Comparing Heads

[louisb]

So you have the flow numbers for two different heads. How do you compare the two? What do you look for? How does the cam play into the comparison? Any thoughts?

Edit: also, if you have the intake and exhaust flow numbers for a set of heads, isn't there a target ratio you are looking for between the two?

Thanks,

--louis

[Bruce]

Look at the mid lift numbers.  A head that has higher mid lift numbers (and lower peak flow) will make more hp than another head with lower mid lift numbers (and higher peak flow numbers.)

Then look at the port volume.  Two heads that have the same flow numbers, the one with the smaller port will have higher air speed, and will make more hp.

Exh/Intake flow ratios are meaningless.

[drgouk]

Look at the mid lift numbers.  A head that has higher mid lift numbers (and lower peak flow) will make more hp than another head with lower mid lift numbers (and higher peak flow numbers.)

Then look at the port volume.  Two heads that have the same flow numbers, the one with the smaller port will have higher air speed, and will make more hp.

Exh/Intake flow ratios are meaningless.

Why are intake/exhaust ratios meaningless? Please explain.

 

[louisb]

Look at the mid lift numbers.  A head that has higher mid lift numbers (and lower peak flow) will make more hp than another head with lower mid lift numbers (and higher peak flow numbers.)

Then look at the port volume.  Two heads that have the same flow numbers, the one with the smaller port will have higher air speed, and will make more hp.

Exh/Intake flow ratios are meaningless.

Thanks Bruce for the info.

--louis

[louisb]

What brought this question on is I am comparing the CNC heads from DRD with the CNC heads from CB.

Flow Numbers for the three heads I am comparing:

CB Wedge ports:

Lift	CB Wedge ports:	DRD L6	DRD L7
.100	52	63	56
.150	79.2	84	80
.200	105	106	100
.250	128	120	122
.300	147	136	141
.350	165	152	169
.400	176.7	163	172
.450	186	173	185
.500	193	183	198
.550	198	195	206
.600	201.5	201	211
.650	204.6	204	214

I am planning to use this cam w/ 1.4 ratio rockers:

Cam:
FK-45
.561" lift
295 deg Advertised Duration
.401" Cam Lift
263 deg Duration @ .050
RPM range for this cam is 2000 - 6500.
Engine is a 2 liter w/ IDAs & 1 3/4 exhaust. 

So anything above .561 lift in the flow chart has no value right?  By mid lift I assume you mean from around .250 - .450ish? So from these numbers the choice would be between the DRD L6 and the CB wedge ports. With the Wedge ports making more power higher in the rpm range and the L6 being better at lower RPMs? Or am I miss reading that? Just trying to see how this all works together.

Thanks,

--louis

[drgouk]

Look at the mid lift numbers.  A head that has higher mid lift numbers (and lower peak flow) will make more hp than another head with lower mid lift numbers (and higher peak flow numbers.)

Then look at the port volume.  Two heads that have the same flow numbers, the one with the smaller port will have higher air speed, and will make more hp.

Exh/Intake flow ratios are meaningless.

Bruce?

[K-Roc]

I/E ratios....

Far better to look at Velocities and Cross sectional areas on an exhaust port than Raw flow numbers,  There is no way to compare intake flow numbers that are basically ambient temeratures and atmsospheric pressure to The Super high combustion temperatures and pressure on the blow down of an exhaust stroke....
To design an exhaust port you need to pay very close attention cross sectional areas and to the velocities at the short turn and the exit of the port, And also just as important you need Zero turbulence,

To answer the question above you can not compare those flow numbers at all because they were not flowed on the same bench.
The shape of a chamber can also greatly influence the way flow numbers come out but not nessicarily mean more power to the wheels...
You would neet to Flow both heads on the same bench, measure the port Volumes to compare and also measure the velocity gradients of the 2 heads for just a start. Even after all that it's still going to as clear as mud.

K-Roc,

[louisb]

Thanks K-Roc, I kind of figured that. Its like comparing dyno numbers from two different engines on two different dynos. For such an expensive part of the motor, it sure is a pita to figure out what to buy.

--louis

[drgouk]

Thanks Darren for the info, now Bruce? 

