[BruceWilkie]

This topic has come up over the years I feel its time to put it in the boost section for additional discussion. Perhaps we can establish some guidelines to how much head flow capacity over NA demand is practical for various applications.

I'll start by reminding that boost pressure is a measure of restriction to flow.

Another point that needs to be emphasized is that as boost pressure rises so does charge temperature. That hotter the charge temp the less dense the charge for any given pressure.

Cylinder head flow capacity can greatly influence both boost pressure and charge temperature and the actual mass airflow the cylinders of the engine receive.

I'll mention now that cfm flow needs to be converted to lbs per minute (or hrs in some formulas) flow to be meaningful. Especially as soon as "boost" is encountered. When an engine is boosted the air entering the cylinders is denser than the atmosphere. Knowing its weight aids in determining this density.

With an NA engine we increase flow capacity to support power production at rpm levels above what the factory equipped cylinder head was intended for.

With a boosted engine we can make some choices. If we select our boosting device to support peak power at the rpm level of the standard head we likely can extend the power past the NA peak rpm simply because we are supplying more air via supercharging.

Now suppose we want to make that same higher rpm horsepower of the previous example, but wish to do it at a lower safer rpm level but same boost pressure and mass air flow(density). If we increase the flow capacity of the cylinder heads and increase the driven speed of the supercharger device we can still produce the same horsepower but now at a "safer" rpm level. (You may need to chose a larger blower or a different turbo to keep things efficient)

Now "mores law" comes in. How about a little more rpm and a little more flow capacity from the cylinder heads. Go ahead, step right up, but you are eventually going to reach trade-offs. Eventually you hit the point where more is too much.

Some generalized examples: An engine with 250 cfm heads is making 700 hp at say 15 lbs boost at perhaps 6000 rpm. The heads are exchanged for heads that can flow 285.(same cam and the manifolding poses no new restrictions) The engine can still turn 6000 rpm and if no adjustment to the supercharger output it will still make 700 hp (likely a bit more due to lower charge temp) but the boost reading will be notably lower as will the charge temperature. At peak power the increased flow capacity behaves much in the same effect as an intercooler! Same power less sensitivity to octane.

If you now adjust or change your supercharger to obtain the same 15 lbs boost pressure reading and same previous discharge temp but with the higher flowing heads, horsepower will potentially now be approx 796. Add an efficient liquid/air intercooler and you are likely at 1000 hp or so. Possibly more.

An approximate 14% increase in cylinder head flow capacity can increase hp by the same approximate percentage.(there are other things to consider of course when you are actually applying this) About the same as you would expect increasing cid from say 400 to 455 with no ME or VE losses. Of course its not going to be exactly 14% in this case but it will be very close.

You might be thinking what if I put 385 cfm heads on?! On paper it looks like you could increase power an additional 35% over the 285 cfm heads or 54% over the 250 cfm heads.
Thats potentially approximately 1075 hp without adding an intercooler.

Your definately going to need a bigger blower or compressor! That in turn will eat up some extra power or increase spool-up time. You are also likely to have a very narrow powerband, likely difficulty at low speeds, and most all the same symptoms you would experience choosing too much head flow for an NA motor. The motor is going to "want" to rpm higher too! If you want the kind of power a 385+ cfm head offers, and can use it, its probably wise to up the cubes a well.

I know we are all about Pontiacs but for some insight to what 285 cfm heads(Brodix 11x), 406 cubes, 6000 rpm redline, intercooled turbos are capable of, check out this SBC 406 from Nelson's shop. On 91 octane and only 7 lbs boost 769 hp, at 14.5 psi over 1000 hp on 91 octane. Adding 110 octane race gas and upping the boost to 18.3 1165 hp. Changing injectors and upping the boost to 28 psi netted 1502 hp at 5600 rpm. BTW Brodix 11x heads advertised flow is not terribly different than out of box E-heads for a Pontiac.

Here is the link.
http://www.hotrod.com/projectbuild/h...bocharger.html

[Tom Vaught]

This topic should go into the "Know your Competition" Sticky.

Good HP numbers. Funny thing is Marty with the same 406 sized engine (but a Pontiac) made more HP with less head 240 cfm cast iron head vs high dollar Brodex stuff with more cfm.

Course they do say that is was a "street engine" even at 1500 hp.

Some very nice work though.

Tom Vaught

[BruceWilkie]

I guess I can copy and paste the last part into "Know Your Competition"

I feel the top half of the post could be an interesting discussion.

[62fatcat]

i agree with some points.
but would rather have real world info. for example bad69bird put bigger better flowing heads on and lost boost, but made considerable more power.

