Cat bypass bolt/nut question

[Inniswhe]

I am installing a used cat bypass that came with the 84 911 I recently purchased.
I have read a great deal on here and am really not sure what to expect perormance wise. I also am planning on installing a SW or 911Max chip and possibly a sport muffler to complete the performance mods.

The more I read the more doubtful the cat bypass will do anything more than make more noise but since it came with the car I might as well install it. PO bought it and never got it installed prior to selling.


I fought with the rusted fasteners today and between the dremel tool and worn nut extractors I managed to get the fasteners all off.

I went out to Canadian Tire tonight to buy some replacement M8 x40 bolts and nuts. They had no SS bolts so I had to go with 8.8 grade carbon steel plated bolts. I bought some M8 copper " manifold nuts" thinking it should make future removal easier. It this a reasonable approach or should I be using another fastener combination for future dissassemby considerations ?

[burgermeister]

Ought to work just fine - copper and steel don't rust together. The bolt will eventually weld itself to the exhaust parts after 20 years of use...
I went with 5/16 SS Bolts and SiliconBronze nuts. A 13mm or 1/2" wrench / socket works on those too, and the local hardware carries the bolts (but not the nuts).

[KatoKato]

See thread:

3.2 Exhaust Modification

[Inniswhe]

I had never read that thread before but it does not appear to indicate anything really definitive regarding the cat bypass performance increase other than indicating a very slight improvement.
There is a significant discussion between premuffler versus cat bypass.Some people claim euro premuffler is better than a cat bypass , others claim little or no difference other than sound.
I personally cannot see how there would be much difference between a cat bypass and a premuffler performance wise. Either should reduce backpressure thereby freeing up horsepower. The premuffler offers a silencing feature however. I recall from my univ. days when we instrumented late 80's BMW 3 series engines in the lab. We performed all sorts of manipulations of the stock arrangement to see how performance would increase/decrease. We always found that reducing the restriction on the exhaust would give more power to the dyno, only stands to reason.

I believe the the improvement for either really depends upon how much the stock arrangement is being restricted by the cat. I must go back and read the Bruce Anderson book again. I know he did some testing on the SSI's and sport mufflers and found significant improvements for the 3.2 engines but I do not recall anything specific regarding the cat bypass option and sport muffler with stock h/x's.

[Joe Bob]

It's not just the cat....it's six cylinders necked into one smaller ID pipe, doing 3, 90 degree bends wrapping 3/4 the way around the motor, then restricted by the cat, then then the single inlet muffler....

Think what six cylinders w/o the cat and equal length heat exchangers striaght back, no bends with a dual inlet muffler would do...

[Wil Ferch]

For bolting hardware..see my suggestion here, posts #7 and 9.

bolts for exhaust system

[burgermeister]

Originally Posted by Wil Ferch

For bolting hardware..see my suggestion here, posts #7 and 9.

bolts for exhaust system

These (above) posts are where I got the idea to use - eeek - SAE hardware on a 911. Don't know why I didn't think of it on my own, but happily I perused the board and found 'em. Thanks Wil.

[richde]

Anywhere know where to find, or what size plug is required to cap off an 02 sensor bung?

[sprintamx]

Possibly silly but important question: Where are the recommended jack and stand locations? I will be installing a Fabspeed muffler this weekend and the thought of trying that at ground level is not enticing.

Thanks guys.

[charleskieffner]

since im up to my keester and finally on the tail end of a very long road with installing GHL headers/w heaters/no cats/dual in dual outs, i have some things that worked for us. 2 years ago yanked off cat and put in bypass. HEAVY ON THE ANTI-SEIZE PLEAZE!

then i yanked off OEM muffy. once again side order of HEAVY ON THE ANTI-SEIZE PLEAZE!

used grade 5 metric fasteners. hell it aint a trophy truck in baja and it aint going into space for NASA!

smeared the hell out of them with the finest LPS ANTI-SEIZE THERE IZ!

