Integrated manifolds, flow, and power

My new car has an integrated exhaust manifold and I want to find a way to improve on it.

The integrated manifold has extended ports inside the cylinder head, dumping out through a large oval port. From that exit it goes directly to a close-coupled cat just below it.

I thought for sure I'd find some info on modifying the stock setup for increased power, but I've been unable to find anything other than a few people with 3.6  Impalas replacing the outlet tubing with larger, and/or higher than stock flow cats. Considering the number of vehicles on the road, some of them being performance oriented, with this kind of setup, I'm really surprised there's no tech info.

Any thoughts or ideas to make a little power? I'm open to pretty much any info.

EDIT: This is the engine/port. Would be great for a turbo application, and that may come. But for now, I'd just like to replace the stock setup with something better for power

I would think the usual rules for porting would apply just like anything else, just harder to access deeper in the casting. That's a surprisingly small hole, but man does it look like a great spot for a turbo.

More recent Honda K series have a similar setup, maybe looking down that rabbit hole will help with general theory on improving this sort of setup. 

This problem is old hat for the Ford 200ci I6, but on the intake side.  Such a pain in the ass for so long that I laughed out loud when I saw an engine with this setup in the junkyard.  Entire books have been written about getting around it.

Common solutions include:  Upgrade the head to one that doesn't have it.  Add spots for a triple 1bbl setup.  Sawzall/mill it flat and mount/weld a new flange.  Change the engine for something in the family that has a better head.  Some combination of the above. 

Here's which direction I am going https://m.imgur.com/a/JgHx3

Long story short, short of pulling the head and doing violent things to it with tools, you aren't gonna improve that side, so you should focus on other areas.

gearheadE30 said:

I would think the usual rules for porting would apply just like anything else, just harder to access deeper in the casting. That's a surprisingly small hole, but man does it look like a great spot for a turbo.

One adapter flange, one turbocharger and voila.

Peabody said:

Would be great for a turbo application, and that may come. But for now, I'd just like to replace the stock setup with something better for power

I'm sure I could do some porting to improve it, but the head's not coming off for now and I was wondering if replacing the stock manifold and close coupled cat with something more akin to a header/collector would be better.

These are my thoughts at this point: The cat isn't doing the power any favours. Eliminating, or replacing it with a high flow unit would probably help a lot. Yes? No?

The exhaust runs though the head and associated water jackets. That cools the flow, the main reason for this setup, so it doesn't exactly play by standard exhaust header rules. Maybe?

The manifold and gasket for every one of these I've ever seen, and I've seen a lot of the Honda ones, is significantly larger than the port. I assume this is done for anti-reversion, so that should stay. Yes?

The reason you're not seeing off-the-shelf headers is that primary cat. It's not legal to sell parts to delete it. You'll have to build your own.

In reply to Keith Tanner :

And there definitely wouldn't be anything for this particular car anyway, but you'd think there would at least be some tech info somewhere. Especially from the Honda, Camaro, and Cadillac applications. I can find zero tech info anywhere

Peabody said:

In reply to Keith Tanner :

And there definitely wouldn't be anything for this particular car anyway, but you'd think there would at least be some tech info somewhere. Especially from the Honda, Camaro, and Cadillac applications. I can find zero tech info anywhere

you have found the void.  now you must fill it.

Peabody said:

In reply to Keith Tanner :

And there definitely wouldn't be anything for this particular car anyway, but you'd think there would at least be some tech info somewhere. Especially from the Honda, Camaro, and Cadillac applications. I can find zero tech info anywhere

GRM did a catalyst comparison many years ago, and found little benefit to high flow cats or removing them all together.  

Given how big of a deal power and economy is, lots of effort is to put into flow when doing development.  One of the big reasons for integrated ports like that is to have great flow without any losses for emissions, lighting off the catalysts as soon as possible- and those benefits very much translate to power.  That also applies to light weight catalysts to get them to heat up ASAP- and at the same time, not getting too hot under full load.