[BruceWilkie]

Originally Posted by 62fatcat

i agree with some points.
but would rather have real world info. for example bad69bird put bigger better flowing heads on and lost boost, but made considerable more power.

He lost restriction to flow(lower boost gauge reading).

When you decrease pressure by installing higher flowing heads yet still turn the same blower speed and engine rpm, the air in the blower(or turbo) doesnt get as warm.

That increases mass airflow (or density). It is the same effect as adding or improving an intercooler.

If he now steps up his blower to match the previous boost pressure reading he wiill gain additional hp.

It will be very near the same percentage in hp increase as the percentage of flow capacity increase .

Compressor efficiency will be the reason it will not be exactly the percentage of flow capacity increase.

Going from a 320 cfm head to a 385 cfm head is a 20.3% increase in flow capacity. If you step up the blower to flow an additional 20.3% more air your hp will increase approximately 20.3%. If you merely add the higher flowing heads and dont change the blower speed boost psi decreases due to less restriction to flow. However the blower (compressor discharge)temp decreases and you gain some power from the "intercooling effect" but not to the potential of the head flow increase.

If bad69bird gets an F2 back on there and adjusts his boost psi to what it was previously with the old heads he stands to gain far more than just the head swap got him.

[Tom Vaught]

Originally Posted by BruceWilkie

He lost restriction to flow(lower boost gauge reading).

When you decrease pressure by installing higher flowing heads yet still turn the same blower speed and engine rpm, the air in the blower(or turbo) doesnt get as warm.

That increases mass airflow (or density). It is the same effect as adding or improving an intercooler.

If he now steps up his blower to match the previous boost pressure reading he wiill gain additional hp.

If bad69bird gets an F2 back on there and adjusts his boost psi to what it was previously with the old heads he stands to gain far more than just the head swap got him.

The runs made at Norwalk 8.44 et were with the F-2 Supercharger spinning at max blower speed, Bruce. That was also with the CV-1 heads with the higher air flow.

He cannot increase the HP of his engine without either changing the supercharger to an F-3 or by going to a Turbo assuming only a boosting device change.

If he added a water to air inter-cooler he could increase his hp again.

If he added even higher flowing heads, same deal.

There might be some HP improvement from using a Dominator Intake or Tunnel Ram intake with lower restriction Carb(s).

The F-1R did not perform to expectations for his specific combination.

My vote would be a Dominator Intake, Dominator carb, and a water to air Inter-cooler if he wants to go faster.

Tom Vaught

[62fatcat]

so was my statment incorect?
he added better heads, kept the same blower speed and made about 135 more hp by his mph numbers.
doesn't this contridict your previos statement.

[Tom Vaught]

What statement was that Brad?

Tom Vaught

[bad69bird]

Originally Posted by Tom Vaught

The runs made at Norwalk 8.44 et were with the F-2 Supercharger spinning at max blower speed, Bruce. That was also with the CV-1 heads with the higher air flow.

He cannot increase the HP of his engine without either changing the supercharger to an F-3 or by going to a Turbo assuming only a boosting device change.

If he added a water to air inter-cooler he could increase his hp again.

If he added even higher flowing heads, same deal.

There might be some HP improvement from using a Dominator Intake or Tunnel Ram intake with lower restriction Carb(s).

The F-1R did not perform to expectations for his specific combination.

My vote would be a Dominator Intake, Dominator carb, and a water to air Inter-cooler if he wants to go faster.

Tom Vaught

Tom, I don't do this too often so let me correct you (LOL), I'm not at max blower speed. I'm only spinning that blower to 54k on each shift and I go thru the traps at 61k. Max speed on the F-2 is 65k.

BTW, I have another F-2 coming baby!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! It's being built as I type.

Originally Posted by 62fatcat

so was my statment incorect?
he added better heads, kept the same blower speed and made about 135 more hp by his mph numbers.
doesn't this contridict your previos statement.

Actually Brad I gained 178hp. Made 1095hp before and did 1273hp this time. So Bruce's figures are close.

[BruceWilkie]

So the head swap at similar blower speed was good for @16.2 percent hp increase. Upping to same boost gauge level of the old heads likely to give you another approx 4 %. for total gain of 20% if no other things like carb/exhaust etc hold you back. A good(modest not best) intercooler should be worth at least another 20% more power on top of that.

When you get that all sorted are you going to be ready for that F3?

