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Username Post: 327/300hp systems mufflers        (Topic#368401)
del.impala 
Contributor
Posts: 657

Loc: delaware
Reg: 04-13-11
05-11-22 11:01 AM - Post#2841037    

Does anyone know for a fact with photos,hopefully what is the inside diameter of the 2 1/2" inlet pipe going into the muffler body. Schaffers restorations says that the inlet pipe is 2 1/2" but when the pipe enters the muffler body it is 2" thru the muffler body and out to the oulet pipe. I thought that the OE mufflers were 2 1/2" thru the muffler body ,then when it exits the muffler it becomes 2". I don't want to drop 1K in exhaust system to find out it's not completly correct. Dcairns, what say you on this please.



 


dgstarr 
"4th Year" Silver Supporting Member
Posts: 310
dgstarr
Loc: Portland, OR
Reg: 04-16-13
05-11-22 11:10 AM - Post#2841039    
    In response to del.impala

327,300hp is 2 1/2 in inlet and 2 inch outlet
327,250hp is 2 inch inlet and 1 7/8 outlet. I purchased my 300hp mufflers from Show Cars and they were correct. Some repro mufflers are 2 inches on both ends, slightly different from OEM.

In 2013 I purchased a complete exhaust system for a 300hp car from Schaffers and one exhaust pipe from the engine to the muffler was incorrect. Rather than pay shipping back to
schaffers from Oregon, I had a local muffler shop build me a pipe.



Edited by dgstarr on 05-11-22 11:15 AM. Reason for edit: No reason given.

 
del.impala 
Contributor
Posts: 657

Loc: delaware
Reg: 04-13-11
05-11-22 11:28 AM - Post#2841041    
    In response to dgstarr

Ok, but do you remember if the 2 1/2" pipe into muffler body stayed at 2 1/2" or did it neck down to 2" at the inlet face,where it remained 2" though out the muffler? A lot of the repo "300 hp mufflers" are only 2" at both ends but are swaged larger at the inlet to appear 2 1/2".



 
Tony1963 
Frequent Contributor
Posts: 1286

Loc: Orlando Florida
Reg: 07-09-18
05-11-22 01:04 PM - Post#2841048    
    In response to del.impala

From what I have seen, it is common for the latter part of the exhaust system to be a smaller diameter than the part that exits the manifold.

Exhaust gasses lose heat and contract rapidly. As such, there is less need for the larger pipe downstream in the system.

Years ago I saw an article in Popular Mechanics where the did a performance test by upsizing the exhaust. The results were minimal and you could see a point where going too large inhibited performance.

What most people forget is that atmospheric pressure in most areas is 14.7 to 14.2. That means that atmosphere will compete with exhaust gasses that exit the system if the piping is too large to keep a velocity of air moving.





 
del.impala 
Contributor
Posts: 657

Loc: delaware
Reg: 04-13-11
05-11-22 01:38 PM - Post#2841051    
    In response to Tony1963

See OP^^^^^^^^



 
dgstarr 
"4th Year" Silver Supporting Member
Posts: 310
dgstarr
Loc: Portland, OR
Reg: 04-16-13
05-11-22 02:12 PM - Post#2841053    
    In response to del.impala

The inlet is a full 2 1/2 inch pipe, not necked down. The 300hp car is the same size as the 409 and high performance 348's since 1959.



 
del.impala 
Contributor
Posts: 657

Loc: delaware
Reg: 04-13-11
05-11-22 02:31 PM - Post#2841055    
    In response to dgstarr

I know the pipe is 2.5 but where it enters into the body of the muffler is it still 2.5 or 2".



 
dcairns 
Frequent Contributor
Posts: 2303
dcairns
Loc: Orange CA
Reg: 11-07-03
05-11-22 03:06 PM - Post#2841056    
    In response to del.impala

Most of what I know on the topic comes from the experts here. Namely that the 2.5 necks down to 2 as it enters the muffler. My car started life as a 283 with a single 2 inch system and that was in '82, so it may not have been the original muffler by then. So I don't have any direct knowledge on the original 327-300 2.5 inch system.

I purchased my 2.5 inch exhaust from Schafers directly. I got the aluminized version and added the resonators from Show Cars. after 10 years, it all still looks great. I do wish I had used the stainless clamps, though.
Here is a close up shot of the 2.5 pipe entering the muffler. It does seem to reduce a bit, just as it enters the muffler, whether that continues down to 2 inch, I do not know. In any event, my 327 turned 383 is quiet enough, but with a healthy little rumble at idle and can give a nice bit of roar at full throttle. More power gets through the exhaust, than the suspension makes me comfortable using for anything but straight-aways :D



- Dave
1964 Impala 4-door sedan



 
del.impala 
Contributor
Posts: 657

Loc: delaware
Reg: 04-13-11
05-11-22 03:14 PM - Post#2841058    
    In response to dcairns

Thank you



 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5352
Mel Foye
Reg: 09-29-00
05-15-22 12:45 AM - Post#2841215    
    In response to dcairns

I am just an old Iowa and Minnesota farm boy so don't expect too much. I resized your picture here so the OD of the muffler was 2.5 at it's largest and the measured the place where it goes in was 2.25.
Things got a lot smarter with this PC box of parts once we got electric to the house. Yep.




It Was On Fire When I Laid Down.


 
del.impala 
Contributor
Posts: 657

Loc: delaware
Reg: 04-13-11
05-15-22 07:36 AM - Post#2841221    
    In response to Mel Foye

thanks!



 
dcairns 
Frequent Contributor
Posts: 2303
dcairns
Loc: Orange CA
Reg: 11-07-03
05-15-22 03:08 PM - Post#2841230    
    In response to Mel Foye

Well, now you had to go and get me curious and get on the garage floor with some calipers...

I am measuring the outside diameters here.

The down pipe is 62mm (2.44 inches)
The larger pipe it goes into (with the clamp on it is 66mm (2.6 inches)
The pipe reduces down after the clam before entering the exhaust is 63mm (2.48 inches) before the muffler.

This is not counting the barely visible part that seems to be reducing more, as it enters the muffler.
And yes, Metric units are easier to record when you are laying on the garage floor with calipers and a ruler .

So it would seem any reduction takes place out of sight inside the muffler. The barely visible reduction as it enters the muffler is suggestive that it could continue to reduce once inside.

- Dave
1964 Impala 4-door sedan



 


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