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Zcardude

L28ET Valve float and spring recommendations, aftermarket cam

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Posted (edited)

I need some help doing a bit of troubleshooting determining if I am experiencing what I believe is valve float due to too much cam:

 

I have an L28ET powered 240Z, running on MegaSquirt, with a t3/to4e turbo, lonewolf intake manifold, 2.25" downpipe to 3" exhaust, fmic, etc. After looking at receipts from the PO, I believe it has this cam: http://schneidercams.com/270-60F-14_LET6.aspx in a hydraulic P90A head converted to solid lifters, with new, stock valve springs. I believe the stock valve springs are very wrong for this cam. After lots of tinkering with wiring to the megasquirt, fixing grounds, new plugs, wires, cap, rotor, and some noise filtering in the megasquirt software, the car drives really well.

 

I've been driving around for a few days, and cruising around, part throttle, and WOT. I start making positive pressure at 2000RPM, and get desired boost by 3500-4000RPM depending on gear and everything is dandy -- up to about 5000RPM @ 18psi, a little higher at wastegate, around 9ish psi, where it seems to hit a complete wall. When it hits this wall, it is able to maintain boost and holds stable AFRs (a little on the fat end - low 11s), but, I can hear what I think is the blow off valve going off a bit, and I am not really able to accelerate without shifting. It doesn't sound like it is having ignition break up or detonation, but it sounds sort of off. The Z is not very fast despite making a lot of cool noises

 

What I believe is happening is that the cam is at the very limits of the lift that the stock valve springs are able to handle, and the valves are floating. Is that a reasonable thing to assume, or should I look elsewhere? The megasquirt was previously wired poorly, but I have it running so well now otherwise I am hesitant to blame it for the engine's current behavior. I am thinking that I should have no problem revving this engine to at least 6500RPM (7000 would be even better and a damn miracle) which would give me a reasonable power band - right now it isn't terribly exciting. I'm only in full boost for 1000RPM, then hitting a wall!

 

Next, if that seems like a reasonable place to look, I was considering doing the Rebello outer valve springs and nothing else, as that seemed like the most cost effective way to get some better valve springs in place and test my theory: http://www.rebelloracing.com/nissan1.htm 

 

My questions are this: Is there any reason I should not do this? Is this enough valve spring to work well with my cam? Is there an even more cost effective solution? Should I hunt down a stock cam setup instead? Do you have any other suggestion for my performance issues? I'm trying to get this sorted out on the cheap, feeling like if I can't get this setup operating correctly, I am going to swap to a newer GM V8

 

Edited by Zcardude

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Posted (edited)

That's really not all that big of a Cam. It should work fine with NEW factory valve springs. The low lift of the Shneider cams ( 0.460" ) makes it pretty easy on the valve train.  Certainly a bit stiffer spring wouldn't hurt, especially on the Intake. .. but you don't need anything excessive. 

 

 However, you may have a different problem. It is very possible that the Cam Timing is off by one Tooth. This will produce the exact symptoms you are describing. Engine hits an absolute wall at around 5,000 . Engine  will just feel sluggish overall. It will build boost, but slower than usual and just doesn't want to accelerate like it should. 

 

I've had this exact problem on my Turbo Audi, and I just finished helping a customer who had a problem Big Turbo L-28 that just would not rev past 5,000 rpm. Engine was down on power and just seemed sluggish. Ran smooth... but way down on Power and wouldn't Rev. Data logs revealed the problem to me. . MAP values at idle on decel were not correct. Only two things can cause that. Huge Vacuum leak or incorrect Cam timing.  Turns out the Cam had been installed 1 tooth retarded.

 

Same problem on my own Audi when I had the Timing belt changed. I let a local shop change it... Well because = Audi. " The Four Rings of Pain " . Car just would not Rev. Built boost OK-ish ( a bit slower than normal ) , but way down on Power and just would not REV. I could hold it WOT in 2nd gear and it wouldn't go past 6,000 RPM/. Fixed Cam timing. Gained about 75 HP and engine revved to 7,200 RPM limiter. 

