jungspike

Is a M&K cat bypass and Fabspeed muffler a good choice for a 3.2 to 3.4 upgrade?

I am in the process of upgrading the engine on 84 911. I currently have a Steve Wong chip, Authority mass flow sensor, polished intakes and matched injectors. I am about to put in Mahle 3.4L 10.3:1 pistons and 964 cams. The question is what should I do for exhaust? The car is a road/autocross/DE car, so I want to keep it street-able (not too loud). I was thinking about headers, but I think that headers are not worth the price, so I am considering just adding a cat-bypass and sport exhaust.

First question: what should I replace the catalytic with? From what I understand a pre-muffler has some noise deadening material and a bypass is a straight pipe? Is there any high performance catalytic converters? If not I'll get a M&K and put my cat converter back on for emissions.

Second question: For muffler I plan on using a Fabspeed exhaust. Although M&K is cheaper and is reported to have good sound, sounds like the Fabspeed has more proof of HP gains.

Third question: Are headers worth it?

Anyone have any advice?

Tim

Ed Hughes

I think headers are worth it, especially if you increase displacement. My experience showed me that the 3.2 I had responded well to the better flow. I started with a cat bypass, and a couple of free-flowing mufflers on the way, and seat of the pants showed the headers were tops.

Fabspeed has long had a bunch of data, but I (and many others) always questioned how valid it was. What is the proof? I'm sorry, but the POS airbox they sell still effects my impression of them, as well as some experiences I had with fitment, droning, etc. I'd not get hung up on them vs MK. Go with the sound you want.

I had B&B headers with a Fabspeed muffler, that was really a Flowmaster with some candy coating, as I recall. With headers and my chip running 93 octane, I dyno'd 204hp at the wheels on an otherwise stock motor.

I then built the 3.4 with the same Mahles you describe and went north of 230 at the wheels. I can DC19 cams.

WHAT are you doing for ignition? Going to 3.4/98mm pistons, particularly at that CR most certainly dictates twin plugging. Not doing so runs a big risk of detonation, both from piston diameter and CR. I ran twin plug with a 964 dizzy and an Andial splitter on my DME.

Do a search on "Ruby Rebuild Redux" thread here for my build.

Edit: Here it is: https://rennlist.com/forums/911-foru...ild-redux.html

wildcat077

Tim,

I started off with a MK premuffler and Fabspeed one in two out muffler four years ago and was very satisfied,then i upgraded to a Fabspeed 1 3/4 OD header system for my 3.2 and last Summer i installed a 3.6 in my car and was able to use my Fabspeed system with the 3.6

There has been all kinds of criticism regarding Fabspeed products but in my case everything was perfect and the quality is second to none.

Cheers
Phil

Amber Gramps

Just stay away from the stupid thermo-form airbox cover. You could build the same quality part with a bathroom heat lamp, a shop vac, and a router.

Reiver

C,mon, you all know cutting holes in an air box gives at least 20HP. Almost as much as painting your calipers red.

jungspike

Thanks for all the prompt advice. Ed, I read that thread you were referring to (multiple times) and saw your posts--lots of great info in there--it answered many of my other questions.

I agree with the twin-plugging recommendation. I am going to have the heads drilled and plugs put in and save the ignition/distributor for later. My pistons came out of a DE car that was not twin plugged and the previous owner had no issues. (FYI: all my parts are used--so I did not pay full price for that Authority mass flow sensor.) I live in Colorado, so detonation is less of a threat... but I probably will worry until the ignition is done.

My plan is to get the engine work done and put the stock exhaust back on. Then, see how it runs and decide what to do next (exhaust or ignition). I guess if I get some detonation, I get an answer the hard way.

I have some 1-5/8 headers (brand unknown) and a B&B "race" muffler that I could put on. I hesitant to do this because I am concerned about the high dB level (heat would also be nice).

Tim

porsche0nut

My reading tells me that 1 5/8" headers are ideal size for a 3.2 - 3.4.... others with more experience can probably comment on it. Stock headers (heat exchangers) with a bypass and sport muffler is a nice setup (my current) but I think it leaves lots of power on the table.

RarlyL8 makes 1 5/8 headers with heat exchangers... I haven't heard any reviews on them yet. Really curious to hear from somebody using them and their impressions.

John@Fabspeed

I give back 5% to all forum members so for the full header muffler kit from me you actually end up getting a really good deal. To complete a full header back exhaust with a true dual inlet dual outlet muffler and a lifetime warranty for <$2,600 is pretty exceptional

redridge

FVD gets my vote... expensive, excellent hardware though...

http://www.fvd.us/us/en/Porsche-0/91...st_System.html

Ed Hughes

Not sure there's anything special there. In the end, its a kit based on SSI's that probably are too restrictive for the 3.4.

wildcat077

Do i get my 5% retroactive ??? I purchased a fine header system which is now
on my 3.6 conversion

Cheers
Phil

Steve Weiner-Rennsport Systems

Tim,

Contact me directly for some feedback and advice about exhausts for your 3.4.

Although you are at 5000 ft, your 91 octane fuel is VERY marginal with single-ignition at that CR. The only way you can make it work safely is by compromising the timing maps and frankly, thats not the path to performance and throttle response. If you use the 98mm wedge-dome Mahle pistons instead of the RSR-type, you can run without twin-ignition at 9.8:1.

porsche0nut

Evan, couple questions about the Fabspeed setup:

1) What size are your primaries on that system?

2) Why so many parts? Looks like it's modular, but overly complicated for somebody who just wants headers and a muffler. Instead of 2 headers and a muffler, you have 2 headers, 2 pipes to go to the muffler, a muffler, and then 2 tips.... that's 7 pieces instead of 3. Now each of those connection points needs a clamp...... your products look fantastic and I don't doubt the quality of them - just wondering why it isn't simpler. This is a case of "less is more" in my opinion.


Steve: Any comment on 1.5" vs 1 5/8" primaries on a 3.2-3.4L engine?

Ed Hughes

That would appear to be a modular system that wouldn't require welding, although, I'm sure you could. Any muffler you bolt up to headers is going to have elbows and such attached to it-usually by welding. I think I'd rather see a bolt flange on the headers than a clamp, however.

tulliotk

You guys have seen how many parts there are in a stock system, right?