Chevy Small Block Evolution - Performance Q&A

Kevin McClelland Feb 1, 2010 0 Comment(s)

The Life Of A Small-Block
The small-block has now been around for 45 years. Yes, it has been through four generations of design, each with its own benefits for specific projects. The old-school group will always be a Gen I small-block crowd-that's a lot of our readers-who still enjoy the regular 355 and 383 builds that fit their comfort level and budget. The pieces for the Gen I small-blocks are plentiful, and you can build decent, reliable power at decent prices.

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Then we move to the Gen II folks who love the early small-blocks but really appreciate the upgrades in the fuel injection and cooling system and parts interchangeability. Good usable cores are plentiful in the wrecking yards, waiting for either a stock rebuild or a warmed-over build.

The Gen III is a total redesign of your familiar small-block. All-aluminum, fuel-injected, a different firing order, nothing interchanged (almost), the familiar engine mounts are gone, and our standard transmissions don't bolt up. This was a real game changer back in '97. Look at the power these engines ended up with out of the LS6-the final LS6 produced a whopping 405 hp SAE through cats and production exhaust!

Just when you thought it couldn't get any better, The General comes along with the Gen IV small-block. The LS2 first saw the light of day in the '05 C-6 Corvette. This was the base engine producing 400 hp and knocking down a mid-20 mpg average over four years. My dad picked his up from the plant in Bowling Green and has never reset the mpg average. It's in the high 24s, and I guarantee you he drives his Vette!

The Gen IVs are the latest in technology, with the new ZR1 Corvette LS9 engine producing 638 hp and 604 lb-ft of torque! This is the most outrageous production engine GM has ever produced. With the family including LS2, LS3, L76, LS4, L92, LS7, LS9, and LSA, from '04 on, that's quite a choice. Many young people out there only know the Gen III engines and up for muscle cars. The aftermarket has embraced the LS engine architecture like the parts manufacturers did back in '55. You can have any flavor of LS engine for your performance level.

So figure out where you are comfortable and pick your engine. We'll support any of the above builds and won't walk away from any of them. All we see above is big power at affordable prices, so pick your poison.

Wheel Deal
Q: I use my '72 Chevy Nova for drag racing. The stock front chassis was removed and replaced with an '85 Pontiac Fiero chassis to reduce front-end weight. I have a problem with the front rotors' bolt pattern. The Pontiac Fiero hub wheel bolt pattern is different from the Chevrolet's. We had to redrill the Fiero rotors for our two front Chevrolet wheels. The new bolt pattern is near the end of the Fiero rotor.

I would like to use Pontiac Fiero wheels to avoid redrilling the Pontiac hub will be eliminated. I have called several wheel companies, but they don't have any Pontiac Fiero wheels 3.5 to 4 inches wide. The minimum width available is 6 inches. Do you know of a company that supplies 3.5- to 4-inch aluminum wheels for a Pontiac Fiero? Who can supply a Pontiac Fiero front disc rotor with a Chevrolet bolt pattern on a hub with no bolt pattern that fits a Pontiac? My main objective is to have a set of wheels and rotors that fit together without drilling the rotors to get the wheels to fit using the Fiero spindles. I appreciate your help on this issue.
Sammie Taylor, Jr.
Moncks Corner, SC

A: Interesting conversion! Nice job lightening up the front of your Nova. Weight costs money no matter how you do it. Finding a set of skinnies for your 5x100mm bolt circle is a little tougher than you'd imagine. Harder than finding wheels is locating rotors for the Fiero spindles that are fitted with a 43/4-inch bolt circle. We found a couple of sets of wheels, but let's take a look at your options.

Not knowing how much material you have to work with, have you considered going with a 41/2-inch bolt circle instead of pushing it out to the standard 43/4-inch Chevy pattern? If you're at the edge of the material with the 43/4-inch, maybe the 1/4-inch difference will get you there. This would be the cheapest option. Then you could run standard 41/2-bolt-circle wheels, which are plentiful from either Ford or Chrysler vehicles.

As for wheels, Weld Racing offers a wheel, PN 766-50412, in its Import Drag line, it's a 15x3.5, has 1.75 inches of backspacing, and comes with the Fiero 5x100mm bolt circle. You can also check out Bogart Racing Wheels, which can build you a set of wheels to any specification; also very nice pieces, but they are racing specific and have a nice price tag to go with them.

Look at both options and choose which works best for you. Good luck with your Nova and remember to keep safety in mind when playing with the rotors and redrilling. There's nothing worse than a too loose front wheel at speed!

