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I went to the test and tune this weekend with some friends and something I wanted to test was the cutouts I added to the exhaust. After a handful of runs getting the timing and the jetting dialed in to the point that I was happy with, I opened the cutouts. The exhaust system on the car is long tubes into a 3" y pipe into a single 3" chambered muffler and tailpipe. I knew this would be restrictive, but I wanted a stock look and relatively quiet highway cruising. The cutouts are 3" diameter and installed after each header and dump out under the doors.
I was very happy with the results!
In a car that weighs 4700 lbs with me in it, 2 miles an hour in the 1/8 is pretty substantial.
It's a single 3" which is why it's such a big gain.
not really..if your single 3” is actually free flowing like you say.. it’ll handle way more power than you’re making.
a single three inch properly designed with a straight through muffler will handle 500 to 600 hp
you aren’t making anywhere near that by the weight and MPH and open exhaust
Last edited by CANADIANOLDS; Sep 23, 2024 at 04:29 PM.
60' was the same regardless. Getting traction is the challenge on the 60'
no, it wasn’t the same. Your quicker 60’ was with it closed , 2.0167 vs open 2.0281
thats .0114 which is significant. I’m saying if it’s that much better closed, there is even more in it open. you didn’t say if you changed any tuning open vs closed. if that’s the case, then you need to work on the open exhaust tuning to get back the 60’ loss. it should pick up everywhere…not a worse 60’ but better everywhere else
Last edited by CANADIANOLDS; Sep 24, 2024 at 03:21 PM.
no, it wasn’t the same. Your quicker 60’ was with it closed , 2.0167 vs open 2.0281
thats .0114 which is significant. I’m saying if it’s that much better closed, there is even more in it open. you didn’t say if you changed any tuning open vs closed. if that’s the case, then you need to work on the open exhaust tuning to get back the 60’ loss. it should pick up everywhere…not a worse 60’ but better everywhere else
For these two runs, yes. But across all the runs I did that night, the cut outs did not have a measurable effect on 60'. The variation came down to my ability to launch without spinning tires.
For these two runs, yes. But across all the runs I did that night, the cut outs did not have a measurable effect on 60'. The variation came down to my ability to launch without spinning tires.
its 4,700 lbs and you can’t get traction? what tires?
its 4,700 lbs and you can’t get traction? what tires?
Ha ha, I know.
They're just cheap all-season tires. This isn't a drag car and I'm not a racer, the whole point of going to the test and tune was to see how restrictive the chambered muffler was. The whole car is just for fun and learning really. I wanted to know so I welded in some cutouts and went to see the MPH difference. The next experiment is going to be cutting out the chambered muffler and welding in a straight through style. Then I also have a couple of other converters on the shelf I want to try.
put in a good straight through 3” and you won’t notice any diff uncorked.
That's awesome.
Great gain CustomBruiser.
As JohnnyBs68S posted the gain works out to a 27 hp difference. Being able to erase the difference with the correct muffler is stellar.
Originally Posted by CustomBruiser
The whole car is just for fun and learning really.
That's what counts, enjoying your ride. My 87 442 was an enormous amount of fun at the track. The 69s gains at the track are much more difficult to come by. She is much more powerful but so hard to see it due to the grocery getter setup. I picked up about 2 seconds in the 442 but only about 1 second in the 69.
Here is a little interesting note when exhaust is under 3 inches in diameter, thanks to Chevrolet and their legendary L82. Moving the Y pipe to just the right spot can give you an additional 5 net horsepower. Below is the actual difference between the 79 L82 and the 80 L82s exhaust. Obviously the longer it takes for those exhaust pulses to converge the better. Of note L82s came with a 2.5 inch exhaust.
Ha ha, I know.
They're just cheap all-season tires. This isn't a drag car and I'm not a racer, the whole point of going to the test and tune was to see how restrictive the chambered muffler was. The whole car is just for fun and learning really. I wanted to know so I welded in some cutouts and went to see the MPH difference. The next experiment is going to be cutting out the chambered muffler and welding in a straight through style. Then I also have a couple of other converters on the shelf I want to try.
okey dokey…🙄
you actuality don’t want to learn,, fun yes, learn no
you actuality don’t want to learn,, fun yes, learn no
I'm not sure what you're trying to insinuate but I learned exactly what I wanted, It picked up 2mph with the cutouts open which was what I wanted to test.
