Back in April I started this thread about how I gained quite a jump from 13.42 @ 102 mph to 12.22 @ 111 mph by chopping the exahust off, doing a jet change and putting an airpan on to seal against the hood. Couple people said it wasn't possible to gain that much. Well, last night I went to the track again in even better conditions and ran a best of 13.16 @ 102 mph with the single 3 inch back on the car. I'm down 9 mph and .94, almost a full second. Next weekend I'll be back at the track with the exhaust off yet again. Next month I hope to finaly have the larger headers I wanted to get the first go around of this.

 

hmmm...i didnt think that 3" exhaust was that restricting... what headers and exhaust do you have right now???

 

Edelbrock shorties going into their y-pipe then into the muffler where the cat used to be which then dumps right below the rear seat. Temp exhaust till I get my dual setup built. I've had other expenses and haven't had the chance to build it yet

 

what muffler do you have? thats 9 mph in the 1/4... thats a TON of power difference right there and i dont think a 3inch exhaust is the problem

 

did you stop and think what the weather did to your ET? It is the dead of summer.

 

I'm gonna do a similar experiment soon.... Might be interesting to see how much I gain taking off my Flowdisaster single 3" exhaust.

 

i'm in the upper 13's on a 3 inch all way out 80 series flow catback and hooker shorties.

gonna swap to a bullet muffler, 3inch by 18 inch body. hopefully its not gonna be incredibly loud like the straight pipe was. but i want that performance i gained

 

The temp was 73 when I ran at night. Just to please you non-believers, I'll cut the damn exhaust off at the track on the 27th after making a couple passes. I'm willing to bet I'll be back well into the 12's again. I wont make a single change to the car during the week.

8/20
Temp 73 F
actual, 13.16 @ 102.7
Corrected ET 13.23
Corrected MPH 102.13


4/15
Temp 79 F
actual, 12.22 @ 111.68
Corrected ET 12.28
Corrected MPH 111.09



Orr89RocZ, it's a single 3 inch in/out Spintech Proshootout. Same muffler that a friend uses on his 9 second Chevelle but his is a dual 3 inch setup.

 

This is what Im using. Its 2-1/2 Y-pipe to 3-1/2 collector goin to a sprint car muffler. Its noisier than hell. Im in the process of goin "back to a sgl 3 inch system. What muffler? I dont know yet.
I'm still working on that one

 

Back a couple of years ago with my old setup I there was a noticable difference between open cutouts and going through the single 3in flowmaster exhaust. Back then I had a milder cam and 2 1/2in y-pipe w'cutouts going into a single 3in american thunder flowmaster. The car always ran about .2-.3 sec faster with the cutouts open vs through the single 3in. Dual 3in is the way to go, now I run identical times through the exhaust and open headers. Sounds awesome too.

 

Evil, what is the weight difference between the 2 setups? if its alot that will effect your times also.

 

yea he ditched baby shamoo on the 2nd run.

 

yeah cuz 9mph is like 90 hp gain

 

Maybe 30 lbs, I can weigh it Saturday after racing.

7plagues, I forgot about the whale in the back of the car helps with traction but man, it's hard on the springs, just look...


btw, that was from the run I did 12.22, you can just about see where the y-pipe ends right about in the middle of the Z28 emblem on the rocker panel.

 

[B]

Possibly the muffler is not far back enough? Having it where the cats were is too close to the engine. If the muffler IS a restriction, it is LESS of a restriction, the farther back it is. I dont believe it can take that much away though.

 

Thing is though, I went from 13.42 @ 102 to a 13.16 @ 102 between the two exhaust systems and a jet change plus carb air pan. The muffler used to be under the gas tank and the tail pipe exiting at the rear bumper. Chopped all that up to what I have now. We'll see what happens Saturday at the track.

 

I beleive everything evilcartman is saying. I experience the same thing with my Monza. I have cutouts on other cars that only net me about 3 tenths but on the monza the cutouts give me almost a second. The difference is so extreme that when I open the cutouts I have to completely rejet the carb. That is just how restrictive the system is on the car,,,and it is a true dual system. Just to give you a quick idea, I run a 406 in the car and the Monza is basically a mini 3rd gen, same chassis design, only smaller. I had a custom dual system fabbed up, I have full length Hooker super comps, I had to go with 2 1/4 pipe diameter because there was no room for anything bigger. The driver side comes off the collector and over to the passenger side where both pipes follow the passenger side trans tunnel, up over the axle and into a Flowmaster muffler with dual inlets and dual outlets and then tailpipes that exit just like the factory did on the V-8 Monzas. There are alot of bends in the system to make it fit, just the nature of it, plus only 2 1/4 pipe, but this is a dual system, not single like the 3inch cat backs. I had to lean the carb down considerably with the exhaust closed up to get the engine to run right. Once dialed in I opened the cutouts and the car went so lean it popped all the way down track and the car actually slowed down 5 tenths of a second. I started fattening the carb up more and more, ended up being 8 jet sizes in the front and 7 sizes in the back. The car picked up 7 tenths of a second over the best pass with the system closed plus the 5 tenths I lost. This 406 absolutely hates this exhaust system I have plans in the works for something else, just not much room to work with. Larry.

