Another exhaust tweak

Working on the new setup, and an issue pops into my head. It's damn tight trying to squeeze in the spare tire bucket.

IM002293_zps7fa9ec31.jpg

The C4 tire bucket (lighter and more easily packaged) I'd planned to eventually use, and the stock tires are about 26 1/2 inches , but the mufflers are only 24 inches apart when the outlets are centered in the bodywork cutouts. If these mufflers were similar to the old ones (with the outlets in the middle rather than the outter sides) I might have had enough room. I considered moving the mufflers over an inch or so on each side but then I would have had to add an "S" bend to get back to the cutout and the baloney tips. I'm not happy with that option at the moment, so I'm just going to proceed with this configuration. In the mean time it looks like I can fit a tire behind the seats when I need to have a spare along.

Got the replacement Y pipe underneath tacked together. Took a bit of sneaking up on it to get the two 3" pipes to fit the slightly squashed 4" pipe and at the angles to point to the muffler inlets. Now I just gotta figure out where to put the sleeve/coupler between there and the mufflers so I can wiggle the assembly apart when needed.

These things better flow decently for the extra PITA that they're causing me.
 
I wuz going to make a comment about your car blowing away in the breeze, but I won't.....temping the devil, now that you live in the plains.....


:shocking::beer::drink: a chrome shark with a 80+ diffy.....interesting.....
 
Got the mufflers all welded up, along with the hanger brackets and put a couple of small beads on the SS tips to hold them in. I like the appearance of the 3" size tips better than the 2 1/2" ones I had on there.

IM002296_zps94f63d2b.jpg

Fired up the engine on the lift and the system is reasonably quiet. I'm trying to do a track day in about a week and a half, and I'm curious to find out what the WOT noise volume is and the backpressure levels.
 
BBShark said:
Did you end up using the larger mufflers (on the bottom of the picture)?

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Yep. Those are the mufflers I chose from the chart you supplied. (Thanks again!) I just put a coat of flat black BBQ paint on them. No particular reason but I've always painted my exhaust systems flat black.

For the expense and hassle installing them they better flow better (ie: less backpressure). I have the pressure gauge hooked up again so I'm hoping to find out at the next track day in a week or two.
 
Spent the day at Heartland Park Topeka. Cooler temps this time (92*F vs 99*F last time :wink:). Hooked the pressure gauge up again to the EPTBox. The backpressure reading with the 3" rear pipes and new mufflers was 10" H20 versus the 24" H2O with the previous 2 1/2" pipes and mufflers.

Things were going well during the second session when I got a damn loud exhaust backfire after lifting at the end of the fastest straight. (I'm speculating I got a misfire due to the spark advance being over advanced at high RPM and high vacuum. I might consider running ported vacuum advance at the next track day to prevent that situation, and see what happens.) I'm going to have to take a look under the car this weekend to see if the backfire damaged any muffler seams or header gaskets.
 
thnks for sharing. I am a little surprised that you had 10" with the larger exhaust. I don't have any comparative info to base that on; just thought it would be in the single digits... Could you "feel" any difference?
 
BBShark said:
69427 said:
The backpressure reading with the 3" rear pipes and new mufflers was 10" H20 versus the 24" H2O with the previous 2 1/2" pipes and mufflers.
Click to expand...

Pretty impressive reduction.

Were they loud?
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They were a little louder than the 2 1/2 inch mufflers. I believe a significant part of that was a leak in the crossover pipe behind the headers. I bottomed out somewhere and dislodged the clamps on the crossover. I fixed it yesterday after putting it on the lift to check out if anything in the exhaust ballooned out from the backfire. Other than the dislodged clamps everything looked fine. I'll note the noise level now that the leak is fixed.

I finally (after nine years) have the car running and licensed (thanks to Tim and Kevin for old car licensing advice), so I'm looking forward to driving it again on the streets. I've hardly driven this car any speed or distance in years without a helmet on.
 
73c34me said:
thnks for sharing. I am a little surprised that you had 10" with the larger exhaust. I don't have any comparative info to base that on; just thought it would be in the single digits... Could you "feel" any difference?
Click to expand...

Well, the reading could have been 9" H20, but with the angle I was looking at the gauge (parallax, IIRC) I just rounded it up to 10".

The car ran well, and I was pretty happy with it, but I don't know how accurate my buttometer is when comparing changes to the car. :amused:
 
High temp sound insulation for exhaust?

