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

Red94Chev · 05-30-2006, 09:14 PM

Are there any aftermarket y-pipes available that are mandrel bent?
Yes, Edelbrock makes them and they are 2 1/2” down pipes into a 3” intermediate pipe. It is sold as an off-road unit, but it would be emissions-compatible with the addition of an O2 sensor bung and a 3” catalytic converter. It is pricey at $160. Another option is using Magnaflow’s y-pipe for 94-95 trucks, 2 1/4” mandrel bent tubing and includes their high flow catalytic converter for $150 – a great deal. Although it is listed for direct-fit applications for 94-95 trucks, it can be used in 88-95 trucks by cutting the 3” end off and welding on an intermediate pipe to connect it to your muffler.

Another option for a true dual exhaust setup that is mandrel bent is to use Magnaflow's catalytic converter/head pipe replacement unit from the 96-98 5.7L. It has 2 1/2" pipe and two high-flow cats. Cut the ends off and run 2 1/2" pipes to dual mufflers and you've got yourself a true dual exhaust setup. Cost on the Magnaflow unit is $316.

Do I need a catalytic converter? Will removing it make more power?
This is somewhat of a loaded question. We all know that catalytic converters are designed to reduce noxious gases that harm our ozone and contribute to global warming. Their fault lies in the fact that they can restrict exhaust airflow and therefore can limit hp. Some people remove their catalytic converter in the quest for more power. Is this the right thing to do? Well let me provide some objective evidence and you can make the decision yourself. A recent article in Sport Truck magazine tested the airflow characteristics of their high flow catalytic converters against stock GM, Ford, and Dodge units. Here’s where auto math becomes important. As mentioned earlier, most people over estimate the CFM requirements of their engine. CFM requirements are based on 3 factors: max engine RPM, intake manifold design, and volumetric efficiency (VE) of their engine. VE? What the heck is VE? Probably the most important factor influencing CFM engine requirements. To estimate your CFM requirements, go to this link: http://www.wallaceracing.com/intakecfm.php. Don’t all assume you have a performance engine. If you haven’t changed heads or cam on your TBI engine, VE at 4500-4700 RPM is only 67%. On a 350 TBI engine, CFM requirement is 383-473 CFM. Shocking I know!! If you have a hydraulic roller camshafts, performance heads and other performance goodies, you can choose a VE between 90-100%, but I bet there is <5% of the TBI crowd out there with that engine combination.

Back to the Sport Truck article, their 3” cat is rated at 360 cfm at 1.5inHg (quoted 422 cfm at 28” H2O) and their 2.5” cat is rated at 307 cfm at 1.5inHg (quoted 360 cfm at 28” H2O). This was surprising and I now know why catalytic converter manufacturers don’t cite their airflow characteristics. No one would buy them!! This is just a misinterpretation of the kind of airflow needed for an exhaust system. Let’s take our TBI engine above with performance exhaust – needing 383-473 CFM of air. Will a single 3” cat suffice? – Sure. Will it affect hp – a little bit, but limits it only by 2-4% or about 4-8 hp. Most people wouldn’t even be able to tell the difference. Let’s say now you’ve got an all out performance 350 with the works, hydraulic roller cam, long tubes, the best performance heads money can buy (95% VE – it is rarely 100% at max RPM!!), shifting at 5700 RPM (computer-limited). You’ll need a lot of air - 658 to 823 cfm and dual 3” catalytic converters (2 x 360 CFM = 720 CFM). Most engines are not that potent though. My engine, for example, with Trick Flow heads, Comp hydraulic camshaft, shifting at 5500 RPM has a VE of 83%. My engine needs 555 to 693 cfm. Dual 2.5” cats are more than enough not to limit hp. However, TBI engines only come with a single 3” cat and it is certainly not high flow. Removing the cat on a 2-into-1 exhaust system will improve power on a heavily modified engine – there’s no question. So depending on how you feel about saving our environment versus the additional expense of 2 catalytic converters and a custom exhaust, only you can make that decision. All I can say is TBI engines with stock heads and cam do not need to remove the stock catalytic converter, unless it is plugged or faulty (or the ancient pellet-type). There is no significant change in power with or without a high-flow catalytic converter. Vortec 350 engines already come with 2 catalytic converters from the factory that is more than enough to meet your performance upgrade potential.

