2.5" DP and Magnaflow--RESULTS UPDATE
 

Bought a 2.5" DP (with welded-on H-Body flange) and Magnaflow cat from a BC member:
http://www.bonnevilleclub.com/forum/...ic.php?t=80900

http://momentoffame.com/photopost/da.../DPCat_000.jpg

Also bought 3 AccuSeal Clamps on EBAY, and rented a chain-type tailpipe cutter from Autozone. Also got some sealant in case of leaks. My new buddy at the muffler shop gave me a 14" length of 16-gauge 2.5" OD stainless exhaust pipe in exchange for a smoke and a chat about baseball.

Cat's ID measured 2.58", while OD on the DP and pipe were 2.50"...had to cut some slots with a hacksaw to make sure the clamp would close it all the way:
http://momentoffame.com/photopost/da.../DPCat_001.jpg
http://momentoffame.com/photopost/da.../DPCat_002.jpg

All I have to do to the new parts now is cut that rear pipe down to size:
http://momentoffame.com/photopost/da.../DPCat_003.jpg

Install pics hopefully coming this weekend :D

Awesome, ANdrew.
Can't wait to hear how it runs with that in place.

Got the chance to start the install this evening.

Best shot at the rear mani to DP nuts was from underneath:
http://momentoffame.com/photopost/da.../DPCat_004.jpg
http://momentoffame.com/photopost/da.../DPCat_005.jpg

Then the DP flange to cat nuts:
http://momentoffame.com/photopost/da.../DPCat_007.jpg

Maybe a week or week-and-a-half ago I cut the pipe holding in the cat just behind the weld with the chain cutter, and I've running with an AccuSeal clamp holding that together since then:
http://momentoffame.com/photopost/da.../DPCat_006.jpg
http://momentoffame.com/photopost/da.../DPCat_008.jpg

(I also went through and PB Blasted / loosened / retightened all the nuts involved in this install at that time, just so I'd be ready when my parts arrived 8) )

Here's the naked rear manifold studs, with lots of anti-sieze applied and re-using the metal DP-to-mani gasket:
http://momentoffame.com/photopost/da.../DPCat_009.jpg

New DP looks to fit fine with plenty of clearance. Yay, the stock cat fits onto the new DP and back into the resonator...
http://momentoffame.com/photopost/da.../DPCat_010.jpg
http://momentoffame.com/photopost/da.../DPCat_011.jpg

Good thing, too...the 2.5" OD straight pipe on the back of the new cat is just a wee bit too big to fit into the cut-off resonator pipe; I think the AccuSeal clamp might have crushed that resonator opening down a touch...I'm going to have to rent a tailpipe expander to open up the neck of the resonator before installing the cat. That's OK though...I kinda wanted to see what the DP alone does, THEN the DP plus cat.

Here you can see the size difference between the stock cat and this Magnaflow :shock:
http://momentoffame.com/photopost/da.../DPCat_012.jpg

More to come!

Looks great Andrew...

Did you cut in front of the O2 bung?

No, behind. The new cat and pipe is bungless, and I'll program out the rear O2 with the tuner.

The stock cat w/bung will be swapped in for special occasions ;)

Ah, dang it...."pfft, pfft, pfft" on the way to work today. I can't make it happen just revving in the parking lot...only under load.

I hope the leak turns out to be at the stock cat-to-resonator joint, where I can fix it up temporarily with some sealant (and perhaps more permanently later).

If this DP is leaking (at the flex?), I'm gonna be an unhappy person :cry: .

It's leaking somewhere where the engine causes two pieces to pull apart. Maybe your neverseize(it looks like anyways..) let the flange nuts to the manifold come a little bit loose?

I did just go take a look under the hood, and it looks as if the left side mani-DP stud is not in as far as the one on the right side...I did remove and re-install those studs (7mm hex head) before installing the new DP, but maybe I didn't get that one seated all the way. Will check that out this evening. Also, perhaps I was a bit too liberal with the anti-sieze ;)

In any case, I did rent the tailpipe expander, so maybe that new cat will be on sooner than I thought...assuming I can find and fix this leak :?

hope you get that leak fix youre cat look the same as the new one i got you should see difference in sound and power

More progress; got the cat and pipe clamped in between the new DP and resonator:
http://momentoffame.com/photopost/data/523/DPCat.jpg

Drove it around a bit, and it does feel like it accelerates more freely...unfortunately I couldn't find a place to really open it up due to traffic. Oddly, no codes were thrown even with the rear O2 gone...maybe they require 2 or 3 startups.

The sound I was hearing is still there. I'm beginning to think this is the downpipe flex "ticking" I read about on the ClubGP forums...anyone familiar with that? Supposedly it's not a leak, but rather the sound of the valvetrain amplified in the single-walled downpipe (???)

