Yellow Bullet Forums banner

1 - 20 of 22 Posts

·
Registered
Joined
·
632 Posts
Discussion Starter #1
Low and mid lift no`s more important than max flow at max lift?
this is were the valve`s are at more than max lift.
any thought`s or theories on this.
I know we have a lot of excellent builders on the bullet ,and i`m excited to hear some of there replys. also lots of knowledgeable
Racers.......THANKS GUYS!!!!!!!!!
Trying to decide on if i should have my heads ported more or not..
My low and mid lift no`s are a little low compared to some cnc ported heads But my max flow no`s at .700 lift are with in a few CFM.. Sorry so long of post guys !!! :rolleyes:
 

·
Registered
Joined
·
1,781 Posts
With mild/lazy lobes yes, in aggressive lobes not as much.
 

·
Registered
Joined
·
1,123 Posts
What is low lift and mid lift to you? defining by cam profile, lift or L/D?

The valve will only see max lift one time but sees every other point exactly twice. You need to see what the piston and both valves are doing at every point through the four cycles to really decide what's best.
 

·
Registered
Joined
·
4,182 Posts
No. I think a flow curve is important based on the build. Max lift might be .600, the valve will be at .600 one time, Yes.
But it will be at .590 twice and some cam profiles will hold the valve open longer at different parts of the flow curve.
Ramp speed, Duration, Cam timing events, Tuned(wave)length and other things will effect how the engine can use air it recieves.
Average flow and Profile can change perfromance.
Someone could evaluate your heads and see what & where they might need improved. (Valve job, Thoat sizing,Port profile size shape)....

Whats the combo? Maybe post the flow numbers, this might help.
 

·
Registered
Joined
·
4,798 Posts
first thing I always look at is cam timing in relationship to crank degrees or piston position, ..
flow curve should take the pressure differential into consideration related to piston speed.

curtis
 

·
Registered
Joined
·
1,630 Posts
I want it to flow everywhere but I am not to worried if it doesn't flow good at .1 and .2.

Another thing, if those other heads cnc ported heads were not flowed on the same bench as yours were flowed on then I wouldn't trust their advertised numbers. I have seen many cnc heads that flowed 20cfm less on my bench than what they claim.
 

·
Registered
Joined
·
632 Posts
Discussion Starter #8 (Edited)
Wow guys !!! Told ya u guys are sharp !! All good points.
Ok some specs . When I had the cam ground gave them flow
Chart. Built cam from there. Cam 264/[email protected] lift .686
110 LS installed @106IC 357 CIDw 10:00 to 1 comp
NOS 250-300HP head flow 28" no piPe on exh.197cc run.
[email protected] [email protected]
Exh [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected]
Ok hope that helps.
 

·
Registered
Joined
·
1,347 Posts
Like Curtis said, your heads don't just see 28" pulling on them, its way more dynamic in a running engine, while I don't have the answers, I have my theories on what matters at what lifts I cannot duplicate it on my flow bench.
 

·
Registered
Joined
·
7,911 Posts
Personally I think there is more important things to worry about than low flow. I care more about the characteristics of the port, like if it stalls, if it's windy, if it's choked... A good cam guy will make you power regardless of flow curve.

For me depending on max lift will help dictate the flow curve. A valve job will change things real quick! You can take a port that moves air all the way too 1.200 and kill it with the wrong angles..

I have several engine builders who want to do their own machine work, which is cool.. I understand. However, I won't give away my custom cutters, so I have taken the time to design the ports around shelf style angles. Is the custom better, HELLYA!
 

·
Registered
Joined
·
55,847 Posts
Wow guys !!! Told ya u guys are sharp !! All good points.
Ok some specs . When I had the cam ground gave them flow
Chart. Built cam from there. Cam 264/[email protected] lift .686
110 LS installed @106IC 357 CIDw 10:00 to 1 comp
NOS 250-300HP head flow 28" no piPe on exh.197cc run.
[email protected] [email protected]
Exh [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected]
Ok hope that helps.
I would look to raising compression before working the heads.
 

·
Registered
Joined
·
14,768 Posts
Another thing to consider is overlap and piston design.
Some of my thoughts:
If the cam only has .650 lift, the lower lift #'s represent a large percentage of total available lift and IMO are important. When the cam has 1.0" or more lift, the lower lift #'s represent a smaller percentage of total lift and are less important and upper lift flow is going to be the focus. I think it's always important to get as much air moving as soon, and as quickly as possible but not at the expense of total airflow if that's what you need. If the heads are big and you have a lazy port, you need to get that air moving...if the port is efficient and sized correctly I don't think it's as critical. A "good" port will certainly make a cam designer's job a lot easier.
 

·
Registered
Joined
·
14,768 Posts
Low and mid lift no`s more important than max flow at max lift?
this is were the valve`s are at more than max lift.
any thought`s or theories on this.
I know we have a lot of excellent builders on the bullet ,and i`m excited to hear some of there replys. also lots of knowledgeable
Racers.......THANKS GUYS!!!!!!!!!
Trying to decide on if i should have my heads ported more or not..
My low and mid lift no`s are a little low compared to some cnc ported heads But my max flow no`s at .700 lift are with in a few CFM.. Sorry so long of post guys !!! :rolleyes:
When you look at acceleration rates you'll find the valve goes right through these areas of the lobe pretty quickly, and some lobes a lot quicker than others.
 

