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November 2012 Chevy High Performance Q&A

Power Tour Leaves

Kevin McClelland Sep 20, 2012
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The Hot Rod Power Tour has come and gone this year. I like to use this phrase on people who don’t understand deadlines. We all live by deadlines. Some are self-imposed and the others are set for us (like tax day!).

I used to work at a company that had no idea what a deadline was. We’d set deadlines and they would come and go with no result, weeks turned into months, and months into years. ... This is when I coined the “Power Tour” phrase. Power Tour is leaving whether you’re there with your hot rod or not. You can’t ask for an extra day—or hour—because they won’t listen. They are going to pull out and get on the road to the next city on a schedule.

chp 01 O  November 2012 Chevy High Performance Qa 2/3

Why I bring this topic up is that my son, Daniel, came out last week and set a deadline to get his RX-7 with its LS2 and six-speed swap running in 60 days! Yes, the engine is built and dropped in, the chassis and brakes are modified and rebuilt. Now we’re down to the simple stuff, like marrying the LS2 computer and harness to the RX-7 original electrical system. One thing I’ve learned about Mazda is the double- and triple-fuse electrical circuits; if you ever blow a fuse you’ll be looking for a while to find the blown one. Unfortunately, this marriage is far from simple. Our good friend Ken Casey at John Elway Chevy has been looking up electrical diagrams of the ’06 GTO electrical system, and Daniel has done a tremendous amount of research of other engine swaps into the Third Gen RX-7 Mazdas. We spent all last weekend rebuilding the harnesses from the GTO and integrating them into the Mazda. We’re about a third of the way on the electrical systems. I sure wish there was a way to test everything without hooking up the battery and checking for smoke. You know how the old saying goes, when the smoke leaks out of the wires, it’s back to the shop to have the smoke put back in them. If not, it won’t run again.

As soon as we finish the electrical we’ll move the car over to my garage and start on the exhaust system. This will be a full dual exhaust with the factory dual cats from the GTO, as we’re building an emissions-legal swap. This will take me a bit of time; it will be built up from mandrel-bent 304 stainless 21/2-inch tubing. Tight doesn’t even begin to describe the exhaust routing. I’m not looking forward to this exercise, as I’ve built my fair share from scratch. But it’s all about the deadline. I’ve got to give Daniel credit for putting a line in the sand. Now we’ve got something to shoot for. Do you need to set any deadlines? Well, get after it and get your project done. Let us know how it worked out and what you learned. Good luck and work safe!

chp 02 November 2012 Chevy High Performance Qa Drawing 3/3

Fuel-Sipping Elky

Hi! We just got a subscription to your magazine at our office, and it is great! I have a question for you: I have a ’72 El Camino with a 307 engine and a TH350 transmission. I have an early ’90s 350 block (one-piece rear main seal) bored 0.060-inch over with flat-top pistons and a 700-R4 transmission to put in it. I’m not sure what gearing I have in the rearend, but it is a 10-bolt.

My heads are camel-hump 462s that sat unused for 30 years and are in pristine shape. I’ve had hardened seats added on the exhaust for unleaded fuel. The intake is factory, and my planned carb is a Quadrajet with Cliff’s high-performance rebuild kit.

I want to get 300-plus horsepower from this engine with good torque, and achieve in the 20-mpg range for fuel efficiency. This will be my daily driver. I do not have a cam selected yet, or my rocker arms and springs. Can you recommend an appropriate cam to achieve this? If it is not possible with this setup, can you recommend a cam, intake, and carb that would let me achieve this? Would I do better by using Vortec heads? This is my first engine build so any help is much appreciated!

Via email

How many people in your office read one issue of our rag? We need to add your office count to our pass-through readership and figure out how to charge you guys! Just kidding, and glad to be of service. Let’s go over the finer points of your engine build.

Starting with a one-piece rear main seal Gen 1 small-block gives you a ton of options for camshaft selection. The block will accept either a standard flat tappet–type arrangement, or you can slide a hydraulic roller camshaft in, as the block is machined for the anti-rotator plates for the lifters and the block has the bosses for the spring spider that holds them down. To use the hydraulic roller you’ll need to scrounge up a set of lifters and hardware from the lifter valley. Good news is there are a ton of Gen 1 small-blocks in the wrecking yards that are just waiting to be snatched up.

