Performance Q&A Tech Section

Our Resident tech guru, Big Mac, tells all.

Kevin McClelland Apr 1, 2009 0 Comment(s)
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The Great Move Is On
It's official. I'm seeking new employment. This gig at Chevy High Performance is the best second job I've ever had (thanks, Henry), but I do need to put food on the table and a roof over our heads! So we're picking up roots that have grown very deep in Northern California for the past 15 years and moving back to Southern California. SoCal is the heart and soul of the performance aftermarket industry, which I'm so in love with and which has served my family well for the past 28 years.

How many projects have you done in your garage in the past decade and a half? How do you start to think about packing up your shop/garage, and how do you get it to a new location without giving away or selling everything? That's what my wife and I are up against. Back in 1993, when we first moved to NorCal, we rented a 24-foot box truck with a lift gate, which we packed to the gills. We were holding things into the box when we pulled down the door of the truck. This didn't include what we stuffed into our Suburban and the '57 Chevy on our open trailer. And one of my buddies still had to trailer down my '68 Camaro months later.

Shift to 2008. Between two full trucks and trailer race rigs, two race cars, and three street cars, we're going to be a little busy shuttling everything down south. We've already rid ourselves of two street cars, including Daniel's '68 Nova. We'll pick a new project when we get settled. It may be really off the wall, but we'll have to wait and see.

So again, how many projects have you worked on in the past 15 years, and how many parts and pieces do you consider priceless? I can easily count six major projects that I've finished over the years, plus a number of minor upgrades. Just to pack up the garage I've got to assemble two complete engines. This is good and bad. Finishing the engines requires many hours, but they move a lot easier complete.

My final ace in the hole is our good friend and neighbor, who has a 53-foot trailer. The first words out of his mouth were, "I'll move your garage!" This was music to my ears. Now to decide what I really need after all these years. When you come across things you moved 15 years ago and haven't touched since, it makes you really take a hard look at them. However, as my lovely wife likes to remind me, when I put the wagon together, things came off the shelf that I'd had since the early '80s.

May I survive to write next month's column. Talk to you soon!

Two or Three Speeds?
Q
I want to race my '67 Chevy II in the eighth-mile at my local Florida Dragway, in the 7.50 index class. Presently the car is powered by a stock ZZ4 Chevy crate engine, a Tremec TKO 600 five-speed, and a 12-bolt Eaton posi rearend with 4.10:1 gears.

I'm also running Calvert bars on stock monoleaf springs and Rancho shocks. I intend to use P255/60R15 Mickey Thompson ET Street Drag radials or a pair of 26x8.5x15 MT slicks tucked into the stock wheelwells. Other than that, I have a six-point 'cage installed and it is NHRA legal. Do you recommend going with a TH350 for consistency? Would you consider any additional changes to the engine or gear ratio? I understand you're a veteran drag racer and would appreciate your recommendations to be competitive in the class.Gerry VeeLand O Lakes, FL

A One thing our Malibu wagon has taught us is that we don't know everything! Not that we ever said we did, but a new car can be a humbling experience. A 7.50 in the eighth doesn't sound too tough, but that equates to an 11.55 e.t. in the quarter-mile! You've got a few things to think about.

First, your transmission question hit right at home with us. Yes, you'll want to convert over to an automatic transmission for consistency and reduced maintenance. We were fighting a consistency problem with a TH350 transmission in the wagon. It would vary sometimes as much as 0.05 second between the 60- and 330-foot clocks. It would make five passes with everything repeating as expected from a mid-11-second car and then throw you a bad run. Well, it turned out that the Second gear roller clutch would skid on the gear change, and you couldn't perceive the problem in the car. It would just show up on the time slip and the win light. A 32-element sprag from ATI took care of all the inconsistency problems in this area.

Next, we changed the trans out for one of the spare B&M Powerglides for my Super Gas Roadster. We figured it was going to kill at least 0.10 second of e.t. over the TH350 because the First gear ratio went from 2.75 (Low gearset) to 1.76 stock Powerglide First gear. What this change did was give us the most consistent 60-foot times, only being off 0.004 second from our best with the TH350. With the Powerglide, our 60-foot only varies around 0.006 second for six runs in a day! The TH350 would sometimes vary 0.02 second because of the very low First gear and the way it hit the tire in the heat of the day.

