Vacuum with Poncams

[Tom N]

Did some searching around and can't really find what I'm looking for.
Looking to hear what kind of vacuum at idle people with Tomei ( 256Dur, 11.5 lift ) poncams see on SR20.
I'm seeing 13-14inhg at idle on a stock compression S15 with these cams. Seems low to me. Saw 18-20 with stock cams.

[codyace]

13-14 is ok, what is it at 1000-1100 rpm?

[Tom N]

13-14 is ok, what is it at 1000-1100 rpm?

That is at about 1100rpms

[codyace]

Ahh, yea that is a little low if it's that RPM...you're certain timing is spot on? That's about the only other thing. In most cars you're usually around 15/16 or so at that RPM with 15*

The motor could be a tad soft, but if it runs ok I'd not worry about it too much.

[Tom N]

I'm not positive timing is spot on. I know mechanical is and cas is installed properly with marks lining up and is set in middle of adjustment. I still have to put a timing light on it. It's a pain on this car. Never really sure if its in diagnostic mode and I have a wire specialties coil harness which doesn't have the little timing wire loop. Need to use my dabbed up plug wire.

[jr_ss]

Cody, this is a fresh bottomend, so I'd like to believe he'd see more than 15-16. I'd say close to 17-18.

Tom, I'll grab that wire tonight if you want to swing by and grab it.

[Tom N]

Cody, this is a fresh bottomend, so I'd like to believe he'd see more than 15-16. I'd say close to 17-18.

Tom, I'll grab that wire tonight if you want to swing by and grab it.


Let me know when your home later. Ill stop by with the car.

It's a fresh motor. 20 over CP 8.5:1 with eagle rods and apexi head gasket. Head is stock aside from cams. It was just cleaned, pressure tested and new valve seals.
Has about 10 miles on it so far.

[jr_ss]

Bring your timing light and we'll get it sorted.

[Tom N]

Bring your timing light and we'll get it sorted.

Will do.
I can't imagine the timing being off enough to cause the car to run 13inhg vs around 18inhg though.

[codyace]

Any luck with this guys?


Being a fresh motor it may simple not be seated yet either. And in regard to the marks lining up on the CAS, for some reason some cams don't cooperate with the marks so you'll need to adjust it a little.

[jr_ss]

We made some head way. His base timing was set at TDC. We tried advancing it to 16-17 like he wanted in "diagnostic" mode, but it wouldn't take it. As soon as we got it there and locked down the CAS the ECU would bring it back to TDC. We managed to get it around 10-11* BTDC but that's all the CAS adjustment would allow. He is going to verify that it is installed correctly and if not swap out to another one to rule it out.

With all that said, engine vac did come up significantly to 19in/hg at 11*, so we are expecting a slight bump once it's at 15-16*.

[Tom N]

I'm sure I installed the cas properly but will double check. This cas was working when the car went down. Not sure why it would now be bad but I'm thinking it must be.

[Tom N]

On a plus side with only 10 degrees timing I am glad to see vacuum close to what the stock motor with stock cams showed.

[codyace]

We made some head way. His base timing was set at TDC. We tried advancing it to 16-17 like he wanted in "diagnostic" mode, but it wouldn't take it. As soon as we got it there and locked down the CAS the ECU would bring it back to TDC. We managed to get it around 10-11* BTDC but that's all the CAS adjustment would allow. He is going to verify that it is installed correctly and if not swap out to another one to rule it out.

With all that said, engine vac did come up significantly to 19in/hg at 11*, so we are expecting a slight bump once it's at 15-16*.

Good to her it was a timing issue...that's 95% of the reason all the time for aftermarket cams to pull poor vacuum.


I've quit using the diagnostic mode all together, and have found a new way to set timing.

1. Obviously verify mechanical timing is correct (engine at TDC, cams outward, 20 links between, etc etc.)

2. Loosen the CAS bolts, but leave the top one a little snugger (this way you can move it and not have it too loosey goosey

3. Warm the car up to operating temp. Once you get there, get your timing light out and ready.

4. With the timing light focused on the crank (it'll be sporadic and jumpy) take your other hand and rev the engine up to mid range using the throttle body...just a quick rev and let off.

5.As the engine comes down from it's rev, carefully watch the timing light on the crank. It'll move back and forth and then just before the revs come all the way down, it'll show the actual timing of the car -15* ignition timing.

6. Rev it a few times and verify. Then adjust the cas so when the car is revving down, that it is set on the TDC MARK (not 15* mark). It'll take some getting used to, but this is a proven way to set timing with going into timing mode (as I think we all know the b13 and S13 ecu's are a bear to get into diagnostics mode). So after a few rev's and come downs just verify that the light shows TDC/0* and you'll know you're then at 15* ignition timing.

