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Not long ago somebody posted if the exhaust could be too big for a mild moter. I am putting a stock 302 in my 73 mustang, as far as i know it is stock. I am eventually planning on putting in a healthy 351C or something quite a bit stronger. I was going to go with a 2 1/2 in dual setup, probably hooker comp headers, and turbo mufflers.

Would i be ok with this. I would much rather not have to put a new exhaust on when i put the new moter in, but this will probably be in there for quite a while, so i dont want it to be too big. If it is a little too big, how much would i be sacrificing?

73 coupe, T-5 tranny. if it matters
 

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2 1/2 is fine, its really the header primary size
 

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1 5/8 is junk go with a set of 2 1/2 headers, an h pipe, some flowmasters and some turn downs, this way you are done with it....foreever.
 

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ya 2 1/2 inch primaries on a 302, that oughta go over quite well
 

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Question, wouldn't exhaust gas velocity suffer because of headers that are larger then the exhaust port?

The way I think of it.... The collectors at the end of the header tubes...have a venturie effect. If you have smaller diameter tubes leaving the heads and meeting at the collector, as the exiting gas from ajacent tubes is flowing by the other header tubes, would it not creat a vacuum on the non operating tubes?

The smaller the header tubes the greater the vacuum, thus creating a scavaging effect when next that tubes exhuast valve opens... and instead of waiting for flow to be created from the exiting mixture from that stroke dumping into a large void... a smaller diameter header tube would be basicly like dumping into a vacuum. So as soon as the exhaust valve is opened, then there is already a vacuum there sucking the exhaust gas out....

Higher flow velocity of gases is a good thing... Right???
 

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Along these same lines, I want to make sure to size my exhaust correcty on my 64 Fairlane. 289 with mildly worked '68 302 4V heads, Performer 289, Perfomer 600, Comp XE256H, C4, 3.00.
I want to use Hooker 6134 headers and was considering full length true dual exhaust with 2 1/4" pipes and glasspacks. Would I be better off with 2 1/2" pipes?
 

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2 1/2" pipes fit well on most Mustangs. Anything larger is more difficult to fit, and anything smaller has no advantage. I think the concensus is that its header size that can be too big. On a stock 302 even 1 5/8" is big but not so big it will kill the low end. I would say run 1 5/8" headers unless your looking for top end out of your motor then maybe larger. If the headers are the right size for your aplication then the only thing to consider from there is the rest of the system large enough.
 

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I am running a set of bbk headers for 5.0l mustang that are 2 1/2", a bbk H pipe for a 5.0l mustang and it is 2 1/2" and 2 40 series flowmasters. There is not a better sounding street car for 200 miles.

But we run AFR 185's, Hydraulic Roller Comps Cam, Edelbrock Performer rpm 2 upper and lower intake, 70mm throttle body, and 75mm mass air.

It runs strong and sounds scary.
 

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On 2006-10-13 11:16, Smidgy wrote:
I am running a set of bbk headers for 5.0l mustang that are 2 1/2", a bbk H pipe for a 5.0l mustang and it is 2 1/2" and 2 40 series flowmasters. There is not a better sounding street car for 200 miles.

It runs strong and sounds scary.
Smidgy when you say you are running 2 1/2 headers are you referring to the primary pipe size(unlikely) or the size of the collector where all the pipes come together which is commonly 3 inch or sometimes 2 1/2 on smaller headers?.......I could notice a difference when I switched from 2 1/4 inch exhaust pipes to 2 1/2 inch pipes on my 306 but I also changed to a much better muffler so most of the gain may have come from that...I would go with 2 1/2 if you have plans to upgrade to more power in the future.

_________________

J-code 306 [email protected] build underway

<font size=-1>[ This Message was edited by: frdnut on 10/14/06 2:33am ]</font>
 

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2 1/2 inch primary is big block territory. I think alot of people are getting confused with the header primary size and collector size.
 

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Yeah, I'm running 2-1/8" primaries and 3-1/2" collectors on my 545.

Not sure how you'd even get a 2-1/2" primary pipe bolted to an SBF head without a serious adapter.

Greg
 

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There's no way those headers have 2 1/2" primaries. I don't even know if there's physically enough space there for those.

2 1/2" pipe size, yes, is perfect size for a mild 302, up to about 450HP.
 
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