I am pretty new to this whole aftermarket stuff on cars. But for a GS 400 what would be the best exhaust to have, that wouldn't be too big and not too loud but to help get that extra horsepower. And does anyone know how many extra horsepower the L tuned kit gives to a GS 400

 

I wouldn't expect any noticable output gain from a different exhaust, although someone posted a 12HP gain I think from one (Borla?).

All replacement exhausts are going to be louder than stock. No one can say except you whether it will be acceptable. Suggest you listen to Borla and L-Tuned if possible to get an idea of the sound.

 

Borla claims 5 to 6 horsepower gain at peak. But if I remember it correctly, Mean Gene has a dyno that proves 7 hp gain or so.

 

Bit & RA are both correct. My dyno runs with Borlas show 5+ HP at the rear wheels so that equates to almost 7 HP at the flywheel ( figuring on 85% driveline efficiency ). Someone else has a GReddy system that has claim to the 12 HP increase ( too loud for me! ).:eek:

 

Hello Mean Gean,

I was wondering if you managed to get some power and torque readings at low to mid RPMs during your dyno tests. The majority of aftermarket exhausts give a little peak hp increase but there's no conclusive data about their effect on low to mid rpm power and torque.

 

Are these exhaust systems cat-backs or just mufflers?

 

Power - Due to the GS downshifting at any full throttle application below 4000 rpms, I ( & Mo ) have been unable to collect any data below those engine speeds. Sorry!
4K - The Borlas & RMM's are just muffler/tip assemblies. I think the GReddy is a true cat-back system but haven't seen it so I'm not 100% sure.

 

when the Rod Millen exhaust is combined with the Rod Millen intake they state that you can gain 20-25 hp

you can also listen to the Rod Millen exhaust on the rodmillen web page

 

I really don't think an intake with cat-back would produce extra 20 to 25 ponnies. Never trust the claim from manufacturer.

 

its just what it said on the advertisment for the exhaust

 

Pilot - Since RMM had the first intake/exhaust combo when I bought my GS4, I took their bait & got that stuff. Using a G-Tech Pro, I found that, while it SOUNDED better/faster, my 0-60 times actually slowed down from an average of 5.8 ( totally stock w/16" ) to 6.0's with the RMM parts!!:eek: Took the GS to my friend's dyno & did some baseline pulls w/stock stuff. Then we swapped over to just the RMM intake (stock muffs ). I only gained about 5+ rwhp ( thus, maybe 6 hp at the engine ). Then we installed the RMM mufflers & found just less than 3 additional rwhp ( 4 flywheel ). Do the math & I come uo with only 10 hp at the engine - about half of what RMM advertised but maybe their GS test mule was stronger than mine. The slowdown was because, while the larger intake allowed more air into the engine, there was no way to increase the fuel flow to match the additional air - I reason that the factory ECU was already running the injectors at max duty cycle( possibly static ). Therefore I was running lean & could hear the pinging caused by a lean condition right before the ECU pulls back the timing. This is why Swift's kit works better - the piggyback ECU is tailored to increase both the fuel flow & timing to accomodate to extra air flow. While I like RMM for suspension & cosmetics, I haven't been very impressed with their performance parts for the GS nor the answers ( or lack of ) I got from their sales staff.