Chevy Car Questions & Answers - Performance Q&A

Kevin McClelland Sep 1, 2009 0 Comment(s)
0909chp_01_z Chevy_car_questions_answers Performance_transmission 1/2

Rough Times For The Auto Industry
Not a day goes by anymore that doesn't spell out the doom and gloom of the U.S. auto industry. By now the pain has worked its way to the imports-Toyota posted its first loss in 50 years! Everyone thought the imports were immune to the challenges facing car companies, but this slump is worldwide.

Bailouts are all we hear about these days. The government is holding car manufacturers to a different standard than any other industry it is looking to help. In my opinion, this is going to be part of the recovery problem for automakers. I'm sure many of you have heard that GM has closed its High Performance Vehicle Operations (HPVO). This was a small job facility in Detroit that gave the finishing touches to such vehicles as the V-Series Cadillac, the Chevy Cobalt SS, HHR SS, and the Pontiac G8 GXP. What this means is that GM is not going to produce these high-performance vehicles any longer. This closure was a requirement of the bridge loans the government gave GM to keep it afloat. Also, Congress is requiring that GM offer 15 hybrids by the year 2012, and I've heard of numbers as high as 24 by 2014! I'm not saying GM shouldn't have to make concessions to get our hard-earned taxpayer money; however, the requirements shouldn't hamstring GM's recovery chances.

History is repeating itself. Back in the fuel crisis in the late '70s, Detroit raced to build small, fuel-efficient cars to give the public fuel economy. This, in combination with emissions regulations, just about killed the muscle car. This time the government believes that if you build it, they will come. With the feds requiring the closure of the HPVO, they have taken away the ability to build high-performance vehicles to fill a niche market. This is the only defense the domestic auto manufacturers have to make exciting vehicles that keep them on the automotive map.

Only time will tell if all of the government's recovery plans are going to make a difference. Today, the market took another turn for the worse and GM hit historic lows. I hope for all our sakes that GM makes it through this very tough time, not only for all the workers who build cars for us, but for the folks connected to every vehicle made. All I know is I can't wait to see the '15 Camaro SS with a 600hp Gen XII small-block that gets 50 mpg. I'll see ya at the dealers in five years for a testdrive.

Great Flow, Less Noise
Q: I am planning to build up the '85 Monte Carlo my father gave me. He bought the car new with a 305, a TH200R-4, and a posi 75/8-inch 10-bolt with 3.73:1 gears. I plan to install a GM Performance Parts ZZ383, a rebuilt CZF TH200R-4, and an 81/2-inch 10-bolt out of a '87 Regal T-type. I already have the transmission and rearend. The ZZ383 cylinder heads have D-shaped exhaust ports that are raised 0.200 inch with angle plugs, and I'm not sure if they would require any special headers.

I'm also not sure if I should go with 15/8- or 13/4-inch-diameter header tubes. GM tested this engine with 13/4-inch headers. I'd like to run a 21/2-inch exhaust system with an X-pipe to keep the sound tame. Any suggestions on great flow with low-noise mufflers?

I also want to run a Quadrajet on this engine with an Edelbrock Performer RPM Q-jet intake PN 7104. The heads are listed as dual-pattern accepting Vortec and early-model intake manifolds. The GM information suggests a Vortec-style intake. Do you think the RPM Q-jet intake would be a better choice over a Performer Vortec? I am going to drive this car on nice days and drag race it some. Any suggestions on a set of full-length headers, mufflers, and intake would be greatly appreciated.
Craig Powell
St. Louis, MO

A: The ZZ383 is a great choice for your Monte buildup. The cylinder heads used on the ZZ383 originally came from the LT4 Corvette engine. GM Performance took a set of LT4 production heads and had them ported, tested, then digitized. These digitized ports were then turned into tooling and cast up as the Fast Burn cylinder heads. So, truly, you have CNC-ported LT4 cylinder heads with an as-cast finish. Isn't technology wonderful?

