440 or stroked Big block
OR
5.7-6.4 modern hemi

Which is cheapest to hit the Hp goal of 650-700HP?

I think there are some build ups in the tech archive that will get you where you want to go.

Yes I have read them just wanting to know dollar for dollar which is the lowest cost option to achieve the goal. Big block or new hemi?

Never built either, but B/RB speed parts have been around for so much longer so my gut tells me it would be cheaper and easier than the hemi to get 650 hp right now.

Used 5.7 Hemi engines are $1500-$2000 on CL, but they don't make 650 hp either. You would need a power adder, or a larger engine as a starting point.

If you post this in the race-only section you may get some more experienced opinions.

Most likely a B/RB. 650 horespower doesn't really have a low cost option. Lol. Or not one that will live very long!

Your goals are achievable with the correct good parts, a good sonic tested 400 block, 4.250 stroke crankshaft kit with the longest forged H beam steel rods you can use, 10.0 to 10.7 to 1 compression with a set of the new Trick Flow 270 CC heads and a matching intake manifold with a 1000 + CFM carb and a good high lift medium duration (245 to 265 @.050 with a LCA from 105 to 110)camshaft and rocker arm kit
My first 400 stroker (511 C.I. 4.375 bore with 4.25 stroke))had 9.25 to 1 compression with a set of mildy ported 906 heads with bigger valves and a low deck six pack set up. That combination made 612 HP at 5500 RPM and 644 Ft. Lbs. torque at 4500 RPM, I put that motor in a 3450+ Lbs. 1971 Duster that ran 10.69 at 124.+ MPH through the complete to the rear bumper 3.0 inch exhaust system on with the air cleaner on
A later change to a set CNC ported Eddy RPM heads picked it up 10.49 at 127+ MPH on Oregon 91 octane pump swill
That was back in the early to mid 2000 so don't ask me about the prices now
I beat the snout out of that motor, I did make a lot of changes to it in the ten years I owned and raced it but it was the same cam and lifters and bore size with the original pistons when I traded it off for my current race car
The cheapest way to make your HP goals may be a used lat emodel Hemi and a lot of NOS, no way to tell how long a stock motor will take 200 to 400 HP of NOS
A decent built pump gas BB stroker motor will make that amount of power for a long time, trust me on that

Personally I'm thinking the 3rd Gen hemi is the way to go. The heads supossedely flow over 300 cfm in near stock trim so they should easily support over 600 hp NA. A turbo or supercharger and you're there.

I'll throw in my two cents. I'd go with a 500CI stroker kit in a 440. Some aftermarket aluminum heads, good intake and carb. I am not an expert at recommending cams, so I will delegate that to someone else. I would think nothing too radical would be needed in the cam area to get to 650 hp. But, if you are going to stroke any block (RB or Gen II hemi), might as well get the most cubes as possible.

After reading it cost $8-10k to build a stock 383 on the other thread, why bother.

You can buy a brand new crate 707HP Hellcat motor for $15k.

https://www.ebay.com/itm/Dodge-6-2L-Hell...m4383.l4275.c10

That 10k figure includes ancillary items as well for building old iron where the hemi doesn't. I just built a 512 and it cost me just a bit over that out the door. That 15k Hemi still needs a harness, fuel system, computer, pan and exhaust. All that stuff being for late model is tons more expensive than it's old school equivalents as well.

Cost parity is coming, but I don't thinks it's there yet.

First question, what's your budget for the "complete" motor?
Carb to pan, headers, distributor, plugs, wires, oil,..... Everything.

Then, is your car currently equipped with a fuel and cooling system capable of supporting a 650hp motor?

If not, are those upgrades budgeted separately...... Or do they need to be included in the "engine" budget?

The question boils down to this. Irrespective of any other factor is it 'cheaper" to build a BB or BB stroker OR new hemi to support a 650-700hp target STREETABLE aka hot rod, restomod or whatever you like (in other words not a full time race car)
This is more of a what if or a bench racing question not a How do I build... question.

I'm pretty sure I'm in the minority here, but a good solid 440 (forged pistons, maybe a girdle and some good heads) with nitrous oxide will get you there. You will be right on the limit of a stock block, but the car can easily be streetable since you won't need a huge cam.

take a look at engine masters they did a show on the 5.7 with mild ported heads and a supercharger with ait to water intercooler that made close to or better than 700 hp frieberger and dulsitch(sic)

"Cheapest" is probably a used 5.7/6.4 with a turbo kit.

The LS guys make more than that with used 5.3's with turbos on them.

Kid at work has a 6.4 challenger one day we were looking at the kenne bell for it. Seems to make good power like 750 or something like that. For a minute I thought that would be a cool setup in an old car, and maybe cheaper than a hellcat crate? But those G3 cost so much to get setup in the car it's crazy. I say for 10 grand you can do a bb with 440 source stroker with trickflow heads and intake. All new parts, make hellcat power. Of coarse it won't have efi and the driveability.

I did a mild, street driver 505" 440 for right at $7,500.
Molnar crank and rods, Mahle pistons and CNC Stealth heads. It's just under 600 HP but more than enough for the street and a blast at the track!

You save a lot of money if you can build it yourself.

I think MarkM hits the nail on the head first. Older car will cost so much more to wire it up with the proper harnesses, etc. to support the newer Hemi.

Next I agree with Cab Burge. Stroked 400. The more I read about stroking a 400 the more I like!

I would think a a Gen 3 with a turbo kit also, but you could also easily run the bill up to equal or far more than your basic B/RB would be to make the same power. It all depends on your approach. But I think it can be done cheaper. The main disadvantage that you have with a B/RB is its already going to need a rebuild unless you find a good engine for a song. Everyone thinks their junk 440 that burns oil and has 100 psi cranking compression is worth what those 5.7s on CL cost...

the real question needs to be how much work can you do yourself? can you weld up a turbo kit? have access to a cnc? have access to tuning software? have a box of carb jets and lots of free weekends?

I think you're looking at the b/br combo to be your best for the buck. plenty of used speed parts on the market to get you to 650hp.