Have a 1974 400 Mopar engine that has stock 8.2 - 1 comp ratio from factory, without getting new pistons, how much would putting on 516 heads with steel head gasket increase the comp ratio on the motor to

If you can get a close guesstimate on the CC diff between those heads you can plug it into KB silvolites (or others) calculators but the 8.2 is an NHRA blueprint spec (for a max milled head(s) and the actual is gonna be in the 7's plus you'll likely be going with a composition gasket making it even worse. There ain't no way around it (that I know of). EDIT the 400 heads would be an open chambered 906/346/452, not sure which one but I think they are pretty close on CC's

Ball park quick n dirty is 1/2 a point. And as said above you're likely in the 7's right now if you were to take real world measurements.

These actually came stock with the .020 steel head gaskets. If you ever did a head swap with equal chambers but used an aftermarket composition head gasket, you actually went backwards in compression ratio! The common Fel Pro gasket is .039, almost twice as thick!

I recall reading many submissions to Mopar magazines over the years asking about how to raise the CR in smog era 360 and 440 engines. It was a common suggestion to mill the heads .050 and use a .020 steel gasket to obtain a 9.0 CR in a 73-78 440.
I did this in 2001 to the first 440 I put in my Charger. I used a Mopar 280/474 cam in the engine and that dude ran great!

On a 440 we went from 7.45:1 to 7.80:1. With your 400 you would see less of a compression increase. If you are fortunate you will see about a 1 (yes one) horsepower increase with your planned head swap. The loss of airflow with stock 516 heads over the 902 or 452 heads will offset the small increase in compression. We did a mild port job on the 516 heads and realized a 62 horsepower increase with the slightly modified 440, 387hp to 449hp.

Here is a dyno test on a low compression 400 that may be of some interest.........

The slug 400 on the dyno.

Get KB240 pistons

Standard volume on 400 heads are close to 90cc ( a NOS 452 set I got was really into 92cc rate )

There isn't really any cheap or easy way to make a significant improvement to the cr of a 400.

Even with the KB pistons, shim gaskets, and 80cc heads, it's still only 9.2-ish compression.

If you could find some TRW L2388F-60 pistons(discontinued), they would be down the hole .006.
That would be a .038 over bore for the 400 block, and the weight difference would likely be enough to necessitate a balance job.

An option would be to (1) source a 440 forged crank (there was one on here for $70 awhile back (I shoulda nabbed it) Mockup some 400 full groove main bearings & mike a reading (2) turn the counterweights to 7.250" & have the mains turned down (to match that dimention). order the KB pistons for that swap & some plasma Moly rings. (3) bore/hone & mockup to check deck height (4) mill pistons and deck accordingly (open or closed chamber heads). (6) some stock 440 rods (7) have it balanced. with offset ground rod journals you'd have 65+ more cubes & quench in the same size external (400) package which would give you a very efficient long block. then the cam/intake/carb/ign to suit your tastes.

Only? Who says that's bad ?

Still if you want, deck the block for even better numbers and voila.

( with 80 CCs I think is a tad more, the deal is stock open heads are REALLY into 90s )

https://www.uempistons.com/index.php?mai...roducts_id=3028

So, the 450 stoker

( with stock 400 rods, I have for sale a standard bore pistons for it, new in box KB215, just in case )

http://www.houstonmopars.org/stroker.html

I have some 440 rods I'd let him have for twenty five (just enough to cover shipping & my gas). EDIT If he offset grinds the rod journals he'd get 470 cubes (what I shoulda done on mine).

Without getting new pistons, if you want to change your cylinder heads, you will be told to build a stroker?

Maybe a 572 II generation Hemi?

Maybe some Brodix B1 B/S heads. stock 65cc chambers, and they can be milled for even smaller chambers size, but the cost would be about the same as a stroker kit?

The B engine dilemma:

Stock 400 is 4.342 x 3.38

Each cylinder has 50.05 cubic inches. That's 820.5cc swept volume.

To get to 8.2:1 there needs to be 114cc above the piston.
Heads if uncut are close to 92cc. Steel shim head gasket is 5cc. That permits 17cc above the piston in the cylinder. If that was the case the piston would be 0.070" down in the hole. The piston would have compression height 1.862".

BUT the stock replacement piston is 1.813. That leaves us 0.119 in the hole. Compression ratio calculates to 7.52:1. Use an 84cc head and you're up to 7.96:1. Use an 80cc head and you're at 8.20:1.

That's all with the factory steel shim head gaskets. If you make a mistake and use the Felpro gasket that's 0.051" compressed, which I think is around 13cc, Your 80cc head now makes 7.7:1.

If you just rebuild the stock 400 with replacement pistons and that thick composition head gasket your true compression would be 7.13:1. No wonder the 400 got a reputation as a dog!

I think 516 heads are close to 84cc so switching will get you 0.44 of a compression increase.

R.

Silvolite 1276-60 piston(+.038 over), steel shim gaskets, 84cc heads= 9.7cr.

Might require a slug of heavy metal on each end of the crank to balance it, depending on how much you can trim off the rods.
A steel 383 crank would also help with the balancing.

I don't see it getting much cheaper to do than that.
Pistons would be down the hole .020".

yeah, it kind of progressed didn't it. I have a '77 440 that is all stock and would like more than the 7-1 cr. I have a set of '67 915 hp heads and thought about a '68-'70 stock type hp cam. What are your thoughts? It's my truck and right now is being used for mainly trailering my Chrysler boat.

When you're in the 8:1 range, each cc is worth less than .1 change in cr.

So, losing 10cc's in chamber volume will boost the cr less than 1 point.

For the 400, if you're at 7.9cr to start with, and reduce the chamber volume 10cc's, you'd end up with 8.5cr.

My opinion will probably be vastly different than most. The best gas truck engine I ever had was a bone stock 440 out of a 1973 Chrysler New Yorker. Do you want to experiment with the engine that hauls your boat around? I don't. I like a truck engine with a small camshaft.

If you install the 915 heads in a truck application you are asking for valve seat recession (I have replaced a lot of 906 and 915 heads used in trucks), the minimum you need to do to them is install hard exhaust seats or stainless steel exhaust valves (The stainless steel exhaust valves? A new revelation to me).

Getting some more air flow with better heads is worth more than more compression to me. Do nothing but put on aftermarket aluminum heads on and you'll go, "Wow, those smaller 78-84cc combustion chamber heads really pepped the 'ol truck up!" But really....it will be the additional air flow that did it.

How I would do a "low effort" 440 tow motor;

I'd shoot for about 8.75cr(1.990ch piston, .085 deck, .040 gasket, 84cc heads), 346/902/452 heads with stock valve sizes and a very minor bowl blend(240-245cfm),and I'd probably run a stock replacement 350hp 440 cam(clevite 229-1327) partly so I could run oem type springs.

Basically, this would be like a stock 71 440 out of a c body.

I'd run a std performer intake and some sort of small-ish 4bbl carb.

So what would happen if you threw a set of 440 rods in the stock 400 setup?