originalmotorhead

I've seen some threads before about the pro's / con's of headers, but I am still undecided as to what I can get away with.

Here's my scenario:
2000 boxster with 2.7L motor.
-has the pre cats build into the stock headers with an o2 sens before and aft the pre cat
I've already removed the secondary / main cats and replaced with the fabspeed pipes.
I have a gutted stock muffler.

I am looking at installing some schnell(or similar)(low cost, hehe) headers which only have 1 bung per header for the o2 senser. I Plan to weld the second bungs into the fabspeed pipes, for the second set of o2 sensors.

My perplexing questions are:
1. Will I get a CEL light? From what I have read, I think this is a YES!
2. Will the motor run properly or will the computer see there is no difference in o2 senser values and run in limp mode or something?

I can live with a CEL light on because i've got a code reader and can reset / check from time to time. But, I don't want to have degraded performance, when I am actially tring to bump the performance.

In the future, i am hoping to maybe have the computer flashed, to take advantage of the bolt on mods but for now I will be using the stock computer program.

No, I'm not worried about emissions, smog tests, etc.

Anyone out here have experience in doing this ? what was the outcome ?

Tom

Tierce

you will certainly have a check engine light because the computer will see no difference between the readings from the first o2 sensor and the second.

Without correcting this, you should notice a power loss.

On another note, how does the muffler sound gutted? And with the Fabspeed pipes. I've got a custom exhaust and it's loud enough as it is, even with stock cats still installed. Those fabspeed pipes have got to make it louder.

AlpharettaRK

I've read that if you just use the pre-cat O2's in the headers and plug in but just tie off outside of the exhaust the after-cat O2's that you will be OK wiith no CEL. This will obviously indicate a huge difference between the pre-cat and after-cat sensors. This is from Boxster Spec races on the Boxster racing board. I haven't done so myself. It's at least worth a shot before welding those other bungs on.
Cheers
Randy

originalmotorhead

my gutted muffler is not really that loud with the fabspeed pipes. originally, i had streight pipes in place of the muffler and i had all 4 cats and that was ok but bone numbing at 2500rpm. when i replaced the secondary cats with the fab pipes, it went to 100% insaine noise so i took my stock muffler and hollowed it out. i get a little drone but not a whole lot. Hard to describe but it is more of a deeper / throaty growl now.

Randy, I think what I will do is pull my two secondary o2's and install plugs in the holes to see if I get a CEL or noticable perf drop and if not, then I'll order my headers.

Tom

AlpharettaRK

Tom -
Let us know how it turns out!
Randy

Macster

willingness to modify your car in a way that increases its emissions output and will likely result in it running less efficiently delivering poor peformance, to boot.

Even though you can clear the CEL everytime it comes on after your ill-considered modifications this erases the long term fuel trims and the ECU has to relearn these again. If the engine is near stock and still at its near factory/baseline condition there won't be too much change in performance. Which means there's no real gain to be had from your mods.

But if the engine not stock and has aged/worn to the point it is not near its factory/baseline condition optimum fueling/ignition timing will not be obtained for some time. And relearning will be required if your mod's have any positive effect on engine performance. And about that time the CEL will come on again.

The only way to know if there is any benefit from the mods you are considering is to take before and after measurements on a dyno and compare the results.

My guess is you'll imagine more gain than the mods deliver.

The stock ECU will fail the post converter O2 sensors for a variety of reasons: That they do not begin reacting to exhaust flow in time, or they react in a false manner to name two that come to mind easily.

If you want increased performance, restrict your driving to cold dry days. The Boxster engine controller retards ignition timing when coolant temperature rises above 196 F. and intake air temperature rises above 86 F. Even on a mild day and certainly on the track these temperatures will be obtained.

Sincerely,

Macster.

originalmotorhead

Not Disagreeing with you Macster, I've gone back n fourth regarding what to tinker with on the car.

As the story goes....Muffler modifications started with intent to increase sound levels a tad, then changed the intake filter to a cone for more sound and 'hopefully' some hp gain. Apparently i found a money tree and decided to plop the 450 bucks for the secondary cat deletes. Again, all in tinkering. the fabspeed pipes(cat deletes) were the biggest ka chunk of cash that i put into it so far. Then I started looking at headers and laugh or not but i just ordered some 'generic' headers from fleabay for 100 bucks. if they are junk, I'll resell for whatever they bring but in looking at all the variations out there, I thought it a relatively inexpensive 'test'. These 'generic' headers have two o2 bungs on each header, but initially, I plan to tie off the secondary sensors since that seems to be a semi prooven way to avoid that cel. I also got to thinking, what if I too an ohm meeter and measured the reading of the secondary o2 sensors while the car was warmed and at operating temp. Then, remove the secondary o2 sensors completely and install resistors that were equiviliant to the reading i took. This in theory would 'fake' out the computer that a specific value was being read from the non existant sensors. I know for GM vehicles, there are the "dummy o2 sensors" that you can buy when you are doing a full exhaust system but i have yet to see one for porsche cars.

