RB26 cams in RB20 didnt work :-(

[browny]

Thanks for the explanation lukevl.

So what you are saying is that hydraulic cams don't have the "lift ramp" you describe because the lifters are self adjusting for valve growth. So if you put in a solid cam the lifters will follow this extra ramp and open the valve early and close it late, which will result in a longer duration (and poor running). Correct?

FYI, in my engine manual the warm clearances for a 32GTR are given as 0.51mm intake and 0.44mm exhaust (both +/- 0.03mm).

[lukevl]

Yes Browny- you got it. If you look at a Solid camshaft, there are no rub marks from the lifter on the base circle, but on a hydraulic you can see rub marks all the way around because of the lifter preload pushing against the base circle. (Thats if you can see the marks. Its easiest on an old school push rod donkey )

Thanks for the settings Browny. I have been told by a few 'performance workshops' that the settings are like 0.35 and 0.4"? I didn't expect there to much truth in that but. Oh well thats good nissan specify the correct settings (Or close to it)

[Cubes]

Luke how dare you doubt Nissan!

[browny]

The manual also has cold settings and from memory they are similar to the values you have been told.

[lukevl]

ylwgtr2 - Sorry mate I did a bit of research and apparently even in running coniditions, a sodium filled valve will expand less in exhaust temperature than an inlet in its lower operating temperature. So yes thats why they hve those settings. Although I didn't exactly doubt this, i know for sure now and so does everyone.

[JH32]

So the end result ... don't run cams meant for GTRs in RB20s or RB25s ?

[lukevl]

Absolutely correct.

[lukevl]

Okay guys, don't say I don't do anything for you. Mechanical and hydraulic lift vs crankshaft angle. make sense now?

[Roy]

I understand what you are saying abot the clearance of the solids, but in order for the above to be anything put a meaningless plot, you will need to post the specs of the cams graphed, as looking at the above id say there is no reason for not running the solid cam with thehydraulics, the only difference is that a cam has slightly longer duration when used with hydraulic lifters...need more info.

[lukevl]

The graphs are not meaningless they have values on the axes! Look at the mechanical GTR profile. IF you ran zero clearance (follow the bottom of the graph) You get about 370 degrees seat duration. A top fuel dragster will run about 340-350 degrees!

Thats about 180 degrees of overlap.

Honestly, I don't know why I bother. Go home champ

[lukevl]

Also I could give you specs and all the hoo-haa but you wouldn't get it and it will not help you to understand the plot.

Sorry boys I'm just a bit cheezed off by this cause I thought it would make it heaps clearer. :headspin:

[Roy]

Honestly, I don't know why I bother. Go home champ

Settle down hillbillie...im asking questions, not arguing with you.

Looking at the concavity of the plots they look the same, hence my being curious whether you have plotted the same cam duration for both solid v hydraulic (it looks like you have for lift)

According to those plots, what is the seat duration for the hydraulics... just to make it clearer where you are reading the 370 figure from

[lukevl]

meaningless plot

It took me almost 10 mins to do them!

Each grid is 100 degrees crankshaft rotation. Figure it out. It is not that hard. Did you do yr 10 science? lol

Look at the lifts, the hydraulic looks like a sine curve and the mechanical looks like a hydraulic but propped up on little linear ramps. I'm going home for beer and sex now and I won't be back till tomorrow so have fun slandering my pictures for the next 24 hours that I slaved over :bs!: for the benefit of the viewing public.

:aroused:

[jnr32r]

lukevl: Im still confused how is it that RB20 cams have 360 degree duration???

[Roy]

Each grid is 100 degrees crankshaft rotation. Figure it out. It is not that hard. Did you do yr 10 science? lol

Nope, was too busy getting bashed by the jocks :Oops:

Looking at the hot running clearance the solid cam would seem to have less duration then the hydraulic... im stumbling thru trying to make sense of the plots nd what they mean, not wanting to argue. Does the plot of the solid cam have less duration then the hydraulic...

They seem to have the same lift, and after 0.05 the same area / curvature... but when looking at the hot running clearance the solid has less duration.

Oh well, good luck chasing your c0cker spaniel around the yard trying to score when your pissed :Oops:

[Ahh32]

here doggy here pup. ha ha

Your 370 degree seat duration don't mean shit, all hydraulic lifted engines would have 360 degree contact.

the only difference it would make would be the .05mm clearance that the hydraulics don't have making them open sooner and close later.

AS for as i can make sense of your 10 minute masterpiece.

GTR cams

Intake: open at -220 degrees close at 5 degrees

Exhaust: open at -10 degrees close at 210 degrees

hydro cams

Intake: open at -245 degrees close at 20 degrees

Exhaust: open at -20 degrees close at 230 degrees

If the GTR cam graph is continued down to 0 to replicate them operating in a hydraulic lifted engine then we get:

Itake : open at -255 degrees close at 30 degrees

Exhaust: open at -30 degrees close at 240 degrees

The only problem i can see is that the intake valve being closing later may cause compression to be lost. easy fix adj, cam gears advanced some more. just don't hit pistons

OK if i have wasted the last 20 mins doing this then boo hoo. they work in my car and that's fine with me.