If you decide to go with the roller selection, we’d recommend a very short camshaft to build tons of slow-speed torque with your 700-R4 and its 0.70 overdrive and lockup torque converter. The factory gearing in your ’72 El Camino is probably 3.08. With a standard 25-inch-tall tire, these gears and trans, cruising down the freeway at 65 mph, your engine will be loafing along at 1,900 rpm! Give the HT383 camshaft from Chevrolet Performance (PN 14097395) a look. It specs out at 196/206 duration at 0.050-inch tappet lift, 0.435/0.460-inch max lift, and is ground on a tight 109 separation angle. All of this will add up to great slow-speed torque and fuel economy. If you don’t want to dig around the wrecking yards for the lifters and hardware, they are offered by Chevrolet Performance as a kit (PN 12371042). Finally, you will need a camshaft retainer (PN 10168501) to set the camshaft endplay. Go on Chevrolet Performance’s website for more information and a dealer near you.

Now let’s move onto the top end of your engine. You have a little problem using your camel-back heads as they have a 64cc combustion chamber. The Vortecs also have this small combustion chamber. With your 350 being punched out 0.060-inch over, and using the flat-top pistons, your compression is just a tick over 10.2:1. This is not a happy number for pump gas, iron heads, a carbureted engine, and a short camshaft. This is a recipe for pinging and detonation. You want to limit your compression to the 9:1 range so this puppy can run on 87-octane fuel. You’ll need to either swap out your pistons for buckets with a 12-16cc dish or go with cylinder heads with larger combustion chambers. If you swap out your cylinder heads, the 72cc combustion chambers will come in at 9.38:1, and 76cc chambers will yield 9.0:1. If you decide to change out the heads, give the Dart Iron Eagle S/S cylinder heads a look. They feature a 72cc combustion chamber, 165cc inlet runners, and come dressed with 1.250-inch valvesprings with 110 pounds on the seat and will accept up to 0.520 inches of lift. This spring package will work perfectly with the Chevrolet Performance roller listed above. These are a great set of affordable replacement cylinder heads, sold under PN 10021171. If you decide to go with the piston change we’d recommend the Vortec heads as they will give you better performance and mileage than the early fuelie heads.

Topping off the engine we’d recommend the Edelbrock Performer intake manifold; PN 2101 will fit standard Gen 1 heads, and the PN 2716 for the Vortec heads. These manifolds, with their dual-plane design, are also incorporated in two sized intake runners to give you a very broad torque curve. These manifolds will also accommodate your Quadrajet, which is a great selection for sipping fuel and making great power.

Any of these combinations will meet your 300-plus horsepower bogey, with a couple making upwards of 325. The main thing is that they will build great slow-speed torque and when dressed with 15/8-inch headers and a free-flowing dual exhaust will knock down 20-plus mpg if you keep your foot out of the throttle. Back in the day, we knocked down over 21 mpg on the Hot Rod Power Tour with a ’67 Camaro equipped with 3.08s, a 700-R4, and a ZZ4 with a Holley 750 double-pumper. The bottom line is to get everything right and mind your right foot. Good luck on your mileage quest!


LS for Torque

I read the information about the big-block torque engines and found it interesting. The dynamics of building an engine to produce low-end power are somewhat confusing to me, especially in the cam selection area. I want to build an LS3 block with a stroker for maximum torque. I’m not really concerned about the top end horsepower numbers, just getting a lot of down-low power.

My plan is to stroke an LS3 to 415 ci and use LS1/LS6 heads to keep high velocity at low to mid rpm. Since my engine would never see high rpm, the range where someone would drive normally is where I want to concentrate a search for torque, say, 1,800/3,000 rpm.

Do you have any suggestions on the camshaft? Also, I plan to keep the compression ratio at 10:1 or less so I don’t need to burn premium fuel. Keep up the great magazine.

Mike O’Brien
Via email

This is the second question in the many months as far back as the Aug. ’12 issue, where we addressed the same type of question. In that answer we recommended going with LS3 rectangular ports, as most of the dyno sessions we’ve reviewed reported higher torque levels with the larger LS3-type inlet port. Well, what you see on the dyno at wide-open throttle and what you feel at transient engine speeds and part-throttle torque can be completely different. Let’s review building another Torque Monster from LS1 and 2 parts.

