With help from Shoe, I finished my FE intake comparo late this afternoon. If you dont want to read all
the details, skip to the end of the post to find the surprising winner. To me, the path traveled is
always interesting, so Ill begin at the beginning.
My brother drove down to my place near Minneapolis from Fargo, ND on Friday afternoon to dyno test and
tune his 428. Near as we can recall, this engine started its life in a 66 T-bird. Rebuilding this
engine for installation in his 68 Cougar has been a 10+ year project for my brother, and he is not
an experienced engine builder, but Ive been coaching him along the way, and it sounded like he pretty
much had everything right with the motor, so we scheduled the tests to get the engine checked out.
He had selected many of the parts for this engine many years back, and one of the parts that he selected
(on my advice) was a PI intake. At the time, I was under the impression that the PI intake was
essentially an aluminum copy of the CJ intake. Over the last few years Ive learned thats not true,
and that there are probably better intakes out there. But we had no definitive answer on which was
best. One of my reasons for acquiring my dyno in the first place was to be able to run comparison
tests on various FE parts, and this appeared to be a good opportunity to do just that. So, given
the basic parameters of my brothers engine, I selected six intakes that I felt would be suitable
for his motor. The contenders are shown in the photo below:
From left to right on the bottom, the 428 PI (casting number C7AE 9425 F), the factory cast iron 428CJ
(casting number C8OE 9425 C), and the Edelbrock Performer RPM. From left to right on the top row, the
Blue Thunder 428CJ, the Edelbrock F427, and the Edelbrock Streetmaster 390.
Details on my brothers engine regarding the heads, cam specs, etc., are given in the following post
I had asked for guesses on which manifold would make the most HP. Based on the responses to that
previous post, including my own guess, we had the following number of forum members predicting first
place for each intake:
Blue Thunder 428CJ: 11
Edelbrock Performer RPM: 4
Factory cast iron CJ: 2
Factory 428 PI: 0
Edelbrock F427: 0
Edelbrock Streetmaster: 0
Other predictions that were less precise included a general feeling from some folks that the CJ intake
was underrated, some comments that the PI intake would be better than the CJ, and also nearly everyone
picked the Streetmaster to finish last.
By mid afternoon on Friday we had the engine set up on the dyno. First order of business was to check
out the engine for stuff like compression and leakdown. As mentioned in my interim results post yesterday,
we found one cylinder, #4, with a significant leakdown of about 40%. It was clearly leaking
through the exhaust valve. We determined to monitor this condition throughout the testing, but decided
to proceed despite the problem. Next item on the agenda was to start the engine and break in the cam.
I would have been more apprehensive about this, but the cam my brother had selected was a Crane hydraulic, purchased new at least 8 years ago. So, I didnt feel we would have any issues with substandard lifters,
since they had been manufactured prior to 1998. We filled the crankcase with Shell Rotella T and a bottle
of Crane Superlube anyway. For ease of valve adjustment, if required, and initial timing, Id had my
brother purchase a Summit timing tape for the harmonic balancer. We installed that, and then spun the
engine and watched for a timing mark. Turns out we were very far retarded, so we adjusted the distributor
until the light indicated 8 degrees BTDC while we were cranking the engine.
Satisfied that we had the timing pretty close, I turned on the dyno electronics so we could spin the engine
and watch for oil pressure. After spinning it multiple times, however, no oil pressure was showing up on
the readout. We went so far as to pull the oil pressure sender line off the oil filter adapter, and watch
for oil to come out, but we got nothing. We had filled the oil filter with oil prior to turning the engine
over, so we began to suspect a problem in the pan. We pulled the pan off, and the pickup and the pump, but everything looked normal. I stuck the oil pump driveshaft into the pump, and put the pickup in a pan of oil,
and spun the drill; sure enough, tons of oil came out of the pump. After scratching our heads about this,
we re-assembled the pump, pickup, pump drive, windage tray, and pan, and tried again. This time, spinning the engine got us instant oil pressure. I still have no explanation for this, but in any case we now had oil pressure, and were ready to start the engine.