Sources: bogartracingwheels.com, weldracing.comSources: bogartracingwheels.com, weldracing.com

Double-Hump Dinosaurs
Q: I'm old-school (just turned 60) and am building a 327 that has been bored 0.040 over. The block casting number is 3903352, with stock rods; pistons are Speed-Pro flat-top with two valve reliefs on each; a PN H660CP hypereutectic, 350hp cam with 0.447-inch lift and 222 degrees duration; an Edlebrock Performer intake; and a Holley vacuum-sec 600-cfm carb. I'm on a tight budget, and I can get a free set of 462 double-hump heads that are ready to bolt on, but I'm afraid they are 58cc and that will push the compression ratio too high to run pump gas. I also have a set of 461 heads, but they will have to be completely rebuilt. I also have a friend with a set of Vortec heads-he says they're just as good as the double-hump heads, but if I go with them I'll have to change intakes. I would like to use the 462 heads if possible because it will be by far the least expensive. If I could use these, what gasket would I need? Could you tell me the approximate power output of this combination? Thank you very much for your advice.
Larry Johnson
Via email

A: Old-school? Haven't you heard, 60 is the new 40! The 461s and 462s are almost as old as you are. Wouldn't you want to take advantage of some of the new technology out there?

First of all, the cylinder heads you listed (even the Vortecs) have combustion chambers between 62 and 64 cc. Making some assumptions on the deck clearance, valve relief volumes, and head gaskets, your compression ratio checks out at 9.1 to 9.3:1, depending on the 62- or 64cc heads. These compression numbers were calculated with a standard Fel-Pro PN 1003 performance head gasket that displaces 9.1 cc. This is a completely safe compression number for pump gas on your little 327. Except for the cost of the manifold, it's a no-brainer to go with the Vortec heads. They will pick up an easy 30 hp over either of the early double-hump heads.

If you wish to raise money for the Vortecs and the accompanying manifold you'll need, why don't you try selling your double-humps? They are going for good money these days on CraigsList (craigslist.org) and eBay (ebay.com) from people who are restoring early iron. In good condition and with the proper date codes, they can bring a pretty penny.

Search around for the best price on a Performer RPM Vortec PN 7516. This manifold with the Vortec cylinder heads should produce somewhere around 350-360 hp on your combination, and around 350 lb-ft of torque. The original 350hp 327s may have been rated at 350 hp, but they were usually far from it. You will have one potent little Mouse with this package. Good luck.

Source: edelbrock.com

Popular Shortbed
Q: I'm about to begin the buildup of a 468 BBC for my '69 Chevy C10 shortbed Stepside truck. I'll be building toward a Pro Touring style theme, and the truck currently has a stock peanut-port 454 out of a '78 3/4-ton truck and a Tremec TKO five-speed (3.27 First) with 3.73:1 gears in the 12-bolt rearend. I'm shooting for a reliable package with a nice spread of torque and good top end, since this build is for a 3,800-pound street/strip truck. Here is what I have acquired so far from top to bottom: a Holley 870 Street Avenger, an Edelbrock 7561 Air Gap RPM-O intake and 61459 RPM-O Heads (2.25/1.89 intake/exhaust valves, 110cc chambers and 290cc runners) with Crower 68340-16 springs and 10-degree locks/retainers, a Comp Cams X4278H cam, a Cloyes Hex-a-Just timing set, Crane full roller rockers, and Comp Magnum pushrods. I will try to get 10:1 compression with SRP -23cc dome pistons, swinging on stock truck rods, and a steel crank with ARP bolts throughout the bottom end of the two-bolt block. Headers are Hedman Elite 1.75-inch long-tubes and will dump into a 3-inch dual exhaust. Does this sound like a strong combination for my goal? What should I expect for peak power and torque? I have considered running a bigger cam to take advantage of the flow the heads offer, maybe a Comp XR274 solid roller, but I don't know if this will give me much more power or create a headache on the street, since I'll also be running power brakes and A/C. Thank you in advance. I love the magazine; keep up the good work!
Adam Reed
Little Rock, AR

A: You have chosen a very popular truck of late. These are bringing very high dollars on the open market, and their styling is timeless. Stick shifts in light little trucks can be a blast, especially with a big-block. Let's look over your combination.

When you run your truck over a set of scales you'll be very surprised what it weighs, probably at least 4,500 pounds! We think it's going to come in closer to 5,000, though, especially with a big-block on the nose.

