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Mamimum safe over bore on a 400 Chevy

24K views 25 replies 14 participants last post by  nosit2 
#1 ·
I ran accross a local guy trying to sell what looked like a super nice and cleaned 400 block. In checking the bore I noticed that it is already .030 over size and will need to go out more to clean it up etc. Is this a good deal or is the .030 already at its safe size? Another thing does anyone out there in Chevelle land do business with Street and Performance out of Mena Arkansas? Brodix and Street and Performance are both super top companies and are both in Mena Arkansas. Has anyone out there done business with these folks and a person who works on enginess at S&P named Brian S ? Thanks
 
#3 ·
I don't know the Co's But as to the 400. It all depends on the block. I have seen some bored .060 over others that were maxed at .030. The block really needs to be sonic tested to check wall thickness before trying anything over .030.
 
#5 ·
It depends on the block, some can go .060", some can not

I do suggest if its a race engine having the water jackets filled {half fill} after hot tanking and the machine shop preps it to be filled then you bore it with a torque plate, this will make it as stable as possible
 
#7 ·
lucky dude, enjoy it. But to the original poster make sure to get it sonic checked as some will clean up and others will be to thin. These blocks are hard to find. I looked for 8 months and the one that I found was cracked along the main webs. Make sure if you buy the block that the guy will return your money for the block if the machine shop says it's no good.
 
#8 ·
If the block is already @ .030 over...it's just about impossible to take it to .040 over. It can be done IF the cylinders wore evenly and IF it don't have much taper by someone on a CK10 power hone (or equivalent), IF you can find someone who wants to fool with it. It is a PITA, to say the least.
SOME 400 blocks can go .060, but for most .040 is pushing it pretty good.


Sonic Checking is your friend:thumbsup:
 
#9 ·
For what it's worth ,these blocks are getting harder to find so don'tcull,l it just yet. As Greghas said.if it isn't wore much hone it to .040 if it is too bad go to .060. As scott said
have it sonic tested if possible. Ihave built many .060 overs with good results.I wore one
out had .065 pistons made, wore it outthen went to.070 still going.Always hone with
deck plate, gaskets and studs or bolts you are going to use. Diferent strokes for diferent folks.Personly I have no need for hard block..I had one coustmer that ran 8 years with the same block no hard block. Door car ran 5.11 in 8th 1 4b no nitrous. Now pick your own poison. Thanks[ olddog ]
 
#10 ·
Heck...we're building another 400 right now that's only .030" over. The .040" over block is gonna sit for now. We just ran both thru the machine shop.
Also have a spare 400 block in my shop that's standard bore.
All the above are 2 bolt mains.
Seems like I've been covered up with 400's lately... ;)
 
#11 ·
bar,

First of all, its really no problem to go .040" if you have a good honing machine. The block is probably worn 2 or 3 anyway, that only leaves .007 to hone, heck we pretty much always leave .005 when we bore them anyway.

Now, I might get some grief about this, but has anyone here actually had a problem with a .060" over bore on a 400 that they can swear was caused by the fact that the block was bored .060" ?? I dont want to hear about the overheating, I think that is bull. If its overheating, its because it is making a lot more power than the cooling system is designed for, not because it is .060 oversize.

Maybe, just maybe, on an all out engine with a blower or lots of nitrous, you might build enough clinder pressure to cause a problem but ....... if you are making that type of power you should be using an aftermarket block, or filling the stock one anyway. All of the major piston manufactuers make .060 over pistons for 400s, they would not doo it if there was a problem.

Just my opinion,
Merry Christmas to all :)
 
#14 ·
bar,


Now, I might get some grief about this, but has anyone here actually had a problem with a .060" over bore on a 400 that they can swear was caused by the fact that the block was bored .060" ?? I dont want to hear about the overheating, I think that is bull. If its overheating, its because it is making a lot more power than the cooling system is designed for, not because it is .060 oversize.



Just my opinion,
Merry Christmas to all :)[/quote

I have seen 2 400 blocks that failed @ .040..both busted cylinder walls out. One was a 5.7 rod/11:1 bracket engine with a fair many passes on it, no NOS or alky, the other a 6" rod 12:1 circle track engine (on alky, the tune up could have caused it so I guess that one is a toss up). These were both "511" blocks.

Seen one "509" block that was .060, 13:1, on alky, bracket engine...lived a long happy life with a "half fill". After four seasons it finally cracked a wall..but it was four long, hard, high RPM seasons that would have gotten the best of nearly anything. I've used a couple .040 "509" blocks that lived just fine.

And no, it's not that bad to hone a .030 block out to .040, but it is a little time consuming, and hard on honing stone sets..most machinists won't fool with it simply because there's more money to be made in less time fooling with something else.
 
#12 ·
The question is about overbore sizes, .030, .040, .060
Well, lets flip the question to what it really is....

Based on personal or professional opinion & experience, what would be the maximum safe overbore on 400 without the expense of sonic checking or block filling?

