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Reader Tech Questions - Ask Anything

Mustang Handling
Pastor Mark Jasa; Los Angeles, CA: Is there a bolt-on suspension for a ‘69 Mustang that will give me Ferrari-like cornering, like one g or more? Also, why are lateral acceleration stats different from track-performance values? For instance, Road & Track will state that a given Ferrari had a cornering ability of say 0.94, but at a given moment on an actual track they might generate 1.2 g according to the in-car test equipment. It sounds like a large discrepancy. Also, what suspension do you recommend I buy for my ‘69 Mustang for track-day use?

Jeff Smith: When you get a really good tech question from a pastor, you have to answer it, right? So here goes, Pastor Mark. Let's dive into the lateral acceleration question first. I think your initial question has more to do with the huge difference between instantaneous g's and average g's. The numbers you mention from the track appear to be instantaneous g's compared with average g's generated during the on-track test. Instantaneous numbers are generated with a g-meter generally near the entry to a corner; these numbers are impressive, but average g's mean much more. For example, we could pull a 1.5 g on a banked course, but that really doesn't mean as much as it might if we did it on a flat surface. The typical lateral acceleration test used to generate an average number is obtained by driving the car on a 200-foot circle and measuring the elapsed time for each lap. The formula is:

Lateral acceleration = 1.227 x [radius / [time x time]

If our car produced an 11-second lap on a 200-foot circle, it would produce this result:

Lateral acceleration (g) = 1.227 x [100 / [11 x 11]
Lateral acceleration (g) = 1.01 g

This number is far more useful in helping to determine how well the car grips the road. However, with the driver located on the left side of the car, driving counterclockwise will almost always create a higher lateral g number than driving clockwise. That's why it's best to drive in both directions and average the numbers. But keep in mind that this test does not tell the whole story of handling. Since the suspension is constantly loaded, a skidpad test only evaluates it at the maximum loaded point. A better test is a slalom, where the car is almost constantly in transition. The time required to run the slalom is also an average and is dependent almost as much on the car's components as it is on driver skill.

To maximize handling, the idea is to be able to plant the tires to generate maximum cornering force. For example, with a car entering the corner, generally the movement of the front suspension is regulated first by the shock absorbers followed by the effect of both the front springs and the front antiroll bar. The springs and front bar determine the total suspension travel, which affects how much the camber changes (either positive or negative) with suspension movement. The springs allow the suspension to deflect, while the shocks determine how quickly or slowly that movement occurs. Changing the front (and rear) suspension to come up with an ideal combination is what determines "tuning" the suspension.

The quickest and most important way you can improve the handling of your car is to improve the traction between the car and the pavement with tires. Upgrading to a 16- 17-, or 18-inch tire and wheel package from a factory 15-inch wheel will do more to improve the handling of your car than any other single change. But traction will only help to the extent that the tires are limited by the suspension. Chassis upgrades will allow the front and rear suspensions to plant the tires properly during cornering. As is the case with most '60s and early '70s cars, under load, the front suspension tends to produce what is called a positive camber gain. This is what causes the car to understeer, or plow, in an aggressive corner. Imagine your Mustang in a hard lefthand turn. Normal weight transfer pushes more weight to the front-right corner, quickly compressing the soft coil spring and shock. This allows the suspension to compress. As this happens, the camber angle of the right-front tire tends to gain positive camber, which is the outward tilt of the top of the tire. This angle is the exact opposite of what is considered ideal for best handling. What is needed is a change in geometry with a modified upper control arm that will create a negative camber gain when the suspension is compressed. This is what occurs when you use components like Global West's tubular upper control arm for the Mustang. In fact, stock early Mustang suspensions were so poor that these cars were the first candidates for the Global West negative roll design back in the mid-'80s. This is similar but actually better than the old Shelby modification, which relocated the upper control arm mounting points. The Global West arms also relocate the mounting position of the upper arms but produce a much more aggressive curve. When combined with matched front and rear springs, adjustable shocks, a front sway bar, and better tires and wheels, the result is nothing less than amazing. While you may not be able to whip up on Ferraris, you could certainly dramatically improve the Mustang's current handling prowess.