Some quick math with your components gives you a compression ratio of 10.3:1. This is assuming your -23cc dome piston is 0.020 inch down in the hole, and you would use a Fel-Pro PN 1037 0.039-inch-thick head gasket displacing 9.7 cc. This is right at the max for compression ratio on the great fuel we are served these days. Small-blocks can handle this amount of squeeze better than a big-block. A manual transmission will give you the control over the load on the engine at slow engine speeds-this is where the engine would want to knock.

The foundation of your engine combination is very sound. We're a little concerned about the XR274 camshaft. You may want to run a larger 'shaft, but we'd stick with a little smaller one. You're going to move your truck with torque, not horsepower. Your current combination should make around 500 hp, with the torque coming a little higher. The 274 camshaft specs out with 230/236 degrees duration at 0.050 inch tappet lift. This cam is going to have idle vacuum in the low teens, and with power brakes and A/C it may struggle to idle well when the A/C is on. Getting the truck stopped is a whole other problem. The XE268 comes in with duration numbers of 224/230 at 0.050 inch. This slight change will help the idle stability and give you more area under the curve with a broader torque curve. The few extra ponies the 274 will give you will be at an engine speed you rarely use. Put the beef in the torque curve, where you need it.

Good luck with your build-up. Send us photos and an update when you get it done. The Readers Rides section needs a nice little street-brawler pickup.

Source: compcams.com

What A Mutha
Q: My application is a 461ci big-block engine in a 3,200-pound '69 Vette with a 2,500-2,700 stall and a Turbo 400 coupled to a 3.35:1 differential. The engine configuration performance objective is for midrange torque and crisp throttle response with a torque peak at 4,200-4,500 rpm and peak operational speed of 6,000 rpm. Intended usage will be street, highway, and occasional road course action.

I'm running a complete Eagle rotating assembly with 10:1 pistons, Edelbrock Performer RPM heads drawing through an Edelbrock Performer RPM manifold, a Holley HP series 750-cfm carb, Hooker Super Comp headers coupled to a 2.5-inch cross-pipe system, and Walker Dynomax Ultraflow mufflers.

My cam selection is a Comp Cams XS-274-S; however, I have become intrigued by the claimed performance characteristics of the Comp Thumpr line. I am skeptical of the claims of low- to midrange torque in concert with good high-end power considering a) late intake valve closing, b) increased overlap, and c) less valve lift (relatively speaking). This tends to contradict, in many ways, conventional cam theory leading to my interest in your opinions of my original cam selection versus the Mutha/Big Mutha Thumpr cam selections relative to my performance objectives. Also, as I am sure you have picked up on, I am staying old-school with flat-tappet profiles. I look forward to your input and thank you in advance. Mac Kirkwood Livonia, MI

A: If we didn't have contradictions to the norm we'd never move forward. Things that wouldn't work 20 years ago because of cylinder head selection or manifold development may work very well these days. Things that work with the LS-based engines didn't work with either small-blocks or big.

We've always been big fans of a large duration spread between the inlet and exhaust lobe. The GM Performance camshafts in the ZZ4s and H.O. 454 and 502 have quite a spread. The ZZ4 has 13 degrees differential, and the H.O. big-blocks have 19 degrees. These camshafts were done almost 20 years ago, and they perform very well for their application. The Comp application of this theme is just extending the same logic. Most performance engines achieve peak cylinder pressure 12.5 to 15 degrees after top dead center (ATDC). On the exhaust side, after the combustion cycle, you have the next cylinder in the firing order at full cylinder pressure, approximately 105 degrees ATDC. That next cylinder is putting all its work into turning the crankshaft. This allows you to use an early exhaust valve opening to blow down the cylinder and really evacuate the previous cylinder. This works well when you have a marginal exhaust port and a restrictive exhaust system.

Comparing the mechanical Xtreme Energy camshaft to a hydraulic Mutha Thumpr is tough to do by the published camshaft specifications. Comp rates its hydraulics at 0.006-inch tappet lift, and its mechanicals at 0.015-inch. The larger number on the mechanical side is to compensate for the added valve lash associated with the mechanical camshaft. This differential of 0.006-inch of lobe lift makes a dramatic difference in duration numbers at this advertised point. With all this being said, the 287TH-7 Mutha Thumpr specs out at 235/249 at 0.050-inch tappet lift, 0.510/0.495-inch max lift, with a separation angle of 107, and is installed at 102. The XS274S Xtreme Energy cam comes in at 236/242 at 0.050, 0.568/0.578-inch max lift, is ground on 110 centers, and is installed at 106. One thing you must take into consideration with the mechanical is the loss of max lift from the lash. The lash point for the solid is 0.016 inch.