 

I've tuned many L-28's with Big Boost and stock Nissan Valve springs. New factory springs should easily Rev well past 6,500 RPM on that Cam.  I've tuned local Turbo cars with T3/T4's with mild Turbo cams like you have and factory springs . The things were scary fast at only 10 and would ZING right past 6,500 no problem. 

 

My own car ( Normally Aspirated L28 10.5 CR ) has a larger Camshaft than what you have.  On NEW Nissan  stock springs it will happily spin well past 7,000. I've hit 7,200 a few times. Now have a Rev limiter on it to keep revs limited to 6,800 RPM 

 

I would double check your Cam Timing via FSM. It could very well be a Tooth off. 

 

If you have a Vacuum gauge, see what it reads on Decel. Just backing off normally or going down a hill, you should pull about 25 in/hg vacuum. If you are down around 20 in/hg ... you can be pretty sure that your Cam Timing is out. All other things veing checked of couse like Vacuum leaks and ignition Timing. But low Vacuum reading on Decel is a sure give away for incorrect Cam Timing. especially combined with the no revving past 5,000 RPM. You won't be floating the valve at 3,000 RPM on Decel.  

 

Edited by Chickenman

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Posted (edited)

BTW.. car I was assisting was at a Dyno shop. Went from a sluggish 198 RWHP Max at @ 15 lbs Boost. To 315 RWHP on 13lbs Boost. Engine easily spun straight up to Rev Limiter at 6,500 RPM . On a Baseline Tune (  one of my own Tunes ).... straight out of the Box.  Just by correcting Cam Timing. 

 

Much more HP to come. Way more ( GTX3076 ).  But this was just an initial test at low boost on a " Safe Rich " baseline tune.  But it made more than Dyno operator was expecting at low Boost and no Tuning  

Edited by Chickenman

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I am sure chickenman is right about the camshaft but if you want a little stiffer springs the Z31 non turbo springs are great for that. But don't use them at high lift cams (>0.480).

 

Shouldn't it be easy to spot if the timing is wrong? The shiny link needs to be in a specific place at TDC?

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Posted (edited)
58 minutes ago, Chickenman said:

BTW.. car I was assisting was at a Dyno shop. Went from a sluggish 198 RWHP Max at @ 15 lbs Boost. To 315 RWHP on 13lbs Boost. Engine easily spun straight up to Rev Limiter at 6,500 RPM . On a Baseline Tune (  one of my own Tunes ).... straight out of the Box.  Just by correcting Cam Timing. 

 

Much more HP to come. Way more ( GTX3076 ).  But this was just an initial test at low boost on a " Safe Rich " baseline tune.  But it made more than Dyno operator was expecting at low Boost and no Tuning  

 

Thank you for your posts! I have not verified cam timing and I will do so before doing anything else. I guess I'm getting ahead of myself here. :D I'm really glad to hear of someone else having the same symptoms, I feel like this car is so close to being awesome just not quite there yet!

 

I'll post back (hopefully with a resolution!) after verifying and adjusting cam timing

Edited by Zcardude

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8 hours ago, turbogrill said:

I am sure chickenman is right about the camshaft but if you want a little stiffer springs the Z31 non turbo springs are great for that. But don't use them at high lift cams (>0.480).

 

Shouldn't it be easy to spot if the timing is wrong? The shiny link needs to be in a specific place at TDC?

 

 Actually I think the latest supersession on the L-series outer springs changes up to the Z31 springs.  I'll have to double check that later. 

