SBC GM FAST BURN HEADS

[BOSSMAN]

I just got in a used pair of GM Fast Burn heads. These are what they use on the ZZ383 crate engine. They are advertised as:

210cc Intake ports - raised .240
78cc Exhaust ports - raised .200 D Ports
62cc Chambers with .400 thick decks
2.00 / 1.55 lightweight valves
I plan on doing a baseline flow test as stock (for out of box performance) and then have my way with them. They are very similar to the LT1 heads that I just got done porting for Wes. They have similar chambers and intake ports (after portwork). I also have the Eliminator Vortec Single Plane Intake that is used with these heads. It's basically an Edelbrock Super Victor Intake. I'm using this stuff for another project.

[BOSSMAN]

Baseline flow on the heads in out of box shape using 4.030 bore and #1206 radius plate (not port matched).
LIFT INTAKE CFM
.100 - 63.93
.150 - 100.33
.200 - 133.69
.250 - 164.20
.300 - 191.46
.350 - 215.47
.400 - 234.94
.450 - 250.51
.500 - 265.79
And anything after .500 lift it falls flat on its face . Very typical for a head like this. The valves that come in these heads are the LT4 sodium filled steams (lightweight valves) and have a 30 degree backcut from the factory. Amazing to see GM finally catching on. I'm shooting for around 290-295 cfm with minimal work but see what happens. I will check the exhaust side at a later date.

[BOSSMAN]

Stock chamber pic:

Custom Valve job now done to these heads. They are now cut for a 2.02 / 1.60 valves, done with a custom intake cutter and a full radius exhaust seat. Also started the chamber work and did the bowl cuts in these pics. I plan to reflow the head just to see what the valve job and a bigger valve size is worth.


Shortened the guides to the casting for the port work soon to begin:

[BOSSMAN]

Flow numbers after Custom Valve Job (listed above) with a backcut on the Intake valve.

LIFT / BASELINE / INTAKE CFM
.100 -- 63.93 -- 71.53
.150 - 100.33 - 111.09
.200 - 133.69 - 147.97
.250 - 164.20 - 167.44
.300 - 191.46 - 191.46
.350 - 215.47 - 214.07
.400 - 234.94 - 235.59
.450 - 250.51 - 253.76
.500 - 265.79 - 269.87
.550 - 257.61 - 280.10
.600 - 253.52 - 258.63

Some good gains from the Valve Job and .020 larger valve with a backcut. This is without any port work yet!