Originally Posted by jessejones473
ok ima do it in the morning. but it runs fine and has decent power. i just know it doesnt have the 350 hp like i was expecting. i was told to dump the 700r4 and also the ebrock carb and go with holley. i would think since its a 40 year old motor i know its been rebuilt, i would think it maybe had some type of work done to it. he said he rebuilt it 6 months before i got it.
Whoa there big fella, calm down this isn't such a disaster. Actually for an automatic the 700R4 is a pretty good choice, especially if it's late 1980 through 192 or so which have the fixes needed in the earlier models.
Yes the engine comes from the heart of the first generation response to emissions which did much to neuter anything that looked like power mostly because of the need at that time to reduce nitrogen oxide in the exhaust and aside from massively reducing cam timing and compression there wasn't the technology of 3 way converters yet available.
So the big issue is to restore can timing and compression. But there are two ways to go about the cam you went the old way which is to use these muscle car era cams which have much of their duration in ramps leading to and from the lobe so they look and sound nasty but without huge increases in compression that today's pump gasoline will not support they end up proving to fuel swilling, moderate power output solutions. The much better choice of cam is the modern fast lifting cam which on the surface appear to have less duration because the long ramps are eliminated. These work with modern heads that have fast burn chambers typical of what is of the well respected L31 Vortec, but there are many modern heads in the aftermarket that include these features.
Changing pistons is not simple and if the engine has been recently rebuilt may not form a cost stand point be that desirable to change. Certainly there is value in going to a modern hypereutectic cast piston with a D dish piston to manage compression to what 92/93 unleaded pump fuel will tolerate which would be optimal. But to avoid taking the bottom end apart and still getting 350 horses can still be accomplished with the pistons you have.
Using Vortec style heads with a cam like the Comp XE268H, with an Edlebrock performer RPM intake with your carb and headers into 2-1/2 inch duals this will easily crank 350 hp. With pocket porting the heads and adding 1.6 rockers this can push 380 without a problem. The XE268H has an available spring kit, I highly recommend using it. Good quality lifters are must, if not Comps, GM part number 5232720 are a good substitute, these are lot more expensive than the cheap 50 buck a set lifters but if you want the cam to live these hard faced flat tappets at 240-350 bucks for the set are the only way to go.
You will also find this head change against the 290 Lunati cams you have in the engine will make a world of difference as the compression will come up which is what is needed. A late to close the intake valve cam like the 290 bleeds a lot of mixture back into the intake as the rising piston forces it out of the cylinder until enough RPM is reached to where the inertia of the mixture can overcome the reverse pumping action of the piston. This is the reason why big cams loose so much bottom end power and move the torque and horsepower peaks up the RPM band also moving them closer together. This is called the Dynamic Compression Ratio (DCR) the effect is that the Static Compression Ratio (what you measure from the volumes) below the torque peak RPM is reduced by the stroke lost in crankshaft degrees to where the intake valve is seated by the cam. Go here and play United Engine & Machine Co. Incorporated
Piston selection affects a thing called squish/quench. This is where the surface of the piston crown approaches the flat step of the head. A flat top piston is ideal for flame propagation by not getting in the way of the flame front and maximizes squish/quench by coming close to the step of the head.
The latter subject of squish/quench boosts the engines ability to extract power form the mixture and extends the range of the fuel's octane. Preferably for a street engine this would be about a .040 inch clearance between the piston crown and the heads step. OEM pistons tend to have a large and deep dish to control compression ratio below the detonation threshold which also tend to cause you to have to raise the octane of the fuel for the compression ratio being used. A D or step dish piston solves both problems by having a flat surface to oppose the set of the head while being dished under the valve pocket to control overall compression ratio. But this has the advantage of allowing more compression as with effective squish/quench the engine will react to the fuel as if the fuel has 4 to 6 more octane than it is rated at.