RB26 Tomei Type R Cams - Results?

[GTSBoy]

29 minutes ago, MJTru said:

But how does a cam with lots of duration relate to ignition timing.
 

Well, one way to look at ignition timing is that the less efficient the engine is (either overall, or at a particular point in the operating range) then the more timing it can take...  or more to the point, the more timing it will want.

So, partial throttle.....that's an efficiency killer, compared to running WOT.  So it will swallow more timing.

Or, if the cams are not in their sweet spot (rpm wise) then the engine will not be trapping as much cylinder fill as it will at the right rev range.  That's an efficiency killer, and you can run more timing.

So when you go to larger cams, the logic of what you can do with timing follows the above.  Where the cams are costing you cylinder fill, you can probably add in some timing.  That would be at the bottom of the rev range.  Where the cams are working to trap more cylinder fill, you'd probably have to back off timing.  Of course both those statements are to be taken as "relative to the same engine with the original/smaller cams".

There may be some traps though.  Longer duration cams can cause increased exhaust reversion at some points, particularly where they are not working well.  The increased amount of hot exhaust gas in the charge in the cylinder can lead to detonation, so you wouldn't be adding timing if that was happening.

[MJTru]

Hmm. Still a bit mixup here sorry. I understand the way you try to explain stuff. Here goes from my stand point.
The cams with bigger lift and especially the long duration let's the cylinder fill situation affect the whole performance by killing power down low due to it causing the peak cylinder pressure to move. We can say we don't know if it's in an advanced or retarded situation. I'm guessing retarding it mechanically speaking. But maybe not. But it does effect the way the ignition timing affect the whole results, power and torque wise. So the cylinder fill rate is delayed letting more air in but depending on flow rpms and turbo capabilities. So as more air is packed in this whole mechanical phenomenon from the stand point of a stock motor vs a motor with cams, and stock time from one to the other, would kill down low power. But if the timing is retarded enough the aid air, if the fuel can handle it, will detonate as the heat rises. But it should raise torque and power further down the rpm band. Basically, sorry if I sound abit confusing here, with duration you have to adjust the timing to gain back abit of down low power lost, but in my opinion you will lose power down low in comparison to a stock setup, until things start moving and flow and resistance gets better. Then everything gets better. Hense why the best result would be the vct system.

[MJTru]

I forgot. How can you adjust adjustable cam sprockets to help the low down power?

[GTSBoy]

Marcus, you really need to be more clear when you say "timing".  It's been really hard to tell, for each use of the word, whether you mean cam timing or ignition timing.

To answer your last question first....adjust cams to reduce overlap in order to make them work better at lower rpm and not as good as they could at higher rpm.

To answer what I think you were asking in the previous post.....actually I can't answer it.  Because I still don't follow which type of timing you were talking about at each usage of the word.  But in general, I have posted earlier in this thread on the subject, and between that post and my most recent one, it covers most of it.  What it doesn't cover is different philosophies that different tuners might have towards the ignition timing options when trying to build boost.  Some want to keep as much (ignition) timing in the engine as they can.  Others are happy to run a fair bit less in order to get the exhaust temperatures up to make the turbine spin.  What works in one case may not work in another.  So YMMV as always.

[No Crust Racing]

Finally got some info for people playing along at home. Copy paste from build thread. 

Maxxed out fuel pump at 20psi. Last time we ran 24ish.

Need new pump then will take it back to finish it off. What to buy for intank? Currently has brand new direct wire 460lph Walbro. 

Detuned for now for safety making same power as before on only 16psi.

Slightly more responsive too, dialled for max response though and now with closed loop boost control. Power is better from the on boost onwards. Will get an overlay of new and old when I'm back there and it's finished but I've seen it myself. 

Will be good when finished off, but driving nicely at the moment.

Sounds like a f**king diesel with the valvetrain noise. Tuner said all clearances on the looser side of within standard specification and he likes them there. Can shim tighter if I want. Pros cons?

Dyno graph and vid of loud idle. 





 

 

[djvoodoo]

Thought i might share some results since i went with Tomei Type R Poncams on HKS GTSS turbos, pump 98.

Prior to putting in the cams, i had the boost turned up to 23-24psi and made 314awkw. 3 psi less and making a few ponies less, but the low end/ mid range is pretty bloody good for pump 98.

I haven't seen many standard Rb26's on pump fuel getting 180Kw under 4000rpm.

Type R are a great match for -9's.