FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: FERoadster on June 24, 2018, 01:33:44 PM
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My cross bolted 390 block (C4 casting) was already at +060 when I got it. Already had a sonic test that showed all cylinders were good at +080 except one (either 4 or 8 ) not at home now for a week or 2. That one cylinder would be @ .097 wall.
My question has 2 options. I want to do a 4.25 stroker kit so new pistons are needed either way.
#1 sleeve the single cylinder and bore all to 4.13
#2 custom pistons with minimum bore just to clean things up.
I have read that 390 blocks at 4.13 bore can have issues such as overheating and cracking.
Keep in mind this will be a street only car, very light, 3.50 gears, headers, RPM intake, aftermarket heads and a C6. So cost is a major factor but so is dependability and long lasting service.
Thougths??
Richard >>> FERoadster
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I would highly advise never boring a 390 out to a 428 bore, even when the sonic test says it's ok. I've ruined a couple of blocks that way because you can't see the pitting and other spots that are behind the cylinder walls.
A thicker cylinder wall will increase ring seal.
I (as well as the other venders) offer forged pistons in .001" increments. There's really no need to bore blocks anymore. Save the wall thickness in case of a rebuild later down the road.
There's really no sense in taking the chance over 17 cubic inches.
BTW, just on a random note, it's a wives tale that a bored out block will overheat. But you can make the cylinder walls thin and weak.
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Agree w Brent on both counts. I've run some pretty thin blocks (not on purpose, but like .040" wall !!!) and didn't see any overheating. There are theoretical arguments it might have SOME local hotspotting the main effect is to weaken the wall and crack it.
Also, going from 4.11 to 4.13 bore is only a 4cid gain. Besides 4.13 bore would give you 455cid and you'd then have a Pontiac.
Also, what is the accuracy and precision on that sonic? .097" is ok but it may really be .087".
Was the sonic checked on a "before & after" piece of cylinder wall?
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Agree w Brent on both counts. I've run some pretty thin blocks (not on purpose, but like .040" wall !!!) and didn't see any overheating. There are theoretical arguments it might have SOME local hotspotting the main effect is to weaken the wall and crack it.
Also, going from 4.11 to 4.13 bore is only a 4cid gain. Besides 4.13 bore would give you 455cid and you'd then have a Pontiac.
Also, what is the accuracy and precision on that sonic? .097" is ok but it may really be .087".
Was the sonic checked on a "before & after" piece of cylinder wall?
Good catch.....I read too quickly and didn't see the .060" over.