FSC Forum - View Single Post - Common performance-minded FAQs about 88-98 OBS trucks

Red94Chev · 05-30-2006, 09:13 PM

What is an adjustable fuel pressure regulator, who makes them, and are they worth it?
A fuel pressure regulator does just as it sounds. It limits the amount of fuel that enters into your injector pod. There is no set value that came from the factory, but most are setup between 11-13 psi. Adding performance mods to your engine may require that you adjust the fuel pressure a bit to allow more fuel in. You can make the existing TBI fuel pressure regulator adjustable at the following link: http://www.thirdgen.org/tbi-afpr. Jet Performance also makes a replacement unit. If you want one that varies with RPM you will need to look into the GM vacuum adjustable regulator. This regulator changes based on a vacuum source and will rise as RPM does. It is still adjustable so that you can tune down the pressure at idle to avoid running rich, yet have enough pressure at wide open throttle to avoid going lean. To hook up a fuel gauge, you'll need one of these: http://marine-performance-parts.com/...843505774.aspx. Or you can hook up an external AFPR like this: http://www.fullsizechevy.com/forums/...-tbi-pics.html.

What are the major troublesome areas to overcome in TBI engines to make awesome power? In Vortec engines?
TBI engines (1988-1995): Quite a few, unfortunately.

Airflow: The TB is relatively small at 490cfm at 1.5inHg. The ultimate TBI mods can be performed to raise this to 520 cfm. If you’re changing heads, cam, displacement, or adding a supercharger, this won’t cut it and you need more air. Larger TB that are direct replacements for your stock TB are made by CFM-Tech and Turbo City (590-620 CFM), or XtremeFI (750 cfm). The 454 TB can also be used (rated at 670 cfm at 1.5inHg), but there are some incompatibility issues with the IAC (Idle air control) and TPS (throttle position) sensors. These issues can be overcome by splicing the 454-style TPS and IAC sensor wires to the wires from the small block TPS/IAC. Keep in mind that all small block TBs aren’t the same. There are slight changes in design in the production years from 1988-1995. Ask for a TB from your model year or send them your original to be modified. Holley also makes a replacement TB (750 cfm) with larger 68#/hr injectors. I think it gets a bad wrap because it doesn’t improve the performance (or sometimes worsens the performance on TBI engines). If you're using the Holley TB, you need a custom chip to make it work properly for your application (i.e. change the fuel injector constant, VE tuning, etc.). The computer thinks it still has the smaller injectors with less air going into the engine. The VE tables need to be recalibrated via the chip to make this unit a performer. Something Holley doesn’t tell you.

Heads: The L05 5.7L head is a swirl port design, meaning that there are these ridges in the intake runner and under the valves to promote better fuel atomization and improve low RPM torque. The truth is it works – at low RPM (3500 and under). Problem is most people are looking for gains in top end hp and these heads are at a mechanical disadvantage to provide adequate airflow for high RPM power. The solution: either port them or replace them. Popular replacement options include using Vortec heads or aftermarket cylinder heads. Because of their centerbolt head design, they are few options for aftermarket heads and some are more expensive than others. The poorest performer IMO is the Edelbrock centerbolt head, but it seems to be the most well-known head for TBI engines. There are also the Torquer S/R from World Castings, AFR 180 or AFR 195, Canfield heads, Pro Topline heads from Racing Head Services (RHS), Patriot heads, and Trick Flow heads. There are three factors that you need to decide which head is right for you: head airflow characteristics (the higher the better), intake runner size (max should be 195cc for a 350 otherwise will start to dramatically lose low speed torque characteristics), and combustion chamber (stock 350 is 64cc for roughly a 9.3:1 compression ratio). The new Eliminator AFR 195 head is arguably the best performing head with huge airflow numbers to generate tons of hp and now available in 64cc combustion chamber (both CNC and non-CNC versions). I chose the Trick Flow 195 heads for my engine: reasonably priced, good airflow, 195cc intake runner, and a 62cc combustion chamber. So make sure you remember these important factors when choosing heads for your engine.

Camshaft: one word - wimpy. Less than 0.400” lift and small (172/180 at 0.050"), it is just a horrible design for making good power. Great for towing and low speed torque, but newer camshaft designs today can improve your low speed torque and provide major hp increases when combined with other performance upgrades. Please read later in the thread on how to choose the right camshaft for your truck. Depending on your engine combination and whether you’ve changed heads or not, there are several performance options that are available.