It was now past 8:00 PM, which is my self imposed limit for running engines on the dyno in deference to my neighbors. But we really wanted to see if the engine would fire. So, we put 92 octane BP unleaded premium in the tank (used for all tests), filled the float bowls of the carb with the electric pump from the dyno, adjusted the float levels, and fired the engine. It lit right off, and ran for 15 seconds before I shut it down. It sounded real good, so I felt that we were ready for a big day on Saturday. Heres a photo of the engine on the dyno:
Saturday morning we got going at about 9:00 AM. After some preliminary testing and calibration work on the dyno itself, we fired up the engine. I got it up to 2500 RPM immediately for cam break-in. We were watching the oil pressure, and it looked really good, around 80 psi and steady. After about a minute, however, I began to notice a different problem. The exhaust temperatures were really high. They climbed steadily past 1200, 1300, and then 1400 degrees. When they hit 1500 degrees with no sign of slowing, I killed the engine. It had run for a total of about 90 seconds. The air/fuel gauge had shown that the mixture was rich if anything, on the order 10:1 or so. Why was the exhaust temp so high? We let the engine cool for a few minutes, then started it again and checked the timing. According to the marks on the tape, it was at about 35 degrees total. Sure enough, the exhaust temps climbed right past 1400 degrees again, and again I killed the engine before they went any higher.
I was wondering what the heck I was missing as I went into the dyno room and stared at the engine, and then it hit me the big vacuum nipple on the back of the carbs base plate was open! It was drawing in a whole bunch of air that wasnt getting metered through the dynos air turbine, so we werent seeing the fact that the A/F ratio was lean. Thinking Id solved the problem, I put a plug on the nipple, and we started the engine again. Again, however, the exhaust temps were high. The situation was improved, but the temps were still too high. Again I killed the engine, and went back in to look. I should have known the small front vacuum nipple on the baseplate was also open! I checked the carb a little more thoroughly this time and found no other potential leaks, so I put a plug on the small nipple and we ran again. This time, the exhaust temperatures came down to some reasonable levels, and we got up to about 15 minutes run time on the engine. But to me, the temps still looked too high. Then I glanced outside the shop at the muffler, and saw big plumes of oily smoke coming out of the muffler system. We stopped the engine again, this time at the 15 minute mark, and went into the dyno room to look again. This time we found another problem; the carb had been installed with a 4 hole phenolic spacer between the carb and the intake, but there was a gasket on only one side. My brother had assumed that the phenolic spacer would seal to the base of the carb. We pulled the carb off and installed a gasket, but this did not really explain the smoky exhaust. I decided to pull the plugs. Number 1 looked good; numbers 2 through 8 were black and oily. Ruh-roh, looked like an intake manifold gasket leak. We pulled the valve covers, and under the valve cover on number 7 cylinder we saw black sooty stains on the nice white aluminum intake. Sure enough, the manifold gasket had been leaking here, at the exhaust port crossover, so I felt it was a good bet that the manifold to head seal was no good. My brother had used good Fel-Pro intake gaskets (not Print-o-seals), so I wasnt sure what the problem was, but as soon as we started unbolting the intake, I figured it out. When the bolt tension was removed, the intake sprang away from the head, revealing a gap between the intake and the gasket. The cork manifold end seals were too thick, and were keeping the intake from fitting down properly onto the heads.
We pulled the intake completely off, scraped away the cork end seals, and reinstalled it with NAPA MS15166X intake gaskets, and RTV under the ends of the manifold. After we had it back on, we realized we had left the valley splash pan off, but we went ahead anyway, and in fact we left the valley pan out of the engine for the remainder of the tests, for the sake of consistency. Also, prior to installing the intake I cut some small 18 gauge sheetmetal pieces to block the heat risers between the manifold and the head. We also ran these heat riser blocks for all the remaining manifolds.
Finally by noon on Saturday, we had the engine back together and ready to run. We fired it up for the remaining 10 minutes of cam break-in at 2500 RPM. Sure enough, the exhaust temperatures were way down from where they had been before, and after a couple of minutes the oil burned out of the pipes and the exhaust coming out of the muffler looked good. We finished the cam break-in feeling pretty good about the way the engine was running.
Time for some dyno pulls. We timed the engine to 38 degrees total, according to the timing tape, and made our first pull. We got 325 HP at 4900 RPM. A/F looked very rich, so we decided to start jetting down to get the A/F correct. Also, the manifold vacuum at WOT was very high, around 2.5 inches, indicating that the carbs secondaries were not opening all the way. We pulled the 77 jets out of the primary side of the carb and installed 74s, and then we replaced the standard vacuum secondary diaphram spring with the light weight yellow spring, to make sure the secondaries would open. Next pull was much improved, with about 345 HP at 5000 RPM. Manifold vacuum at WOT was down to 1.0 inch, which sounded about right to me. A/F ratio was getting better, but still needed work. Over the next several pulls we continued to jet down, all the way to 67s in the primary, before we saw a decrease in HP. We then jetted back up to 70s in the primaries, where we had the best power and a reasonable A/F number of about 12:1 or so.
