400ci Engine Blueprinted

Our original budget 400 suffered from both poor ring seal and Model T compression. With a 10.2:1 squeeze and better pistons and rings, this motor pushed up more than 500 lb-ft of torque and added more than 60 hp! Yahoo!

Our original budget 400 suffered from both poor ring seal and Model T compression. With a

Some engines just won’t go away. Back in the May ’11 issue, we brought you the first part of our budget-built 400 small-block Chevy. The idea was to bolt a set of iron Vortec heads on a junkyard 400 short-block, add a cam, and enjoy the torque. Right away, we ran into snags. The block was so nasty it demanded help while retaining the stock crank, pistons, and rods. The cam failed with less than a week before our deadline necessitating an unplanned thrash to rebuild the engine a second time because all that dead cam metal wiped out the main bearings. By the time we were finished, we had never worked so hard to produce so little power. The 400’s problems were multiple: The cylinders waffled like ice cream cones, preventing anything approaching ring seal, and the compression was a sickly 8.2:1 due to ugly 0.060-inch piston deck heights. In case you missed the story, the best power numbers were gained with a set of GM Performance Parts Vortec Bow Tie heads supplied by Scoggin-Dickey, and even then the 400 managed only 401 hp and 458 lb-ft of torque. We were underwhelmed.

Rather than kick the motor to the curb, we decided to build this engine correctly. The plan was to retain the original test’s cam, Vortec Bow Tie heads, Weiand intake, Holley 750-cfm carburetor, and exhaust headers so we could honestly evaluate the power increase from better cylinder sealing and a bump in compression. The difference was astonishing. You’ve probably already jumped ahead to the dyno test, but if not, the new torque numbers came in at a tire-shredding 501 lb-ft at 4,000 rpm, and horsepower leaped up to 466 at 6,000 rpm. That’s a peak horsepower bump of 65! We did cheat a little with a couple of new parts, but you’ll have to read the whole story to find out what we did.

We returned the block one more time to Barrington for a 0.030-inch bore and torque- plate-hone procedure that ensures the cylinders will actually be round. Barrington also align-honed the block for us because we added ARP studs, which changes the way the caps are loaded to the block.

We returned the block one more time to Barrington for a 0.030-inch bore and torque- plate-

While we originally planned to reuse the stock crank, Scat’s Tim Lieb suggested adding an important option. All production 400 small-blocks were built as externally balanced engines. The problem with building a performance 400 that might see rpm above 6,000 is the external weight spinning around on the crankshaft snout; it acts like a rock on the end of a string, adding load on the crankshaft that could cause eventual failure of the front main bearing. Lieb suggested an internally balanced crankshaft assembly that would require 6-inch rods and a short- compression-height piston to allow room for larger crankshaft counterweights. This package costs a little more than the standard 5.7-inch rod and cast crank system, but it offers much greater durability. One other possible advantage is the improved rod-length-to-stroke-ratio from the 6-inch connecting rods. Since it’s always a possibility that we will lean on this engine harder at a later date, we opted for the internally balanced rotating assembly and had Scat balance it for us.

The most obvious change to this different rotating assembly is that with a 6-inch rod, the piston compression height becomes very short, which moves the wristpin up into the oil control ring. This requires an oil support ring that is supplied with the pistons. It’s important to note that this support ring comes with a small dimple that should be placed with the raised portion facing down so it will not move relative to the piston.

Assembly

The correct procedure for establishing main-bearing clearance on the No. 5 main is to torque the main-cap bolts along with the oil pump. The oil pump housing distorts the housing bore, and in our case changed the clearance by 0.0005 inch.

The correct procedure for establishing main-bearing clearance on the No. 5 main is to torq

Once our machine shop, Barrington Engines, ensured that all the cylinders were properly bored, the torque plate was honed, the main bearings were align-honed, and the decks were level, we had a great foundation. By the time Barrington finished squaring this block and making the holes round, the thought occurred to us that we had $800 invested. We looked up the price of a Dart SHP block from Summit. It comes in at $1,499.41 (plus shipping). While this block is more expensive, it’s a new casting with four-bolt mains and 350-size main journals, which means slower bearing speeds over the larger stock 400 size. You will still have to hone this new block, so factor in that cost—it’s worth considering before investing $800 in a 40-year-old block.

We will not spend too much space documenting the assembly other than to mention that we did have to mix in quite a few Federal-Mogul 0.001-inch undersize bearing halves with the Scat rods to get bearing clearances to achieve our ideal 0.0025-inch clearance target. The main bearings were easier because Barrington align-honed housing bores, which established more consistent bore diameters. We also mocked up the engine to measure deck heights and then had Barrington machine the deck surfaces to create a much more consistent deck height.

Cam Specs

Comp Cams Thumpr 287TH7 hydraulic flat-tappet camshaft
Camshaft	Duration at 0.050	Lift	Lobe-Separation
Intake	235	0.490	107
Exhaust	249	0.475

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  Don Barrington Jr. showed us a slick way to check crankshaft endplay without having to bolt the crank in the block. First, place the bearing half in the cap and position it over the crank. Then use a feeler gauge to measure the endplay. If there is sufficient clearance, you can hose-clamp the two bearing halves together and then gently sand the thrust bearing on a flat surface using solvent on 400-grit wet/dry paper.