[Sydneykid]

********Warning, this is a long post, read it at your peril.*********

Hi Luke, I have been staying out of this up to now because I have successfully done the GTR cams in RB20 more than once. So I KNOW it works. What I am going to do in this post is use plain English, I am going to avoid technical jargon as much as I possibly can. That way the non tech heads can read it and understand.

The Camdoc output shows the difference in ramp which I would expect (and have seen many times before). On a "solid" camshaft you have to have a “gentle” ramp, particularly on opening. If you don't have a “gentle” ramp it means the tappets are noisy as they go from zero lift to some lift very quickly. This makes noise (tappet rattle) and the car manufacturers don't want this, so they have a “gentle” start to the valve opening. If you use a "hydraulic” camshaft with “solid” followers you get this knocking at initial valve opening as there is no “gentle” ramp. This also wears out the camshaft and the follower. I never use a “hydraulic” camshaft with “solid” followers for this reason.

If you look at the Camdoc output you will see that the closing ramps are both pretty much the same (ie; the “hydraulic” has a gentle ramp on closing, this is the same as the “solid” camshaft). This is what you would expect, you don’t want the valve slamming into the seat too fast/hard. This would break a valve head off and/or wear out the valve seats. The hydraulic and the solid followers act exactly the same at this point. The hydraulic follower is full of oil and sealed off from the oil supply galleries. Oil (being a liquid) is incompressible, so it acts exactly the same as a solid follower would.

But this is NOT the same as using a “solid” camshaft with “hydraulic” followers, the “gentle” ramp is there, so there is no noise or wear. It doesn’t have to be there but it makes no difference if it is.

So having gotten rid of ramp as a possible reason, let’s look at another….

Both camshafts have ZERO lift at some point (in fact many degrees of crankshaft rotation). This gives the oil time to be “squeezed” out of the follower while it is lined up with the oil gallery. The “squeezing” is done by the valve spring, if the valve isn’t fully closed, the valve spring “pushes” against the follower and forces the oil out of the follower until the valve closes. No more spring pressure, so no more oil is squeezed out of the follower. That’s how hydraulic followers run with zero clearance, hot or cold.

So I don’t give a rats arse about the ramp, that is too late in the cycle to make any difference as to whether or not the valves are closed at zero lift.

This now leaves only one possibility…………..

I have checked back on the RB20’s I have done with RB26 camshafts. I have not done an RB20 upgrade used R34 GTR cams, I have a top end on the way that I will try shortly, but not as yet. I have done 2 with early (1989) GTR camshafts, these are definite I removed them from the engines myself. One of these I was converted to solid followers using GTR valve springs but not by me. I have done one other with what I was told where R33 GTR camshafts, but I didn’t remove them from the engine so I can not be sure. What I did do was check the lift, as it is the easiest to do confirm that I was being sold GTR cams. This would not confirm which model of GTR, they might have been R32.

It may be possible that later model GTR camshafts have a larger base diameter, this doesn’t affect timing or lift. But what it could do is push the followers open and past the oil gallery. This means they would be “solid” all the time because they could not bleed off the oil to give clearance. Draining the follower before installing the camshafts would have no effect on this problem. In fact it would create another, as no oil would flow into the follower if the gallery didn’t line up ie; they would rattle their heads off.

There is one other related possibility, the oil gallery lines up with the follower but the base diameter of the camshaft is so great that, even with all of the oil out, there is still no clearance and the valves stay open.

Where do I go from here, well I am going to measure the base diameter of some GTR camshafts. I have a late (1993) R32 pair of cams and an R34 pair on the way. I will compare that with the base diameter of a pair of RB20 camshafts. If there is a large enough difference to cause this problem I will post it up. Otherwise I can only say it is an “installation” problem. If the R34 GTR cams come up OK in the base diameter test, I am going to install them in an RB20 and take pictures of what I do. Then post them, so anyone can copy the process.

Hope that makes some sense, so Luke can say “f**k he’s right again”.

[Clint32]

Thanks sydney kid, that makes perfect sence when explained your way when you have a little mech knowledege, i have gtr exh cam in my rb25 head so hopefully it will be no problems, only has 8.8mm lift anyways

[GTR-NUTTER]

sydneykid so do you recomend any particulat gtr cams or just any would be fine

K

[Sydneykid]

sydneykid so do you recomend any particulat gtr cams or just any would be fine

K

As I posted above, I don't know. I am going to compare a couple of sets that I have with standard RB20 cams. The only thing I am interested in is their base diameter. One pair are late R32 and the other set is R34. The R34's should be in the machine shop early next week. I also have a few sets of aftermarket RB26 cams, one set of Jun, two sets of HKS and one set of Tomei. I will publish what I find.