LT1 to SBC Intake Bolt Pattern
The Procedure
Fix the bolt pattern. The four corner holes are correct, all the rest are wrong. I first filled all the wrong holes with JB Weld, and sanded smooth when dry. Then I bought stock standard V-8 gaskets to locate my new holes. I have 1986 and prior heads so my middle two holes on each side will be on an angle. If you have ‘87+ heads your center two holes will be straight up. I hand drilled with no guide, basically guessed at the angles. I had lots of filing to do when I put the intake on the engine due to minor errors on the hole angles. Marking and drilling the holes.
Finished, or so I thought. I had lots of filing to do for final fit. I used washers under the intake bolts to ensure a good grip.
Some of the holes are close to the plenum so allen head intake bolts were needed.
Look closer at these two center holes. I had to grind lots into the casting to get the bolts to start because of the angle of pre ‘87 heads. You late model guy/gals won’t have this problem.
Close up.
You can get your LT1 converted at LT1 intake.com
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The LT1 map sensor hole you can plug using Epoxy Putty like JB weld epoxy or Quik Steel. Thats what i used when i was converting the manifold.
There are different ways you can do the PCV valve too. you can run the LT1 style setup which is just a U-shapped tube connecting the two pcv ports shown in the pic and run breathers in the valve covers, or you can block the one larger PCV hole, and run the PCV valve from the valve cover into the smaller PCV hole on the LT1 manifold. Then throw a air breather on the other side of the motor.