vbls

iTrader: (17)

ok i sold my Weiand aluminum intake, it has 27mm runners on it,
i bought the FAST 92, i measured them and they are only at 24mm, even my heads are at about 25mm. why is this? shouldnt they be bigger? should i get the fast ported? and if i do, will the runners be opened up?

gMAG

iTrader: (1)

It might have more to do with velocity and runner shape (producing volume), than it does size.
I don't know for sure, just my 3 cents.

01ssreda4

iTrader: (96)

Bigger is not always better when it comes to airflow.

trans_am7935

iTrader: (15)

this is what GM thought as well, which is why the Cathedral port heads were all based on high velocity vs pure volume. this is what allows the LS motors to get such great gas mileage. also if you can get the port velocity up, then you can shove the same amount of air in there then with a big port low velocity port.

bww3588

iTrader: (49)

Port velocity is where it's at. Higher velocity allows more air in over a given duration of valve off seat time. This allows for smaller cams to make more power.

jlcustomz

Also i,m prettysure the runners taper to progressively larger away from heads & have a bellmouth inlet to shove more air in .
I,m currently looking intothis subject as i,m planning on making my own intake.

vbls

iTrader: (17)

so porting wouldnt make much more difference without the heads being ported as well

trans_am7935

iTrader: (15)

this is true to an extent. the FAST 90/92 intakes start to fall off after about 270-275cfm, and if you have heads that flow better then that, then porting will benefit them. but yes on an LS1 the FAST intake on ported heads is usually the restriction. porting could bring the stability up to 285-290 or so

vbls

iTrader: (17)

ok i have stock heads, so ill wait on the porting

trans_am7935

iTrader: (15)

you will actully see a loss of power down low, or at least a little lack in throttle response under 2000rpm with a FAST and stock heads/cam, i did