2 years later(last week) time to pull everything off.


well everything came off fine but O2 sensor. started to use super zoomy special secret tool from pelikan to remove. wasnt really wanting to come out.
decided that buying new one was better route to avoid possible rethread nightmare. "if it aint broke DONT FUCH WITH IT APPLIES HERE BIG TIME"

the difference btwn cat and no cat IS noticeable. the difference btwn no cat and GHL single in/single out is VERY APPARENT!

the difference btwn no cats/headers/dual in-dual out is" NIGHT DAY I THINK I BOUGHT A NEW CAR DIFFERENCE!"

i dont have to run cats here because i CAN! but i was going to keep my OEM heat exchangers in case i ever sell car outside of state.

BUT>>>>>>>>>>>>> GHL while using my car as NEW JIG AT THEIR SHOP came up with simple idea of ditching 996 type clamps for pipes from engine to muffler and instead of 996 clamps we changed it to FLANGES and now whomever buys car can mount (2) cats(GHL) in place of straight pipes and pass ANY EMISSIONS ANYWHERE! actual test and VIZUAL TEST!

sooooooo.........best bet if yer short on bucks. ditch the cat, single in/single out exhaust(pick yer poison) and be happy with new found relativley cheap horsepower.

if hell bent like me to eeekkk every iota of horsepower out figure on :

cost of headers w/without heater boxes

new 2 in 2 out muffler

new exhaust studs??? how lucky are you???

new exhaust nuts and washers

new gaskets

various special tools to remove heatexchanger barrel nuts a standard nuts

anti seize

and a hell of alot of beer and patience!

dremel tool to cut valance. hope that helps!

no i did not need to remove oil lines nor change them(cost savings there)

[Inniswhe]

I had to fight to get the cat out , there were some stubborn fasteners. I used a combination of dremel, punch, 4" angle grinder, propane torch, then new MAPP gas torch, significant cursing, a couple of smashed/bruised nuckles.

I have the carbon steel and copper coated steel nuts but I believe I will try and find the stainless steel bolts recommended. I have never seen the "silicon bronze" manifold nuts. I think they may be the same as the ones just labeled "bronze" manifold nuts next to the copper ones on the shelf where I bought the copper ones at Canadian tire. They just looked like brass to me?

Do you put anti seize on the gaskets as well as the nuts/bolts ?

I think I will run this setup with just the stock muffler and performance chip for now and see how it is because I could see me going to the SSI's and dual inlet/outlet exhaust if I feel the need. Would that setup yield more power than the cat bypass and a M&K 1 in 1out. Both systems running a chip tuned for upgraded exhaust. Again varying opinions but it appeared from the Bruce Anderson book he thought the SSI system was best.

On another note, I am going to set my valve clearance so I think it would be easier to do before I put the cat bypass in place. This is my first valve setting on a 911 and was planning on doing the back method. My question is regarding draining the oil and temperature of the oil/ engine. The car is apart so I cannot run the engine to heat up the oil before draining. Is that an issue ?
Also how sensitive is the valve adjustment to the engine temperature. My shop is cold . I ran run my electric heaters overnight to warm the car up somewhat but my shop will only get to about 60F and the engine would be cooler, probably 40F. Does that throw the clearances off by much ? Maybe this should be on a separate thread.

Thanks all

[squelch]

I am installing a Fabspeed pre-muffler in a day or two. I went out to buy the nuts and bolts. I found 5/16 x 1 1/2 SS bolts, but could not find these silicon bronze nuts mentioned above. Any ideas where to find them. No one I talked to had ever heard of them. I ended up getting bronze lock washers and brass nuts. Will this suffice, or should I get SS nuts and washers?

Thanks

[charleskieffner]

i didnt put anything on gaskets only dry. as far as oil, doing valves yer gonna loose alot.
go ahead adjust them cold .004 intake/exhaust for my 3.2 and then do oil change. add 10-11 qts. then fire and do SOP on oil stick check.

i was happy with just cat bypass, then happier w bypass/GHL single in/out...............then really happy with headers dual in/out. but watch your A$$ on changing out heat exchangers for SSI or headers or headers w/heater boxes. those damn threaded studs can turn your life upside down real fast if you break them.

and guess what??????????????????

you have 12 CHANCES OUT OF 12 OF BREAKING THEM!

im not a gambler and i hate those odds. so PBR BLAST THE HELL OUT OF THEM and use OXY/ACTL to loosen them. being EINSTEIN HERE AND HAVING A BOATLOAD OF MONEY doesnt gurantee success getting them off in one piece!

