N42 head with flat top pistons?

[kensval]

I know this is an old thread, but just in case anyone checks this out, I have a couple of questions. I'm getting ready to start for the 1st time my rebuilt l28e with the stock N42 head and new flat top pistons. Looking into the #1 cylinder when the piston is at TDC, there looks to be precious little room for the spark plug. I'm assuming the rebuild shop (who have done lots of other Z car engines) would not have suggested the flat tops if plug clearance were to be an issue. The block was not decked, but the head was shaved .001". I have a Fel-Pro gasket under the head, which I'm assuming is 1 mm. I know my compression ratio will approach 9.9:1. So, here are my questions: Will I need to run higher octane gas? I'm assuming so. If this indeed the case, where should I set the timing? Will the stock 10 deg. BTDC be good enough with premium gas (93-95 octane), or will I still get detonation?

I'm looking forward to finding out how much more power she'll have with the extra compression and newly rebuilt fuel injectors.

[LeonV]

I know this is an old thread, but just in case anyone checks this out, I have a couple of questions. I'm getting ready to start for the 1st time my rebuilt l28e with the stock N42 head and new flat top pistons. Looking into the #1 cylinder when the piston is at TDC, there looks to be precious little room for the spark plug. I'm assuming the rebuild shop (who have done lots of other Z car engines) would not have suggested the flat tops if plug clearance were to be an issue. The block was not decked, but the head was shaved .001". I have a Fel-Pro gasket under the head, which I'm assuming is 1 mm. I know my compression ratio will approach 9.9:1. So, here are my questions: Will I need to run higher octane gas? I'm assuming so. If this indeed the case, where should I set the timing? Will the stock 10 deg. BTDC be good enough with premium gas (93-95 octane), or will I still get detonation?

I'm looking forward to finding out how much more power she'll have with the extra compression and newly rebuilt fuel injectors.

If it's a plug meant for the L (e.g. NGK projected-tip plug), you'll be fine.

With a compression ratio close to or at 10:1, you better be running pump gas, and even then there is a chance of detonation depending on timing. We can't tell you whether or not you'll get detonation without being there, nor can we tell you where to set initial timing without knowing what distributor you're using.

A stock-headed L28 tends to make most use of the mixture with around 34-36 degrees of total timing, as demonstrated in dyno testing. The total timing depends on your initial timing plus the maximum centrifugal advance of your distributor. At your compression ratio, you may or may not need to back off on timing. There have been people that needed to go to 28BTDC to ward off knock, and there have been others that had no problems at 34BTDC, all with flat-tops and N42 head.

FWIW, upping the compression ratio alone doesn't produce much of a change in torque, maybe a 1-2% gain, which likely won't be noticeable. Compression ratio is usually increased in order to keep cylinder pressures up when using a more aggressive cam. Without swapping cams (and matching intake/exhaust manifolds), the gain from a bump in compression is minimal.

[kensval]

It's a D6F4-01 distributor. I also have a spare engine out of a 280ZX with it's stock distributor, but haven't changed it over to my older engine. There seem to be a lot of people that recommend the swap, but I don't know just what I'd gain out of it. I was planning on using the same NGK plugs I was using before, which are the ones spec'd by NGK for the engine. I had also considered a set of those gimmicky E3 spark plugs, but they would definitely have to be indexed to work properly I think.

BTW, will a normal inductive timing light work on a stock '76 Nissan ignition 280Z system? I need to go buy one anyhow, so if there's some really good one to get let me know.

Thanks for the advice.

Ken

[Travel'n Man]

I have completed this build- you may want to check out my garage area.

[LeonV]

I use a plain, inductive timing light, probably from Kragen or something. Some people prefer dial-back timing lights, but it doesn't make much of a difference. Use the plain-old NGK plugs, BP6ES.

[kensval]

The NGK website specs a BR6ES. What's the difference?

[kensval]

Ah. Now I see. The BR6ES has a resistor, the BP6ES doesn't.

[Lazeum]

For timing, we can't really help without also knowing the cam spec. I could assume you've got the stock unit with your EFI system.

For your reference, I was having Flat top & N42 head with MSA stage 2 cam (Schneider 274/274). I had to run 28-29° TOTAL advance Max without detonating.

I have DCOE carbs that needed some initial advance too; around 10-15° with no vacuum adv.

You have to make sure you can setup properly your timing then

With stock cam it could be even worse but injection might make things less difficult than carb setup.

Edited September 14, 2011 by Lazeum

[kensval]

It is a stock cam. I have never made any internal adjustments to the distributor, either. I think at first I'll worry about just getting it running stably, then tweak it. The FSM provides decent instruction on distributor adjustment. I've also considered looking for a whole new ignition system for the future, probably a distributorless coil-on-plug system.

You know, it used to be that I had all the time in the world to work on my vehicles, but never enough money to buy the parts I wanted. Now it's the other way around. Can't win.

[Lazeum]

I fully understand you're point of view. It is the other way around for me... Time but no money (mortgage)

My point is you might never be able to get your engine running well without detonating with your current setup; either it will run very poor at idle because of advance too low or it will ping at higher rpm.

One easy way to overcome this would be to use an MSD 6AL-2 unit but it you could keep your vacuum advance effective it would be a big plus.

DIS systems are the best but you would need an ECU to manage that. If you choose one, you'll be able to tune your engine for new cam, fuel and so on, so making your engine well shouldn't not be a problem anymore.

[kensval]

Well, it ran with the dished pistons, bad rings, a slightly (.001") shaved head with a 5 angle valve job, dirty injectors, and 10 deg initial advance. Now I've got pefect rings and flat top pistons. So, other than extra compression and new injectors, nothing has changed. Should run all that bad. I guess I'll see...

[ozconnection]

Fuel mixture ratio's will influence your engines knock thresholds.

The stock cam won't help your knock situation, too much cylinder pressure because of a lack of valve overlap unless you use high octane fuels, water injection, retarded camshaft timing or run very conservative ignition timing which leads to.........

Get a 'dial back' timing light. I bought an Innova from ebay and it's tops. You can plot the advance curve verses the rpms to create a simple 2d map of your distributor advance curve. A good starting point if/when you later run an ECU controlled ignition setup.