Question 2:
IF the block was sonic checked, and is intended to be filled, what is the minimum allowable cylinder wall thickness??
 
#13 ·
John,
My personal opinion:

1. For most street engines, I see no problem going .060 on a 400. That is without sonic testing.

2. With sonic testing, on a street engine I would be happy with .090, on a race engine or something with boost or nitrous I would personally like to see .125 or more, especially on the thrust side.

I have a 400 block at the shop we will probably sonic test on Wednesday. It is already .030. I will post the results after we test it.
 
#15 ·
The further you bore it the better it will be if you fill the block. We used to use concrete umpteen years ago when dad was doing it then our machine shop switched to an epoxy filler that does not crack like concrete fill.

It all also depends on clylinder wall clearance and piston material too, i would say {no proof-just me thoughts} that a forged piston would put less stress on the cylinder wall than a hyper KB piston etc

Another thing is are you running steam holds? Another thing that helps is to have a machine shop tap into the back of the cylinder head and run a coolant line from the back of the cylinder head to the front of the intake manifold and run the rear bosses of the intake to an adaptor plate under the thermostat housing, this helps pull the heat out as fast as possible

I dont like to run a thermostat or a restrictor plate, this is the return for hot water to go to the radiator to be cooled, i like to play with the pulleys to find the sweet spot, the performance market is starting to realize this as they now make restrictors to limit the flow in the lower hose so the water stays in the radiator to get cooled longer and the water gets to the radiator quicker without a restrictor plate
 
#16 ·
It all also depends on clylinder wall clearance and piston material too, i would say {no proof-just me thoughts} that a forged piston would put less stress on the cylinder wall than a hyper KB piston etc
Butch,

Not to start a fight or an argument. But can you please explain to me how a forged piston puts less stress on a wall than a hyper? Is it clearance? Is it material? Is it machining? Is it Rod offset?

Im just asking you to substantiate some of your claims.

In my very small knowledge of metalurgy and engine building, I would think that other than piston slap in a big bore, the rings ride in the cylinders and not the actual piston. What real difference does it make as to what pistons you are running? I don't think I have ever heard of an aluminum piston wearing down a bore.

I know there are hardened aluminum materials that are claimed to be harder than steel, but when did they start making pistons out of such stated material? Especially when a piston is not what wears down a bore, the rings do.


When it comes to building engines, there are guys like Mike (wolfplace) and BillK ( BillK) that have been in the engine building industry for years. Please stop bringing up things that can really screw up somebodies build. Misinformation is worse than having no information.
 
#17 · (Edited)
Kyle,

For starters if you read what i typed {no proof, just my thoughts}. We use alot of hyper pistons from KB and it seems as if the piston skirts of these scuff up the cylinder walls a bit more than forged pistons, this is probally due to a tigher fit of .0015" piston skirt to wall clearance with a KB hyper piston and material.

So you say that the piston skirt does not come in contact with the cylinder wall?? Why do you think all the piston skirts are being coated now days? Answer- to reduce friction between the cylinder wall and the piston skirt. Friction makes heat, This further prooves my theory {as i stated no proof, just my thoughts}, this allows you to take more heat out of the cylinder walls {moly skirt coatings} due to a reduction in friction and less heat on the cylinder wall itself.

Look at a cylinder wall, you can see wear all the way down the bore, granted you are correct that the rings produce more wear, i agree 110%. But any friction in the cylinder is heat, any heat that can be stoped or reduced is a good thing. This is why you molykote piston skirts, and how much friction is inbetween the piston skirt and cylinder wall when the bore of the stock over bored 400 does deform a little? How about the thrust side of the piston, friction or no friction there?

Please take another look at my post, im not talking about wearing the cylinder out with the piston skirt, this is where you didnt read my post and are putting words in my mouth. I simply said " a forged piston would put less stress on the cylinder wall than a hyper KB piston" due to material for the most part. Try to do some machine work to a KB hyper piston, they are so dang hard the piston shop that does piston alterations will not touch them because it destroys the cutters due to it being so hard, this is why they crack very easy, because they are hard. I {again, no proof-just my theory} have seen less wear with a forged piston than a KB hyper piston.

Again, this claim is my theory based on wear properties we have seen between KB hypers, Bill Miller and TRW forged pistons. We have used ALOT of KB hyper pistons and they work but you cant push the envelope with them, My 13:1 compression engine actually runs cooler and has more cranking psi than my 11:1 engine did, my 11:1 engine was kb hypers set at .0015" and the forged pistons are set at .0065"-.007", everything is the same except for the cam, same fuel, same cooling system, the 13:1 engine has 240-250 cranking psi and the 11:1 engine had 165psi so by all means the 13:1 engine should run hotter but it doesnt, why? I would say less friction with a forged piston verses a KB hyper piston. This right here is real world and is not my theory or any engine builders theory, this is straight proof on our engine, the higher ompression engine with more cranking psi runs cooler with everthing else being the same except for cam but to compare another thing, the 13:1 compression has more cranking psi which should have a great deal more heat but it doesnt !

