IcemanG17

After fixing the AFM on my 84 L jet.....the race shop installed a proper race exhaust.....a single 3.5" with borla X1's....vs the stock-ish exhaust I had before....my old setup was 85-6 tubular headers into the factory downpipes, with the single cat removed & replaced by straight pipe, then into the factory setup with a single magnaflow rear muffler....so basically a single 2.5" system On this setup my previous best was 193whp-233 torque (mustang dyno) (pic attached)

The new setup is this:

Same headers and down tubes, into dual 2" pipes where the S4 style cat would be then into the single 3.5" system about where the cat ends....

RESULTS..... 221whp-253torque!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It took a bit more fuel and some timing adjustments, but this is a GAIN of 28whp-20 torque by just changing the exhaust and properly tuning it...... I will post the pic of the new dyno chart later today....not to mention it sounds MEAN......

It makes me wonder how much a proper header would get me?

IcemanG17

almost forgot.....automatic with runs done in 3rd gear

hacker-pschorr

Nice work.
Finally someone did a good before and after, not changing 10 things and guessing how much each part added.

Did you try to add any more timing with the previous setup?

911tracker85

pictures please. I just cobbled together muffler replacements on my 84 due to the old pumpkin sounding like an empty garbage can. I am at the point I would like to consider some modest cost HP upgrades. doing a better exhaust is one, but in the past have seen similar threads that did not report such an improvement.

PorKen

Are the down pipes the original 16V 50mm OD? Changing just those to the 32V 55mm would likely give you that kind of increase, w/o the extra noise.


(My old '85 5-speed makes over 300 rwhp/tq with a 32V down pipes converted to a Y, into a '84 cat back 65mm single with a mod'ed pumkin.)

IcemanG17

Yes....we added timing and fuel.....

the 83-84 USA have VERY conservative timing....less base timing and a much less aggressive distributor than the earlier cars.....

I know it was far to lean on the early dyno pulls...that were around 210whp-248torque....by "adjusting" the AFM to increase fuel (don't know how but it works wonders on miati) and changing timing got the better results.....I will find out exactly how much timing and fuel changes it took later today when I pick up the car....I will post the exact method-timing as soon as I know it

I also will take pics of the exhaust from under the car

PorKen

A simple but effective way to tune the WOT fueling on L-Jet is to install a WOT switched (reed) relay to add resistance to the Temp II input.

As L-Jet is analog, it is super sensitive to the Temp II.

IcemanG17

I also found this VERY true.....it makes HUGE difference in running....even slight changes can be the difference between barely running or running perfect....my temp I sensor in the AFM was at least 50% low....supposed to be 3-4k ohms and it was 1200ish...

After I see the AFR's in person, I will consider installing a potentiometer to the TempII was a way to trim AFR...cheaper than an adjustable pressure regulator!..or even just a 200ohm resistor

danglerb

Maybe getting some Y merge effects?

hacker-pschorr

This thread will come in handy when I sell the 85/86 manifolds and the SS Y-collector off my 81

Fabio421

Doesn't the fact that you "fixed the AFM" make these gains slightly questionable? I'm not saying you didn't make the gains, just wondering how much was due to the AFM and tuning. Either way, thats an awesome increase no matter what the cause.

Iwanna928

Hacker What are you replacing it with?

Awesome job on the exhaust. All 16v should have this as there first mod! They really come alive!

What does a stock 928 in your my dyno at usually?

hacker-pschorr

Good point, the air/fuel on that dyno run would help answer that question.

MSDS headers to a single 3" exhaust (that's already on the car after the SS-Y I'll be selling).
Followed by a 3" X-pipe and dual 3" exhaust.

Mongo

Brian, do you have a picture of the exhaust setup? I can't believe the power gained from a 3.5" single exhaust on a 16v car. Impressive!

AO

Hey... I resemble that remark.

We should be able to get a good idea of what my exhaust mods did this time. No one is allowed to break down on the way to the dyno.