What is a smog pump (on pre-93 trucks) and can I remove it?
Your smog pump (AIR pump) is simply what it sounds like. It is a pump that sends air to your catalytic converter via a little round tube. This helps complete the combustion of residual exhaust gases in your catalytic converter along with quickly heating up your cat during cold starts. Replace the catalytic converter with a modern unit and the AIR system becomes redundant. It is located on the lower side of your accessory bracket right underneath the AC compressor on the passenger side. It has an upper and lower bolt that attaches it to the bracket. These bolts can be removed and your smog pump will come right out. Here is an article on smog pump removal: http://www.thirdgen.org/serpentine

I have a lot of performance components already on my 305 engine, but I want more power. What should I do?
Well, any performance upgrade that you can do on a 350 engine can also be done on a 305 engine. If you want more than that, then add a supercharger or buy a 350 long block or 383 short block with aftermarket heads and swap over the parts you want. 350 engines are so plentiful that IMO, there is no excuse for not having one for the serious performance-minded individual.

I like the 454SS, but I have a small block in my truck. Would you recommend a 454 engine swap in place of my engine?
Well, any engine swap is possible. There is no doubt the 454 engine is super cool and you can swap it into your truck, but because of the extra torque, you’ll need to upgrade the transmission, preferably to the 4L80E or Turbo 400. The upgraded 4L65E found in performance trucks/cars may also be used, but right now they are relatively new and difficult to find in the wrecking yard. A new transmission would be pretty expensive, but like I said, anything is possible. Another option is to buy a World Products assembled small block short block. They make these up to 454 cid (http://www.worldcastings.com/prods_pages/101202.htm). I think the “most wanted” of all the big block swaps is the 572 GM Performance Parts engine. Man, that engine would be so cool in an OBS truck. If you can afford that engine, then you can afford the swap.

Personally, I think doing a LS1 swap is very affordable right now. There are enough donor vehicles in the wrecking yard from crashed Vettes, Camaros, and Firebirds to make this an awesome engine swap project. Jimmy P is currently installing one on his 1989 Silverado project: http://www.fullsizechevy.com/forums/...d.php?t=144018. Another modern engine swap would be to use the 5.3L out of the NBS trucks.

Are there any nitrous systems designed for my TBI or Vortec truck?
Yup. Nitrous Works, Nitrous Oxide Systems (NOS), and Venom Performance all make nitrous oxide systems for 88-95 TBI-powered trucks. For Vortec-powered 96-98 trucks, NOS and Venom have systems available. Visit their respective websites for more information and where to buy. You can add up to 125 hp with these kits. Nitrous kits on trucks get a bad rap from the ricer market, but they can safely add power for not too much money. Kits are priced between $600-800 and can be easily installed yourself. It provides the same power as a supercharger, but at a fraction of the cost. When used properly, a good nitrous system is a welcome addition to any truck engine. The problem is you can only use it at WOT and you have to keep refilling the nitrous bottles.

Where can I find TBI-engine related performance parts for my truck?

