RB25DET Timing Issue/Clarification

[Nismo34GTT]

I recently purchased a R32 drift car from Japan that is pretty well built.  It has a RB25DET block with a RB20DET head, which I've never seen before, but the car pulls like a mother at the track.  I decided to go ahead and do all the routine maintenance on the engine recently, including changing the timing belt.  I was trying to get ready for a drift event today, and in my haste I made a careless mistake.  I did not set the engine to TDC before removing the timing belt, and thus I didn't see if the timing was actually set to factory or not by whoever built/tuned this motor. 

I put the timing back to stock and installed the belt.  This is how I've always done cars - put them to their factory settings.  When I start the car now, it runs hella rough.  I have a Power FC on it and the knock was in the 40s to 60s upon start up.  After some tweaking I got the knock down to 0-5, but it still runs like crap.  I disconnected the TPS and connected my timing light to coil #1.  I set the timing on the crank pulley to 15 degrees; however the power FC shows 22-23 degrees.  When I adjust the power FC to a -7 or -8 on the timing, it shows 15 degrees on the power FC; however the engine no longer shows 15 degrees on the crank pulley. 

I'm fairly new to performance engines. This engine was running amazingly well before I took it apart, and now I can't get the timing set for the life of me.  Based on what I've observed, I'm guessing the previous mechanic had set the exhaust cam 2 teeth off (8 degrees) from the stock timing mark.  This is the only thing that makes sense to me as to why the Power FC and Crank Pulley timing marks don't match, as my thinking is that the Power FC was tuned with the exhaust cam 8 degrees off.  I've read where people do 4 to 8 degrees on the exhaust cam to get more mid-range power and quicker boost from the turbo; and since this was a drift car that would make sense to me.  Because I'm new I thought it would be best to ask the community about this issue before I reset the timing.  Thanks in advance for your help! 

[Nismo34GTT]

I retarded the exhaust cam by 1 tooth (about 4 degrees according to other forum postings), and now the FC is showing 28 degrees while the gun is showing 15 degrees on the crank pulley...  Now we are off by 13 instead of 8 like before, which leads me to believe the exhaust cam was advanced 8 degrees before I pulled it apart the first time...  Going to advance it next and re-test. 

[Nismo34GTT]

The car is running at it's best with the exhaust cam advanced 4 degrees.  It ran really well at 8 degrees advanced and another configuration with the exhaust advanced 4 and intake retarded 4.  At stock timing it runs good, but sounds more like a NA motor where it's "lobing", and that's not preferential for induction engines from the reading I've done.  So at the end of the day after testing 6 different CAM configurations, we set the exhaust to 4 degrees advanced and the intake to stock position. We chose this configuration because it had the lowest knock readings on the power FC (2-4). 

Now the Question is...  HOW do I set base timing in this configuration?  And is it better to use the wire on the ignition module for coil pack one, or to loop around the 3 wires of coil pack one with the timing light?  I seem to get a better signal from the ignition module, but most posts I've read say to use the coilpack.  They also say to disconnect the TPS, which seems to make very little difference on my end. 

Edited March 8, 2020 by Nismo34GTT

[GTSBoy]

7 hours ago, Nismo34GTT said:

HOW do I set base timing in this configuration?

Not sure I understand.

1. Find TDC via usual mechanical method (screwdriver through sparkplug hole at least, dial gauge indicator by preference).
2. Check TDC mark on crank pulley. Remark if necessary, along with 10, 15 & 20° marks if you like.
3. Put timing light on motor and adjust CAS until you get required base timing (15 or 20° depending on model and manual/auto).

 

[GTSBoy]

9 hours ago, Nismo34GTT said:

And is it better to use the wire on the ignition module for coil pack one, or to loop around the 3 wires of coil pack one with the timing light?  I seem to get a better signal from the ignition module, but most posts I've read say to use the coilpack.

The best way is to pull the coil off the plug and use an HT lead to make the connection and put the inductive trigger around that.

9 hours ago, Nismo34GTT said:

They also say to disconnect the TPS, which seems to make very little difference on my end.

That's because the ECU will f**k with the timing at idle if it can't keep the target idle speed just with the IACV. When you disconnect the TPS you disable that. The smart approach here though is to install Nistune, so that you can do it from a laptop.

[Ben C34]

I am reasonable sure one tooth is much more than 4 degrees., more like 8 degrees on the pulley which is 16 degrees on the crank. That is some crazy adjustments you are making there, pretty brave .

[Nismo34GTT]

The cam gears have 48 teeth.  The crank rotates twice for each cam rotation.  360 degrees divided by 48 teeth = 7.5 degrees.  Now you halve that because the cam turns at 1/2 the speed of the crank, which gives you 3.75 degrees.  I don't think I'm being brave at all, but rather setting the motor for optimal performance in drifting.  Advancing the timing should create faster spool, use less fuel, and give more power in the lower and mid range bands. 

