Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaft - NCRS Discussion Boards

Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaft

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  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15645

    Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaft

    Development of the Special 300 HP configuation was chronicled in a 2010 Corvette Restorer article that is posted on the Corvette Forum as a pdf attached to the following thread:

    https://www.corvetteforum.com/forums...camshafts.html

    I recommend you read it to understand the full story of the objectives and development of this configuration including other dyno tests. A primary objective was to increase top end power and revs of the 327/300 HP engine without affecting the strong low end torque and butter smooth 450-500 RPM idle in Neutral with a manual transmission and Drive with an automatic and without affecting visual appearance. The engine must also pass a NCRS Performance Verification test, which one did. The primary modifications are traditional "head massaging" to improve port flow, different valve timing to optimize performance with the new port flow characteristics, and optimizing the spark advance map for maximum detonation-free torque bandwidth.

    This partcular L-75 is from a '64 Convertible that has been in the owner's family since 1984. The block is bored .030" and fitted with Federal Mogul L2166NF-30 forged pistons (SHP/FI type, 5.3 cc dome), and the compression ratio was limited to 10.2:1 with .041" thick composition head gaskets. The weak, first design 327 connecting rods were replaced with Eagle SIR5700 pressed pin rods that yield a reliable 7000 rev bottom end, and the original 3721SB AFB was rebuilt without modification to the OE rods and jets.

    Typical Flint-machined 327 heads flow about 200/135 CFM at 28" H2O depression, 0.5" valve lift, yielding an E/I flow ratio of about 0.68. Typical "head massaging" techniques increase flow to the 220s/170s CFM range. These heads comfortablely met objectives with the following test results, CFM at 28" H2O depression.

    Lift......... I flow........E flow.... E/I flow ratio
    0.3"............185...........147.............0.7 9
    0.4..............215...........173.............0.8 0
    0.45............225...........179.............0.80

    Note that with the actual true maximum rocker ratio of 1.44:1, maximum valve lift of OE cams is in the range of less than 0.400" to slighty less than 0.450".

    Head massaging increases exhaust flow a greater percentage than inlet flow yielding a higher E/I flow ratio, and this value is important in establishing optimum valve timing. Typical OE and aftermarket camshafts have equal or greater exhaust duration due to the restictive exhaust port. Equal duration is best if the E/I ratio is near 0.75 and greater exhaust duraton than inlet if less than 0.75. E/I ratios greater than 0.75 will respond well to less exhaust than inlet duration with a late opening exhaust valve that lets cylinder pressure work on the piston longer. Like modern small block engines, the modest duration inlet event is retarded relative to traditional designs. In fact, other than less lift due to the flat tappets the McCagh Special camshaft inlet event has nearly the identical .050" lifter rise timing points as the LS3 camshaft!

    The final WOT spark advance curve is as follows using the black springs from the Mr. Gasket 928G spring set, and a 15" B22 VAC is intalled in the original single point distributor along with a 28-32 oz. point set.

    Revs....Total WOT advance
    500............12
    1500..........28
    2500..........35
    3000..........36 (maximum)

    Attempts to increase total WOT advance further into the optimum range of 36-40 resulted in some low speed roughness. This is because the '64 distributor only offers 24 degrees centrifugal advance. For '66-67 total centrifugal advance was increased to 30 which allows less initial and low speed advance, and the '67 engine tested in the "Tale of Two Camshafts" article showed one percent better power across the range at 39 versus 36 degrees total WOT advance. The owner has 93 PON fuel commonly available, and the engine never detonated either in road testing or on the dyno.

    Another significant difference between the early C2 327/300s ('63-'65) versus late ('66-'67) is the air cleaner. The later vesions' open element 14 x 3" filter offers virtually zero restriction. In fact the '67 tested actually showed a one percent decrease in power across the rev range when the air cleaner was completely removed. Those two silenceing snorkels on the early air cleaner sure look restrictive, and the dyno would quanify it.

    The test plan called for two pulls with the air cleaner installed and if within about one percent established a baseline. Then at least one pull with the air cleaner lid removed. All pulls were planned to be 1000 to 6000 RPM (and we almost made it). Though the installed 215/70R-15 97W (168 MPH) Pirelli P6000s are about ten years old, they have spent virtually their entire life inside, look near new, and I was confident they would easily tolerate the near 140 MPH speed at 6000 with the 3.36:1 axle.

    The Dynojet model 224C chassis dyno is a new model that replaces the 248C. The shop proprieter said the roller is smaller than the 248C, but the results are very comparable. The shop had a good external cooling fan setup, which gave confidence that the fan clutch would not tighten, which can cost considerable torque and power.

