J-spec technical questions...Help!!

[mikeyb10supra]

Hey Guys

 

Lovely weather were having down here just got soaked on my way to work in London......gotta love it!!!!

 

Anyway back to business......and before anyone says anything I did search for this but could not find anything that answers my question

 

Right......my Second CAT(at least I think its the second one) the one closest to the Exhaust is rattling like F*ck and its driving me mental.....now im fortunate that I have a freind of the family who owns an exhaust shop and has all the machines to custom make me a de-cat pipe for me.

I will fully de-cat in the future but for now I just want to replace this one as its driving me mental....so my question is, could I get one made up with a 3" bore or would this be to much......also I know if I replace both I will get overboosting probs.....will the same apply if I replace just one with a large Diameter pipe and would it be wise to fit a restrictor ring ??

 

Thanks again

 

Mikey

[Guest paperboy]

I have a second decat only, not sure what diameter it is but deff. no need to fit a rest. ring simply makes the turbos spool faster

[mikeyb10supra]

Thanks for the reply

 

 

do you have a boost gague?? what sort of boost are you hitting with the de-cat in, you need to keep an eye on it cos it will screw your turbo's quickly if its creeping over 18psi

[mikeyb10supra]

^bump

[Nic]

You should be okay if you only remove the second cat, I would guess you'll be hitting around 0.9bar max.

 

The first cat nearest the turbos is the most restrictive, if this is removed on a J-spec then you will normally boost over 1bar and need to fit an FCD.

 

3" is the average size for most aftermarket exhaust systems, some go up to 4".

 

Why not get rid of both cats, fit an FCD and restrictor ring to limit boost to 1bar, this will absolutely bring the car alive.

[mikeyb10supra]

Thanks Nic

 

So will I be ok with a large 3" de-cat pipe the same as my cat-back exhaust Piping??

I dont want to go to mad in case the boost gets out of control

 

I will fully de-cat soon, only thing is its £££ thats the issues at the mo

 

So just going to remove the one for now because its rattling like anything

[Jspec Germany]

You should be okay if you only remove the second cat, I would guess you'll be hitting around 0.9bar max.

 

The first cat nearest the turbos is the most restrictive, if this is removed on a J-spec then you will normally boost over 1bar and need to fit an FCD.

 

3" is the average size for most aftermarket exhaust systems, some go up to 4".

 

Why not get rid of both cats, fit an FCD and FCD to limit boost to 1bar, this will absolutely bring the car alive.

 

Learning everyday. Some questions to piggy-back on this thread. I've got a Blitz boost gauge fitted in my pillar pod that shows full-boost to .8 bar at WOT. Is this possible with only an HKS Super-Dragger and HKS hardpipe/filter? Pretty sure both cats are still in place. If I go to a 3" 2nd Decat (probably from CW), is it a straight bolt in or do I need to worry about any sensors plugging in (Jspec auto), and should I worry about boost getting to 1 bar? I'd like to keep the stock turbo configuration for now and don't wanna run em too hard as this is a 2nd car daily driver. Just a little extra kick in the arse. Car has 130,000 kms on it and can't go single for at least a year or more. Thanks for all the good dope. Joining this club has been the best move I've made since buying the car.

[Nic]

Thanks Nic

 

So will I be ok with a large 3" de-cat pipe the same as my cat-back exhaust Piping??

I dont want to go to mad in case the boost gets out of control

 

I will fully de-cat soon, only thing is its £££ thats the issues at the mo

 

So just going to remove the one for now because its rattling like anything

 

Yes you should be okay replacing second cat with the 3" decat pipe, although it does vary from car to car and also it will depend how un/restrictive your cat back exhaust is. I'd say go for it, the most you are going to boost is to 1bar, anything over this and you'll hit stock fuel cut.

 

Next mod I would suggest is a boost gauge, you can get mechanical ones quite cheap if money's tight

[mikeyb10supra]

Yeah I did toy with the idea of a mechanical one but thought I may hold out for an electrical one......are the mechanical ones very accurate in your opinion?

[Nic]

Learning everyday. Some questions to piggy-back on this thread. I've got a Blitz boost gauge fitted in my pillar pod that shows full-boost to .8 bar at WOT. Is this possible with only an HKS Super-Dragger and HKS hardpipe/filter? Pretty sure both cats are still in place. If I go to a 3" 2nd Decat (probably from CW), is it a straight bolt in or do I need to worry about any sensors plugging in (Jspec auto), and should I worry about boost getting to 1 bar? I'd like to keep the stock turbo configuration for now and don't wanna run em too hard as this is a 2nd car daily driver. Just a little extra kick in the arse. Car has 130,000 kms on it and can't go single for at least a year or more. Thanks for all the good dope. Joining this club has been the best move I've made since buying the car.

 

Stock boost is around 0.8bar so yours sounds completely normal. Yes 2nd cat is simple bolt on. The max you will be able to boost to (assuming you don't already have a Fuel Cut Defender fitted) is 1bar if the ECU senses over this, it will automatically cut the fuel.

 

If you are buying the decat pipe from Chris I would give him a call, he is a very helpful guy and I'm sure will be glad to answer any other questions you have. If you do find you are hitting fuel cut at WOT then Chris can supply a restrictor ring for you to limit boost.

