Upping the Comp ratio on a 400, engine builders please

OK SUPER LOW BUCK DEAL. basically stock '76 400, runs well, doesn't smoke but low on power. I want to do nothing more than swap out the low compression pistons for some KB240 ones, I do not want to do this if it needs to be bored oversize, I do not want to do any thing other than bump the compression.

QUESTION....when the heads come off, with a dial/bore gauge what is the maximum the cylinders can be to use standard bore pistons /rings???

If it has too much wear and needs to be bored, I will not take it apart father and it will go right back together.

If I can go the route of new pistons, I will mill the heads and deck the block only minimal to clean-up the surfaces, and be able to use fel-pro composite gaskets and gain cc's

Oversize pistons and rings cost no more than the standard size. If you are into the block far enough to deck it, it is only about $180 to bore and hone with a deck plate. Maximum? Best call the manufacture directly.

Why not bore and hone it if you're going to deck it?

Stock head gaskets I believe are steel and only .020" thick, Felpro's are .039 thick.

If the bore looks smooth and shiny it needs to be honed minimum.

The KB240's require the bore to be pretty tight .002-.0025" so I don't believe a well worn engine will be that tight.

Sound like this is waste of effort to even take it apart.

my experience with the kb's i've used is that the bore size needs be on the money to achieve recommended clearance. .001"-.002" larger and they're pretty noisey, in fact they're a little noisey cold at .002"-.0025".

I would like to do alot more and have thousands to put into it...However consider it an old school, shade tree, no money to do it "right" build.
The pistons and rings are being donated to the cause so I don't have to buy $600 new ones, money will still be spent on bearings and gaskets. But little else.

I understand from the replies I am looking for a max bore to be 4.342.

We're there not oversize rings once available?

something like a .005" over ring won't do anything if the bores too big for the piston. the top ring gap will need to be opened up to around .030" anyway. taper will be the issue. setting the gap at the top of the cylinder may be too tight at the bottom. seems like it would be easier to just mill the heads .060" and ring and bearing the old stuff.

If the bore tapered is over .003 from top to bottom I would bore it and replace the pistons and rings That being said some old time mechanics back when I was young, right after dirt was invented ,use to say if has over .015 taper bore it

Thanks guys, I will consider this idea further. I may post results, if things work out. LOL.

What is your budget? IMO, it is really hard to tear into a short block, change a bunch of stuff, and come out on the cheep.

Also, in my limited experience, it seems that a really good set of heads on even a well seasoned short block, can give a big bump in performance.

If you sell what you have, and buy some aluminum heads, have them gone through, mill to 70 or 72 cc, you might not be into it for much more $ than what you are thinking now, with a more certain outcome. Just a thought.

This is my experience as well.

Cheapest option in my mind is, mill the heads about .060-.070, steel shim gaskets, adjustable pushrods(if you don't have an adjustable valvetrain now).

While the heads are off and apart, have them cleaned and do a quicky bowl blend.

On a really tight budget like that, I'd just put a high stall converter in the car and run with the low compression engine.

The motor is 40 years old. I feel that is why it's down on power. Going thru all the work and expense you are talking about to only increase the compression, and nothing else, I feel will give you less than exciting results. The motor is tired dude. I recently tore down 4 1976 400's. It will need everything.

Better to hear 'em than to smell 'em.

You'll probably fine a pretty good ridge at the top of those cylinders. At least make sure the new rings dont crash into that.

Run a ridge reamer on the top of the cylinders prior to piston removal. Ball hone with an appropriate grit to match the rings, and put it together. If you're worried about piston slap you may consider knurling the pistons and then use a flat file to size the pistons to the individual cylinder. You'll have to check with a machinist as to whether a hypereutectic will take a knurl the same as a cast piston.

Stock bore is 4.342. Rings are available in 4.350 for $40. That's .008" over. File fit the rings. Run the steel shim gasket sold through Summit for $25.

https://www.summitracing.com/parts/dcc-4286754/overview/

It'll use a little oil and make a little noise, maybe, but it'll run, just don't expect to get 200k miles out of it.

