383 engine building

[LonleyDuster]

Hello all, I'm building a 383 for my 68 satellite. I have a 68 block and 906 heads. I won't be racing this car, but I like the sound of headers and a loping idle. I will be using the heads in stock configuation. This is a no a/c or power brake car. Can I have your opinions on piston and cam selection? Thank you.

 

[69HEMICORONETR/TCONV]

I would keep the compression a 9 to 1 to make it "Pump Gas Friendly" ...if it is going to be a All street engine, .....If it is a street only engine and won't be seeing any "Action" there no need to go too exotic on the pistons or the cam, Just enough to make is sound lumpy. are you using an Automatic or a 4 speed ?

 

[LonleyDuster]

It's an automatic, could I use stock pistons and shave the heads to create that compression? How high of cam lift can I go without changing valve springs?

 

[Meep-Meep]

I think 9.5: 1 CR will be good. I personally like closed chamber heads because of the quench, which will help reduce the possibility of detonation. Cam selection should be based on intake valve closing vs. CR rather than lift. It's usually hard to find these numbers while shopping for a cam (all you get is lift and duration) so next best thing is to stick with the manufacturers guidelines regarding compression ratio. Shoot for about 160 PSI of cranking pressure. The cam you should end up with will be in the 270-280 deg range, about .480 lift and 110 deg lobe separation (108 will be lumpier but will also blow off more cylinder pressure) and have a power band in the 2000-6000 RPM range. A good single spring with a damper producing about 120-130 lbs of seat pressure should be fine. If you end up with 8.8:1 or so then you should consider a different cam.

 

[68ChargerAG]

I have always understood that shaving the heads down to increase compression is not a good idea because it will change your intake manifold geometry, thus opening another whole can of worms. They should only be shaved enough to make them flat if they are out of spec. I would say you should use high compression pistons to get higher compression, especially if you are buying new pistons anyway.

I have a 383 and went with a Comp Cams cam with around 0.48 lift and did have to use stronger springs with dampers (as Meep-Meep described), so if you want to use stock springs you will probably have to stick with something smaller than that. Not sure if that helps you much though.

 

[63RedFury]

When you buy a cam you should buy springs to match.Comp cams has a great tech line.Give Comp your enginge size,carb size,type of intake,header size,compression ratio,gear,and weight of the car and they will give you a cam to match your combo.

 

[LonleyDuster]

Thanks for the help. Are 906 heads (78.5) considered closed chambered heads? Also, will I need to get hardend exhaust seats for occasional driving?

 

[Meep-Meep]

No, 906's are open chamber and hard seats are recommended unless you want to use a lead additive. You could just use race gas or lead additive, but eventually you will wind up at the cost of the hard seat installation.

KB has a piston that has a quench dome, which turns the open chamber head into a closed chamber. You will need to make a trial assembly before you have the engine balanced in case you have to remove material from the piston dome because of head interference. KB's are set up for floating pins so have the rod bushed to allow for easy removal and assembly of the pistons and rods during the test fit stage.

 

[69 Runner]

Build it with a 9.5-10.0 compression. Slap in a Hemi grind cam (.474-280*) straight up. Use a DP4B or an M1 dual plane intake, 625cfm carb and headers. You'll love the thump, and it's very streetable. I ran this setup for years in my Bee (with a bunch of tweaks) got 15mpg on the highway and ran 13.40s

 

[5.7 hemi]

625cfm seems a tad small for the carb.

 

[Meep-Meep]

In my experience the 108 LC 280 deg cams like the Torker and a 700 DP or a 750 vac secondary. Every time I ran a dual plane it slowed the car down. I suppose I could have upped the CFM but never tried that.

 

[69 Runner]

It was modified:yes:

 

[Meep-Meep]

Ahhhhh-Haaaaaa!