Hi ! Here are my flow calculation for some LSJ engine parts :

ADDED COMMENT : These flow numbers are calculated at ambiant air temperature AND pressure.

Stock Throttle Body (67 mm) : 625 CFM.
EDITED : Stock Head : One intake port : 250 CFM @ stock 0,395" valve lift. One exhaust port : 145 CFM @ stock 0,395" valve lift. Stock head is said by GM to be efficient up to 275 WHP; it is clearly possible to make more WHP than that, but in a unefficient way (several HP losses caused by heat and restriction).
Stock Exhaust manifold ("Header") : 425 CFM.
Stock Downipe (DP) with cat : Plus or minus 370 CFM or less.
Stock Cat-back Exhaust (2,5" inlet to 2,25" outlet with stock muffler) : 300 CFM.

Now here are some replacement parts :

GMPP Exhaust manifold ("Header") : (30 more CFM than stock) : 455 CFM.
Shorty or long tube Header with 1,75" primaries and 2,5" outlet : at least 500 CFM.
Shorty or long tube Header with 1,75" primaries and 3" outlet : at least 725 CFM.
Shorty header with 1,5" primaries and 2" outlet : Waay not enough, who cares LOL.

Stock DP w/o cat : 425 CFM.
2,5" DP with VERY HIGH FLOW cat : plus or minus 450 CFM.
2,5" DP w/o cat : 500 CFM.
2,75" DP with VERY HIGH FLOW cat : plus or minus 475 CFM.
2,75" DP w/o cat : 600 CFM.
3" DP with VERY HIGH FLOW cat : plus or minus 500 CFM.
3" DP w/o cat : 725 CFM.

Stock catback with only the rear muffler replaced (the last portion is still in 2,25" tubing) : 350 CFM.
Stock catback with last portion replaced for 2,5" tubing and straight through muffler : 450 CFM.
2,5" catback : From 450 to 500 CFM (must be a straight through muffler).
2,75" catback : From 550 to 600 CFM (must be a straight through muffler).
3" catback : From 650 to 725 CFM (must be a straight through muffler).

Hope this can help ...

Regards )

 

you kick ass.

that is all

 

wow thats awesome thanks

+1 rep

 

Great info!!

 

Very nice...
Now lets account for some BOOST!

 

WOW! Nice info! How did you get all that?

 

I'm going to assume that he used basic flow dynamic calculations....
Pretty time consuming if your doing it by hand....

 

whats the stock intake manifold flow?

just out of curiousity

 

The stock intake manifold flow is more limited by the air filter itself, but i dunno what's that flow ...

 

hmmm, good point. i'll dig something up

 

good info indeed

 

good job man

 

If you were to factor out the air filter, and even an intake....what would be the upper limit of air flow thro the intake manifold? I assume as this point the lamnova(sp?) cores themselves become the restriction....

shoot me a number or at least an educated guess....

and yea....wicked awesome post!

 

+1 for this one.

 

k&n number ru-4990

for those of us who have a k&n intake system

some quick specs.
Base Outside Diameter: 6 in (152 mm)
Flange Inside Diameter: 3 in (76 mm)
Flange Length: 1.875 in (48 mm)
Flange Type: Centered
Height: 5.563 in (141 mm)
Top Outside Diameter: 5 in (127 mm)


i'll give k&n a call tomorrow see if i can't dig up some cfm info on these little guys

 

Great Job

 

EVERY part of my exhaust system flows 725 CFM

 

what header?

 

I'm pretty damn sure that this K&N filter flows way more itself than the stock airbox. But i was talking more about the stock air filter cfm, which is so dense and packed.

 

great job , good info man

 

ahhhhhhhhh, now i see
kudo's good sir!

 

jmc007, just noticed one thing, how does the stock manifold (1.75" D shaped outlet, flow equal to the 2" catless downpipe?

https://www.zzperformance.com/products_img/543_3.jpg

Just wondering...............

 

Awsome in fo man. Nice find.

 

If you look at the caliper on the picture, it doesn't seem to touch on both sides. Also, the manifold collector isn't long, so it's less rectrictive than a long downpipe of the "same" diameter.

 

This info really needs to be sticky'd.

There are lot of misconceptions about the LSJ exhaust that could be cleared up with this thread.