Performance Chips:
Wester’s Garage - http://westers_garage.eidnet.org/Index2.htm
Wait4Me - http://www.wait4meperformance.com/
TBI Chips - http://www.tbichips.com/

Larger Throttle bodies:
CFMTech - http://www.cfm-tech.com/index.htm
XtremeFI - http://www.xtremefi.com/
TurboCity – http://www.turbocity.com/default.php?cPath=16

TBI injectors:
TurboCity – http://www.turbocity.com/default.php?cPath=16

What are performance chips or performance tunes and how do they work?
Performance chips are essentially a memory chip that contains a set of instructions that tells your computer (and your truck engine) how to respond to incoming sensor data. Performance tunes differ in that the set of instructions are contained on flashable memory housed inside the computer. Therefore, there is no chip to replace. Chips are available for both the TBI and Vortec Engines. Jet Performance, for instance, makes performance chips for Vortec engines. Other performance chipmakers are out there as well, including Wester’s Garage, Wait4Me, TBI Chips, (Ed Wright) Fast Chips, etc. They can vary in price from under $100 to over $500. Burning your own chips can save you some money or at least allow you to fine tune your engine as you continue to upgrade your engine.

What is chip burning and is it necessary?
Chip burning is simply making your own custom PROMS. You will find that the biggest gains on these engines will come from burning your own chips. The stock chip is very weak and can barely support the factory set-up. Anytime you mod your truck you should look into burning a new chip to maximize its potential. You can get away with the stock chip with basic bolt-ons, but once you add a major upgrade (i.e. new camshaft) chip burning is a must. Alternatively, you can have a performance tuner make one for you, but it will be difficult to get your engine dialed in properly since the chip is made using info on your engine combination, but it is not YOUR engine without any feedback to see how well the tune is working. The solution: datalogging. There is free software available that you can install on a laptop computer and use a special connector to plug the laptop into your cars diagnostic (ALDL) port. Driving the truck while this software is running will collect performance-related data about your engine. These data will tell you what your engine is doing with respect to timing, air:fuel ratio, etc. at respective engine RPM. You can save this data and send it to a chipmaker that will burn you a chip based on the info you sent them. Retest with the datalogging software and finetune the chip again. This strategy will essentially accomplish the same thing as if you were burning the chip yourself. You can find this program from the following link.
Link to data log software
Link: Good starting post for TBI prom tuning

Is my TBI or Vortec speed limited?
Yes, the ECMs have a fuel shut-off circuit once the vehicle reaches the maximum limited speed. Any chipmaker or aftermarket chip/tuner will remove the governor circuit to allow higher speeds. There is no RPM limiter, but max RPM on Vortec engines seems to be 5800 RPM. This is written into the computer code. Some people are trying to develop ways to get around this.

How can I learn how to burn my own chips for my TBI or Vortec engine?
Lots of good resources here/lots to read and way too much to cover:
http://www.fullsizechevy.com/forums/...ad.php?t=45225
http://www.thirdgen.org/techboard/tb...free-tune.html
http://www.thirdgen.org/techboard/di...uide-book.html
http://www.fullsizechevy.com/forums/...d.php?t=126937
http://www.fullsizechevy.com/forums/...d.php?t=139132

What is a torque converter and how does it work?
The torque converter is an amazing piece of automotive engineering that connects the output of the engine to the input shaft of the transmission. It is a fluid-coupling device that also acts as a torque multiplier during initial acceleration. Torque converters are rated in terms of stall speed. Stall speed refers the RPM that a given torque converter (impeller) has to spin in order for it to overcome a given amount of load and begin moving the turbine. In other words, it refers to how fast (RPM) the torque converter must spin to generate enough fluid force on the turbine to overcome the resting inertia of the vehicle at wide open throttle. Most torque converter are rated using a reference load of 230 ft-lbs at 2500 RPM. Engines producing more than 230 ft-lbs at 2500 RPM will give you more than advertised stall speed. The opposite is true for engine with less than 230 ft-lbs at 2500 RPM. The increase or decrease in advertised stall speed is only 100-200 RPMs.

How do I choose the right converter for my application?
Choosing the right torque converter is similar to choosing the right camshaft. It can be difficult and it is easy to get bogged down in technical information. The main factor is related to your camshaft choice, since this affects the powerband of the engine. A good rule of thumb is for advertised cam durations up to 260 degrees, a 2000 or 2400 stall converter is a good choice. Advertised cam durations up to 272 degrees, a 2400 or 3000 stall converter is a good choice. Advertised cam durations over 280 degrees, a 3000 to 3600 stall converter is a must.

