally planned to test this with the same Holley carbs as the other 2X4 manifolds, until Tom P rained on my parade by informing me that Holley carbs dont fit on the F262. I hadnt even tried putting carbs on the manifold until I read his post on that topic, and sure enough he was right. So, I thought I was out of luck on testing this manifold, because Ive never owned an AFB carb in my life, and the only Edelbrock carb Ive ever owned didnt work for me at all and went down the road quite a while back.
As it turned out, my Y-block pal has a selection of AFB and Edelbrock carbs, and he found a matched pair of Edelbrocks that he could lend me for testing. I dont have any of the tuning tools necessary to set these carbs up, so it was going to be a bolt on and go deal with this intake, but I figured it was better than not testing it at all. So, late Saturday night I got the intake installed and ready to run. I must say that Ive never seen so many vacuum fittings in my life as what are on those Edelbrock carbs! I must have had to plug five holes in each one. Getting the linkage to work also required quite a bit of fabrication. Further, although the throttle plates have a mechanical secondary actuation, the carbs have that vacuum operated door on the top of the secondaries, and there wasnt a good way for me to cobble up the linkage so that I was sure that the vacuum doors were opening. So, I had to rely on the vacuum opening during the dyno pulls.
Heres a picture of the F262 installed on the engine:
Sunday at noon I fired up the engine and ran the pulls with this intake setup. It actually ran pretty well, and although it was down on HP from most of the other intakes, it wasnt terrible or anything. Heres a plot of the results:
Also, A/F with this intake and carb setup was pretty good, right around 12.9:1, so I think that the results are valid for general comparison purposes.
In summary, here are two graphs showing all the multiple carb intake results, superimposed on each other. The codes shown on the graphs indicate the induction setups as follows:
TRIPOW01 = Factory 406 tripower intake, reproduction tripower carbs
660X2MR9 = Factory medium riser intake and 660 carbs, 63 jets
427X2LR1 = Factory low riser intake and 660 carbs, 63 jets
MTXRAM02 = Mickey Thompson crossram, 660 carbs, 63 jets
EDXRAM01 = Edelbrock XF66 crossram, 660 carbs, 63 jets
TWEDGE03 = Dove tunnel wedge, 660 carbs, 67/69 jets
BBTUNL01 = Home made tunnel ram intake, 660 carbs, 65/66 jets
DOVETR01 = Dove(?) tunnel ram intake, 660 carbs, 65/66 jets
BTMR01 = Blue Thunder medium riser intake, 660 carbs, 63 jets
EDF26203 = Edelbrock F262 intake, Edelbrock carbs
On Sunday Kevin, Shoe and I continued testing a few more single 4 intakes. I have two more to go, hopefully finishing up by next Friday, so next weekend I should be able to post report number 5, with the data from all the remaining single 4 intakes that were not included in reports 1 through 3. Stay tuned
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