About to build my first L28, have some questions.

[ArchetypeDatsun]

I am now running a P79 head in my L28ET just finished it lastnight, I would really recommend asking Skib for advice since he was the one that helped me. All I need is a new CHTS, and valve adjustments and I'm good to go but it starts a lot better than my last set up. I'll post up some pics.

Edited October 11, 2011 by 280zx@541

[Gollum]

It's been fairly well covered here, but I'll add my 2 cents to the pile.

 

The Compression of the flat top + P79 issue is WAY overblown. Both a dish+P90 and flat top+P79 have shown to be capable of well beyond 300whp under boost on pump gas.

 

The liner topic is almost mythical. Though people on this very forum HAVE had issues with P79 liners melting up on them, they've been very isolated incidents while others (like howlermonkey) point out that it isn't always an issue. If you want to grind them out, feel free to do so. Shouldn't really help or hurt flow much in a turbo application (or NA really either)

 

 

 

The key to getting ANY motor to run nice ARs without detonation is good management. The L motor is no different. I've seen SEVERAL people blow up flat top+P79 combos because they tried to use the stock L28E management, or tried to use stock L28E injectors, or tried to use stock L28E AFMs. It simply won't work well. If you want to try to use the L28ET EFI, then do it right and get every piece, including dizzy from 82-83. That being said, just go MS and be done with it. Install a trigger wheel and add some coil packs for MS to trigger. People have shown timing logs from MS and even the L28ET dizzy has very sporadic spark when compared to what you'll get from a good trigger wheel.

 

And of course, I can't leave this post alone without advertising the best magic bullet to hit the car scene in the last 30 years (in my very honest but humble opinion). If you're willing to buy all new fuel lines, fuel injectors, and a large aftermarket pump, just go E85. That will eliminate ALL fear of detonation due to a "scary" 8.5:1 (a ridiculous fear in my opinion) and the cooler combustion temps will probably also help prevent any possible liner failure. It just means much larger injectors are required and you need rubber and lines that won't deteriorate. Small budget increase when you're already looking at MS3 + turbo, etc.

 

As far as turbo fitment, I've see T4's fit with flange adapters. The stock turbo location is a little high and can stand to be lowered a little. Depending on what turbo you're wanting to run, and what kind of money you're looking at spending, you might just be better off getting a new manifold made. Not everyone's cup of tea, especially considering people make it past 300whp on the stock manifolds + turbos that bolt on without modification.

[NewZed]

I got my N42 thoughts confused with my flat-top thoughts, in my previous post. Any thread with "flat tops" in it seems to drift in to detonation discussion.

 

The OP's original question was - "1. Ideally, what prep work would you do on a P79 head prior to application on a moderate turbo setup?" That seems like a reasonable concern.

 

 

Who's running 300+ HP with a flat-top/P79 combination? I'm curious, specific examples are always more educational.

[Gollum]

I'll do some digging for some people running turbo+flat top setups, but I also expect you to search as well. That said, I find it funny going through old threads like this one -

 

http://forums.hybridz.org/index.php/topic/13564-i-need-help-on-my-280zx-turbo-project

 

Notice that though people are suggesting starting with a turbo motor, nobody is freaking out about the compression, or saying that the NA motor can't be turbo'ed. It's just me guess, but I'm betting people like scottie were suggesting starting with the turbo for a COMBINATION of reason, and a big part of that is that the oil pan is already tapped for oil return, there's already an oil fitting to go to the turbo at the pressure sensor. There's already larger injectors. It already has a turbo exhaust manifold. The list goes on. Yet, nobody (at that time, in 2002) seemed to care to bring up the compression aspect.... Food for thought?

 

There's two people here who did NA->turbo conversions. Cody is still fairly active, send him a PM and find out how much boost he braved before he wreaked that first Z of his

 

http://forums.hybridz.org/index.php/topic/20021-has-anyone-put-a-turbo-on-a-na-block

 

More people you can PM

 

http://forums.hybridz.org/index.php/topic/23501-calling-all-flat-top-piston-turbo-z-owners/

 

 

You can see a similar discussion that comes up quite often in the NA realm too. User: Mack has run MUCH higher compression on pump gas than others recommend, or even think possible (again, some people). Some people say running anything above 9.5:1 NA is just too much for pump gas, yet there's people running 10.5, even 11:1 on street driven Z cars. There's WAY more that's going on than just static compression that results in detonation issues. Some people are convinced that more timing with lower comrpession is the "only" way to get better street power. I'd say that's true, but it's not THE truth. I'd say a higher level of truth is that each gas type has it's own compression and timing curve abilities and requirements. If you run a lower compression NA motor, you're in some ways wasting money by running high octane gas just to run a few more points of timing. Some people will also say "well I put race gas in and bumped the timing and got 15 extra HP!"... Well yea, but what power did you gain at the same as stock timing versus lower octane gas? The higher octane gas probably has more energy potential, so really you're just utilizing it better by matching your timing TO THAT FUEL. You might know all this already, I just want to make sure it's clear why I've said that FLAT TOPS are FINE on a turbo motor.