What are the drivability concerns of a higher stall torque converter?
Proper torque converter selection is the key. You will not have any drivability problems if the torque converter is matched properly to your application. Mismatched components are where problems come in. For instance, if you have an engine that needs a 3000 RPM stall and you install a 2200 (2000 to 2500 RPM) stall converter, it will normally not even provide a 2000 RPM stall, but act very similar to the stock converter you just replaced. How come? Because the engine needs to operate in its optimum RPM range and since the stock torque converter is below that range, it is not getting enough load from the crankshaft side to operate as designed. In other words, the low-RPM torque is much lower on this engine and therefore reduces the advertised stall speed of the converter to under 2000 RPM, similar to the stock unit (around 1600-1800 RPM). Symptoms include engine stalling when in gear while stopped, low stall speed, hesitation when at going to WOT, and bogging of the engine when leaving from stop under WOT. Likewise, too high a stall speed is not good either. Symptoms include high “revs” to pull away from a stop, “marshmallow” accelerator feel when driving at part throttle, transmission and possibly engine overheating, and a pronounced engine rev when nailing the throttle from a cruising speed.

How do I determine the stall speed of my torque converter?
You should be able to footbrake stall the converter to its rated stall speed. If your torque converter has a 2400RPM stall speed, you should be able to footbrake stall the converter to about 2400 RPM.

So when should I upgrade my torque converter?
IMO, not until you’ve upgraded your camshaft. A 2500 RPM stall torque converter installed on a stock TBI engine is a major mismatch. A 3000 RPM stall converter on a stock TBI engine is just plain ridiculous, and you’ve just lost the majority of your engine’s powerband.