We recommend going with a Powerglide transmission and a transbrake if legal in your class. Not that you're going to want to hit the tire at full throttle, but you can chip the engine power back accurately for repeatable launches. Next, you're going to need about 100 hp over your stock ZZ4 engine. This will give you enough padding to run the number when the weather turns hot and humid back in Florida. Remember, there is no replacement for displacement. This is especially true in hot, muggy conditions. It will be easier to make your 450hp goal with a 383- or 400ci small-block.

We also recommend using slicks and running a 4.56:1 rear gearset. This should put you through the lights in the 6,500-plus rpm range. Also, go with a 10-inch converter, which should stall in the 4,500 rpm range. This will put you right at torque peak of a 450hp small-block.

Finally, your engine will need a little help. You may want to pick up another engine from a local racer or buddy and sell your ZZ4 H.O. It is a perfect street engine and can be built into the engine you need. Heads, camshaft, and intake will get you there, but you will be pushing the short-block. Look around and see what deals you can come up with. Hope this gets you started. Good luck, and have fun with your new race car.

Old-School High Rise
Q
After doing some research I found you had influence on the design of the Edelbrock Torquer II intake and the evolution of the Edelbrock single-plane intakes.

I'm in the middle of doing some upgrades to a Gen V 454 for a marine application. I recently installed a set of pocket-ported GM Vortec heads, oval-port (not peanut ports) with Ferrea Super Flow intakes and tulip-flow exhaust valves. The vane in the intake port has been blended slightly as part of the pocket-port work. The heads have a heart-shaped chamber, which should raise the CR to close to 9:1. The current intake manifold is an Edlebrock Streetmaster single-plane with a Q-jet carb and Mercruiser 496 exhaust manifolds (these have individual runners like shorty headers, which dump into a nice, gentle, sweeping exhaust elbow).

Stage II of this project is to install a Comp Cams XE262 flat-tappet cam (nitrided special grind) 218/224 duration at 0.050 inch tappet lift, 0.524/0.532 inch max lift on a 110 center and nitrided lifters. The max target for this application (marine) is 5,000 rpm. Currently I'm running the stock cam, which specs out at 213/217 duration at 0.050 inch, ground on 114 center.

I'm running a Streetmaster single-plane due to height clearance issues. I understand this is a single-plane manifold, which should provide the best of both single- and dual-plane worlds (up to 5,000 rpm). The engine pulls very strong with the stock cam. Do you feel this would be a much stronger engine with a dual-plane like the new Weiand Street Warrior dual-plane, or a Performer RPM? I would have to do mods to the engine cover to make an RPM fit. I'm looking forward to your reply.
Rich Chrzanowski
Via e-mail

A Don't you like to use Sawzalls? That's one of the best tools ever invented. Steel, wood, plaster-nothing gets in its way! Yes, I spent five years working in the R&D department at Edelbrock in the early '80s. The Streetmaster line of inlet manifolds had been out for several years when I got there to address the emissions performance market. Applying the knowledge found from racing single-plane manifolds and downsizing them into appropriate street manifolds was the goal. It worked very well for the day, and then we moved on to the Torquer II line of street-performance manifolds. The Torquer II manifold has a larger cross-sectional runner and improved runner designs over the Streetmaster and will give you better upstairs performance.

The current design of street-performance dual-plane manifolds will outperform these early single-plane designs, especially in a marine application, where you need the most torque to get the boat out of the water right at torque peak. With a performance dual-plane, you should experience a good 20 lb-ft gain over the single-plane design.

I really like your combination of parts. The iron Vortec oval-ports are very nice castings with the inlet port from the early cast-iron oval-port heads. The differences from the early heads are a raised exhaust port with a nice short-side radius turn, and a kidney-shaped combustion chamber. These heads work very well stock and, with the port work, will run much better than any GM oval-port. The camshaft you have selected will give you great torque and run out of steam right around your target; with the "water manifold" you have to run on the exhaust side. As for the manifold, we recommend getting out the Sawzall. The gains in part-throttle performance and torque peak will be worth the mods. This will round out your package of the Stage II upgrades. Retain your Q-jet and run a PN 7164 Performer RPM.

