Help me analyze my cam vs. Horsepower vs. RPM range

Discussion in 'Street/strip 400/430/455' started by rkammer, Jun 27, 2020.

  1. rkammer

    rkammer '71 GS455 Arctic White

    I'm pretty happy with the max HP from my stock manifold 464 build. (see below dyno run). But, I didn't expect max HP at only 4800 when we designed the cam. (see cam card below). So, I'd like some advice on whether I should try to retard the current cam to raise the RPM range or just go for another cam. This cam has a very mild idle. My engine build is below my signature and basically it's a 10.5 motor with TA Stage 1 heads with additional porting, stock valve train, stock exhaust manifolds, Performer intake with a QJ. I've got plenty of room for more valve lift (pic of pistons below) if I need it. Again, I'm pretty happy with HP but would like peak RPM to be in the 5200-5500 range. Low end torque is currently outstanding and then some.

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  2. johnriv67

    johnriv67 Well-Known Member

    Looks like you might be running into valve control issues, as at 5100 rpm both torque and horsepower fall off considerably.
     
  3. johnriv67

    johnriv67 Well-Known Member

  4. BQUICK

    BQUICK Well-Known Member

    Should spin to 5500 and still make power.
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    I think something else is wrong as well. My cam has 2 degrees more intake duration and 1 degree more exhaust. My LSA is narrower at 112 degrees and it is a roller, but still. Your cam should make power all the way to at least 5500. Your Dynamic Compression ratio is 8.10. That is great.

    470CamCard.jpg
     
    Last edited: Jun 27, 2020
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    My engine went to 6000 RPM. Made peak power at 5900.

    Motor2FinalPull.jpg
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

  8. BrunoD

    BrunoD Looking for Fast Eddie

    Most likely the culprit here are the springs.Put a spring a notch above the ones you have in and see.Just my opinion.Bruno.
     
    chrisg likes this.
  9. rkammer

    rkammer '71 GS455 Arctic White

    Any chance the cam was installed 4 degrees advanced instead of straight up? It was ground at +4 deg.
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    When the cam was installed, if it was degreed in correctly, it was installed with an intake center line (ICL) of 111*. That would make it 4* advanced like just about any cam card you'll see recommends. If it was straight up, it would have been installed at 115* ICL.
     
  11. rkammer

    rkammer '71 GS455 Arctic White

    Just checked my original calculations using the online calculator. It was 7.96. You got it pretty close. :)
     
  12. 87GN_70GS

    87GN_70GS Well-Known Member

    With only 48 degrees on the intake from advertised (276) to 0.050" (228), that's pretty fast valve action. I suspect either not enough adv intake duration or valve train stability issues. What valve springs? What are the spring open and closed #s?
     
  13. rkammer

    rkammer '71 GS455 Arctic White

    The builder's notes say closed pressure = 1.860 @115 lbs. open 1.260 = 310 lbs and coil bind = 1.100
    Lift on the cam is just under .500
    Not sure which brand of springs he used (Wildcat Performance in 2015)
     
  14. johnriv67

    johnriv67 Well-Known Member

    That cam just must suck. The ramp rates are SO aggressive
     
  15. No Lift

    No Lift Platinum Level Contributor

    OK. This is a case of not enough information when asking a question assuming this is the same cam and engine setup that you are quoted above talking about in another thread. Also, can I assume that it runs those ET's with a full 32-34* of timing? Does it pull smothly to 5500 with no noteworthy power dropoff in the seat of the pants when it runs those times or just getting on it on the street? If it was rolling off that bad according to the dyno chart you would certainly feel the power going away especially by 5500. If you are running 12.7's then think how fast it will be when you run a cam that doesn't "work"(according to tribal lore).

    If you have run those times with the car and is not falling on its' face then what you have is wasted dyno runs. From my actual experience making some chassis dyno runs you could be losing as much as 10 HP per 2* of retarded timing.(On one session I wondered what happened to the power and mid-testing I realised my timing was retarded because of a severly worn distributer gear which I corrected, plus I run a S4 system which made it even worse.) On top of that the power peak was also lowered by at least 400 rpm. The peak torque rpm changed only 100 rpm and picked up about 5 TQ per 2*. If your timing is retarded it will affect your peak power and keep getting worse as the rpm goes up because as the rpm goes up is when your advanced timing becomes more and more important. Torque isn't affected as much because it is at a lower rpm when it peaks. Your numbers may vary but I can guarantee you if you only had 25* of timing you've got at least 4-500 rpm before it peaks and a bunch more power to be had.

