Im trying to get de cat pipes for my 92 manual jap import N/A. Ive heard that doing this wil sustantialy increase the old BHP ! Is this the case ? Do you know any companies that sell them ?

 

Cheers Mike

Not sure about "substantial" but it is an improvement. Not as much as de-catting a TT though, but still worth doing, for the better exhaust note at the very least!

Check the LINKS for places that sell them.....Z Center etc.

This is likely to make an N/A much louder - excellent !

 

Please check the trade forums first - support our traders - they help support our bulletin board.

10 ish bhp on a tt

check this mate, we just decatted my missus NA on Monday.

 

http://www.300zx-mods.co.uk/images/vids/CatVDecat.wmv

Stu - it's password protected????

:confused:

Not when I click on it its not.

Nigel - the password is "numptie" ;)

If your car is a daily driver then think twice before decatting an NA.....It will be very loud especially with aftermarket cans.

If its a weekend car than go ahead....It will dull the low end response, but should increase power at the top end!:D

Hmm, it's something I've been thinking about, but I've got a SWB, so I figured it might be hard to find something off-the-shelf. Got my local custom SS bloke to have a look - he said the Z's he'd seen had one of two different arrangments for the cat section, and mine was the more expensive one :( Dunno how right this is, of course ;)

If I could find SWB off-the-shelf, would I be using the same as a TT? I assumed not because of back pressure issues, but I know nothing :/

 

Anyway, what also concerned me was that the NA crawls off the line like a bloated dog, so what's this gonna be like with the reduced low-end grunt that de-catting brings? It's possible my cats are clogged with muck - would that explain sluggish pull-offs?

 

Heh, mine is a daily driver, with two 3.5" Apexi backboxes - didn't realise there'd be any chance of it getting *louder*, and not sure whether it bothers me as long as it's legal :P

I've never heard of it dulling the low end response :confused: Revs pick up quicker so that can only help can't it?

 

Mine's decatted, but was when I got it.

Mine is an NA, decatted straight through SS, Not a daily driver as such, but certainly drive it most day, nice rumble when started, gets "sportier" when standing on the loud peddle. havent noticed any depreciation on idle, but the car was crap off idle when i got it, just means givimg the peddle a bit more

Originally posted by baby ice dog

Hmm, it's something I've been thinking about, but I've got a SWB, so I figured it might be hard to find something off-the-shelf

The cat or decat section of the pipe is the same for SWB / LWB / NA / TT.

 

The only difference is the rear.

Ah, the same eh? Good, thanks :) What about back pressure issues from using a TT de-cat? I guess if Jock's is straight through, then it can't be much of a problem, right?

 

As for Pete, well... I'd heard a couple of times that reducing the back pressure in an NA would give weaker low end, but better high end, response. SS man kinda backed this up, but still reckoned de-catting was worthwhile because they're such a gunk-trap - back pressure could be maintained by using a smaller diameter pipe for the replacement section than one would for a TT. I dunno how much sense this makes - is he saying here that a gunky cat provides *too much* resistance? :S Pff, custom SS was gonna cost a bomb anyway.. as long as a TT de-cat isn't really going to screw things up, I'll go with that :)

 

Anyway, sorted - nippier revs would be nice, being able to use 2+2 bits makes it easy & cheaper, and if Jock isn't complaining about performance then it's almost certainly gonna be an improvement on what I have :D Yay! Thanks everyone :)

I thought TT vs. NA had different diameter exhaust? I could be imagining that :D

 

Reducing the backpressure on an NA will lose you low down torque, but gain high end power, yes.. The reason being that the exhaust gasses start moving that much faster that at low revs you start over-scavenging the cylinders (sucking part of the fuel/air mixture from the next cycle out of the cylinder before the exhaust valve gets chance to shut). At least if my memory of the theory is right, anyway.

 

On a TT, you get all the backpressure you need (with respect to cylinder scavenging, anyway) from the turbos.

I dunno the airflow theory in any detail, but...

 

General tuning theory is that on an NA engine you tune for power at revs and let high gear ratios deliver your torque; on a turbo you tune the engine for monstrous torque at the crank everywhere in the rev range, and use lower gear ratios so you have to change gear less often. (Gear change in a turbo introduces lag, so it's a bad thing.)

 

This is why the NA has a higher final drive than the TT, and it's also why the TT has a higher top speed once delimited.

 

Er, or something.

Originally posted by smw1

check this mate, we just decatted my missus NA on Monday.

I still have yet to test the performance on my decatted Z NA.

 

I was surprised to find it now has a quieter idle but sounds a lot meatier in the higher rpm range though.

 

I'll keep you posted on the performance when I get a chance to test it properly.

Haven't had a chance???????

 

Get out there! :D

I dont think i will bother - already got crap low pull off! - and becaueof my apex 4" cans - its loud anyway when its at high rpm! Thank you for your responces though

Mike