IT IS A HUGE CRAP SHOOT!

bottomline worth every penny to have shop do it and not have a weekend turn into a week or more of hell getting stud removed . engine out of car not such a big deal. engine in car..........a pretty big deal!

i honestly should have opted for headers w/heat boxes first for all the hassle i have gone through. but i have learned alot from it.

[burgermeister]

Originally Posted by squelch

I am installing a Fabspeed pre-muffler in a day or two. I went out to buy the nuts and bolts. I found 5/16 x 1 1/2 SS bolts, but could not find these silicon bronze nuts mentioned above. Any ideas where to find them. No one I talked to had ever heard of them. I ended up getting bronze lock washers and brass nuts. Will this suffice, or should I get SS nuts and washers?

Thanks

I mailordered them ... boltdepot.com, item 3482, $0.43/pc + shipping

[squelch]

My Fabspeed Premuffler came in today. My cat bolts were a biatch to get off, but I finally got them all using a combination of heat, long wrenches and a cutoff wheel.

Regarding bolt sizes... 5/16" bolts fit the stock exhaust parts perfectly. However, the Fabspeed premuffler's holes are larger at 7/16", so the question is, do I"
1. Use the 5/16" and not worry about the slop on the premuffler side.
2. Drill out the factory holes to 7/16"
3. Find some way to shim down the larger holes using a bit of metal tubing or something. I don't even know if this is even possible.

I was also disappointed to find that the Fabspeed did not come with new gaskets. Has anyone else gotten new gaskets with their cat bypasses/premufflers?

[Inniswhe]

I went back and looked at the store where I bought what appear to be copper manifold nuts. They were tagged brass manifold nuts but are copper in color . There were other sizes that were brass color. What color are the silicon bronze nuts ?
I suspect the nuts I have are copper coated steel but don't know for sure . Would anyone know if these would be compatible with the st.steel bolts I picked up today or do I run the risk of them gauling if it is indeed steel under the plating?

I am not going to mail order any nuts, I am going with these nuts that I have and either the M8 st.steel or carbon steel bolts I have.

[charleskieffner]

godbless good american made cutoff wheels and vehicle lifts.

cant even imagine doing on ground!

a thought on this after it finally being completed today.


use all metric bolts-duh

put some miles on and heat cycle. on/off warm/kalt

come back retighten everythang.

now if you do headers GHL and dont change oil lines look at angle of dangle btwn passenger side rear oil line and pass. hot exhaust pipe. hmmmmmm

looks like weez gonna get me some high temp heat wrap for the oil line. like NASA DOES!

dual in dual out sounds incredible especially at high revs!

its dark here and we are waiting for satellite(bus sized) to explode above our heads. sooooo.... gonna quit playing mit der exhausten geheaders and getrinken bieren.


now were gonna get in touch with senor wong and talk about a easy quick removed from stock to wong chip .....chip!

bullet proof water proof shock proof anti satellite missile proof............chip

[burgermeister]

Originally Posted by squelch

My Fabspeed Premuffler came in today. My cat bolts were a biatch to get off, but I finally got them all using a combination of heat, long wrenches and a cutoff wheel.

Regarding bolt sizes... 5/16" bolts fit the stock exhaust parts perfectly. However, the Fabspeed premuffler's holes are larger at 7/16", so the question is, do I"
1. Use the 5/16" and not worry about the slop on the premuffler side.
2. Drill out the factory holes to 7/16"
3. Find some way to shim down the larger holes using a bit of metal tubing or something. I don't even know if this is even possible.

I was also disappointed to find that the Fabspeed did not come with new gaskets. Has anyone else gotten new gaskets with their cat bypasses/premufflers?

Whatever you do, bolt the whole mess up loosely first, then tighten your muffler straps, then tighten all of the flange bolts, or it will never ever fit.

A clamped joint relies on friction of the clamped together parts to keep it tight. The bolts are not loaded in shear in such a joint, so any excess clearance between bolts and flange holes is not an issue. I'd consider it a benefit for future disassembly.

I would not expect an exhaust part to come with gaskets, btw....