The squish section of exhaust

[kmckmc]

Hi,

Does it make sense to replace the squish section with a round section?

What options are out there?


Cheers,

[davidjt]

Depends what else you plan to do or have already done: the squish may account for a few bhp, but for example flowing or replacing the pre-cat housing would probably be more useful. From the point of view of gas flow it's 'orrible.

[kmckmc]

HI,

I have already taken out the main cat, and I intend to keep the pre-cat.

So, I was just wondering what kind of additional advantage my Elan will gain by replacing the squish with a round section.

Cheers,

[Enright]

You MAY find that you experience boost creep to the point where you reach the fuel cut-off point.
Admittedly it's unlikely with the pre-cat still in, but it is possible.
If that happens, the only solution is to either re-fit the squished part or port the wastegate.

[kmckmc]

You MAY find that you experience boost creep to the point where you reach the fuel cut-off point.
Admittedly it's unlikely with the pre-cat still in, but it is possible.
If that happens, the only solution is to either re-fit the squished part or port the wastegate.

I was concerned that my Elan might not pass the emission test if I were to taken out both the main cat and pre-cat. So, I decided to keep the pre-cat.

In my case (pre-cat still intact), if there is no significant benefit associated with replacing the "squish," I will not bother.

Thanks.

[Enright]

What is the pass limit for the emission test where you live?
I may be able to tell you how close your car will be able to get to it.

[kmckmc]

My intended set up:

With Pre-cat, main-cat already taken away, replacing the squish with a round section.

What kind of gains will my Elan get?

Cheers,

[Enright]

I don't know.
I have a 91 SE which has no pre-cat or main cat.
It was recently emissions tested at 0.68% CO (the pass rate for non-catalytic converter equipped cars here is 3.50%), and hydrocarbons were 103ppm (the pass limit is 3500).

[Doug]

i agree that removing or hollowing out the cat cells from the pre-cat is a better benefit to flow in the Elan than removing the main cat

if I had to pick (and I did on my car in the past), I'd vote to remove/replace/or hollow the precat and replace the main cat with a goo new one -- the main cat is tons more efficient for emissions than the tiny pre-cat.

[Dave M]

if I had to pick (and I did on my car in the past), I'd vote to remove/replace/or hollow the precat and replace the main cat with a goo new one -- the main cat is tons more efficient for emissions than the tiny pre-cat.

There is a lot of horsepower available in intake/exhaust improvements, but boost creep continues to come up again and again as soon as the exhaust is opened up. You can try a replacement, but it might be money wasted if you keep hitting the fuel cut-off. It's my hope that someday I can try some R&D on Peely and prototype an O2 housing/downpipe with a separate runner for the wastegate. Hopefully this would help on the creep side and improve overall flow. We'll see how much time I get over the summer to try.

FWIW, years ago I replaced my exhaust with a new high-flow cat and no "squish" along with an identically-sized intake (both 2.5") and saw maximum HP go up 25. The max HP increase was 40 at different rpm. Granted, this was running 20 psi, but it gives you an idea of the power available.

[palchiu]

kmc, your special made exhaust system is done?