We are way beyond the 70's when catalysts were first being used.

Aftermarket high flow cats can have a good result on a boosted car, but on an NA Miata (the GRM test vehicle) you'll never see much gain from exhaust mods especially with a stock muffler in place. The catted downpipe we offer for the Mazdaspeed is pretty darn effective, and we've seen results from swapping stock Miata cats for high flow ones on aftermarket turbo cars. The newest of those examples is from 2005 though, and it was an old car then.

On our ND turbo kits, we retain the stock cat in the stock location so it lights off fast.

The days of low-hanging fruit with a little IHE work are long gone.

AngryCorvair (Forum Supporter) said:

Peabody said:

In reply to Keith Tanner :

And there definitely wouldn't be anything for this particular car anyway, but you'd think there would at least be some tech info somewhere. Especially from the Honda, Camaro, and Cadillac applications. I can find zero tech info anywhere

you have found the void.  now you must fill it.

I did that for 20 years with the Suzukis. That energy has left the building.

Keith Tanner said:

The days of low-hanging fruit with a little IHE work are long gone.

I'm just fiddling at this point, it gives me something interesting to think about, and I know they're way better than they used to be.

But... back to back testing on the 5cyl Colorados showed a 17HP increase deleting the stock close coupled cat, no tune. I know that was a dozen years ago, but more recently, I think it was Magnaflow,  made high flow cat down pipes for the 3.6 Impalas that made a worthwhile difference.

EDIT: Just looked it up, 20HP/23lb.ft on the Impala

Are they that much better in that time?

I wouldn't expect any of this to make any noteworthy changes without a retune to go with it. IIRC in the GRM test the car actually made less power with the cat totally removed than with any of the aftermarket cats with them all on the same engine tune. I assume roughly the same would apply here.

The car is supported by HP tuners and will definitely be tuned.

I thought the big benefit to the integrated manifold was, aside from not having a manifold, and it's weight to deal with, was the increased fuel economy afforded by not having to enrich as much under load.

Regardless, I find it difficult to believe that you can't make some improvement by replacing the stock unit with something else. Compromises are plenty on mass production vehicles, and I'm surprised I can't find any tech on the subject.

In reply to Peabody :

As Keith pointed out, it's quite illegal to sell parts to do what you want.  So there's going to be very, very little public tech on the subject.

Well, Magnalow used to sell these products for the Impala but I really expected, considering the number of vehicles with this technology, to see at least something from the DIY community, or put a different way, it's become unusual to look for tech info of any kind these days and not find anything  

And it's piqued my interest 

The only way Maganaflow was able to sell a catalyst replacement was to show that it was still effective enough via testing.  That threshold has gotten much harder as regulations have progressed.   Meaning that it's become really hard for companies like Magnaflow to do that anymore.  Which is also to say really expensive.   Combine that with the likely very marginal performance returns means that it's not likely worth their time.   So just sell mufflers at a premium.

And thanks to a certain part of the modifier market, the EPA has really gotten more strict with enforcement- to the point that getting a usable HPTuners system has gotten a lot harder.

Which may explain why those systems were discontinued.
 Regardless, I was less interested in discussing cats and more interested in learning how to treat the flow from one of these cylinder heads for the purposes of making more power. Do you treat it like a shorty header? What's the best way to exit the large oval port and transition to the much smaller exhaust? Does it even matter?

One interesting thing, I measured the first  cat this morning and it's huge. The volume inside is roughly double the engine displacement. It reminded me of something Vizard used to talk about, an anti reversion box, which was supposed to be about double the displacement, and as close to the cylinder head as possible for the best gains.  

The reasons that cats are being discussed is that one of the the parts you want to modify has the catalyst attached to it.  

In terms of the port flows, I'd wager that a good CFD program will be very helpful in making meaningful changes.  Given that's what's used to design those ports and flows in the first place.  One thing to note, much of the acoustic tuning of the exhaust is defined by the location of the catalyst surface, which isn't going to change.