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Discussion Starter · #1 ·
I have a 4.3 L99 engine laying around and wanted to konw howmuch can u bore a L99 out to 350,355,383 just tryin to see what i can do with it jus want a project engine.
 

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I dont think you can bore that out to anywhere near a 350

the 4.3 is like a 265 ci motor.
 

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Discussion Starter · #3 ·
but the L99 and the LT1 has the same block if im right but different internals.
 

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l99 and lt1 blocks are differant. the l99 has the same bore as a 305. the biggest you could go would be like 320 ish cid, bored out .30 with a 400 crank. but youd still have crappy heads with small valve and lots of shrowding around the valves.
just start off with an lt1, it'll make more power.
 

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the same as the 302 in the '69 z28. gm did that to meet the 5.0l limit for trans am racing.
if your starting with a 350 why go smaller?
 

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The L99 is not the same block as an LT1.
The L99 has a 3.75" bore diameter where
the LT1 has a 4" bore diameter.
I would only bore the L99 to .030.
But its easier to build an L99 stroker
by using an LT1 crank to make a 5 Liter or 305 cubic inches.
Ive got one in the Blue Snail
and it makes just about as much torque as a stock LT1
and gets better mileage cruising. I call it an LT9, LOL!


-Nab
 

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Theoretically the L99 block should be capable of reaching about 360 cubic inches. That is .030" overbore with a long 4.00" stroke. If you were to do the same with an LT1 block, then you would have ~50 more cubic inches.
 
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