More Info
Global West Suspension Components; San Bernardino, CA; 909/890-0759;

Holley vs. Edelbrock
Tom Herman; via It seems a Holley carb is worth 10 to 20 hp over a similar sized Edelbrock. My question is why?

Jeff Smith: I'm not sure what your question bases its assumption on, but there are a few details about both carbs worth considering. When it comes to the smaller four-barrel carburetors, such as the 600-cfm fuel mixers, our experience indicates there is very little difference in terms of power potential. The Edelbrock Performer carburetors are based on the older Carter AVS (air valve secondary) series of carbs. These carbs use a mechanical-secondary actuation and then control secondary airflow with a spring-loaded secondary air valve door that opens as primary airflow velocity increases, feeding air and fuel to the engine as needed. These carbs come in 500-, 600-, and 750-cfm sizes. The Edelbrock carbs seem to enjoy a reputation for running well right out of the box. For performance applications under 450 hp, the 750-cfm Performer or EPS 800-cfm carbs would be a good choice. Above 500 hp, these larger-cfm carbs may be limited based on maximum fuel flow because of a single fuel inlet and needle and seat compared with a dual-inlet Holley of the same cfm rating.

Let's assume for a moment that we have a 400hp single-four-barrel small-block Ford and we've decided to use a 600-cfm carburetor. Let's say we've chosen to compare a Holley 0-1850 ($253.95 Summit Racing) vacuum-secondary carb with an Edelbrock PN 1405 ($273.95 Summit Racing). The prices are very similar so that's not really an issue. From a power standpoint, the difficulty in comparing these carburetors is that they are generic performance carburetors. As such, they will probably be very close in terms of horsepower, but to get maximum benefit we would need to tune them for the engine in question. The best way to do that would be with a wide-band air/fuel (A/F) ratio meter to ensure the ratio is somewhere around 12.5:1 to 12.8:1 at wide-open throttle (WOT) and a leaner 13.5:1 to 14.7:1 at part throttle for good throttle response and driveability. More than likely, these carbs will be close but may require some tuning with jetting, power valves, or idle-mixture adjustments to achieve these numbers. If we were to put both carbs on the engine on the dyno, our opinion is that you would be hard-pressed to see more than a 5hp difference between the two. Frankly, you would need a very repeatable bracket car to see even that small a difference, and even then, the difference would be measured in hundredths of a second.

Both carbs have tuning advantages and disadvantages. There's no simple way to change the secondary opening rate for the Edelbrock, but on the Holley you can swap secondary diaphragm springs (the Thunder Series Edelbrock carbs are more expensive but do offer secondary adjustment). Primary metering adjustment for the Edelbrock is really easy. It uses a combination of metering rods and jets, and you can access the primary metering rods from the outside of the carb with a simple Torx screwdriver. The Holley requires you to drain and remove the fuel bowl to change jets. The same is true for secondary metering adjustments on the Edelbrock because the top needs to be removed to access the secondary jets. The latest version of the 0-1850C Holley has also eliminated the external float adjustment, which means both carbs require disassembly to adjust the float. This might be a long answer to a very short question, but in my opinion there would be a very small, if any, performance advantage of one carb over the other. As the saying goes, "You pays your money, and you takes your pick."

Flow Pipes
Kyle Buesing; via I have seen several cylinder head flow bench tests in books and magazines, including Car Craft, in which there is a flow reading on the exhaust, with and without a short section of pipe attached, and there are higher flow numbers with the pipe attached. Since an assembled, running engine is not used with either setup, what flow number is relevant and which one is useless gibberish? The two different numbers could mean the difference between needing a single-pattern or dual-pattern cam. Tricks on a flow bench to change the numbers mean nothing if it does not reflect something that would actually be used on a running engine, such as attaching an intake manifold to the cylinder head on the flow bench. This has made me curious for quite a while, and any light you could shed on the subject would be greatly appreciated.

Jeff Smith: I've noticed the quality of questions over the past couple of years has been steadily improving in that they are more in-depth and reveal our readers are putting some genuine thought into them; great job, guys! This is especially true with this question, Kyle. Not long after we began testing cylinder heads on the flow bench, I learned that adding a short length of pipe to the exhaust port tended to improve the flow numbers by roughly 5 percent (slightly higher at higher valve lift numbers and less for very low lift numbers, such as 0.100 inch, where the volume and flow velocities were very low). This was not intended as a trick as such but rather an attempt to replicate the real-world situation in which the exhaust port is mated to a header tube. The reason the pipe is short is because the flow effect of the pipe occurs mainly in the first 6 or 8 inches, so the pipe can be short and still see the same net results as if it were 32 to 36 inches in length. If your question has to do with which number is more accurate, I would say the flow numbers with the pipe.