    From my experience on the chassi dyno I found that a fairly mild cam but very good heads like yours will get to the HP peak in a hurry and then because of the good airflow of the heads the HP will carry put longer without fdropping off much like a typical curve. It is the usual story of goods heads helping out a milder cam to make a wide torque and HP band. Your exhaust manifolds may affect how far it stretches out.

    Your cam doesn't seem to actually be a "Thumper" since it is a custom grind, just that they use the same cam P/N but a different Grind number. That being said if you do have a dropoff that you can feel about 53-5400 rpm then try using minimal preload on the lifters. Maybe only .010" or so and that will extend the rpm range somewhat. The fast ramp cams have problems when there a greater than .500" lift with more duration. I think you are in the range where you should be ok as long as the preload isn't excessive. No more that .030" preload. Been there and done that and I think that problem is overblown once you realise what is going on. If you are actually having "rev" problems consider running Comp Pro Magnum lifters on any flat tappet hydraulic cam because you can set them at just about zero preload and they act close to sold lifters. Rev problem all but fixed.

    Also you can't compare what a hydraulic roller does compared to a flat tappet hydraulic as far as rpm range, power peak or peak power. The 413 example Larry mentions falls along the line with what I did with a cam that was 242/248 in both a flat and roller that I actually ran in my car and on a chassis dyno. It was a true apples to apples test. Lifts were also very similar because I ran 1.65 on the flat and 1.60 on the roller. Not only did the roller pick up 38 TQ/32 HP it also increased the power peak from 5400 to 5900.

    In the OP's case I would expect that cam to peak out around 53-5400 but still have a very flat curve for a few hundred rpm past that. If it was me I'd venture out to chassis dyno for a couple of pulls just to verify. If you are not having a drop off in how it pulls then go with that preload setup. Otherwise reset the preload to minimal. Also one thing I like to do before the dyno shop is to swap out my thermal clutch fan to a non-thermal steup. This will keep the testing a little more accurate because the non-thermal clutch is a know quantity on all tests. The engine might run a bit hotter but if you have a thermal clutch fan on there as the engine gets hotter it will start to tighten up and could cost a variable 20-30 HP compared to a constant 10 HP drain of the non-thermal. That is also why I run the non-thermal at the track if I don't have much cool down time, no strange ET changes.

    If the first paragraph questions are YES then mystery problem solved.
     
  16. rkammer

    rkammer '71 GS455 Arctic White

    Thanks, Mike. I appreciate all your insights. Actually my times were 12.9 not 12.7 (fine point) at 107. Total timing was 34 deg. all in by about 2800. And, it was not falling off above 5000 at least seat of the pants wise.

    Now I have to throw something into the works that I mentioned several years ago when I first got the motor back but failed to mention with this thread. When the engine was dyno'd 5 years ago by the builder, he set total timing at 34 deg. BUT didn't plug the vacuum advance at the carb. Claimed most of the engines he built didn't have any vacuum advance. So, the 10 degree vacuum advance was included in the total of 34. So under power the dyno run were with only 24 degrees of total timing. When I got the motor into the car and went to power time it, I realized the problem and power timed it with 34 deg. with vacuum adv. plugged.

    So, I should have included this info in my original post. Does the lack of that extra 10 degrees of timing help to explain the low HP peak on the dyno? I expect that the 468 HP is actually more than that. How much? Who knows.
     
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    There is your problem right there. It amazes me that the builder would make a mistake like that. What a waste of a dyno session.
     
    Last edited: Jun 30, 2020
  18. johnriv67

    johnriv67 Well-Known Member

    Unless the engine builder was using ported vacuum, using vacuum advance or not wouldn’t have mattered. Mechanical advance is separate from vacuum advance.

    Edit: I reread that, Larry is right. There’s the issue.
     
  19. No Lift

    No Lift Platinum Level Contributor

    Doesn't matter how the engine only had 24* of timing just that it didn't have around 34* like you now have it. I'd take it to a chassis dyno and extrapolate how much HP 10* less timing costs you. For less than $100 they usually let you get in 3 runs as long as they aren't tuning the car. Make sure the car is cool going in with the timing at 24*. Make a run to 5500. Reset timing to 32* and make a pass to 5500. I'm sure there will be a big jump. Make a third pass to 5500 just to have some fun. Doesn't matter what it actually puts out. What ever the difference is at the wheels between run 1 and 2 you can pretty much add to all the test points of your original engine dyno test and get an idea of what it can do at the flywheel. Not exact but ballpark. Also this will tell you where you engine is really making peak power at.

    I hope the engine guy gave you a discount for the dyno run because it was his screwup.
     
  20. rkammer

    rkammer '71 GS455 Arctic White

    True but, when he set max timing without a load on the engine the 10 deg. vacuum advance would still be in as it was connected to full time vacuum. Larry's response considered that as you've probably realized.
     

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