383 Chevy Small Block Engine - Muffler Tech

383 Chevy Smalll Block Engine Engine Part

A Flowmaster-muffled 3-inch exhaust system compared to a 2 1/2-inch system was worth more midrange torque than peak horsepower but is still a solid idea for any engine making over 450 hp.

A Flowmaster-muffled 3-inch exhaust system compared to a 2 1/2-inch system was worth more

Muffled Power

The open-header test led us to question whether this same collector extension concept would apply with a muffled system. That's when we realized that we'd already performed that test when we evaluated the difference between a 2 1/2- and 3-inch exhaust-pipe system using Flowmaster Super 44 mufflers. The following data indicates that the larger 3-inch pipe system is worth roughly an average of 5 lb-ft of torque and horsepower throughout the entire powerband. The best improvements on our 383 small-block occurred between 4,900 and 5,500 rpm with 11 lb-ft of torque and 11 hp, and there was only one small place in the torque curve where the larger pipes lost 4 lb-ft of torque. At first we attributed this power gain to reduced exhaust backpressure, but now we think that it may be a combination of less backpressure and tuning effects that increase airflow through the engine. Also, it could be that adding an H- or X-pipe in the system in the proper place actually enhances the torque curve even more, possibly eliminating that slight power drop in the 3-inch system at around 3,900 rpm.

2 1/2-inch vs. 3-inch Exhaust With Mufflers TestFlowmasterFlowmaster

	2½-INCH		3-INCH
RPM	TQ	HP	TQ	HP	TQ	HP
2,700	385	198	390	200	+5	+2
2,900	400	221	404	223	+4	+2
3,100	418	247	424	250	+6	+3
3,300	427	268	437	274	+10	+6
3,500	433	288	435	290	+2	+2
3,700	430	303	428	301	·	·
3,900	423	314	419	311	·	·
4,100	421	328	417	326	·	·
4,300	426	349	429	351	+3	+2
4,500	440	377	446	382	+6	+5
4,700	455	407	463	414	+8	+7
4,900	461	430	471	439	+10	+9
5,100	462	449	473	460	+11	+11
5,300	459	463	470	474	+11	+11
5,500	453	474	463	485	+10	+11
5,700	445	483	454	493	+9	+10
5,900	438	492	444	499	+6	+7
6,100	431	501	433	503	+2	+2
6,300	422	506	424	508	+2	+2
6,500	407	504	411	509	+4	+4
Peak	462	506	473	509	+11	+11
Average	432.8	381.0	437.9	385.7	+5.1	+4.7

'An old drag racer trick is to spray-paint the collector extensions; where the paint stops melting is the proper length.
'An old drag racer trick is to spray-paint the collector extensions; where the paint stops
We also tested this same collector extension technique on a set of Hedman 1 1/4-inch headers and found similar results. These smaller headers still produced an average torque increase of 14 lb-ft between 3,500 and 4,800.
We also tested this same collector extension technique on a set of Hedman 1 1/4-inch heade
Most street small-block header collectors are 3 inches in diameter, while big-block headers generally use a 3 1/2-inch-diameter collector. Collector length is a tuning variable and is ultimately determined by each specific engine combination.
Most street small-block header collectors are 3 inches in diameter, while big-block header