Don Terrill’s Speed-Talk

"Generally" speaking, let's take two examples in an effort to gain some knowledge about flow gain related to power gain.

Example one: a conventional SBC 23* head on a 408 CI SBC that makes about 670 horse [like a Brodix Track 1] a good head that flows 300 with careful work is improved to 310. What is the potential power gain?

Example two" a 15* SBC head on a 420 CI SBC that makes about 850 horse. This heads flows 385 and is improved to 400 flow. What is the potential power gain?

Well, it all depends. I have done this very example many times, and sometimes the results are great, but other times, the results are just so-so--My experience has been that most engine builders are way to conservative on the camshaft grind. This can be a major player in any kind of test like this.Both of your examples sound very mild, especially if you are talking about drag race engine. This probably is not what you wanted to hear.


JOE SHERMAN RACING ENGINES

I like big cams

That is what I am talkie about. What you might thing as big, is not that big at all.. I based this on the out put of the examples you gave, Not very tongs at all.


JOE SHERMAN RACING

There is no good answer. You could pick up that cfm, but make the port noisy, kill wet flow, c/d... Basically go backwards.

ParDeus wrote:There is no good answer. You could pick up that cfm, but make the port noisy, kill wet flow, c/d... Basically go backwards.

Very true, heads I do a lot of have a swirl dam that when completely removed gains 10CFM but then in the running engine it needs 3-5 degrees more spark advance to compensate, the power is never better, and the octane needs went up. I found a smaller 5CFM gain modifying the dam and the spark needs don't change so thats the way I go.

Next issue is how much is really gained with the intake manifold mounted, you can make the best port in the world by itself but once you mount the intake and flow it again it can be depressing. Market I am in the heads are flowed as if the fuel injector flows air so I learned to just sell the heads more based on real world user performance gains but it took awhile to get there.

If done right about 1 hp per CFM...your results may very!

Do you ever reach a point of saturation?

Stan

Stan Weiss wrote:Do you ever reach a point of saturation?

Stan

There is always a point of diminishing returns.

I am under the impression that the OP is just looking for an idea of what to expect.

"Generally" speaking, let's take two examples in an effort to gain some knowledge about flow gain related to power gain.

Dragsinger wrote:I like big cams

And I will not lie!

Dragsinger wrote:"Generally" speaking, let's take two examples in an effort to gain some knowledge about flow gain related to power gain.

Example one: a conventional SBC 23* head on a 408 CI SBC that makes about 670 horse [like a Brodix Track 1] a good head that flows 300 with careful work is improved to 310. What is the potential power gain?

Example two" a 15* SBC head on a 420 CI SBC that makes about 850 horse. This heads flows 385 and is improved to 400 flow. What is the potential power gain?

If the port size is increased to get the additional flow, to the point to where the velocity drops, the engine will lose power at some point.

The physical size of the intake runner is determined my several factors like displacement, and RPM. You have to maximize flow from this perameter. A sewer pipe would flow a lot of air, but make no power.

When you say "careful work" I take that to mean it won't be aimlessly hogged out. That said, I could agree with the 1hp per CFM theory.

I had a Super Stock head that I increased the flow on by 10 cfm by changing the valve job. It had over 10hp gain on the dyno. I was pretty happy with that.

Cedarmachine wrote:

Dragsinger wrote:I like big cams

And I will not lie!

You other brothers can't deny...

When a cam walks in with a itty bitty base circle, and a large lobe in your face..

Next issue is how much is really gained with the intake manifold mounted, you can make the best port in the world by itself but once you mount the intake and flow it again it can be depressing.

Nick, I'm in 100% agreement here. It's not a complete waste of time to flow heads without the intake, but pretty close to it. The intake changes everything. Some "improvements" on bare heads are actually negative when the intake is on.

Since Edelbrock, for example, sells both heads and intakes, their marketing department is missing a great opportunity to sell both as a package. If I were doing it, I'd perfect the package and show charts of how much better their head/intake pair are than their heads with competitive intake.

I had a friend recently pay large bucks to have a pair of heads perfected by one of the top guys in the business, but bolted the same old intake on them and was surprised when the car was no faster than with out-of-the box heads.

PackardV8 wrote:

Next issue is how much is really gained with the intake manifold mounted, you can make the best port in the world by itself but once you mount the intake and flow it again it can be depressing.

Nick, I'm in 100% agreement here. It's not a complete waste of time to flow heads without the intake, but pretty close to it. The intake changes everything. Some "improvements" on bare heads are actually negative when the intake is on.

Since Edelbrock, for example, sells both heads and intakes, their marketing department is missing a great opportunity to sell both as a package. If I were doing it, I'd perfect the package and show charts of how much better their head/intake pair are than their heads with competitive intake.

I had a friend recently pay large bucks to have a pair of heads perfected by one of the top guys in the business, but bolted the same old intake on them and was surprised when the car was no faster than with out-of-the box heads.

With modern day heads flowing so well I think many guys overlook what happens when the intake is bolted on.

The first heads I ever ported went from upper 280 cfm to a little over 300 but with the intake bolted on dropped back to 280, so that became the first intake I ever ported...

I always wanted to do a test with a really good out of the box head with a ported intake vs a ported head and out of the box intake vs a fully ported induction system...all I need is $$$$$.