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Old 10-31-2012, 09:28 AM   #10
Devs93
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Do you need one and which one? Well, in most cases, no. But there are times where a limited-slip or mechanical locking differential is extremely useful, especially in a truck. Winter traction is a good example, particularly with 2WD trucks. While the limited-slip differential is an excellent way to control traction in street rods, light duty/street performance pickups and all types of tarmac running racecars, it isn't the best solution for the serious off-road vehicle. Why? Because it's input torque, not wheel slip that determines when power is transferred to the other wheel. So for winter roads, the boat ramp, and the back-woods, two-track, gotta-get-over-the-mountain types, choose the mechanical locking differential. IMO, either of these two is better than the open differential design.


Will an MSD or equivalent ignition box improve the power and performance of my truck?
IMO, a MSD ignition box will not outperform a well-tuned and maintained stock HEI setup. I think they have their applications with superchargers and nitrous systems, but not on a mildly modded 350 engine. And it’s debatable whether or not it improves fuel economy with more complete combustion. Does it start faster or easier in winter? I don’t believe so – that’s a myth. Quicker throttle response? Again – a well-tuned HEI distributor works just as well – no difference in throttle response. So why use one? I can think of a couple reasons: 1) RPM limiter capability, 2) some have the capability to adjust your timing/retard without having to play with the distributor, 3) may make up for a poor tuned HEI system, bad/faulty wires, etc. – not a great reason, but it will make your ignition user friendly and resistant to the common faults of poor maintenance, 4) more consistent ignition and higher speak energy when above 6000 RPM. IMO save your money for performance upgrades that are proven to make more power. The stock ignition can easily support 400-450 hp and operate flawlessly to 6000 RPM.


What about power or underdrive pulleys? Do they make more power and how do they work?
I have March Power Pulleys – IMO you won't notice any difference in power. They are designed to slow the fan speed at higher engine RPMs, so that's where your benefit will be. Unfortunately, TBI's only rev to about 4500-4700 RPM, so I don't feel they are worth it, particularly if you have a clutch fan setup. With the clutch fan engaged, they probably improve power (see next question), but I wouldn't buy them again and get electric fans instead. They can also reduce the amperage of your alternator at idle despite the smaller alternator pulley. This is particularly important at night with your lights/fog lights on, stereo pumping, A/C or heater on full blast, and you’re at the stop light with your brakes on. Oh yeah, you know what I’m talking about.


What about electric fans? Do they make more power and how do they work?
I wouldn’t expect performance miracles from an electric fan. They do improve power, but not in the way that you’d think. I’d called them more of a power retainer than a power adder. Here’s how they work. Installing an electric fan on your engine removes the parasitic action of the motor turning the fan to facilitate air flow across the radiator. Normally, a clutch fan helps to reduce to the fan speed when the engine does not need maximum cooling from your engine-driven fan. Removing this fan improves power, but like a 2-3% hp improvement versus a clutch fan. OK so how can these electric fan manufacturers claim a 20+hp improvement? Well it does happen, but on a HOT engine with the clutch ENGAGED. Yup, that’s right – they are also including the hp that you would normally lose due to the engaged fan. So e-fans really do work.



What about suspension upgrades? How can I make my truck handle better?
The easiest way is to replace your rubber suspension mount bushings with polyurethane bushings. At a minimum, you should replace your front sway bar mounts and sway bar end links. Make sure you use lots of grease before installing them or they will squeak. Energy suspension also sells sway bar mounts with greasable zerks. Next upgrade would be to add a rear sway bar available from companies like Hotchkis, Belltech, or Hellwig. I installed the Hellwig rear sway bar on my truck. It works well and improved the cornering capability considerably. I would recommend getting the axle mounts tack welded in place (any muffler shop will do it), because they will not hold with the U-clamp design. Another option is using sway control bars from Summit or other auto parts stores (http://www.autopn.com/autoparts/swaycontrol/index.html). They are cheaper than adding a rear sway bar. Of course, you can also install a drop kit, particularly one with drop springs and drop shocks. Lower center of gravity and stiffer springs and shocks will definitely improve your handling, but your ride quality may suffer. Too harsh of ride? Use spindles or drop LCAs instead and you can retain your stock front springs. There are also rear shock extenders that will allow you to use your stock length shocks. Another option is bagging your truck for better handling and ride quality.


OK, I’ve got ALL the right performance parts, heads, cam, tranny upgrades. Is there something I’m missing?
Could be. I’d say the most commonly overlooked areas that have a huge impact on performance is fuel supply and computer tuning. “Yeah, but I’ve got a performance chip, an AFPR, and larger injectors so I’m covered.” You may think so, but in most cases your truck is not meeting its potential. How many of you guys datalog to make sure your performance components are working at their maximum potential? How many of you guys install a fuel pressure gauge when you install your AFPR? You’re not alone – in fact, a majority of people don’t and yet it is the easiest way to both improve your engine’s power and fuel economy!! What’s that, you say, better fuel economy? Oh yeah, baby!!

Most people do not understand how much fuel they really need. With ANY performance upgrade, you may need to make changes in the amount of fuel delivered and WHEN it is delivered for your truck to run tip-top. Many will buy an AFPR and play with the pressure settings, but they fail to purchase a fuel gauge!! Please read my tutorial of properly matching fuel to your performance upgrades: http://www.fullsizechevy.com/forums/...d.php?t=200226. In order to refine the fuel deliver for the best power and fuel economy, you have to be able to adjust the computer settings. This is why doing your own chip burning is so important. Please refer to the chip burning section in this thread for ways to either do it yourself or empower yourself with “datalogging” so that a chip/tune specialist can properly make a chip/tune for your engine.

Another method for fine tuning your engine is to adjust your fuel mixture via the O2 sensor and a digital volt meter. Keep in mind that the ECM controls fuel tables as well, so if you’ve changed heads/cam or injectors, but haven’t changed your chip to recalibrate your fuel tables– this is not going to work. However, if you’ve done mild mods or re-calibrated your ECM for your engine mods, this is a good way to fine tune the air:fuel mixture for optimal performance. The article is here: http://www.thirdgen.org/o2tuning.

If you’ve spent major dollars on performance upgrades, you owe it to yourself to properly tune the combination that you have. Guaranteed this is the single best way to make power. Assuming you have the right parts is like throwing money (and hp) away and defeats the purpose of why you are upgrading your engine in the first place.
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