05-30-2006, 09:14 PM	#4
Red94Chev Kick Ass!! Status: Offline Join Date: Sep 2005 Member ID: 33983 Pics: My Gallery Location: Edmonton, AB Age: 33 Posts: 924	Re: Common performance-minded FAQs about 88-98 OBS trucks Are there any aftermarket y-pipes available that are mandrel bent? Yes, Edelbrock makes them and they are 2 1/2” down pipes into a 3” intermediate pipe. It is sold as an off-road unit, but it would be emissions-compatible with the addition of an O2 sensor bung and a 3” catalytic converter. It is pricey at $160. Another option is using Magnaflow’s y-pipe for 94-95 trucks, 2 1/4” mandrel bent tubing and includes their high flow catalytic converter for $150 – a great deal. Although it is listed for direct-fit applications for 94-95 trucks, it can be used in 88-95 trucks by cutting the 3” end off and welding on an intermediate pipe to connect it to your muffler. Another option for a true dual exhaust setup that is mandrel bent is to use Magnaflow's catalytic converter/head pipe replacement unit from the 96-98 5.7L. It has 2 1/2" pipe and two high-flow cats. Cut the ends off and run 2 1/2" pipes to dual mufflers and you've got yourself a true dual exhaust setup. Cost on the Magnaflow unit is $316. Do I need a catalytic converter? Will removing it make more power? This is somewhat of a loaded question. We all know that catalytic converters are designed to reduce noxious gases that harm our ozone and contribute to global warming. Their fault lies in the fact that they can restrict exhaust airflow and therefore can limit hp. Some people remove their catalytic converter in the quest for more power. Is this the right thing to do? Well let me provide some objective evidence and you can make the decision yourself. A recent article in Sport Truck magazine tested the airflow characteristics of their high flow catalytic converters against stock GM, Ford, and Dodge units. Here’s where auto math becomes important. As mentioned earlier, most people over estimate the CFM requirements of their engine. CFM requirements are based on 3 factors: max engine RPM, intake manifold design, and volumetric efficiency (VE) of their engine. VE? What the heck is VE? Probably the most important factor influencing CFM engine requirements. To estimate your CFM requirements, go to this link: http://www.wallaceracing.com/intakecfm.php. Don’t all assume you have a performance engine. If you haven’t changed heads or cam on your TBI engine, VE at 4500-4700 RPM is only 67%. On a 350 TBI engine, CFM requirement is 383-473 CFM. Shocking I know!! If you have a hydraulic roller camshafts, performance heads and other performance goodies, you can choose a VE between 90-100%, but I bet there is <5% of the TBI crowd out there with that engine combination. Back to the Sport Truck article, their 3” cat is rated at 360 cfm at 1.5inHg (quoted 422 cfm at 28” H2O) and their 2.5” cat is rated at 307 cfm at 1.5inHg (quoted 360 cfm at 28” H2O). This was surprising and I now know why catalytic converter manufacturers don’t cite their airflow characteristics. No one would buy them!! This is just a misinterpretation of the kind of airflow needed for an exhaust system. Let’s take our TBI engine above with performance exhaust – needing 383-473 CFM of air. Will a single 3” cat suffice? – Sure. Will it affect hp – a little bit, but limits it only by 2-4% or about 4-8 hp. Most people wouldn’t even be able to tell the difference. Let’s say now you’ve got an all out performance 350 with the works, hydraulic roller cam, long tubes, the best performance heads money can buy (95% VE – it is rarely 100% at max RPM!!), shifting at 5700 RPM (computer-limited). You’ll need a lot of air - 658 to 823 cfm and dual 3” catalytic converters (2 x 360 CFM = 720 CFM). Most engines are not that potent though. My engine, for example, with Trick Flow heads, Comp hydraulic camshaft, shifting at 5500 RPM has a VE of 83%. My engine needs 555 to 693 cfm. Dual 2.5” cats are more than enough not to limit hp. However, TBI engines only come with a single 3” cat and it is certainly not high flow. Removing the cat on a 2-into-1 exhaust system will improve power on a heavily modified engine – there’s no question. So depending on how you feel about saving our environment versus the additional expense of 2 catalytic converters and a custom exhaust, only you can make that decision. All I can say is TBI engines with stock heads and cam do not need to remove the stock catalytic converter, unless it is plugged or faulty (or the ancient pellet-type). There is no significant change in power with or without a high-flow catalytic converter. Vortec 350 engines already come with 2 catalytic converters from the factory that is more than enough to meet your performance upgrade potential. What is a smog pump (on pre-93 trucks) and can I remove it? Your smog pump (AIR pump) is simply what it sounds like. It is a pump that sends air to your catalytic converter via a little round tube. This helps complete the combustion of residual exhaust gases in your catalytic converter along with quickly heating up your cat during cold starts. Replace the catalytic converter with a