Anyway, last weekend I swapped out the chambered muffler for a flow through muffler and it made a big difference above 4000 rpm on the street. Experiment successful, a single 3" chambered muffler kills a lot of flow.
As JohnnyBs68S posted the gain works out to a 27 hp difference. Being able to erase the difference with the correct muffler is stellar.
That's what counts, enjoying your ride. My 87 442 was an enormous amount of fun at the track. The 69s gains at the track are much more difficult to come by. She is much more powerful but so hard to see it due to the grocery getter setup. I picked up about 2 seconds in the 442 but only about 1 second in the 69.
Here is a little interesting note when exhaust is under 3 inches in diameter, thanks to Chevrolet and their legendary L82. Moving the Y pipe to just the right spot can give you an additional 5 net horsepower. Below is the actual difference between the 79 L82 and the 80 L82s exhaust. Obviously the longer it takes for those exhaust pulses to converge the better. Of note L82s came with a 2.5 inch exhaust.
My y-pipe is 3" from the 3" collectors and is fairly long when combined with the collectors on the headers to go around the trans pan. I wonder where that falls relative to the optimum point.
I'm not sure what you're trying to insinuate but I learned exactly what I wanted, It picked up 2mph with the cutouts open which was what I wanted to test.
Anyway, last weekend I swapped out the chambered muffler for a flow through muffler and it made a big difference above 4000 rpm on the street. Experiment successful, a single 3" chambered muffler kills a lot of flow.
nope on learning how to test successfully. correct on the muffler swap out.
until you address the traction problem you say you have getting off the line, all your testing is a waste of time and you learn nothing. when track testing, traction is #1 on the list
That's really cool info, thanks!
My y-pipe is 3" from the 3" collectors and is fairly long when combined with the collectors on the headers to go around the trans pan. I wonder where that falls relative to the optimum point.
The ideal situation is to have both primary pipes an equal length, but not easy if you need to clear undercar obstacles & cannot run the exhaust down the trans tunnel.
Without significant experimentation & testing, the optimum length is hard to determine.
Generally, somewhere between 18-24" is a reasonably good merge point... looks right about where you are.
Too short is more detrimental than too long.
I've got updates. I made a few improvements and headed to Milan yesterday to test them out and have fun.
1. I replaced the mechanical fuel pump with an electric pump back at the tank. This was to address a suspicion that lack of fuel pump capacity was causing it to lean out on the top end. I had added jets at the track last time and got AFR to 13:1ish but couldn't really get any richer. With the electric pump, I had to pull those jets back out and am now pretty happy with 12.8:1 all the way down the track.
2. I noticed looking at slow motion video of my launches from Northern Michigan that it was squatting on launch. A lot. So I added anti-squat in the rear by moving the lower control arms down at the axle. This had the desired effect and looking at video from Milan, the rear stays really close to ride height and the front comes up as it should on launch and I was able to launch over and over with no wheel spin.
3. I cut out the FlowMonster muffler and put in a flow through muffler with a perforated core and glass packing. This made a huge difference but would it get back everything the cut outs were giving?
4. Swapped out the stock converter I had put in for Power Tour for my Boss Hogg Street Bandit.
Run #1
This was through the muffler and tailpipe.
Run #3
Opened exhaust cut outs.
Run #4
Added 2° timing
Last edited by CustomBruiser; Oct 17, 2024 at 05:31 AM.
Reason: spelling
I did some testing a few years ago on a 2000 Z28.
Essentially a stock LS1 with a cam & headers & a 3" dia. exhaust.
The car had 3" collectors to a 3" y-pipe merging into a single 3" pipe running back to a straight through muffler.
Leaving the dual 3" to single 3" merge "Y" in place we changed the exhaust behind that point to a single 4" system & it picked up .2 sec.
The following modification was to replace the dual 3" to single 3" merge with a dual 3" to single 4" merge collector. This picked up an additional .1sec
Looks like your previous test may have been limited by your fuel issue.
