backdating SC exhaust

[surflvr911sc]

I have an opportunity to buy a set of pre74 heat exchangers and 2in/1out Anza muffler for my SC. Is this a good idea or should I wait and do SSI's next year.

What about emissions? Do I just drill and tap a hole for the O2 sensor? What about the CAT? I don't want to change it out every two years but I might consider it.

Any advice would be great, I never considered backdating.

[Bill Douglas]

I believe the SSIs are fractionally better (power wise), but if this setup is a good deal, go for it. A mufler place could do the C02 thingie for you for very little cost.

[82SuperC]

I've often wondered how to do the backdating in Cailfirnia without an emmissions problem. In addition to the O2 Sensor, will you be running a cat bypass pipe and replacing the catalytic converter upon emissions testing? As I understand it, the pre-74 exhausts do not allow for a catalytic converter in the exhaust chain. This is something I was considering doing but opted out because I did not want to substitute the stock exhaust every two years for testing. Is there a elegant way of doing this and still meeting emissions? I don't think you can pass the visual without a catalytic in there somewhere. Anyway, your thoughts would be appreciated.

[marcesq]

Since the SSIs (or pre'74 heat exchangers) have 2 outlets, you would have to hook up 2 cats which would be impossible without some serious pipe bending. Not only that, the cats would take away most if not all of the HP gains achieved by the back dating.

The long and the short of it is change out the systems every 2 years or move to a state that does not have emission tests!!

Wish I had a better answer.

[surflvr911sc]

I not getting a real good feeling about backdating here. It seems that holding out for SSI exchangers would be the better choice. Then I could run a cat by-pass and just have to connect the cat for smog, right?

[speeder]

Ryan, I've tossed around the same decision, but holding out for SSIs. More $$, I know, but I truly believe that they are automotive works of art, probably the highest quality aftermarket parts sold for a Porsche, and actually increase value of the car, IMO.

[pbs911]

With either the SSI or pre-74 exhaust you lose the cat. Neither comply with California emissions standards.

A cat by-pass pipe is used in conjunction with the OEM exhaust and not the SSI or pre-74 exhaust.

I installed the pre-74 exhaust and muffler and noticed an improvement in performance. Maybe a little faster, but they did spread the torque curve out.

You can drill a hole in the cat by-bass to install the O2 sensor so that is not a problem.

[bornrich]

With SSI (or the pre-74 HE) there is no room for a cat (s). So you either chance it with the smog tester not regognizing that you don't have a cat or remove the SSIs and reinstall the stock HEs , the cat and muffler. Then return to the SSIs after the test. By the way you need a new muffer with the SSIs (two in vs. one in).

[rfix'n]

I've toyed with doing this mod but my job moves me around and I fear CA may be in my future someday. Is it as simple as seeing if the smog guys catch the no cat and if they do then you do the swap to the oem system and then re-test? Or are there penalties for failing the first time?

[speeder]

I'm going to save my stock exhaust, problem is that it is not just a simple switcheroo due to oil lines, etc. I'm banking on big stainless heat exchangers on SSI's plus O2 sensor fooling some tester. Not that far-fetched, most of them were in diapers when my car was new.

[bornrich]

The easy thing to do is go to the smog station and ask for an offline test first. Now this will cost money but better to know before you go online for the test. You only have problems is you don't do the pre test and fail the online test. You may then be labeled a gross polluter and have to go the the state smog referee.

[pbs911]

My SC passed two years ago with the pre-74 exhaust. Your best bet is to request a pre-inspection which is not connected the the DMV. That way you will know if the car passes or not.

[911nut]

Originally posted by surflvr911sc


It seems that holding out for SSI exchangers would be the better choice. Then I could run a cat by-pass and just have to connect the cat for smog, right?

You won't be able to hook cats up between SSI's and the muffler. There isn't room. Besides, even if you could it wouldn't be CARB approved.
I recommend keeping the stock heat exchangers, installing a bypass pipe and a more free-flowing muffler (the major source of backpressure is the muffler) and disconnecting your O2 sensor. Reset the idle mixture to 3.0-3.5% CO. This will increase torque and make the car more fun to drive.
Re-install the sensor and the cat and re-adjust the mixture at certification time. Save yourself $800 and a lot of aggervation.