modern unit and the AIR system becomes redundant. It is located on the lower side of your accessory bracket right underneath the AC compressor on the passenger side. It has an upper and lower bolt that attaches it to the bracket. These bolts can be removed and your smog pump will come right out. Here is an article on smog pump removal: http://www.thirdgen.org/serpentine I have a lot of performance components already on my 305 engine, but I want more power. What should I do? Well, any performance upgrade that you can do on a 350 engine can also be done on a 305 engine. If you want more than that, then add a supercharger or buy a 350 long block or 383 short block with aftermarket heads and swap over the parts you want. 350 engines are so plentiful that IMO, there is no excuse for not having one for the serious performance-minded individual. I like the 454SS, but I have a small block in my truck. Would you recommend a 454 engine swap in place of my engine? Well, any engine swap is possible. There is no doubt the 454 engine is super cool and you can swap it into your truck, but because of the extra torque, you’ll need to upgrade the transmission, preferably to the 4L80E or Turbo 400. The upgraded 4L65E found in performance trucks/cars may also be used, but right now they are relatively new and difficult to find in the wrecking yard. A new transmission would be pretty expensive, but like I said, anything is possible. Another option is to buy a World Products assembled small block short block. They make these up to 454 cid (http://www.worldcastings.com/prods_pages/101202.htm). I think the “most wanted” of all the big block swaps is the 572 GM Performance Parts engine. Man, that engine would be so cool in an OBS truck. If you can afford that engine, then you can afford the swap. Personally, I think doing a LS1 swap is very affordable right now. There are enough donor vehicles in the wrecking yard from crashed Vettes, Camaros, and Firebirds to make this an awesome engine swap project. Jimmy P is currently installing one on his 1989 Silverado project: http://www.fullsizechevy.com/forums/...d.php?t=144018. Another modern engine swap would be to use the 5.3L out of the NBS trucks. Are there any nitrous systems designed for my TBI or Vortec truck? Yup. Nitrous Works, Nitrous Oxide Systems (NOS), and Venom Performance all make nitrous oxide systems for 88-95 TBI-powered trucks. For Vortec-powered 96-98 trucks, NOS and Venom have systems available. Visit their respective websites for more information and where to buy. You can add up to 125 hp with these kits. Nitrous kits on trucks get a bad rap from the ricer market, but they can safely add power for not too much money. Kits are priced between $600-800 and can be easily installed yourself. It provides the same power as a supercharger, but at a fraction of the cost. When used properly, a good nitrous system is a welcome addition to any truck engine. The problem is you can only use it at WOT and you have to keep refilling the nitrous bottles. Where can I find TBI-engine related performance parts for my truck? Performance Chips: Wester’s Garage - http://westers_garage.eidnet.org/Index2.htm Wait4Me - http://www.wait4meperformance.com/ TBI Chips - http://www.tbichips.com/ Larger Throttle bodies: CFMTech - http://www.cfm-tech.com/index.htm XtremeFI - http://www.xtremefi.com/ TurboCity – http://www.turbocity.com/default.php?cPath=16 TBI injectors: TurboCity – http://www.turbocity.com/default.php?cPath=16 What are performance chips or performance tunes and how do they work? Performance chips are essentially a memory chip that contains a set of instructions that tells your computer (and your truck engine) how to respond to incoming sensor data. Performance tunes differ in that the set of instructions are contained on flashable memory housed inside the computer. Therefore, there is no chip to replace. Chips are available for both the TBI and Vortec Engines. Jet Performance, for instance, makes performance chips for Vortec engines. Other performance chipmakers are out there as well, including Wester’s Garage, Wait4Me, TBI Chips, (Ed Wright) Fast Chips, etc. They can vary in price from under $100 to over $500. Burning your own chips can save you some money or at least allow you to fine tune your engine as you continue to upgrade your engine. What is chip burning and is it necessary? Chip burning is simply making your own custom PROMS. You will find that the biggest gains on these engines will come from burning your own chips. The stock chip is very weak and can barely support the factory set-up. Anytime you mod your truck you should look into burning a new chip to maximize its potential. You can get away with the stock chip with basic bolt-ons, but once you add a major upgrade (i.e. new camshaft) chip burning is a must. Alternatively, you can have a performance tuner make one for you, but it will be difficult to get your engine dialed in properly since the chip is made using info on your engine combination, but it is not YOUR engine without any feedback to see how well the tune is working. The solution: datalogging. There is free software