Merry Christmas :)
 
#18 ·
Kyle,

Just a point, you dont need to say this engine builder has been doing it for this long etc. All engine builders learn something new each day base upon what they see, im not saying anything bad about wolfplace or billk but ask them they learn something new at least every week as all of us engine builders do, youg or old. If you find an enine builder that says they dont learn something new just about every week you can bet they are not your best choice, the perormance world changes designs everyday so engine builders learn something different every week. Wolfplace, Billk, myself and im gonna say probally 99% of all engine builders do testing with new things based off their knowledge and past, some find improvments for power, some find improvments for wear.

Come out here and see some of our junk small blocks run with big block race cars, our small blocks only run 15's on a good day :waving: :noway:

We have made our customers cars quicker by applying some of our theory with some carburetor tricks but they say we are batty, why did Pat {him and Jason are dyno tuners} from Greg Anderson Racing call us from Their North Carolina Engine factory to try it this past year?

Do we advertise, No. I dont like to advertise, if i need to beg for work i would rather close. Im busy enough, if i advertise i would be taking work from someone who needs the work. Remember, our shop is consisted of two people. We build alot of engines and all of our customers race engines we do the heads yearly and the bottom ends every two to three years
 
#21 ·
gcoats;1623190And no said:
Greg,
First of all, Merry Christmas and I cant believe I am actually doing this instead of opening presents :)

I dont know which machinists you are dealing with, but I bet it does not add 10 minutes to honing time to hone out .010" compared to .005". No measurable extra wear on the stones either because at that point you are using the coarse roughing stones. I would rather hone out .010 than try to set up the boring machine to do it and hope that the previous guy bored the block straight.

As far as the KB pistons being harder on the block, I cant say that I have noticed it but they are definitely hard. And believe me pistons absolutely, without a doubt rub on the cylinder walls and will wear them. Like Butch said, why do you think they are all going to coatings, including the oems.

As far as my comments on the 400 blocks, I made them relevant to 90% of the guys on this site, those that will realistically never build a 400 that makes much more than 400hp or turns more than 6500 rpm. I did say that on race motors I would not go .060. Actually prefer a Dart block myself.

Merry Christmas to all,
 
#25 ·
Greg,
First of all, Merry Christmas and I cant believe I am actually doing this instead of opening presents :)

I dont know which machinists you are dealing with, but I bet it does not add 10 minutes to honing time to hone out .010" compared to .005". No measurable extra wear on the stones either because at that point you are using the coarse roughing stones. I would rather hone out .010 than try to set up the boring machine to do it and hope that the previous guy bored the block straight.
Merry Christmas to you, too, Bill!!:beers:

Uh, the machinist I was referring to that don't like honing to the next oversize is ME!!:D Of course, that's using a CK10, another machine may be quicker, I can't vouch for that. I would'nt dream of trying to bore from .030 to .040 on a block that has been ran any amount of time, especially (like you said) if someone else bored the block. Locally, only two shops' boring equipment references the main bearing centerline, and neither is top notch stuff (the one I was using was a Quik-Way). Everybody else still uses bars (one shop still uses an old Van Norman bar, its an antique in itself). Only having (assuming ~.003 wear in the top, and a perfect 4.155 starting bore which isn't likely, either) .0035 to remove per side would be a nightmare with that in mind..

Seriously, we left .003-.004 after boring on race stuff, and it may take two hours to get the final hone just right..then we let everything cool completely down and re-check. Sometimes needed to do a little more touch-up. We shot for .0003-.0005 taper, which is difficult on that machine, perhaps that's why it took so long.

I hated honing, anyways. That's probably the biggest reason I said that about honing from 4.155 to 4.165..:thumbsup:
 
#22 ·
BillK,

Did you have an excellent Christmas morning? Plan on eating some Turkey or Ham today? Im having Honey Ham and Meatballs in Sweer and Sour sauce. I cant wait until diner time !!

Merry Christmas to everybody and remember please if your going somewhere drive safe and be alert
 
#24 ·
I've been shopping performance/race machine shops for my 400 locally and learned a few things.

All 400 block, regardless of casting # are the same and the whole 4 bolt thing is a myth...... they are stronger.

80% of 400 blocks are cracked.

In addition to having them mag'ed......400 blocks should be pressure checked since so many of them are cracked.

Sonic testing is overkill and a waste of money.

And any 400 making over 400 hp needs splayed main caps.

I'm sure there's more, but that's what comes to mind right now.


Its good to know !!
 
#26 ·
my 3.800 stroke +.030 bore (413 cubes) 400 block just made 793hp 759trq on dyno saturday. stock 4 bolt caps with studs and no block fill. dont believe all the stories you hear about the weak 400 blocks. this is true pump gas street motor on spray. going back on dyno in a few days with my new fogger setup to hit 1000hp mark.
 
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