[surflvr911sc]

Well now I doubt the SSI too. I really don't want a problem with the smog Nazis. I already have to go to a "Test Only" station for my actual test. A friend, ex-mechanic and smog guy, said CA does that to gross polluters and randomly, so he thinks my number was drawn. I'm not going to do anything right away but I was planning on next year.

I recommend keeping the stock heat exchangers, installing a bypass pipe and a more free-flowing muffler (the major source of backpressure is the muffler) and disconnecting your O2 sensor. Reset the idle mixture to 3.0-3.5% CO. This will increase torque and make the car more fun to drive.

I think 911NUT's idea might be the best way to go for me. I'm not trying to win any races here. Anyone have input on this idea?

[bornrich]

That is what I going to do (except I'm not going to disconnect the O2 sensor). I going to purchase the Pre muffler from Fabspeed and a singlein single out GHL. I can easily swap the cat in if i need to. I will pre test it after I get it installed just to see if It will pass with out the cat.

[Early_S_Man]

surflvr911sc,

If the 'pre-75' Exhaust System is $300 or less ... go for it! None of the other options mentioned above make any sense from hp or wallet standpoint! There isn't any hp gain with SSI over the '74 system! It is esthetically pleasing, but your wallet hurts a LOT longer!

Unless advertising hype is being quoted above for purposes of amusement ... all of the nonsense about torque gains using another muffler with stock SC heat exchangers and cat bypass is without foundastion, and no gains have ever been found! Unless, of course, the catalytic converter is blocked and causing running problems! Under those circumstances ... a new catalytic converter would show significant hp gains!

The OEM Porsche muffler is one of the very best on the market ... and 'back pressure' is NOT the problem with SC exhaust systems!!! Tuning, or lack of same, i.e. the unequal length and lack or a proper collector where blending of the flow from the three cylinders can occur ... is the REAL PROBLEM! The popular Flowmaster ... even in a 3" in/3" out size will not give a significant hp increase, and zero torque increase over the OEM muffler ... if bolted to the stock heat exchangers! Neither will a straight megaphone!

Louder is not always more powerful, and Walker DynoMax mufflers have proven to be quieter and give more power than Flowmasters on dyno tests with 'crate' motors from Mopar, Chevy, and Ford! The only problem with the Walker's is they tend to make everything they are bolted to ... sound like a MOPAR!!! They were, afterall, the OEM supplier to Chrysler all during the performance era of the '50's and '60's! Now, if you don't mind your SC sounding like the black Charger R/T in 'Bullit' ... For many years, the undisputed champion muffler for 'hot' or modified V-8 Detroit Iron was the OEM Chrysler 'Street Hemi' muffler ... that just happened to be a Walker product in the Mopar box! The only problem was its' huge size ... over 37" long!

The 'pre-75' or SSI system corrects all of the above problems ... and yields 10 hp, since that is what was lost from the '74 to '75 CIS engine boondoggle! An additional 10-12 hp is available at the sacrifice of significantly higher noise level with the dual outlet 'sport' muffler that Pelican and others sell:

911 Dual Pipe Sport Muffler PEL-SPM-911-01 $399.00

[emcon5]

Originally posted by Early_S_Man
Now, if you don't mind your SC sounding like the black Charger R/T in 'Bullit' ...

Hmm,

I'm not altogether sure that is a bad thing.

Tom
(Warren is talking about Mopars, does that mean he is finally going to tell us about the 'Cuda?)

[pbs911]

An additional 10-12 hp is available at the sacrifice of significantly higher noise level with the dual outlet 'sport' muffler that Pelican and others sell:

Sounds like a good HP bang for the buck. But what is "significantly higher noise level"?

[Early_S_Man]

Paul,

I can't really tell you in hard dBA numbers, because I haven't measured them! Probably above 100 dBA, from what I have heard! Not as loud as open headers with megaphones, but still irritating to the more 'sensitive' ears!

But, they are loud eniough that the factory rallye cars equipped with them couldn't drive through Switzerland in the late '60's and early '70's! Mark Wilson had one on his car, and said it was loud. Some wives and gf's probably wouldn't tolerate riding in a car so equipped, and it probably wouldn't pass noise restriction limits at some track events with 90-92 dBA limits!

[speeder]

Warren, Are you saying that if I put SSIs on my SC, there will then be a 10-12hp difference between a 2-in/1-out and 2-in/2-out muffler? I thought that the stock 2-in/1-out, (or aftermarket Danske equivalent), was not too restrictive? What gives? TIA.