Easy Power Modifications

[PorscheOwner]

1984 928 Automatic

What are some not super expensive and easy to moderate (difficulty-wise) modifications that I can do to my 928 for some good HP gains?

[RKDinOKC]

Y-pipe exhaust

[Danglerb]

928 automatics are fairly fast cars, but none feel sporty like a 5 spd does, and nothing cheap makes them feel quick off the line.

[dewolf]

There is nothing cheap about these cars. I bought the 928 for nice long comfy cruising and a 944T for fun.

[wills928]

Want to go fast:
right foot to right gas peddle!

[1984928]

All I've done to mine is a rear muffler bypass and a very slight (2 degree) timing bump and I can get rubber on the 1-2 and 2-3 shifts if I really have my foot in it.

[laneyamps]

Hi There,

As others have already mentioned, the best thing for ANY 928 is to replace that original exhaust system right away! Y-Pipe, Headers, and Cat Back...the whole 9 yards. That will give you a healthy boost in overall performance, with the least amount of money. Maybe 20-30 HP gain?? That said: It's not real cheap, however, it's the best way to go, and still the least expensive option.

You CAN get a supercharger for all years of 928's....but, at $6000, I opted NOT to do that. I don't have $6000 to throw away...

ALSO, jageng.com makes an electronic shifting kit for the automatic trans 928's. You may know that the 928 (from a dead stop) always starts in 2nd gear (for fuel economy), and this little kit enables you to override the kickdown, electronically. It attaches to your shifter button. Only $135 bucks! It's also handy for highway driving, because you can use it to kickdown if you need to pass someone, or, just enjoy some spirited driving.

No, I do not work for those guys, I just thought it was a pretty cool item to mention. I'm thinking of getting one, myself....Doesn't look very hard to install, either.

[dkkim81]

Where are the best quality and most affordable parts for the exhaust modifications? Y-pipes, cat backs and headers...anything else? Should I take it to any muffler shop around the corner to do those changes?? Or take it to a specialist? What to do?

[PorscheOwner]

Thanks everyone for your input so far.

Originally Posted by laneyamps

Hi There,

ALSO, jageng.com makes an electronic shifting kit for the automatic trans 928's. You may know that the 928 (from a dead stop) always starts in 2nd gear (for fuel economy), and this little kit enables you to override the kickdown, electronically. It attaches to your shifter button. Only $135 bucks! It's also handy for highway driving, because you can use it to kickdown if you need to pass someone, or, just enjoy some spirited driving.

I will definitely look into this, have you used it? Is THIS LINK what you were referring to?

Originally Posted by 1984928

All I've done to mine is a rear muffler bypass and a very slight (2 degree) timing bump and I can get rubber on the 1-2 and 2-3 shifts if I really have my foot in it.

What do you mean by rubber?

[XLR8928]

Definately advance your timing. Euro setting of 27-28 degrees works really well, and costs $0. Summit racing sells a kickass 2 into one Y pipe, and its cheap.
They also sell a myriad of different mufflers, (I'm partial to the magnaflow's), or if you like loud, a simple muffler delete sounds awesome. A true dual with an X pipe is a good setup but will cost more $, (my favorite). Synthetic fluids in your drive train, good for a few ponies, with better shifting to boot. And lets not forget a K&N air filter, not cheap, but very effective.
-Kerry

[PorscheOwner]

Originally Posted by XLR8928

Definately advance your timing. Euro setting of 27-28 degrees works really well, and costs $0. Summit racing sells a kickass 2 into one Y pipe, and its cheap.
They also sell a myriad of different mufflers, (I'm partial to the magnaflow's), or if you like loud, a simple muffler delete sounds awesome. A true dual with an X pipe is a good setup but will cost more $, (my favorite). Synthetic fluids in your drive train, good for a few ponies, with better shifting to boot. And lets not forget a K&N air filter, not cheap, but very effective.
-Kerry

27-28 that seems like a lot but I am by no means an expert on the matter. I assume that I will need to run 92-93 octane?