Exhaust: There were many different styles of exhaust from 1988-1995. All were a 2-into-1 design using a catalytic converter. Older designs used AIR injection with a smog pump and a less efficient pancake-style (pellet) catalytic converter. It is unclear when monolithic (high flow) converters were introduced. Some say in 1996 with the introduction of the Vortec engine. I just took the stock catalytic converter off my 1994 350 truck and it was a monolithic design and replaced it with a high flow unit from MagnaFlow. Don’t know if the stock one is considered high flow or not, but it was pretty plugged so any comparisons would be meaningless. What do you want for exhaust? Replace everything!! Now with what? You have several options again. The best exhaust system IMO is long tube headers with 2.5” true dual exhaust (2 mufflers, 2 catalytic converters, etc.). Another option is shorty style headers (direct-fit), stock or aftermarket y-pipe, 3” intermediate pipe. If you choose not to run a catalytic converter, this combo can be used to make good hp if you’ve changed heads/cam on your engine. On a TBI engine with stock heads and cam, running a 3” catalytic converter WILL NOT greatly limit the hp potential of your motor. A 3” high flow cat can roughly flow 360 cfm of air. I know it doesn’t sound like a lot, but most people overestimate the required air for their engine. A stock 350 TBI engine with performance exhaust only needs 355-444 cfm of air with a 4500 RPM redline and 65% VE. A section on the effect of larger TB is listed earlier in this thread.

Vortec engines (1996-1998):

Fuel injectors/Intake manifold: The fuel injectors on Vortec engines cannot be replaced with standard aftermarket injectors (22-23#/hr). As far as I know, there is no direct-fit AFPR that is available for their engines. Perhaps the stock one can be modified or a universal AFPR can be used, but it will require some creativity and ingenuity. In fact, Vortec Stroker has a 383 using the stock Vortec induction making 400 hp, so it is possible to make big power using this setup: http://www.fullsizechevy.com/forums/...ad.php?t=83738. Airflow is the biggest bottleneck in the Vortec system since the fuel injector poppets are in the intake tract. A direct bolt-on marine version of the Vortec induction system is available that uses larger 24#/hr fuel injectors that are mounted outside of the intact tract and allows better performance up to 5800 RPM. This is one way to get around this potential bottleneck. Another way is to replace the whole induction unit with another MPFI system, like the Holley Stealth Ram or GM’s RamJet.

Heads: The Vortec heads are great heads, but there are not without their problems. The valve springs only support up to 0.470” lift camshafts. Since the Vortec engines use hydraulic roller cams, it would be silly not to upgrade the springs in order to take advantage of today’s high lift roller camshaft designs with lift in excess of 0.500”. Chevy High Performance has an article on upgrading your springs here: http://www.chevyhiperformance.com/te...ort/index.html. In this example, the valve seats are machined and larger springs are installed. Springs are also available that will increase your valve lift without machining the valve seats. Comp Cams Beehive 26915 or the Beehive 26918 springs can be used as direct replacements without machining the heads and will allow up to 0.550” lift. Contact Comp Cams or Crane Cams and ask them directly for which springs they’d recommend if you are unsure. Here’s another article on everything you wanted to know on Vortec heads: http://www.chevyhiperformance.com/ho...458/index.html. The ideal aftermarket head for the Vortec engien IMO is the Edelbrock Etec head. A serious performer for the money.

Camshaft: better than a TBI engine and it’s a roller camshaft, so it’s pretty good, right? Nope. If you want to make big power increases, you have to change the camshaft. This bottleneck is intertwined with the previous two bottlenecks. With more fuel and heads that support high lift, a 400+ hp engine is entirely possible. Again, the combination of parts selection is the key here. Installing a camshaft in a stock Vortec engine is not going to perform miracles, but will improve performance. Please read later in the thread on how to choose the right camshaft for your truck.

