[talbertmt]

Hey guys I have a general question about which cam I should go for in my 383 I am building. My current setup is a cleaned 350 block bored 30 over. I had the motor decked to .010. I am using flattop pistions with the 5 cc valve reliefs and the head casting numbers are 3795896. I have a set of z 28 springs on them but I will be willing to change them for a cam match. I am also running a set of COMP Cams Pro Magnum Roller Rocker Arms 1.6 ratio. I am in need of making this rig run on 93 octane gas and at the moment with a .040 gasket I am showing a 11.38 : 1 compression and I have talked to some of my Mechanic friends and they have all told me that it will diesel on pump gas unless I get a large cam. Any help would be great.

[k-star]

To much static compression for the octane the engine is going to run on CAN'T be fix with a large cam. It's a very poplar theory, but it's not the way to fix it.

You need to get your static compression down to 10.1 with iron heads, and 10.5 ish with aluminum heads for it to work with a bit of safety margin built in for tuning.

What everybody thinks is that a big cam with a later closing event that kills cylinder pressure (cranking) will crutch an engine that needs a higher octane to operate out of the detonation zone..But all you need to do is think about what the engine is doing at say 6500rpm and you will realize right away it's not the way to go.


Keith

[jbvcw71]

It really depends on what kind of cam you're running.
Stock cams (250 duration) with heated intake crossover wont tollerate much more than 9 to 1.
A dished 350 piston (15cc) & composite Gasket .038 compressed will put in the realm of 8.5 to 1 & will work VERY WELL on low octane Pump Gas
& up to 265 Duration Cams (Very Streetable & work Well with auto trans Stock converters)
Dish Pistons can be had for as cheap as $60 a set.
They are perfect with the EXCELLENT head choice you have made.
The 896 Casting is a Closed Chamber 283/327 Design that utilizes the Combustion chamber of the FUELIE heads without the costs.

The Closed Chamber Combustion Chambers make 20-30 more HP & Torque everywhere in the rev range, compared to open chamber (70-75cc) Smog Castings !!!

(Buy some 13/16" Gasketed plugs wherever you see them, they're getting harder to come by...)

Keep those flat top slugs for your next build that uses open chamber (75cc) heads. They'll work perfectly!

[jbvcw71]

You only need to find a way to add 11 cc's to your existing combination.

Machining piston tops.
Porting Combustion Chambers
Thicker than typical Head gasket

I calcuate you'll need 11 cc's more than you have to achieve 9 to 1 comp.

Personally I'd take some metal off of the pistons (valve relief area)
& polish the combustion chambers with an egg shaped carbide cutter.

I wouldn't change the shape of the combustion chamber much, just relieve the path of the intake valve.

Also make sure you block off the heated crossover *intake* to keep the charge cool.