  

  Don Barrington Jr. showed us a slick way to check crankshaft endplay without having to bol
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  Once the full floating pins were spiral-locked in place, we carefully installed the Total Seal rings and then lubed the wristpin area before installing the pistons. These pistons did not have notch marks to indicate front to back, so we had to be careful to install the pistons so the valve reliefs lined up properly with the heads.

  

  Once the full floating pins were spiral-locked in place, we carefully installed the Total
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  Installing the pistons is easy if you have a 4.155-inch tapered ring compressor like this one from ARP. With 1⁄16-inch rings, the radial wall tension is reduced, which makes installing the pistons fairly easy with your thumbs. Pistons with thinner 1.5mm rings are even easier.

  

  Installing the pistons is easy if you have a 4.155-inch tapered ring compressor like this

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  Here is the forged Scat crank and complete rotating assembly in place in the block. This engine did not employ a windage tray, which could have been helpful in making a little more power if we ever wanted to spin this engine up past 6,000 rpm.

  

  Here is the forged Scat crank and complete rotating assembly in place in the block. This e
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  Don’t forget to include the three oil-gallery plugs behind the timing chain. Production engines use small, press-in plugs, but we tapped the block to accept tapered pipe plugs to ensure a durable lubrication system.

  

  Don’t forget to include the three oil-gallery plugs behind the timing chain. Production en
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  On the same Westech dyno, we tested the engine with the same Weiand Air Strike dual-plane intake. You can also see the 1-inch-tall, Wilson-tapered carb spacer that was worth a solid 5 hp.

  

  On the same Westech dyno, we tested the engine with the same Weiand Air Strike dual-plane

Testing Day

We also experimented with a set of Comp red aluminum guided roller rockers that bumped the rocker ratio from 1.5:1 to 1.6:1. This adds another 0.032 inch of valve lift and reduces friction over the stock stamped rockers. This one change was worth an extra 20 hp, so clearly these heads want more valve lift. End

We also experimented with a set of Comp red aluminum guided roller rockers that bumped the

With an increase of two full points of compression and good ring seal, we expected some serious power improvements over the stock baseline, and we weren’t disappointed. Right at the first pull on the dyno with 36 degrees of timing (versus 44 degrees with the old engine), the 406 grunted out 486 lb-ft of torque compared with the previous 458 and produced between 20 and 30 lb-ft of torque increase across the board with similar gains in horsepower with the peak of 436 hp at 5,200 rpm. The biggest problem now seemed to be that we needed some way to make the engine breathe better at higher engine speeds to make more horsepower. The limitation seemed to be valve lift, so we thought the simple addition of a set of 1.6:1 rocker arms might help.

Generally, an increase from 1.5:1 to 1.6:1 rockers is usually worth about 0.030 inch of valve lift, and since our cam barely made 0.490-inch lift, that seemed like a good solution. We also tried a 1-inch-tall Wilson tapered spacer that was worth roughly 3 hp at the peak with no loss of torque down low. We also drained the 10W-30 break-in oil and tried some thinner-viscosity Lucas 0W-20 race oil, hoping to push over the 500-lb-ft plateau. All these little efforts really paid off. The rockers alone were worth almost 20 hp, which helped us excel to 501 lb-ft of torque and upped peak power to 466 hp at 6,000 rpm, and the engine responded positively to nearly all the changes. All this really proves that quality machine work and proper engine assembly techniques really do pay off with big rewards. We are already thinking about how to make even more power with this 406ci, and we might have to start calling it the BFH because it brings down the big freakin’ hammer on torque.

Power Curves

This graph illustrates the big differences in torque between the previous combo and our latest version. Note how the shape of the curves remains basically the same, since we did not change the cam, heads, intake, or exhaust. But look carefully at how the horsepower curve dips slightly between 5,300 and 5,900 on Tests 2 and 3. The dip is more pronounced in Test 3, which is where we added the rocker ratio. Our theory is that the valvesprings are right on the ragged edge and became “fussy” in this rpm range. The fix is a different (not necessarily higher load) valvespring that would probably take care of this. The big news is the huge gain in torque between Test 1 and Test 3. This would make an excellent street engine.

Dyno Numbers

Test 1 is the best power we pulled from the original test of the engine from the May ’11 issue. Test 2 is with the same Bow Tie Vortec heads, Comp cam, Weiand intake, Holley carb, and dyno exhaust with no mufflers. Test 3 added a Wilson-tapered carb spacer and a set of Comp 1.6:1 roller rockers and performance pushrods.

Power Curve

*Average power numbers were calculated between 3,200 and 6,000 rpm to ensure a fair comparison.

Parts List

Machine Work

*These separate part numbers and prices for the pistons and rods are for reference.