Ran the '69 at a Porsche club track day last Friday. Car ran great, with no major handling issues or breakdowns. It did have a bit more interior exhaust noise than desired (even when wearing a helmet). I assumed that the new mufflers were just too loud under WOT, but on the weekend autocross I noticed something when I loaned the car to a young guy who I have "Big Brothered" for a bunch of years. (He recently bought his first Corvette (an '89), but lost the clutch last week when the hydraulic line between the cylinders split open.) Well, I noticed that while he was driving my car on the autocross course that the exhaust volume was very quiet (I revised my opinion upward right there about the quality of the Dynomax mufflers), even in the areas where the engine was at near WOT condition. I've kinda come to the conclusion that a good share of the interior noise was coming up through the floor from the EPTB under the seats. I'd like to try (if it exists) a thin sheet of high temperature heat/sound deadening material on the top side of the EPTB itself to dampen the vibrations. Can anyone recommend a material that might do the job? I'm thinking the surface temps are about 3-4 hundred degrees F at times in that area.

Thanks.
 
Exhaust crossover Part Deux

Decided to try a different version of the crossover. The first iteration worked well but it was a bit of an annoyance getting the center D shaped section to seal well without using some hi-temp gasket sealer. So, I decided to try something else. After a couple of minor setbacks getting the shape right so I could get the damn thing back out after tack-welding it I finally got something to work.

IM002332_zps3628b405.jpg

It slips up into the leftside pipe reducer nipple, then I rotate the pipe to buttup with the rightside nipple, and then slide the sleeve over the rightside interface. I then put a couple hose clamps on the sleeve to make a tight (hopefully leak-free) fit.

Took some time off from working on the car to fix my lawn tractor muffler. The original muffler was rusting out and getting too damn loud, and I wasn't in the mood to spend the money buying another overpriced part at the dealer. I looked around for material in the garage and decided to use some 4" tubing for the housing, and some smaller pipes for the inlet and outlet. I made three expansion chambers in it along with some SS wool for some dampening. Fired up the tractor and the noise level is damn decent. It took a few hours of my time, of course, but I've probably got less than ten bucks in material cost in it.

 
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that looks nice. getting those damn things to be leak free can be royal PITA. i like the lawn mower exhaust too nice improvization (sp?)
 
Have you tried V-band clamps or whatever these things are called? I bought one and I am really impressed- it does not leak and is super easy to tighten/loosen .... No gasket .... Not cheap though .... Think I bought OTX brand on ebay , $40 a pop .....
 
MYBAD79 said:
Have you tried V-band clamps or whatever these things are called? I bought one and I am really impressed- it does not leak and is super easy to tighten/loosen .... No gasket .... Not cheap though .... Think I bought OTX brand on ebay , $40 a pop .....
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Haven't tried any band clamps yet (I'm too damn cheap ;) ). This arrangement (the sleeve and worm-drive clamps) was the lightest (and cheapest) configuration I could come up with.
 
I dunno guys, 6 bolts and my entire exhaust system flops on the ground, except the headers, of course....I don't have loops under the pipes on my cross support, and utilize those band clamps, I suppose to call them, about 6" of metal and two bolts, wrapped around the pipes and tightened snug....

:crutches:
 
69427 said:
Ran the '69 at a Porsche club track day last Friday. Car ran great, with no major handling issues or breakdowns. It did have a bit more interior exhaust noise than desired (even when wearing a helmet). I assumed that the new mufflers were just too loud under WOT, but on the weekend autocross I noticed something when I loaned the car to a young guy who I have "Big Brothered" for a bunch of years. (He recently bought his first Corvette (an '89), but lost the clutch last week when the hydraulic line between the cylinders split open.) Well, I noticed that while he was driving my car on the autocross course that the exhaust volume was very quiet (I revised my opinion upward right there about the quality of the Dynomax mufflers), even in the areas where the engine was at near WOT condition. I've kinda come to the conclusion that a good share of the interior noise was coming up through the floor from the EPTB under the seats. I'd like to try (if it exists) a thin sheet of high temperature heat/sound deadening material on the top side of the EPTB itself to dampen the vibrations. Can anyone recommend a material that might do the job? I'm thinking the surface temps are about 3-4 hundred degrees F at times in that area.

Thanks.
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Well, my initial premise that the noise was coming from the EPTB was correct, but for the wrong reason. I pulled it out today to weld in some additional inner vertical walls to tie the top and bottom surfaces together to keep the box from acting/vibrating like a big bass drum (my initial guess as the reason for the box noise). Once I got it out I got a good look at the top (floorboard side) of the box.



It's a two inch tear in the top wall. I had a significant backfire at the end of the main stretch at Topeka last summer. The top of the box was oil canned pretty well, and the rip was right by the single internal stiffening wall. I peened the shape back down and welded a patch over the area. I'm anxious to see how much quieter the car will be inside after this repair.
 
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