I agree that dyno testing is the only realy way to know what the motor is doing and i have not done that to date so i have no baseline. Dyno testing after all my work would only tell me what i have gained or lost over what the 'norm' hp is for this series of cars but not mine specific.

My thought is that in time I would like to send the ecu out to be reprogrammed to see if that would provide any benefit.

So maybe i am wasting my time and money but to daye I am only out $600 bucks over 4 years worth of tinkering.
Tom

Macster

Generally cheap car engine hop up parts are the most expensive ones you can buy. You can spend much more money and time trying to overcome their cheapness and still not have as good as you had with stock setup or even with an aftermarket setup offered by a reputable company.

If you have a money tree, cut your losses and buy a quality exhaust system from a reputable manufacturer that other people can vouch for regarding qualility, performance, service. You can probably run across some Boxster owners with these systems installed at Porsche meets, auto-xs, track events, etc. and maybe even get a listen. I'm sure you'll get an earful regarding which systems to avoid and which ones to buy.

There are those who have claimed to have found ways to fool the engine controller regarding missing O2 sensors and modified converters. I do not know how good these techniques/tricks are.

Part of my job is working on devices use to verify/confirm a vehicle meets emissions requirements applicable for the region where it is registered and I'm uncomfortable with people who seek to attempt to mess with their vehicles and interfere with the very clean operation coupled with good performance of their vehicles for the sake of nothing more than more noise or even some HP gain for a vehicle used on the street.

Sincerely,

Macster.

originalmotorhead

My headers came in and I'm planning to install em this weekend.

Anyone know the torque specs for the bolts that hold the headers on the heads ?

I'm going to stop by the local stealership and purchase a couple of the bolts and hope that is enough voodoo to keep the existing ones from snaping when i take them out. I've heard of those bolts snaping when the headers are removed. Guess I best buy a tap and easy out too. :0

Any suggestions from people who have removed their headers ? Is there a technique to it or all luck?

Tom

Macster

Factory manual (electronic copy which is not as good as hard copy which is at office) gives 25nm or 19ftlbs for the bolts that hold exhaust manifold to head.

Mechanic at local Porsche dealer told me -- was asking about having exhaust manifold on driver's side replaced cause the small converter that is part of the exhaust manifold and is monitored by O2 sensors is worn out -- told me that you can count on 1 maybe more bolts snapping off. Says it is SOP to drill out broken bolt and drill/tap head to take thread insert to restore threads.

Been a long time since I dealt with frozen bolts and I don't know which technique to use.

Giving head of bolt smart whack with hammer -- dead straight though. Since bolts underneath hard to believe any penatrating oil will have much success wicking its way up into threads but might not hurt. If you can give each bolt several applications and let the stuff work its way into the threads as far as it can go.

Porsche tech advised he had best luck with impact wrench that jarred bolt loose vs. using hand wrench and even/steady pressure.

Applying concentrated heat to bolt then letting everything cool down to as cold as it can get. Another way would be to pre-drill bolt through its center with small drill bit. The hole allows some of the tension of the bolt to relax and loosen its grip on the hole.

Which one or ones to try? Which ones will deliver best results? I have no idea.

Toyed with idea of taking car into Porsche dealership service department and having exhaust manifold *gasket* changed and letting Porsche shop deal with the bolts, and fixing any that broke off, then afterwards when I got car back then removing bolts -- now fresh and likely easy to remove -- and replacing exhaust manifold and possibily the gasket myself. I can source new manifold for around $300 but dealer wants to charge me close to $1000 to replace it. Big markup in parts price and labor is costly too.

Don't know what I'll do. I have no place to work on car where I live and some work I do on car at where I work but if I'm there and run into trouble I'm stuck with car parked in building in way of shipping department and me without any way to get around to source anything I might need. Would have to have all new hardware, thread inserts, proper sized drills and spares, drill motor, everything/anything for any contingency.

Sincerely,

Macster.

originalmotorhead

I did some searching on this site and found several references to heating each bolt with a propane torch till as hot as possible as to transfer much heat as possible to the head. theory is the bolts are steel and the head is aluminum and head will expand(open) more then bolt will.

Friends at work advised me to use an impact gun vs hand wrench.

Everywhere I read to replace all the bolts and not to reuse any due to corrosion. There were a couple websites (boltdepot.com) listed for sourcing the bolts and it sounded like dealer is expensive but pelican had them for a buck each or local hardware but get high a grade strength as possible? I plan to call my local dealerships and then shop the local hardware before I mess with online ordering. what i found ws the bolts are M8x1.25x28mm (28mm long by 8mm wide) sounded like 25mm and 30mm long bolts were readily available in hardware stores. Not sure if using a washer for the gap is wise or not. Antiseize cream on the reinstall was a must !

I am in similar prediciment as i have my 'other' car in shambles too so I am thinking I'll take a vacation day on a friday so i have a 3 day weekend in case the "oh crap snap" happens.

Tom

Macster

material around the bolt while at the same time of course heating the bolt. The result in the bolt will swell and the hole will shrink as the metal around the hole heats up but has no where to expand to except into the hole. Small holes in large masses of metal only grow in size when the entire mass is heated evenly.

