280z L28 Rebuild, Power Questions

[Patcon]

I don't think smog will be able to tell what the compression ratio is. Whether you can get the EFI to run properly with it, is another story. You could always add a rheostat on the temp side of the EFI to dial it down some but that still might not work.

If I were going to build a motor and wanted more power, I would probably ditch the factory EFI. It's not very tunable. Build what you have to and get it running and then mod it after you move and know what the new rules will be at your new address.

High compression motor with SU's, or SU throttle bodies, ITB's or go turbo. with as much displacement as you can afford

[madkaw]

Can you guys get away with a 123 dizzy ? 

[Patcon]

16 hours ago, madkaw said:

Can you guys get away with a 123 dizzy ? 

I did some looking but can't tell. There is a California dealer but he could be selling to Smog exempt owners

[ckurtz2]

I currently am running a stage 1 comp cam in my Z with a full exhaust on stock EFI. First thing to note, it is absolutely worth it as there is a significant change in the power band. However, it was the biggest PITA as I had no idea what I was doing at first, as adding a cam by itself will make bone stock EFI run like crap.

Second thing to note is that having an adjustable FPR is a must. It adds just a slight advantage in tuneability to the stock efi. A cam means less vacuum at idle, which the way the stock FPR is set up means it will be higher fuel pressure which isn't fantastic for how your car with idle. I also had to "tune" the EFI by tweaking the AFM, fuel pressure, TPS, and running non ported manifold vacuum to the distributor at idle. Thus the engine timing is fully advanced at idle, and then the mechanical advance swings in under throttle.

Because I tweaked the EFI unfortunately I sacrificed how well it runs at cold start(too rich), but once it is up to temp it drives great. In time I will find a way to fix the cold start.

In short yes you can cam stock EFI, however, it isn't just a plug and play swap.

 

[siteunseen]

I've got the potentiometer or rheostat that Patcon talks about on my coolant temp sensor. I think you could add enough fuel through that to make the efi run with a mild cam. Somebody needs to try it. I'm just too busy. 

I do know I can flood mine down to stalling, barely run with it.

 

[Ownallday]

On 1/28/2023 at 3:29 PM, Patcon said:

I don't think smog will be able to tell what the compression ratio is. Whether you can get the EFI to run properly with it, is another story. You could always add a rheostat on the temp side of the EFI to dial it down some but that still might not work.

If I were going to build a motor and wanted more power, I would probably ditch the factory EFI. It's not very tunable. Build what you have to and get it running and then mod it after you move and know what the new rules will be at your new address.

High compression motor with SU's, or SU throttle bodies, ITB's or go turbo. with as much displacement as you can afford

Would a bump in compression though make it easier to fail the sniffer test though? I didn't want to exactly bump compression up too much as I would like to run 87 octane still or max 91.

I already have another Z that has a nicely build motor with triple webers and she pulls hard, I use it mostly for track driving, this new build is mostly for daily driving occasions and spirited mountain driving.

15 hours ago, ckurtz2 said:

I currently am running a stage 1 comp cam in my Z with a full exhaust on stock EFI. First thing to note, it is absolutely worth it as there is a significant change in the power band. However, it was the biggest PITA as I had no idea what I was doing at first, as adding a cam by itself will make bone stock EFI run like crap.

Second thing to note is that having an adjustable FPR is a must. It adds just a slight advantage in tuneability to the stock efi. A cam means less vacuum at idle, which the way the stock FPR is set up means it will be higher fuel pressure which isn't fantastic for how your car with idle. I also had to "tune" the EFI by tweaking the AFM, fuel pressure, TPS, and running non ported manifold vacuum to the distributor at idle. Thus the engine timing is fully advanced at idle, and then the mechanical advance swings in under throttle.

Because I tweaked the EFI unfortunately I sacrificed how well it runs at cold start(too rich), but once it is up to temp it drives great. In time I will find a way to fix the cold start.

In short yes you can cam stock EFI, however, it isn't just a plug and play swap.

