NastyZ28.com - Camaro High Performance Tuning

Welcome to the high-performance tuning section of NastyZ28.com. A Stock Camaro is designed to appeal to a wide variety of owners in general. With some careful tweeks, you can tailor your car to better suit your driving style or requirements. This section contains information on some of the alterations & modifications that can be done to improve or enhance your cars performance over it's stock potential. These modifications are applicable to either Drag Racing or Road Racing, and at various performance levels - from a performance street machine to maximum effort race only vehicle. So, be careful and fully understand these alterations before pursuing them. Keep in mind, highly altered machines usually do one thing well. The trick for a street machine is for it to do everything a lot "better" than it could before. "Better" is subjective, and defined by the owner.

High Performance Engine & Chassis building & tuning has been broken up into the following sections:

A lot more information is available in the NastyZ28.com forum. You will find specifics on a wide variety of topics including brakes, tire fitment, performance engine alterations, suspension modifications, Fuel injection and modern (overdrive) transmissions. among other things.
We also have a section dedicated to Competition Vehicles.

More Articles:
"Ten Step Soup Up" & "cheap speed secrets". - A logical, step by step process to making your car an awesome performer.
Get some of this 1972 Camaro NHRA J/Stock Eliminator
Fuel Injection - TPI/TBI, concepts, technotes, swaps. (page Obsolete)

Super Tuning an Engine

Supertuning: is when you take what you have, and make the most of it by tweeking the ignition system and then the carburetor. Supertuning means often doing the same things you would do when you dyno-tune an engine, except in this case, you don't need a dyno. While a dyno is nice so you can see if you're actually getting results, supertuning "concepts" by themselves should be beneficial and can be felt via the "seat of the pants" method (often equating to a 1/2 second improvement in 1/4 mile ET) and substantially improved throttle response.

The purpose of supertuning is to achieve maximum performance. Since the factory engineers need to balance performance with emissions, noise and fuel economy, the car isn't set up for maximum performance.

If you need more performance and are not afraid to make major changes to your engine, refer to the other sections of this file for component selection.

Any engine will benefit from this process, however the mid/late 70's smogger motors will really wake up with these changes.
Beware of valve float at 4500 + RPM.

*Trick kit*, spring kit. other parts.

Exhaust
Simply put, I'd put headers onto everything I own.

Carburetor Tuning

Prior to tuning the carburetor:

Make sure ignition is good, fuel pressure is adequate, and throttle is opening completely.

Check these things before starting to tune your carb:

Carb Links:
How to Tune Your Car's Carburetor - by Gerard Forgnone
Holley Rebuild - excellent graphical depiction

Initial Carb Tuning & Tips

make sure throttle opens 100%
set idle speed/mixture screws and time engine
adjust idle mixture for highest vacuum reading, reset idle speed

primary calibration: back down until stumble, then go up 1-2 jet sizes.
adjust pump cam to tailor the pump shot to carb
don't mess with the accelerator pump
Setting the Jets

Make one change at a time.
It generally takes 2 jet size difference to see a change.
Set the timing and baseline the car. then adjust 2 sizes up on secondary size. If car likes the change it will speed up, else it will slow down. This will establish the way you need to approach fuel metering.

Starting line requires primary adjustments. Top end power comes with secondary adjustments. Make several jet changes until the car stabilizes at its best performance level. Log the jet sizes and weather information.

Secondary Air Valve Spring Adjustments

After optimizing jet settings begin with optimizing other variables which will make the car leave hard, and optimize 60 foot times. Switching to a lighter or heavier secondary air valve spring could help. This is valid only on vacuum secondaries.

Float Level Adjustments

Altering the float levels alters the fuel curve. A high float level richens the mixture while a low level leans the mixture. Adjust for proper jetting prior to playing with the float level, as adjusting the float level can cover up jetting and squirter inadequacies. After messing with all the carb adjustments, retime the engine.

Squirter Changes

The accelerator squirter is a quick and easy change to help the car get off the line. Higher number squirters have bigger holes.

Testing

Part of optimizing a car is to go test it. Each change you make produces a response and gives you a trend. Write down where you started and what you changed to, so you can get back to a baseline. Notes help you become an even more experienced racer. If you just make changes, it's easy to get lost.

After dialing-in the mains and the fuel pressure, see how the engine responds to intake manifold spacers. A four-hole spacer under a carburetor that's too big can help pick up air speed and signal. It makes the venturi think it's longer and more efficient. An open spacer adds plenum volume. One fixed rule about spacers is to go testing first, then write the rules later. In other words, take it one step at a time.

High Performance Engine Building & Tuning

Cylinder Head Selection Tips

Engine displacement makes power, components move the power around the RPM range.

Intake Manifold Selection Tips

Header Selection Tips & Tuning
Paint the collector or mark the collector with a grease pencil. Where the paint burns off orthe grease melts is where the header should be cut for maximum flow.