We'll assume you have this engine in some type of pleasure boat for skiing. Make sure your skiers are warned of your new found torque, and have fun!

Source:edelbrock.com

Dot What?
Q
I have an interesting problem with a brake system on a '37 Chevy street rod. When the brakes are lightly applied, as in a parking lot (1-2 mph), the pedal goes to the floor, only intermittently. It may happen twice a day or only once a month. I have replaced the (7-inch dual diaphragm) booster twice and the master cylinder (1 1/8-inch-bore '79 Corvette) six times, the last three times with brand-new AC Delco parts (started with remanufactured). I am using DOT 4 fluid. I was told DOT 5 will cause this, so I flushed the system and have had DOT 4 in it for four master cylinders and one booster. I'm also using four-wheel disc brakes (GM calipers) and 2-pound residual valves, one front and one rear. I have an adjustable brake bias valve in the rear only. The brake pedal has never gone to the floor while driving above 2 mph. My engine is a 260-horse GM crate with 19 inches of vacuum in gear at idle with the vacuum advance disconnected. The system is well sealed with no leaks anywhere, and the pedal is firm except when it's headed for the floor. I am an ASE-certified master mechanic who is going bald trying to solve this problem. Help!Henry JamesVia e-mail

A Boy, we feel your pain. We wish we had the silver bullet, but you've covered the bases. We have a few ideas-and a few questions. Maybe these will trigger some ideas on your end to find your problem. We really want to help!

First, let's talk about DOT brake fluid. DOT 3 brake fluid has been around for decades. It is a glycol-based fluid that works very well but has the nasty habit of attracting moisture into your braking system. Back in the early '80s, DOT 4 (also glycol-based) came along, basically obsolescing DOT 3 fluid. They both have a boiling point of around 500 degrees Fahrenheit until moisture attacks the fluid, then it drops quickly. Issues of moisture and paint corrosion from glycol-based fluids led to DOT 5 silicone-based fluid. This was touted as the best thing since sliced bread, and people began to switch over. But silicone fluid has its own set of problems with aeration and lack of lubricity. The biggest problem with silicone- and glycol-based fluids is their lack of compatibility with each other. Mixing even small amounts will create a sludge that looks amazingly like Italian salad dressing and is about as effective as brake fluid. In some cases, the hardware designed for one fluid will not accept the other. Brake caliper and master cylinder seals, hoses, and other parts won't always work correctly when the type of fluid is changed.

So here's a question for you: Since this is a street rod and you probably have a "clean firewall," have you mounted the master cylinder and booster under the driver-side floor along the framerail? We assume so, because you're using residual check valves to prevent the bleed-down of fluid from the calipers back to the master. Since glycol and silicone fluids really don't like each other, and you said that you flushed the system when you switched from DOT 5 back to DOT 4, maybe you have some salad dressing left in your residual checks. It wouldn't take much to allow them not to seal, bleeding fluid back to the master. This would cause the pedal travel to refill the calipers on the initial application of the brake pedal. If the stuff is floating around in the check-valve chamber, that would explain why the problem is intermittent.

You really have covered most of the bases. Hopefully, the residual checks are the problem. They are easy enough to swap out and won't break the bank. Good luck, and make sure to tap those brakes before movement!

Businessman's Hot Rod
Q
First I just want to thank you guys for the great magazine. I got my second issue just a few days ago. I am 15 years old and just bought my first car, a '72 Buick Skylark with a 455. I need some advice on building the engine. I know it's not a Chevy, but it applies to all big-blocks. Which intake manifold makes more power, an Edelbrock Performer or a B-4B? I heard it was the B-4B, but it is the same design they used 40 years ago so it may be outdated. I am going to use a cam from TA Performance that specs out at 0.460 inch max lift, 223/230 degrees duration at 0.050 inch lift, and 284/288 degrees advertised duration. I will also be using a Q-jet carburetor and stock exhaust manifolds with iron heads, but I plan to swap to aluminum heads later. Will I be able to get away with cast pistons or will I have to upgrade to forged ones? I am going for a compression ratio around 10:1. I would also like to know what kind of power this combo would make. Any advice would be greatly appreciated and will help a young gearhead have the meanest car in the high school parking lot!
Nick Larson
Maple Valley, WA

A We know it's not a Chevy, but you're a new member to the performance fold, and we must not let you go astray! At least you're in a GM vehicle, and I have a soft spot in my heart for big-block Buicks. I owned a '70 Buick GS 455 four-speed convertible that I sold to my dad about 10 years ago. He has gone on to finish the restoration I started, and it's an award-winning original car that he loves to show.

