Reducing exhaust fumes from cammed L77.

[daves8]

I get a bit of drone at around 1600 to 1900 now. Before the cam upgrade I was getting drone everywhere under 2500rpm. I'd say it's more my catback being responsible for the drone. I have an xforce catback. I can't stand the sound anymore. The only time I don't mind the sound is when you floor it. Everywhere else it sounds like crap.

Have you got the Rex 1 3/4 headers or the triple stepped headers that have 3 pipe size differences. These go 1 3/4" to 1 7/8" to 2".

I have the 1 3/4.

Mine have droned at 1000-1100 with 3 different cat backs.

 

[blackvxss]

I have often thought Difillipo 1 7/8 headers would sound better (more beat / note separation) than my 1 3/4 Rex short 4-1s

What does the cat do to note in your mind?

I bought some ebay 100cpi cats and made car sound raspy put ballistic cats on and much deeper sound(i didn't think there would be any difference but there was)

Sureflo Exhaust sell them

 

[blackvxss]

These are VF2 Euro 5 cats (pretty restrictive), but I think too big to fit behind your headers.

View attachment 251948

the cat flows well (look at the size its the exit bend thats restictive) some exhaust shop cut off the entry exit pipes with larger diam to suit aftermarket exhausts no real loss on dyno.

 

[daves8]

I bought some ebay 100cpi cats and made car sound raspy put ballistic cats on and much deeper sound(i didn't think there would be any difference but there was)

Sureflo Exhaust sell them

Ive got the 100 CPI cats that GM Motorsport make, specifically for the Rex headers……

They seem ok…..

 

[RevNev]

the cat flows well (look at the size its the exit bend thats restictive) some exhaust shop cut off the entry exit pipes with larger diam to suit aftermarket exhausts no real loss on dyno.

Cat systems capable of passing ADR emission testing will rob an engine of power. Merely having a cat in the exhaust stream doesn't make a car emission compliant as many people are misled to believe. The legal sanction for emission tampering is the same charge for ineffective aftermarket cats as it is for complete cat removal, so why bother with 100/200 cell cats that are totally illegal when you can pipe the illegal cats that come with the headers or exhaust system and cop the same charge if caught!

Alternatively with a 340 header or Pacemaker shorty and piped stock cats, a failed emission test results in a defect notice to replace the cats having reached their effective service life instead of the emission tampering charge and EPA sanction you'd receive with long tube headers and a modified/aftermarket cat arrangement.

 

[lmoengnr]

I bought some ebay 100cpi cats and made car sound raspy put ballistic cats on and much deeper sound(i didn't think there would be any difference but there was)

Sureflo Exhaust sell them

+1 for Ballistic cats.

 

[blackvxss]

Cat systems capable of passing ADR emission testing will rob an engine of power. Merely having a cat in the exhaust stream doesn't make a car emission compliant as many people are misled to believe. The legal sanction for emission tampering is the same charge for ineffective aftermarket cats as it is for complete cat removal, so why bother with 100/200 cell cats that are totally illegal when you can pipe the illegal cats that come with the headers or exhaust system and cop the same charge if caught!

Alternatively with a 340 header or Pacemaker shorty and piped stock cats, a failed emission test results in a defect notice to replace the cats having reached their effective service life instead of the emission tampering charge and EPA sanction you'd receive with long tube headers and a modified/aftermarket cat arrangement.

Years ago i did shorty headers on my VE with the factory cats modded, later when bug hit put a cam in. cant remember exact figures but with pacie 4>1 headers and highflow cats made like 5rwk more up very high gains only over 4ooorpm. The factory cats do flow well when modded.

 

[blackvxss]

Ive got the 100 CPI cats that GM Motorsport make, specifically for the Rex headers……

They seem ok…..

got them on my VF and seem good only done 21000k though

 

[RevNev]

Years ago i did shorty headers on my VE with the factory cats modded,

What was "modded" with the factory cats out of interest?

 

[Ginger Beer]

I had some VF SS cats that I gave to a mate, he then cut the ends to suit some 3" pipe and he said it passed an emissions test with a camed LS when he was getting it regoed/engineered