OK, down to the bottom line. Will the newly designed Mutha Thumpr be a better camshaft for your application over the mechanical Xtreme Energy camshaft? It's going to be a toss-up, with benefits both ways. The mechanical should give you a little more top-end engine speed; however, the XE lobes are very aggressive to get those lift numbers. The softer (less aggressive) hydraulic lobes may be better for the valvetrain stability upstairs. Again, we like the large spread on duration numbers, and the Mutha Thumpr is right in the sweet spot. Even with your Edelbrock cylinder heads, the exhaust port still can use some help. Leaning on some extra exhaust duration certainly won't hurt. Good luck and Thump on!

Source: compcams.com

Won't Brake Me
Q: I have a '70 Chevelle with a 454-cid (bored 0.030-over to a 461 cid). I'm running a two-speed Powerglide trans with a transbrake. I was told if I ran the transbrake on the street it would get too hot. I'm running a 3,500 stall. I'm running a trans cooler and 4.56:1 gears. Any help would be appreciated. Thanks.
Randy Duggins
Midland, OH

A: Transmission brakes hold the vehicle and allow you to go to full power before releasing the fury of your big-block. The transbrake itself doesn't increase the transmission heat unless it's being used. The heat comes from the torque converter being held at full stall without any rotation of the input shaft. How transmission brakes work is they direct fluid pressure to First and Reverse gears at the same time, locking the transmission from rotating. When you release the transbrake, the Reverse gear is released and the vehicle is launched at whatever torque is being applied to the converter. Regular driving without using the transbrake will not increase the transmission temperature.

Now, studies have been done on 1,000hp/800-lb-ft big-blocks on the rate that the transmission fluid is heated during this full-stall event. The fluid temperature rises at a rate of 100 degrees F per second coming right out of the converter. This is why you don't want to be at full stall on the transbrake any longer than needed. Also, when you do a full-stall test to see what your converter will stall to, make sure you idle the car for 15-20 seconds afterward to flush out the hot fluid from the converter and through the cooler.

Enjoy those neck-snapping launches. Just remember, Johnny Law isn't going to be very happy with your antics. Keep the transbrake use to the strip.

Laguna Pretender
Q: I'm looking at purchasing a '76 Chevy El Camino with a Laguna nose. The powertrain is a 350ci with a four-speed. Did Chevy actually produce this car or could it be that someone added the nose years later? The owner is adamant that this is a factory car, but I have been unable to find anything on this one. If it is an actual car, could you tell me how rare it is? Any help would be greatly appreciated. You guys have a great magazine, and thanks a lot! Todd Dixon Philipsburg, PA

A: We're pretty sure about this one. If you check the body tag under the hood, the first line of numbers after "ST" will give you the model year then the body code. The Laguna Type S3 was only built in a two-door sport coupe in '76. Its body code is 1AE37. The El Camino was built under two body codes: the two-door pickup delivery (1AC80) and the two-door classic pickup delivery (1AD80). GM built the Laguna series from 1973 to 1976. As for a Laguna El Camino, we can't find one from any of those model years. A 350ci with a four-speed manual, that is rather rare.

Check out the body codes. If it's one of those listed above, then there's no question about it. It's a standard El Cam with a Laguna nose attached. Good luck.

Flaming Malibu
Q: I have a Carter street pump feeding an Edelbrock single fuel pressure regulator. The dual feeds from the regulator are feeding a Holley 80457S 600-cfm carb. This 600 has dual-feed bowls from a Holley 3310S 750-cfm carb that has been running without a problem since 2006. The fuel pressure gauge started showing 0 with the engine running fine. There was no stalling or flooding, but a very inconsistent flat spot or hesitation was noticed. After replacing the Carter pump and regulator, and ensuring the Russell bronze fuel filter was clear, the engine starts now with 6.5 psi but idles down to 0 psi. The necessary float level setting with the engine warm has created a serious flooding problem the last two days on cold initial starting. The first day I backed off the float setting to get the car out of the garage for fear of a fire. When I started the engine cold I noticed that the fuel pressure was 6.5-7.0 psi and the floats stuck, flooding the engine.

