PorKen

I did some measurin' while I had my car on the lift, and I think I may have found the reason my dynographs level out at 312 hp/301 tq - the rear cat/x-back is only ~2" (52mm) ID pipe! Somehow, I had just assumed it was 2¼". I'm going to have to make myself a new exhaust!

Anyhu, here's what I've measured so far. Please add any factory or aftermarket measurements you can find, and I'll update the list.

I was surprised by many of these. The 32V tubular 'header' has only a ~2" ID collector!

PorKen

OD - outside diameter

SS tubular manifold collector - 55.0

Ott/SLC X-pipe - 63.5

down pipes
32V - 55.0
16V - 50.0
X-p - 63.5

exhaust pipe
single - 65.0
duals - 55.0
S 'dual' - 52.0

dual resonators thru-pipe - 58.0

pumkin
dual inlets - 52.0
outlets - 58.0


ID - inside diameter

Ott/SLC X-pipe - 59.5

32V SS tubular manifold
exh gasket - ??.?
inlet - ??.?
collector - 52.0
flange - 55.0
flange gasket - 56.0

16V cast iron manifold
exh gasket - ??.?
inlet - 41.5
inlet, 10mm inside - 36.5
flange - 51±0.5
flange gasket - ??.?

down pipes
32V - 52.0
16V - 47.0
X-p - 59.5

exhaust pipe
single - 62.0
duals - 52.0
S 'dual' - 49.0

dual resonators thru-pipe - 55.0

SS muffler connector ball - 52.0

pumkin
dual inlets - 47.0
outlets - 55.0



Lengths

32V SS tubular manifold 'collector'
distance from last branch edge to flange outlet
left (LHD driver) - 55
right (LHD pass) - 30


pipe wall - 1.5 (1/16)


millimeters (inches)
47.0 (1-13/16)
50.0 (2)
52.0 (2-1/16)
55.0 (2-3/16)
58.0 (2-9/32)
59.5 (2-11/32)
62.0 (2-7/16)
63.5 (2-1/2)
65.0 (2-9/16)

toofast928

For N/A engine, duel exhaust. 2" is all it needs.
Ken try Magnaflow mufflers much better than Borla.

PorKen

Nice. Just go ahead and throw facts into the discussion. I can't make 400 chp (340 rw) with facts!



I've been confusing myself with ID and OD measurements, and I should have dynoed with an RMB, I didn't realize the pumkin has undersize inlet pipes!

I think there may be a turbulence restriction at the 32V manifold to X-pipe flange. It goes from 52 to 59.5 mm ID in jagged steps. I'm going to use a short piece of 55 mm OD pipe to extend the SS manifold through the flange/gasket, and into the X-pipe, with a flare at the end.

I'm thinking of extending the 2½" pipe from the X-pipe to the big resonators. I can cut out the 55mm OD pipe, and clamp the 2½" pipe over the inlet pipe of the resonators, which sticks out ~2".

If I do make a complete 2½" rear system, I'll put a butterfly on the shorter left side, with a crossover at the first bend before the trans, to keep it quiet at low speeds.

doktor-t

My exhaust story:

I built an 2,5" X-pipe (ott style) and made it the same length as the stock cats.

Then I put the stock (2,1/4") rear part of the exhaust back along with the pumpkin, resonators and all that. and took the car for a drive. It seemed a bit stronger and after that I went home again.

I then built the rest of the exhaust system from dual 2,5" pipes all the way back from my x-pipe. In place of the pumpkin I put straight-through mufflers. Took the car for a drive and found out that it lost it´s entire bottom-end torque.

Then I put the stock 2,1/4" pipes with stock resonators back after my x-pipe and then built a dual 2,5" RMB. Then a testdrive again. Bottom-end torque was back along with good power all over the register. Obviously this is the hot ticket for the 5 liter engine if it´s not stroked or got ported heads or so.

The same 2,1/4" resonators can be found on the GTS (i think) and that car got more displacement so I like to think these 2,1/4 pipes is good enough for our small engines. Exhaust gases gets "smaller" the further it travels from the engine and therefore tubing doesn´t need to be all that big in the rear parts of the exhaust. Another thing to take in considerations it gasspeed. Bigger pipes can get a lower speed for the exhaust gases because they get to cold. Here is where things like Thermotech tubingwrapp comes into play.

Well this is science and I don´t wanna get to deep into this

Long 2" pipes is too small for 32v´s . 2,1/4" Is enough. 2,5" Maybe for a GTS, definatly right for a 6,0 liter stroker.



/Tobias

slate blue

I have a 5.0 litre 2V and I made the exhaust and designed the mods for the engine, it has been basically successful although I don't know what is holding the engine back as I have tried to get it past the 400 chp mark but all the changes have lead to no where essentially.

The exhaust was the biggest improvement and is a mixture of 2.5" and 3" pipes in a dual configeration. https://rennlist.com/forums/showthre...hlight=exhaust

The best thing you can do is go for a bypass valve, my car has heaps of bottom end, so much so you can't use it. I also thought that the pipes or passages are too small in the factory manifolds and should and could be reasonably easily modified.

Greg

PorKen

This has got to make for a better top end! Back to the dyno!

I recycled a spare set of S4, and 86.5 mid exhausts (GTS resonators), and made a nifty X-tail pipe. I used a stock ball connection to make a X-over, and tips from an old pumkin for the ends.

At idle and mininum part throttle, it is only about as loud as the modified pumkin it replaced! Unlike the mod'ed pumkin, which was rumbly at idle, then never got any louder, this one gets louder in relation to pedal pressure. It must be the X-over, because it is only in a certain rpm range where it quiets down. Just by luck it is in the 700-1500 range!

After I paint them black, I reckon they will pretty much disappear under there.




Clearance is fine, and it's all SS, of course.