 

Good to know, does Arizona have any smog laws? Does your Z pass with all the modifications you've done? I figured even a slightly bigger cam would hinder the low end a little but would pull in the higher end. By the sounds of how much had to be changed to the afm and advancing timing sounds like it may not pass here in California which is a bummer. Cam is easy and I suppose I can always upgrade after the move.

On 1/28/2023 at 6:01 PM, madkaw said:

Can you guys get away with a 123 dizzy ? 

Does the 123 have any advantage power wise or just the adjustment to timing and pin lockout?

 

[Patcon]

Idk how compression would change the motor emissions

[SteveJ]

1 hour ago, Patcon said:

Idk how compression would change the motor emissions

I would think the higher compression would drive higher temperatures would drive higher NOx, and my friend, Google, was able to find links to say that is the case.

Also, according to my friend, Google, in typical operation the EGR lowers the oxygen concentration and absorbs heat to reduce NOx formation.

[Zed Head]

Seems like a lot of effort being expended here that will most likely lead to failure to pass.  As I understand California they have the visual inspection, the idle emissions measurement, and the 2500 RPM cruise emissions measurements.  Three chances to fail.

I used to spend a couple of hours messing around back and forth at the emissions station in Oregon (free checks as you long as you're making improvement), dialing in the AFM, the timing, sometimes the fuel pressure, so that I could pass just idle emissions.  On a 76 with no catalytic converter, mostly original engine parts.  The MSA AFM that I had bought in the past just ran rich at idle so I would have to change back to an older original AFM that I had picked up.  Then after a couple of years of dinking around with the engine just to see what it would do the idle emissions would be out of spec again.

[Ownallday]

4 hours ago, SteveJ said:

I would think the higher compression would drive higher temperatures would drive higher NOx, and my friend, Google, was able to find links to say that is the case.

Also, according to my friend, Google, in typical operation the EGR lowers the oxygen concentration and absorbs heat to reduce NOx formation.

I've been getting too many mixed responses on that response but it seems to me that the case would make it harder to pass, question is how much added compression is too much? I am sure just a thinner head gasket should cause no harm.

3 hours ago, Zed Head said:

Seems like a lot of effort being expended here that will most likely lead to failure to pass.  As I understand California they have the visual inspection, the idle emissions measurement, and the 2500 RPM cruise emissions measurements.  Three chances to fail.

I used to spend a couple of hours messing around back and forth at the emissions station in Oregon (free checks as you long as you're making improvement), dialing in the AFM, the timing, sometimes the fuel pressure, so that I could pass just idle emissions.  On a 76 with no catalytic converter, mostly original engine parts.  The MSA AFM that I had bought in the past just ran rich at idle so I would have to change back to an older original AFM that I had picked up.  Then after a couple of years of dinking around with the engine just to see what it would do the idle emissions would be out of spec again.

Starting to sound like it. Yea I believe its three test visual I am not worried about as all stock components will be in the car and anything that can be visually inspected I can hold off on. Just trying to avoid taking apart the motor again but a Cam is not that hard and can be done inside the engine bay. I believe I have a new AFM or rebuilt AFM so hopefully that gives me no problems as I always had AFM problems in the past on my last car. It seems to me I will have to do just a stock rebuild for now aside from the thinner head gasket and port and polish and just do the extra work when the time comes. At least it'll give me an opportunity to see how stock power really feels like and see if I can feel any improvements from there as I do all the mods in the future. 

[SteveJ]

Just remember to get a pre-test before you go for an official smog test. I don't know when you are thinking about moving, but there's no need to get your car labelled as a "gross polluter."

[Ownallday]

53 minutes ago, SteveJ said:

Just remember to get a pre-test before you go for an official smog test. I don't know when you are thinking about moving, but there's no need to get your car labelled as a "gross polluter."

Thanks for the heads up. Planned on getting a pre test as I am actually unsure if the stock cat that was on the car originally is good or not so don't wanna take that risk. The move will probably be around 2 years so either before I right after I will have to go in for another test. Wish I could throw two catalytic converters on to increase my chances but I am sure that will fail visual instantly.