My engine is STILL at the race engine shop for boring, porting, polishing, balancing and blueprinting for street buildup with Offy manifold, Eddie 500, Dual Dutra Duals, larger valves, etc. It's a 225 /6. Should I ask him to bore it .060, even though it only NEEDS .030 to straighten it out? I believe the block was cast for aluminum and that it will usually withstand boring up to .100, or at least .090. The builder said he will sonic check the block to see how much he can safely bore it, and I'd like it to have at least .030 in case it needs a later re-bore and rebuild.
Second question, with .030 and with .060, what would the cubes be? I expect the head to be shaved .10, and possibly deck the block a little, so these may change the measurements, but assuming no shaving or decking, what cubes would these borings add? Thanks.

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Restored '62 Signet, 229 4bl, Offy intake, auto, Dual Dutra exhausts, shaved head and block, high stall converter, 1.6 roller rockers, etc.

Is this the original 62 engine that you are working on? The early ones could be bored out to .060, no more. The later blocks however used a thinwall casting that could only be bored out to .030.

At .090 I think you will probably break into a water jacket.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Can those blocks be sleeved if they are bored out too far?

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

No, this is a 1973 engine. The '62 engine runs good, but is a little on the low end of compression. I'll set it aside in case I sell later. Thanks.

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Restored '62 Signet, 229 4bl, Offy intake, auto, Dual Dutra exhausts, shaved head and block, high stall converter, 1.6 roller rockers, etc.

Well, youre in luck because 73 was the last year that yould could bore .060. In 74 they switched to a thinwall casting.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

I personally would not bore out any engine more than necessary. What's the purpose to bore it out to .060??? All you gain is a few measly cubic inches displacement on a piece of paper. So boring it out to .060 gains you 7 or 8 cubic inches. Consider that a typical Briggs & Stratton 3.5 HP lawnmower engine is about 9 cubic inches. If those extra few cubic inches are so critcial, why not just couple a lawn mower engine to the front of your slant 6??

Stick with .030 or the minimum necessary. Then you may someday get another boring out of it. Also remember that thinner cylinder walls trasfer more heat to the coolant sometimes causing "overheating".

My 25 cents worth (2 cents adjusted for inflation).

This is something I have always wondered and just have to ask. I'm not picking on you Jeb, just throwing this out to the general populatoin of "experts" out there.

If boring an older slant out to .060 (.030 per side) is OK, and boring it out to .090 (.045 per side) "will probably break into the water jacket"........ Does this imply that at a .060 overbore you will have less than .015 cylinder wall thickness of brittle cast iron? What prevents this from blowing out from normal combustion pressure and operation?

Does not quite add up to me.

FYI... I have a 1975 model year Slant 6 with a "sleeved" cylinder (out of place wrist pin put big groove in cylinder wall). I expect that it was bored out considerably over .060 to fit the sleeve in the block, then the sleeve was bored to .040 to match the other cylinders. This was one of those engines that came from the factory bored .020 over and .030 did not quite clean up #1 cylinder. This engine has 80,000+++ miles on it since it was bored and the one cylinder sleeved.

When I have a slant engine bored, I go to .030 over. This allows room for future boring, if necessary. I don't know about the 1976 and later blocks, but any of the earlier blocks can be bored .060 with out problems, and most can go .080, but the wall thickness should be checked. Some of the racers are going .100, but that definitly reqiures checking the wall thickness, and I think filling the block, to help support the walls.

The main reason the racers go to .100 bore is to be able to run a better ring package. There are many more choices of rings for 3.5 in bore, then for the smaller bore sizes.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I say go 0.030" if that's all it needs. I wouldn't bother paying for sonic checking at that bore, or 0.060". There is a lot of meat in these blocks.

That said, many of the racers go 0.100" or more. 0.130-0.140" is not out of the question, even w/o block filling (Cameron Tilley).

I would not worry about boring 0.100", but it is just not necessary, as Charlie said, unless you want to use a non-Slant piston/ring setup.

Lou

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Home of Slant6-powered fun machines since 1988

I have my 67 block bored out .100 to fit my kb pistons.

I drive it everyday and everything runs great.

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73' Duster 225
<img src="http://longrod.moparpages.com/enginedone.JPG" width=200>

That's interesting. Myself, I have never gone larger then .060, and never had a block sonic checked. I knew you could go .080, but didn't realize, some were going more then .100. I wasn't sure it block filling was required at .100, just going by what some of the racers wre telling me about their motors.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I can only think of one really good reason for boring out more than is necessary, and that is if there is a type of piston (material, compression, or crown shape) that is only available in the larger size.

And as for it having thick walls because it was "cast for aluminum," I think that's incorrect. My understanding is that the aluminum sl6 blocks were made using a completely different process than the iron blocks, which are just conventional sand core castings. So the wall thickness has nothing to do with the fact that there was also an aluminum version of the block at one time. Looking at the photos of aluminum blocks (elsewhere on this site) they're an open-deck freestanding cylinder design with thin iron sleeves- none of that bears any relation to the thick-walled iron blocks.

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My '87 225 is .080" over (out of necessity). No overheating problems whatsoever.

.030" over = 228.7 cid
.060" over = 232.7 cid
.080" over = 235.4 cid
.100" over = 238.1 cid

Assuming the stroke remains stock of course....

-S/6

Thanks for the replies. I think I'll reconsider and go with the .030, if that cleans out the cylinder walls. Thanks again, everyone.

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Restored '62 Signet, 229 4bl, Offy intake, auto, Dual Dutra exhausts, shaved head and block, high stall converter, 1.6 roller rockers, etc.

I believe there is an advantage to a larger bore when using large valves.

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Yeah....Im the one who destroyed this rare, vintage automobile.....