What I have is a 8:5:1 300 horse motor, not sure of heads. 600 holley,727, 2400 stall, 323 suregrip. What do I need for a 450 horse motor.

What is the intended usage for this motor?

Just a hotter street car, weekend driver. Maybe a trip to the track. Another words more bottom end.

Most important in my opinion is a C/R up around 10.1 to 10.5 for a street 383, look for some close chamber heads 915's, stealth, even a set of 516, with bowl work and bigger valves would be better than open chamber heads, also don't over do the cam, 220 to 230 at.050 for good all around low to mid range. 230 to 240 for hot street. On my worn out stock 68 383 hp motor with factory flat top, i replaced the 906 with 915's, and replaced the cam with a vodoo 220/226 475/494 112cl and was very very pleased with the power and performance, its about 9.8 cr with .040 fel pros with a quench of around .040 to .050.

What about a stroker kit?

here's my build...

383, 440 stroker kit, 438 cu. in.

eddy RPM heads--84cc chambers, OOTB
zero deck flat top pistons with valve reliefs
10.5:1 compression
comp XE275HL cam
RPM intake
1 7/8 headers
holley 750HP

made 505 hp on the dyno, tons of bottom end. over 500 ft lbs torque from 3000 rpm through 5800 rpm

with stock 906 heads reconditioned to like new, all else being the same, it was about 9.5 compression, and maybe only about 450 hp, due to the lower compression AND lower airflow of the heads

I'm assuming you're not looking for a full bottom end rebuild (??). 450 ponies from an 8.5:1 383 is a tall order. But here's some tips on getting the most out of it: I'd first focus on getting the compression up.
-Make sure you're running .020 head gaskets.
-Closed chamber heads are a must on a 383; Eddy RPM's or Source Stealths. 516 castings with oversize valves and an MP-template port job will work, but once you spend the money to have that work done, you're most likely within a McDonalds lunch of a set of stealths.
-Short stroke, low compression motor, so too much cam duration will kill your bottom end, Something in the range of a Comp XE275HL grind would be my choice.
-A 383 will be a high RPM motor, so bigger carb than you might think. I have a 750 on mine, and it works well.
- 1-3/4" headers are fine for a 383.
- Gears, Gears, Gears.... 3.91's for a street ride.
- I like the RPM manifold for a street car, but a single plane will work well, and maybe make a little more top end.

Tuned right, that outline should get you around 400 ponies, and will allow you to hold your own on the street.

with alot allready said.

Compression is the key. Use 915 or reworked 516 heads at a minimum or look into aftermarket.

Stroker would help, but it will still have the same problems if the heads aren't changed or looked into. The problem seems to be piston choices are really slim. DO NOT believe the charts from the piston makers because more often than not their piston will sit too low.

I am pushing right at 400 with 2.14/1.74 ported 516 heads, Comps nostalgia .474 cam, Holley SD and a 650 mighty demon. Not a stroker here. All in all I am happy with the mill. Its got great low end and has great idle, and drive quality. There is probably more in the motor That I may try to find later, but for now it is just fine for cruisin around town.

Ademon your build sounds good! I guess I do not need 450 horse,just a bit more. What do you think his build is rated at?

What heads are on there now?

compression, cam and carb. If you want to keep the 3.23's you'll need a cam in the 220-230's-470-480's range. Pick up a used dual plane intake like a DP4B, a set of headers will help and have your distrib curved. Not sure you'll have 450 but it will be a strong runner.

Not sure what heads are on there. I plan on changing to 3.91's.

Well dropped the motor off to the shop today. They will start tearing it down on Tue. Just wanted to get a few more piston choices from any body. I know there not many for the 383. Come to the idea that 400 hp or around is more realistic. They will also let me know what heads are on it. It's safe to say that the holley 600 has to go even if it was jetted differently. Any more thoughts would be great. Thanks

$3500 that is with me putting the motor back in. A total rebuild on their part.

The deal is this...Unless you tell them what parts to use most machine shops are gonna do a regular rebuild..Most shops are chevy/ford oriented, not saying they aren't capable machists just that they know what parts to put together to make a strong running brand X but probably not a strong 383...By design 383's are hard to get proper compression ratios out of with shelf pistons & stock cylinder heads...

I found a new set of the 12.5 TRW's .030 for my new 383. coupled with Muscle Motors stage 1 iron heads, I'm right at 10.5:1. A comp xe285-hl, rpm intake 1 3/4 headers and 4.10's. Should make my duster scoot.

https://board.moparts.org/ubbthreads/show...rue#Post4933738

Use eigher a KB162 piston or a 2316 Federal mogul/TRW to keep your compression height correct. Anything less than these are a waist of money and super-low compression. Even with these pistons and an 85CC or so head, your barely at 9:1.

Follow the link on a Purestock 383 thread.

If your shop is mopar literate he should now how to do it.If they are not you will have to be specific with what you want and how to get there.A true 9.5-1 with iron heads is about max for pump gas.Any money spent on porting the heads(knowledgeable porting work that is)is well spent.Most of your power gains will come from here.
The lunati voodoo cam 60302 would be a good street cam with the 3.23's.Maybe the 60303 with the 3.91's as long as you have a true 9.5-1.A performer rpm or dp4b intake,a 700dp(or 750 vacuum holley),1 3/4 headers,and a 2600-2800 stall converter will wake that thing up.Make sure you have your dist recurved or just use the mp electronic one to get your advance in sooner.Running more initial advance will help with the idle and throttle response as well.