We didnt dare dream this stuff as really possibile for a Pontiac twenty five years ago.(well at least publicly)

1273+4%= 1323 add intercooler and maybe another 20% = 1588

[Torment]

Hmmm.... The head flow deal sounds great - seems easy. Some years back I swapped E heads in place of a set of mildly ported Dport's under my 8-71 and went slower... Bigger ports, bigger cfm, same valve size, same chamber cc... lost power.

So what happened? Why did more flow equal less go?

Then I swapped on a set of decently ported 614's, same valve size again, slightly smaller chamber and installed the requisite headers, and picked up about 100hp over the Dport.

Now I've got a set of 340cfm HP's and if I infer the above correctly I could pickup near 200hp with 400cfm HP's? I can't help but be skeptical.

[bad69bird]

Originally Posted by BruceWilkie

So the head swap at similar blower speed was good for @16.2 percent hp increase. Upping to same boost gauge level of the old heads likely to give you another approx 4 %. for total gain of 20% if no other things like carb/exhaust etc hold you back. A good(modest not best) intercooler should be worth at least another 20% more power on top of that.

When you get that all sorted are you going to be ready for that F3?

We didnt dare dream this stuff as really possibile for a Pontiac twenty five years ago.(well at least publicly)

1273+4%= 1323 add intercooler and maybe another 20% = 1588

At Norwalk I went 8.44 @ 166.97. If you use the wallace calculator based off the MPH it says that I made 1325HP. Based off that information, I would believe that I already made the "1323" number. Now, with my car I've always had to use the MPH and not the ET because of the timing that I pull out off the hit. Also the air was total chit at Norwalk, 3600' and 90-95 degrees on that run, and the converter was flashing 700 RPM lower than normal. In hind sight, the trans might have been going on it's way out. With good air, not even awesome air, I would think that my car would MPH between 170-172MPH. On Friday at Norwalk the air was 2900' (that's what I was told) and the car went 164 MPH that evening. So a difference of 700' and about 20 degrees picked the car up 3 MPH. At E-town when the blower broke, the air was -168' and 50 degrees. Can you imagine what the potential would have been for the MPH/HP on that day! I believe that I might have seen 175-176 MPH with a big "IF" the track was able to hold a DR...which I have my doubts. So I truely believe that 170-172 MPH range is not out of the question.

Now as far as the F-3. I highly doubt it. I would without a doubt have to put an I/C on...no question. For the proper I/C, which would be a 2400-3000HP model, the piping, V-bands, pump, cooling lines, AN bungs for the trans lines to run it thru the I/C, clamps, water release valve, silicone boots and whatever else I forgot. I would be looking at approximately 3-4k, plus the cost of the F-3. I would also front mount it, which means I would have to relocate my radiator and convert my water pump into re-location deal. You are probably talking about a 10k conversion. That's with me doing a majority of the labor and getting parts at dealer or actual company cost. I would love too, but unless I was able to receive a MAJOR sponsorship, I can afford it.

Plus, I just remembered I don't think my motor made enough HP N/A for the F-3 (can't remember what the N/A number is). I would have to change the cam and probably have the heads ported...add another 5k to that price tag and maintenance really just went thru the roof! LOL Oh...and I might as well change over to a dominator too!

Bottom line, the F-3 conversion would be great and I would love to be the one to push the limits of a boosted blow-thru pontiac. I believe that I some of the very best and brightest people in my camp to achieve that goal, but the price tag and maintenance would be very costly.

[BruceWilkie]

I need to clarify just what I mean about % of flow increase gains. It isnt just the intake flow increase the exhaust has to be able to handle the additional power. Camshaft requirements can change quite a bit. (Same for NA) If you increase head flow capacity yet want to stay in the same rpm range your cam profile requirements change! Typically less duration at lower lifts and greater duration at higher lifts on the intake side. Intake closing and opening points change. On the exhaust side earlier openings and high rates of lift help expel the exhaust. Again you do this to optimize power in the rpm band you want to run in.

So basically to peak hp at same rpm range with high flowing heads as with smaller heads you need to decrease seat duration and possibly .050 duration as well, meanwhile maintaining same or greater lift. The exhaust side of the cam needs to be able to handle the increase on the intake without negatively impacting the intake efficiency.

Your carburetion, manifolding, and exhaust system all need to meet the new demands of the increase in flow capacity. THERE IS NO FREE LUNCH! The efficiency of your blower and intercooler will also impact the effectiveness.

If you run any blower add higher flowing heads yet have done nothing to increase blower output you SHOULD see a decrease in boost pressure and yet likely at least some gain from the cooler discharge temp.

If You still get the SAME boost reading at same engine and blower rpm after swapping on higher flowing heads you have a restriction somewhere! Carb, manifold, exhaust, and even the cam profile could be suspect.

