Timing problems.

[XTCoX]

Hi all, new to the communinty, I had a few questions regarding why I cant seem to run more than about 2 degrees advance at idle without getting detonation.

 

First the basics, its an L28 with flat +1mm pistons, N42 head, 1mm headgasket.

290F schnieder, .495L/.290D.

Crane Hi-6 CD system, LX92 coil

Mallory Unilite, which has 24 degrees mech. adv @ 3k

91 Octane.

SU carb with some modded SM needles, tuned with a wideband for 12:1 at WOT and just rich of 14.7:1 everywhere else. I got close but its not ideal. Searching for needles atm.

 

Im pretty sure it has something to do with the fact im running 91 in a 10.1:1 cylinder. But im in socal so the easy fix of buy better gas isnt an option. Got any cheap addive recommendations that wont eat my fuel system?

 

The reason im even calling it a problem? The damn thing WILL NOT PULL past ~5500rpm. It will hit the limiter I have at 7k... begrudgingly. Its super happy and pulls really well up to 5k, but refuses to continue on up in the same way despite a nearly dead on 12-1 afr.... was I right in looking at timing next?

 

Even with the timing almost on top of TDC it knocks from time to time, but ever so slightly and under full vacuum (partial throttle) below 3.5k. Gotta be kinda hot too.

 

Any help is greatly appreciated. The engine was just rebuilt by a shop that I probably shouldnt mention right now considering the other can of worms I think I have with a potential rod knock less than 4k miles into the rebuild. Not to mention they didnt time the thing before they gave it back, AND, when I pulled the valve cover off to address the metallic, intermittent knock coming from within the bowels of the engine by doing a valve adjustment (kinda silly, I know), I find the valves are all out of whack. As in a couple thousandths difference beween almost each of the 12 valves o.0

 

All it did was shut the valves up so I could hear the knock better....

 

Thanks in advance all

Edited December 22, 2013 by XTCoX

[Lazeum]

I had the same bottom end / head combo as you but with a milder cam. I was pinging as well.

Since you have a Mallory Unilite, try to lower mechanical advance. You don't need special tools to adjust it. Just get some drill bits with different sizes as template and some maths to figure how much advance you'd like.

 

At idle, you might need around 10-14° without vacuum advance, try to achieve 30° max timing for a first start and see how the engine behaves. It means you need around 16° mech advance.

My setup was happy with 30° max timing to avoid knock (around 2500/3500 rpm at high loads) but was giving up some hp at high rpm where ping vs. toning was not the issue.

 

Since, I've changed the head & my timing management, problem are gone on my side 

Edited December 22, 2013 by Lazeum

[madkaw]

Did you degree the cam or did the shop?

[XTCoX]

Thanks for the quick replies!

 

I had heard the advance curve on the Unilite was adjustable, so I'll give that a shot (: gotta look up the process though, I haven't recurved a distributor before. Thanks for the quick math Lazeum haha

 

Also, Lazeum, what head and timing management did you switch to? Like a shaved p90 or p79?

(But with the p90, I couldn't boost it until I had forged pistons and a CR of like 8:1 right?)

 

Madkaw no I didn't degree the cam, the shop did. Also one of the problems I had on the list considering it's not behaving up top.

[XTCoX]

Oops, just saw your signature with your engine specs.

 

Think the carbs might have something to do with this problem?

 

I've seen SUs pull hard through the rpm range, but could the top end bogging have something to do with using needles that aren't perfectly identical? Could I be causing a harmonic imbalance between the cylinder banks?

Edited December 22, 2013 by XTCoX

[Lazeum]

If you can read AFR, you should be able to spot any issue with SU's. Some unbalance could create some issue but it might be big to create such effects. I guess you should also feel some symptoms at low rpm if it would be the cause. I don't think this is your problem but I'm in front of a keyboard to ptovide such info, not in front of your engine...

 

Cam timing is a good point, you should double-check it.

 

Regarding Unilite setup, you have to plates bolted together you can adjust to change their offset.

Here are 2 shots to show you how it looks inside & how I adjusted it.

 

 

 

 

My head is a P79 head prepared by Braap & Rebello to meet my expectations: Torque at low rpm, wide rpm range.

I has been shaved by 1mm only but ports & comb' chambers have been modified significantly.

 

For timing management, here's the link to my setup install.