For this same reason, if you were really interested in accurate flow numbers on the inlet side, I would flow the head with the intake manifold you were planning on using so you would have a more accurate idea of the difference in flow with and without the manifold. Keep in mind that any additional ducting on the inlet side will be a restriction, but a better intake port is still going to flow more than a poor one, regardless of the manifold choice.

Your question about camshaft choice based on the exhaust side is also well taken. The standard seems to be if the exhaust port is capable of 70 to 75 percent (or more) of intake flow, you should consider choosing a single-pattern cam (the same exhaust duration as the intake) or a cam with only a small amount of additional exhaust duration—perhaps along the lines of 4 to 6 degrees. Conversely, a cylinder head with poor exhaust flow to the intake (like the LS-series rectangle-port L92 heads) can really benefit from a dual-pattern camshaft with 6 or more additional degrees of exhaust duration.

Your question also reminded me of a flow bench test Jim McFarland had me do probably 25 years ago when he was the engineering vice president at Edelbrock and I was first learning how to run a flow bench. He made up four exhaust stubs that were about 12 inches in length using 1 5⁄8-tubing and welded to exhaust flanges to fit a small-block Chevy head. The first pipe was straight, the second had a 30-degree bend, the third a 60-degree bend, and the last had a very tight 90-degree radius bend just downstream of the mounting flange. He had me flow-test each pipe across the entire valve-lift curve and then compare the flow numbers. Not surprisingly, the straight and the 30-degree bend pipes flowed the best, the 60-degree pipe offered less flow, and the 90-degree pipe flowed the least. Then he had me measure the lengths of the inside and outside turns on the pipe. This represented roughly 4 inches of difference, with the inside radius obviously being shorter. We marked the outside radius point where the lengths were the same and trimmed the pipe with a belt sander until the pipe exit was angle-cut to equalize the short and long side radii. Then he had me flow-test the pipe again. Amazingly, the flow increased to the point where this modified 90- degree-bend pipe flowed almost as well as the one with the minor 30-degree bend.

The point of this exercise, as I learned from McFarland, is that you can fool air into acting like the pipe is not bent if the effective lengths of the pipe on the short and long side radius are as similar as possible. In a practical application, the idea is to minimize how tight the radius bends are with header or inlet pipes, or, if that's not possible, to attempt to equalize the lengths of the walls of the port or flow pipe. In the case of an exhaust header, this might not be possible, but at least you should attempt to make the headers exit the exhaust port as straight and as long as possible before the first bend. That's why the dyno headers at Westech are shaped the way they are. I call them Sprint Car headers because that's what they look like. This is not an accident and the difference in exhaust flow between these Sprint Car headers and a tight set of chassis headers is measurable. Another excellent example of this is the tunnel-ram intake manifold. If you look at the original design of the very early tunnel-rams, they were all flat-bottom boxes with curved runners leading to the port inlets. Then somebody realized that if they created a V-shaped floor, the ports could exit the manifold with a straight shot directly into the ports, and power improved. Development ideas like this are why horsepower numbers keep improving by reducing restrictions to airflow.

Four-Valve Tuning
Logan Farnsworth; Kaysville, UT: I am a member of the University of Utah Formula SAE team, a collegiate engineering competition in which the teams build a small, open-wheel race car using an engine no bigger than 600 cc. The motor we are using is a 600cc, dual-overhead-camshaft engine from a Honda CBR600 F3. Because of the rules, we are required to use a 20mm restrictor following the throttle, which effectively reduces the efficiency of the engine at higher rpm, which is where the engine makes most of its power. I was wondering if it would be feasible to adjust the cam timing on just the intake camshaft to reduce the overlap, as I know having a smaller overlap moves the torque curve down the rpm range. The F3 engine makes peak horsepower at about 12,000 rpm, and we are hoping to have peak horsepower occur at about 10,000 rpm because that is about where the restrictor should limit the air intake if we did our math correctly. I have already done some research, and I know there is an adjustable cam sprocket available for these motors. The stock cam specs are: intake open 15 BTDC and close 35 ABDC; exhaust open 38 BBDC close 7 ATDC. I also know that the next motor in the same family, the CBR600 F4, has the cam specs of intake open 22 BTDC close 43 ABDC; exhaust: open 38 BBDC close 7 ATDC. My thought was to adjust the intake cam on the F3 motor to close at the same time as the F4 so the specs become intake open 7 BTDC close 43 ABDC. Would this have a negative effect on the performance of the motor in the lower rpm range or would it just effectively move the peak power down?

