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

1/10/2018


 

Small Block - Big Mouth Ports  (Tested June 2012) (updated Jan 2014)
    This tech article is to show the power gains with out BigMouth intake ports over our standard full CNC Stage 3 ports. The tests show how much power difference the large ports make even with a less agressive engine build-up. 

These 3 dyno tests show two different things. 

Test 1: The difference the larger port volume of the BigMouth ports makes over a more agressively built engine

Test 2: The power and torque differences between a single plane and dual plane intake on the same engine.
                     

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

Big Engine "Engine A"

Small Engine "Engine B"

 

 

Big Engine /Standard Ports

Small Engine/Bigmouth Ports

 

 

4.080" Bore

4.030" Bore

4.00" Stroke

4.00" Stroke

418 Cubic Inches

408 Cubic Inches

14.4:1 Compression Ratio

11.5:1 Compression Ratio

Standard 195cc intake port volume with standard pushrod location Our Standard Stage 3 CNC port

"BigMouth" 206cc intake port volume with pushrod moved over .200" *

Camshaft: HTL6872AS-6

Camshaft: HTL 6468AS-6

1.6: ratio offset rockers

1.6:1 ratio offset rockers

Edelbrock Super Victor w/ competition porting work

Edelbrock Super Victor w/ competition porting work

AED 1000 (Custom built) Carburetor

850 Holley (stock) Carburetor

"BigMouth" Small Engine Advantage

114 Octane Race Gas

92 Octane Pump Gas

RPM

Torque

HP

 

Torque

HP

 

Torque

HP

3000

 

 

 

442.3

252.7

 

 

 

3100

 

 

 

441.0

260.3

 

 

 

3200

403.8

246.0

 

446.4

272.0

 

+43

+26

3300

401.9

252.5

 

446.5

280.6

 

+45

+28

3400

401.8

260.1

 

441.4

285.7

 

+40

+25

3500

398.9

265.8

 

436.8

291.1

 

+47

+26

3600

401.3

275.1

 

436.4

299.1

 

+35

+24

3700

405.7

285.8

 

440.5

310.1

 

+35

+25

3800

421.7

305.1

 

442.5

320.5

 

+21

+15

3900

423.2

314.2

 

449.4

333.7

 

+26

+19

4000

434.4

330.8

 

453.1

345.1

 

+19

+15

4100

456.8

356.6

 

468.5

365.7

 

+12

+9

4200

470.0

375.8

 

494.3

395.3

 

+24

+20

4300

534.3

437.5

 

525.4

430.1

 

-9

-7

4400

532.8

446.4

 

536.0

449.1

 

+4

+3

4500

547.0

468.7

 

546.7

468.4

 

0

0

4600

547.0

479.1

 

547.4

479.4

 

0

0

4700

547.5

489.9

 

551.1

493.2

 

+4

+4

4800

559.7

511.5

 

561.2

512.9

 

+2

+1

4900

566.7

528.7

 

555.0

517.8

 

-11

-9

5000

564.7

537.6

 

557.7

531.0

 

-7

-6

5100

565.6

549.2

 

547.7

545.4

 

-18

-4

5200

563.9

558.3

 

545.2

551.5

 

-18

-7

5300

555.8

560.9

 

541.2

552.7

 

-14

-8

5400

552.9

568.5

 

538.3

560.6

 

-14

-8

5500

539.9

565.4

 

536.9

566.8

 

-3

+1

5600

526.7

561.6

 

530.3

574.0

 

+4

+13

5700

525.8

570.7

 

516.9

582.7

 

-9

+12

5800

523.3

577.9

 

522.3

585.7

 

-1

+8

5900

513.3

576.6

 

517.8

580.6

 

+4

+4

6000

509.4

582.0

 

516.5

596.7

 

+7

+14

6100

504.0

585.4

 

520.4

601.4

 

+16

+16

6200

498.6

588.6

 

512.2

609.7

 

+20

+21

6300

496.6

598.1

 

506.8

624.2

 

+8

+26

6400

494.2

602.2

 

494.9

624.2

 

0

+22

6500

481.3

595.7

 

488.3

627.2

 

+7

+32

6600

 

 

 

497.5

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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