(Surprisingly, in some cases of extracting a broken bolt using an electric arc welder (or other style welder) to weld a nut to the protruding end of the broken bolt so heats the bolt so quickly that upon cooling the bolt is loose and one can remove the broken bolt by hand. I suppose the bolt in being heated this much loses its tension (its stretching condition is relaxed) and thus the bolt becomes loose. Thus one "trick" might be to arc weld a nut to the top of the bolt then let the bolt and head material get "dead" cold again and then attempt to loosen the bolt.)

The bolt's fit in the hole is not an interference fit. The contact is by the thread faces of the bolt and the hole. And not both faces of the thread but just the thread faces of the bolt that face the head and the thread faces of the hole that face away from the bolt head.

The major dia. of the internal thread is a bit larger than the min. major dia. of the external thread and the min. minor dia. of the internal thread is a bit smaller than the min. minor dial of the external thread.

In short the contact is the at the face of the threads centered (ideally) on the pitch dia. No contact should exist at any other place.

The bolt is under tension -- stretched -- from tightening torque. The bolt if it breaks will do so because the friction of loosening is increased by the metal to metal contact and any corrosion that has set up over the years these two metals have been in contact. This corrosion has probably created places for cracks to form at the base of a thread of the bolt, which in a proper thread form will have a radius. But this won't help if corrosion present.

A sharp blow with a metal hammer to a cold bolt's head, straight blow and not a glancing blow, mechanically shocks the bolt and can cause the bolt and hole thread faces to separate by a tiny tiny fraction of an inch (even at the molecular level is all it takes) and thus some of the grip these two metals have developed will be reduced to the point (it is hoped) that the loosening of the bolt does not result in it twisting in two.

I would always source new fastener hardware of the right grade. The hardware is so cheap relative to the cost of dealing with reusing hardware that has been compromised by years of harsh service it makes no sense to even bother. (Smash the threads of old bolts with a hammer before throwing them away or some helpful soul will see these perfectly good bolts in the trash and pick them out and put them back in your "good bolt" drawer....)

The bolt holes want to be clean and dry. Clean threads by running a properly sized tap in the hole ot the bottom not to enlarge the threads or deepen them but simply to scrape as much corrosion from the thread surfaces as possible. A suitable cleaner then is used to flush any of the debris this operation creates so the thread hole is clean and free of any thread penetrate or old thread anti-seize compound.

If you remove a bolt that brings some hole metal out with the bolt threads, then this hole needs to be fitted with a thread insert. In fact, it is not a bad idea to treat all holes to this thread insert step. Upon subsequent tear downs the threaded insert is easily renewed.

Sincerely,

Macster.

originalmotorhead

both local p car dealers did not have the bolts in stock so unless i can find some of equal quality at a hardware or speciality store, then i'll be forced to order some, which is 5 days, so no chance of me tinkering with this over the coming weekend.

oh well. i'll think of it as forced planning : )

tom

Turboflyer

I would suggest unless there is significant aluminum on the threads you just clean the holes. Use a tap that is referred to a thread chaser or cleaner, not a tap made specifically for new threads. As far as inserts. Great idea if the head was off and set on a bench where you can ensure a perfect perpendicular hole with the right squaring tool. Otherwise you may indeed create a monster. By all means use a torque wrench as not much torque is required on those aluminum heads. I do not have the value in front of me but recall something like seven foot pounds maybe ten always look up the value. Memory can strip threads and snap bolts. Also you might measure the thickness of your header flange to see if it is the same as the stock flange. You will want to add or subtract that to your stock bolt length. What ever you do take the car some where so you don't have to worry about how long it takes. That will inevitably lead to poor decisions and increased work load not to mention stress.

Macster

flutes of the tap making this face flat will see the edge no longer a cutting tool but just simply some thing that still is almost the size of the internal threads but will not remove any additional metal from the hole and existing thread forms (which were probably formed by a roll tap and not a cutting tap). It will remove most surface corrosion and any thread lube or locking compound.

That the leading face of the flute is removed means the overall diameter of the tap is slightly reduced as well.

After chasing the threads and cleaning the hole thoroughly a trial fit of the new bolt to ensure one can thread it fully into the hole by hand is called for.

As for torque I agree that one should know the torque value to use. Neither the digital factory manuals nor hardcopy factory manuals I have and in fact the hardcopy I have opened to the exhaust system section give a tightening torque for the exhaust manifold to head bolts. Worse actually in the line drawing while the exhaust manifold bolts are shown they are not even assigned a location number.

As for threaded inserts, the existing hole will be the guide. If one was drilling a new hole into a solid ideally having the solid part on a bench and being able to use a drill bushing/guide to ensure the hole is perpendicular would be nice, but one can enlarge an existing threaded hole to then tap the new hole to take a threaded insert.

If one doesn't feel up to doing this then he can arrange beforehand to have someone who is up to on standby -- a mech that makes house calls?... -- or face the fact that he will have to take the car to a shop that has qualified personal to deal with this contigency. There is at least one other option should the need to install an insert arise: No time like the present to learn how to do this.

Sincerely,

Macster.