When GM tested this engine, it used 13/4-inch headers because the header tube lined up with the roof of the exhaust port. Several manufacturers produce a D-shaped exhaust port header-the trick is to find a set for your G-body. Hedman Hedders has two very nice full-length headers in its Hustler racing line. We've used the 15/8-inch set (PN 65218) in our stocker, and they clear the angle plugs and fit the raised roof exhaust port. The only issue with these headers is they don't fit with A/C. The header tube routing on the passenger side will hit the A/C box on the firewall. The 13/4-inch header is PN 65217; both have very good clearance around frame and suspension components. As for an X-pipe, check out the X-Treme Exhaust Equalizer (PN 18813 for a 21/2-inch system). This is a very nice X with a fully hand-welded junction, which aids in the scavenging of exhaust gases and gives you that unique X-pipe exhaust note. If the A/C is an issue, check with Stahl for custom headers that will clear the A/C and specific CNC header flanges to fit the Fast Burn cylinder heads.

Mufflers are a personal preference. There are many quality high-flow mufflers on the market today, and each sounds different. The floorpan on your Monte has limited room for large, quiet mufflers. There is a little room under the rear seat of the car, and you can install 4-inch-thick, 10-inch-wide case mufflers. This isn't going to stop much sound. Check with Borla, Flowmaster, and Magnaflow for their recommendation for that type of space. Then add tailpipe resonators (secondary mufflers) to help cut down the noise. I've built many systems with this layout and had very good results quieting down nasty exhaust notes.

Finally, this engine would love a Q-jet. However, we'd choke it down with a Performer inlet. Try that Performer RPM PN 7104 you mentioned. It will supply that engine with the airflow that the cylinder heads and camshaft need. We also like the traditional Gen I inlet bolt layout. The dozen 3/8-inch bolts holding down the manifold is better than the eight 5/16-inch bolts of the Vortec design. Good luck with your Monte!
Sources: borla.com
flowmastermufflers.com
hedman.com
magnaflow.com
stahlheaders.com

Tick, Tick, Tick
Q: I have about 500 miles on my new 350 Chevy ZZ4 crate engine and have followed the GMPP break-in procedure to the letter. I used Valvoline 20W-50 Racing Oil (with zinc) and prelubed the engine prior to initial startup. The valves have been ticking since startup, so I tried adjusting the valves using the EO-IC procedure, zero lash, and then a half-turn down from there. The valves still tick slightly, just as they did before the adjustment. Any help correcting this problem would be greatly appreciated.
Paul Biddle
via email

A: You're probably not going to like our answer. For the most part, slight tappet noise is normal with the ZZ4 camshaft. The acceleration rates on the inlet lobe of that camshaft are pushed out to the max. With the very short duration number of 208 at 0.050 inch lift, and max lift numbers of 0.474 inch, you won't find a higher-lift cam with that duration in the aftermarket. That camshaft was originally designed for the ZZ3, which was also used at the time for the H.O. 350 Camaro emissions-legal engine package. To achieve 308 hp through the cats, the production exhaust manifolds, and all the emissions equipment of an '87 Camaro, GM had to pull a few tricks out of the bag. Pushing the camshaft without increasing the duration was one of them.

Factory tappet preload is one turn from zero lash. You can try to go to this tighter setting, but this probably won't help much. What Chevrolet did in the later years to quiet down the valvetrain was to install covers over the valve covers. This kept down the injector clicking and the tappet noise. They're also on the LT4 '96 Corvette; this also damped the high-pitch ticking. If you can run down a set of these covers it will also help with the noise. Give the valve adjustment a try with the tighter preload. The standard EO-IC procedure works just fine with this camshaft. Hope we've been some help.

