im building a 383 tpi street motor and was wondering if my exhaust would be ok ?? its a 3 inch factory style exhaust going into a magnaflow 3" in and 2 2.5" out .. horsepower im hoping for is 400-450 ...

 

LTR Id opt for a 1-5/8 primary, opinions will vary.

 

Wrong forum, moved to exhaust.

 

For the 383 tpi im building I purchased a set of Dyno Don's 1 3/4" headers with a 3 inch Flowmaster catback.

 

Quote:

Originally Posted by 85Iroc-Z

For the 383 tpi im building I purchased a set of Dyno Don's 1 3/4" headers with a 3 inch Flowmaster catback.

the 1 3/4 is a tad large unless you plan on some 6k+ R's but it will not hurt your cruse, the 3" Flowmaster is a good choice. There is a factor in exhaust that most people do not understand, you have to tune it!! or at least understand what is going on in there. When we say tuned headers that means equal length runners to the general public, but to a seasoned mechanic, it means that the exhaust pulses reach the collector in a timed sequence. What does this mean in "the real world"? To answer this we first need to digress into the 2 cycle world. The expansion chamber works on expanding and collapsing pressure waves, expands when the exhaust port is first opened, and then collapsing before the port is closed. This collapse sucks the last of the exhaust gasses out of the combustion chamber. So now in our 4 stroke engine, the exhaust pulses operate in the same fashion, to help pull the next pulse down the pipe. continued

 

to continue with my disortation, LOL,

the next phase is the pumping action pushing the exaust farther down the pipe and out. if you use pipe that is too large, it will defeat its purpose and cause more back pressure, instead of carring the "pulsed" velocity on down the pipes it will cause the exaust to have eddie currents and esentially stall the flow. I hope that this makes sense? I am in no way an expert but I do have 35 years of experimenting to draw uppon, here is what I have found out works best for me Small blocks under 327 2", 327 and above 2 1/4" , big blocks 2 1/2", This is duals all the way out the back. Do not cut them short, the sonic wave gets screwed up, "that is another discussion" go all the way to the back of the car. as far as singles for a small block 3" all the way from the Y to the back, or dual 2 1/4 stingers at the back just my 35 cents worth of opinion.

 

If you dont think a single 3 will flow enough, just throw a cutout in there and you will be fine