And as for exhaust I think it already has a different muffler on it. I really don't want to change the exhaust because the note right now sounds really nice both in sound and volume.

[76FJ55]

The 2nd gear start didn't come into play till S4 (or was it 86.5) production. your 84 will have a normal 1st gear start.

The 928 wasn't designed as a stoplight racer so no cheap mod is going to launches like a drag car.

My suggestion would be to ensure the car is running optimally for the factory setup first. Also make sure your kick down cable is adjusted correctly, as well as the WOT switch below the pedal (which effects trans kick down).

Then after it is dialed start looking at doing mods. From what I've seems, that the exhaust is a good place to start.

Originally Posted by PorscheOwner

What do you mean by rubber?

I think he means that he gets slight wheel spin during the 1 to 2 and 2 to 3 shifts.

[PorscheOwner]

In the spring of 1987, the automatic transmission shift program was changed to start out in second gear and roll to a stop in second gear under certain operating conditions. If the driver starts off with a heavy throttle input, the transmission downshifts to first gear.

Ok, so shifter mod will do nothing for me. And what is everyones input on timing adjustment?

[1984928]

Yes, I mean tire spin. My car comes down to 1st gear at a complete stop on it's own. Also if I pull it into 2nd at a stop it will stay in 1st until I rock the shifter to 3rd and quickly back to 2nd, then it will shift to 2nd and stay there till I put it in to 3rd and so on.

[PorscheOwner]

Still need input on the timing debate. Also where do I go for performance parts such as sway bars, and stuff in the handling department.


wow check out this mod haha Quite sad what people do to these beautiful vehicles.

Porsche : 928: eBay Motors (item 170512797998 end time Jul-16-10 16:31:48 PDT)

[76FJ55]

Probably the most popular suppliers are:

928sRus
928 Specialists
928 International
928 Motorsports

I'm sure there are other sources, but these should get you atarted. By the way Roger at 928sRus prefers to do most of his communication by phone or email, his website is rather limited but don't let it fool you, he has a lot to offer.

[PorscheOwner]

So mainly, why is everyone saying y-pipe? Isn't the resonator the y-section currently?

[Landseer]

No, the catalytic convertor exit is where the flow is combined on the 84 and there is lots of pressure drop.

They are suggesting eliminating the cat and its integral downpipes and replacing it with a Y-pipe.


A better set-up for 1984 starts at the engine.

Replace cast iron collector pipes with A) MSDS headers or B) 1985 or 1986 stock SS collectors which have higher flow than 16V units.

Then, depending on which are used, you probably want to add a pair of sport cats on the inlet to a Y that brings the two streams together.

Then probably a mid resonator like a same-side offset magnaflow.

Then pipe to the discharge point behind the driver's wheel.

(Duals are more expensive than single pipes and gain nothing.)

Here's a set-up similar to what is described. I think its 3 1/4 inch stainless tubing from the MSDS flanges. Sound is incredible but its a little loud for me. And it has the added issue of having no air pump and bullet mufflers instead of cats, so even though its not an emissions testing state, I can pass visual only if the inspection guy isn't looking. That's the struggle right now --- how to get inspected. Previous states where the car lived were more lenient, or else, their inspectors were....its federal law we are messing with when we delete cats.

The inspection guy is supposed to look at the EPA sticker under the hood and trace the emission lines, including air pump, and also check underneath for the connection of air to the cats. New port cats don't use an air pump, so there lies a dilemma. There is no provision for replacement of earlier generation emissions gear with newer generation gear. This is a twin-dizzy euro, so no sticker. Instead, federalization papers that show addition of an air pump and catalytic convertor. Which are no longer on the car.


YouTube - ‪Chris starts Chewy, Porsche 928‬‎

[PorscheOwner]

Removing the CAT is not an option. This is a daily driver and needs to pass inspection without any issues.

[Landseer]

ctures of some systems. Can't find the one in the clip above.

Left is stock USA 84 exhaust.

Right is an $1100 system.
85 aftermarket replacement pipes and air cat (legal)
Magnaflow same side in/out resonators
Magnaflow dual-in, dual-out short muffler (still needs tip work)