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Unfortunatly the 993 is an open chamber head at 74-7cc’s so compression with stock pistons is in the high sevens to low 8’s. A stock stall converter limits the cam to not more than 220 degrees intake at .050 inch lift such a cam should have an LSA 110 degrees, preferable more. This should be enough cam to get close to 300 horsepower. Raising the compression through head milling a less expensive option than a better piston design to up the compression would reward you with considerably more torque and horsepower and reduce the fuel burn getting them. A thin shim style head gasket would improve the squish/quench clearance for better detonation resistance with added compression but these like a nice clean and accurate mating surface but this gets around the cost of milling the block decks.

Modern 64cc chamber head’s would be a huge difference allowing 300 horses on a cam of about 200 degrees intake at .050 lift which is more stock converter stall and high intake vacuum friendly.

Bogie
 

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Discussion Starter · #4 ·
Unfortunatly the 993 is an open chamber head at 74-7cc’s so compression with stock pistons is in the high sevens to low 8’s. A stock stall converter limits the cam to not more than 220 degrees intake at .050 inch lift such a cam should have an LSA 110 degrees, preferable more. This should be enough cam to get close to 300 horsepower. Raising the compression through head milling a less expensive option than a better piston design to up the compression would reward you with considerably more torque and horsepower and reduce the fuel burn getting them. A thin shim style head gasket would improve the squish/quench clearance for better detonation resistance with added compression but these like a nice clean and accurate mating surface but this gets around the cost of milling the block decks.

Modern 64cc chamber head’s would be a huge difference allowing 300 horses on a cam of about 200 degrees intake at .050 lift which is more stock converter stall and high intake vacuum friendly.

Bogie
Wow! Thanks
 

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Assuming you're asking about a hydraulic flat tappet?

The Crane 274H06 grind is another good limit of the stock converter cam. The tight 106° LSa makes for a nice rumble at idle and pumps up the low and midrange torque.
You can still get that grind from the Summit Racing house line.
# SUM-1785
CHEVROLET Summit Racing SUM-1785 Summit Racing® Camshafts | Summit Racing

If you haven't already thought about it, you really should replace the valvesprings in the rebuild.

Agree with Bogie on the head gasket choice.
Steel shim at .015"-.018" thick, or the Mahle/Clevite/Victor-Rienz #5746 composite at .026"-.028" thick if head and block aren't flat enough for a shim to stay sealed.
I would not use anything thicker, you need to preserve compression and tighten quench clearance as much as you can.
 

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Discussion Starter · #8 ·
Hey guys how about this one? Too big for stock converter???
Hydraulic Flat Tappet
Exh. Duration @ .050 in. (Deg)
224
Int. Duration @ .050 in. (Deg)
224
Lobe Separation (Deg)
114
Exh. Centerline (Deg)
119
Int. Centerline (Deg)
109
Exhaust Valve Lift
0.465 in (11.811 mm)
Intake Valve Lift
0.465 in (11.811 mm)
 

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That cam is pretty much someone’s idea of the L46, L82 cam. It is sitting at the cut line of what is comfortable to live with using a factory stall converter.

This pretty much is the same cam GM puts in the 290 horse, 350 crate engine. This combination similar to your build is a nice cam married to less than ideal head’s, hence only rated at 290 horses where this cam on that short block with L31 Vortec head’s or reasonable aftermarket facsimile would hit numbers about 340 hp or upward of 40 more ponies.

So this sets a stage for looking in the future to making a head change. If you haven’t sunk any money into rebuilding the 993 head’s I would recommend not doing so, budgets being budgets that money on the aftermarket would make a big dent in the cost of new head’s. Most everybody selling head’s also makes a cast iron version of their aluminum heads that is a lot more budget friendly. Plus in cast iron you skate around the cost’s associated with aluminum head’s which should include zero decking the block or replacing the pistons with raised crown versions which are the two methods used to correct the squish/quench clearance with aluminum’s need for a thicker head gasket. Aluminum head’s are also mostly .1 inch taller due to the thicker sectional thickness of the casting which add the cost of longer pushrods. On the positive cost side aftermarket heads fit either the standard 1955-1986 or the 1996 up Vortec intake bolt pattern so with aftermarket heads you’re not forced into buying an intake that fits the Vortec bolt pattern. So there are some significant cost differences between buying a set of junkyard or new for that matter L31 Vortecs agsinst the costs of aftermarket renditions.

If you are bound to using the 993’s either the thin .015 or the .019 FelPro shim will help get the compression up and tighten the squish/quench clearance while certainly a .030 mill cut will get the compression up without being so much that the intake needs to be remachined as well. Here again FelPro comes to the rescue with 1/16th thick intakes gaskets or 1/8 inch thick. You can use these to fiddle the intake fit on milled head’s.

To a good extent the cam you’re looking at with a 114 LSA moderates what would be bad habits when combined with lower compression than ideal. If you used a cam of this timing having an LSA under 110 degrees with these head’s it would be miserable on the street. This was GM’s SMOG era performance cam.

The problem with cam to stall speed is mostly two things where big and bigger cams idle fast, reduce low end torque and move the torque and horsepower peaks to higher RPMs. On the street the fast idle on a stock stall converter wants to drag you through stops, it takes a lot of foot pressure to keep the vehicle in place which is tiring. The second is low speed performance is degraded essentially right at highway cruise RPM, on the race track the engine at launch is way under its torque curve and is slow to get into motion from a dead stop. So the higher speed stall converter puts some lower RPM slip into the system to reduce pull at idle when stopped and gives the engine space to spin up into its optimism power curves when launching into a drag race contest. The downside of higher stall is increased ATF temps when operating for long periods under the stall speed, so more cooling of the tranny oil is called for.

Anyway a lot of discussion the bottom line is this cam is just reaching the upper limit of what is considered OK with a typical production stall speed converter. You might see some minor challenges with the higher idle speed it will want but nothing to an extreme requiring you take technical action, you‘ll just know the engine is running some cam.

Bogie
 
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