kdrolt

This one gets rehashed over and over --- "How much air does a TBI flow?"

Here's one link, of many, on the CF (Crossfire) Vault that have measured data. You can search there for the others.
The key points you need to remember is that Crossfire engines (LU-5 305 on 82-83 Fcars; L-83 350 on 82 and 84 Vettes) have two separate near-identical single-bore throttle bodies. The injectors on these are the same type used on TBI Fcars (a CF Fcar is a TBI Fcar) but they usually have slightly mismatched pairs (64 and 66 lb/hr used on the Vettes for example) for reasons I won;t mention here.

The single bore on each TB is identical in inside-diameter (42.8 mm or 1 and 11/16 inches) to the ones used on the dual-bore TBI used on 305/350 on F and Bcars of later model years (1989+). So the flow data from the below link is applicable to the dual TB units used here. CF engines use two single-bore (or single-venturi) TBs, and the single TB used on 1989+ Fcars is a has dual-bores. Systemwise, the cross sectional (flow) area is the same for both.

http://www.crossfire.homeip.net:81/c...hrottle+Bodies

Other useful points -- Vette owners modify their TBs to larger bore diameters to get more airflow, and some of them are area-wise the same as the 454 TBI unit. The so-called ultimate TBI mods don't have to be performed to the same degree on CF TB units because the casting already has the right entry shape. Look at TBI pix of a CF TB, compare it to a 2v Fcar TB unit, and you'll see why.

Read and search for more info on the CF Vault if you want more. Don't ask me -- I'm just the messenger.

kdrolt

Addendum to this post, and summarized from looking over several posts at the CF Vault:

Stock single bore TB (42.8 mm or 1.68" inside diam bore)
one injector tower gasket @13.6"
285 CFM (each), 570 CFM together.

Stock single bore TB (42.8 mm or 1.68" inside diam bore)
two injector tower gaskets @13.6"
286 CFM (each), 572 CFM together.
This one, 572 CFM together, is the closest to a stock Fcar 2bore TBI

Stock TB, injector tower REMOVED for study @13.6" - 288 CFM (each) total, 576 CFM together.

stock single bore TB bored to 2" inside diam
two injector tower gaskets @13.6"
333 CFM (each), 666 CFM together.

stock single bore TB bored to 2.130" inside diam
two injector tower gaskets @13.6"
379 CFM (each), 758 CFM together.

Holley dual bore 2" inside diam TB
670 cfm (their rating, unknown depression)

Notes

1. the extra injector tower gasket (stacking them vertically to raise the injectors) makes a slight difference on the 2" and 2.13 TBs, but makes almost no difference in airflow on the stock-size TB's. You'll have to find the orig posts on the CF Vault to see the before/after comparo of single v double gaskets.

2. Removing the injector tower means removing both the injectors and the injector mounting. There is almost no difference in airflow, so the injectors/tower really don't impede the airflow at all, contrary to what's often seen on TGO.

So the above measurements refute a mythical "improvements" made by TGO TBI owners: raising the injector to increase airflow past the injector.

To compare other depressions (aka the pressure differential across the TB when it was flowed):

new_flow = old_flow*sqrt(newdp/olddp)

where newdp and olddp are the new and old depressions (depression is the height of the column of water used in the test manometer). Depression is a form of a pressure measurement, rather than a vacuum measurement -- so take care not to mix units of pressure and vacuum.

Lastly, more depression means more pressure difference and hence greater flow. The above equation is an approximation along a flow streamline, so it's useful but it's not perfect. HTH.

---

EDIT: See also

TBI AirFlow - FULLSIZEforums - Chevy Truck

va454ss

iTrader: (1)

So, based on the above flow numbers, one could assume a dual bore TB with a 2.2 bore size would flow >800 cfm?

Lionsden

They might look something like this.

seanof30306

iTrader: (4)

are those flow numbers at 3"HG or 1.5" HG?

kdrolt

Neither.

Each data point in the 2nd post above says "... at 13.6", which means measured steady-state at pressure difference equal to 13.6 inches vertical column height of water.

If I did the math right, 13.6" water equates to 0.99 inches of mercury (Hg), which is slightly less pressure testing differential than when testing at 1.5" Hg, so I would expect the airflow values to all be slightly higher if they were corrected for flow at 1.5" Hg. Use the equation listed in the earlier post to find the correction.