I am planning a high flow Y pipe. The stock Y pipe works very well for low RPM response and torque. That "crisp" feeling. I want to keep as much or all of that power and feel as possible while increasing peak flow capacity. No easy task.
This is not easily measured on the dyno either since most dyno runs start above 3500rpm but most street driving is below 3500rpm. Also, feel is not measured on a dyno nor is transient response which is part of the feel but REALLY important for actual performance.
This is similar to the difference between skid pad peak numbers vs. actual time around a race track. Sure, high skid pad numbers are impressive but not very valuable unless your car is faster in actual use. Same as peak horsepower numbers. Great bragging rights, not so great when a "less" powerful car outruns you! Some people may be thinking "no way" but, ah, yes, way, definitely way, happens much more often than people realize.
Lexus sedans are for the most part heavy cars with small engines. 4 liters is 242 cubic inches. Most 6 cylinder cars, when I grew up, were larger and in fact most performance 6 cylinder new cars are very close at 3.5 liter and 3.7 liters.
Engine displacement or size (in liters or inches or whatever) is a big factor in low RPM power/torque. Another is efficiency or how well the systems work together to CHARGE the engine at low RPM with air. A BIG part of this is a high velocity exhaust system that prevents reversion. The stock system is VERY good at this. It is also much smaller than MOST people are used to seeing on performance engines.
A few years back I contributed a high flow racing 2-1 merge collector 2.25" into 2.50" to the first car to run the S&S headers. A 2.25 to 2.50 Y pipe was built using this. Peak power went up by ONE horsepower. Low speed feel was terrible. The part flowed too well BACKWARDS. It hurt velocity and allowed reversion.
Because of that and other evidence I have been recommending the STOCK Y pipe for some time. I have always said a better system COULD be built it was just unlikely that most muffler shop efforts would beat the stock Y and most likely be worse.
So, I am finally able to focus on this situation. I will build a performance Y pipe for my LS which has a nearly identical Y pipe to the GS. The LS is heavier so it is even more important to keep low end power. If I successfully make a better than stock Y then we will have a repeatable design to copy.
My experimental Y pipe will feature a high velocity one way merge like the stock part does. It will be smaller than 2.25" but larger than stock. The LS Y pipe is VERY similar to the GS4xx. The LS and GS engines are identical.
Look closely. This picture shows the LS400 Y pipe on TOP of a GS400 Y pipe. The GS430 Y pipe is also identical except it has a center catalyst instead of a center resonator. The GS has a larger inside diameter center resonator than the LS400.
This is not easily measured on the dyno either since most dyno runs start above 3500rpm but most street driving is below 3500rpm. Also, feel is not measured on a dyno nor is transient response which is part of the feel but REALLY important for actual performance.
This is similar to the difference between skid pad peak numbers vs. actual time around a race track. Sure, high skid pad numbers are impressive but not very valuable unless your car is faster in actual use. Same as peak horsepower numbers. Great bragging rights, not so great when a "less" powerful car outruns you! Some people may be thinking "no way" but, ah, yes, way, definitely way, happens much more often than people realize.
Lexus sedans are for the most part heavy cars with small engines. 4 liters is 242 cubic inches. Most 6 cylinder cars, when I grew up, were larger and in fact most performance 6 cylinder new cars are very close at 3.5 liter and 3.7 liters.
Engine displacement or size (in liters or inches or whatever) is a big factor in low RPM power/torque. Another is efficiency or how well the systems work together to CHARGE the engine at low RPM with air. A BIG part of this is a high velocity exhaust system that prevents reversion. The stock system is VERY good at this. It is also much smaller than MOST people are used to seeing on performance engines.
A few years back I contributed a high flow racing 2-1 merge collector 2.25" into 2.50" to the first car to run the S&S headers. A 2.25 to 2.50 Y pipe was built using this. Peak power went up by ONE horsepower. Low speed feel was terrible. The part flowed too well BACKWARDS. It hurt velocity and allowed reversion.
Because of that and other evidence I have been recommending the STOCK Y pipe for some time. I have always said a better system COULD be built it was just unlikely that most muffler shop efforts would beat the stock Y and most likely be worse.
So, I am finally able to focus on this situation. I will build a performance Y pipe for my LS which has a nearly identical Y pipe to the GS. The LS is heavier so it is even more important to keep low end power. If I successfully make a better than stock Y then we will have a repeatable design to copy.
My experimental Y pipe will feature a high velocity one way merge like the stock part does. It will be smaller than 2.25" but larger than stock. The LS Y pipe is VERY similar to the GS4xx. The LS and GS engines are identical.
Look closely. This picture shows the LS400 Y pipe on TOP of a GS400 Y pipe. The GS430 Y pipe is also identical except it has a center catalyst instead of a center resonator. The GS has a larger inside diameter center resonator than the LS400.