Carburetor Troubleshooting

Definition of some of the problems you could come across when first dialing-in a carb.

"Bog" simply means that the car accelerated and quit before restarting, it layed an egg.

A "stumble" is a softer version of the same.

"Sag" means the car started out strong, kept going but is not pulling hard enough. In a street machine, you want total smoothness as the throttle first opens, a good "tip-in".

"Will not take the gas" says that the engine doesn't want to follow the throttle. You just mashed the pedal, and the car fell flat on its face.

"Dialing-in the midrange" establishes the area covered by the main jets. You can cover up idle transition with richer jets and completely miss the boat. You may need more idle and pump shot, or less of either one. Once midrange is good, do not change it to dial-in the top end.

"Spit-backs" means burning in the intake manifold, likely to be valve leaks from the intake side, or extreme leanout, or a fuel supply problem. Late timing is another cause. A "surge" refers to the car alternately picking up power and losing it. More than likely it's a fuel supply problem. A steady, high-speed miss may or may not have anything to do with the carburetor. Change the coil, check polarity at the magnetic pickup. Poor cable connections limit a perfectly good MSD box.

There are dozens of other little problems that may not have anything to do with the carburetor. That's why smart racers do cylinder leakdown tests, compression checks and look for intake manifold leaks or bent valves.

You want good idle quality, being able to drive through the pits and not foul the plugs.

If you have an automatic trans, take a vacuum reading and add a power valve that's a minimum of 2 sizes down from that. The power valve can be removed ONLY IN A CAR THAT IS RACED ONLY. It's either idling or floored and the power valve isn't required.

If you have a long duration cam and are having idle problems, crack the secondaries with the adjustment screw and open the butterfly valves .010 - .025 inches in the secondary slot. This will back the primary down to where your idle needle will be a little more responsive.

If the car launches and then dies, work on pump squirters and pump cams. Put in a larger squirter, and go from there. Keep going until it stops. Even if the car stumbles, you can look at the mph of run, this is called best jetting, a jet change can be evaluated in the traps, even if the car lays down on the line.

Fiddle with carb spacers, taller one gives more top end RPM, while one with 4 holes results in better low-end torque and possibly better reaction times.

Limit variables of tuning. Two steps in jets is like one change of heat range in plugs or a degree in timing. Change the things your most familiar with.

Response Problems

When you transfer a carburetor from a small to a big block, the engine provides a different signal. You first have to re-tune the carburetor to match what the engine wants. At idle, the bigger engine will want more fuel without opening up the throttle with relation to the transition slot. This means opening up the idle feed or putting in a call for a metering block that will match the new application. The primary throttle plates will want a larger idle feed. You've just changed the cam and closed up the centers, given the engine more overlap and killed the carburetor signal. Now you need either more jetting or smaller high-speed air bleeds or a booster that gives more signal.

A carburetor that's been ported and massaged for airflow,without opening up the venturis, will generate more signal and can work better on a small engine.

Won't Idle Down

Check the throttle cable and the return springs. A heavier return spring is not a fix for a throttle holding the carburetor open. See what's holding open the throttle, such as idle adjustment, or a fast idle set too high on the chocke assembly. A large air leak into the intake speeds up the idle. Try a squirt of solvent at the intake gaskets, under the carburetor base and the vacuum lines. A throttle return spring at the wrong angle will not pull back the throttle without excessive pressure. Make up an extended bracket to bring the spring up to the right height, in line with the cable.

Large drillings in the throttle plates will not allow the engine to idle down, even though the blades are closed. Close them off and redrill or simply install new plates.

Won't Take The Throttle At Tip-in

At very low throttle openings (tip-in), the accelerator pump is not covering up for idle system problems. Now you see a sag or bog, then the engine picks up again as you open the throttle further. Richen the idle feed and fix the relationship between the throttle plate and the transition slot.

Transition

The system controlled by the main jets does not want to come in early. The idle system is at the end of its delivery and the main jets do not want to feed because they're not getting enough signal. There are many ways to fix the problem. Less high-speed air bleed will help. You can go a little richer on the mains. Any air bleeds above the fuel level will slow down the initiation of the main jets. This goes for the small air bleed in the dogleg of the high-speed air channel in the metering block. The drawback of small high-speed airbleeds is that the system goes rich under full power. Now you have the information to go play.

Pump Shot

Check for ample pump shot as you open the throttle. Next, check for pump delivery when the throttle is moved little and very slowly. If you have no pump shot, the umbrella seal above the pump is leaking. Replace it. You can get into a hidden leak between the metering block and the main body, at the center.

Accelerator pump shot is an easy way to fix the transition from idle to full throttle. If you begin with more pump shot, the real problem may be covered up without fixing it. Working with tip-in feel is a step in the right direction. Increasing nozzle size will give you earlier pump shot fuel delivery.