What's That Smell?
Q: My '95 LT1 Camaro has an OBD-I computer, and the engine has been rebuilt. I've got ported stock heads, a Comp Cams 218/224-duration, 0.565/0.570-inch max lift cam, a ported MAF, a 52mm Edelbrock throttle body, 32-pound Siemens injectors, midlength Pacesetter coated headers/Y-pipe, and a Hooker after-cat with a straight pipe in place of the cat. My problem is that even before I rebuilt the car, it always smelled rich. Even with the stock exhaust and cat on it. I was told the car has split BLM readings when the computer was scanned. It has a computer tune on it for my modifications. I've also heard that the split BLM readings can be caused by the EGR hole on the throttle body not lining up with the cast hole on the front of the manifold (I think this hole leads to the emissions passages in the floors of the ports in the manifold). The car is mostly rich at idle and low-speed or part-throttle driving. Have you ever heard of this problem? Thanks.
Mike Topczewski
via email

A: Several things could be contributing to the rich-smelling exhaust. First, without a catalytic converter unburned hydrocarbons are coming right out the tailpipe. This is the rich smell. As you stated, you had the converter on it earlier and it still smelled. Was the cat functioning properly? Was the cat up to temperature when it smelled this way? Unless the converter is up to temp, it can't eat up the bad stuff in the exhaust. Let's look at the other factors you listed.

The BLMs you refer to are the Block Learn Memory fuel trim tables in the calibration. You have short-term and long-term BLMs. These fuel tables are adjusted by the O2 sensors based on the air/fuel ratio it is monitoring. BLMs are stated a few ways: 128 is right in the middle of the fuel trim window for the cell it's running in. Below 128 the cell is adding fuel, and above it's leaning out the mixture. It's not uncommon to have a slight difference between the banks of the engine. Any more than 2 percent, we'd be looking for a reason. That said, if you are to trust your BLMs with aftermarket components like headers, ported MAFs, and aftermarket injectors, they must be up to OEM quality. If your headers have an air leak, they will cause an imbalance in the block learns. Unless the fuel injectors flow exactly the same, again the block learns will be off. And if the BLMs make no sense at all, we've seen the O2 wires swapped from bank to bank-this really screws up the mix and the controller is trying to fuel the wrong side of the engine!

If the block learns in these types of ranges, the controller is fueling the engine at 14.7:1 at idle. The fact that your throttle body isn't lining up with the cast hole in the front of the manifold isn't the EGR circuit. This hole in the manifold in some models is for the idle air control. If this didn't line up at all it would not allow idle air to flow from the throttle body into the manifold. This is probably not the problem, because if you have idle control, you are getting idle air to all eight cylinders through the passages in the manifold.

When you port the MAF, you throw off the mass air calibration in the software. The MAF flows more air than the computer thinks is going through it. If they corrected this in your computer tune, great; however, the only way to properly calibrate a MAF is on a flow bench with the complete ducting and airbox attached to the air meter. Most calibrations have enough room to accept modified MAFs, but because of the ton of modifications you have, you may have run out of room. Anyone good with tuning software can verify this for you.

The rich exhaust smell you're getting is most likely caused by the overlap of your performance camshaft. When an engine has a lope at idle, it is a misfire. When the engine lopes, it allows unburned fuel to pass through the engine. This challenges the EFI system to figure out if it's unburned oxygen from a lean mixture or oxygen rich from a misfire. Either way, the answer for the EFI system is to add fuel. This is why you can chase your tail trying to calibrate fuel injection systems with performance camshafts. It's always a compromise.

Down in the Hole
Q: Can you tell me about how far down in the hole the pistons are in this engine? Mine is a PN 10067353 that was made in Mexico. Thanks.
Fred
via email

A: Production tolerances for deck clearance for Gen I small-blocks come in somewhere between 0.020 and 0.030 inch down in the hole. Most of the engines we've dissembled have fallen in around 0.022-0.025 inch. This, combined with a thin head gasket, will give you a decent deck clearance. However, when many people swap out cylinder heads on these engines they go with the standard Fel-Pro-type head gasket, which comes in at 0.038 inch. If you do the quick math you'll see you have just killed whatever quench you had and have a deck clearance in the low 0.060-inch range. Make sure when changing a cylinder head not to go with a gasket any thicker than 0.028 inch.

