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Cat Size?

levinboy

By levinboy,
in Engines & Forced Induction

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levinboy Grand Master

levinboy

Posted
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Hey all quick question had my exhaust checked out as it was hanging a little low, and realised i had a a full kakimoto exhaust haha only bought the car at the end of feb ;) so score.

My question to you all is what size cat should i run as it still has the compliance cat on it :( , the size of the exhaust is about 3.5 inches so i was thinking 3.5 or would a 3inch cat be alright??

Any help would be greatly appreciated

Thanks

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levinboy Grand Master

levinboy

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what size is the exhaust?

Bit surprised you didnt notice... given the fact it would be signifigantly louder than factory...

The Kakimoto exhaust is actually really quiet most people are surprised that it is that quiet, i knew it had the catback but wasnt sure on the front pipes and yesterday i confirmed it.

It looks to be around 3.5 inches

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R31Nismoid Grand Master

R31Nismoid

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The Kakimoto exhaust is actually really quiet most people are surprised that it is that quiet, i knew it had the catback but wasnt sure on the front pipes and yesterday i confirmed it.

It looks to be around 3.5 inches

I suggest you have a good look and measure :)

3.5" exhaust = 4" cat min

3" exhaust = 3.5" cat min (although i would still use a 4")

You can get 4.5" items IIRC but i dont think you need to go that large

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levinboy Grand Master

levinboy

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I suggest you have a good look and measure :)

3.5" exhaust = 4" cat min

3" exhaust = 3.5" cat min (although i would still use a 4")

You can get 4.5" items IIRC but i dont think you need to go that large

ill have a good look and measure hopefully tomorrow

then start shopping around :)

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R31Nismoid Grand Master

R31Nismoid

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Would it matter if you use say a 3.5" cat with a 3" cat back? Wouldn't the exhaust gas going from 3.5" and hitting the 3" flange be a restriction?

No because have a look @ a CAT

It’s a honeycomb, there is no way its going to flow as much as an unimpeded straight piece of pipe not matter what the manufacturers “claim” they flow, so hence I’ve always been a firm believer of 3.5” at a minimum, preferably 4” if you can.

All you do is weld 3” flanges to it and have it taper to 3.5” or 4”, pretty common stuff and any exhaust shop will be able to do it.

The CAT poses a big restriction if you are making reasonable power.

Even with only 280rwkw currently and a 3.5” exhaust… I can tell if I have my 4” CATCO “Hi-Flow” CAT in the car, is just a straight 3.5” pipe of pipe.

It’s not major, but you can feel the difference so there is at least some minor restriction even @ what I would call mild power levels by todays standards.

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GTScotT Grand Master

GTScotT

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I suggest you have a good look and measure :D

3.5" exhaust = 4" cat min

3" exhaust = 3.5" cat min (although i would still use a 4")

You can get 4.5" items IIRC but i dont think you need to go that large

Ash, this info is a little misleading, could you please clarify.

Someone may interpret this info as the flange size. The ID of flanges should never step down in line of flow. IE having a 4" flanged cat meet a 3.5" flange on a catback is bound to cause turbulence issues.

From experience, a cat with 75mm ID meeting a 80mm front pipe on a fairly typical SR setup held back power by roughly 50rwkw. FYI gutting the cat did not help either, yet sure enough replacing with an 80mm cat to match fixed everything.

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rob82 Mentor

rob82

Posted
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3in 100 cell will flow upto 250-280rwkw

3.5in 100 cell will flow upto 300-330rwkw

4in 100 cell will flow 360-400rwkw

5in 100 cell will flow around 500rwkw

if you double the cell count you knock off about 25% of the previous figures. Most 100 and even 200 cell cats won't meet euro4 emmissions. For that you need at least 400cell. Hence why c63 amg have twin 7in cats to make the poer they do and still meet emmissions.

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scotty nm35 Grand Master

scotty nm35

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Im currently running one of the Loboka 100cpsi fleabay cats. They slip on to a 3 inch pipe, have a 4 inch body and seem to flow quite well, just got 245awkw at RE with one fitted last night. At $150 its a bargain I think. Any larger than a 4 inch body and you will most likely have ground clearance issues.

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juggernaut1 Proficient

juggernaut1

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IMO I'd be running whatever cat flows the same as the rest of your exhaust.

You have a 3.5 inch exhaust .....so 3.5 inch flanged 100cpi cat with 5 inch body might be the go.

CES sell this spec.....Ballistic cats can also be had in this spec off the shelf:

http://www.surefloexhaust.com.au/cc.htm

Currently in the process of fitting the CES cat and it looks like a quality item as you would expect.....the honeycomb in my Metal Cat collapsed and wedged itself at the back of the cat body.

Edited by juggernaut1
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SiR_RB Grand Master

SiR_RB

Posted
Posted (edited)

I'm assuming the 200 cell cats flow more than the 100 cell?

I've got a 3" xforce high flow on mine atm, and was thinking of changing it to a 3" catco metalcat, flows up to 709cfm. Only stickiNg with the 3" cat cos my hks cat back is also 3".

Anyone tried this cat before?

Edited by SiR_RB
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levinboy Grand Master

levinboy

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I suggest you have a good look and measure :P

Meaured quickly today looks to be just under 3.5inch

Ah k thanks ! Who sells 100 cell cats with the skyline flanges already welded on? All complete bolt on cats that I've come across are 200cell

I know just jap sell the 3" catco cats at a really good price

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R31Nismoid Grand Master

R31Nismoid

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Ash, this info is a little misleading, could you please clarify.

Someone may interpret this info as the flange size. The ID of flanges should never step down in line of flow. IE having a 4" flanged cat meet a 3.5" flange on a catback is bound to cause turbulence issues.

From experience, a cat with 75mm ID meeting a 80mm front pipe on a fairly typical SR setup held back power by roughly 50rwkw. FYI gutting the cat did not help either, yet sure enough replacing with an 80mm cat to match fixed everything.

Ah ye sorry - brain non functional moment :P

Taper upto the flange rather than down... NFI what i was thinking :D

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