[Nic]

Yeah I did toy with the idea of a mechanical one but thought I may hold out for an electrical one......are the mechanical ones very accurate in your opinion?

 

Chris Wilson swears by them, personally I've always had electronic ones on my car so can't really comment.

[eyefi]

you probably wont overboost with one cat still in place but when you fully decat a 3" pipe will overboost.

 

stepping up and down sizes in exhaust pipe cross section will increase back pressure and turbulance, not good. ideally you want a smaller smooth pipe that's the same diam.

 

why do you want to use a bigger pipe than is necessary or useful?

[mikeyb10supra]

Thanks for the response

 

So should I opt for a pipe the same size as my exhast cat-back pipe then??

[eyefi]

no, decat as small as possible (CW size is about optimum). stepping up a size when you hit the cat back is no big deal. i doubt you'd like a 2.25" exhaust (i wouldn't) my point was just really to avoid stepping up or down sizes if possible and a 3" 2nd decat isnt going to help any so why bother?

[Jspec Germany]

How big is the HKS Super Dragger Exhaust? I thought it was 3", but I could be wrong. Big f*cking pipe, I tell you that much. It would make sense to use a decat pipe the same size as the cat-back exhaust, especially if leaving the front cat on, wouldn't it?

[eyefi]

if yr definately going to leave the front cat on then yes i would match the catback. i think he's going to remove the front cat later though.

[jase_93tt]

My apexi gt spec front pipe is 75-80mm bore, the blitz middle pipe looks to be around 80mm at sight, all coupled up to an Apexi N1 rear section which measures 85-95mm bore.

 

On a turbo car, the quicker you get the exhaust gases out, the better IMHO. Who cares about boost creep, fit a boost controller to help control the boost and an TRL VFCC to raise the fuel cut limit and give you some overboost protection and away you go.

 

Just make sure youve got plenty of fuel and the sparkies are a grade colder

[Jake]

Who cares about boost creep, fit a boost controller to help control the boost and an TRL VFCC to raise the fuel cut limit and give you some overboost protection and away you go.

Please don't post 'advice' like this in the tech section. You clearly don't know what you're talking about.

[mikeyb10supra]

Agreed Jake.........he will care when he has to replace his turbos in two weeks

 

And FYI JaseTT a boost controller will not control boost only raise it.....hence the boost restriction plate which will hold it at a resonable level and then you can use the controller to raise it slightly.....your running the risk of having out of control boost which you cannot harness!!

And a FCD will not give you overboost protection if anything it will make it worse for you by allowing essesive boost with no restrictor ring fitted!!

read your boost gague JaseTT if its over 17-18psi your Screwing your turbos in a big way and they wont last 5 mins

[JohnA]

...On a turbo car, the quicker you get the exhaust gases out, the better IMHO.

 

...humble indeed....

Have you ever thought what really spins a turbo? Kinetic engergy or heat?

....Heat I hear you say?

so why then are you keen to get rid of all of it ASAP?

...and what about combustion chamber temps? If they had to be really low, F1 cars would be running cryogenic setups.

 

Food for thought, regarding generalisations....

[Jspec Germany]

Wow, a lot of different opinions here. Some that make more sense than others. So bottom line, I need to find out what the diameter of my Super-Dragger is and then buy a 2nd decat to match. If I eventually get the 1st decat, I'm gonna' need to fit a restrictor ring, upgrade the fuel pump, and get a boost controller which also monitors and raises boost, but doesn't limit it. I already have a blitz mechanical boost guage in a pillar pod. For now, I'd like to concentrate on keeping the stock turbos, but running .9-1.0 boost safely and reliably.

[mikeyb10supra]

...humble indeed....

Have you ever thought what really spins a turbo? Kinetic engergy or heat?

....Heat I hear you say?

so why then are you keen to get rid of all of it ASAP?

...and what about combustion chamber temps? If they had to be really low, F1 cars would be running cryogenic setups.

 

Food for thought, regarding generalisations....

 

 

I think he is refering to back pressure mate....if thats the case then he is correct.....less back pressure = more POWER

[JohnA]

I think he is refering to back pressure mate....if thats the case then he is correct.....less back pressure = more POWER

Not always (without readjusting everything for a new balance)

And backpressure is not the only game in town.

 

That's why blanket statements and generalisations can lead to inaccurate interpretations.

[jase_93tt]

My comment was a err'ing on the comical side and wasnt actually intended to be taken seriously. :0

 

On a more personal and serious note - Ive removed both de-cats and have a very free flowing exhaust. Under heavyload, the boost shoots very quickly to 1.25 bar. Fitting a restrictor ring to bring the boost down to safer levels is necessary. Im going to bring mine back down to 0.9bar or so and then use the controller to raise it to whatever pressure I require. At the moment, the profec isnt doing jack as it can only increase the boost.

 

HTH

 

J

[Jspec Germany]

Ok, got the Apexi 2nd decat from Supradibbs, just need to make some gaskets and get it fitted. Hope the bore is the same diameter as my Super-dragger and there's no issues with the flange bolting up to the stock 1st cat. No boost controller yet either. When do colder plugs become necessary? If I leave the 1st cat in place for awhile will I be safe running at or around .9 bar? Walbro is planned for August. Thanks.