Delivering slow-speed torque is all about building cylinder pressure at low engine speeds. You must have proper-sized components and valve timing events to achieve the desired effect. You have already keyed in on the fact that you want to keep the intake runner small for the displacement of the engine. The LS6/LS2 cylinder head casting number 243 will be a great choice on your 4.0-inch stroked 6.2L LS3. The only issue is these cylinder heads have a small 64cc combustion chamber, which will kick up the compression on your 415-cid displacement. We will need to look into some dish-style pistons to take up some swept volume. As for the best inlet manifold for torque, you’ll want to hunt down a LQ4/LQ9 6.0L truck intake. This manifold will give you the longest inlet runners with a large plenum volume. These components with quite a short camshaft package should give you the tire twisting torque you’re looking for.

Check out Lunati’s complete rotating assembly, which features Wiseco 14cc dish pistons forged from 2618 aluminum and CNC profiled. The rods are Lunati H-beam made from 4340 steel and measure 6.125 inches, center to center. Rounding out the bottom end is a Lunati Pro Series non-twist forged crankshaft made of 4340 aircraft-quality steel, weighing roughly 45 pounds. This will give you a bulletproof foundation to build as much torque as you wish. With these dish pistons and your small 64cc combustion chambers, you’ll be around a 10.25:1 compression ratio. If you open up the combustion chambers to match your larger 6.2L bore of 4.065 inches, it’ll put you right into the 10:1 range.

As for camshaft selection, we need to go a little unconventional to build torque in the 1,800- to 3,000-rpm range. Again, your displacement is going to eat up most camshafts, making them react smaller than they spec out. Two selections should fit the bill. First, let’s talk about the COMP Cams XFI RPM hydraulic roller 259. This camshaft specs out at 206/212 duration at 0.050-inch tappet lift, 0.515/0.522-inch max lift, with the separation angle ground on 112 centers, and the intake centerline on 110 degrees. This is the smallest camshaft COMP offers, and it will close the intake valve 59 degrees ABDC. This will give you 121 degrees of crankshaft rotation to build slow-speed cylinder pressure. As for the second selection, we’ve stepped up the duration numbers a bit, but it’s still quite advanced for an EFI LS-type engine. This camshaft is the shortest in COMP’s lineup of LSr Cathedral Port camshaft profiles. The grind number is 265LRHR12. It specs out at 215/233 degrees duration, 0.604/0.610-inch max lift, the separation angle is also on 112 centers, but the intake centerline is advanced another 3 degrees to 107. This cam has quite a bit more overlap, but with its tight centers and advanced installation the intake closes at 60 ABDC, which is within 1 degree of the really short cam. This cam is what COMP offers for small-displacement, heavy vehicles needing to produce high slow-speed torque. This cam with the LQ4/LQ9 inlet manifold will run out of breath around 5,000-plus rpm, but it should pin you in the seat from 1,500 up. We’d try the larger of the two.

Please let us know how this experiment works out for you. Not too many individuals are looking to build high, specific torque engines these days. Most have switched to oil burners for their high doses of torque. We’re with you; we still like our petrol-burning engine. Good luck.,

NOS slacker

I’ve been reading your magazine since I was a little motorhead. Your Q&A has been helpful throughout the years. My ’76 Camaro has a 383 pump-gas engine that runs in the 11.40s all day long. The car weighs 3,800 pounds with me in it. It has an Edelbrock Victor Jr. intake with a set of Canfield aluminum heads (215 cc). The cam is a solid roller with the duration at 0.050-inch tappet lift at 263/273, and is ground on a 110-lobe separation angle. The pistons are forged flat-tops; with the TH350 tranny with a 4:56 gear she goes through the lights at around 7,000 rpm with 29.5-inch tires.

I’m a foot braker and was thinking of going to a transbrake. I get 3,000-stall speed out of my 3,800 converter. Will a transbrake give me more stall speed off the line or just help with more consistent launches? Also, I hit it with a 150 shot of juice, but she only picks up two tenths at 11.17, is this normal? Any help will be greatly appreciated. Thanks and keep up with the great articles.

