Exhaust Pressure Testing

[deanm11]

Thank you all for contribution to this thread. I have modified my setup based on it.. NA for now, maybe boost in the future. Full headers and pretty much straight through design components including the little pup mufflers someone mentioned and the longer Stainless Brothers bottle mufflers grafted in Borla S-type mid-section, into S-type mufflers. Its a few notches louder than I'd like. Especially cold morning startups...

I have a second set of S-type mufflers so I could easily experiment a bit. I think the Helmholtz setup is more about resonance than volume level... but is there a similar approach that might offer more of a volume reduction. I can open the can in the back next to the input elblow and 180 on top of the muffler like some aftermarket Helmholtz designs... question is what can I fit in only the about 13" muffler body length up top there that would possibly offer noticeable muffling... or some other modification to the mufflers? Maybe a baffle in the inlet elbow? Resonated tips ?

I see a number of inserts designed for sound attenuation though most are probably too big to fit in the short elbow in the S-type.

https://www.summitracing.com/parts/pte-h3844?rrec=true

https://www.summitracing.com/parts/cci-3di03r?rrec=true

https://www.summitracing.com/parts/sch-42530?rrec=true

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[WIST2019GT]

@engineermike quick question. I don't have a boost gauge but I went from a completely stock exhaust to long tubes without cats (fastory resonator and catback) and my airload stayed exactly the same. Should I have seen a drop in airload as I would see LESS boost with less restriction?

 

[engineermike]

@WIST2019GT no, air load is a function of airflow/rpm. With a centrif setup, reducing backpressure should result in a small increase in airflow, so airload would go up. Load is also strongly influenced by atmospheric conditions, so that can throw off the data.

 

[WIST2019GT]

@engineermike new question. If I added a wastegate to each side of my exhaust (not my exhaust, but - see image) and ran a say 3psi spring, when the exhaust back pressure hit 3psi ahead of the factory 2.25 neck down it would push the gates open allowing more flow. Would this work instead of running a full 3 inch exhaust?

 

[engineermike]

@WIST2019GT I’ve contemplated similar ideas myself. What size wastegate? A typical 44 mm would help but to get the most benefit would need larger. Also, you could actuate the wastegate with boost pressure which would open it before the exhaust had a chance to build backpressure.

 

[WIST2019GT]

@WIST2019GT I’ve contemplated similar ideas myself. What size wastegate? A typical 44 mm would help but to get the most benefit would need larger. Also, you could actuate the wastegate with boost pressure which would open it before the exhaust had a chance to build backpressure.

That was my thought as well. I was thinking a 38mm on both sides with a light spring. On a centi car like mine I could have it open at 3psi of boost. I am not sure how you would calculate flow, but looking at the 2.25 + 1.49 for a 38mm gate I think would outflow a 3 inch pipe?

 

[engineermike]

A closer estimate would be equivalent flow area, or the square root of the sum of the squares, about 2.7”. However the sum of the flow area is a rough estimation anyway because of the flow area to perimeter ratio is worse. Making it more accurate is a bit more complicated but it’s safe to say it will act smaller than 2.7”.

 

[WIST2019GT]

A closer estimate would be equivalent flow area, or the square root of the sum of the squares, about 2.7”. However the sum of the flow area is a rough estimation anyway because of the flow area to perimeter ratio is worse. Making it more accurate is a bit more complicated but it’s safe to say it will act smaller than 2.7”.

so I would be better off with two 44mm gates or maybe even 60mm gates.

 

[engineermike]

so I would be better off with two 44mm gates or maybe even 60mm gates.

If you want at least the flow area of dual 3” then you’ll need the 60’s.

 

[K4fxd]

Does this type of X pipe add any turbulence or back pressure?

 

[engineermike]

I think I’d want the narrowest point to maintain the total cross sectional area of both main pipes. It’s hard to say if that one does just looking at the pic but it does look better than some I’ve seen.

 

[K4fxd]

I think I’d want the narrowest point to maintain the total cross sectional area of both main pipes.

It is 3 inches at the intersection but is open to both pipes. The pipes are 3 inch ID. I can dig it out and snap a pic of the inside.

Link to amazon. Scroll down to reviews and there are several pics of the inside.
https://www.amazon.com/gp/product/B082TVK8KQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

 

[engineermike]

I like this one better for flow:

https://www.amazon.com/dp/B088WJMSXC/ref=emc_b_5_mob_i

 

[K4fxd]

I can't find any views of the inside but it looks to be 2.5 inch or 2.75 and necked up to 3 inch.

 

[engineermike]

Now that you say that, I agree. Maybe just stick with a good ole H pipe? Cooler with an adjustable orifice or valve in the crossover.

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