#19---Smallblock Big Mouth Ports on the Dyno

1/10/2016


 

Small Block - Big Mouth Ports  (Tested June 2012) (updated Jan 2014)
    In this series of tests we are showcasing our CNC ported Edelbrock RPM LA heads (#60779-S3) with the large port volume intakes and the intake pushrods moved over .200”. With this modification the pushrod pinch is removed and now the narrow spot is the gasket opening. Moving the pushrod over increases the port volume 11cc to a total of 206cc. The cross section is 2.574 square inches, a Largemouth to be sure. We didn’t test the heads on the same short block but we will show the differences in two engines to give you an idea of what the Largemouth port volume does for horsepower.

                      ----------------------Comparitive Dyno Tests--------------------

Big Engine / Standard Ports
 
Small Engine / Largemouth Ports
4.080”
Bore
4.030”
4.00”
Stroke
4.00”
418 cubic inches
Final Displacement
408 cubic inches
14.4:1
Compression Ratio
11.5:1
Standard195cc intake port volume with standard pushrod location
Our standard Stage 3 CNC port
Edelbrock RPM LA Fully CNC ported
2.08” intake & 1.60” exhaust valves
“Big Mouth” 206cc intake port volume with pushrod moved over .200”   *
HTL6872AS-6 *
“real” Chrysler flat tappet cams
HTL6468AS-6
1.6: ratio standard offset
“real” Chrysler rocker arms
1.6:1 with intakes offset .200”
*
Edelbrock Super Victor w/ competition porting work
Intake Manifolds
See Below
AED 1000 (Custom built)
Carburetor
850 Holley (stock)
114 octane race gas
Fuel
92 Octane pump gas
602 HP
Average maximum horsepower after 3 runs
631 HP w/ Victor Single plane manifold
583 HP w/ RPM Dual Plane manifold

566 lb/ft
Average maximum torques after 3 runs
561 lb/ft w/ Victor Single Plane manifold
567 lb/ft w/ RPM Dual Plane manifold

                                                                              

  Small Block Engines
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 RPM
418 Engine with Stage 3 CNC Edelbrock Heads
195cc port
 
    340 Victor Single Plane Manifold with Competition porting
 
Performer RPM Dual Plane manifold with
Competition porting

Performer RPM Dual Plane

Vs
340 Victor Single Plane
          Torque HP   Torque HP   Torque HP Torque HP
3000
 
 
 
442.3
252.7
 
459.0
262.2
Performer Advantage
+17 +12
3100
 
 
 
