350 Motor 350/400 HP build

I have a 1978 chevy lwb 4x4 pickup that I'm building an engine for,I'm trying to get the engine in the neighborhood of 300-350 hp 350-400tq the engine is a 1974 350 casting #3970010 2 bolt main factory rated @ 145hp I'm doing a complete rebuild and I'm going back with flat top pistons that are supposed to provide 9.65:1 compression ratio in a standard bore 350 and I'm having the block bored .030. I already bought a low mileage(39,000 miles) set of 906 vortec heads and I'm planning to use a rv cam because I want lots of torque also I'm using a dual plane pro comp aluminum intake manifold (idle-5500rpm)and a holley 650cfm carb and 1 5/8 headers with flowmaster dual exhaust will this combo even come close to what I'm trying to achieve or am I being to optimistic any help would be greatly appreciated.


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Ayuh,.... Flat-top pistons, 'n Vortec heads can be a Problem....

If ya mill the block to get .043 or so quench, yer comp ratio will be Too High....

Gonna need the piston part number. When I put a flat-top piston into your combo with 64cc heads, it comes out 10.2:1 static compression ratio. This will not work for what you want to do.

Ok I have'nt bought any engine parts except the heads so far so if you can recommend a better piston to bring the compression down that would be greatly appreciated,and what would be the ideal compression ratio for what I'm looking for in your opinion?

OK, couple of ways to go here....

L31's are limited to 0.420" max valve lift with the stock spring and retainer arrangement because at lifts over that, the retainer can smash into the seal. This leaves 0.030" retainer to seal clearance @0.420" valve lift. You can use the stock spring/retainer/seal arrangement if you use a cam that has a 0.420" or less valve lift and make good power for a street motor. The stock arrangement used rail rockers to center the rocker over the valve tip.

Or, you can do some machine work, cutting the O.D. and the height of the valve guide boss to accept springs/retainers/seals that will allow more cam lift. You can also cut the heads for screw-in studs and guideplates if you want to use a conventional 350 stamped rocker or aftermarket roller rocker.

Or you can install springs and retainers that are meant to be used with more cam but no machine work such as the Crane kit 10309-1. This still leaves you with rail rockers and pressed-in studs. You can pin the studs with a Mr. Gasket kit 806G.
http://www.sallee-chevrolet.com/Cyl...eads/Vortec.cfm
http://www.race-mart.com/Mr._Gasket-MRG-806G.html
http://www.race-mart.com/Crane_Cams-417288.html

Personally, if I were on a budget, I'd opt for the short lift cam, pin the studs and use the rail rockers. Now, what do you want to do? Once you determine that, we can help you with the rest of the build.

So, which way do you want to go?

Your guesstimate on CR is probably fairly close. I get just over 9.6:1, using the following numbers:

• standard SBC 350 bore and stroke
• 4.1" head gasket bore
• 0.041" HG thickness
• 64cc chamber
• -5cc valve relief
• 0.025" piston deck clearance

The above assumes a virgin deck, "true" FT pistons (not dished like most factory pistons), and that the deck and chambers are spot on to what the factory intended.

This gives a too-wide quench* distance of 0.066". You want the quench to be close to but not less than 0.040". There is some leeway here but that's the target.
*HERE is a thread you will find useful to bone up on quench.

In many cases the 0.041" quench is gotten by zero decking the block and using a commonly available 0.041" HG. Another option to get a better quench measurement is to use a thinner HG but to use a 0.015" steel shim HG you need a good flat decks and the surface finish is important- this means in most cases the head and block decks will need to be cut a small amount to bring them into spec. Tightening up the quench will also raise the CR. You'll have a CR of 10.2:1 w/an 'ideal' quench of 0.041" and all else as above. This is too high, though- at least for pump gas and a mild RV-type cam.

There's a page HERE that shows the correlation between CR and cam duration @ 0.050" lift. To run 10-plus CR will mean you need a lot more cam than any RV grind, pump premium will be needed at the very least and there's no safety margin for anything that might cause detonation. And if the CR causes the total timing to be lowered from max power total timing, you've defeated much of the reason you did the build in the first place. Lowering max power total timing to run a higher CR is the worst possible move. So now you're left w/some decisions to make:

• You can lower the CR by using dished pistons, preferably inverted dome or D-cup to maximize the quench/squish effect.
• You can use heads w/a bigger chamber or modify the Vortec heads by opening up the chambers. 68cc chambers brings the CR down to 9.8:1- much more reasonable, IMO but </= 9.5 would be better.
• You can run a bigger camshaft.
• You can build the engine w/a too-wide quench and deal w/it.

You will need to measure the short block and heads for the dimensions that give you the CR to be sure of what you have. No telling for example if the heads or block was decked previously. Manufacturing and machining tolerances can change things so you need to see just what you're working with in order to know what needs to be done.

Once that's done you can go about making decisions and choosing parts. The carb, intake and exhaust system you have will do for what your goals are, so that's a plus. This post basically just scratches the surface. Not knowing your skill level or experience, I cannot really go much further. If you're still learning, pick up a book or two by David Vizzard on the SBC engine.

Cheapo to build, cheap gas 350 street motor....
These pistons...
http://www.summitracing.com/parts/UEM-KB142-030/
This cam...
http://www.summitracing.com/parts/HRS-CL112011-11/
L31 heads from a boneyard, casting # 12558062 or 10239906. Magnflux 'em for cracks. Fit new STOCK springs and seals. Make certain seals are fully seated on the guide boss by tapping them with a socket and small hammer. The stock springs will work well with the mild cam and will not pull the rocker studs out of the heads. Doesn't matter whether the heads have hard inserts in the exhaust or induction hardened seats, either way will work. Same casting, both styles flow the same. Give 'em a good valve job and otherwise leave 'em alone. Use the rail rockers that came on the heads stock.
If the main bearing bore out of parallel, align-hone or align-bore the main bearing bores in the block and cut the block decks for 9.015" block deck height, referenced off the main bearing bore so that you know the block deck height is equal on all four corners. This will insure that the heads sit level and flat on the deck and that the intake manifold will sit square to the heads with no gaps to cause an internal or external vacuum leak. Use GM head gasket #10105117. Static compression ratio will be 9.1:1 and squish will be 0.042". Use Edelbrock #7116 Performer RPM intake manifold or give up ~30 hp with a short Performer intake. 600 carb is all you'll need.
Makes 365 hp @ 5000 rpm's with a double torque peak of 420 ft/lbs @3500 and 4000. Should make this power on crummy cat-pea pump gas without detonation and make a real nice daily driver motor.
Cam begins making power at 1200, so it's your call whether or not you need a looser converter. If I did anything at all with this combo, it would be a mild 2000 stall unit just so I didn't have to contend with the vehicle creeping at stoplights and also to get up into the 1500 rpm low range of the RPM intake manifold when the light turns green.