3 inch or 3.5 inch exhaust for my 434 sbc

General Engine Discussion

Moderator: John_Heard

Post Reply
Message
Author
434 nova
Posts: 95
Joined: Fri Dec 28, 2007 12:32 pm

3 inch or 3.5 inch exhaust for my 434 sbc

#1 Post by 434 nova » Sat Apr 10, 2010 11:05 pm

How much hp can a 3 inch exhaust support. My 434 sbc has about 650 hp and am looking to spray about 300 on it, i am trying to keep the car as quiet as possible but i am not trying to restrict it, if you know what i mean. Also what mufflers should i use? Thanks for any help.

sg7365
Posts: 25
Joined: Tue Feb 02, 2010 3:47 pm

Re: 3 inch or 3.5 inch exhaust for my 434 sbc

#2 Post by sg7365 » Sat Apr 10, 2010 11:34 pm

I have been running (big) sbc for ten years. My current car I am running a 3.5" with the Dynomax bullet mufflers.
My last car with a 415 Motown I ran a 4.00" Dynamax with bullet mufflers. I measured it without the mufflers and it was 115 db. After putting the bullets on and measured it-it was 93 db. These are really nice and least exspensive that I've seen.
NHRA says in my class, its measured 50 feet away, at a right angle to the vehicle at a no-load rpm of 3,500. Sound suppression device not mandatory if vehicle passes testing. Must be no more than 95 decibles as measured on the "A" scale of the db meter.
Just my two cents.

Also on a system like yours I assume it makes good hp-it is always a good idea not to restrict the exhaust gas flow ie like a normal automotive type muffler--it will kill the engine, you may spin a bearing due to the back pressure these normal type automotive mufflers-they restrict the exhaust flow too much and the pressure will back up into the crankcase thereby putting pressure into it and actually push back the oil from the oil pump. It doesn't take much pressure in the crankcase. That is one of the reasons why there is negative pressure in the crankcase. You may get oil leaks elsewhere you really don't want.
The exact holds true for a diesel engine. Could you imagine if you restrict the exhaust flow on a 18:1 compression diesel engine. Possible a crankcase explosion and or restrict oil to the bearings--spinning them and ruining the engine.

Also don't forget the crankcase evacuation system either a vac pump or ones that go onto the header and cause a vacuum while the engine is running piped via to the valve cover or top half of the engine.
So--go with ones that will not impede or restrict the exhaust gas flow. 3.5 or 4.00 is good.
Again my two cents. I know you know most of this but I didn't want to leave anything out.

Ron

Post Reply

Who is online

Users browsing this forum: No registered users and 23 guests