02 delete on '80 SC?

[C-Pierce]

heres something to chew on....

I have a '80 SC that I am doing a motor job on and I want to backdate the exhuast with SSis preferably, I see that the SC specific ones are more expensive I assume this is becuase of the O2 Bung? anyhow. I believe I can delete my O2 sensor from my SC without a big issue but I am wondering what the general public thinks. this would alow for older style heater boxes or the less expensive Ssis... and there are NO Smog or emissions on cars this old here in VT....

thanks in advance

PS looking for SSIs and muffler 2in1out
oil lines and a rear decklid too.!!

Chris

[Scott R]

If this is a US 80 then don't do it. Weld in a new bung and re-install it. I have dyno sheets posted here that show you get more power, and better AFR's on the 80' with it installed. Plus the 80 has a bastard fuel system that somewhat relies on that thing to operate.

[C-Pierce]

yes it is a US car...

is there a difference in the ssis inside diameter for the different years? I know the exhuast ports are larger on my SC than they were on my '76 S...

so will backdateing with older heater boxes or ssis (sans O2 hole) make a difference?

thanks
Chris

[Scott R]

Originally Posted by C-Pierce

yes it is a US car...

is there a difference in the ssis inside diameter for the different years? I know the exhuast ports are larger on my SC than they were on my '76 S...

so will backdateing with older heater boxes or ssis (sans O2 hole) make a difference?

thanks
Chris

I have SSI's froma 3.2 on mine, but you just need the "thick flange" variety for your 80. And if it doesn't have an O2 bung, you can weld one in very quickly.

[C-Pierce]

As I have looked at my heads I suppose I could cut my exh studs down to the thin flange length then I could use just about anything. thoughts?

Scott R what is the inside diameter of those, same as others?

thanks
Chris

[stlrj]

Not much to gain performance wise by going to SSI's on an SC so why bother?

Is it appearances (bling can be blinding) or are you suffering with the burning discomfort of too much ca$h in your pocket?

Boredom? In desperate need to fix something that "ain't broke?"

Wow, am I starting to sound like my father?

[C-Pierce]

2 reasons-
- one the current heater boxes are junk

-second I have heard that the dyno results show that early heater boxes are the optimum exhuast elimination device for torque and HP gain. maybe these results are not correct? PLEASE PLAESE show me differently I would love to see that I am looking in the wrong place for the gains I desire.

What is a better way to gain hp in an SC? without major tweaks?

I am also adding the 964 cams.

Bling? I dont have any of that..

C

[psalt]

Chris wrote,
I believe I can delete my O2 sensor from my SC without a big issue but I am wondering what the general public thinks.

Chris,

Keep the O2 sensor, it does far more good than harm. It is out of the loop after 35% throttle, so anyone that says it hurts performance doesn't understand it. You can fatten up the mixture for cold starts and WOT, but still have good mileage and emissions. You also can check the mixture and the operation of the CIS with a dwell meter at the test port, which beats guessing with the part swappers. A O2 bung is a $5 addition to what ever exhaust you want.

What you want to delete is the vacuum retard, it does nothing but harm.

Paul

[C-Pierce]

Please explain the elimination of retard..

Just plug up the vac line?

Chris

[Greek55]

Originally Posted by stlrj

Not much to gain performance wise by going to SSI's on an SC so why bother?

Are you saying backdating doesnt increase HP and torque or that you can backdate, but not to spend the money for the SSI brand?

[Paulporsche]

AFAIK the SSIs are a close copy, somewhat improved, of the early exhaust, except rendered in stainless steel. The CLAIMS have always been for about a 15hp gain over the later stock setup. I think Bruce Anderson's book mentions a mod from the late 70s/early 80s in which these engines were increased to 3.2L, twin plugged and fitted w/ early exhausts @ the factory to give 220-230 hp. I don't know how each component affects the final figure.

My engine, which was originally a 3.0 has no O2 sensor or other emissions equipment w/o any adverse effects I know of. However, if psalt says CIS troubleshooting is improved w/ it, then why not keep it?

I also recently plugged the vac retard. You can either remove the line from the cannister and cap it, or you can plug it w/ a BB and put it back in place. Someone correct me if wrong, but I don't think you necessarily have to cap the port on the dizzy.

The engine seems to start more easily, warm up and idle smoother, and pick up off the line better w/ the retard removed.

I am using a Dansk 2in/1out exhaust and like it. It's louder than stock but not too bad. For these nearly 60 YO ears, it's as loud as I would like. Apparently you can pick up some hp ( 5-10?) w/ a 2 out.

[psalt]

Please explain the elimination of retard..

Just plug up the vac line?

Chris

Hello Chris,

The distributor has two vacuum lines, advance (orange) and retard (grey braided). The advance is a good thing, it advances the timing under low load cruise for better fuel economy, and it is irrelevant at idle or WOT. The retard is strictly a crude device to meet the curb idle HC emission test and has the side effect of raising the engine and oil temperature at hot idle. When you remove and plug the grey line, and cap the nipple, the idle will increase and you will need to reset it at 950 rpm with the big idle bypass screw on the throttle body (you can use your fingers). The US SC with lambda CIS is detuned for 87 CLC octane fuel. If you want to improve the performance of the engine, do everything you can to reduce running temperatures, use the highest octane fuel you can find and advance the timing a few degrees. A hemi head engine with domed pistons needs more than 21 degrees of advance to make best power. If the engine runs hot, or you have garbage fuel, or your are burning oil, you need to be careful with pinging.