I want to add a supercharger to my engine. How do I do that and what are my choices?
First off, supercharger kits are mainly designed and calibrated for the stock engine. It will tolerate mild performance upgrades such as headers and low-restriction exhaust systems, but if you want to start changing cylinder heads and camshafts, you’re going to need to find someone to custom tune your engine or do it yourself. Be prepared to troubleshoot A LOT when adding a supercharger to your engine. It is not as easy as it seems, although the power gains (and particularly the torque gains) are outstanding and well worth the efforts. Depending on your power output, you may need to upgrade the transmission as well, so keep this in mind before investing in a supercharger kit.

TBI engines:
There are three quality manufacturers that I know of: Whipple Industries, Weiand, and ATI ProCharger. Each has their selling points. The Weiand emissions-legal kit is the least expensive at under $3000, but hood space is definitely an issue since the TB sits on top of the unit. There is also a super-cheap $1500 non-emissions kit available that uses a carb setup. Here is an article from someone who has done this to their 350 engine: http://www.thirdgen.org/weiand142install. Definitely needs a cowl induction hood and you may need to modify it to make room for the air filter. A shorter open element filter with K&N Xtreme filter lid may work, but since I don’t have one I wouldn’t know. It uses a 144 roots-style supercharger that adds between 25-30% additional hp/torque. The potential for more boost is possible, but it is limited by the enormous heat that is generated by the roots-style blower. The Whipple supercharger is popular because of its efficiency and low-RPM performance, adding 40-45% more power. Full boost is achieved at low RPMs making this an excellent choice for trucks that need to tow. The ATI ProCharger is the only centrifugal supercharger available from a major company. It is intercooled and therefore provides 8-9 pounds of boost (2-3 more than the Whipple supercharger). Power is improved by 65%, but it is mainly in the upper RPMS. Don’t count on this supercharger to improve your towing capacity significantly around town. On the highway, sure, but you won’t have the torque that the Whipple unit provided down low.

Vortec engines:
In addition to Whipple and ATI mentioned above, there is also Vortec Engineering and Powerdyne, both of which are centrifugal supercharger designs. These superchargers will add up to 50% more power.

Will roller rockers or higher ratio rockers improve power?
Yes and maybe. Roller rockers will reduce frictional parasitic losses on the valvetrain components to free up a few ponies. Higher ratio rockers have their applications: useful on stock cams to improve lift and therefore flow more air, maximize the airflow potential of aftermarket heads and camshafts. They also have their drawbacks: Stock TBI heads have low flow potential and using higher ratio rockers with an aftermarket camshaft may not improve power over the aftermarket camshaft alone since the maximum airflow of the heads have been reached; Vortec heads only allow valve lift up to 0.470” and installing higher ratio rockers may surpass the valve lift depending if you’re running the stock cam or not. With the stock cam, 1.6 ratio rockers are dangerously close to that upper limit, but still under. So how do I decide? Guess it depends on your engine combination and what your future upgrade plans are. Keep in mind that higher ratio rockers will increase the advertised duration of your cam. Comp Cams now has a new XFI series of camshafts designed to use their beehive springs and 1.6 ratio rockers. There are both hydraulic and hydraulic roller versions of the XFI cam. The advantage is that you precisely know the advertised duration of the camshaft with its higher lift potential.

How do I choose the right camshaft for my engine?
Oh man, probably the most common question on this forum and the one with the most answers. You can get really technical answers or very simple rule-of-thumb answers. The reason there are so many different answers (and camshafts for that matter) is because it highly depends on your engine and transmission combination and how you plan on using your truck (towing, racing, daily driver, etc.) Transmission? What does that have to do with it? Well first of all, you can choose slightly more duration with a standard transmission because you can essentially adjust the stall of the engine when starting out from a stop. Automatic transmissions don’t have that luxury and usually stall at about 1100-1300 RPM. If you choose a high duration cam with a narrow LSA (lobe separation angle) for a lopey powerful engine, you’ll gain hp up top, but lose torque down low. More importantly, installing a large duration cam in TBI engines with their torque-producing, low RPM cylinder heads is a major mismatch. The heads will not be able to support the power above 4000 RPM where the cam will be making its most power. The results = a dog of an engine down low and on the high end.

Here are my recommendations for cam choices based on the engine combo you have (all of which need custom chips or performance tuning to work properly and maintain fuel economy. This is required for ANY camshaft upgrade.)