Any insight would be greatly appreciated, as all my previous engine experience is with small-block Chevys and a few Pontiac motors, so dual-overhead cams are something very new to me. Also, for more info on the team or competition, here is the team website:

Jeff Smith: You are correct that the intake closing point is the most important of the four valve events. The intake duration, and therefore the intake closing point, determines where peak torque will occur. The later the intake closing, the higher rpm at which peak torque is achieved. Peak torque then establishes the beginning point of the power curve, which is defined as the rpm band between peak torque and peak horsepower. I researched this engine and found the stock power rated at 105 hp at 12,000 rpm and 48.7 lb-ft of torque at 10,500 rpm with 12.0:1 compression. This makes the stock powerband 1,500 rpm wide. With a restrictor plate, you said you calculated that peak power will occur at 10,000 rpm. That means if you maintain the same powerband, peak torque should be somewhere around 8,500 rpm. So this is where it would be preferable to have the intake closing point establish peak torque. If the stock cam closes the intake at 35 degrees after TDC, we need to close the intake sooner to establish a lower torque peak by at least 8 degrees and maybe even earlier.

Because the engine is inlet restricted, it seems to me it would be beneficial to build more torque at a lower rpm to help the car come off the corner (assuming tire spin is not a problem). Overlap is the period during which exhaust closing and intake opening points cross over. We have to be careful here because we have lots of valve area, so too much overlap can kill cylinder pressure. Is there an octane and consequently a compression ratio limit? One way to build cylinder pressure in the lower rpm range is to close the intake valve sooner. If you can't add more compression, you can alter the point at which maximum effective pressure occurs with cam timing. I've listed your intake lobe specs again (remember, you have to add 180 degrees to intake opening and closing to get total duration) so we can evaluate what' s going on here:

F3 intake open 15 BTDC; close 35 ABDC = 230 degrees

F4 intake open 22 BTDC; close 43 ABDC = 245 degrees

This intake lobe opens 7 degrees sooner and closes 8 degrees later.

Your proposed F3 open 7 BTDC; close 43 ABDC = 230 degrees

This intake lobe closes later, which improves high-rpm power, which is not your goal.

My proposed F3 intake: open 15 BTDC; close 28 ABDC = 223 degrees

This closes the intake valve earlier, moving the torque peak lower.

The above change shortens the total intake duration and closes the intake valve sooner. Both are in an attempt to lower the peak engine rpm power point to 10,000 rpm. You may also have to experiment with overlap to help the midrange torque. That may require widening the lobe-separation angle slightly, but the only way to know for sure is to test the engine, since there are several other variables that also affect the torque curve. Also, the width of the powerband is another essential consideration because if you widen the powerband, the car will be much easier to drive and will require fewer gear changes. Every shift is an interruption of the application of power. A peaky, narrow powerband requires more gear changes. That's why I think an approach that widens the powerband without sacrificing average power will be the most successful. More area under the power curve will make the car quicker off the corners and easier to drive, reduce the number of shifts, and lower the lap times. Before you go this far, it might be worthwhile to data-log a lap and then establish a hysteresis curve that will reveal the rpm band where the engine spends the majority of its time. Obviously, this is affected by track length, gear ratio, tire size, and drive technique. But all of this will point you in a direction. The teams that concentrate on peak power and build a high- powered but peaky engine will suffer—especially in short, tight autocross courses that dominate the Formula SAE competition.