As per TDC, there is no need to re-mark it.  TDC is still TDC regardless, as this is based on the crank position and the crank pulley has not changed it's position on the crank.  It can't change position because of the key-notch. 

What I am trying to figure out is the base timing.  The cam being advanced 4 degrees changes the position of the CAS.  The CAS position is what adjusts the timing in regards to what the flashing light shows on the crank pulley.  Because the CAM is advanced 4 degrees, this means the crank should be about 8 degrees retarded before the CAS is in the "stock" position for 15 degrees BTDC.  So does this mean that base timing is now set to 23 degrees BTDC or 7 degrees?  If I go to 15 degrees with the exhaust cam advanced, we aren't going to actually be at 15 degrees BTDC because the exhaust cam is not in the stock position. 

 

 

[Nismo34GTT]

Guess it's just trial and error for me then.  Really thought there would be some people here who have some knowledge on this kind of tuning.

When the car came in, the knock at idle was steady around 0-2.  When I was drag racing it, I saw the numbers hit up to 60, even up to 65 a couple of times.  That's with the tune it came with. 

With the exhaust advanced, the crank is showing 30 degrees as the timing (but the power FC is now showing 21/22), which matches the math above.  We are 8 degrees advanced, so the real timing is 8 degrees retarded from the mark on the crank pulley...  Question answered.  With the timing at 22, knock at idle is 0-2 and bounces sometimes up to 20/25, then back to 0-2.  When I'm going WOT she hasn't gone above 25 on the knock.  The last run was 18-20.  She's boosting hella fast and breaking the tires on shift through 3rd.  The Apexi turbo on this beast causes her to spool about 500rpm faster than a normal turbo of the same size, and now she's spooling even earlier thanks to the advancement of the exhaust cam, plus the knock has gone down.  She's a mean one. 

[GTSBoy]

You are wrong on nearly every point, but I don't have time to deal with it right now. So wait.

[Ben C34]

3 hours ago, Nismo34GTT said:

The cam gears have 48 teeth.  The crank rotates twice for each cam rotation.  360 degrees divided by 48 teeth = 7.5 degrees.  Now you halve that because the cam turns at 1/2 the speed of the crank, which gives you 3.75 degrees.  I don't think I'm being brave at all, but rather setting the motor for optimal performance in drifting.  Advancing the timing should create faster spool, use less fuel, and give more power in the lower and mid range bands. 

As per TDC, there is no need to re-mark it.  TDC is still TDC regardless, as this is based on the crank position and the crank pulley has not changed it's position on the crank.  It can't change position because of the key-notch. 

What I am trying to figure out is the base timing.  The cam being advanced 4 degrees changes the position of the CAS.  The CAS position is what adjusts the timing in regards to what the flashing light shows on the crank pulley.  Because the CAM is advanced 4 degrees, this means the crank should be about 8 degrees retarded before the CAS is in the "stock" position for 15 degrees BTDC.  So does this mean that base timing is now set to 23 degrees BTDC or 7 degrees?  If I go to 15 degrees with the exhaust cam advanced, we aren't going to actually be at 15 degrees BTDC because the exhaust cam is not in the stock position. 

 

 

https://www.google.com/imgres?imgurl=https%3A%2F%2Fwww.torque-gt.co.uk%2Fmedia%2Fcatalog%2Fproduct%2Fcache%2Fa95ad56dd2a79ef00be2f8cdc9ab0431%2Fh%2Fk%2Fhks_rb_cam_pulley_exhaust.jpg&imgrefurl=https%3A%2F%2Fwww.torque-gt.co.uk%2Fhks-adjustable-exhaust-cam-gear-pulley-rb26dett-rb25de-t.html&docid=ZEmr9xpMHGTIlM&tbnid=cCh28LctIOGQFM%3A&vet=1&source=sh%2Fx%2Fim

 

You have divided by 2 rather than times by 2.

I would slow down and have a decent think at this stage, rather than trying random combos of valve events.

pretty much no one sets cams up one tooth out, no one would do 2 teeth out. It is normally in the 4 degree range, which is half a tooth, and why vernier cam gears exist

[Ben C34]

3 hours ago, Nismo34GTT said:

  If I go to 15 degrees with the exhaust cam advanced, we aren't going to actually be at 15 degrees BTDC because the exhaust cam is not in the stock position. 

Igintion timing is relative to the tdc, it does not matter where the cams are set.

what would happen is the cas would need to be rotated by thr same amount the cam has been moved to sethe timing correctly but there is no further calculation of actual timing regardless of anything .

where the timing light flashes is where the timing is

[GTSBoy]

4 hours ago, Nismo34GTT said:

The cam gears have 48 teeth.  The crank rotates twice for each cam rotation.  360 degrees divided by 48 teeth = 7.5 degrees.  Now you halve that because the cam turns at 1/2 the speed of the crank, which gives you 3.75 degrees.  I don't think I'm being brave at all, but rather setting the motor for optimal performance in drifting.  Advancing the timing should create faster spool, use less fuel, and give more power in the lower and mid range bands. 