7. Tighten cas bolts and you'll be good to go!

[Tom N]

Good to her it was a timing issue...that's 95% of the reason all the time for aftermarket cams to pull poor vacuum.


I've quit using the diagnostic mode all together, and have found a new way to set timing.

1. Obviously verify mechanical timing is correct (engine at TDC, cams outward, 20 links between, etc etc.)

2. Loosen the CAS bolts, but leave the top one a little snugger (this way you can move it and not have it too loosey goosey

3. Warm the car up to operating temp. Once you get there, get your timing light out and ready.

4. With the timing light focused on the crank (it'll be sporadic and jumpy) take your other hand and rev the engine up to mid range using the throttle body...just a quick rev and let off.

5.As the engine comes down from it's rev, carefully watch the timing light on the crank. It'll move back and forth and then just before the revs come all the way down, it'll show the actual timing of the car -15* ignition timing.

6. Rev it a few times and verify. Then adjust the cas so when the car is revving down, that it is set on the TDC MARK (not 15* mark). It'll take some getting used to, but this is a proven way to set timing with going into timing mode (as I think we all know the b13 and S13 ecu's are a bear to get into diagnostics mode). So after a few rev's and come downs just verify that the light shows TDC/0* and you'll know you're then at 15* ignition timing.

7. Tighten cas bolts and you'll be good to go!


The cas was installed correctly. I swapped it just to see what happens. New one acted exactly the same. I tried timing it again by trying to get it in diagnostic mode and I think the problem is I'm not getting it in diagnostic mode.
So I tried your way and with the cas turned back to about the middle I see TDC when it throttles down. Car seems to drive good and vacuum is at 19 at 1k rpm idle. I assume its close to 15* now.
I really miss how easy it is to time a 4g63.

[slideways2004]

I really miss how easy it is to time a 4g63.

My S14 SR was fairly easy to time with the same method as stated by Cody.

Don't see it mentioned but you ARE using an actual spark plug wire stuffed into the #1 coilpack aren't you? If not, you HAVE to do it that way for accuracy.

I experimented with the little loop and I found some cars that were spot on and some cars that were 20 degrees off!

[Tom N]

Yes I'm using a spark plug wire. I have a Wire Specialties could harness and they don't have that loop anyways.

If Cody's method truely is accurate, and I'm not saying it isn't but I don't know for sure as it won't go into diagnostic mode, then it's not hard to time.
But with a 4g63 you simply ground a plug that's on the engine side if the firewall and its in diagnostic mode. There's no guess work about it. Very simple and precise.

[inopsey]

My S14 SR was fairly easy to time with the same method as stated by Cody.

Don't see it mentioned but you ARE using an actual spark plug wire stuffed into the #1 coilpack aren't you? If not, you HAVE to do it that way for accuracy.

I experimented with the little loop and I found some cars that were spot on and some cars that were 20 degrees off!

dont use a spark plug wire; too dangerous. there is no difference if you use a clamp on style timing light on the harness to coilpack 1. i also have used a spark plug wire and just clamped the light on to the harness before the coilpack and got the exact same reading. the cheap lights ive seen are clamp on style anyhow.

[codyace]

Yes I'm using a spark plug wire. I have a Wire Specialties could harness and they don't have that loop anyways.

If Cody's method truely is accurate, and I'm not saying it isn't but I don't know for sure as it won't go into diagnostic mode, then it's not hard to time.
But with a 4g63 you simply ground a plug that's on the engine side if the firewall and its in diagnostic mode. There's no guess work about it. Very simple and precise.

The method I described works without ever having to have the car in diagnostic mode, which is why I actually prefer using it when I don't have my laptop and consult reader (or if a person's car doesn't have a working consult port) as it's a real pain the butt to get the older b13 and s13 SR20 setups into diagnostic mode manually...there are some cars (mine included) that I've never EVER been able to manually trick.

With that said though, I do have NissanDataScan and a Cable for the Consult plug so I am able to get into diagnostic mode...and I can 100% verify that my timing being set with the method I describe above mimics the timing result when using timing mode in NDS and or Conzult.



I experimented with the little loop and I found some cars that were spot on and some cars that were 20 degrees off!

I can agree to this too. I'm unsure why or how it's so different on some cars. Probably down to wiring and or how much other interference is on that same ground.


dont use a spark plug wire; too dangerous. there is no difference if you use a clamp on style timing light on the harness to coilpack 1. i also have used a spark plug wire and just clamped the light on to the harness before the coilpack and got the exact same reading. the cheap lights ive seen are clamp on style anyhow.

The cheaper and older the timing light is, the better it seems to work with the coil pack harnesses. The one I keep in my little diagnostic laptop bag is a Craftsman one from at least the mid 80's...got it for 5$ at a yardsale as it was small and had long leads. Works great!