IcemanG17

I disagree that there is a large performance gain from the cast iron header vs the tubular steel header, other than being much lighter.... On my 1984 automatic the 1st engine had stock cast iron headers and made about 190whp.....with an engine that cranked at about 145psi.....the next engine was better with an average of around 155psi WITH the tubular header made about 198whp..... I would estimate the 8whp gain was mostly due to the higher compression from the less worn engine....

I think the MSDS headers are a significant improvement for a 16V car that doesn't need to be smogged.... My 4.5L 1981 engine with Euro cams-intake-ported USA heads makes 265whp-289 torque which is the highest NA non euro 16V dyno I have ever heard of....it runs MSDS into a Y then single 3.5" out.... For example a stock 1979 4.5L with the same race exhaust makes 222whp-233 torque....so the porting-euro cams-intake plus .5 increase in CR account for 43whp-56ftlbs.....

mark kibort

I need to build you a 5 liter to stick under all that good stuff. I bet it would make 310-320 at the rear wheels!

danglerb

Apples and oranges, the principle difference between the cast iron and steel manifold is the interior diameter, the steel is bigger, so not as good on low end torque, better on higher rpm HP. Stock 4.5L has no higher rpm HP to improve, not so with a stock Euro S 4.7L or a 5.0L Euro hybrid motor.

MSDS headers are tuned for dynamic flow, cast and steel manifold are not, just static flow.

*** I had all the pieces in my hands today, steel 85/86 exhaust manifolds and associated head pipes and factory dual cats, neither part looks very practical to modify. Plan B right now is to make the same 2.25 passenger side adapter/extension others have made in the past and leave the rest alone.

Issues; nothing is straight, not in the direction front to back that needs to be changed. The steel manifolds angle down about 45 degrees from the rear cylinder exhaust port, so any shortening will also raise the height of the flange. The dual cat assembly has integral heat shields over all the most likely places to add 2.25" of forward extension, exposed head pipe is all angled or curved.

I'm not giving up, just stopping banging my head for the moment. What "seems" like it could work is much more messy, redo the 8 welds for all the runners on the 5/8 cylinder manifold moving the "log" straight forward and changing the angle on each runner. Likely easier to just remake that manifold, but nothing close to as easy as the passenger side extension.

The rest of my current plan B, rework my existing locally fabricated single exhaust to make a factory style slip fit to the dual cat and call it a day, pass smog, think again longer term later.

danglerb

Wish I could, but Calif smog inspections very likely would end up with a "Calif only catalog" cat, and I think I am better off with a set of factory dual cats than a single cat from the weak offerings in the Calif approved catalog.

Sending you a PM on adapter.

Landseer

You might be making it too hard.

We put the car on a lift at a muffler shop with the 85/6 headers installed.

Held the 87 cats in place, made a few cuts, made a few cherry red bends to the cat donwpipes.

The exhaust guy basically made it all fit. Took about 90 minutes. SAE tubing actually fits almost perfect to extend the passenger side.

The shop got a kick out of seeing the car, and seeing their guy fix it and drive it in and out of the bay. I think it cost $120 total.

danglerb

Isn't that the idea?

I'm just poking at finding a better way, which isn't a reasonable choice for any one person, but the basis of all human progress.

85/86 manifolds have been on the car for years, and initially that is what I did, take it to the local muffler guys, and they fabbed a set of head pipes, Y merge, aftermarket cat, and single pipe exhaust with a Magnaflow muffler. I'll drive it that way back to them with the factory dual cats in the rear hatch, and drive it home with those installed. I just don't want to mess with the factory dual cat head pipes if a small adapter gets me around it for now. That could change once its in the air and any unplanned issues arise.

When working with skilled professionals I tend to first try my latest crazy idea, then have them do whatever they think will work.

hernanca

Has anyone looked into whether the stock 85-86 928 manifold tubes are made from Incoloy (Inconel) 800, as the 944 guys seem to believe makes up part of their stock manifolds from the same era (see thread reference on last page (post 81, page 6) of "180 degree alternative" thread)?

If so, modifying the 85-86 manifolds may be even less straight forward (I have only welded once in my life, so I dont know what difference it might actually make).

IcemanG17

at my current weight, i need a power factor around 310-320 to max out GTS4....much better than the 277 I have now....

Sean has a spare 5L shortblock at the shop right now.....hmm

justaguy

Get after it!. The block had a water pump failure and needs repair. Send me the pistons and I'll machine them.

Tom at 928 international told me that they only saw a 5 hp difference between the 85-86 stock exhaust manifold VS headers on Marks race car. So I'll be running the stock 85- 86 exhaust on the 5.0L that I'm building at the moment.

cgraner

Does a 1985 Porsche 928 US Spec Automatic full OEM exhaust bolt directly up to a 1984 Porsche 928 US Spec Automatic at the manifold flanges of the 1984 engine?

Darklands

On the cast manifolds yes, if you change to the S3 stainless manifolds no.

928FIXER

Has anyone ever done the manifold swap using the matching front pipe,and if so,how good did it fit an early chassis?

Darklands

The exhaust is the same on all cars but the 4V cars have a different pattern for the manifold. If you put the stainless ports on 2V heads one side has a 2"? gap.