TBI 5.7L with stock heads, stock or 2000 RPM stall torque converter: Duration at 0.050” lift 206/216 with LSA 112. The Crane cam 113904 is my top choice, but as long at you stick to intake duration under 206 degrees, you’ll have a safe computer-friendly cam with gobs of power 4500 RPM and lower. Good for towing and performance applications and good all-round choice. Power level maxes out at 280-300hp.

TBI 5.7L with after market heads, stock converter: Highest lift possible is the key here to take full advantage of your performance heads. My choice would be Comp’s 260 XFI hydraulic camshaft, 216/223, 0.499”/0.492” lift with 1.6 ratio rockers or the Crane 113904 with 1.6 rockers (0.470”/0.499”). Expected power levels will be around 320-345 hp.

TBI 5.7L with after market heads, 2500 RPM stall converter, 3.42 or higher rear end: "XFI" 268 Hydraulic Flat Tappet Camshaft, 224/231, lift 0.520"/0.515" w/1.6 Rockers, or Comp’s Xtreme Energy Computer Controlled XE262H with 1.6 rockers (218/224 at 0.050” lift, 0.510”/0.517”). Dyno simulations of these combos produce 365+ hp at 5500 RPM. Yes, from a TBI. Tuning and proper fuel deliver is a must.

Vortec 5.7L engine without spring upgrade: Crane’s 109815, 204/214, 0.429”/0.452” lift.

Vortec 5.7L with spring upgrade: Comp cams Xtreme Energy Computer Controlled XR254HR (206/212, 0.480”/0.488”) or Comp cams Xtreme Energy Computer Controlled XR264HR (212/218, 0.488”/0.495” lift).

Vortec 5.7L with performance Vortec heads (i.e. Edelbrock 170 E-Tech heads with max valve lift of 0.575”) and fuel/induction system upgrades: Comp’s 260 or 268 XFI hydraulic roller series, 210/218 or 218/224 at 0.050” lift, 0.560”/0.555” or 0.570”/0.565” lift, LSA 113, 1.6 rockers. You could even go with 280 XFI cam with a 2500 stall torque converter. How does 400+ hp sound?