One reason you want the O2 sensor connected is that if you actually do make modifications to the engines, you will need to adjust the mixture. A properly working CIS lambda system will allow you to richen up the mixture for WOT and it will bring the mixture back to stoich at cruise and idle. If you haven't already, hook up a analog dwell meter to the test port, check that it is functioning properly, cold, hot and above 35% throttle, then reset your mixture to 35-45 dwell, hot closed loop. Set the ignition timing to 7 BTDC (vac disconnected @ 950 rpm) as a start, this will get you closer to the ideal set up on a stock engine. A two inlet muffler system will definitely improve performance, just don't expect the moon.


Paul

[Gunter]

Originally Posted by C-Pierce

2 reasons-
- one the current heater boxes are junk

-second I have heard that the dyno results show that early heater boxes are the optimum exhuast elimination device for torque and HP gain. maybe these results are not correct? PLEASE PLAESE show me differently I would love to see that I am looking in the wrong place for the gains I desire.

What is a better way to gain hp in an SC? without major tweaks?

I am also adding the 964 cams.

Bling? I dont have any of that..

C

A few years back I faced exactly your situation: US 1980 SC stock and decided on SSI's and a Flow-thru muffler.
There is no doubt in my mind that this added ~15 horses!
If you order SSI's for your US '80 SC, they will come with the OX bung and thick flanges. (Recommended!)
I found no adverse effects by disconnecting the OX sensor.
However, I went further by building a SS 3.2 with 964-cams and used the CIS from a '78-'79 without Lambda.
If you use 964 cams, I would recommend that you bore out the heads to 39 mm and get the larger intake '78-'79 CIS, which is much easier to adjust and maintain. (No more Lambda)
Complete arly '78-'79 CIS sell for about $400.- and you can sell your '80 CIS for about the same amount.
If you keep your '80 CIS, 964-cams plus SSI's with a 2in/2out will give you about 20 extra horses if you disconnect the OX sensor and set the mix rich.
I recommend that you service the ignition distributor.

[GothingNC]

I have SSI's with the 02 sensor installed but disconnected.

Here is an an older thread about it

why disconnect the O2 sensor?

[C-Pierce]

I thought that the reduced size on the intake was done so that the air would speed up in a "ram" effect.- better breathing seems like a good idea.

thoughts on the Dansk heater boxes?

I can get both at cost, just dont know which to get..

thanks
C

[fred cook]

I have exactly this setup. My Pcar is a 1980 SC coupe. I installed SSI exhausts about 3 years ago. Once installed, I used a CO meter to reset the fuel injection to show about 3% at idle and then had to reduce the idle rpm back to 950. With the SSI exhausts my 3.0 pulls much harder in the upper rev ranges (4k or greater) and I have to be careful because it will top 7,000 rpm very easily. Even with the richer settings I still get the same or better fuel mileage in town and on the road and more "seat of the pants" performance when going thru the gears. I have had the O2 sensor unplugged for several years and have not noticed any idle or running issues. In my opinon this is one of the best mods that can be done to the SC engine.

[zotman72]

Last year, my '80 SC was converted to '74 HEs with a welded in O2 bung (a nut) and 2:1 stock muffler . Runs great and there is more to enjoy in hp and grunt. No sure why the fella (stlrj) above wrote there was not improvement, as there most certainly is. YMMV

[Scott R]

Originally Posted by psalt

Chris wrote,
I believe I can delete my O2 sensor from my SC without a big issue but I am wondering what the general public thinks.

Chris,

Keep the O2 sensor, it does far more good than harm. It is out of the loop after 35% throttle, so anyone that says it hurts performance doesn't understand it. You can fatten up the mixture for cold starts and WOT, but still have good mileage and emissions. You also can check the mixture and the operation of the CIS with a dwell meter at the test port, which beats guessing with the part swappers. A O2 bung is a $5 addition to what ever exhaust you want.

What you want to delete is the vacuum retard, it does nothing but harm.

Paul

Thats not entirely true, the AFR's all the way to 5800 RPM's are effected on my dyno sheets. You can search on my user ID for them, thread is "disappointment at the dyno." The FV on the 80' goes to full duty cycle when you unplug the sensor, regardless of RPM.

[psalt]

Scott wrote,

The FV on the 80' goes to full duty cycle when you unplug the sensor, regardless of RPM.

Hello Scott,

Are you confusing WOT with rpm ? I can't tell what you are trying to say, but this statement is false. The FV is a pulsed injector and it cannot ever be operated at "full duty cycle" by design. When you unplug the sensor, the system goes into default mode and pulses the FV in the mid range (around 50% hot). The fuel curve equals mechanical CIS setting with a 50% FV duty cycle pressure +/- O2 fuel trim. The throttle switch is not rpm related, once you open the throttle past 35%, it grounds the same circuit as the temperature sender, it goes open loop using the cold enrichment for WOT acceleration. Once you modify the engine the calibration will be off, but with the O2 sensor connected the system can correct cruise and idle.

[Scott R]

Originally Posted by psalt

Scott wrote,

The FV on the 80' goes to full duty cycle when you unplug the sensor, regardless of RPM.

Hello Scott,

Are you confusing WOT with rpm ? I can't tell what you are trying to say, but this statement is false. The FV is a pulsed injector and it cannot ever be operated at "full duty cycle" by design. When you unplug the sensor, the system goes into default mode and pulses the FV in the mid range (around 50% hot). The fuel curve equals mechanical CIS setting with a 50% FV duty cycle pressure +/- O2 fuel trim. The throttle switch is not rpm related, once you open the throttle past 35%, it grounds the same circuit as the temperature sender, it goes open loop using the cold enrichment for WOT acceleration. Once you modify the engine the calibration will be off, but with the O2 sensor connected the system can correct cruise and idle.

I assumed it was full by the dyno sheets but 50% makes sense as well, but it sure does go nuts when the sensor is unplugged. It was about a 25HP difference on the loss side with it disconnected.