J's 82

Hello all,

looking at different posts and different flow numbers and was curious about the effect of intake flow numbers vs. exhaust flow numbers..

It seems a lot of folks have heads that gain a tremendous amount of flow on the intake but the exhaust gains a relatively small amount by comparison..

The question is this.. is it possible to outflow your exhaust port with too much intake flow? What would the better head be one with better intake values with so/so exhaust or a head with slightly lower intake values but with better exhaust values?

Now I know exhaust will never match intake for flow but I am interested in how these numbers interact..

thanks!

car_ramrod

I know that the LT1 heads have pretty bad exhaust flow characteristics. thats why our cars like cams with a lot more exhaust duration vs intake duration than say the LS series which has way better flowing heads. Back to your question, i know that theres an optimum ratio of intake to exhaust head flow, and if im remembering correctly for a NA engine you want your exhaust to flow 75% of what your intake does. Also you have to keep in mind the different flow bench methods that manufacturers use to obtain their numbers (i.e. using a pipe on the exhaust port to produce better numbers) hope this helps

CR

Fastbird93

It seems to be that the better your exhaust numbers, the better your overall numbers are going to be. The LT1 likes exhaust flow.

Ai

The LT1 is just SBC stuff.. and IMO on NA stuff, some of these silly 80% E/I ports aren't such a great idea. Luckily, most of the people claiming inordinately high exhaust numbers, aren't really making them. On the sets I've flow tested anyway

74-75% is nice & what most people think its optimum for NA stuff. Most of my stuff will be around that & slowly tapering to closer to 72% or around there depending on the casting etc. Small ports run well on the street & if I don't need a billion cfm to meet the power goal, great .

Perry93TransAm

I have heard the 75 % rule as well but was wondering how much water that held. Isnt velocity more important on exhaust and not the actual volume ??

J's 82

thanks for all the input! There is a method behind the madness of my question.. I plan on being a guinea pig for the edelbrock heads (in the interest of science of course).. I noticed on there website the intake numbers are shallow but the exhaust numbers were pretty good..

Needless to say I plan on taking them to a flowbench and getting the numbers.. If I don't like what I see out of the box a bit of porting may be in order.. I will make sure to post pics of them..

eventually bumping the heads around will be a XE 224/230 cam and off to the dyno.. I'll post some numbers on that too..

thanks again!

BradZ28

I seen someone in another post that had gotten flow numbers like 275int and 245ex from a respected shop. Pretty wild compared to most on the exaust side.....

Fastbird93

That HAD to have been flowed with a pipe.