Where is Dan when you need him ??

You are going to do ALL that and you can't come up with MAYBE another $300 to BORE it ... seriously ???

Ignore the ridge reamer recommendation , if you don't know what you are doing with it then you will do more HARM than good to the block.

I have personally been burned by someone that didn't know how to use one ... had to sleeve a block because it took .075 overbore to get a clean pass, top to bottom, on one cylinder , .040 on the one next to it , the 2 next to those at .030 , the other side would have cleaned at less ...

I just had to take a block to 4.402" because some talking chimp used a ridge reamer. Block surface cleaned up at 9.965 deck height, and that was with .020 slope from one end to the other.

Either do the shortblock right, or just do head work and stick it on the stock shortblock. S/F....Ken M

After having gone down this road, I wouldn't even crack open the cylinder heads. If you're not going to do it right to get a good seal, don't bother. Your money would be better off spent on alternative upgrades. I would do a centrifugal supercharger, or maybe a transmission/rear gear upgrade instead.

I have had a blast doing stuff on the cheep. I'd just stick a cam in it 😄

I agree. Usually if the ridge is that bad, the block needs an overbore, and most people usually take too much out with a ridge reamer making things worse.
Been there and done that and learned from my mistake.

A friend raced a low compression 400 engine with decent results. It had a decent sized cam and ported heads, with 6-pack intake and headers. He just used a high stall converter and higher gears to get past the weak low end torque.

i didn't know people used ridge reamers anymore.

seems like buying a used bottle kit and strapping it in is your best bet based on all the parameters.

Ebay Turbo!!!

If its a OLD block.. they were soft(before they
started putting more nickle in them) you HAD to
use a ridge reamer to even get the piston out of
the bore.. yeah I still own one somewhere around
here but havent used it in over 20 years(maybe 25)

i remember them from back in the day. folks breaking pistons trying to push them thru the ridge,..lol. used to be able to rent thru the mail. i just thought things have progressd to a point to where they were obsolete.

i was thinking about a 360 i put together. this was 100,000 mile dakota engine. always unleaded fuel and the oil changed religiously. from what i can remember running a dial bore gauge thru the cylinders that there was next to none taper! that 400 may not have a ridge; if taken care of.

If you're not boring or power honing the cylinder then ignore the recommendation to ignore using the ridge reamer and use the ridge reamer. It's not rocket science. You may be able to rent one from an auto parts store.

If the new top compression rings run up and over a ridge at the top of the cylinder, even after use of a ball or three finger glaze breaker, it will destroy the new rings and pistons. Even if you use the same piston it will destroy the rings and piston because the new bearing raises the piston height in the cylinder, even thought it's only a thousandths of an inch.

Removing the ridge isn't just for ease of piston removal.

It's easiest to use before piston removal because you can square the tool on top of the piston. It's not rocket science unless you're the guy that screwed it up for JohnRR, and the instructions are an easy read.

Mine sat on the deck so it was square to the deck
but I believe any 400 block has plenty of nickle
in it... so it might be ok

Every block I had come into the machine shop where I worked that had a ridge reamer used on it was screwed up. Not all, but the vast majority of people will remove way too much material from the bore w/ a reamer.
I've taken a lot of motors apart that had big ridges and never used a reamer. Not worried about saving the pistons, so I just knock em out. If it has a big ridge, the pistons shouldn't be getting reused.

I bet the moly rings, harder block and superior efi fuel control had something to do with that.

your probably right. i know leaded fuels ate up engines. as much as we curse unleaded, it does make the cylinders last longer and better oils are a plus.

That is my thoughts also. If it has a slight ridge, take care of it when honing the block. If it has a large ridge, the bores are worn to the point where it really needs overbore and larger pistons/rings. Re-ringing a worn out bore and piston is a waste of money in my opinion.

I think some people are afraid or intimidated to take their stuff to a machine shop and get a professional opinion?