The remainder of the day on Saturday, and the afternoon on Sunday, was devoted to intake swapping and dyno tests. One glitch in the process came when we were running the Performer RPM, and saw the timing tape fly off the harmonic balancer. I grabbed the tape to try to use it as a reference to make some marks past 30 degrees on the balancer, so we could time the engine the same even with the tape gone. But when I held the tape up to the balancer, I discovered that the tape was for a different diameter balancer; where the tape said 38 degrees, the balancer actually showed about 33 degrees! So, we were running all the tests at 33 degrees total timing. Rather than change it after we had already run two intakes, we kept that total timing number for the remainder of the tests. There may be more power available with any of these intakes if the timing was advanced further, but for comparisons sake we left the timing as it was.
Also, several times during the testing, and again tonight after all the testing was completed, I checked the leakdown number on cylinder #4. There was essentially no change throughout the testing, and the last check showed 36% leakdown, as compared to 40% leakdown at the start. So, the engine appears consistent in this respect, and I believe the test results are valid.
So, here are the final results for peak HP production:
Edelbrock Streetmaster: 385.8
Edelbrock Performer RPM: 374.6
Blue Thunder 428CJ: 366.9
Factory Cast iron CJ: 363.0
Factor Police Interceptor: 357.1
Edelbrock F427: 353.6
The STREETMASTER!!!! Nobody would have guessed it. I can hardly believe it, but I assure you its no BS, because Shoe was there with me today when we ran it and he can verify the results. Here is a table with peak HP and torque, and average HP and torque over the 2500-5300 RPM Range:
As mentioned in my previous post, none of these intakes has been modified in any way. All are completely unported. Here is a list of the intakes and their respective port size openings as measured at the intake flange:
Streetmaster: 1.80 X 1.07
RPM: 1.95 X 1.15
BT: 2.35 X 1.35
CJ: 1.95 X 1.20
PI: 1.95 X 1.20
F427: 2.00 X 1.05
Heres a plot of HP and Torque for all six intakes:
Heres a plot of the best and worst, Streetmaster and F427, showing a 38 ft-lb spread in torque and a 32 HP spread in HP:
Heres the top 3 intakes compared with each other:
Finally, here's the top two intakes compared with each other:
I have the following comments on these results:
1. Were all a bunch of idiots. NOBODY picked the Streetmaster to win. Most of us picked it to finish LAST. As an FE guy, Im ashamed of myself. Lets all keep this quiet, so that the price of Streetmasters on ebay doesnt go up (I bought mine for $115 two weeks ago LOL!)
2. Many of the dual planes make more low end torque than the Streetmaster, but by 3200 RPM it is passing most of them up, and by 3800 RPM it is making the most torque.
3. The Performer RPM actually makes more average HP, across the range, than the Streetmaster, by 0.6 HP. However, the Streetmaster makes more average torque, by about 1.5 foot pounds. Down low, the Performer RPM makes more torque, but up high, the Streetmaster makes more power.
4. The F427 is pathetic. The only mitigating factor may be the ports are so small that they could be limiting the performance. Ill find out more about this in my next intake shootout, where Ill be port matching all the intakes to 427MR heads. But the F427 will have to pick up a LOT to catch the other intakes.
5. The Blue Thunder was disappointing, to me anyway. I figured it would come on strong at the higher engine speeds, but it really didnt. Go figure.
Heres a final little tidbit of information. We get lots of questions on the FE Forum about which of these intakes will fit on the shaker equipped Mustangs. I had never had the collection of intakes next to each other for measurement purposes, so Shoe and I took the opportunity to look at this. The factory cast iron CJ intake and the BT intake have the carb in exactly the same spot. The PI intake has the carb moved towards the rear of the intake about 1/8. The F427 intake has the carb moved to the rear about 3/8. The Performer RPM has the carb moved to the rear of the intake by about ¾. Ive got to believe that this would cause a clearance problem with the shaker.
And the Streetmaster has the carb in exactly the same position as the cast iron CJ intake and the BT intake, so Ill bet the Streetmaster would work just fine with the shaker!
Yikes, what fun this was! You guys have no idea. Stay tuned for my next intake comparo, involving a total of 20 intakes, and all port matched to MR heads, to be tested on my 428CJ with a bigger cam, better heads, and more compression, coming this summer
1968 Shelby GT 500 Convertible, all aluminum 489" 1030 HP Supercharged FE
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1969 R code Mach 1, 706 HP 511" all aluminum FE, 10.457 @ 127.47, 2005 Drag Week Winner, Naturally Aspirated Big Block