 

If you want to run an OEM EFI setup, just get a L28ET longblock and be done with it.

 

If you want to do a low buck turbo L motor use whatever you got, and run a good programmable EFI in order to tailor the fuel and timing to THAT SETUP.

 

I've seen lots of blown up turbo L motors, and more often than not it's from a bad tune. It doesn't matter if it's flat top 7.4:1 or a 8.5:1. Run the TIMING REQUIRED for THAT fuel at THAT compression ratio and you won't have detonation issues. And in fact, running flat tops on the P79/90 will give you a ton more QUENCH thus you might be able to run similar timing maps anyways. But also remember that with a smaller combustion chamber with flat tops the distance for the flame front to travel is smaller, thus less timing is needed to optimize timing. Where people get messed up is they say "well I can run more timing on my dish setup, so it must be better". That's a very closed minded way to look at it. On a larger chamber more timing is REQUIRED, not allowed. It's just perspective, but it changes everything.

 

Want a real mind bender? There's people running alcohol classes at the drag strip running non-intercooled roots superchargers on motors with 13:1 compression and higher! I bet they're not running extremely advanced timing, but I bet there's nobody out there telling them "you're loosing power by running such high compression"......

[Gollum]

Another good thread to look at http://forums.hybrid...p-progress-pics

 

Flatblack is another member that just came to mind. He was running a NA-T conversion and I'm sure he was probably knocking on the door of 300hp. He's someone who's still around often that can be PM'ed.

Edited October 11, 2011 by Gollum

[Leon]

...each gas type has it's own compression and timing curve abilities and requirements. If you run a lower compression NA motor, you're in some ways wasting money by running high octane gas just to run a few more points of timing. Some people will also say "well I put race gas in and bumped the timing and got 15 extra HP!"... Well yea, but what power did you gain at the same as stock timing versus lower octane gas? The higher octane gas probably has more energy potential, so really you're just utilizing it better by matching your timing TO THAT FUEL.

 

Higher octane fuel does not have a higher energy content, that is a common misconception. Higher octane has a higher resistance to ignition, thus it is used with engines running higher compression ratios (or boost) which generate more heat in the cylinder. Minimum octane required changes with many factors, including ambient temp, pressure, and compression ratio, among other things. Use gasoline with an octane rating high enough for MBT timing.

 

The thing is, spark timing is a very important factor in engine operation, with compression ratio being a more minor one. A bump from 7.5 to 8.5:1 compression may net 2-3% gains, but drop spark timing a few degrees from MBT and you're way down on torque production.

 

Now, NA L-engines have been turbocharged in the past with good results. As long as the tune is correct, there should not be a problem.

 

My 2 cents.

[Gollum]

Higher octane fuel does not have a higher energy content, that is a common misconception. Higher octane has a higher resistance to ignition, thus it is used with engines running higher compression ratios (or boost) which generate more heat in the cylinder. Minimum octane required changes with many factors, including ambient temp, pressure, and compression ratio, among other things. Use gasoline with an octane rating high enough for MBT timing.

 

The thing is, spark timing is a very important factor in engine operation, with compression ratio being a more minor one. A bump from 7.5 to 8.5:1 compression may net 2-3% gains, but drop spark timing a few degrees from MBT and you're way down on torque production.

 

Now, NA L-engines have been turbocharged in the past with good results. As long as the tune is correct, there should not be a problem.

 

My 2 cents.

 

Let it be shown for the record I don't disagree with this at all. I said "probably" because the scenario I was describing is usually when people put race gas in which isn't anything like pump gas and they do it for tuning reasons, then they see how much extra timing they can run and how much power it produces and assume it's "just timing", which isn't necessarily the case.

 

Timing is VERY important, but it's not always a linear comparison from setup to setup. That's what gets people screwed up when comparing setups. Even in the datsun case, comparing a P90 with dish pistons and a P90 to flat tops is NOT apples to apples for timing requirements. It's a completely different combustion shape and flame front speed, thus different optimum timing requirements.

 

For example, if you took detonation out of the picture, and could run "optimum" timing at all RPM, you'd see that a flat top+P90 combo started falling off power SOONER, than dish+P90, regardless of which one is making more or less. This example should hopefully show how one engine might "require" more or less timing versus another. If guy A is runing 32 total timing, and guy B is making more power with 35 total timing, that doesn't mean guy A will make more power by adding in 3 degrees of total timing.