First of all, the Buick big-blocks are completely different from any of the other GM big-blocks, from Chevy, Pontiac, or Oldsmobile. The Buick is a large-bore, short-stroke, very high-torque engine with a great slow-speed powerband. The main problem with the Buick design was the oiling system. The oil pump is located in the front cover of the engine, which is aluminum. With heat, the cover expands and the pressure drops. Also, the main and rod bearing journals are large. With the dropping pressure at high temps, and the large bearing surfaces, they had their fair share of spun rod bearings. The large-bore/short-stroke architecture of the engine promotes higher engine speeds. All you need to do is feed the engine air, and it loves to rev. The stock heads will give you great power into the mid-5,000 rpm range. The stock cast pistons will live well at these engine speeds. If you wish to push your little Buick, you'll need to modify the complete bottom end to accommodate the higher engine speeds. You should also join the Buick GS Club of America (buicksca.com) and go to school on the message board.

As for B-4B versus Performer, I was right in the middle of the controversy at Edelbrock. I had installed a B-4B on my GS, and the cold air scoop air cleaner assembly no longer lined up with the hood. It turns out that on the B-4B, they'd moved the carb forward to center the Q-jet. The stock manifold had the carburetor moved rearward approximately 3/4 inch, and this is what all the cold air system lines up with. Finding this problem, Edelbrock recasted the B-4B with the carburetor's original location to work with the stock air cleaner system. Does the B-4B run better than the Performer? Slightly. If you're not running the cold air system, go with the B-4B.

With your buildup of parts, you should be in the range of 375 hp at 525 lb-ft of torque. The best thing you could do is install a set of full-length headers. This will give your Buick the best bang. The stock exhaust manifolds are really bad, and you would make well over 400 hp with headers added.

One final parting shot, Nick. We better not hear about you screwing around on the street, seeing as how you're so close to Seattle Raceway. Keep your playing to the strip, not the street!

Sources:buickgsca.comedelbrock.com

Smog Police Expanded!
Q My '96 GMC Yukon has a 350 Vortec engine, an overdrive transmission, and 3.42:1 gears. I have to replace the engine and want to know what I could replace it with for added grunt. It must run on regular gas and be able to pass emissions in Massachusetts. Could you recommend a crate engine or other engines? I'm an old-school hot rodder. When it comes to the new stuff, I'm lost!
Tom Hayes
Via e-mail

A I began to research the emissions regulations in the state of Massachusetts, and I uncovered a few things I wasn't aware of. First of all, in 2002 the California governor signed AB 1493, which directed the California Air Resources Board (CARB) to adopt regulations that would achieve the "maximum feasible and cost-effective reduction of greenhouse gas emissions from motor vehicles." In 2004 CARB adopted the regulations, which will affect new cars sold in California beginning with '09 models. The regulations will result in a 23 percent reduction in greenhouse gas emissions from new vehicles by 2012 and a 30 percent reduction in global warming emissions from new vehicles by 2016.

If you're thinking those Californians are just jumping off a cliff again, we'd have to somewhat agree with you; however, 16 other states have adopted the California language for greenhouse gas (GHG) emissions reduction. In 2006 Massachusetts announced the state's adoption of California's vehicle emissions standards, also starting with '09 vehicles.

What does all of this mean to you, Tom? Well, you must live by the same emissions constraints we do here in California. You may install aftermarket performance components as long as they carry a CARB executive order (EO) number. The EO process is a very stringent emissions testing program much like what Detroit must certify its cars by. It's a costly program for the aftermarket parts manufacturers, but it makes their parts legal for sale and use in these states.