I'm not going to address your angular arithmetic. But the question to consider is....do you have any idea how close your valves are getting to your pistons with your wild adjustments?

4 hours ago, Nismo34GTT said:

As per TDC, there is no need to re-mark it.  TDC is still TDC regardless, as this is based on the crank position and the crank pulley has not changed it's position on the crank.  It can't change position because of the key-notch. 

Oh. Really. The outer pulley on the balancer is bonded to the inner by a rubber section. These can decrepitate and move the outer relative to the inner. Then all of a sudden your magic trusted TDC mark is anything but. My advice to you was to prove that it is correct and deal with it if it wasn't because you have embarked on a free-for-all approach to adjusting your cam position relative to your crank. It would be wise for you to at least know that one of your reference points was correct.

4 hours ago, Nismo34GTT said:

The cam being advanced 4 degrees changes the position of the CAS.  The CAS position is what adjusts the timing in regards to what the flashing light shows on the crank pulley.  Because the CAM is advanced 4 degrees, this means the crank should be about 8 degrees retarded before the CAS is in the "stock" position for 15 degrees BTDC.  So does this mean that base timing is now set to 23 degrees BTDC or 7 degrees?  If I go to 15 degrees with the exhaust cam advanced, we aren't going to actually be at 15 degrees BTDC because the exhaust cam is not in the stock position. 

None of this matters if you use a timing light and know where TDC really is. None of it. The CAS may end up rotated all the way one way or the other as a result of your wild changes, but if the light flashes on your required timing mark (we'll assume 15° here because surely no-one would drift an auto Skyline) then the timing is correct. It has nothing to do with the relative positions of the cams, etc, because you move the CAS to compensate for all that shit. And here's a wild tip. If you can't get the timing light to show you 15°, then you have either got a slipped balancer pulley or you have done something stupidly to far from normal at the cam gear.

1 hour ago, Nismo34GTT said:

Really thought there would be some people here who have some knowledge on this kind of tuning.

3 f**king hours. # f**king hours. That's how long you waited before declaring SAU as being bereft of knowledge? Really? Ferfuuxsake!

1 hour ago, Nismo34GTT said:

When the car came in, the knock at idle was steady around 0-2.  When I was drag racing it, I saw the numbers hit up to 60, even up to 65 a couple of times.  That's with the tune it came with. 

With the exhaust advanced, the crank is showing 30 degrees as the timing (but the power FC is now showing 21/22), which matches the math above.  We are 8 degrees advanced, so the real timing is 8 degrees retarded from the mark on the crank pulley...  Question answered.  With the timing at 22, knock at idle is 0-2 and bounces sometimes up to 20/25, then back to 0-2.  When I'm going WOT she hasn't gone above 25 on the knock.  The last run was 18-20.  She's boosting hella fast and breaking the tires on shift through 3rd.  The Apexi turbo on this beast causes her to spool about 500rpm faster than a normal turbo of the same size, and now she's spooling even earlier thanks to the advancement of the exhaust cam, plus the knock has gone down.  She's a mean one. 

When it was pinging its tits off you probably had some stupid combination of settings that simply had your ignition timing too far advanced because you thought that you could set it based on cam angle arithmetic.

This is an example of too much rocket surgery and not enough basics.

[Dil-Dog]

Something to also consider when you are setting your ignition timing is that according to the Workshop manual, you MUST also have your idle all the way down to 600rpms. believe it or not this is actually something that alot of people overlook. the average RB is around 800-900 rpm on idle. You just gotta be slow and easy with your idle air screw and you will get it 

[MoMnDadGTR]

13 hours ago, Dil-Dog said:

Something to also consider when you are setting your ignition timing is that according to the Workshop manual, you MUST also have your idle all the way down to 600rpms. believe it or not this is actually something that alot of people overlook. the average RB is around 800-900 rpm on idle. You just gotta be slow and easy with your idle air screw and you will get it 

very good point I had troubles setting mine later finding out my idle was to high. I had to replace my iacv and my intake gaskets to get the car to idle proper without cranking iacv screw super far in. might be time for a nistune m8 

[GTSBoy]

Mine idles as 60-650 all day every day. All it takes to get it there is to set the idle speed target in Nistune.

[MoMnDadGTR]

4 hours ago, GTSBoy said:

Mine idles as 60-650 all day every day. All it takes to get it there is to set the idle speed target in Nistune.

yes great way to set idle.  I tried to go about this but could not achieve the idle speed with leaking intake gaskets and iacv. I could get it to 900ish with idle screw all the way in. nistune, iacv, intake gaskets good to go now. was very misleading almost made me think my timing belt was out.  Found the leaks spraying brake cleaner around engine with it running mainly around intake listening for sputters didn't bother with turbo side

Edited March 18, 2020 by MoMnDadGTR