05-30-2006, 09:13 PM	#2
Red94Chev Kick Ass!! Status: Offline Join Date: Sep 2005 Member ID: 33983 Pics: My Gallery Location: Edmonton, AB Age: 33 Posts: 890	Re: Common performance-minded FAQs about 88-98 OBS trucks What is an adjustable fuel pressure regulator, who makes them, and are they worth it? A fuel pressure regulator does just as it sounds. It limits the amount of fuel that enters into your injector pod. There is no set value that came from the factory, but most are setup between 11-13 psi. Adding performance mods to your engine may require that you adjust the fuel pressure a bit to allow more fuel in. You can make the existing TBI fuel pressure regulator adjustable at the following link: http://www.thirdgen.org/tbi-afpr. Jet Performance also makes a replacement unit. If you want one that varies with RPM you will need to look into the GM vacuum adjustable regulator. This regulator changes based on a vacuum source and will rise as RPM does. It is still adjustable so that you can tune down the pressure at idle to avoid running rich, yet have enough pressure at wide open throttle to avoid going lean. To hook up a fuel gauge, you'll need one of these: http://marine-performance-parts.com/...843505774.aspx. Or you can hook up an external AFPR like this: http://www.fullsizechevy.com/forums/...-tbi-pics.html. What are the major troublesome areas to overcome in TBI engines to make awesome power? In Vortec engines? TBI engines (1988-1995): Quite a few, unfortunately. Airflow: The TB is relatively small at 490cfm at 1.5inHg. The ultimate TBI mods can be performed to raise this to 520 cfm. If you’re changing heads, cam, displacement, or adding a supercharger, this won’t cut it and you need more air. Larger TB that are direct replacements for your stock TB are made by CFM-Tech and Turbo City (590-620 CFM), or XtremeFI (750 cfm). The 454 TB can also be used (rated at 670 cfm at 1.5inHg), but there are some incompatibility issues with the IAC (Idle air control) and TPS (throttle position) sensors. These issues can be overcome by splicing the 454-style TPS and IAC sensor wires to the wires from the small block TPS/IAC. Keep in mind that all small block TBs aren’t the same. There are slight changes in design in the production years from 1988-1995. Ask for a TB from your model year or send them your original to be modified. Holley also makes a replacement TB (750 cfm) with larger 68#/hr injectors. I think it gets a bad wrap because it doesn’t improve the performance (or sometimes worsens the performance on TBI engines). If you're using the Holley TB, you need a custom chip to make it work properly for your application (i.e. change the fuel injector constant, VE tuning, etc.). The computer thinks it still has the smaller injectors with less air going into the engine. The VE tables need to be recalibrated via the chip to make this unit a performer. Something Holley doesn’t tell you. Heads: The L05 5.7L head is a swirl port design, meaning that there are these ridges in the intake runner and under the valves to promote better fuel atomization and improve low RPM torque. The truth is it works – at low RPM (3500 and under). Problem is most people are looking for gains in top end hp and these heads are at a mechanical disadvantage to provide adequate airflow for high RPM power. The solution: either port them or replace them. Popular replacement options include using Vortec heads or aftermarket cylinder heads. Because of their centerbolt head design, they are few options for aftermarket heads and some are more expensive than others. The poorest performer IMO is the Edelbrock centerbolt head, but it seems to be the most well-known head for TBI engines. There are also the Torquer S/R from World Castings, AFR 180 or AFR 195, Canfield heads, Pro Topline heads from Racing Head Services (RHS), Patriot heads, and Trick Flow heads. There are three factors that you need to decide which head is right for you: head airflow characteristics (the higher the better), intake runner size (max should be 195cc for a 350 otherwise will start to dramatically lose low speed torque characteristics), and combustion chamber (stock 350 is 64cc for roughly a 9.3:1 compression ratio). The new Eliminator AFR 195 head is arguably the best performing head with huge airflow numbers to generate tons of hp and now available in 64cc combustion chamber (both CNC and non-CNC versions). I chose the Trick Flow 195 heads for my engine: reasonably priced, good airflow, 195cc intake runner, and a 62cc combustion chamber. So make sure you remember these important factors when choosing heads for your engine. Camshaft: one word - wimpy. Less than 0.400” lift and small (172/180 at 0.050"), it is just a horrible design for making good power. Great for towing and low speed torque, but newer camshaft designs today can improve your low speed torque and provide major hp increases when combined with other performance upgrades. Please read later in the thread on how to choose the right camshaft for your truck. Depending on your engine combination and whether you’ve changed heads or not, there are several performance options that are available. Exhaust: There were many different styles of exhaust from 1988-1995. All were a 2-into-1 design using a catalytic converter. Older designs used AIR injection with a smog pump and a less efficient pancake-style (pellet) catalytic converter. It is unclear when monolithic (high flow) converters were introduced. Some say in 1996 with the introduction of the Vortec engine. I just took the