You asked about a crate engine. Well, the only truly emissions-legal engine for your truck is a direct replacement L31 small-block. GM Performance Parts offers its HT383E crate engine, which by the letter of the law isn't legal in Mass. However, there's no way the emissions tech in your state can tell that the engine has been swapped unless they disassemble the engine and check the displacement. Do I recommend that you follow these misleading tactics? Of course not! The engine is sold under PN 17800393 and is a direct bolt-in for your L31. To get the most out of this engine, you will need computer tuning done by a professional service because an aftermarket calibrator won't have the proper tune for this engine.

To keep everyone happy and make a very painless refresh of your engine, install a new L31 crate engine from GM. The long-block (PN 12530282) carries a three-year/100,000-mile warranty on parts and labor and will put your truck back to showroom-new in the engine department. Then we would install a few other parts, including a set of GM Performance Parts 1.6 roller rockers (PN 12370839) and a K&N fuel injection performance kit (or FIPK, PN 57-301-2). To tune the engine, go with a Hypertech Power Programmer III (PN 32000). And finally, choose an after-cat exhaust from the manufacturer of your choice for sound and performance. These upgrades to the stock engine will give you an honest 30 additional horsepower and at least 1 mpg gain in fuel economy-you'll see more performance and economy, but this is a safe estimate. Above all, the listed modifications will be in compliance with your state's emissions regulations. Welcome to our new world!

Sources:gmperformanceparts.comhypertech.comknfilter.com

Tale Of Two Engines
Q
I may be in over my head. I have acquired two donor vehicles which I plan to transplant the running gear from into two street rods. One is a '90 van with a 350 TBI engine and a TH700-R4 trans. The other is an '88 Trans Am with a 305 TPI engine and a five-speed. I'd like to install the TPI system on the 350 van engine and run it with the five-speed, and run the TBI system on the 305 with the TH700-R4 transmission. Is this possible, and if so, what needs to be done to accomplish this? Thanks for any help you may provide.
Sonny Davis
Via e-mail

A If you put both engines into a bucket and shook them around long enough I'm sure they would come out the way you'd like! You do have an interesting mix of components to work with here. Let's see if we can get you there.

First, the 350 TBI engine has a great short-block to work with. However, you'll want to change out the cylinder heads. We would take the complete top end off the 305 and camshaft and drop it right into the 350 short. The TPI cylinder heads are about the best iron heads of their day. Now, this isn't much to write home about, but it's what you have. The 305 heads will boost the compression about three quarters of a point and give you standard (not swirl) inlet ports.

Moving on to the 305, swapping the 350 heads onto your 305 will drop your compression. You could pick up a set of swirl-port LO3 305 heads to match the TBI inlet manifold. Also, install the LO5 350 TBI camshaft into your 305. Then you'll have a complete LO3 305 TBI engine.

Now for the electrical wiring side of things. With your 305 and the TH700-R4, we'd recommend using the stock 350 van harness and computer. You will need to swap out the chip in the ECM for a '90 van calibration with a 305 engine. Also, swap out the TBI injectors for the 305 injectors. If you leave the 350 injectors in the pod, it will run too rich.

For your TPI-injected 350, things get a little touchier. Use the harness and controller from the Trans Am. Since the '88 engine controls use a mass airflow sensor, things are a little more forgiving. With this you'll need a custom chip to change the engine displacement. You'll also need to match the injectors to the calibration. Give Tom Woodside at GMCOPO a call. He can spec out the proper injectors and help you with the calibration changes.

Using up the components you have to make two nice street rod projects isn't that tough. Just a few gaskets-and hours turning wrenches-will get you there. Enjoy your cruising.

Source:gmcopo.com

Short Course
Q
I'm trying to figure out what stall to go with. I built an '86 Monte Carlo with a small-block 350 that is bored 0.040 over, with Scat 6-inch H-beam rods, Keith Black 0.150 dome pistons, Dart 200cc heads with 62cc chambers, a Speedway solid cam with 0.531/0.533-inch max lift ground on 106 centers that is good for 3,000 to 7,000 rpm, and a Victor intake with a 750 Holley. The trans is a TH400 with a Hughes transbrake. The rearend is a Winters Grand National with a 5.43:1 gear for eighth-mile racing. I used to have a TH700-R4, but I smoked it. I might try a 4.56:1 gear if the 5.43:1 gear is too steep. I thought I should go with a 3,500 stall. The car weighs about 3,400 pounds. I still want to make the car streetable. Could you help me out? Thanks.
Trevor MacNeill
Via email

