2.5 Inch exhaust to small?

[WicKeD_SS]

I would like to know is 2.5 Inch exhaust would be to small for a 650 to 700 HP BBC? I have a Ridetech 4 link and want tail pipes and stainless works has a kit for my 4 link but its 2.5. Would 3 inch be that much better ?

[Ron Sutton]

I would like to know is 2.5 Inch exhaust would be to small for a 650 to 700 HP BBC? I have a Ridetech 4 link and want tail pipes and stainless works has a kit for my 4 link but its 2.5. Would 3 inch be that much better ?

2.5" is not optimum for 650 to 700 HP. If you want to pick a hp number & max rpm you care about, I'll run some quick calcs and post the diameter you should run.

[MarkM66]

Personally, if it was my only option, I'd rather sacrifice a few hp, and have it go over the axle.

[Twoblackmarks...]

What about loudness, is that any problem?

You can have 3 inch into the muffler and 2.5" out of the mufflers?
To help quiet it Down, and easier to fit in the rear too. :)

[Vegas69]

Personally, if it was my only option, I'd rather sacrifice a few hp, and have it go over the axle.

What about loudness, is that any problem?

You can have 3 inch into the muffler and 2.5" out of the mufflers?
To help quiet it Down, and easier to fit in the rear too. :)

Yep, If I had kept my car it would have 2.5" tail pipes after the muffler.

[Bsinclair]

I have a 3" stainless back to my mufflers also on my 68 camaro ride tech 4bar set up. With the muscle bar in place I do not have enough room to run even 2.5" over my axle. Ridetech recomends going under the rearend which im not a big fan of. The 48hr car is done this way and looks good but its also blacked out so you dont notice it from behind. I used vband connections on the entire system and welded the outlet of the muffler with one to later install tailpipes. I think if I run them under the rear I will end up ceramic coating them black so they are hidden.

[FETorino]

Hot gas needs more room than cool gas. Go 3" to the mufflers for sure. The restriction from the muffler back created by the 2.5" pipe won't be that bad. Of course if your 3" muffler's cfm rating (if it exists) is less that 750 each then that is your cork anyway.

From one exhaust article I read and saved a while back.

Once the available flow exceeds about 2.2 cfm per hp, the gains possible by increasing muffler capacity drop to less than 1 percent.

Knowing that 2.2 cfm per open-pipe hp means zero loss from backpressure allows us to determine how much muffler flow your engine needs. Just make a reasonable estimate of its open exhaust power potential and multiply by 2.2. For instance, a V-8 making 700 horsepower on open exhaust will require 700 x 2.2 = 1540 cfm.

A section of straight pipe the length of a typical muffler, rated at the same test pressure as a carb (10.5 inches of mercury), flows about 115 cfm per square inch. Given this flow rating, we will see about 560 cfm from a 2.5-inch pipe. Houston we have a problem.:(



Read more: http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/viewall.html#ixzz2eyrgMmkk

:cheers:

[Ketzer]

Personally, if it was my only option, I'd rather sacrifice a few hp, and have it go over the axle.

^^ This ^^

That being said... My car also BBC, 600+ hp has a really poorly done 2.5 exhaust (crimped in the bends). I hope to revamp this winter so interested to hear what everyone says...


Jeff-

[Ron Sutton]

Hot gas needs more room than cool gas. Go 3" to the mufflers for sure. The restriction from the muffler back created by the 2.5" pipe won't be that bad. Of course if your 3" muffler's cfm rating (if it exists) is less that 750 each then that is your cork anyway.

From one exhaust article I read and saved a while back.

Once the available flow exceeds about 2.2 cfm per hp, the gains possible by increasing muffler capacity drop to less than 1 percent.

Knowing that 2.2 cfm per open-pipe hp means zero loss from backpressure allows us to determine how much muffler flow your engine needs. Just make a reasonable estimate of its open exhaust power potential and multiply by 2.2. For instance, a V-8 making 700 horsepower on open exhaust will require 700 x 2.2 = 1540 cfm.

A section of straight pipe the length of a typical muffler, rated at the same test pressure as a carb (10.5 inches of mercury), flows about 115 cfm per square inch. Given this flow rating, we will see about 560 cfm from a 2.5-inch pipe. Houston we have a problem.:(



Read more: http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/viewall.html#ixzz2eyrgMmkk

:cheers:

This is correct is you're looking for optimum power. If you're not looking for optimum power, what is the purpose of the question?

[Vegas69]

Drivability, dumps get old from a noise and dust perspective on a street car.

I take my previous statement back, 3" over the axle with modifications to your trunk or under with black powder coating is my pick with this hp level.