stock catalytic converter off my 1994 350 truck and it was a monolithic design and replaced it with a high flow unit from MagnaFlow. Don’t know if the stock one is considered high flow or not, but it was pretty plugged so any comparisons would be meaningless. What do you want for exhaust? Replace everything!! Now with what? You have several options again. The best exhaust system IMO is long tube headers with 2.5” true dual exhaust (2 mufflers, 2 catalytic converters, etc.). Another option is shorty style headers (direct-fit), stock or aftermarket y-pipe, 3” intermediate pipe. If you choose not to run a catalytic converter, this combo can be used to make good hp if you’ve changed heads/cam on your engine. On a TBI engine with stock heads and cam, running a 3” catalytic converter WILL NOT greatly limit the hp potential of your motor. A 3” high flow cat can roughly flow 360 cfm of air. I know it doesn’t sound like a lot, but most people overestimate the required air for their engine. A stock 350 TBI engine with performance exhaust only needs 355-444 cfm of air with a 4500 RPM redline and 65% VE. A section on the effect of larger TB is listed earlier in this thread. Vortec engines (1996-1998): Fuel injectors/Intake manifold: The fuel injectors on Vortec engines cannot be replaced with standard aftermarket injectors (22-23#/hr). As far as I know, there is no direct-fit AFPR that is available for their engines. Perhaps the stock one can be modified or a universal AFPR can be used, but it will require some creativity and ingenuity. In fact, Vortec Stroker has a 383 using the stock Vortec induction making 400 hp, so it is possible to make big power using this setup: http://www.fullsizechevy.com/forums/...ad.php?t=83738. Airflow is the biggest bottleneck in the Vortec system since the fuel injector poppets are in the intake tract. A direct bolt-on marine version of the Vortec induction system is available that uses larger 24#/hr fuel injectors that are mounted outside of the intact tract and allows better performance up to 5800 RPM. This is one way to get around this potential bottleneck. Another way is to replace the whole induction unit with another MPFI system, like the Holley Stealth Ram or GM’s RamJet. Heads: The Vortec heads are great heads, but there are not without their problems. The valve springs only support up to 0.470” lift camshafts. Since the Vortec engines use hydraulic roller cams, it would be silly not to upgrade the springs in order to take advantage of today’s high lift roller camshaft designs with lift in excess of 0.500”. Chevy High Performance has an article on upgrading your springs here: http://www.chevyhiperformance.com/te...ort/index.html. In this example, the valve seats are machined and larger springs are installed. Springs are also available that will increase your valve lift without machining the valve seats. Comp Cams Beehive 26915 or the Beehive 26918 springs can be used as direct replacements without machining the heads and will allow up to 0.550” lift. Contact Comp Cams or Crane Cams and ask them directly for which springs they’d recommend if you are unsure. Here’s another article on everything you wanted to know on Vortec heads: http://www.chevyhiperformance.com/ho...458/index.html. The ideal aftermarket head for the Vortec engien IMO is the Edelbrock Etec head. A serious performer for the money. Camshaft: better than a TBI engine and it’s a roller camshaft, so it’s pretty good, right? Nope. If you want to make big power increases, you have to change the camshaft. This bottleneck is intertwined with the previous two bottlenecks. With more fuel and heads that support high lift, a 400+ hp engine is entirely possible. Again, the combination of parts selection is the key here. Installing a camshaft in a stock Vortec engine is not going to perform miracles, but will improve performance. Please read later in the thread on how to choose the right camshaft for your truck. I want to add a supercharger to my engine. How do I do that and what are my choices? First off, supercharger kits are mainly designed and calibrated for the stock engine. It will tolerate mild performance upgrades such as headers and low-restriction exhaust systems, but if you want to start changing cylinder heads and camshafts, you’re going to need to find someone to custom tune your engine or do it yourself. Be prepared to troubleshoot A LOT when adding a supercharger to your engine. It is not as easy as it seems, although the power gains (and particularly the torque gains) are outstanding and well worth the efforts. Depending on your power output, you may need to upgrade the transmission as well, so keep this in mind before investing in a supercharger kit. TBI engines: There are three quality manufacturers that I know of: Whipple Industries, Weiand, and ATI ProCharger. Each has their selling points. The Weiand emissions-legal kit is the least expensive at under $3000, but hood space is definitely an issue since the TB sits on top of the unit. There is also a super-cheap $1500 non-emissions kit available that uses a carb setup. Here is an article from someone who has done this to their 350 engine: http://www.thirdgen.org/weiand142install. Definitely needs a cowl induction hood and you may need to modify it to make room for the air filter. A shorter open element filter with K&N Xtreme filter lid may work, but since I don’t have one I wouldn’t know. It uses a 144 roots-style supercharger that adds between 25-30% additional hp/torque. The potential for more boost is