A When setting a car up for eighth-mile drag race competition, you may think that you can gear the car for top rpm in high gear at the eighth-mile mark, just like racing the quarter-mile. This would work out just perfect if our cars were geared to the race track. By gearing the car for top speed at the eighth-mile, you run into the problem of having too much gear multiplication on the starting line for the tire to hold traction. Going over the engine specs and the vehicle weight you listed, you should be in the low 11s or high 10s based on how well the car works on the starting line. This will put you at about 122 mph in the quarter and around 95 mph at the eighth.

Now we have to cast some assumptions. You're probably running a 28x10-inch slick on the rear of the car unless you have done chassis work in the rear. With a 28-inch-tall tire, your 5.43:1 gears are going to put you through the light in the quarter at 122 mph and approximately 8,000 rpm. I think you're going to be out of power by 7,000-7,200 rpm based on your package. Also, if you multiply the 5.43:1 gear by the First gear ratio of your TH400 of 2.48:1, you come up with a starting line ratio of 13.46! Your 10-inch tire isn't going to be too happy with that.

Now let's go back to your eighth-mile package. The 5.43:1 gears will put you right at 6,500 rpm in the eighth at 95 mph. This is perfect gearing if you can keep the tires under the car. This is where a two-speed Powerglide really has an advantage. With its 1.76:1 First gear and your 5.43:1 rear gear, you have a starting line ratio of 9.34:1. This is just about perfect for a consistent bracket car.

As for your question about stall speed, I think you're right on target with the 3,500 rpm range. We've been very pleased with our B&M Nitrous Holeshot 3,600 10-inch converter that we run in our wagon in bracket mode. The Nitrous Holeshot is fully furnace-brazed and fully balanced, and it has heavy-duty needle bearing thrust packages and new turbine hubs, which are key features along with anti-balloon plates. It's not too loose driving the car around the pits, but it flashes very well and stalls easily on the brakes to 2,600 rpm and would probably go higher. The only problem is that my 9-inch stocker slicks won't handle much more. It's back to that gear thing! Check with B&M and look into the Nitrous Holeshot (PN 20482).

Source:bmracing.com

Killer Cruiser
Q
My '70 Chevelle is nearly show-quality and is driven on the weekends and in good weather only. My recent upgrades include an LS2 (510 hp from Turnkey Engine Supply), electric fans and fuel pump, tubular control arms, all-new suspension hardware, a TH700-R4 trans (which I'm not totally impressed with), and four-wheel disc brakes (13-inch front and 12-inch rear). By the way, all of my upgrades were from articles and ads I saw in CHP magazine.

I have a 12-bolt non-posi with 3.31:1 rear gears (I believe, based on some calculation). What would be a good rearend gear setup to deliver better 0-60 performance without sacrificing highway driving by pushing the rpm too high? I do understand that everything is a trade-off. My driving style is mild. I prefer cruising, and I'll never drag race the car; however, I'd like a little more off-the-line performance. Any suggestions? Thanks.
Sam Dommer
Via email

A Sounds like you have a very nice blend of late-model performance and early-model style. I ran into a very similar situation when I installed an LT4 and a TH700-R4 in my '65 El Camino. The engine bay had a ZZ4 in it previously and I had 3.31:1 rear gears. The car ran great, but we wanted a lower dragstrip e.t. so I swapped out the rear gear to a 4.10:1. The car did pick up 0.1 second in 60-foot, but that was about it. It also made the car less of a weekend cruiser. The major difference I see between our cars is that you must have around a 26-inch-tall tire, as you're running 12-inch rear brakes. My car had 14x7-inch Rally wheels and a 24-inch-tall tire. This makes a huge difference when working out gear ratios.

First, a very easy formula to determine engine speed at any mph is final gear ratio multiplied by the constant 336. Then multiply the result by the desired mph. Then divide the sum by the tire diameter. This will give you the engine rpm at that mph. To get your final gear ratio, you must multiply the rearend gear by the Fourth gear ratio of your TH700-R4, which is 0.70. You need to go for a drive and determine what you consider a proper cruising rpm at freeway speeds.