All You Need Is Wrenches
Q: I read every article concerning your bitchin' Camaro. I salivated over the five-speed tranny swap and it got me thinking. There's an '88 I can purchase for next to nothing, but it has a V-6. How difficult would a V-8 swap be? The same buddy has a World Class T-5 five-speed that he'll throw in the deal-$500 for a car and tranny! The car runs, and the tranny is out of a wrecked '92 Firebird. Is this doable or wasted cash? Love the mag.
James "JB" Hale
Wichita, KS

A: The swap you're considering is a complete bolt-in with the right components. You may want to check in your buddy's parts pile to find the V-8 engine mounts for the frame and the engine-mount cups for the engine block. The K-member in the Camaro is drilled for different mounting locations for the various engine combinations. The engine mounts (isolators) that bolt to the frame are different between the V-6 and the V-8. The GM V-8 mounts are PN 22188497. The engine-mounting cups are different between the V-6 and V-8 also, and they're different from left to right. On top of that, the right-side engine cup is discontinued, and there is not a single one left in the 5,000 GM dealers across our great country! Here are the part numbers to help you in your junkyard search. The right-side cup is PN 14039436, the left-side PN 10213125. (Thanks to Ken Casey at Burt Chevy for running this information down for us.)

With all the third-gen parts cars lying around, this would be a simple swap. If you can pick up a clean V-6 car for dirt, jump on it. For the price of the car and a decent small-block, you could have a very nice Camaro for little cash. Enjoy your new project.
Source: burt.com

Quicker on the Cheap!
Q: I've got a '91 Chevy shortbed pickup with a Chevy Fast Burn 385 crate engine with the Hot Cam kit. It is carbureted with a Quadrajet and has a TH700R-4 transmission with a 2,500-stall converter, a 12-bolt rearend out of a 454 SS pickup, and 3.73:1 gears. It also has a B&M Mega shifter. I raced it in a bracket series about seven years ago and it was running mid-13s at 100 mph. I went through the traps at 4,200 rpm and I would like to be around 6,000. I want to get back in racing, but I want to go faster. I've got a TH350 trans with a TCI 3,000-stall that I was thinking about installing. I need advice on what to install that will be cheap-I have a baby on the way. Much appreciated.
Stephen Swartzman
Topeka, KS

A: It may be tough building up your racer with a child on the way, but we've got a few inexpensive tricks up our sleeve to bring the engine closer to its powerband. We'd stick with the TH700R-4 trans for the streetability aspect of the truck. Going to the TH350 would require a lower rearend gearing to get the truck to accelerate in First gear. The TH700R-4 has a 3.06:1 First gear as compared to the TH350's 2.52:1. That half point of gear ratio is huge when you're trying to get a heavy vehicle moving. From the information you've given us, we're assuming that you're running 30-inch rear tires. This works out the 4,200 rpm at 100 mph and 3.73:1 gears. You could purchase a set of 26-inch-tall M/T ET Streets that would dead hook your truck on the starting line. This would also bring the engine speed up to around 5,000 rpm at about 103 mph. This is where we think the speed would come up to with the engine running longer in its powerband. Now, to bring the engine up to 5,500 rpm, you'd need to swap out for 4.11:1 rear gears. This would be a good compromise between keeping the truck on the street and making it more of a race truck. If you made your ratio change with both the gear and the tire diameter, it would give you the ability to swap back to the 30-inch street tires for everyday driving.

If you want to go with the tire swap idea, we'd use a set of Mickey Thompson ET Street tires. These are purpose-built, DOT-legal, bias-ply racing tires. They give you outstanding traction and decent tire life, but we would only run these at the track. If you pick up an extra set of rear wheels that are 10 inches wide and get a set of 26x11.50-15LT tires, these have a section width of 12 inches and a tread width of 9.8 inches. These will fit well in the wheelhouse of your '91 pickup and take all the power that your 385 can throw at them.