Third-Gen Firebird LS Swap
Greg Deford; via I was wondering if you could give me some info on the brand of motor mounts Josh Kunkel used on his Camaro? Also, when I was looking for an LS engine, some are listed as manual or automatic, is there a difference or is it that they are just equipped with a flexplate or flywheel? Tom Fogelsong mounted a T56 to a 5.3, I am assuming it was from an automatic since it came out of a Suburban. Would there be an issue with the pilot bearing? I'm planning on putting an LS 6.0 into an '87 Firebird.

Jeff Smith: We've kept in touch with Josh and his father, Russ Kunkle, since they always bring a nice car to the Car Craft Summer Nationals in St. Paul every July. To answer your question on engine difference, there is absolutely no mechanical difference between a manual transmission– and automatic transmission– equipped engine except that the manual comes with the pilot bushing. If you are using a T56, the stock LS pilot bushing is what you want. For your motor mount question, I contacted Russ and this is what he told me:

"The mounts we used on the Camaro were from Spohn and we bought the motor and transmission mounts as a set. The motor mount is actually a new frame mount and uses the fourth-gen motor mount. They make tranny mounts for either the 4L60E or the T56. We used the stock fourth-gen F-body pan; Spohn has it figured out. It's tight, like 1⁄2 inch between the pan sump and the K-member, but it fits. Josh kept the 4L60E with the mount bolted right up to it, and we put a Yank 3,600-rpm-stall converter in front of it. So far, the only folks I know of that make long-tube headers for this particular swap is Stainless Works—Spohn sells those also with a Y-pipe, but it's pretty spendy. We used the stock manifolds and made our own Y-pipe from 21⁄2-inch mandrel bends and merged them into a single 3-inch. I think a guy could use the shorty headers, but he would still have to fab the Y-pipe. The rest is a Flowmaster American Thunder system. The pilot bearing shouldn't be a problem. In our Nova, we put a TKO-600 behind the 6.0L we bought as a kit, removed the flexplate, and popped the bearing in the end of the crank. The clutch, pressure plate, and flywheel are LS7 stuff that bolted right on."

Spohn makes a very cool front K-member (PN 703-LSX, $515.00 Spohn) that uses the stock Camaro steering and is lighter and stronger than the factory piece. The Spohn motor mount kit (PN 971, $85.00 Spohn) adapts an LS engine to either the factory subframe or the new Spohn K-member. Spohn also makes a trans crossmember to adapt the T56 six-speed to these earlier F-bodies (PN LSXT56XM, $105.00 Spohn).

As Russ mentioned in his reply, the conversion to a manual would only require the flywheel, clutch, pressure plate, and factory hydraulic release bearing. You will also need a clutch pedal and actuator rod from a donor car. You have your choice of clutch companies, and there are a bunch to choose from, such as ACT, Centerforce, Hays, McLeod, Ram, Sachs, and a ton more. All these companies will sell a performance replacement of the stock clutch if you choose to go with something better than stock. We are most familiar with the Centerforce line, which includes the Dual Friction system that uses an organic lining on one side of the clutch with a puck-style friction material on the other side. Combined with the Centerforce pressure plate, this system is more than capable of handling the power. A stock pilot bushing should be added, and Centerforce suggests adding a new hydraulic clutch master cylinder as well as a new hydraulic throw­out bearing as part of the swap. These last two components are factory replacement pieces we found for a decent price at Rock Auto. We compared the master cylinder piston diameters (Dorman PN CM39838, $39.78 from Rock Auto) and they are the same as the 2002 master, so that's not an issue. The hydraulic release bearing is also available (Dorman PN CS360058, $68.89 Rock Auto). Be aware there may be compatibility issues between the later-model hydraulic throwout bearing and the early master cylinder with hose connectors.

Also be aware that these late-model, metric-style clutch assemblies use an alignment pin arrangement to align the pressure plate to the flywheel as opposed to shouldered bolts used in older clutch assemblies. If you are reusing a factory flywheel, always use new pins and factory flywheel bolts. Also, since the factory flywheel, clutch, and pressure plate are balanced as an assembly, if you reuse the factory flywheel, the assembly should be checked to ensure it is in fact neutral-balanced with the new clutch assembly.

More Info
Centerforce; Prescott, AZ; 928/771-8422;
Rock Auto; Madison, WI; 866/762-5288;
Spohn Performance; Myersville, PA; 888/365-6064;

Ask Anything—We've Got Solutions!
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