Anyway, supposedly this flex ticking can be addressed by using header wrap around the flex. (Does this actually fix it? Who knows...nobody ever follows up threads on ClubGP with testimony regarding success or failure :x )

I have been having the same problem with my 93. When I torque the motor the EM flange pushes against the downpipe and it opens at the bottom to give me the pft pft pft sound. I tried an exhaust shop that told me they didn't have a big enough donught gasket for it. So I bought one from the dealer and it is bigger but I still have the leak. I will watch this thread closely to see what you find out. My only next step was a new downpipe that would hopefully be the correct angle to stop this leak.

I kinda hope I'm having the same problem, as I want to believe the flex is OK :?

My very next step is to act as if there is a leak between the rear EM and DP, to rule that out.

My '98 had no donut between the EM and the DP...looking through parts catalogs, it seems the '97 and earlier had it:
http://www.napaonline.com/masterpage...st+Pipe+Gasket

Maybe I should get one of these?

On the other hand, I wonder if it would be a good idea to stick a huge ring of exhaust sealant on the EM (with or without the metal gasket???), as pictured by the red ring (kind of like sealing a coolant neck with RTV):
http://momentoffame.com/photopost/da.../DPCat_013.JPG

Opinions, anyone?

The shop that I went to that didnt have a gasket put that sealer on it and it lasted about 20 miles and that was it. Sorry, but that will not solve the problem there because there is too much movement in that area. It is made to move around due to the motor torque with it being mounted sideways. I would for sure try the gasket first in your case. I know how you feel though I hate exhaust leaks and I can't get rid of it without a good exhaust shop and some money. :(

Yeah, that sealant dries to something quite brittle, so I can see where the ring o' sealant idea won't cut it.

I can confirm now that there is a leak between the rear EM and DP flanges...this morning on cold startup, I saw some moisture bubble up out of that joint.

It looks to me like in 1998, GM switched from a donut to an embossed gasket to seal that joint. The rear EM is interchangeable from '97 to '98, and the flanges on this 2.5" DP look to be recycled from a stock DP, so I'm thinking that the stock '97 donut I linked to earlier might do it. It's worth $10 to find out.

The CEL came on during my ride to work, so I guess the PCM figured out the rear O2 is gone. I'll have to program that out.

my 97 doesn't have a doughnut there, flat metal gasket with a lead ring.

The napa catalog shows a flat gasket for '98 LeSabre:
http://momentoffame.com/photopost/da...P_gask_new.jpg

But a donut for '97 LeSabre:
http://momentoffame.com/photopost/data/523/DP_Ring.jpg

Maybe the switchover year for Bonneville was earlier?

Anyway, $11 later and I've got the donut (FEL-PRO 60640):
http://momentoffame.com/photopost/data/523/60640.JPG

It is a tapered ring measuring 3.02" OD at the fat end, 2.78" OD (2.51" ID) at the skinny end, and 0.58" thick (not counting a small lip on the fat end)

I'm assuming the fat end goes into the rear EM, and the skinny end goes into the DP. I guess I'll find out this evening ;) .

The bonne and Riv changed over in 97. 96 and prior were donuts.

Ben had a leak(just one of many he has :lol:) just like yours. I think he fixed it with a new flat metal gasket. I don't know, but I think that gasket may be directional(based solely off of the way the used one from Ben's car looked. visual comparison of the inner ring vs. which way seemed to sit best in the DP flange). Just a thought? Those two flanges shouldn't be moving I wouldn't think. That's the job of the flex pipe.

Take all of this with a grain of salt. We're comparing a 97's to 98's and it's already mentioned that they changed over.

the little lead ring on the flat gasket has to go to the dp side

The tapered part of the gasket goes to the DP. I just want to note incase anyone is following this with the same problem. I do not have a flex pipe on mine. This is why there are springs on the flange bolts, a ball type of gasket, and a flared end to the DP to allow for movement when the engine twists back against the solid exhaust. My DP is just enough off that it opens up under heavy acceleration and the flanges meet at the top. I could probabally have a shop cut it off and bend it but I don't have the money for that right now.

Boss and boss's boss are traveling, so I went home after lunch 8)

LEAK FIXED!

But I didn't use the donut...it wasn't going to fit anywhere; I guess the different years used different DP's and/or EM's after all. Wonder if napa will take a return? (If not, anyone need a donut?)

Problem was something I mentioned earlier...the left side rear EM stud wasn't seated all the way in the manifold flange (I think you can make that out in one of the earlier photos); removed it, cleaned the threads with a dremel and wire brush, and it went back in smooth as butter. Reused the original flat gasket, flanges mated up nice, and BAM! No leaks :D

(Note to self: don't screw up the stud seating when doing the heads later :shock: )

Freeway testing confirms..."pfft, pfft" is gone.