Try the tire swap first. This may give you the performance change you're looking for. Keep your spending to a minimum until you know how much it costs for formula and diapers for the new little Chevy fan. Good luck and congrats!
Source: mickeythompsontires.com

I Hear You Coming
Q: I hope you can help me out with this one. I just had a shop install a 350 small-block in my '72 Chevelle and I'm very disappointed with the performance of this engine, which was supposed to see 440 hp at 5,900 rpm and 450 lb-ft at 4,400 rpm. The engine specs out at 10:1 compression, a 230 duration at 0.050-inch tappet lift, single-pattern camshaft with a max lift of 0.512 inch, and it's ground on a 108 separation angle. The cylinder heads are Pro Topline angle-plug with 210cc inlet runners, 2.02/1.60-inch valves, roller rockers, and an Edelbrock RPM Air-Gap with a Barry Grant 650-cfm Speed Demon, lit by an MSD distributor and a 6AL box. The engine is backed up with a TH350 trans and a 3,000-stall converter.

The problem is keeping the car running correctly. Under hard acceleration it pings like there's no tomorrow! Every time I take it back to the shop, they keep it a couple of days, change the plugs, and send me on my way. The engine has less than 300 miles on it. I have taken it to a couple of shops and they told me the carb and manifold should be changed to a single-plane with a 750 carb. Is this true? I've put a lot of money into this car and need some help. Also, what type of plugs do you run in angle-plug heads? Any advice you can give me would be greatly appreciated.
Ken
Via e-mail

A: Well, you've given us just enough information to make us dangerous! First let's talk about the heads. We would love to know if you have aluminum or cast-iron Pro Topline cylinder heads. The famed Racing Head Service is back in the cylinder head business. RHS, part of the Comp Cams family, has been quiet for several years and has had a resurgence with the acquisition of New Zealand's Pro Topline. RHS has renamed the cylinder heads "Pro Action" cylinder heads. This is important when it comes to spark plug selection. If you truly have the Kiwi cylinder heads and they are the cast-iron version, they accept a 14mm, 0.450-inch reach, tapered-seat plug. If the cylinder heads are RHS stateside iron castings, they are machined to accept the 14mm, 0.708-inch reach, tapered-seat plug. If you have the aluminum heads, either from Pro Topline or the new RHS Pro Action, both use a 14mm, 0.750-inch reach, flat gasket-style plug. Since you're having pre-ignition/detonation issues, you'll want to run a relatively cool heat range spark plug. All these plugs have an extended tip electrode.

Let's start with the aluminum head selection at 14mm, 0.750-inch reach, 5/8-inch hex gasketed plug. With NGK plugs, you need a BCPR7ES, Champion RC9YC, and in AC pickup, a FR1LS. As for the Kiwi-built iron heads, which take a 14mm, 0.450-inch reach, 5/8-inch hex tapered seat, use NGK R5674-7, Champion RV9YC, and AC is R41TS. Finally, if you have the newer Pro Action RHS head, you need the 14mm, 0.708-inch reach, 5/8-inch hex tapered seat. Pick up an NGK BPR6EFS, Champion RS9YC, or AC R42CLTS. This should put the proper heat range into your engine for a baseline. You may need to move up a heat range based on the performance, but we're starting to the cold side based on your pinging issues.

Now for your engine rattle. First of all, either you have too hot a plug (hopefully we took care of that above), you're running too much ignition timing for the cylinder pressure, and/or you do not have a high enough octane fuel. Also, the engine could be too lean on your fuel mixture. If your engine is equipped with cast-iron cylinder heads with the 10:1 compression, it's going to be tough to keep this engine out of detonation at peak power spark advance with the current pump super unleaded of today. Yes, this engine may have made 450 hp on an engine dyno under controlled conditions, but bolt that engine in a car, heat sink the engine, and pull around a 3,800-pound Chevelle, and she'll knock.

Is the RPM Air-Gap and your 650 Speed Demon out of place on your engine combination? Absolutely not. We've made over 460 hp and 444 lb-ft of torque with a 350-cid small-block. Yes, this was with a 750 carb, but you're right in the ballpark with the 650 cfm. A Victor Jr. and a 750-cfm carb would run well but lose some midrange torque for the gain of a few horsepower

If you are confident that the air/fuel ratio is on the safe, rich side, you need to start with some ignition timing curves. As a baseline, set your total spark advance at 3,500 rpm at 32 degrees. With this total timing spec, you may need to limit the spark advance in the mechanical advance. To get good slow-speed engine performance, the initial spark timing at idle should be 16-18 degrees. You'll need to limit your mechanical advance in the distributor to approximately 7 degrees. You can either do this with bushings supplied by MSD for its distributors or you'll need to weld up the advance mechanism in an HEI style to limit its travel. All this work can easily be done by Performance Distributors, or you can use your engine and a timing light as a distributor machine. We don't recommend the latter unless you're very experienced in all facets of distributor modification. We do it all the time on the engine dyno.