Tim Chitwood
Via email

I just have to ask, are you related to the famous daredevil Joie Chitwood? Chitwood’s team thrilled fans around the country for over 55 years with their last performance way back in 1998. Check out the videos on YouTube of their most impressive car control. OK, now that I got that out of my system, let’s see if we can help you find some e.t.

Let’s start with your 150hp nitrous shot—and we have to start with the basic questions: Do you have enough fuel delivery with the car already running 11.40s? You must maintain at least 5-6 psi of fuel pressure at the carb and nitrous fuel solenoid during the whole run. What are you running for ignition timing? We’re pretty sure since you are running on pump gas it’s in the low 30s. This should be fine, but if you are in the high 30s or anywhere close to 40, your engine is trying to kill itself when you add the nitrous. What is your bottle pressure when you are running? You need to have a bottle pressure of 950 psi. Most aftermarket nitrous systems tune their nitrous and fuel jet very conservatively. They usually expect the fuel pressure to be in the 4-5 pound range and the bottle pressure at 950 psi. This will make the system very rich if you’re running 6 to 6.5, which is normal. Also, if there is any restriction on the nitrous feed side, you’ll just be pumping in a ton of fuel without adding the appropriate amount of free oxygen riding along with the nitrogen. Most nitrous kits have a stainless steel filter screen on the AN fitting feeding the nitrous solenoid. The screen is on the pipe thread side of the fitting, so the only way to check this out is to remove the fitting from the solenoid. This screen gets plugged with crap from the assembly of the Teflon nitrous line that runs from the trunk, or from not taking care when changing bottles and getting dirt into the line and fitting. Check all these things, as we would expect at least a 0.5 reduction in e.t. if everything is working properly.

Now back to your transbrake. From the specs of your engine build, it sounds like you need more torque converter stall speed. With your cam specs, single-plane inlet, and 215cc runner heads, we bet your torque peak is in the 5,000-rpm range. If you can’t foot-brake the car past 3,000 rpm, we’d bet the car is pretty flat off the line and really starts pulling. You didn’t mention what your miles per hour was in the lights, but 11.40 calculates out to approximately high 114 mph. Yes, a transbrake will possibly give you a few more rpm if you can’t hold the car with the brakes above 3,000. The main thing with the transbrake is that you are going to want to run a two-step rev limiter so you can set a launch rpm. This will allow you to adjust your launch and vary your reaction times.

Now for the downside of a transbrake; if you don’t control the launch rpm you can really be hard on parts. If your rearend and axles are not up to the task of getting hit at full torque load from a standing start, you’ll find the weak link. The transmission must be built with higher-quality parts to also withstand the added punishment. Finally, the torque converter must be reinforced to prevent “ballooning” as you sit at full throttle against a locked transmission. Now, if you can control your aggression against your parts, you can run with more pedestrian components. For instance, in our ’80 Malibu wagon we’ve got an 8.5-inch corporate rearend outfitted with Strange gears, spool, and 35-spline axles. We’ve added an LPW Ultimate differential cover with axletube braces. This covers most of the weak links in the rearend, but we still only hit the rearend with 3,000 rpm off the transbrake, even though the converter at full stall will go to 4,500 rpm. The other reason we keep the rpm under control is that we’re running a B&M Nitrous Holeshot 3,600 10-inch torque converter, which isn’t really made for transbrake use. If we keep the rpm under control, the converter doesn’t know if we’re leaving off the foot brakes or the transbrake.

With your combination, we’d recommend a Powerglide trans with a transbrake. They take less horsepower to turn, and the transbrakes are much simpler than converting a TH350 to a transbrake. You may think you would run slower with the two-speed. We actually went about 0.08 quicker with the Powerglide than our low-gear (2.75 First) TH350 trans, and with more consistent 60-foot times. You can swap out the input shaft for a Turbohydro spline input and use your current converter. If the dollars will allow it, we really recommend the B&M converter we’re running. It gives you great stall speed and limited slip at the top end for good mph for a 4,500-stall converter.

The transbrake will help you be much more consistent with your reaction times. Your 60-foot times will get tighter, and you’ve only got to move one thing to launch instead of two! Good luck with your Camaro, and we hope you find your extra nitrous performance. chp




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