 

.

 

Jones

A 406 pumps out alot of air. More so than a 355 at racing speeds. Especially trying pump that air thru a 2 1/4 inch dual exhaust into a flowmaster muffler that was ment as a stock replacment rather than a race muffler.
So yes your car would most certainly respond greatly to the cutouts(2).

Evil

Where did you purchase the foam used on the cold air box? It looks like the Moroso stuff. Is it? Looks like you fabbed your on base also.
I still need to fab one up for use with a air cleaner.

 

Yeah it's the Moroso's replacement 4 inch high foam. Found the part number at Moroso's site, plugged it into Summit Racing's online store and ordered it up. As for the base plate, made that too. Cardboard first to get everything centered right then cut out the aluminum. Think the engine is off center by about an inch and a half or so. Took a cheapy air cleaner and cut the bottom plate up a bit and rivited the ring to the aluminum plate to clear the float adjusters.

 

Just got back from the track a half hour ago so here's how it went. I made zero changes from a week ago to the car. Conditions were crappy.

Last week, 8/20 ran a best of 13.16 @ 102 mph
This week, 8/27:

1st run, with exhaust = 13.43 @ 98.25 mph 1.82 60' (VHT sprayed on track right before pulling up to line)

2nd run, dumping out of y-pipe = 12.74 @ 105.14 mph 1.79 60' (really layed over on the top end)

3rd run, dumping out of y-pipe = 12.79 @ 108.17 mph 1.96 60' (track was getting slick and spun bad)

4th run, nitrous pass still dumping from y-pipe = 11.57 @ 120 mph 1.89 60' (car got sideways at the hit of the button till about the middle of 1st gear)

Too tired right now to plug in the numbers for corrected times, temps were right around 90 on the first run and 78 on the last run. Much different than last week when it was in the lower 70's. So there you have it, do what you will with the info but I'm changing my exhaust to dual 3 inch and Hooker long tubes

 

Thats what I like to see, real world results and changes at the track. Very cool Your car responds much like my Monza does. My other cars only respond .3 to .5 tenths but they all have much larger dual systems to begin with. But hey, a tenth is a tenth, here and there they add up. Let us know how the new headers and dual 3 inch work out, thanks, Larry.

 

Evil
Before your 1st run with the VHT, how long before your run was the VHT sprayed? Mite make a diff. if the VHT had not set up
properly before the run.


2nd run it layed down at the other end going thru Y-pipe. A lean condition maybe caused by jetting, not enough Fuel volume or pressure?


3rd run, you spun Ok why?

4th run thru y-pipe with nitrous. You ran within 2 hundreths and 1 mph of your Sig best with the Squeeze. Thats good
Did you make your Sig run "with" the nitrous and a FULL exhaust?
If so I'd say your going slower if you just matched that time goin thru the Y-pipe . Any Ideas?

 

1st run, I had just done the burnout and they started spraying down the track with VHT. It dead hooked and felt great. MPH was down from the regular 102-103 that I've been getting. Mind you though, it was around 90 degrees when I made this run compaired to being in the 70's on previous runs.

2nd run, lean condition due to a tiny bit of something on the rear float bowl fuel screen.

3rd run, spun probably due to the track going away, water on the start line from first time racers tracking it up there or tire pressure.

4th run, the 11.55 @ 119 was made through full exhaust exiting at the rear of the bumper (original setup). I'm sure if it hooked up and was tune right it would have clicked off a lot better time last night instead of the 11.57. It was popping a bit in 2nd gear till the end of the track.

Here's a video of the 2nd and 4th run, you can see the flashes out of the y-pipe on the nitrous pass. Other thoughts, it was slower last night looking at the raw numbers from a week ago and previous runs. Next race is Sept. 17th so we'll see what she does then.

 

I watched the video. Couldn't tell how hooked up you were. But the run did "look" pretty solid. I saw the flashes out the y-pipe
looks like some tuning issues. Probably minor. Et and mph was right there. Having never used nitrous before its hard for me to tell just how much effect it has on mph vs et. For example Last time I ran my "OLD" car back in the early 1980's I ran 10.90's at 122mph. BB 67 camaro auto with 5.87 gears and a 30" tall tire.
I have yet to get my 3rd gen to the track. Our 3rd gens are "very" simular

 

Talked with a friend today about the flames out the exhaust and he said it was running too rich. I probably didn't have the bottle pressure up or some other factor was going on. He's been messing with nitrous cars for a few years now and had left earlier in the night before he could check over my car. It really should have ran better than it did but oh well. His car didn't even start because of a goof up one of the crew members did

 

That's a pisser