The spark plugs and spark advance specs we've given you will get you in the ballpark. If, after these changes, you are still experiencing timing knock issues, mix a batch of super unleaded with 108-octane leaded racing gas. Mix your gas at a 50/50 mix and this will give you approximately 100-octane gas. This, I'm sure, will take care of your spark knock challenge. You should be able to find a combination of spark timing, air/fuel mixture, and spark plug heat range to keep your engine happy. Also, keep that thing out of knock for the first couple of thousand miles. When your engine goes into knock, it is building tremendous combustion heat and pressure. This is wreaking havoc on your poor engine's attempts to break in properly. Good luck!
Source: performancedistributors.com

Seems Like a Lifetime
Q: I am on the 11th year of a frame-off restoration of a '63 Impala SS Convertible. Five years ago the engine was completed as follows: a 400 GM small-block making 377 cid with a 350 crank, 6-inch rods, 10.2:1 hypereutectic flat-top pistons, a Comp Cams XE268 hydraulic cam, zero-decked and balanced. The upper end uses AFR 180 CNC aluminum heads with 1.5 stainless steel roller rockers, Edelbrock EPS intake and 1401 600-cfm carb, and a HEI distributor. The exhaust is 15/8-inch full-length headers, 21/2-inch exhaust through Flowmaster 50 series mufflers. Transferring the power is a close-ratio T10 four-speed, 3.70:1 rear gears with a post. Tires are 26-inch-tall P235/55R16 Goodyear Eagle 1 NASCAR street tires. A second rear upper control arm was added for traction. My guess is the car with me in it will weigh right around 4,000 pounds.

Over the course of the build, I don't know how many people have told me what they think I should have done differently powerwise-350, 383, 406, different cams, carbs, heads... I have tried to build for a larger car that will make me proud of its performance on the street. Since completion may be several years away, can you tell me what kind of power numbers I might expect, or how to improve on what I have? Since I have no intention of adding a rollcage to my convertible, a time at a dragstrip will be hard to come by. What could I expect at the track, and at what rpm should my heavy car be shifted for the best quarter-mile performance?
Bob Thayer
Spokane, WA

A: It seems we have something in common. Between 1985 and 1996 my '57 Chevy race car was parked, since everything seemed to get in the way of its completion. I was running the car in 1985 when the engine expired. That gave me a chance to update it with several things I'd been wanting to do to it. I basically had to threaten myself that if it sat for 10 years I would sell it! (If you did the math, it was parked for 11.) All I know is good things take time to build. Your Imp will be done when you're happy with it.

I really like the engine combination for your car. I think it will be perfect for a heavy four-speed car like your 'vert. The camshaft is mild enough to build great torque and will carry the power where it's fun to row the gears. Everyone has a perfect build in mind, but it stays there until we put the parts together and run it. You should see an easy 420 hp by 420 lb-ft of torque. The horsepower peak should fall right around 6,000 rpm with the Comp XE268, and we'd shift it right past 6,000. The AFR heads are going to want to breathe and will carry the power upstairs with your relatively mild camshaft.

After you get the car running you may want to install a little larger carburetor. However, for a street cruiser, the 600-cfm carb will give you great street manners and decent fuel economy.

As for a quarter-mile e.t., that is a little tougher. Four-speed cars can be rough to launch without a ton of wheelspin or bogging the engine. It's very safe to say your Imp should run in the 13s at 100-plus mph. Weighing 4,000 pounds is nothing; your engine will pull this around with no problem.

Get your Impala done and do some top-down motoring for all of us!

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

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