Head flow and power differences question / discussion

[coloradohill]

I am curious how much difference does let’s say 30-40 cfm of head flow make in HP.

Example: N/A small block 416 cu. 11.5 / 1 +/- compression

With a set of heads that flow 325 +/- compared to heads that flow 293 +/-

Everything else on the engine would be the same,intake,carb(s), cam,headers,ect.

Will the different heads be noticeable driving on the street or on a dyno only?

(edit)
What I am really trying to find out is, is there such a thing as too much flow and after a certain number, does the power curve go flat ? Or, is it always best to have the highest flowing heads available?

Let me know your thoughts and if I forgot mention anything.

Thanks in advance.

 

[MOPAROFFICIAL]

If the flow increase is inside the usable lift range... you'll make more power.
Only in a situation where the port is much bigger than it needs to be for the given flow number will you see flat spots or tq losses etc.
If it's only flowing more at peak lift you're gonna see less in returns, minimal hp increases

Who are you discussing this with and what over exactly.

 

[OldmanRick]

Everything else on the engine would be the same,intake,carb(s), cam,headers,ect.

Kinda depends on what you have here. For a street car i wouldn't spend the extra coin to update to the 325's if you already have the 293's.

 

[coloradohill]

If the flow increase is inside the usable lift range... you'll make more power.
Only in a situation where the port is much bigger than it needs to be for the given flow number will you see flat spots or tq losses etc.
If it's only flowing more at peak lift you're gonna see less in returns, minimal hp increases

Who are you discussing this with and what over exactly.

The flow increase is in the same lift range. The less lift, the less of a difference. .300 lift= 2cfm diff., .400=11cfm, .500=14cfm, .600= 32cfm.
Not really discussing it with anyone in particular. Trying to decide on whether to use the heads I have ( Indy 360-1 ), or Trick Flow that I have an opportunity to purchase.

The pros of the Trick Flows is the ability to use any stock port intake setup.
The Indy heads require using a single plane Indy intake or modify the intakes I have.

Less headache with the Trick Flow if I want to change intakes.

Kinda depends on what you have here. For a street car i wouldn't spend the extra coin to update to the 325's if you already have the 293's.

I have the 325,s but for change ability, may use purchase the 293,s.

 

[273]

I am curious how much difference does let’s say 30-40 cfm of head flow make in HP.

Example: N/A small block 416 cu. 11.5 / 1 +/- compression

With a set of heads that flow 325 +/- compared to heads that flow 293 +/-

With the 2hp per cfm rule of thumb, 293 cfm = 586 hp, now it can make more than 2hp:cfm but if it making a lot over 586 hp your probably under headed.

Also depends on the gains on the flow curve, if both heads have similar 200-500 lift curves but the 325 keeps going over 500 vs 325 is better everywhere makes a difference .

Everything else on the engine would be the same,intake,carb(s), cam,headers,ect.

If everything here is getting you well under 2hp:cid eg.. 475-500 hp with the 293 cfm/586 hp head the 325 cfm might not add anything or not much, if making 550-600+hp the 325 probably add a decent amount depending on cam.

Will the different heads be noticeable driving on the street or on a dyno only?

if making well under the 325 hp 2hp:cid probably effects throttle response, but probably make the 293 cfm heads hp + with lesser cam, which makes for worse driveability large cam or heads?.

(edit)
What I am really trying to find out is, is there such a thing as too much flow and after a certain number, does the power curve go flat ? Or, is it always best to have the highest flowing heads available?

Richard Holdener has tried to find out if you can over head size and flow on the dyno, he has found bigger generally don't lose power but there's point where gains are smaller and smaller to not at all, but as for real world performance and driveability that question is still up in the air, with a 416 I think you have less chance of side effect especially if 550+hp is the goal.

Let me know your thoughts and if I forgot mention anything.

Thanks in advance.

 

[coloradohill]

Richard Holdener has tried to find out if you can over head size and flow on the dyno, he has found bigger generally don't lose power but there's point where gains are smaller and smaller to not at all, but as for real world performance and driveability that question is still up in the air, with a 416 I think you have less chance of side effect especially if 550+hp is the goal.

This is what I’m basically trying to find out. I will look his videos up.
550-600 is the goal.
Thank you

 

[coloradohill]

I found this after creating the post. It’s interesting but I wanted to get others to share their knowledge and chime in.
Cylinder Head Tech: Airflow vs Power

 

[273]

This is what I’m basically trying to find out. I will look his videos up.
550-600 is the goal.
Thank you

I generally notice that a typical serious street strip type build does 1.7 - 1.9 hp per cfm

293 = 498-557 hp
325 = 553-618 hp

 

[coloradohill]

Sounds like I should stay with the highest flowing head I have.
Thanks

 

[ch1ll]

Just a few ideas to consider from my limited porting knowledge and lack of real world experience.

