How to Beef Up Old 350
I want to build the cheapest, to the lowest degree expensive small-block 350 Chevy that can make around 400 to 450 horsepower. How would I do that? I have a 350 Chevy truck engine brusque cake with a one-piece rear main seal. I actually don't know what it was originally in but I'm pretty sure it was a truck. I'd like to put this engine in a '69 C-10 pickup to terrorize the streets. How much power could I make? — B.C.
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Jeff Smith: Before we get started, permit's only say that the terms "lots of horsepower" and "cheapest" are at opposing ends of the same discussion.
It's not easy. Frankly, the easiest manner to make 400 to 425 horsepower would be to buy a 5.3L truck engine and put on a carbureted intake manifold, a 750 cfm Holley carb, headers, and stick in a mild hydraulic roller like Acme's Stage 2 truck cam with 218 degrees of duration.
That's not what you asked, but that would be the easiest style to achieve 400 hp. Of course, adapting an LS to your truck would be expensive and not function of your programme. So at present let'due south accost your question.
Information technology's not piece of cake to brand 400 hp with a basic 350 Chevy using stock heads.
The appearance of modernistic engines that make 400 hp or more has colored the reality of the by. In our experience, y'all must accept a decent set of cylinder heads in order to make 400 hp on a basic, low-compression 350 c.i.d. small-block Chevy.
Let'southward start by assuming (here we go) that your short block is in decent shape. That means you can't feel an border at the height of the cylinder wall from bore wear. If you lot can feel a ridge, then you lot are wasting your fourth dimension to try to brand ability. A ridge of any thickness means the cylinder bore is worn and the rings won't seal and all your money spent on good parts will simply pressurize the oil pan when that cylinder pressure leaks past the rings. Simply we'll play along and presume the short block is audio.
The biggest detail that will improve power is a good set of heads. The more air the heads can move through the combustion space, the more than power the engine will make. But aftermarket heads price money that you lot don't want to spend. The best iron production cylinder head that Chevrolet ever produced was the Vortec that came on truck engines from 1996 up through when the LS engines kickoff appeared in 1998.
The Vortec head is a bit of an adjunct from the traditional small-scale-cake Chevy caput. It demands its own, specific intake manifold and features smaller ane.94/ane.50-inch valve sizes and a meaty 64cc sleeping room.
This smaller chamber helps add power by adding compression. Y'all can still find these heads in the junkyard but be careful equally engines with a long service life tin can suffer cracks that make them unserviceable.
Let's commencement with the first benefit to using these heads — the smaller bedchamber. Nearly all traditional heads for a mid-seventy's and later on 350 c.i.d. small-block came with 76cc chambers. This was done to reduce pinch so that Chevrolet could achieve the emissions requirements.
With the smaller 64cc chamber Vortec heads, this means more power. Allow's presume that your 350 comes with typical iv-eyebrow pistons that measure about 0.020-inch down from the deck.
If nosotros use a stock limerick gasket at 0.041-inch thick with a 76cc chamber, we end up with a compression ratio virtually 8.five:1. In most product 350 Chevys, this is really loftier. Loose product tolerances oft limit these engines to barely eight.0:one. By only adding a 64cc chamber caput, the pinch jumps to 9.6:i. That's worth x-12 hp with no other changes.
But the real dazzler of the Vortec is its additional airflow even using 1.94/i.50-inch valves. The all-time thing to exercise here is brand certain the valve seats are in decent shape and seal properly and exit them alone. Our period bench tests from dorsum in the day reveal these heads to flow around 230 cfm at 0.500-inch lift at a fourth dimension when a production iron minor-block head generally couldn't catamenia 200 cfm without porting. Plus, the Vortec will add 20 to almost xxx cfm in the mid-lift valve positions like 0.300-inch and this is where the additional cylinder filling actually crams the air in for a mild street engine. Peak flow numbers are only accomplished at one indicate, just mid-elevator valve lift occurs twice — in one case on the mode upwardly and again every bit the valve is endmost.
By adding the Vortec head, nosotros have the makings of a more powerful engine with more compression and airflow.
Next, nosotros add a camshaft. Your engine may be equipped with the fixtures in the block to allow a hydraulic roller cam, just since we don't know if this is the instance, nosotros'll assume that information technology is a flat tappet engine. Since your budget is express, that points us to a flat tappet hydraulic cam package.
Back when nosotros were testing these combinations, our favorite was a conservative cam from COMP called the Xtreme Free energy 268H. With advertised specs of 268/280 it offered 224/230 degrees at 0.050-inch tappet lift with valve elevator numbers of 0.477/0.480. This added valve lift creates a trouble for those Vortec heads unless changes are made to either the valve springs or machining the heads to improve retainer-to-seal clearance. So permit's bear upon on that.
The Vortec heads apply a very alpine valve guide boss. With stock springs and retainers, there is only about 0.475-inch of clearance between the bottom of the retainer and the tiptop of the valve guide seal. This limits valve elevator to an absolute maximum of 0.450-inch lift. At that place are two possible remedies to allow additional valve lift.
The first involves machining the valve guide meridian by using a COMP cutter (PN 4726) and arbor (PN 4732) and a ½-inch drill motor or drill press. Cutting the top down by roughly 0.050-inch or more than will be sufficient. This also cuts the guide diameter down to use a 0.530-inch diameter seal, which means new seals are required. If you are considering this, practice using this tool on a junk caput showtime to make sure yous get all the dimensions correctly cutting. There accept been reports that some of the cutters may make the guide O.D. likewise pocket-size for the 0.530-inch seal.
Of course you could pay a auto store to perform this work, which isn't that much more than doing it yourself and may be the best solution if you don't have experience with machine tools.
When we performed this little machining practise, the cutter worked perfectly and produce sufficient clearance for a 0.500-inch lift cam.
If y'all decide to alter springs, COMP offers a 26915 beehive spring and matching retainer that will produce a little more clearance to allow up to roughly 0.500-inch of valve lift. We oasis't checked that lately so if you go this route, information technology would be worthwhile to verify those numbers.
The Vortec caput likewise requires several components that are different from the traditional small-block Chevy parts list. Let's get-go with these heads require guided rockers that have ii small ridges that straddle the valve stem tip. This was done to eliminate the need for pushrod guide plates. The Vortec head too requires its ain unique intake manifold, centerbolt-fashion valve covers, and spark plugs.
For your application, we'd suggest an Edelbrock Performer RPM intake. Remember that this will likewise crave a Vortec fashion intake gasket.
The combination of the heads, Xtreme Free energy cam, Performer RPM manifold, 750 cfm carburetor, and headers will push button your 350 into the 410 to 420 hp range — again bold the rings are in decent shape.
Of course, if all this chasing around looking for a fix of used heads and and then spending time and money modifying them seems similar a lot of piece of work, Summit has a solution every bit a make new pair of atomic number 26 Vortec castings that are fitted with all new valves and springs.
The Summit Vortec sports a 175cc intake port, screw-in rocker studs, the aforementioned 1.94 / ane.50-inch valve sizes and a 67cc combustion chamber. Flow numbers are better than the production heads and the heads are capable of accommodating a 0.500-inch-plus elevator camshaft. For the money, this might exist the simplest and easiest way to get to your 400 to 450 hp goal.
Source: https://www.onallcylinders.com/2020/06/05/ask-away-with-jeff-smith-getting-400-hp-from-an-old-small-block-chevy/
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