possible, but it is limited by the enormous heat that is generated by the roots-style blower. The Whipple supercharger is popular because of its efficiency and low-RPM performance, adding 40-45% more power. Full boost is achieved at low RPMs making this an excellent choice for trucks that need to tow. The ATI ProCharger is the only centrifugal supercharger available from a major company. It is intercooled and therefore provides 8-9 pounds of boost (2-3 more than the Whipple supercharger). Power is improved by 65%, but it is mainly in the upper RPMS. Don’t count on this supercharger to improve your towing capacity significantly around town. On the highway, sure, but you won’t have the torque that the Whipple unit provided down low. Vortec engines: In addition to Whipple and ATI mentioned above, there is also Vortec Engineering and Powerdyne, both of which are centrifugal supercharger designs. These superchargers will add up to 50% more power. Will roller rockers or higher ratio rockers improve power? Yes and maybe. Roller rockers will reduce frictional parasitic losses on the valvetrain components to free up a few ponies. Higher ratio rockers have their applications: useful on stock cams to improve lift and therefore flow more air, maximize the airflow potential of aftermarket heads and camshafts. They also have their drawbacks: Stock TBI heads have low flow potential and using higher ratio rockers with an aftermarket camshaft may not improve power over the aftermarket camshaft alone since the maximum airflow of the heads have been reached; Vortec heads only allow valve lift up to 0.470” and installing higher ratio rockers may surpass the valve lift depending if you’re running the stock cam or not. With the stock cam, 1.6 ratio rockers are dangerously close to that upper limit, but still under. So how do I decide? Guess it depends on your engine combination and what your future upgrade plans are. Keep in mind that higher ratio rockers will increase the advertised duration of your cam. Comp Cams now has a new XFI series of camshafts designed to use their beehive springs and 1.6 ratio rockers. There are both hydraulic and hydraulic roller versions of the XFI cam. The advantage is that you precisely know the advertised duration of the camshaft with its higher lift potential. How do I choose the right camshaft for my engine? Oh man, probably the most common question on this forum and the one with the most answers. You can get really technical answers or very simple rule-of-thumb answers. The reason there are so many different answers (and camshafts for that matter) is because it highly depends on your engine and transmission combination and how you plan on using your truck (towing, racing, daily driver, etc.) Transmission? What does that have to do with it? Well first of all, you can choose slightly more duration with a standard transmission because you can essentially adjust the stall of the engine when starting out from a stop. Automatic transmissions don’t have that luxury and usually stall at about 1100-1300 RPM. If you choose a high duration cam with a narrow LSA (lobe separation angle) for a lopey powerful engine, you’ll gain hp up top, but lose torque down low. More importantly, installing a large duration cam in TBI engines with their torque-producing, low RPM cylinder heads is a major mismatch. The heads will not be able to support the power above 4000 RPM where the cam will be making its most power. The results = a dog of an engine down low and on the high end. Here are my recommendations for cam choices based on the engine combo you have (all of which need custom chips or performance tuning to work properly and maintain fuel economy. This is required for ANY camshaft upgrade.) TBI 5.7L with stock heads, stock or 2000 RPM stall torque converter: Duration at 0.050” lift 206/216 with LSA 112. The Crane cam 113904 is my top choice, but as long at you stick to intake duration under 206 degrees, you’ll have a safe computer-friendly cam with gobs of power 4500 RPM and lower. Good for towing and performance applications and good all-round choice. Power level maxes out at 280-300hp. TBI 5.7L with after market heads, stock converter: Highest lift possible is the key here to take full advantage of your performance heads. My choice would be Comp’s 260 XFI hydraulic camshaft, 216/223, 0.499”/0.492” lift with 1.6 ratio rockers or the Crane 113904 with 1.6 rockers (0.470”/0.499”). Expected power levels will be around 320-345 hp. TBI 5.7L with after market heads, 2500 RPM stall converter, 3.42 or higher rear end: "XFI" 268 Hydraulic Flat Tappet Camshaft, 224/231, lift 0.520"/0.515" w/1.6 Rockers, or Comp’s Xtreme Energy Computer Controlled XE262H with 1.6 rockers (218/224 at 0.050” lift, 0.510”/0.517”). Dyno simulations of these combos produce 365+ hp at 5500 RPM. Yes, from a TBI. Tuning and proper fuel deliver is a must. Vortec 5.7L engine without spring upgrade: Crane’s 109815, 204/214, 0.429”/0.452” lift. Vortec 5.7L with spring upgrade: Comp cams Xtreme Energy Computer Controlled XR254HR (206/212, 0.480”/0.488”) or Comp cams Xtreme Energy Computer Controlled XR264HR (212/218, 0.488”/0.495” lift). Vortec 5.7L with performance Vortec heads (i.e. Edelbrock 170 E-Tech heads with max valve lift of 0.575”) and fuel/induction system upgrades: Comp’s 260 or 268 XFI hydraulic roller series, 210/218 or 218/224 at 0.050” lift, 0.560”/0.555” or 0.570”/0.565” lift, LSA 113, 1.6 rockers. You could even go with 280 XFI cam with a 2500 stall torque converter. How does 400+ hp sound?