[DaleTx]

X2 ^^^

My car has a 670HP 427” and makes peak power at 6,900 rpm. I ran 3" exhaust with 2.5" tail pipes at first, and then switched to 3" tail pipes. After having tried both set ups… I would recommend 3” all the way for sure. I didn’t think the 2.5” would restrict it that much but when I made the switch… there was a noticeable difference up in the higher rpm range. The engine responded well with the larger diameter tail pipes. I don’t have numbers to back this up… just seat of the pants feel. Also, the 3” tail pipes sound better and have a deeper tone than the 2.5".

[Flash68]

No way I'd run a 2.5 inch exhaust on that engine with that power. I don't need science to tell me that. :D

[FETorino]

No way I'd run a 2.5 inch exhaust on that engine with that power. I don't need science to tell me that. :D

But you're just more in tune with your emotional side than the rest of us. You just feel things.:rolleyes:

The rest of us have to rely on hard facts.

:cheers:

[GregWeld]

Gee ---- In the old days if we wanted max hp we uncorked the headers!


Seriously - how often do you need "max" hp on the street....

[GregWeld]

No way I'd run a 2.5 inch exhaust on that engine with that power. I don't need science to tell me that. :D



Agree....

[Flash68]

Gee ---- In the old days if we wanted max hp we uncorked the headers!




Sure, but then Rob :y0!: will link some article that shows you that uncorked isn't always best for max power. You know, cold hard facts and stuff.

:rules:

[FETorino]

Sure, but then Rob :y0!: will link some article that shows you that uncorked isn't always best for max power. You know, cold hard facts and stuff.

:rules:


Next time I'll just post "I feel a 3" pipe will really wake that motor up" since that seems to be what you want.:lostmarbles:

:action-smiley-027:

:cheers:

[GregWeld]

I'm not arguing with Rob --- he carries the GOLD Starbucks card and sadly -- Flashy -- you don't.


Coffee makes me FEEL like I have more HP and makes me rev more freely too! So I gotta go with my seat of the pants evaluation.


Technically -- I think it's just the caffeine...

[GregWeld]

BTW DAVE --- Have you ever walked SEMA with ROB and RON????


They go from booth to booth - never really seeing the killer cars or the hot chicks -- but man can they talk smack with the engineers!


HAHAHAHAHAHAHAHAHA

[FETorino]

I'm not arguing with Rob --- he carries the GOLD Starbucks card and sadly -- Flashy -- you don't.


Coffee makes me FEEL like I have more HP and makes me rev more freely too! So I gotta go with my seat of the pants evaluation.


Technically -- I think it's just the caffeine...

I thought Dave was already on the hook for your Coffee this time. :mock:

BTW DAVE --- Have you ever walked SEMA with ROB and RON????


They go from booth to booth - never really seeing the killer cars or the hot chicks -- but man can they talk smack with the engineers!


HAHAHAHAHAHAHAHAHA


I'm calling BS and offer a pinhole camera photo of the #1 reason to go to SEMA last year as evidence of my focus.

Don't hate me cuz I'm a multitasker.

:cheers:


http://i291.photobucket.com/albums/ll306/superjinca/LasVegas-20121031-00682_zps4292a6d4.jpg (http://s291.photobucket.com/user/superjinca/media/LasVegas-20121031-00682_zps4292a6d4.jpg.html)

[WicKeD_SS]

Wow thanks for all the help guys think ill just make 3 " work under or over with trunk mods... Thanks again!

-Brian

[GregWeld]

Brian ---


This group is always too happy to help you expend maximum effort and money building your car!!


HAHAHAHAHAHA



Sadly --- The help is pretty dang accurate and usually comes from "been there done that".

Do it right and do it once.

[Ketzer]

What about the oval exhaust? Never see it used? Seems like you could gain just enough clearance if you planned the bends correctly?


Jeff-

[FETorino]

What about the oval exhaust? Never see it used? Seems like you could gain just enough clearance if you planned the bends correctly?


Jeff-

Spintech has a chart of their oval stuff and how it sizes compared to the roundy round stuff.

:cheers:

http://i291.photobucket.com/albums/ll306/superjinca/ovaltubeschart_zps2aed517b.jpg (http://s291.photobucket.com/user/superjinca/media/ovaltubeschart_zps2aed517b.jpg.html)

http://www.spintechmufflers.com/images/uploads/oval%20tubes%20chart.pdf

[meenaggie]

Here is 3" over the rear axle and out the back in my 68 camaro running Ride Tech air bar, Rick's tank stock width with notched corners and DSE mini tub. The 3" is a cut up (highly modified) Dynatech kit. In short, it will work without the trunk mods. Shocks are hanging so rear end could be raised to ensure clearance.

[Ketzer]

Looks like clipped corners are a must.



Jeff-

[meenaggie]

Yes, notched corners are a must. No way it would of fit without the notched corners unless the trunk floor plan was heavily modified. Rick's offers the tanks with clipped corners as a "standard" option. Bends over the axle and mandrel bent so no crimped area or restriction.