Cfm is only part of the story.
Port efficiency comes into play.
Your air speeds throughout the port, as in no dead spots.
And there are more.

Your intake manifold is going to be your choking point with either of those 2 heads. You would have to flow the combination together and compare both choices.

With heads that flow in that range, I believe a tunnel ram would be your best choice.

 

[coloradohill]

Just a few ideas to consider from my limited porting knowledge and lack of real world experience.

Cfm is only part of the story.
Port efficiency comes into play.
Your air speeds throughout the port, as in no dead spots.
And there are more.

Your intake manifold is going to be your choking point with either of those 2 heads. You would have to flow the combination together and compare both choices.

With heads that flow in that range, I believe a tunnel ram would be your best choice.

I have read and talked to others a little about airspeed and intake flow as well.

I appreciate your input, my current choice for intakes is what is making me second guess which heads to go with.
I have the Indy single plane they sell with the heads. I also have a Trick Flow single plane which would work well with those heads. I have a six pack setup, and the tunnel ram that I have been running for a few years now.
I've been thinking more about staying with the tunnel ram and selling the others.

Thank you.

 

[RAMM]

If anyone has already mentioned it , I apologize. I didn't read every single post closely.

Part throttle and "tip-in" is where you will see the biggest differences, with the TF being superior over the Indy's. You might make more power with the Indy's but considering where the engine will spend 98% of its time unless you are an avid racer--I'd go TF and sell off the Indy stuff. Just my two pennies. J.Rob

 

[coloradohill]

If anyone has already mentioned it , I apologize. I didn't read every single post closely.

Part throttle and "tip-in" is where you will see the biggest differences, with the TF being superior over the Indy's. You might make more power with the Indy's but considering where the engine will spend 98% of its time unless you are an avid racer--I'd go TF and sell off the Indy stuff. Just my two pennies. J.Rob

I don't think that has been brought up in this post. When I talked these options over with my builder, he said the Indy heads are a little over kill in his opinion for a street car. Maybe this is what he means.
I'm not trying to second guess him, just trying to understand and make the best choice.

What part(s) of the intake system (top end) contributes to or effects throttle efficiency and tip in performance the most? In other words, what makes the Trick Flows the best for this situation?

Thanks for your input.

 

[rumblefish360]

Kinda depends on what you have here. For a street car i wouldn't spend the extra coin to update to the 325's if you already have the 293's.

100%!

With the 2hp per cfm rule of thumb, 293 cfm = 586 hp, now it can make more than 2hp:cfm but if it making a lot over 586 hp you’re probably under headed.

How so? Big call considering there is no other information.

If everything here is getting you well under 2hp:cid eg.. 475-500 hp with the 293 cfm/586 hp head the 325 cfm might not add anything or not much, if making 550-600+hp the 325 probably add a decent amount depending on cam.

Flow curve dependent.

if making well under the 325 hp 2hp:cid probably effects throttle response, but probably make the 293 cfm heads hp + with lesser cam, which makes for worse driveability large cam or heads?.

Could you clarify this?

Richard Holdener has tried to find out if you can over head size and flow on the dyno, he has found bigger generally don't lose power but there's point where gains are smaller and smaller to not at all, but as for real world performance and driveability that question is still up in the air, with a 416 I think you have less chance of side effect especially if 550+hp is the goal.

Engine masters did the same. Freiburger claims he failed since the test of, “Is there such thing as too large of a cylinder head” test didn’t show what he was after. Darn shame.

Maybe some day I’ll try it myself.

Sounds like I should stay with the highest flowing head I have.
Thanks

IMO, not knowing anything else except this is an”Street car,” I’d stick with the 293 heads. I have a set of TF heads on the wife’s car. The small super efficient port is really quite good and super drivable. Provides a good top end charge and excellent low speed torque with feeling any dead spots down low in the rpm range, good pedal feel on tip in from idle and at any point driving.

If anyone has already mentioned it , I apologize. I didn't read every single post closely.

Part throttle and "tip-in" is where you will see the biggest differences, with the TF being superior over the Indy's. You might make more power with the Indy's but considering where the engine will spend 98% of its time unless you are an avid racer--I'd go TF and sell off the Indy stuff. Just my two pennies. J.Rob

While I don’t know if I’d sell off the Indy stuff so quickly, I agree 100%.

 

[rumblefish360]

I don't think that has been brought up in this post. When I talked these options over with my builder, he said the Indy heads are a little over kill in his opinion for a street car. Maybe this is what he means.
I'm not trying to second guess him, just trying to understand and make the best choice.

