How much flow needed thru cats

[mycarhasposessedme]

Hi guys,
I have an opportunity to get in on a group buy of a metal substrate
cat for my project.
It has a 4inch body and necks down to 3 1/2 at each end.
My engine is setup as a twin turbo, designed to make 600hp.
I have 3inch down pipes from the rear of the turbo's.
I intend on running a 3 1/2 inch single system but am unsure on whether to run 1 or 2 cats.
For example merge the pipes before the cat with a single cat system or merge after the cats with a twin cat system.
I would prefer to run only one cat as it fits easier on my project but dont want to restrict exhaust flow.
The manufacturers claim up to 50% more flow over a conventional ceramic cat.
Personally I feel that this cat will be okay to run only one without creating a restriction at this power level, but I could be totally wrong.
Any input would be greatly appreciated
Cheers
Trev
(edit) the pics below are the same 4inch body but have been reduced to 3inch in and out

 

[Zuffen]

As it's only flowing 535 or so CFM it looks a bit light on for 600hp.

 

[mycarhasposessedme]

Thanks Rod,
I think that the 535cfm flow that they show in the pics is only to demonstrate the loss compared to 589cfm flowing in.
As the chart shows maximun flow rate set at 589.
It doesn't mention how many inches of water its at either so hard to read anything from it.
I seem to recall that 2.2cfm per hp at 5-6 inches of water is whats needed for a free flowing system.
I'll look further and see if I can find anymore flow figures.
Cheers

 

[mycarhasposessedme]

Hmmm yes its looking like I may need 2.
Maybe two 3inch versions then merge into a 3.5 inch single system.
My brain hurts from reading exhaust stuff, betta go to bed.

 

[400ZED]

i was running 6 pound bcak pressure before my cats and i could not find anyone to tell me how much i was meant to have i removed the cats and got down to 2 pound. with maybe some smal horse power increase, but some other things changed at the same time.

measurements were taken at 5-6000 prm on the dyno. after i got the measurments no one could tell me what pressure i should have.
Have you guys heard anything about correct back pressure, suposidly less is not always best.

 

[TOBES]

I have always heard that back pressure in an exhaust should be as low as possible. I can't see any situation where back pressure would be any benefit.

Where people go wrong is they increase the pipe size to the max to reduce the back pressure and loose gas velocity in the system. This reduces the scavenging effect in your headers and X/Y pipes and looses power and torque, especislly at lower revs. They then decide that the back pressure is too low???

If you read JBrady's work he hammers this point.....

 

[Peewee]

Hmmm yes its looking like I may need 2.
Maybe two 3inch versions then merge into a 3.5 inch single system.

Much better idea.
Merge it after twin cats as the exhaust will be cooler.

 

[mycarhasposessedme]

Just a follow up on the cats, purchased 2x 4inch body, 3inch in and out, stainless metal cats, pics below.

 

[JBrady]

Very nice. I like your picture showing how well light goes through the core. Cats such as these create very little restriction.

You may want to fab some heat shielding as cats operate at very high temps.

 

[Gazzasore]

How many holes per square inch
200 high flow cats
400 normal cats