Free 383 for Blaze

[74Blaze]

Longish story. Blaze has not been running well for over a year. After throwing new parts at it, checking for vacuum leaks..., I finally came to the realization that it more than likely jumped timing. I put the current engine in it in 2007. It is 290 HP GM Crate 350. Yes, I could put a new timing chain in it, but I have just received a free 383. The 383 came with the '55 Bel Air that a good friend of mine purchased last year. The story goes that it is a fresh rebuild (built ≈20 years ago) that was never re-installed in the '55. The owner had a stroke and never recovered well enough to finish the re-do of the '55.
So what I know is it's mid-90s 350 Block, with mid-60s Corvette 2.02" Heads. What I've been told is that it has 11:1 compression and a Lingenfelter Cam. Also, in it's previous configuration, it was running nitrous. Bore Scope shows that the Pistons look new and have Valve Reliefs on the tops. I'm still trying to figure out exactly what I have. My main concern is whether it has a realistic Cam for my trail-rig application.
Picture of my current 350 and a few the 383 are below.

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[xm20k]

The Z part number comes up as an old comp custom lobe of 250@50 with 501 lift on a 110 lobe sep which if it is 11:1 makes sense as it would be an older lower lift version of my 388 cam. its gonna be a race/bracket cam that's gonna want a 3k stall converter idle fairly rough and is gonna need high octane fuel at that compression ratio ie 91-93 depending on tune,cooling,etc. or race fuel ie.100-110. It's going to be the complete opposite of what you want for a 4wheeler unless you plan on being wide open the whole time.

Just what I could find im at work and a quick googlefu on my phone so might not be correct.

 

[74Blaze]

opposite of what you want for a 4wheeler

Yep. That's what I was afraid of. They guy used the '55 as a street racer back in the 80s & 90s. I'll need to figure out what Cam I want in it for my trail rig. I don't mind the 11:1 compression as I'm thinking that it should run fine on 91-93 octane with the right Cam. No need to worry about the stall speed as I'm running an SM465 manual.

 

[74Blaze]

Trying to figure out my best options. If I calculate it right. Using the 383 long block with my 290 HP 350 Heads (76cc Combustion Chambers & 8.5:1 Compression) would drop the compression ratio from 11:1 (62cc Combustion Chambers on the 2.02" Heads) to ≈9.4:1.

Can somebody check my math?

 

[ChuckN]

Trying to figure out my best options. If I calculate it right. Using the 383 long block with my 290 HP 350 Heads (76cc Combustion Chambers & 8.5:1 Compression) would drop the compression ratio from 11:1 (62cc Combustion Chambers on the 2.02" Heads) to ≈9.4:1.

Can somebody check my math?

You could get a rough estimate, but it won’t be accurate.

The size of the valve reliefs , how far the pistons sit in the hole (was the block decked?) and how thick the head gaskets are plays a huge part and could make the ratio vary by a point.

 

[ChuckN]

Are you planning on pulling the heads and what-not for a refresh? You could get a better idea of what you have there.

The good thing is that (I’m assuming) it’s a roller cam block. For a cam, I’ve had good a good experience with Howards- I called them up, told them my setup (rear gear, converter, weight, intended usage) and then the picked a cam out for me.

 

[74Blaze]

"(I’m assuming) it’s a roller cam block"

From what I understand the block (Casting number 10243880) can be used with a Roller Cam, but it currently has non-roller solid lifters (which I won't be using). I will be pulling the Heads, unless I decide to use the 2.02" Heads which are currently on it. The engine was completely re-built years ago and never installed in a vehicle. The problem is that is that it was built as a street race engine for a '55 Bel Air. I want to use it in my '74 K5 trail rig, thus I'm trying to figure out my best options to turn it from a high RPM Horsepower set-up to a low RPM torque motor.

 

[ChuckN]

Ok, so then what you could do is take a mechanics ruler across the deck with a feeler gauge with the piston at TDC and see how many thousandths it is below deck. Then, see if the pistons have a stamping on them (unless they are stock) and see if you can find out how many CCs the reliefs are. After that, aim for 35-45 thousandths piston to head clearance with the head gasket, then pick your poison with whatever cylinder head you use (chamber volume) and that will tell you your compression ratio.

Then I’d call a cam company that you trust and tell them what you’re going to do with it and your setup and let them help you pick out your cam.

Apologies if this is rudimentary and you’re already aware of this.

 

[74Blaze]

Thank you, ChuckN. I will do as you suggest. I'm not so worried about the exact compression ratio. What I want to end-up with is a torquier, yet reliable engine so I can better enjoy my Blazer. I'm more convinced that the 383 with the Heads off the GM Performance 350 is the better way to go. I will consult an expert (or several) before selecting a Cam that will be suitable for my application. I'll probably sleep on it for a few weeks before purchasing all the necessary parts. My goal is to have it ready for enjoyment by next Spring, so no huge hurry.

 

[ChuckN]

Thank you, ChuckN. I will do as you suggest. I'm not so worried about the exact compression ratio. What I want to end-up with is a torquier, yet reliable engine so I can better enjoy my Blazer. I'm more convinced that the 383 with the Heads off the GM Performance 350 is the better way to go. I will consult an expert (or several) before selecting a Cam that will be suitable for my application. I'll probably sleep on it for a few weeks before purchasing all the necessary parts. My goal is to have it ready for enjoyment by next Spring, so no huge hurry.

Awesome! Best of luck to ya!

Lots of internet keyboard warriors will tell you that a 383 has to breathe with big heads, but if you’re building a 4000rpm torque monster then there’s no real need.

 

[bucket]

Are they actually earlier style heads, or do they have the accessory holes?

Iirc, the 290 crate heads kinda suck.

 

[xm20k]

Post the casting numbers on the heads, it doesn't look like they have accessory holes but that doesn't mean they are the good camel hump heads.

 

[74Blaze]

Are they actually earlier style heads, or do they have the accessory holes?

They are the old vintage Corvette style Heads. No accessory holes. That was one of difficulties in using them. I would have get creative in mounting my Steering Pump.

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[ChuckN]

I had camel hump heads on mine previously- my truck came with this kit installed and it works so good I’m going to continue to use it for now, even though I have accessory holes with the new heads.
https://www.ictbillet.com/products/...MDohb6rX55nCHWIHaC0uIn71eLivloV8aAubjEALw_wcB

 

[ChuckN]

They are the old vintage Corvette style Heads. No accessory holes. That was one of difficulties in using them. I would have get creative in mounting my Steering Pump.

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Likely typical 1.94/1.5 valves with 165cc intake runners. The “461X” head is floating around out there and people talk about their existence but it’s likely they just your garden variety.

If they need a rebuild, you could probably spend the same amount of money on something like a Skip White aluminum head (well regarded by many) and get accessory holes back.