At What Throttle Angle Do You Leave?

If you're leaving at 3500 rpm off the foot brake, check the rpm at which you leave and find the throttle angle needed. Now, set up the pump cam to match that throttle angle. Otherwise, you've used up the pump shot and not received the benefit of extra fuel delivery. When leaving against a trans brake or against a Line Lock at full throttle, there won't be any pump shot.

Track Troubleshooting

Make sure you've checked all the "pre-tuning" items mentioed above.

Here are some of the things you may see your car doing at the track. The following will help narrow down problems and cures. With that out of the way, here are some common carburetor problems and their solutions:

Problem: Carb won't idle properly

Attach vacuum gauge to manifold vacuum at a location below the throttle blades. Block the tires and warm engine in neutral. Put car in gear and take note of vacuum reading on gauge. Example: if vacuum gauge reads 6.5 inches of vacuum, take note of this number, and remove the primary bowl on carburetor. Check the primary jets first. Are they the right size according to your Holley manual? If yes, check powervalve. It should be two sizes smaller (smaller in vacuum number) than you vacuum reading. In the example, the vacuum reading was 6.5, so the carburetor should be fitted with a 4.5 powervalve to function properly.

Problem: Off-idle stumble.

Check float level first by unscrewing sight plugs on fuel bowls. Fuel should be right below threads on primary side, should just barely leak out on secondary side. Readjust air mixture screws. Turn in until engine falters, turn back out until highest vacuum reading. If it has four corners, go to other other side and repeat process. If stumble still exists, there's likely a pump squirter/pump cam problem. With engine off, look down the primary side of the carburetor. Operate the throttle linkage and watch the stream of fuel from the squirters. It should begin as soon as you open the throttle blades. If it doesn't you have an incorrect pump cam. If you've adjusted the float level and checked the squirters but a stumble still exists, try a larger squirter number.

Bog coming out

On takeoff, the fuel is going to rush back and will sit in the bowl at an angle. On the primary, up front, it rushes toward the jets, while on the secondary, it wants to move away from them. Jet extensions reach into the fuel and solve the problem. Bowl extensions add extra capacity. The secondary power valve is above the jets and the first to be uncovered on takeoff. Raising the secondary fuel level may help. If the carburetor leans out on takeoff, try blocking off the secondary and going up eight numbers on the jet size.

Leaves 200 Feet and Dies

There are a number of things to check, from fuel system and ignition to battery. If the battery is mounted with the plates crossways, they can deflect, touch, and short. Plates should always be in the direction of car motion. A kill switch can shut off at the wrong time.

If the fuel tank is not built right, the fuel can be pulling away from the pickup. Did you see the pressure gauge needle blip on launch?

Top-end Shutoff

In a mild version, the engine is still making power, but not as much as it should. You can suspect a fuel problem; one way to find out is to get a pressure gauge at the top end. If the car is just leaning out at the top, you may feel a high-speed flutter and hear pops. In a more extreme case, you feel the car nose over, telling you that the fuel system can't keep up with the air demand, so the engine quits making power.

High Pressure, No Flow

You can have a high-speed lean-out and good pressure. When the needle and seat doesn't open far enough, you'll see good pressure but no fuel volume. For instance, if the float is not contoured and is hitting jet extensions, it can't drop far enough down; now the needle is operating partially closed-not enough fuel. Yet the pump is putting out so the gauge reads normal pressure.

Blubbers Down The Track

It generally ties in to a rich condition with the fuel level set too high or too much jet. The sound is different than with a high-speed miss due to ignition. Water in the fuel can also cause missing and power loss.

Steady Miss

A bad coil or ignition system problems are the prime candidates. When in doubt, change the coil, if that doesn't help then look at the distributor cap and rotor. Check polarity at the magnetic pickup, and spacing for the pickup; get the ignition wiring out of bundles and away from other wiring. The ignition box is generally alive and well or dies, with no in-between.

High-Speed Breakup

Scoops can induce a high-speed problem by causing turbulence over the carburetor. Air must come straight down into a Holley, rather than across it. This type of problem should disappear when the base under the scoop is removed or when an air cleaner is built into the scoop. Here, the air cleaner element acts as a flow straightener. You need at least four inches above the air horn for clearance to turn the air around. If the air cleaner is too low, the lid will act as a choke and the carburetor will have a sooty look. You may find this on a Camaro where a low hoodline left little room for the air cleaner. If spacers have been added between the carburetor and manifold, there's less room for the air cleaner, aggravating the problem. Smart dyno shops make back-to-back runs, first without an air cleaner or scoop and then with one. Any drastic power change catches the problem before the engine gets to the track.