I/E ratio's are just another part of the puzzle, To head you in the right direction in my experience, You just to know what is ideal first, That is what the Dyno is for. And ultimately the track.

[Bruce]

There are plenty of head porters that ignore the E/I ratios, and their heads make great hp.  Here's an example.  Alan Uyeno's heads push his full steel, pump gas street car in to the 11s, yet has an E/I ratio that is all "wrong". 
When the end result violates the rule, the rule is flawed.

[drgouk]

There are plenty of head porters that ignore the E/I ratios, and their heads make great hp.  Here's an example.  Alan Uyeno's heads push his full steel, pump gas street car in to the 11s, yet has an E/I ratio that is all "wrong". 
When the end result violates the rule, the rule is flawed.

 i/e ratio is right, Just wrong compared to what most people think is right. So i/e ratios can be used to compare heads, but not soley. And you need to now what the ideal ratio is.

[Bruce]

....you need to now what the ideal ratio is.

So what is the ideal E/I ratio?

[drgouk]

According to your above post you already know, What is an i/e ratio that is all out of wack?

[Bruce]

I know that there is no such thing as a perfect E/I ratio.  I want to know what you think is a perfect E/I ratio.  After all, you proclaimed there was an "ideal" ratio.

[drgouk]

Bruce, Why would i want to tell you that?? As i said  above it is part of the puzzle, There is not a blanket I/e Ratio, High rpm engine? Low Rpm? Nos? Turbo? Cam?? etc My point Is that it is not MEALINGLESS if you know what your looking for and you have done the research on a dyno.

[Bruce]

..., There is not a blanket I/e Ratio, .....

So now there's no such thing as an ideal E/I ratio?

[drgouk]

..., There is not a blanket I/e Ratio, .....

So now there's no such thing as an ideal E/I ratio?

Yes  there is an ideal I/e ratio, Its the one that makes the most power! All i was saying that its not say 90% for every engine, It is based on what application, And whats going in the engine.

[dougmische]

Pie are squared

But most pie are round.

[louisb]

I like pie. 

--louis

[Fastbrit]

Pie are squared

But most pie are round.

Aha! Zee old mathematician's joke, ja?  )

[team97]

Pie are squared

But most pie are round.

Aha! Zee old mathematician's joke, ja?  )

Pie are round, corn bread are square

Glenn

[Fastbrit]

Pie are squared

But most pie are round.

Aha! Zee old mathematician's joke, ja?  )

Pie are round, corn bread are square

Glenn

Hey Glenn– quite posting, get writing!  )

[louisb]

Pie are squared

But most pie are round.

Aha! Zee old mathematician's joke, ja?  )

So a mathematician, an engineer and a computer scientist were out for a walk one hot and dry day when they happened upon an ice chest full bottles of cold (warm?)  beer. But none of them had a bottle opener. The engineer when back to his lab and designed the perfect bottle opener made of pure titanium. The computer scientist went back to his lab and wrote this elaborate software program that would instruct a machine to open the beer bottles. So the engineer and the computer scientist returned to the location of the ice chest only to find the mathematician finishing the last of the beer. Wondering how he got the bottles open they asked him. His reply was "I just assumed they were open and thus it was true".

A little, bad, mathematical humor. 

--louis

[Bill Schwimmer]

Pie are squared

But most pie are round.

Aha! Zee old mathematician's joke, ja?  )

Pie are round, corn bread are square

Glenn

Hey Glenn– quite posting, get writing!  )

The story of the California Look VW " – coming your way SOON!
  As soon as Gaskey spills the beans on our misspent youth...  sorry is this a thread hijack??

[Fastbrit]

The story of the California Look VW " – coming your way SOON!
  As soon as Gaskey spills the beans on our misspent youth...  sorry is this a thread hijack??

Go ahead and hijack all you want, Bill. I've already got enough to put Doug Mische behind bars, so he'll need you guys to keep him company in the penitentiary…! )

[Rennsurfer]

Crikey! Math sucks and makes my tiny brain hurt... can we please talk about something worthwhile, like sushi, Cal Look books, or Mexican food?

Gaskey, are YOU the reason we're waiting for the book?

 

Speak now or forever hold your piece. I mean, peace.