    For reference, a typical Flint-built late 327/300 will make low to mid 190s SAE corrected RWHP at about 4500 and is all done at 5000. SHP/FI engines are in the range of 220-240 at higher revs. The test showed that the early air cleaner reduced peak torque by 3.2 percent and peak power by 6.1 percent compared to the run with the lid removed. The higher the air flow (RPM) the greater the loss. The owner is working on a simple and inexpensive solution to capture this lost power, and both the problem and solution are discussed in the following threads:

    https://www.corvetteforum.com/forums...00-hp-327s.htm

    https://www.corvetteforum.com/forums...p-engines.html

    Perhaps more impressive than the L-79-like top end power with a smooth (500@ 18") idle is the prodigious low end torque, maybe even more than Flint-built. The objective was 90 percent of peak at 2000, and the test shows no later than 1200 and maybe even as low as 1000. Next time the pulls need to start at 700. The owner says this low end torque/power is even more useful and impressive than the additional top end power relative to his recollection of the original engine's characteristics.

    A graph of the SAE corrected RWHP and torque (with and without the air cleaner lid installed) is attached, and a summarly follows. Without the air cleaner lid the pull is virtually identical to the '67 engine in the referenced article, at least within the narrow 3000-5000 RPM range that the '67 engine was tested. Getting off idle to redline pulls is tough for no logical reason.

    90 percent torque bandwidth: <1200 to 4400, peak torque 281 lb-ft @ 3250
    80 percent torque bandwidth <1000 to 5100
    90 percent power bandwidth 3750 to 5800 (est.), peak power 217 HP @ 5100

    Given the generally accepted driveline/tire efficiency of 0.85 for rear drive, manual transmissions with a direct drive gear, SAE net at the flywheel is 331 lb-ft and 255 HP. From my library of small block lab and chassis dyno tests my empirically derived net/gross factor is 0.89, which yields SAE gross estimates of 371 lb-ft and 287 HP. The advertised SAE gross ratings are 360 lb-ft @ 3200 and 300 HP @ 5000.

    The best feature of this configuartion is the very broad torque and power bandwidths. It doesn't need a close ratio transmission. Wider ratios with a top gear that yields about 1500 at 60 would work just fine.

    The glitch in the no air cleaner lid run is likely the secondary air valve opening of the AFB. The dyno system picks it up because it samples data at a very high frequency, but it happens too fast for the driver to feel. I've seen this with many other carbs. I don't know why the second baseline run does not show the same anomaly.

    As a final note the old AFB showed a quite consistent WOT A/F ratio in the proper range - a bit rich down low, which is typical, finishing sufficiently rich to be below my 13.5:1 maximum requirement at peak revs. Note that removing the air filter lid leaned out the mixture about the same percentage as the increase in power due to the similar percentage increase in inlet air density, and that matches what physics tells us. Carburetors meter fuel based on air volume flow, not mass flow. That's why they run rich at high altitude if set up for low altitude.

    Duke
    Attached Files
    Last edited by Duke W.; April 9, 2022, 11:51 PM.
  • Mark L.
    Very Frequent User
    • July 31, 1989
    • 560

    #2
    Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

    Duke, The timing for this thread couldn't be better. I'm in the early stages of a complete restoration of a 67 300 hp. I do plan to have mild head porting done as well as running it in on a dyno. Is the McCagh cam now the preferred profile? If you have any preferred parameters to test out on the dyno let me know. Maybe we can incorporate it into the plan. Thanks

    Comment

    • Duke W.
      Beyond Control Poster
      • January 1, 1993
      • 15645

      #3
      Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

      If you do the pocket porting, port matching and chamber relieving to achieve similar flow numbers, you should see similar results. The McCagh Special cams were ground by Crane, but they were bought out by Comp Cams, and I don't know what happened to their lobe masters.

      The McCagh Special uses the same lobes at the 3896929 cam that was original to your '67 327/300. The lobes are swapped and the inlet event is retarded several degrees with the same LSA. What you need to do is find a cam grinder that has these lobe masters and then grind to the following spec.

      Inlet .050" lifter rise duration: 202 degrees, point of maximum lift 116 deg. ATC

      Exhaust .050" lifter rise duration: 194 degrees, Point of maximum lift 108 degrees BTC

      The above POMLs yield a LSA of 112 degrees

      Inlet lobe gross lift: 0.2733"

      Exhaust lobe gross lift: 0.2600"

      There are some other issues I need to discuss with you, but since I hate email, give me a call. There's no message machine, but I'm around most of the time, especially late afternoon early evening, Pacific time.

