darnie

iTrader: (1)

I was jw whats the difference when you have heads ported with having a bigger intake, or exhaust number.

take for example prc 5.3 stage 2.5 heads

Lift Intake Flow Exhaust Flow
.200" 147 cfm 111 cfm
.300" 206 cfm 145 cfm
.400" 254 cfm 185 cfm
.500" 291 cfm 204 cfm
.600" 312 cfm 223 cfm

vs say

http://www.airflowresearch.com/image...bc/220ccCP.gif

vs heres a shot of mine


now i know you can change the CC to increase or decrease compression. i also know that the runners make a good deal but dont quite understand it.

so basically if you had 2 heads same cc's same runners, but say 15-20 diff cfm on say the intake and or exhaust does it just come down to what cam you would run to see the best results? Jw

darnie

iTrader: (1)

so i been reading the past few hours, and ive gotten the concept of the intake runners, basically smaller runners for street apps and bigger runners for high end screamers and Big blocks? now i know say a 59cc will bump the compression up over a 62cc motor witch is good on a NA motor correct?

Now what im still stumped on is the over all flow numbers. and how to properly read the chart. like in my chart i have a .551 lift so is that the only number i should worry about?

whitedakota

iTrader: (1)

Sub'd. I'd like to know this info myself. I'm about to head and cam my truck very soon.

Gadgetized

iTrader: (9)

This is one of those areas that will be a debate until the end of time. It will come down to a personal prefference more than anything. Flow numbers are subject to dispute as they have been accused of being inflated. Every head manufacturer wants to sell their product, and a higher flow number looks more attractive. You need to look at your combo, and see what will benefit you the most. You need to determine your mods, cam, desired RPM's, your bore size, intake system, exhaust, vehicle weight, and desired use(there are more involved than that, but those are a few main ones in my book). Some people suggest a smaller runner as it will increase the air speed, making an engine more street friendly. Some people like a larger runner as it will help with higher RPM's. Some people like a high number at max lift, and others only look at mid numbers as your cam is only at peak lift very briefly. Explain more what you are looking for out of an engine.

amanuel

Subd
m here to learn as well:p

Gadgetized

iTrader: (9)

The bore is important because if the valve is so large it can not flow if it is too close to the cylindewr wall. The flow numbers you posted are on a stanrard LS1 bore of 3.900", but those numbers might go down drastically if that head was placed on a stock 3.78" 5.3 bore. Here is a pic of a stock 5.3 bore with a 2.02/1.57 head. You can see how close the valves are to the cylinder.


Here are the same sized valves in a 6.0 4.00" bore.

Here is some rough grinding of the chambers to help the outside of the valves flow better in the 6.0 4.00" bore.

Gadgetized

iTrader: (9)

Hopefully some of the sponsors will chime in here as they have a vast knowledge and hands on experience with this stuff. What are the sizes of your valves?

darnie

iTrader: (1)

ya im just interested, i was lucky and got my heads and intake manifold custom built to my cam from a friend of a friend and he did a really clean job. personally i dont think ill switch the set up im running just in for the info incase i need it. i got over a dozen buddies with trucks that are wanting to do small stuff and one or 2 that may do heads and cam just wondering so if they have questions i know more of what im talking about thanks for the help guys... and dont be afraid to thread jack it its a open ended question.

smokeshow

iTrader: (16)

Lol Gadget, people will debate about it because most truly don't understand it. Something as quantifiable as an engine isn't subject to opinion unless there is a lack of knowledge on the topic.

darnie

iTrader: (1)

well i got 2 open ears.....