Sound is "growlier" than before, which I like. Seems to accelerate better...and oddly, it seems like it doesn't decelerate as quickly when I take my foot off the gas :?:

Scanning and tuning (perhaps this weekend) should say for certain if I gained anything.

Excellent! Looking forward to seeing the results. :twisted:

Where have I been? Totally missed this thread. Glad you got it fixed, Andrew... I hope you have some good results with the 2.5" DP, as I'm itching to get one myself. Let us know how it fares in your VE tests.

Got to open it up on my little stretch of deserted road in the foothills...initial quicky scans and VE calculations are pointing to good things :shock:

UPDATE: After it cooled down to 70* F this evening, I took some more runs with scans, and did some more VE calcs...

WOW! Just WOW!!!

Preliminary estimates are +15-20 ft-lb torque at 4200 rpm, and at least +15-20 hp at 5200 rpm...and these scans (and estimates) were with PE turned off (i.e., with no added fuel under WOT, or 14.7:1 all the way to 6k rpm with no KR ) and without the extra 4 or 5 degrees of WOT spark advance I expect to be able to add before my tuning's all done.

I had heard a bigger DP would reduce KR, but this is unreal. Also, I see nothing in the scans indicating any "low end loss"; makes me wonder if my old cat was plugged up or something...

I hope to have the full story by early next week. :D

wow that nice keep us posted on the progress

I gotta say, if it's true that my old cat was plugged or whatever, this new cat may mostly be "giving back" lost power...I have GOT to get to a dyno sometime.

did you look in youre old cat could you see daylight true it .i don't think mine was plugged but my new one is half the size

Yes... yes you do! Quickly, before I come San Diego and start flour-bombing your house!

Uh, it seems I had a bit of a spreadsheet error in my earlier estimates, and imported the wrong "before" data... http://www.bonnevilleclub.com/forum/...smiles/pat.gif

After a number of additional tuning runs over the weekend, the final tally is about +4 to 5 ft-lbs @4200 rpm and +4 to 5 hp @5200 rpm.

I did manage to add 2 to 3 degrees of timing advance in many "high load" spots in the timing table (and as many as 6 degrees in low-to-medium areas), and this probably accounts for the increases.

I'll post the final VE curve tomorrow.

That's good to hear...

The original gains seemed a bit overstated for the changes made. 4-5HP and torque is respectable from a mod like this and great to see.

I have to agree, every little bit counts on a NA setup. :D

As promised, here is the latest VE graph:
http://momentoffame.com/photopost/data/523/DPCat_VE.JPG

The 2.5" DP and Magnaflow cat show an increase in calculated VE across the entire range, but with diminishing return above about 5k rpm.

Here's the new latest calculated improvements vs mod levels:

Mod Level---Torque (@4200rpm)---HP (@5200 rpm)
Stock-----------+0 ft-lb--------------------+0 hp
PLIM------------+10 ft-lb-------------------+8 hp
PEM-------------+6 ft-lb--------------------+5 hp
L67TB----------+16 ft-lb--------------------+17 hp
SRR-------------+4 ft-lb---------------------+9 hp
DPCat-----------+5 ft-lb---------------------+4 hp

For an estimated total of about +41 ft-lb @4200 rpm and +43 hp @5200 rpm over stock (or at least, over where I started from :P ).

Again, having bought alot of hard parts used, I'm now about $450 into parts/gaskets with what's charted above.
That's just over $10/hp (if my calculations are close), so I'm happy so far.

(As always, these are calculated estimates only, not yet backed up by actual dynos...)

The exhaust is louder and "throatier" than before, probably because the new DP is a single-wall (instead of a double-wall like stock). For the most part, I like it...but there is a slight "droning" sound between about 2500 and 3000 rpm that I could do without, and start-up in the driveway in the morning is louder. Should this DP ever temporarily be removed for any reason ;) , I'll probably use some header wrap just to try to muffle it a bit.

As I've mentioned before, something's severely holding back the upper-end performance (above 5k rpm), and it's likely the restricted intake tracts in the stock L36 heads:
http://www.bonnevilleclub.com/forum/...ic.php?t=77163

Modded heads (and better valvesprings) are down as a winter project, so I'll probably work on some low-cost UIM modifications between now and then (kinda modeled after zzp's HV inserts; TJ and BillBoost know what I'm working on).

If the head work pans out the way I'm hoping it will, the rest of these mods will probably synergize very nicely with them. If the head work doesn't give me what I'm looking for, I'll have to give serious consideration to some stronger medicine :twisted:

once the car is running decent.... I will be doing some before and after testing on your HV3.247389 project :lol:

well that good to know because i still have the stock down pipe .i think that the next thing to take care .andrew are youre PEM welded or just ported

Remember, I have the "fake" front ported exhaust manifold...no welded-on material on the outside.

I may step up to a PowerLog (v2) someday...like this DP/Cat, that can easily be swapped for stock when necessary.