BTW with a roots blower it is possible to get a slightly different boost reading in the plenum area than in a port. (saw it on a friends car while investigating an inconsistant boost reading initially thought to be an intermittant leak. About 1.5 lbs varience. Relocating near center of plenum resolved the issue) I would think the same could occur with any type supercharger.

[62fatcat]

Tom,
the statement i was refering to was, i beleive in the first post that if you keep the same blower or airflow and increas the head flow cfm that you would probably make less power.
maybee i just didn't understand the statement, wouldn't be the first time.
ps,
i sent you an email.

[Tom Vaught]

Originally Posted by 62fatcat

Tom, the statement i was refering to was, i beleive in the first post that if you keep the same blower or airflow and increas the head flow cfm that you would probably make less power.
maybee i just didn't understand the statement, wouldn't be the first time. ps, i sent you an email.

What I was getting at Brad was using the same blower at the same rpm
means that you fixed the amount of density (mass flow) going through the engine. If the mass flow stays the same, the hp stays the same.

If you increased the cfm numbers on the engine, (lower restriction to flow) then the restriction number will drop (BOOST on the gage). The heads are better but the CORK in the system is now the supercharger at a fixed speed. It controls the mass flow. Course if the air charge is cooler than the mass flow goes up. The reduction in mass flow heating the engine actually sees is probably minimal as the blow-thru carb is is what is lowering the charge temp in the intake tract.

IF you added a water to air inter-cooler then the HP will go up as automatically you have now increased the density of the charge per cylinder event. You might take 200 degrees off the charge temp on a gasoline engine. E-85 would be a different deal.

Hope this helps.

Tom Vaught

[BruceWilkie]

Tom V quote: "If you increased the cfm numbers on the engine, (lower restriction to flow) then the restriction number will drop (BOOST on the gage). The heads are better but the CORK in the system is now the supercharger at a fixed speed. It controls the mass flow. Course if the air charge is cooler than the mass flow goes up. The reduction in mass flow heating the engine actually sees is probably minimal as the blow-thru carb is is what is lowering the charge temp in the intake tract."


Tom can you explain something that puzzles me about that statement? Bad69bird ugraded to higher flowing heads. Did not change blower speed or rpm range yet gained. Besides the heads, he changed manifold and IIRC he changed his carb hat. Heres my question. If the blow thru carb is supposedly not going to allow additional charge cooling where did the approx 16% gain come from? I highly doubt it all came from the exhaust side as that isnt that great of a percentage of flow thru increase over his previous heads from what I know.

I believe the gain was an increase in density from charge cooling effect of less restriction to flow. Why? Draw-thru roots blowers can be intercooled. Pressure and charge temp drop and more hp is made. My friends 32 Ford sbc 350 with 6-71 has an ice water intercooler. When the ice/water tank is empty and the pump is off, boost pressure rises nearly 1.5 psi (from 7 to almost 8.5)and power is notably down. Its strictly a street rod the intercooler more for show and not frequently used but it definately works. The blower pulleys arent changed nor has engine rpm band. Physical restriction to flow is unchanged but cooler air after the blower still increases density(mass-flow). The blower doesnt heat the charge as much because of the contraction of cooled air below it causes less restriction to flow through the blower. That causes an increase of mass flow (density), a loss of pressure, yet still an increase of power.

I'm thinking even with a blow-thru centrifugal, less restriction to flow beneath the carb is still going to be less restriction to flow between the carb and the blower thus still cooling the charge.

Was bad69bird's carb not too restrictive? Did less pressure and cooler temp underneath it change the differential thru it so flow density could still increase even though the blower speed wasnt increased?

I am inclined to think its because less restriction to flow beneath the carb still translates to less restriction between the carb and the blower. To me that equates to lower discharge temp and pressure from the blower and denser charge(greater mass flow) at same blower speed and engine rpm.

[Tom Vaught]

PM to you Bruce.

Tom Vaught

[62fatcat]

Tom,
thank you.

[jdw_poncho]

Will header sizing affect the HP just as much as head flow? I'm having more flanges cut out next week and havent decided on what size hole to use. If you use a smaller diameter tubing does the velocity caused by the small tubes make up for the volume loss? I guess I'm applying the same principal to the intake, larger volume less density in the intake tract? Larger volume (header) less boost/turbine speed?

Any good mathmatical solution for this? I would assume 1.5" tubing would be fine for most applications. Its a lot easier to build headers that fit with 1.5" tubes rather than 2".

[62fatcat]

you must be talking about a turbo setup, correct?