Everyone has his own opinion what this should be, and I'll give you my recommendation. Currently, with your 3.31:1 rear gear, you have a final gear ratio of 2.31. This ratio, with a 26-inch tire at 2,200 rpm, results in 73.71 mph. A 3.54:1 gear has a final of 2.48, which results in 68.70 mph at 2,200 rpm. With 3.73:1 gears, you have a final of 2.61, which works out to 65.20 mph at 2,200 rpm. Finally, the 4.10s give you a final of 2.87, resulting in 59.32 mph at 2,200 rpm. So now go out and drive your car and decide how much engine noise and feel you want at cruising speed. If you were running a big-block, you could tolerate a higher gear, but the torque curve of your LS2 could use a little slow-speed help. I wouldn't go any lower than 3.73s in the rearend with your engine. Again, this is my opinion.

As for gears, Richmond, Strange, and Zoom all offer high-quality ring-and-pinions. Your best support and technical advice is going to come by way of Randy's Ring & Pinion, which has a complete inventory of rearend components you'll need to set up the perfect diff, from posi's and gears to bearing and shim kits.

Source:ringpinion.com

Get Your Heat On
Q
My '87 Camaro IROC-Z came from the factory with four-wheel disk brakes. I recently added a Baer Sport Brake Kit up front, which is basically a 1-inch-larger, drilled and slotted rotors and dual-piston calipers. I'm told it's the same as an '88 Corvette would have used. In the rear I upgraded my differential to a Strange S60, which allows the use of my '93-97 Camaro rear disk brake system. Do I need to add an adjustable prop valve on the rear main brake line? I was told no because my car had a factory four-wheel disk prop valve already. Could you explain any differences between the factory '87 rear brake setup and the '93-97 rear brakes I'm using? The rear is new, so I haven't been beating on it yet. After a leisurely 10-mile drive, I used a temp gun and I'm seeing 220- to 240-degree temps in the rear and 180-200 degrees in the front. That seemed backward to me, but I didn't want to condemn it yet, with all the changes made and the addition of an extra piston in the front calipers. I was expecting to see higher temps in the fronts over the rears. Thank you for any insight.
Dave Mosler
Via email

A Nice brake system, but make sure you don't have any loose fillings in your mouth when you go out to test your brakes. Those Baer brakes really slam the nose to the ground when you jump on them. We did some digging to spec out your brake conversion and ran into many roadblocks.

Ken Casey at Burt Chevy spent half a day trying to spec out rotor and caliper piston sizes for us on both third- and fourth-generation Camaros. Unfortunately, GM has dropped many of the dimensions from its computer catalogue. Since most of these parts covered five or six years of application with one part number, GM didn't see the need to give out the technical specifications.

Here is what we've come up with. Your '87 Camaro with the J65 rear disc brake option came with 10.5-inch rear rotors. The '93-97 Camaros came with 11 17/32-inch rear rotors, which are slightly larger than 11 1/2 inches. We were unable to spec out the caliper piston size difference between the '87 and the '93-97 calipers.

Now let's talk about your brake heat for a moment. The Baer front system uses 13-inch rotors that are drilled and slotted for cooling. The four-piston calipers they utilize are from a fourth-gen Corvette. The brake pads they come with are for street/sport driving, and those take a bit of heat to bring into operating range. We assume the rear brake system you are using is factory pads and components (not drilled or slotted rotors). The factory pad must give great stopping friction from stone-cold brakes so little old ladies don't hit you in parking lots. They will build heat faster than the performance-style pads on the front. Also, the front brakes receive much more cooling air than the rear brakes do. The rear wheels and brakes are stuffed up into the rear wheelhouse, reducing cooling air to them.

Finally, the bottom line for brake bias is going to come from testing. After you're comfortable with all your new components, you need to go out to a safe place and do some 60-mph panic stops, just below the threshold of locking the brakes. You should be able to stand on the brakes and stop very quickly, and possibly just begin to lock the right rear brake in about the last 10 mph before coming to a stop. If the rear brakes lock before this, you need to add an adjustable rear prop valve and back off the rear brakes until you reach this point. This will give you the best stopping performance for your car.

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

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