How much overbore is safe on 109 block?

[Snorman]

.020"?
.030"?
.040"?

Looking at a shortblock and want to know what is safe.
Thanks!
Sean.

 

[cool 84]

My dad ran a .040 109 block before the stage motor. It was a racegas only car boost was always 26lbs with 27 degrees of timing. It had 100s of runs, every weekend we were out racing for a couple years. Combo was ported irons and intake, TE62, THDP, 210-205 cam, FM intercooler, etc. It was a pretty stout combo with no reliability problems.

 

[Snorman]

I'd be running a set of ported irons (227/184), ported intake, PTE FM, TE63e, 57's (that I'm now thinking might be marginal), small cam and the other usual stuff (Mease DP, catback, etc.). I'll run good gas and ~24-25psi.
With that combo, I'd be safe with a .040" overbore?
Block has been sonic tested.
S.

 

[re-evaluating]

Keep all the wall thickness you can

I would keep the bore as small as possible, I in fact bored my .020 block to .025 instead of .030 for that very reason. If you are talking a block that will be limited to reasonable boost levels it might be ok but what fun would that be. I would much rather run a .020 bore and a .020 .020 crank than a .030 or .040 bore with a std. std. crank.. Just my opinion... Good luck

 

[ThikStik]

Were fortunate now also in that there are pistons avaiolable in small OD's. I will be going .010 using CP's instead of 30 with trw/spedpros. I think ther are JE's in even smaller OD's.

 

[JToups386]

Less is more, in this case.
Start with .010 if at all possible, and leave room for future rebuilds. You certainly won't notice any performance gains from the additional .030 vs. .010, etc. Stock being a 231 cid, I believe you end up with a 234 cid at .030 over. No gain there.
I'm not sure if anyone still makes a .040 piston, unless you want to spend big bucks for custom stuff.
I run the TRW .030's, and have been happy with 'em. However, if money wasn't a factor, I would've started out with some JE .010's, just to preserve the block for innevitable future rebuilds.

 

[ARI inc.]

Is it best to just leave the bore stock when building a block if possible, or will boreing it out help a lot? what are the typical gains?

 

[ARI inc.]

Is it best to just leave the bore stock when building a block if possible, or will boreing it out help a lot? what are the typical gains?

 

[JToups386]

There is no noticeable gain to boring it. The only reason you would bore it, is to clean it up, per marks on the cylinder walls that honing won't remove, or to make the cylinder "round" again. Any good machinist can tell you what you need to do in regards to boring it out. As mentioned before, the less you bore, the better off you'll be in the long run, as long as you have a round hole that is unmarked.

It would be different if you were able to do the same as we do to the new LS1 blocks, where you can bore a 346cid block into a 382cid motor, per bigger sleeves. However, on the Buick 3.8, I cannot see any gain from a net 3cid by boring it to .030. These blocks are becoming harder to find, therefore you would want to allow for future rebuilds by only boring as little as possible.

Make sense???

 

[ARI inc.]

Yea it does, thanks alot for the info. The LS1 is a AMAZING motor, right now my brother has taken a heads,cam, and nitrous car too 630 RWHP and 700 ft lbs on the stock bottom end. Will it last 20 runs....i dunno but it is fast as hell. with the old nitrous setup with a 150 shot he went 10.7 @ 128 in a 6-speed. the new setup uses the new nozzle system with a separte fuel system for nitrous. If you wanna check it out i can post some pics.

 

[strikeeagle]

Haven't you heard? Our blocks need to be UNDERBORED...

 

[ThikStik]

This is a boreing thread.

 

[JToups386]

Sheesh! You should be honed...!