Differences in Supercharged verses normally aspirated heads

[new engine builder]

I am making at least that much or maybe a little more, I streetdrive this car all over. Besides I only got a 383, not a 413. And Just a little FYI, you can never trust an in house engine test.

I have seen AFR heads out of the box that flow nowhere NEAR what AFR says they do. As a matter of fact this is more the norm with AFR.

I will stick with what I have, its proven.

I can make a good bit more power with a cam change. It has a 254/254@.050 so I got room to grow.

You might want to read the dyno test again.
It was done by Porting Dynamics not AFR.
As far as a cam change I.M.O.,you don't have enough compression to support a larger cam than what you have and still run it on pump gas.
I would look more at cams that are asymmetrical.

[jimivice]

The orignal post is a very valid question. It puts to task the common thought of just bolting on a blower and there will be an increase in power. Well that is obvious. I really don't care about boasts of H.P. of a particular combination. Unless, it was thought out. I'm not concered with efi vs carburation, that is a given. What I'm looking for is a guideline. I want to pick up H.P. from an existing blower motor. If all variables stay the same as far as boost,c.r. and camshaft. Will porting the cyl. heads increase H.P.. I feel it will. The common thought is I'm wasting my time. If that is true ,the motor will not make anymore power. This I can't beleive. If a normally aspirated motor benefits from head porting, why wouldn't a blower motor?

[raynorshine]

i don't think you are wasting your time porting your heads. i believe the better an engine runs na, the better it will run with boost.. may have to run different cam, usually wider lobe sep. etc..

[1989TransAm]

"I have seen AFR heads out of the box that flow nowhere NEAR what AFR says they do. As a matter of fact this is more the norm with AFR."

I have seen any number of independent flow tests recently on the new AFR Eliminator series of heads that meet or exceed the advertised flow rates. This includes my own set.

[FASTFATBOY]

I am making at least that much or maybe a little more, I streetdrive this car all over. Besides I only got a 383, not a 413. And Just a little FYI, you can never trust an in house engine test.

I have seen AFR heads out of the box that flow nowhere NEAR what AFR says they do. As a matter of fact this is more the norm with AFR.

I will stick with what I have, its proven.

I can make a good bit more power with a cam change. It has a 254/254@.050 so I got room to grow.

You might want to read the dyno test again.
It was done by Porting Dynamics not AFR.
As far as a cam change I.M.O.,you don't have enough compression to support a larger cam than what you have and still run it on pump gas.
I would look more at cams that are asymmetrical.

Why would I put and asymmetrical cam in an engine with a head I/E ratio of almost 80%?

BTW I run 12.5 to 1 compression.

Just askin.

[airflowdevelop]

The orignal post is a very valid question. It puts to task the common thought of just bolting on a blower and there will be an increase in power. Well that is obvious. I really don't care about boasts of H.P. of a particular combination. Unless, it was thought out. I'm not concered with efi vs carburation, that is a given. What I'm looking for is a guideline. I want to pick up H.P. from an existing blower motor. If all variables stay the same as far as boost,c.r. and camshaft. Will porting the cyl. heads increase H.P.. I feel it will. The common thought is I'm wasting my time. If that is true ,the motor will not make anymore power. This I can't beleive. If a normally aspirated motor benefits from head porting, why wouldn't a blower motor?

Don't believe it!!!

I have suprised many customers and Dyno operators with properly designed heads on blown applications. Everyone wants to believe that the blower will "make up" for a poor induction design.... could not be farther from the truth!

I don't understand why we get caught up in the N/A motor is "sucking" the charge in while a supercharged motor is getting the charge "pushed" in... Both engines have a depression across the valve, only the supercharged engine has a greater depression.

In my experience you are best to treat a supercharged application the same as a N/A application on a really...really good air day!

One word of caution though. Do NOT get cuaght up in high I:E ratios for blown applications. This WILL cost you power. You are better to design the exhaust port intelligently and never bolt it to the flowbench....then to maximize exhaust flow. Don't worry too much about the charge "backing up" .... I have never seen this happen before. Just did a set of heads for a 1620hp sbc w/ little tiny 1.57 exhaust valves... Definently shows no sign of trouble getting the exhaust out.

for every bar of boost (1 atmosphere...14.7psi) you can figure your intake cfm to hp calculation almost doubles.

[MadBill]

...If all variables stay the same as far as boost,c.r. and camshaft....

If you keep the same blower drive ratio after porting, boost will go down but power will go up. If you step up the ratio to maintain the same boost, power will go up more. (octane permitting...)

