|Porting (hacking) a cross-fire manifold...|
Supposedly, a good porting job on a cross-fire manifold is worth a 1/2 second e.t. on the 350 vettes...|
Porting the manifold on the stock 305 shortblock and adding a 2100 stall torque converter cut .35 off my e.t....from 15.75 to 15.4...
UPDATE! - See the bottom of the article for the mistake I made - PAY ATTENTION!
|Stock cross-fire intake manifold from 84 vette...before and after the first day of hacking
|Slight runner inlet modifications :) We used a die grinder and bits made for aluminum (they don't get caked up with the metal)...
|little ports...BIG PORTS...We matched to a felpro gasket...
|After sandblasting...of course, after I installed it, someone said I should have
removed the heat shield to make sure there was no trapped particles...oops...
Note the EGR block off plate...
|SWAPPING THE INTAKES...|
1) Disconnect battery
2) Drain coolant
3) Move alternator out of the way, and remove bracket that attaches to manifold
4) Remove A/C support brace that attaches to manifold
5) Remove upper radiator hose
6) Remove heater hoses
7) Disconnect vacuum hoses from intake and throttle bodies (labeling them is a good idea!)
8) Disconnect all wiring for EGR, IACs, Injectors, O2 sensor, ground (on an intake stud), CTS (look at the wires - these tend to bend and lose their insulation), etc
9) Disconnect throttle & TV (transmission downshift) cables (and cruise control cable if equipped)
10) Remove throttle & TV cable brackets
11) Air cleaner studs
12) Remove intake top plate
|Look at the amount of oil in the manifold..this motor probably has close to 100k miles on it, so no big surprise...|
13) Mark #1 on the distributor cap
14) Remove the distributor cap
15) Mark the rotor position (I used a crayon on the firewall)
16) Remove distributor clamp and distributor
17) Remove the thermostat housing and thermostat
18) Remove oil pressure sending unit (I think its only in the way on the f-bodies..) to access the rear most intake bolt
19) Remove the intake manifold (12 bolts)
20) Remove the throttle bodies from the top plate (2 bolts each)
21) Clean, Clean, Clean - the bottom of the thottle bodies, the heads,the thermostat housing, etc... make sure when cleaning the head where the manifold attaches, you put something in each port and in the lifter valley. That way you catch most of the small stuff so it doesn't get into the motor
22) Move CTS sensor, or install new sensor in new manifold
|The ports look the same size, but its really just that the ports are very dirty - if you look at the
top left port on the old manifold you can see how small they are...
|Someone has done some grinding on the old manifold - see a few shiny spots where they
removed casting flash and worked on the runner inlets? Very minor mod...
|Reinstall in reverse order...
Some items to note:
1) Intake manifold torque sequence - I was told to start with the middle bolts and do a circle of the inner bolts, then move to the next set out, do a circle with those, then keep moving outward. Hard to describe - maybe I'll do a graphic :)
2) There are multiple schools of thought on intake sealing - i used the blue silicone on the ends, without the cork pieces. Use the blue silicone around the water ports when installing the intake gasket - that way you do not end up with a water leak into the lifter valley...then you would have to do all this again!!!
3) I used teflon tape on the fuel connections into the throttle bodies
4) I used the red silicone around the two holes for the egr, then bolted the plate over them
5) Check your timing once you get it all back together.
|I had to match the alignment pins on the bottom of the throttle bodies - i had some in the plate already, so it was just a matter of pulling the extras.
I didn't rebuild the throttle bodies this time. I will likely have a set bored in the future, so i'm procrastinating for now.
|This is the plenum gasket from the FelPro MS91440 set...
|The finished product...
With the ported manifold and a 2100 stall torque converter, I gained .35 in the 1/4 mile. I went from 15.75 to 15.4...|
UPDATE - after I'd installed the manifold, some observant folks on the Crossfire Injection Forum noticed that I had
not removed the heat shield - they speculated that blasting grit would be under that shield and would clog my oil system...|
Since I had the manifold back off to replace the heads & cam, I decided to rectify the situation...Here's what I found...
|Look at the CRUD! What appears to be bubbles in these pics are actually the blasting material suspended in the oil...
|I will be cleaning the manifold, tapping the bosses and reinstalling the heat shield with fasteners and loctite...
|Here's another pic once the manifold was opened after the original porting project...Look at the discoloration from the fuel, you can definately see how it flows...
|Thanks to Robert, Mike & Luis for all their help!!!|