·
Registered
Joined
·
20,824 Posts
Wow guys !!! Told ya u guys are sharp !! All good points.
Ok some specs . When I had the cam ground gave them flow
Chart. Built cam from there. Cam 264/[email protected] lift .686
110 LS installed @106IC 357 CIDw 10:00 to 1 comp
NOS 250-300HP head flow 28" no piPe on exh.197cc run.
[email protected] [email protected]
Exh [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected] [email protected]
[email protected]
Ok hope that helps.
You will need to make up your mind N/A or spray.
 

·
Registered
Joined
·
2,294 Posts
i would think average flow, and a cam lobe designed to take advantage of that would be real important, as for a cam seeing max lift once, thats a given, the cam should see max flow twice....in my opinion i would think a head that averages, lets say 200 cfm, with a peak of 275 would make more power then a head with 300 cfm peak, and an average flow of 175, given all other factors were proper, ie velocity, lobe design...but i could be wrong
 

·
Registered
Joined
·
461 Posts
It all depends on how you define that very ambiguous term, " Low Lift".

Low lift as far as I am concerned is the lowest 25% of the NET valve lift and I really give a tinkers damn what it doing down there. All your doing down there is relying on the dynamics of Positive and negative wave formation to clean the chamber out before the real air speed / piston speed action starts taking place in the port.

Other than the lowest 25% of net lift the port should flow great EVERYWHERE, not stall out, go backwards, get turbulent or loud. I do not accent flow curves up or down dependent on cam profile unless its a 4 or 5 valve head then everything changes.
 

·
Registered
Joined
·
20,824 Posts
The question was asked here once before so I cut and paste what Curtis had to say then.

HOW IMPORTANT ARE LOW LIFT FLOW NUMBERS, .200 .300 .400.. DO THESE NUMBERS REALLY MATTER TO MUCH
OR SHOULD WE BE MORE CONCERNED WITH THE NUMBERS ABOVE .300 TO .400
__________________

Answer given:

The subject is a complex one, ..

The first thing I looked at regarding the flow curve is the piston speed, .. and where in the lift to piston relationship has the highest demand on the cylinder head. We are dealing with a pressure differential that is dynamic, .. it changes at different
areas of the valve lift so it should change as well.

The lower lift is even more complex then that, .. on really efficient cylinder heads lowlift flow can have cross flow out the exhuast during overlap, or reversion back up the intake, .. and more. So typically you'll see the .100"-.200" lift numbers killed off a little, ..

Then, .. during the high demand areas where the cylinder is really asking to be filled, .. .600"-.800", .. ( greatly depends on engine combo and cam )
the head should be the most efficient. That doesn't necessarily mean the biggest raw cfm number from a bullshit bench, .. but the most efficient in it's velocity profile for what you're tying to accomplish.

So the short answer is ALL numbers matter, .. the entire curve needs to to designed to the application.
The second answer is as always, there's a BUNCH more to making power and being fast on a race track then just CFM numbers.

Hope this helped, ..

Curtis
__________________
Race Flow Development
5 Axis CnC porting.
http://www.raceflowdevelopment.com


I post this just so the understanding of buying a CNC head means its what you need, OR BUYING A BIG FLOW NUMBER HEAD THINK TWICE
 

·
Registered
Joined
·
632 Posts
Discussion Starter #19
special thanks to Chad,Curtis and Darin for your input.
and all the racers that replied . :) Have a great weekend!!!!
 

·
Registered
Joined
·
1,229 Posts
The question was asked here once before so I cut and paste what Curtis had to say then.

HOW IMPORTANT ARE LOW LIFT FLOW NUMBERS, .200 .300 .400.. DO THESE NUMBERS REALLY MATTER TO MUCH
OR SHOULD WE BE MORE CONCERNED WITH THE NUMBERS ABOVE .300 TO .400
__________________

Answer given:

The subject is a complex one, ..

The first thing I looked at regarding the flow curve is the piston speed, .. and where in the lift to piston relationship has the highest demand on the cylinder head. We are dealing with a pressure differential that is dynamic, .. it changes at different
areas of the valve lift so it should change as well.

The lower lift is even more complex then that, .. on really efficient cylinder heads lowlift flow can have cross flow out the exhuast during overlap, or reversion back up the intake, .. and more. So typically you'll see the .100"-.200" lift numbers killed off a little, ..

Then, .. during the high demand areas where the cylinder is really asking to be filled, .. .600"-.800", .. ( greatly depends on engine combo and cam )
the head should be the most efficient. That doesn't necessarily mean the biggest raw cfm number from a bullshit bench, .. but the most efficient in it's velocity profile for what you're tying to accomplish.

So the short answer is ALL numbers matter, .. the entire curve needs to to designed to the application.
The second answer is as always, there's a BUNCH more to making power and being fast on a race track then just CFM numbers.

Hope this helped, ..

Curtis
__________________
Race Flow Development
5 Axis CnC porting.
http://www.raceflowdevelopment.com


I post this just so the understanding of buying a CNC head means its what you need, OR BUYING A BIG FLOW NUMBER HEAD THINK TWICE

what we have been doin in the class racing world is concentrating on how fast we can get the air in there, not worried about how much?? Also different angles on the valve jobs too...bla bla bla bla...I'll hush now....lol
 
1 - 20 of 22 Posts
Top