441.0
260.3
 
464.5
274.1
+23
+14
3200
403.8
246.0
 
446.4
272.0
 
469.8
286.3
+23
+14
3300
401.9
252.5
 
446.5
280.6
 
477.3
299.9
+31
+19
3400
401.8
260.1
 
441.4
285.7
 
474.8
307.4
+33
+22
3500
398.9
265.8
 
436.8
291.1
 
471.8
314.4
+35
+23
3600
401.3
275.1
 
436.4
299.1
 
475.0
325.6
+39
+56
3700
405.7
285.8
 
440.5
310.1
 
482.5
339.9
+42
+29
3800
421.7
305.1
 
442.5
320.5
 
494.2
357.5
+52
+37
3900
423.2
314.2
 
449.4
333.7
 
514.7
382.2
+65
+49
4000
434.4
330.8
 
453.1
345.1
 
534.7
407.3
+81
+62
4100
456.8
356.6
 
468.5
365.7
 
546.9
426.9
+78 +61
4200
470.0
375.8
 
494.3
395.3
 
554.9
443.8
+60
+48
4300
534.3
437.5
 
525.4
430.1
 
557.6
456.5
+32
+35
4400
532.8
446.4
 
536.0
49.1
 
563.5
472.1
+27
+23
4500
547.0
468.7
 
546.7
468.4
 
560.9
480.6
+13
+12
4600
547.0
479.1
 
547.4
479.4
 
567.4
497.0
+20
+18
4700
547.5
489.9
 
551.1
493.2
 
561.2
502.2
+10
+9
4800
559.7
511.5
 
561.2
512.9
 
558.2
510.2

Victor Advantage

+3

+2

4900
566.7
528.7
 
555.0
517.8
 
551.6
514.6
+4
+3
5000
564.7
537.6
 
557.7
531.0
 
550.1
523.7
+7
+8
5100
565.6
549.2
 
547.7
545.4
 
553.3
537.3
+6
+8
5200
563.9
558.3
 
545.2
551.5
 
551.4
545.9
+6
+6
5300
555.8
560.9
 
541.2
552.7
 
541.0
546.0
0
+6
5400
552.9
568.5
 
538.3
560.6
 
536.0
551.1
+2
+9
5500
539.9
565.4
 
536.9
566.8
 
533.6
558.8
+3
+8
5600
526.7
561.6
 
530.3
574.0
 
523.2
557.9
+7
+16
5700
525.8
570.7
 
516.9
582.7
 
516.1
560.2
0
+22
5800
523.3
577.9
 
522.3
585.7
 
518.9
573.0
+4
+12
5900
513.3
576.6
 
517.8
580.6
 
509.6
572.5
+8
+8
6000
509.4
582.0
 
516.5
596.7
 
510.3
583.0
+6
+13
6100
504.0
585.4
 
520.4
601.4
 
495.9
576.0
+25
+25
6200
498.6
588.6
 
512.2
609.7
 
486.2
573.9
+26
+36
6300
498.6
598.1
 
506.8
624.2
 
 
 
   
6400
494.2
602.2
 
494.9
624.2
 
 
 
   
6500
481.3
595.7
 
488.3
627.2
 
 
 
   
6600
 
 
 
487.5
621.9
 
 
 
   
6700
 
 
 
479.4
623.0
 
 
 
   
6800
 
 
 
442.3
631.2
 
 
 
   
6900
 
 
 
441.0
629.8
 
 
 
   

 
As you can see, the big engine with the standard 195cc ports had all the advantages except for port volume:
  •     418-vs-408 cubic inches
  •     14.4:1-vs-11.5:1 compression (Race gas-vs-pump gas)
  •     Larger cam (* During testing 2 larger cams were tried on the big engine with no power improvement)
  •     Super Victor competition ported intake-vs-340 Victor competition ported intake
  •     1000cfm custom carb-vs-box stock 850 Holley carb
         But, it still had less power than the smaller 408 cubic inch engine with the Largemouth Edelbrock heads and much milder parts….29HP less! If we had installed these Largemouth heads on the bigger engine it should have made well over 675hp.
 
Single plane intake -vs- Dual plane intake
  The charts below shows the torque and horsepower advantages between the two intakes used in the dyno test shown above. What is plain to see is that up to 4800rpm the dual plane intake is much stronger and from 4800 up to 6000 it is pretty much a trade-off. In other words, if you don't stay above 6000 rpm the dual plane is the best way to go. Obviously the horsepower and torque numbers are not going to be as high on a milder engine build but the performance differences will remain relative.
 
                                                Click on either chart to enlarge.
 
                              Horsepower                                                Torque                                                    
 
 

   
Special Test:
We tried a competition ported Edelbrock RPM dual plane intake with the same 850cfm carb. Obviously it cannot flow the air of either of the single planes, but it represented itself very well with 583hp and 576 lb/ft of torque. But look at the lower RPM torque versus the single plane intakes. The small engine made more torque with the RPM intake rthan the big engine. Especially at the low end, 67 lb.ft more.


             Chart shows torque increase with RPM Dual Plane Intake Over a Single Plane Intake                                      

RPM
Big Engine
Small Engine
3300
+76 lb/ft
+31 lb/ft
4000
+100 lb/ft
+81 lb/ft
4400
+31 lb/ft
+37 lb/ft



To view the flow chart for this head click the button below.
 
                             
     What these test show is the need for more port volume on these larger cubic inch engines enabling them to make maximum power. What we did was plug the original pushrod holes and move the pushrod over .200” and then use .200” offset rocker arms. The port opening was CNC’d to the Largemouth configuration. This operation can be performed on any existing small block Edelbrock RPM cylinder head. But now we move the pushrod over .350" for a "BIG MOUTH" port with more port volume and air flow. To complete the conversion you will need is our 4 LH and 4 RH intake rocker arms and slightly longer 3/8" pushrods. Give us a call!
Jan 2013 update: We are now moving the pushrods over .350" on LA heads and .420" on the Magnum heads. We have 1.6 ratio rockers for both applications and the big port heads are both called "Big Mouth". And, we can retro-fit your existing heads to Big Mouth. Check out our listings in the appropriate sections of our website.
 *
The "Big Mouth" ports both LA & magnum are now 225cc.



                                                                                                    Offset Rocker
                      

                                 Standard Ports                                              BigMouth Ports

 
 

 

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