I cut off the old rear pipes 6" past the body of the resonators, and used another set of front pipes for the rear. They only needed a little extra bending on an existing radius to fit perfectly.

doktor-t

This might actually work. I think it will be the same increase in power as a RMB with its better flow. Maybe this can even produce better HP by the use of the H-pipe. In C5 Vettes they use H-pipe at the rear, stock.

Nice thing is that it will give some duals att the rear too. Perhaps dual tips at each end of these could be nice? Black satin finish..... I love those exhaust-tips found at the BMW M5 E39 2000 year model.

PorKen, when are you going to get the car dynoed again?

BTW, my -86 32v has become so much stonger than last summer thanks to some upgrades in the exhaust, fan/smogpump and induction- trackt. These 85-86 32v is probably quite underrated or is it that they respond well to modifications?

Best regards

/Tobias

PorKen

I did a bit of finish work on the rear pipes, including painting. One thing I noticed is that larger the size of the connecting H-pipe openings, the quieter the idle became. (I originally had made rough holes that were smaller than the cross pipe with a cutoff wheel.) Another thing, the exhaust tips are much hotter, ie. the exhaust is not slowing and cooling closer to the engine.

With this new setup, and 4° cam retard I've had since the last dyno, I have power all the way to redline. I can really feel it 'cam in' past 5K. Of course, I need to get the dyno to be sure - I could be fooling myself, because of the louder exhaust!

I bought a nice chipburner (Batronix), so I am wanting to put in a GT rev limit, 6750, to take advantage of the high rpm pow-wa. I might modify or replace the kickdown relay, too, as it is set to kick down a few hundred rpm below the current rev limit of 6520(?).

The 4-speed super low first gear is a joy now, instead of a curse. I need it too, because at low rpm it feels a bit tired. I can use second all the way to 80+ mph with no 'shortness of breath'. With retard, shifting down is not as much of a 'jolt', either.

That cutout you have is schweet. That's an OZ piece, isn't it? I think I saw it in Autospeed. I think I would put it right after the (front) X-pipe, on the left side, so the exhaust is forced down the right side at part throttle?

IMO, H-pipes are for sound reduction, whereas X-overs are for extraction.

I like those small chrome rolled tips too, and I think quads would look great (this is a photoshop pic from a few years ago).



The S³ is underrated. It has 'GT' cams, though, so it's hard not to make more power than the ultraconservative 288 chp (~244 rw)! The small mods I've done have added ~70 rwhp - like bolting on a stage 1 supercharger.

Have you put in chips, or done any of the EZ-F'r mods?

doktor-t

PorKen

I think you´re right about the H-pipe, (beeing a noisereduceant) especially when put so far back as after the rear axel.

I didn´t know that S3´s has GT cams, could it be better from the factory? You especially has proven by actual numbers that S3´s answers very well to modifications and is truly underrated. Somewhere in my hunt for more power I kind of suspected this because my "butt-dyno" tells my car is so much faster now it´s feelable. A few weeks after purchasing the car I started to think it was tiered and didn´t deliver the power I wanted and started to think about turbocharging. Now I´m not so sure anymore because I´m quite happy with the power some easy and cheap modifications gave.

I haven´t put in any chips thou. If I haven´t understood everything wrong, there isn´t any really good chips out there, right? As for EZ-F mods I´m going to do a modification to the Temp2 sensor but I´m still a bit worried that I´ve might understood it all wrong.

See, I purchased a 20k ohm resistor and plan to cut one of the wires to the Temp2 sensor and weld it in were the wire is cut (i.e in series). Would this be the right way to go or should I unplug the Temp2 sensor entirely and the put in the 20k resistor in its place in the socket?

If I could put it in series with the tempsensor connected I would prefer to wire an extra curcuit with a toggleswitch just to be able to switch the additonal 5° of advance off if necessary. Better safe than sorry

This is for me the big question, otherwise I´m not scared to do modifications. I just want it to be right the first time.


As for exhaust-tips, I like the Photoshoped picture, this would be a great upgrade to the rear. It was exactly what I had in mind.

slate blue

The bypass valve is an Oz piece and you are correct about Autospeed, it is correctly positioned to do what you want it to do, It is closed at part throttle, the pickup is quite amazing.

Greg

PorKen

Tobias,

You can put the 20K resistor in series, or to earth. (Remember, you must also disconnect the WOT input to the EZ-F for it to work.) If it pings, you can connect the octane loop. 20K (+5°) + octane loop (-3°) = +2°

It will make a huge difference!

...

Greg,

Interesting. If it works as you say on mine, it would go well with the retard I've dialed in. It doesn't wake up until >2000 rpm, but then there's power to redline. I've gone ahead and ordered a vacuum heat riser valve used for header installs, 2.5" with a three bolt flange. Hedman 21120, <$30!

I can't find a picture of the Hedman unit, but I imagine it's similar to this Thorley unit.


Speaking of the stock headers, I think someone should make a shorty header to bolt up to X-pipes. There's room for it, and the large headers often don't end up making more power.

soupcan

I am installing one of these to quite my Dual 2.5" Exhaust for family drives, maybe I will set it up to be progressive to add some more bottem end torque.

doktor-t

A huge difference in power is allways wanted so this weekend I´ll get down to business with the installation of the resistor. I will put it in series with the temp2 sender along with an extra circuit and toggleswitch just to be able to switch it off if pinging should occur during hot weater or something.

Otherwise I don´t think I have to worry to much about pinging since the lowest octane you can buy in Sweden is 95 octane and if you have no problems with pinging running 87? octane gas I should be fine right? IF, any problems should occur I can switch to 98 octane but I dont´t belive that will be necessary.


/Tobias

Landseer

Great thread, do these things apply to the early 86? Not sure if S3 is late 86?