      310
      372
      5527

      Duke

      Comment

      • Mark L.
        Very Frequent User
        • July 31, 1989
        • 560

        #4
        Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

        Duke, I sent you an email regarding this topic. Not sure if you've seen it.
        Or, if you can give me a call 6-8pm EDT sometime that would work. 508-7257305. Thanks
        Mark

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15645

          #5
          Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

          I responded yesterday and my end shows it was sent. I asked you to call me because I have a lousy long distance plan. Late afternoon or evening PDT is best for me. Messages are not accepted. I'm usually around, but can't always get to the phone fast, so let if ring at least 7 or 8 times.

          It appears that Elgin and Howard's Cams can grind the '67-up 300 HP cam, which means they should be able to grind the McCagh Special since is used the same lobes, just swapped with the same LSA and the IPOML retarded to 116 ATDC.

          310
          372
          5527

          Duke

          Comment

          • Mark E.
            Extremely Frequent Poster
            • April 1, 1993
            • 4505

            #6
            Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

            Two questions after re-reading this today:

            - Why are engines designed with E/I flow < 1? Related: Why are intake valves larger than exhaust valves? Seems like ideally in vs. out flow capacity should be equal, or even E/I > 1 since gases expand after combustion.

            - Why are dyno pulls in top gear? Seems like engine output can be measured in first gear more safely and with less drivetrain wear.

            Beginner questions I know, but curious.
            Mark Edmondson
            Dallas, Texas
            Texas Chapter

            1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
            1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15645

              #7
              Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

              Under high load conditions the cylinders have 50-100 psi residual pressure when the exhaust valve starts to open and that quickly blows down to exhaust system pressure by the time the piston gets to BDC. This blowdown wave is the "bark" you hear from unmuffled engines.

              Meanwhile at most you have something less than atmospheric pressure to fill the cylinder with fresh charge unless the engine is boosted.

              Many years of empirical evidence going back to the early days of the IC engine show that exhaust flow equal to about 75 percent of inlet flow is "ideal", and it calls for equal cam duration on both sides. Actually it can be less or even more. The original 265 heads had an E/I flow ratio of about 0.75, but with the big port 461X and most later SB heads showed up it dropped to 0.65 and Chevrolet eventually discovered that a longer duration exhaust cam with the extra duration at the front end to open the valve earlier was best for broadest torque bandwidth. The modern LS and LT engines are similar in this regard.

              It turns out that traditional "head massaging" increases big port SB head E/I flow ratio to about 0.80, which means exhaust cam duration can be LESS than inlet duration by opening the exhaust valve later. This allows gas pressure to work on the pistons longer, which is why the Special 300 HP configuration makes off idle torque like an old two-stroke Jimmy diesel without excessive top end pumping loss, and letting the late phased inlet event make L-79 top end power while maintaining the OE 300 HP engine's butter smooth low rev idle behavior due to the very low overlap.

              There is more info on this subject in the "Tale of Two Camshafts article" (link in post #1). You should read it.

              Conventional front engine rear drive vehicles with direct drive transmissions are usually dyno tested in that direct drive gear. This is because in direct drive the transmission efficiency is 98-99 percent, but 95-96 percent going through the counter shaft in an indirect gear, so the direct drive gear will usually make the best power.

              Of course tire speed ratings should be considered. A "327 LT-1" (massaged heads, high strength conn. rods, LT-1 cam) configuration revved to its maximum useable revs of 7200 with a 3.08 axle will be spinning OE revs/mile tires at nearly 185 MPH! It's usually okay to slightly exceed a tire's max speed rating, briefly, if it is in good condition and no more than half worn, but if not, a lower gear should be used.

              In this case what I do is a couple of direct drive gear runs to the tire speed rating or a little above. Then make runs in third gear to maximum RPM assuming that's reasonable for the tire speed rating. Then the percent difference can be computed over the rev range where the curves are concurrent and the higher rev range that was run in third gear can be factored up with this difference to estimate what it would be in direct drive.

              Since tire rolling resistance is a significant part of drive train loss, the higher the tire pressure the lower the loss, so I usually recommend setting cold tire pressure at the maximum placarded on the sidewall for chassis dyno pulls.

              Duke
              Last edited by Duke W.; September 21, 2022, 07:04 PM.

              Comment

              • Mark E.
                Extremely Frequent Poster
                • April 1, 1993
                • 4505

                #8
                Re: Chassis dyno test results - Special 300 HP configuration w/McCagh Special camshaf

                Thanks Duke.
                Mark Edmondson
                Dallas, Texas
                Texas Chapter

                1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                Comment

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