383 HP valve sizes

[Richie]

Hi everybody:

I have a really good 1968 383 but it's a dished piston engine. To make it an HP equivalent I'll need flat tops and do I need to change valve sizes and to what? It has 906 heads. It was rebuilt about 1500 miles ago but it will all be taken apart again because it's been sitting so long after I got it and I can't have it with the low comp. anyway.

 

[R413]

Every 906 head came with 2.08 1.74 valves. Nothing bigger or small, ever.
Wheather a 383 2bbl or a 440 6bbl.

 

[PurpleBeeper]

Hi everybody:

I have a really good 1968 383 but it's a dished piston engine. To make it an HP equivalent I'll need flat tops and do I need to change valve sizes and to what? It has 906 heads. It was rebuilt about 1500 miles ago but it will all be taken apart again because it's been sitting so long after I got it and I can't have it with the low comp. anyway.

R413 is correct. To convert to”HP” you’d install flat top pistons and a slightly larger cam….done! Oh, and maybe a different carburetor. Now it’s an HP motor

 

[69Bee]

You have 2 piston options:
1) Silvolite 1267, Piston Compression Height 1.824", Piston Volume +10cc 4v, Flat Top Piston
2) Kieth Black 243, Piston Compression Height 1.840" (piston ~+0.018" above deck), Piston Volume +6cc 2v, Flat Top Piston
Nevermind, my mistake...

 

[lewtot184]

Speed- pro 2315

 

[69Bee]

Speed- pro 2315

383 piston 0.030" OS (4.280" Bore)
Stroke 3.375"
Rod 6.358"

 

[DanielSlocum]

Whatever pistons you use....weigh them on a gram scale and compare to your originals. If they vary more than 20 grams,a rebalance will be needed i.m.o. .
If heavier.....you can take that amount off of the small ends of your rods to compensate. A machine shop can do that for you instead of a more expensive total balance job [at like $300 or more] . Good luck.

 

[R413]

Just balance it, money well spent. They are not very precise from the factory.

 

[BSB67]

You have 2 piston options:
1) Silvolite 1267, Piston Compression Height 1.824", Piston Volume +10cc 4v, Flat Top Piston
2) Kieth Black 243, Piston Compression Height 1.840" (piston ~+0.018" above deck), Piston Volume +6cc 2v, Flat Top Piston

The OP has a 383.

 

[69Bee]

The OP has a 383.

Then what the hell am I doing thinking it was a 340 for??? LOL, thanks...

 

[DeltaV]

R413 is correct. To convert to”HP” you’d install flat top pistons and a slightly larger cam….done! Oh, and maybe a different carburetor. Now it’s an HP motor

And a windage tray?

 

[Richie]

Okay thanks everyone.

 

[Curiousyellow71]

Is it standard bore and has the original dished piston? Was it rerung? There may be more wear you can't see with the naked eye. I've seen cylinders that looked great but were completely shot when you measure it. Some cylinders can be straightened back out with a fixed hone. Do some measuring before you throw pistons at it.

 

[Richie]

Is it standard bore and has the original dished piston? Was it rerung? There may be more wear you can't see with the naked eye. I've seen cylinders that looked great but were completely shot when you measure it. Some cylinders can be straightened back out with a fixed hone. Do some measuring before you throw pistons at it.

The shop will find that out. I trust them I've known the family almost all my life.

 

[PurpleBeeper]

And a windage tray?

Yep, good point