[AA Performance]

...If all variables stay the same as far as boost,c.r. and camshaft....

If you keep the same blower drive ratio after porting, boost will go down but power will go up. If you step up the ratio to maintain the same boost, power will go up more. (octane permitting...)

MadBill,if we put several pressure sensors in the intake track, say 1 in the manifold, 1 in the start of the intake port , 1 next to the valve & 1 in the chamber, are you saying that all these pressure sensors will read higher to lower pressures & why?

[new engine builder]

Why would I put and asymmetrical cam in an engine with a head I/E ratio of almost 80%?

BTW I run 12.5 to 1 compression.

Just askin.

12.5 to 1 on pump gas??
I might have to get out my BS spray again.

[MadBill]

...If all variables stay the same as far as boost,c.r. and camshaft....

If you keep the same blower drive ratio after porting, boost will go down but power will go up. If you step up the ratio to maintain the same boost, power will go up more. (octane permitting...)

MadBill,if we put several pressure sensors in the intake track, say 1 in the manifold, 1 in the start of the intake port , 1 next to the valve & 1 in the chamber, are you saying that all these pressure sensors will read higher to lower pressures & why?

Boost is just the po' boy's way of indirectly measuring mass flow. It is the pressure drop across the restriction of the intake system. If you increase the flow by spinning the blower faster, the mass flow and boost goes up. If you reduce the restriction by improving the port, the flow increases due to improved blower efficiency, but the boost goes down.

In your scenario, the pressure in the chamber would rise Vs. the unported intake, but the pressure gradient from the blower outlet to the cylinder would be so much less steep that the blower outlet pressure would be less.

This might be a useful visualization: Let's say that your engine is running at 6,000 RPM WOT and showing 10 psi boost. Now imagine that the intake valves all suddenly stop opening. What is the immediate effect on boost pressure?

[FASTFATBOY]

12.5 to 1 on pump gas??
I might have to get out my BS spray again.

I guess you are a little behind on GEN2 advantages?

[Dave Flanders]

I've got a question - considering boost is only backpressure, does this mean that there is more effective flow across the valve seat area on a blown application than a typical flow bench would indicate? The way I see it, if the higher pressure areas like the plenum just have higher pressure but not higher velocity wouldn't that mean that at the highest pressure differential location (the valve seat) the velocity would be much higher than N/A?

I run a turbo 4 cylinder with an aftermarket head which has decent but not stellar peak flow numbers (260 @ .600). I've been considering trying a well ported iron head done by a friend of mine which flow wise will kick the alu. head's ass up to .500" lift but has a little lower peak numbers.

My cam only has .580" lift, would it be beneficial to give up some peak head flow to gain more low to mid lift flow? Fuel is methanol so it's taking up a lot of room, boost runs 40+ psi. with about 1:1 TIP ratio.

[MaxFlow]

Dave, If the chamber is as efficient I would think the cast iron with higher average numbers will make more power.

Is 580 lift the max for you? I guess experimentation has led you to the cam you have?

I think Larry Meaux has stated that the average at or around 80% of tvl are the numbers to look for. My experience shows he is very right on that subject. So flow numbers from .300 to .500 averages would be most important? I'm sure the jury is still out on this one.

[maxracesoftware]

Dave, If the chamber is as efficient I would think the cast iron with higher average numbers will make more power.

Is 580 lift the max for you? I guess experimentation has led you to the cam you have?

I think Larry Meaux has stated that the average at or around 80% of tvl are the numbers to look for. My experience shows he is very right on that subject. So flow numbers from .300 to .500 averages would be most important? I'm sure the jury is still out on this one.

in the early 1980's i discovered around .85% percent of
Cam;s theoretical max lift on the FlowBench gave decent correlation
to what gains i saw on the DragStrip

then after getting a SF-901 Dyno,
i refined it to .87% PerCent ( from .85 % ) after a few years
of FlowBench -to- Dyno -to- DragStrip correlations

if its theoretical max valve lift of = .580" ... then .580 times .87= .505"
so i'd concentrate on .500", 400", and 300" Lift FlowBench Numbers

[Dave Flanders]

.580" lift is just what I have to work with. I've run the same cam and alu. head for 10 yrs. now, just can't afford to buy a new one.

The chambers are different- the iron head is the old 2.3 Pinto while the alu. head has a more modern figure 8 (Yates?) design. AFAIK though there is not a huge difference in total timing numbers in between the two in NA circle track applications.

Mainly I was wondering if boost can change the characteristics of a given head - if the boost across the valve seat area can increase the lower lift flow numbers beyond what the density alone would do? If I've described it well enough....