2 1/2 inch exhaust on a 318...

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BoredandStroked

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Howdy Folks !
I finally decided what engine I am going to build for my car. A 318 with 4 barrel carb, 360 heads, 4 inch stroke, .030 overbore at least no more than .040 . Hopefully making around the 450-550 hp mark. I would like to know if 2 1/2 inch exhaust would be good for this build. I want to use the TTI headers of course and fab up my own exhaust. So would 2 1/2 be just perfect or a little smaller or go up to 3 inch? Thanks everyone !
 
BoredandStroked said:
Howdy Folks !
I finally decided what engine I am going to build for my car. A 318 with 4 barrel carb, 360 heads, 4 inch stroke, .030 overbore at least no more than .040 . Hopefully making around the 450-550 hp mark. I would like to know if 2 1/2 inch exhaust would be good for this build. I want to use the TTI headers of course and fab up my own exhaust. So would 2 1/2 be just perfect or a little smaller or go up to 3 inch? Thanks everyone !
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I have 3" on my motor thats much milder than yours. May not be ideal, but i have room to grow without havig to mess with the exhaust :thumblef: With your combo i'd run 3"...just my 2cents.

-Mike
 
400 cubic inches (392 IIRC) at 400hp will do fine with 2.5" pipe. If you're looking for a real 500-550, you'll be moving more air, and will need 3" pipes. 2.5 will run decent, but you will be leaving some power on the table with a desired 550hp and 2.5" pipes. On a side note, you'll be spending an awful lot on those 360 heads (or any factory iron) to make that kind of power (500+). You can make the target much easier with Edelbrocks or MP big port Commandos.
 
I have personally seen the 360 heads make 580 horsepower with potential to make up to 600. The port job ran about 800-1000 dollars on it... port match, polished, new and bigger valves and a few other things. But I do agree with the Edelbrocks. I dont know to much about the MP big port heads so I can not comment on them. So let me get this straight.... 400-500 will do good with 2 1/2 inch pipe and over 500 should be 3 inch pipe? Thanks all!
 
400-500 will do good with 2 1/2 inch pipe and over 500 should be 3 inch pipe?
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For a street ride, yep. Racing is different.
 
Ok enlighten me on how racing is different. Need to know this kind of stuff since I plan to get in it after this project. Beginners level first you know haha. Thank you!
 
On the street you are looking at great variations in RPM range. In racing you are focusing on a realitively small RPM range. Also, for instance, in racing if the car is a little soft in leaving you might add a little longer collector. ie:you tune the exhaust...Not practical for the street. As in most things you do for the street, you have to make compromises.
Mac
 
In racing, cops dont get called by people on cell phones complaining your car is too loud.. In racing, you dont necessarly need to hear things like sirens of that cop car, firetrucks/ambulences, the stereo, anyone in the car. The full boogie treatment would be 3", with an X pipe and low restriction mufflers.
 
I totally agree Moper ! We have some really ignorant and moronic people and police around here so I totally understand that. I was going to go with an X-pipe of course and very low restriction mufflers. Just didnt know if I should go with 2 1/2 or 3. Anyone have any idea on which muffler is the best sounding and performing. I can not listen to the sound clips sadly because I have stone-age dial up hahaha. Thank you all!
 
How much power does the engine make. Be conservitive rather than probable best day and tuned for power. You gave a hundered HP difference in power. And thats a whole lot at the level your describing.
Street bound cars can live with a compromise of alot of variables on the build from front bumper to rear tail pipe. Race cars, dedicated ones, are set up to extract everylast bit of potential there could be in the engine and chassis.

On mufflers, the chambered units I like are from Hooker. There Aero Chamber. Less powerful cars can use most any other chambered muffler with good results.

For the straight through units, Hooker (Again) and Dyno max have excellent choices. The list really goes on & on. It's a personal prefrence.

IMo, if your looking to max out the combo above 470 HP, an honest 470, 3 inch pipes.
 
OK the reason I had 100 hp difference was b/c I am not very sure of the compression or the type of head. With the rate of gas prices I dont want to have 10:1 - 12:1 compression and have to run top grade. I am really thinking between 8:1 - 10:1 so I can get low grade. It is already 3 dollars a gallon where I live and top grade is up to 3.20 - 3.30. So really I am thinking between 400-450 hp on the engine. So 2 1/2 inch pipes with chambered mufflers? Thanks for the info!
 
I think of it this way. Pump gas is already $3 a gallon here (yes that 87oct) so why not go for broke (literally) and run high compression and some race gas.

on the street you probably wont feel the differance from 2.5" to 3" but your gonna hear it. Also Im willing to bet a a 2.5" system with an X pipe and some straight threw muffs will out flow my 3" pipes with no cross over and chambered Flowmaster.
 
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