Cylinder head port sizes.
03-13-2014, 08:43 PM
#41
dan,while combustion chamber is important as gm learned in the 60s,the best combustion chamber in the world will not cover issues caused from crappy port design.im not busting your balls im just stating facts.the pic of your heads looks good and im sure you are giong to see improvement ,your head guy did a really nice job.
But, what is interesting, is I notice cylinder head companies like AFR, and Brodix, now offer an as cast head, but with CNC ported combustion chambers as an option. maybe Dans head guy was on to something after all? .100-.700 from the Brodix site comparing an as cast 340 head, and an as cast w/CNC chamber option (around 200-250 bucks extra per head). look at the low lift numbers.
.100 .200 .300 .400 .500 .600
BB-2 X 2.300 Intake 153 221 276 322 357 363
1.880 Exhaust 122 138 171 198 216 229
BB-2 X
(CNC Combustion .100 .200 .300 .400 .500 .600 .700
Chambers) 2.300 Intake 153 225 285 333 368 365 365
1.880 Exhaust 132 176 211 235 254 264 270
03-13-2014, 08:50 PM
#42
Registered
Yes! What you're seeing here is how different physical properties make the readings deceiving. Common logic is more boost = more air, and that's a bit misleading. More boost = more resistance to flow.
In your case your flow path became more efficient, thus lowering resistance to flow.
Beware, engineer ramblings below-
How come we (uhh, I mean those that have forced induction) monitor boost when we could be monitoring mass air flow? Obviously the technology exists... This would really only be good for testing, as once you have the runners/valves/cam dialed in, theyre not changing. Ambient pressure, especially for those on the sea, is pretty close to constant. Temp is almost moot.
You'd use a MAF setup to do real time flow testing of blower/head/cam combos, derive some constants/coefficients for the setup, and have a pretty damn good baseline.
I dunno, maybe people do this already,
In your case your flow path became more efficient, thus lowering resistance to flow.
Beware, engineer ramblings below-
How come we (uhh, I mean those that have forced induction) monitor boost when we could be monitoring mass air flow? Obviously the technology exists... This would really only be good for testing, as once you have the runners/valves/cam dialed in, theyre not changing. Ambient pressure, especially for those on the sea, is pretty close to constant. Temp is almost moot.
You'd use a MAF setup to do real time flow testing of blower/head/cam combos, derive some constants/coefficients for the setup, and have a pretty damn good baseline.
I dunno, maybe people do this already,
03-13-2014, 11:01 PM
#43
Registered
iTrader: (2)
Cole beat me to it . Best analagy I have , the blower motor builds from here are the marine version of a blown 62 Chevy pick up , with a 3000 rpm stall convertor and a powerglide . And its permanently towing a small boat . And there are hills everywhere .the off idle throttle response lost from the big ports doesn't get a chance to be missed . And with the reduced couple of psi lost at the same blower rpm to the bigger ports helps curb detonation pulling that boat and powerglide through the hills ..no science cut and dry boring analogy, finding the balance between the 0 psi a 8-71@ 10% overdri e gives ya spooled up on a milk crate and the 20 lbs you would likely see 10% overdriven on a peanut port single exhaust wagon
03-14-2014, 01:50 AM
#45
Registered
I agree. Port flow is important. I remember speaking with Dan's head guy a few years back. He really stressed working on the chambers in a big block chevy head. Kept telling me how important low and mid lift flow is, rather than just flow at high lifts. At the time, I didnt put much thought into what he was preaching. I always assumed, as far as chambers, you polish them smooth, to eliminate hot spots. Never thought much about them as far as airflow.
But, what is interesting, is I notice cylinder head companies like AFR, and Brodix, now offer an as cast head, but with CNC ported combustion chambers as an option. maybe Dans head guy was on to something after all? .100-.700 from the Brodix site comparing an as cast 340 head, and an as cast w/CNC chamber option (around 200-250 bucks extra per head). look at the low lift numbers.
.100 .200 .300 .400 .500 .600
BB-2 X 2.300 Intake 153 221 276 322 357 363
1.880 Exhaust 122 138 171 198 216 229
BB-2 X
(CNC Combustion .100 .200 .300 .400 .500 .600 .700
Chambers) 2.300 Intake 153 225 285 333 368 365 365
1.880 Exhaust 132 176 211 235 254 264 270
But, what is interesting, is I notice cylinder head companies like AFR, and Brodix, now offer an as cast head, but with CNC ported combustion chambers as an option. maybe Dans head guy was on to something after all? .100-.700 from the Brodix site comparing an as cast 340 head, and an as cast w/CNC chamber option (around 200-250 bucks extra per head). look at the low lift numbers.
.100 .200 .300 .400 .500 .600
BB-2 X 2.300 Intake 153 221 276 322 357 363
1.880 Exhaust 122 138 171 198 216 229
BB-2 X
(CNC Combustion .100 .200 .300 .400 .500 .600 .700
Chambers) 2.300 Intake 153 225 285 333 368 365 365
1.880 Exhaust 132 176 211 235 254 264 270
Last edited by mcprodesign; 03-14-2014 at 01:59 AM.
03-14-2014, 02:15 AM
#46
Registered
Al these numbers are swell but a N A motor can only make so much pressure without being supercharged. take for inistance a pro stock Car. They have this huge air scoop and the thing has like a 6 in hole in the front. The biggeer the " air box" the more volume and increase in flow. it does not make boost . It can only take a few pounds of pressure ( in the airbox) because anything more does nothing. I think it's like 4 pounds of pressure or something. In this type of instance a pressurised "air box" or air scoop has the Carberators mounted inside the air box. This creats Air pressure and fuel pressure. Kinda like supercharging. But only like 4 pounds
03-14-2014, 09:28 AM
#48
Registered
iTrader: (3)
Al these numbers are swell but a N A motor can only make so much pressure without being supercharged. take for inistance a pro stock Car. They have this huge air scoop and the thing has like a 6 in hole in the front. The biggeer the " air box" the more volume and increase in flow. it does not make boost . It can only take a few pounds of pressure ( in the airbox) because anything more does nothing. I think it's like 4 pounds of pressure or something. In this type of instance a pressurised "air box" or air scoop has the Carberators mounted inside the air box. This creats Air pressure and fuel pressure. Kinda like supercharging. But only like 4 pounds
03-14-2014, 11:27 AM
#49
Registered
Its pretty simple. You can just ram air. (Like my v drive was) or you can ram fuel and air. By having the carburators in the airbox (see pic) it creates fuel and air pressure not just air pressure. A forced flow where the more volume in the air box is better. Once a ceartain amount of air pressure is achieved ( by going fast and pressurising it) the n a engine will not take more pressure than say the 4 pounds or whatever the number is. I think thats why porting is so improtant on n a engines. So no vortexes ir anything else interfears with that small amount of oressure.
03-14-2014, 12:09 PM
#50
Registered
Refering to the above few posts only, I don't want to derail this thread, but on a N/A motor you can exceed 100% cyl filling/ volume qiuckest by choosing the right valve event timing matched with a free flowing exhaust header to scavange the the spent fumes and at higher RPMs get better volumetric effecincy. (this is taking for granted the intake side is up to snuff). No need to hold the exhaust valve open so long in a boosted motor as the boost pressure will assist in exhausting the cyl. at the same time you don't want to blow raw mixture out either. each motor motor will require it's own combination.
Now back to the regularly programmed discussion. FWIW.
Now back to the regularly programmed discussion. FWIW.
