exaust too unrestrictave?
Drifting
Joined: Dec 2002
Posts: 1,861
Likes: 2
From: New Zealand
I don't know what sweet thunder is, but I recently swapped from factory style side pipes to undercar exhaust on a 9.3:1 compression 350.....I've had the side pipes on for 2 years and didn't re-tune anything, but I think the car ran and idled better with the more restrictive undercar exhaust.......
Open for discussion.....
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Originally Posted by standup
So what was the answer ?????
I don't know what sweet thunder is, but I recently swapped from factory style side pipes to undercar exhaust on a 9.3:1 compression 350.....I've had the side pipes on for 2 years and didn't re-tune anything, but I think the car ran and idled better with the more restrictive undercar exhaust.......
Open for discussion.....
I don't know what sweet thunder is, but I recently swapped from factory style side pipes to undercar exhaust on a 9.3:1 compression 350.....I've had the side pipes on for 2 years and didn't re-tune anything, but I think the car ran and idled better with the more restrictive undercar exhaust.......
Open for discussion.....
Drifting
Joined: Sep 2006
Posts: 1,986
Likes: 21
From: Columbus MN
An exhaust system can only be too restrictive if the low restriction causes other problems. In my case, the drop in restriction from adding full length ceramic Dynomax headers and custom-bent pipes (breath-out) created a breath-in problem.
The jets in my Holley carb were not big enough to handle the increased airflow through the carb resulting from the new exhaust. New jets required and "bigger" accelerator pump fixed that problem.
The jets in my Holley carb were not big enough to handle the increased airflow through the carb resulting from the new exhaust. New jets required and "bigger" accelerator pump fixed that problem.
Thread Starter
Safety Car
Joined: Nov 2006
Posts: 4,449
Likes: 0
So what was the answer ?????
I don't know what sweet thunder is, but I recently swapped from factory style side pipes to undercar exhaust on a 9.3:1 compression 350.....I've had the side pipes on for 2 years and didn't re-tune anything, but I think the car ran and idled better with the more restrictive undercar exhaust.......
Open for discussion.....
I don't know what sweet thunder is, but I recently swapped from factory style side pipes to undercar exhaust on a 9.3:1 compression 350.....I've had the side pipes on for 2 years and didn't re-tune anything, but I think the car ran and idled better with the more restrictive undercar exhaust.......
Open for discussion.....
randommj
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Le Mans Master
Joined: Jan 2007
Posts: 5,485
Likes: 7
From: Peekskill NY
I posted a thread a while back - (2" vs.2 1/2" exhaust), and the general consensus was mixed. Some said 2" ran better with a bit of back pressure and not to waste my time with 2 1/2", wouldn't notice much performance gain. Others said a less restrictive exhaust would be better, which makes sence. I'm using stock manifolds, intake & Q-Jet. Jury's still out as far as I'm concerned. I'll need to replace my exhaust this spring/summer, so I'd also like to get more opinions on this.
Glenn
Glenn
Le Mans Master
Joined: Dec 2006
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Some guys posted Dyno results comparing sidepipes and straight back exhaust. Ths sidepipes showed a reduction in HP.
Thread Starter
Safety Car
Joined: Nov 2006
Posts: 4,449
Likes: 0
Le Mans Master
Joined: Dec 2006
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Racer
Joined: Nov 2006
Posts: 435
Likes: 7
From: Wake Forest NC
I remember that years ago, Corvette exhaust manifolds were coveted. After looking in vendor's catalogs, the earlier SB had 2.5", and 65> had 2". Horsepower ratings during both periods were pretty good (high) measured at the flywheel. Are the results in this thread using factory manifolds or headers before the exhaust systems?
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
I remember that years ago, Corvette exhaust manifolds were coveted. After looking in vendor's catalogs, the earlier SB had 2.5", and 65> had 2". Horsepower ratings during both periods were pretty good (high) measured at the flywheel. Are the results in this thread using factory manifolds or headers before the exhaust systems?
Pro
Joined: Aug 2005
Posts: 627
Likes: 1
From: Naperville IL
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Side pipes CAN be more restrictive, and those dyno results were recorded at very high RPMs. At normal driving speeds and RPMs the two are almost equal. When you really let the motor scream is when there is a difference, and it's marginal at that. Unless you're watching your track times, and need every tenth you can get...stick with straight. If you're a cruiser...you will never notice.
Safety Car
Joined: Apr 2002
Posts: 4,653
Likes: 6
From: North Royalton, OH
St. Jude Donor '06-'07
The factory pipes are VERY restrictive with their reverse flow design. If you cut one open you will see the inner chambers are very small. Switching to an aftermarket side pipe (i.e.Hooker) results in a huge gain in air flow.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
My understanding is the hooker 1 7/8 port side pipe headers are equal length primaries into a 4" and the best flowing exhaust available depending on the inserts used. The max flows also advertise a 23HP increase over open headers??? How does that work?
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
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2.5" is pretty decent up to the 500-550 hp range....but I would use 3' if I was starting from scratch. Uncapping my old 427 with 2.5" pipes and Flowmasters showed very little improvement. it was running low 11's@123.
A fellow I know just replaced a full 2" system on a '61 283/270 car with a full 2.5" including manifolds along with the *off road* mufflers. no back up dyno tests yet...but seat of the pants difference is very impressive.
Factory sidepipes are very restrictive. The mufflers neck down to like 1.5'-1-3/4" internally. The Hookers are Ok if you completely remove the mufflers. On the big blocks the Hooker mufflers are racking up almost a 100 RWHP loss on 500+ Hp motors.
If you install some decent mufflers on them they are fine....but those 4" pipes are pretty small internally.
Under light throttle none of it really matters much. It only takes a few HP to drive down the road..but when you put your foot in it....you better have good stuff!!
What gets confused as having better performance with pipes capped up is often better scavenging happening in the rpm range you're dealing with with the long exhaust pipes. My 540 was up 40 ft lbs at some very low points on the chassis dyno when capped up with Flowmasters...but was down over 50 RWHP as RPM climbed!!
JIM
A fellow I know just replaced a full 2" system on a '61 283/270 car with a full 2.5" including manifolds along with the *off road* mufflers. no back up dyno tests yet...but seat of the pants difference is very impressive.
Factory sidepipes are very restrictive. The mufflers neck down to like 1.5'-1-3/4" internally. The Hookers are Ok if you completely remove the mufflers. On the big blocks the Hooker mufflers are racking up almost a 100 RWHP loss on 500+ Hp motors.
If you install some decent mufflers on them they are fine....but those 4" pipes are pretty small internally.
Under light throttle none of it really matters much. It only takes a few HP to drive down the road..but when you put your foot in it....you better have good stuff!!
What gets confused as having better performance with pipes capped up is often better scavenging happening in the rpm range you're dealing with with the long exhaust pipes. My 540 was up 40 ft lbs at some very low points on the chassis dyno when capped up with Flowmasters...but was down over 50 RWHP as RPM climbed!!
JIM