Cat Comparison, 200 versus 400cpi

[ivan129]

I'm replacing my rear mufflers and building a better dual 2.25" mandrel bend exhaust and am considering fitting low cell count cats. I guess to help me justify the cat replacement / upgrade I'd like to gather some feedback from forum members as to whether there are any real gains in going to low cpi cats. Application is a mildly modded NA 1UZ.

Questions:-
Does anyone have actual data on HP gains / differences that compares 200cpi cats versus 400cpi cats. I'm not talking about published data put out by the cat manufacturers I'm talking about someone's actual dyno results, somone who has done back to back dyno runs comparing the difference between 200 & 400 cells per iinch cats. Do 200cpi cats make more HP?

How much does a cat contribute to reducing exhaust noise? Will 200cpi cats make the exhaust louder. Wanna remain street legal.

What type / construction should be used? Ceramic or metal.

There are long catalytic convertors and short ones, ones with heat sheilds and ones without. What should I use / be looking for in making a choice?

Thanks.. hoping for some good replies..

 

[JBrady]

I'm replacing my rear mufflers and building a better dual 2.25" mandrel bend exhaust...

Ivan, not sure which year or model Lexus you have.
I certainly understand the desire to build a "better" exhaust.

Please define your goals. Total horsepower, NA/turbo/supercharger/nitrous and your vehicle use.

Since you want to remain "legal" I am assuming moderate mods with good driving manners and good part throttle performance.

All factory USDM Lexus 4.0 and 4.3 liter V8 sedans came with the same basic design exhaust. Dual catalysts bolted to the exhaust manifolds with dual 50mm (1.97") mandrel tubes converging into a single center 60mm (2.36") tube.
This part we generally refer to as the "factory Y pipe".
The design of the merge is excellent for low speed torque and drivability.
This Y pipe has worked well on the 300hp/310tq GS400 engines and some have made 400rwhp through it utilizing a supercharger.
If you plan to build a "better" part than the factory Y pipe you will find it harder to improve on than expected.

 

[JBrady]

The 1998-2000 model year VVTi 1uzfe USDM engines came with high flow metal substrate catalysts. These are very good and should be utilized if your vehicle has them. The earlier and later engines used ceramic core cats which are sufficient and should also be retained.

The stock manifolds are less than perfect and should be replaced with better flowing parts if possible. The no longer manufactured S&S headers or the PPE headers are available for a number of applications and will work much better than stock. The best stock ones were the 1999-2000 GS/LS400 semi tri-Y models. All the SC400/SC430/GS430/LS430 had single tube designs that are not very good.

The GS400 stock Y pipe is fine as is.
The other stock Y pipes can benefit to removing the center resonator or catalyst.
Cut the pipe AFTER the merge and replace with a 2.5" straight pipe or 2.5" ID smooth internal flowing resonator type muffler.

After the single center section a well designed system of 2.00" or 2.25" mandrel bent tube with high flow mufflers will work nicely.

 

[ivan129]

200CPI versus 400CPI cats

Thanks for your reply. My 1UZFE NA engine is fitted to a 300zx Nissan. A friend of mine did the exhaust for it but fitted poor quality muffers. ie. Nicely polished stainless steel mufflers with mild steel cores and they rusted out within a few months. I'm now going to build my own system. The car is just a street driven mildly modded 1UZ. Some head porting, lextreme valve springs, std cams, 4 into 1 extractors, (1.625" primarys, 3" collector, 2.5" oulet) COP, injectors, purpose built plenum with ram tubes and twin tbs & after market ECU. After reading many of the articles on this forum I have in mind to build my exhaust system using twin 2.25" mandrel bends from the extractors into 2 x cats (???CPI) two be position just behind the auto. 2.25" out of the cats into a kiss/x-pipe located under the rear section of the tailshaft and then carry on with the 2 x 2.25" mandrel bends to magnaflow 12138 rear mufflers.

The cats removed from my old system (above) are 400cpi ceramics and are in like new condition. What I'd really like to know:-
1) will there be any real gains in switching to 200cpi cats? How much RWHP?
2) will the exhaust be louder?

Thanks

The 1998-2000 model year VVTi 1uzfe USDM engines came with high flow metal substrate catalysts. These are very good and should be utilized if your vehicle has them. The earlier and later engines used ceramic core cats which are sufficient and should also be retained.

The stock manifolds are less than perfect and should be replaced with better flowing parts if possible. The no longer manufactured S&S headers or the PPE headers are available for a number of applications and will work much better than stock. The best stock ones were the 1999-2000 GS/LS400 semi tri-Y models. All the SC400/SC430/GS430/LS430 had single tube designs that are not very good.

The GS400 stock Y pipe is fine as is.
The other stock Y pipes can benefit to removing the center resonator or catalyst.
Cut the pipe AFTER the merge and replace with a 2.5" straight pipe or 2.5" ID smooth internal flowing resonator type muffler.

After the single center section a well designed system of 2.00" or 2.25" mandrel bent tube with high flow mufflers will work nicely.

 

[JBrady]

I doubt you would notice the difference in power with 200cpi vs your current 400cpi cats. The 200s may be a touch louder but with mufflers that would also be minimal.