available that you can install on a laptop computer and use a special connector to plug the laptop into your cars diagnostic (ALDL) port. Driving the truck while this software is running will collect performance-related data about your engine. These data will tell you what your engine is doing with respect to timing, air:fuel ratio, etc. at respective engine RPM. You can save this data and send it to a chipmaker that will burn you a chip based on the info you sent them. Retest with the datalogging software and finetune the chip again. This strategy will essentially accomplish the same thing as if you were burning the chip yourself. You can find this program from the following link. Link to data log software Link: Good starting post for TBI prom tuning Is my TBI or Vortec speed limited? Yes, the ECMs have a fuel shut-off circuit once the vehicle reaches the maximum limited speed. Any chipmaker or aftermarket chip/tuner will remove the governor circuit to allow higher speeds. There is no RPM limiter, but max RPM on Vortec engines seems to be 5800 RPM. This is written into the computer code. Some people are trying to develop ways to get around this. How can I learn how to burn my own chips for my TBI or Vortec engine? Lots of good resources here/lots to read and way too much to cover: http://www.fullsizechevy.com/forums/...ad.php?t=45225 http://www.thirdgen.org/techboard/tb...free-tune.html http://www.thirdgen.org/techboard/di...uide-book.html http://www.fullsizechevy.com/forums/...d.php?t=126937 http://www.fullsizechevy.com/forums/...d.php?t=139132 What is a torque converter and how does it work? The torque converter is an amazing piece of automotive engineering that connects the output of the engine to the input shaft of the transmission. It is a fluid-coupling device that also acts as a torque multiplier during initial acceleration. Torque converters are rated in terms of stall speed. Stall speed refers the RPM that a given torque converter (impeller) has to spin in order for it to overcome a given amount of load and begin moving the turbine. In other words, it refers to how fast (RPM) the torque converter must spin to generate enough fluid force on the turbine to overcome the resting inertia of the vehicle at wide open throttle. Most torque converter are rated using a reference load of 230 ft-lbs at 2500 RPM. Engines producing more than 230 ft-lbs at 2500 RPM will give you more than advertised stall speed. The opposite is true for engine with less than 230 ft-lbs at 2500 RPM. The increase or decrease in advertised stall speed is only 100-200 RPMs. How do I choose the right converter for my application? Choosing the right torque converter is similar to choosing the right camshaft. It can be difficult and it is easy to get bogged down in technical information. The main factor is related to your camshaft choice, since this affects the powerband of the engine. A good rule of thumb is for advertised cam durations up to 260 degrees, a 2000 or 2400 stall converter is a good choice. Advertised cam durations up to 272 degrees, a 2400 or 3000 stall converter is a good choice. Advertised cam durations over 280 degrees, a 3000 to 3600 stall converter is a must. What are the drivability concerns of a higher stall torque converter? Proper torque converter selection is the key. You will not have any drivability problems if the torque converter is matched properly to your application. Mismatched components are where problems come in. For instance, if you have an engine that needs a 3000 RPM stall and you install a 2200 (2000 to 2500 RPM) stall converter, it will normally not even provide a 2000 RPM stall, but act very similar to the stock converter you just replaced. How come? Because the engine needs to operate in its optimum RPM range and since the stock torque converter is below that range, it is not getting enough load from the crankshaft side to operate as designed. In other words, the low-RPM torque is much lower on this engine and therefore reduces the advertised stall speed of the converter to under 2000 RPM, similar to the stock unit (around 1600-1800 RPM). Symptoms include engine stalling when in gear while stopped, low stall speed, hesitation when at going to WOT, and bogging of the engine when leaving from stop under WOT. Likewise, too high a stall speed is not good either. Symptoms include high “revs” to pull away from a stop, “marshmallow” accelerator feel when driving at part throttle, transmission and possibly engine overheating, and a pronounced engine rev when nailing the throttle from a cruising speed. How do I determine the stall speed of my torque converter? You should be able to footbrake stall the converter to its rated stall speed. If your torque converter has a 2400RPM stall speed, you should be able to footbrake stall the converter to about 2400 RPM. So when should I upgrade my torque converter? IMO, not until you’ve upgraded your camshaft. A 2500 RPM stall torque converter installed on a stock TBI engine is a major mismatch. A 3000 RPM stall converter on a stock TBI engine is just plain ridiculous, and you’ve just lost the majority of your engine’s powerband.