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Ok, it's late so I haven't gotten around to adjusting anything yet, but I set the engine at tdc and am thinking that the issue is not that the cam timing is off by a tooth, but due to a worn or stretched timing chain. The adjustment marks look like this:

 

xMxt3et.png

 

Looking at the haynes manual, I am thinking if I move the cam gear from position 1 to position 3 tomorrow, I should have the cam timing close to correct. I will try this out and report back unless someone recommends otherwise

 

This is my first L-series and I have never had to adjust cam timing before, so some questions: Would this amount of mis-adjustment still cause my RPM wall near 5000RPM? Is it possible to be off by a tooth and have the timing this close to spec? It seems like this is an adjustment issue and not an issue with improper cam gear installation

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7 hours ago, Zcardude said:

Ok, it's late so I haven't gotten around to adjusting anything yet, but I set the engine at tdc and am thinking that the issue is not that the cam timing is off by a tooth, but due to a worn or stretched timing chain. The adjustment marks look like this:

 

xMxt3et.png

 

Looking at the haynes manual, I am thinking if I move the cam gear from position 1 to position 3 tomorrow, I should have the cam timing close to correct. I will try this out and report back unless someone recommends otherwise

 

This is my first L-series and I have never had to adjust cam timing before, so some questions: Would this amount of mis-adjustment still cause my RPM wall near 5000RPM? Is it possible to be off by a tooth and have the timing this close to spec? It seems like this is an adjustment issue and not an issue with improper cam gear installation

 

It looks good I think. Is the top timing mark on the sprocket aligned to the shiney or marked link in the chain?

 

tm2b.jpg

 

Can you ever get it passed 5000 RPM? How is ignition controlled? From megasquirt as well?

 

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From the FSM, I believe it is retarded but I would love to be told that I'm wrong. My setup looks to be somewhere between these two:

 

2aXpKXS.png

 

I was thinking that the notch on the sprocket should be to the right of the groove.

 

Looking at my timing chain, I'm noticing any timing dots or shiny links. Possibly an aftermarket replacement chain? Here is what I see at the "1" position with the engine at TDC, same position that I took the previous pic of the cam timing mark at. Looks like there is some markings on the chain links, but they are on other links as well, notice the link before the "1" mark:

 

DcPj79t.png

 

 

18 minutes ago, turbogrill said:

 

Can you ever get it passed 5000 RPM? How is ignition controlled? From megasquirt as well?

 

 

I've never had it past 5k RPM. Ignition is controlled by the megasquirt, it is running an MSD street fire ignition box. I am getting pretty strong spark. New plugs/wires/cap/rotor

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I agree... Cam Timing looks OK. Definitely not off a Tooth by those photos.  Did you physically confirm TDC using a Piston stop method, or just go buy the Damper Mark? Piston stop method is most accurate.  #1 Piston at TDC has to be dead nuts on in this situation. 

 

 That being said ,  I may however, have found some incorrect Ignition settings in the MSQ you sent me by E-mail. 

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Cam timing looks ok and shouldn't cause the issues you're seeing. The shiny links are used to set timing on chain install, the groove and notch are used for all other checks and adjustments as OP has done. My money is on a calibration or crank sensor issue.

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Ended up triple checking that piston 1 was at TDC and then not adjusting cam timing based on feedback from this thread. I just finished throwing everything back together and loaded up some different ignition settings on the megasquirt based on Chickenman's feedback. The car starts and runs fine but I have not driven it yet because it is late and I don't want to wake up the neighbors. This thing is bit loud :D I will report back with whether or not a simple tune change fixes the issue tomorrow!

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Just took the car for a spin and it drives a lot better. Still not perfect but definitely having no problem spinning past 5000. I turned the boost down a bit to test with, but I am definitely able to rev over 6000RPM now thanks to switching my spark settings. I guess I should have started out in the megasquirt forum! The car still seems to sort of lay down a bit after 5000RPM but I am attributing that to the tune being way too fat (low 10s on my current tune) up there, and I can clean that up a bit with some more street tuning and then a dyno.

 

If anyone is reading this and wondering what the heck I changed given my issues: I had a dwell type of fixed duty, with a dwell duty% of 50. Chickenman recommend that this was wrong and that MSD boxes like my Street Fire, actually can use a standard dwell, with a nominal dwell of 2 and a spark duration of 1.

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