 

 

 

(But with the p90, I couldn't boost it until I had forged pistons and a CR of like 8:1 right?)

That statement is very wrong You can surely boost your engine if you'd like but bottom end has to be modified with dished pistons (at least) to lower compression ratio. You do not need forged pistons as long as you keep some hp target reasonable, stock dished units are perfectly fine.

[XTCoX]

Thanks very much for the insight

 

It makes me feel better knowing it's not just supposed to be 'bolt on and go' with that high rpm performance, I thought I was doing something wrong! Haha

 

Looks like once I sort out the timing bug, I'm giving BRAAP a call about headwork!

 

In regard to your shiny ignition system the main advantage over a CD distributor system is the advance curve control yes?

Edited December 23, 2013 by XTCoX

[Lazeum]

I haven't seen Braap around for awhile. Not sure if he's still doing some headwork but the difference between my previous stock N42 head with stg II MSA cam & Braap's head is night & day.

 

My ignition system allows to control every single point of timing map, exactly as you could do with EFI system. If it knocks at 3500rpm, I could reduce timing at the exact point without modifying anything else around. I've got also load controlled ignition with Webers, something a dizzy can hardly achieve.

[madkaw]

Have you verified your timing with a light- total advance ?

[NewZed]

Two problems were described - one, it won't pull past 5500 RPM, and two, it suffers detonation if the timing is advanced toward a "normal" range.  Those two things aren't necessarily related.  The power peak below 5500 RPM is pretty typical for the stock 280Z L28.  Usually the cam is pointed to as the cause. 

 

Maybe your Schneider cam just isn't designed to breathe at high RPM.  I assume that the restrictions of the intake ports and manifold play a part also.  Whatever it is, the behavior sounds about like my factory stock 280Z L28.

 

On the detonation issue - cylinder pressure will give a good idea of how the compression ratio (CR) and the cam profile, and its timing, are working together.  High CR will raise "static" cylinder pressure, and the valve timing of a performance cam grind is supposed to lower it.  Cylinder pressure, not compression ratio.  Measure cylinder pressure and see what you get.  Over 200 psi seems to get people closer to detonation problems.  170-180 psi is common for a stock engine.

Edited December 24, 2013 by NewZed

[XTCoX]

I have checked the static timing with a light, it's basically on top of TDC ad idle but I have not used it to check full advance. Good idea I'll get on that.

 

I am also unfamiliar with how a load controlled ignition works, but I'm guessing it's for going up hills? Correct me if I'm wrong, but isn't the vacuum advance supposed to do that to some extent?

 

And the engine isn't stock, that's the thing... Full 6-2-1 exhaust, flat tops, and the power band of the cam is supposed to be 4-7k, for road racing.

 

It's very frustrating considering the engine isn't stock but I'm still having those stock issues.

 

If by stock you mean there has been no actual modification of the head then yes. I'm feeling that the cam profile was too aggressive for an unmodified n42.

 

I will check the cylinder pressures and get back to you. If it is over 200, do I retime the cam or get a bigger gasket?

[madkaw]

Vacuum advance ?

[NewZed]

I have checked the static timing with a light, it's basically on top of TDC ad idle but I have not used it to check full advance. Good idea I'll get on that.

 

 

And the engine isn't stock, that's the thing... Full 6-2-1 exhaust, flat tops, and the power band of the cam is supposed to be 4-7k, for road racing.

 

 

I will check the cylinder pressures and get back to you. If it is over 200, do I retime the cam or get a bigger gasket?

Did you build the engine originally with these performance mods, or did you buy it this way?  You said it was rebuilt but didn't say who put the packge together.  If you bought it then confirmng what you have is a good idea.  Confirm that zero on the damper pulley is actually TDC, cylinder pressure is not too high (if the heads been shaved CR could be higher than calculated), advance mechanisms work right (a spring could have popped off of the centrifugal mechanism),  cam timing is correct (does Schneider provide a mark for reference or do you have to use a degree wheel?), etc., stuff like that.  Considering what you said about the way you received the engine it seems reasonable to assume that somehting else might be screwed up too.

 

Make sure that what you think is detonation is actually detonation, if you can.  Maybe detuning the engine with retarded timing is just covering up an exhaust leak or some other noise that sounds like detonation.

[XTCoX]

I had selected the parts individually and had the shop assemble it, so everything is confirmed.