This same flooding happened to me once before with the single-feed bowls that came stock on the 600-cfm carb. After tapping the bowl the overflowing gas stopped. This flooding scares me, to think if it occurs when engine is hot. I'm being told that Holleys are notorious for this sticking needle and seat problem. The car is street driven. I suspected vaporlock, but again the setup had run perfect since 2006. I'm in serious need of help. Rufus Martin Via email

A: The last thing you need is flames in your Malibu. We'd be suspect of your fuel pressure gauge. We've got an inexpensive "mail order" pressure gauge screwed directly into the Magnafuel regulator on our Malibu wagon. When the engine is cool, the gauge reads somewhat accurately. When the engine warms up the pressure drops about 2 to 3 psi. When we screw in a quality Snap-On test gauge, the pressure is rock solid at both cold and hot operation. Your problem sounds the same. You set the pressure when the engine is cold and the pressure drops when hot. Then you adjust the pressure hot and the engine is running. When you start the car cold the fuel pressure gets a run at the needle and seats and they can't control the pressure and flood over.

Also, Holleys can maintain very accurate fuel bowl settings without the sticking of needle and seats if the pressure is correct. The "center hung" bowls that you've upgraded your carb with have very little trouble. You may be hearing old wives' tales about the Holley needle and seat troubles. Stick with the Holley brand needle and seats sized for the carburetor that you're running. Installing performance, larger needle and seats are no way to go on the street. If you have carb-kit needle and seats, replace them with original Holley units, PN 6-504. These needle and seats are 0.110 inch with a Viton tip needle and are used in all center-hung float assemblies for the 4150 model carbs. Check the Holley website for the proper technical info on adjusting the floats properly.

Again, we think your fuel pressure gauge is going to be the culprit. You've changed the regulator, which would be our next best thought. Hopefully a simple adjustment of the floats and fuel pressure setting will mellow out your fireball. Be safe.

Source: holley.com

Make It Stop
Q: My '95 Chevy S-10 two-wheel-drive truck came with a four-cylinder and a five-speed transmission. Since then I have installed a 350ci small-block with tall valve covers and no room for a power brake booster. I can hardly get it to stop now. I've used several different standard brake master cylinders with the correct brake rod, but no luck. When you apply the brakes, the pedal feels like a booster failure in a power brake system. I have disc brakes in the front with drum brakes in the rear.

The engine is a 0.040-over 350 with flat-top, four-valve-relief hypereutectic pistons with about 10.2:1 compression. I'm using World Products Sportsman 2 with 64cc chambers and 2.02/1.60-inch intake/exhaust valves, an Edelbrock Victor Jr. intake, and a 750-cfm Holley. The heads and intake have been ported and polished. Also, an MSD billet distributor and 6AL box and Blaster 2 coil. The valvetrain consists of all Comp Cams items: stud girdles, Pro Magnum roller rockers, Magnum pushrods, solid lifters, and an Xtreme Energy XS 282 S cam. The transmission is a B&M 350 turbo with a B&M Holeshot 3,600-stall converter. The headers are Hedman full-length 15/8 with a 21/2-inch Flowmaster dual-exhaust system and have 4.10:1 gears.

This truck is mostly used for street. How or what can I use to stop the truck? We have tried everything. Also, any idea about how much horsepower I might have? Stanley Wilcher Via email

A: When you removed your power booster unit and replaced the system with a manual brake master cylinder, did you use the same master cylinder pushrod location on the pedal? Most people do. The reason you have very little brakes is that you don't have any pedal ratio (leverage) over the manual master. With power brakes you need much less pedal effort to create a ton of pressure-the booster does all the work for you. A normal power brake pedal ratio is in the 4:1 range. When you run manual brakes you must increase the pedal ratio to gain leverage over the master. You'll find manual brake pedal ratios somewhere in the 6:1 to 7:1 range. Take a look at your brake pedal. Usually The General uses the same pedal for both manual and power applications. There will be two locations for the pedal pushrod to mount. The only difference will be the location of the master cylinder. You will need to remount the master to put it inline with the new pushrod location.

If you don't have two locations on your pedal for the pushrod, it's very easy to figure out the proper location. First, you need to know the total length of the pedal from the pivot point to the center of the brake pedal pad. Divide this length by the length of the pushrod location to the pivot point. This will give you the pedal ratio. Move the pushrod location to bring you into the above listed ratios.

As for the ponies from your little small-block, we'd peg it around 430-440 hp, with around 420 lb-ft of torque. This should be pushing around your little S-10, and we can see why you need some brakes. Be safe and get this puppy stopped!

Technical questions for Kevin McClelland can be sent to him at chevyhi@sorc.com.

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