What part(s) of the intake system (top end) contributes to or effects throttle efficiency and tip in performance the most? In other words, what makes the Trick Flows the best for this situation?

Thanks for your input.

In my opinion, It’s a combination of parts that lead to certain outcomes. What I think your engine builder is saying is the Indy head ports are large for a street car, which a street car is certainly heavier than a race car, a set up the Indy head is more suited for and probably designed for.

The whole engine should be seen as a system. The single plane gives the best HP up top and not so much torque down low vs the dual plane. These things you know and have seen on stuff like engine masters.

Pretty much, any intake you use is a limitation on the cylinder head unless it’s a tunnel ram port matched to the cylinder head on the engine block to be used and the displacement is small. As in not taxing the capability of the carb, intake and cylinder head.

Increasing the displacement, adding a large cam and attempting to spin the engine to 9K ….. yea… limitations are here.

Let’s get back to reality and your engine.

There’s a lack of information on your engine here.

In general, what is to large for on set up is not enough for another. To say the Indy heads are too large for a street engine is a generalization and probably more on point than anything with most people. The larger ports can and probably will contribute to a soft bottom end for a “STREET CAR” trying to be driven in a civil manor. Or like Mom would drive it to Sunday church & dropping the kids off at school.

This is the area I’d suggest error smaller on the side of caution is a good idea.

List out the engine specs! The goal of the vehicle & what your after.

 

[coloradohill]

The first post gives the build so far. What I am trying to decide is which head is the best option.

I understand how the combination of parts work together, that's why I'm trying to make an informed decision.

The car is a '67 notchback, 904 Andrews Racing trans with a rmvb. low set gears built for 550 hp. Converter is an Ultimate 9.5" to handle 800 hp. I have 3:23 and 3:55 gears to use.

The rotating assembly is a Molnar 416 stroker from @PROSTOCKTOM (thanks again).
[FOR SALE] - 416" Molnar Technologies Complete Balanced Rotating Assembly for 340 Block - New

CR will be 11.5 +/-

The cam will be a roller built for this combo.

My goal is to perform better than the 400 hp 340 that is in the car now. Why? Just because.

I will be driving it to church on Sunday but not like mom would and my kids were homeschooled, so I won't be dropping them off there.

If I left anything out that needs to be thought of, let me know.

Thanks again.

 

[furrystump]

I run 117 at 3353 lbs. Calculator says 519 RWHP. Which seems pretty high to me. The heads flow 274ish average. So 1.9 hp per cfm seems close. The thing is my intake is considered “not great” which is probably accurate, but the intake tract starts to flow first at the valve opening. How much depression signal the head can create impacts what the intake will flow. Higher depression, more flow. You almost can’t have “too much” head flow in a LA motor and “excess” head flow can overcome a “not great” intake. Of course there are limits, the velocity gets so high turbulence or fuel separation occurs. It seems to me it is a pretty serious build albeit not a dedicated race car. I would go bigger CFM head. Gives you room to grow or if car usage changes. Just my two cents.

 

[coloradohill]

Thank you sorry for the short reply but I’m driving to work using voice text.

 

[PROSTOCKTOM]

If it were mine I would stick with the Trickflow heads over the Indy heads for your application. That way you can play around with different intakes and several other reasons.

As previously mentioned, and to me personally air speed is more important that peak flow.

You're never going to hook it up with either head on the street and you're not using the engine for all out dedicated drag racing.

The best idea is to just build another short block and use both sets of heads. LOL

Tom

 

[coloradohill]

The best idea is to just build another short block and use both sets of heads. LOL

Yes lol but then I’d have to buy another car for the second engine and I’d have to clean out the other side of the garage for the second car and probably Build a bigger doghouse in the backyard. But I’ll keep your suggestion in mind.

 

[PROSTOCKTOM]

Yes lol but then I’d have to buy another car for the second engine and I’d have to clean out the other side of the garage for the second car and probably Build a bigger doghouse in the backyard. But I’ll keep your suggestion in mind.

No need to do all of that just swap out the engines a few times a year when you get bored. LOL

Tom

 

[coloradohill]

Well, truth be told this car is had five different engines in and out over the last eight years, but I’ll keep that in mind if I get bored

 

[273]

Here's a few videos that might help

 

[coloradohill]

I did watch this last night.

 

[273]

This is what I’m basically trying to find out. I will look his videos up.
550-600 is the goal.
Thank you

550-600 hp is a fairly wide target, peak hp rpm of 550 hp vs 600 hp is somewhere in the 6000 rpm vs 6700 rpm depending tq per cid ratio (efficiency). that's a fairly big difference in requirements. Need to narrow the goal and how streetable is streetable ?