The detonation would sound like loose change in the engine.

 

I just took it for a second opinion at an import specialty shop, to diagnose that sound in the depths of the engine?

They said I'm about to spin a main, and that it might have been the detonation that did it. Fack.

The sound comes and goes at different rpms and varies with load, but is undoubtedly getting worse.

 

In order to verify all the timing (cam, pulley mark) I'm gonna have to pull the head and take a look right?

[XTCoX]

FYI the engine was built by R Rated motorsports, through Datsun Parts LLC.

 

While I can't speak to the quality of the rebuild, I can share a story.

 

When I called Al, and told him the timing wasn't set (knock) and the valves were really loud he basically wrote me off like I was just hearing things/stupid. He seemed to be feeling a strange combination of surprise and irritation when I told him I was gonna work on it. So I adjusted the valves and backed off timing until it wouldn't knock.

 

Sure enough, it nearly throws a rod two weeks later cause of the subtle detonation I was apparently confusing for standard engine noise, at which point he kindly pointed me to the 30 day warranty, and told me it's my problem.

 

Of course we did only pay for an engine. Tuning wasn't included. What did I learn..? >

 

Now, I don't know how long engine rebuild warranties typically last, but 30 days seems sketchy for a part that should go 100k miles with no problems... But again, I have no idea what's typical.

 

Guess that's what happens when you don't think things through the whole way though... I got what I paid for.

Edited December 25, 2013 by XTCoX

[NewZed]

An internet search on Datsun Parts LLC would have thrown up some flags.  Yours is the clearest case of bad product that I've seen described though, besides the sand in the cylinder head story (see below).   I'm sure that many people are just too embarrassed to share their experiences.  A warranty for normal use is one thing, mis-representation is another.  You might take your engine to someone who knows the engines and see if you have a case for a lawsuit, or PayPal or credit card claim.  If it's worth your time.  You'd be doing the rest of the world a favor.

 

Here's a fairly recent thread on this guy - http://forums.hybridz.org/topic/105897-l28s-from-datsun-parts-ebay-store/

 

 

I hope this doesn't ruin your holidays.  You might actually have some good parts there.  My impression is that the guy buys used parts individually and reassembles them in to packages.  Who knows, he might mean well, just doesn't know what he's doing.

Edited December 25, 2013 by NewZed

[XTCoX]

An internet search on Datsun Parts LLC would have thrown up some flags. Yours is the clearest case of bad product that I've seen described though, besides the sand in the cylinder head story (see below).

 

*My impression is that the guy buys used parts individually and reassembles them in to packages.* Who knows, he might mean well, just doesn't know what he's doing.

Thats what I like to call "hitting the nail on the head".

I've actually been party to the scavenging, he took some parts off me in the course of doing buisiness with him. My bad, everybody.

 

At least I won't forget to do my homework next time hahaha good lord! There's a novel of bad press out there on him.

 

I should've known something was wrong when I called him asking for the valve adjustment spec, and he gave me different values from what Schneider recommends for the grind. I even asked him why and he said, quote "that's just how I've always done it". No reason or anything.

 

I had to email Schneider to get a reason for using one spec over the other. It was a single sentence reply: .010/.012 better mid torque, .008/.010 runs better and opens the top end. Al was convinced .010/.012 was better, and the other would harm the engine, or something... He even asked why I was bothering to adjust the valves, because I guess he did it before he gave it back to me, and valves aren't supposed to move once you set them (he said sarcastically).

 

Funny, considering when I pulled the valve cover to check them, they were all out of spec. Only two valves (on different cylinders, I might add) were close.

 

Fail.

 

It would be worth my time to get the legal gears moving, provided I can make a case that it was a bad rebuild... I feel like it wouldn't work considering I messed with the timing, which would throw into doubt who messed up and when..

 

I can say, however, for anyone else out there, that I haven't been satisfied with any of the business Ive done with Datsun Parts LLC. Though I'm too embarrassed to say exactly how much, I'll say that each and every part I've gotten from him has had something go wrong.... Believe me, I wish that were an exaggeration, but it's not. I had to return two separate heads to him for leaks, and now my block is on the fritz.

 

Not to mention abysmal customer service. He was always irritated and impatient when I spoke with him... If you're looking for support after you finish your transaction, get it in writing.

Edited December 25, 2013 by XTCoX