Flat In High Gear

It works backwards, and acts flat in high gear, but the car picks up as soon as you start to lift. The carburetor is way too big for the combination, or the cam, intake or exhaust are too small. You get no response to a large jet-size increase, even through the rest of the fuel system is okay and you've checked that there's enough float drop. Do a little figuring on your slide rule, check the tach and see if you're pulling enough air through the carburetor.

Camshaft Selection Tips, Definitions and Tuning
Critical Cam selection variables

Duration: Duration is how long the cam holds the valves open. It's expressed in degrees of crankshaft rotation (remember, the cam rotates at half then speed of the crank). Holding the valves open longer allows more air and fuel into the engine and also allows more to get out through the exhaust. Longer duration (higher number) improves top-end power but almost always sacrifices low-end torque. Lower duration improves low-end torque and makes the car idle better, but it limits top-end power, and you can get only so much valve lift with a short duration cam due to the rate-of-lift limitations of the lifter. Roller cams, have the advantage of allowing high rates of lift with relatively short duration.

The confusing thing about duration is the difference between "advertised" and "at .050-lift" duration. At .050-lift duration is measured from the point where the cam moves the lifter up .050 inch until .050 inch before the lifter is all the way back down. Most cam manufacturers differ in where they start and finish measuring for advertised duration. Some start at .004-inch lift, some at .008-inch and some measure it somewhere in between. That's why the .050-lift numbers are the best to go by. A 280 cam (advertised duration) from one manufacturer could actually have less at-.050 duration than a 278 cam from another, due to the different points at which the companies measure advertised duration.

Lift: The cam's basic function is to open the valves. Lift refers to how far the valve is opened (or lifted) off its seat. A street performance cam will usually have between .450 - and .550-inch lift. More lift can increase power, and increased lift without changing duration increases power without affecting the point of peak power on the rpm band. The rocker arms have a direct effect on lift because they don't have a 1:1 lever ratio. A cam that has .318 inch of lobe lift (that's how far it lifts the lifter) will open the valve .477 inch with 1.5:1 rocker arms (.318 x 1.5 = .477) and .508 inch with 1.6:1 rockers. Generally, a stock engine will tolerate .500-inch lift before the valves hit the pistons or the valve springs hit coil bind, but any time lift is increased, these clearances should be checked.

Lobe Separation Angle: This is the relationship between the centerlines of the intake and exhaust lobes. A 110-degree lobe separation angle means that the peak opening points of the intake and exhaust lobes are 110 degrees apart. This is ground into the cam and can't be changed without changing cams. Lobe separation angle is another way of expressing overlap, which is the term formerly used by cam manufacturers. Overlap is the amount of time that both valves are open in the same cylinder When both valves are open at the same time, cylinder pressure drops. A cam with 106 degrees of lobe separation angle will have more overlap and a rougher idle than one with 112 degrees, but it'll usually make more midrange power.

Overlap: Overlap (lots of duration and tight lobe-separation angles) decreases cylinder pressure, especially at low rpm, which allows an engine to run a higher compression ratio and still work on pump gas. High cylinder pressure, which is caused partly by a high compression ratio, is what makes an engine detonate on pump gas. Decreasing the cylinder pressure by adding duration is just like taking compression out of the engine, but mostly only at low rpm. A compression ratio of 11.5:1 running on pump gas is not unheard of when the cam has enough overlap and duration to bleed off the low-speed cylinder pressure.

Centerline: is the lobe position at maximum lift relative to the crankshaft position in degrees.

Horsepower is a combination of additional duration and additional lift within limits.

Using a cam with more lift and more duration affects other things, like piston to valve clearance.

Lobe center impacts torque curve and horsepower peak because of where you start and end the cycle, much the same as duration does. The earlier you open the valve, the earlier you close it. A tighter lobe has more overlap. A tighter centerline starts torque curve sooner, and doesn't give a wide powerband. A wider lobe doesn't start the torque curve sooner, but it continues to make torque longer and has a broader powerband.

Rocker arms affect cam lift at the valve.

Cam Tuning
* Tightening the valve lash gives a bigger cam (more duration and overlap), which affects cranking compression and lowers bottom end torque. If the car goes quicker, you'll have to use common sense; is the track so slick the suspension can't hold it? Is the chassis working, did the 60 foot times remain the same? If so the suspension is okay
- but it picked up power on the top end, so you should move the power range of the cam by retarding it from the baseline, in 3 - 4 degree increments and then fine tune it a degree at a time.

* If the car likes looser valve lash, then advance cam to put more bottom end into the car. Say the car leaves the line harder and picks up at the 60 foot but the speed falls off. You need a bigger cam to help retain the speed. When you tighten the valves you let more air in and you'll need more fuel. Also, go back to the header to find out where the cam runs best, you may want to add some primary or change the collector length.


Last updated: 10/20/2011
Author: MadMike Maciolek


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