valve improvement.?

flat top 460 with dove heads. and stock valves with rv cam in motor. THEN.

. IF you put the biggest intake and exhaust valve in the head and a mild port job on the exhaust and still have the rv Cam. 12:1 compression say. would you see a big power gain? and at the same time not need to rev past 6000 rpm.. ?

racinghabbit wrote:flat top 460 with dove heads. and stock valves with rv cam in motor. THEN.

. IF you put the biggest intake and exhaust valve in the head and a mild port job on the exhaust and still have the rv Cam. 12:1 compression say.  would you see a big power gain? and at the same time not need to rev past 6000 rpm.. ?

No. You may see no gain at all, in fact may see a loss. Arbitrarily going bigger is seldom better, especially when it comes to induction.

well... I never would have guessed

racinghabbit wrote:well... I never would have guessed

What usually happens is you lose torque with not an appropriate gain in RPM so, the horsepower stays near the same.
The torque loss is usually not worth a very slight improvement which might be gained in horsepower.

racinghabbit wrote:well... I never would have guessed

In the induction system, velocity is king. Velocity is what creates VE (volumetric efficiency or "cylinder filling") and VE is what makes power. When you enlarge the induction you reduce velocity, thereby reducing potential VE. In order to maintain the right amount of velocity you have to increase airflow by either increasing rpm or cubic inches, or both. If the ports (which includes the valve diameter) are too small and the velocity is too high, then yes, increasing valve size and port area will increase power but you have to know these things before you just arbitrarily start making things bigger. We work with formulas based on engine displacement, rpm and where we want peak power, that give us cross sectional area and velocity numbers to shoot for. To do it right, there's a lot more to it than just making it bigger.

Simply installing a larger intake valve with no bowl work does little to increase air flow excepting some gains at low lift due to increased curtain area. Indiscriminate hogging out of the intake port making it larger and killing velocity WILL hurt torque.

Work with in 1.5" if the valve yields the most bang for the time spent.

One can significantly improve intake airflow in the passenger car iron heads with out increasing intake port minimum cross section:

No need to even touch the port entry.
Back cut of 27 to 30* for improved low lift flow. Significant increases at 1 2 3 and .400" lift.
Blend machining ridges in bowl and radius short turn to pick up about 25 cfm at .500" to .600" lift.
You can get another 5 to 7 cfm by tear dropping the guide boss.

Better flow with no loss in velocity = better cylinder filling = additional torque.

Same applies on the exhaust side. Back cut exhaust valve and work the bowl and remove thermactor boss to pick up 25 to 50 cfm with a small increase in minimum cross section.

To illustrate my point:

Two 9 to 1 466" combos.
Performer intake (untouched) and 750 holley
Proper ignition curve and total timing.
Tight quench
213 / 227 voodoo hydraulic cam.
2" dyno headers

360 to 375 hp with properly prepared but unported passenger car iron small chamber heads.

430 hp with budget ported 2.11" / 1.65" small chamber castings ported as described above. 271 vs. 300+ intake flow. 135 vs 180 exhaust flow. (with pipe).
Add a Jomar power cone and get another 10 HP. Torque in the 545 to 550 range.

Same combo with 2.19" / 1.75" small chamber castings with better airflow (+20 cfm) but larger cross section made less torque and no more HP. In this application the budget heads were more than adequate.

It is all about the combination of parts, appropriate cross section vs. displacement vs. rpm peak as Randy and Scott F. mentioned.

Hope this helps.



S

thanks... very helpful

The Mad Porter wrote:Simply installing a larger intake valve with no bowl work does little to increase air flow excepting some gains at low lift due to increased curtain area. Indiscriminate hogging out of the intake port making it larger and killing velocity WILL hurt torque.

Work with in 1.5" if the valve yields the most bang for the time spent.

One can significantly improve intake airflow in the passenger car iron heads with out increasing intake port minimum cross section:

No need to even touch the port entry.
Back cut of 27 to 30* for improved low lift flow. Significant increases at 1 2 3 and .400" lift.
Blend machining ridges in bowl and radius short turn to pick up about 25 cfm at .500" to .600" lift.
You can get another 5 to 7 cfm by tear dropping the guide boss.

Better flow with no loss in velocity = better cylinder filling = additional torque.

Same applies on the exhaust side. Back cut exhaust valve and work the bowl and remove thermactor boss to pick up 25 to 50 cfm with a small increase in minimum cross section.

To illustrate my point:

Two 9 to 1 466" combos.
Performer intake (untouched) and 750 holley
Proper ignition curve and total timing.
Tight quench
213 / 227 voodoo hydraulic cam.
2" dyno headers

360 to 375 hp with properly prepared but unported passenger car iron small chamber heads.

430 hp with budget ported 2.11" / 1.65" small chamber castings ported as described above. 271 vs. 300+ intake flow. 135 vs 180 exhaust flow. (with pipe).
Add a Jomar power cone and get another 10 HP. Torque in the 545 to 550 range.

Same combo with 2.19" / 1.75" small chamber castings with better airflow (+20 cfm) but larger cross section made less torque and no more HP. In this application the budget heads were more than adequate.

It is all about the combination of parts, appropriate cross section vs. displacement vs. rpm peak as Randy and Scott F. mentioned.

Hope this helps.



S

Great answer............ Been there done that. It works.