Minor Piston Damage

[kiwi303]

 

 

 

I've seen on numerous occasions cars that are far less capable spank other cars that are far more capable. Know of daily driver Yugo that was stomping many C5 corvettes, and even Porsche on one track, witnessed first hand a bone stock '85 Chevrolet Celebrity OE junk type tires with a tired 2.8 V6,, (I think I still have that VHS around the house) annihilate all the C5 Vettes including trailered Z06 race car on race tires, a couple FD RX7, S30 Z cars, L6 and V8 powered, etc. Driver was the factor there, not the car definitely not the engine.

 

[NewZed]

The timing on the stock CR motor was 34 degrees, and the high CR motor 28. Both had stock ignition systems (280Z). Premium unleaded (93) was used in both engines.

 

Thanks for the numbers, and the dynamometer results. So, assuming that the N47 and N42 are essentially equivalent in this case, I should be able to just replace the dished pistons in my N42/N42 stock motor with flat tops and achieve an ~19% increase in peak horsepower and 7% increase n peak torque. Or, if the effect is solely due to CR increase, I could swap my N42 head for a Maxima N47 head and get a similar result (assuming negligible difference in cam lobe profiles or a cam swap).

 

Again, not trying to stir things up but that seems to be what's being shown here, and this is the best head to head (piston to piston, CR to CR?) comparison I've seen reported. Especially considering the variability between dynamometer setups that I've seen discussed in other threads.

 

I'm on a low budget so a simple piston or head swap for ~20% increase in HP seems like a good deal!

 

 

(Note to Admins - of all the forums out there, this is the last one that I would expect to have dynamometer flagged as misspelled...!)

[BRAAP]

Thanks for the numbers, and the dynamometer results. So, assuming that the N47 and N42 are essentially equivalent in this case, I should be able to just replace the dished pistons in my N42/N42 stock motor with flat tops and achieve an ~19% increase in peak horsepower and 7% increase n peak torque. Or, if the effect is solely due to CR increase, I could swap my N42 head for a Maxima N47 head and get a similar result (assuming negligible difference in cam lobe profiles or a cam swap).

 

Again, not trying to stir things up but that seems to be what's being shown here, and this is the best head to head (piston to piston, CR to CR?) comparison I've seen reported. Especially considering the variability between dynamometer setups that I've seen discussed in other threads.

 

I'm on a low budget so a simple piston or head swap for ~20% increase in HP seems like a good deal!

If you do this, let us know how it goes. 7% gain in torque across the entire rev range "should" be expected with 2 full points of compression ratio increase, if you don't have to pull any timing, but those gains with just over 1 point of compression bump and that much retarded timing is not the norm and any engine builder would agree highly unlikely from compression bump alone. Other factors at play such as induction system differences, exhaust differences, possibly cams, etc. I repeat, compression ratio bump alone, especailly with that much less igniton timing, can NOT and will NOT deliver that much more gain, there are other factors attributing to that gain.

 

Over the years having seen first hand and reading online from those that have done the open chamber flat top piston L28 combination, they more often than not follow the example in this quote, same engine, same dyno. Quoted from another thread on this exact topic;

http://forums.hybridz.org/index.php/topic/85907-attn-flat-top-28-with-e31n42-head-guys/page__p__815174__hl__fromsearch__1#entry815174

...

One specific example I dealt with first hand;

One of my customers, (now a great family friend and HBZ member, Mike Hintz) had a shop build hi-po L-28, their recipe was an L-28 with flat top pistons and Z car N-47 head, stock EFI and Schneider stage 2 cam. With 92 octane super unleaded he had detonation issues that could be heard at higher RPMS outside of the car WOT and also showed up very audibly on the while it was optimally tuned for power on the dyno at Torque Freaks. After many discussions back and forth I convinced him to let me build him a P-79 head and go back to a stock cam. He agreed and wanted back to back dyno com and after putting it all together and re-tuning the EFI and ign advance for this combo. He couldn’t be more happy, maybe he’ll chime in. The engine ran WAY smoother, pulled harder everywhere in the RPM band, took it back to the same dyno and the lower compression stock cammed combination gave 10ft lbs increase across the entire RPM range over the previous big cam high compression combination with a solid 15 HP increase at peak, and best of all, no more detonation. He has since switched over to standalone EFI and are considering installing an aftermarket cam now that he as fuel control to take advantage of the aftermarket cam.

 

 

In short, I do not endorse L28 builds with flat top pistons and E88, N42 N47 heads for ANY street application unless a thicker head gasket is used to drop the compression down to below 9.7:1 or so. If flat tops are is on your must have list, then I recommend the P79 or P90 head.

The car in that example can been seen here;

http://forums.hybridz.org/index.php/topic/53922-wolfd-79-280zx/

 

 

 

The public discussions of people that have actually done this I feel speak for themselves. With so many threads on this and other forums covering the Flat top open chamber heads rattling and not performing up to par vs that combination actually working and being an improvement, that alone should be a flag to those considering such combination that more is at play to make this combination work successfully than just slapping an N42/47 head on a flat top short block. I am not saying it shouldn't be done, just go into it knowing the most likely outcome and hopefully if do find the fix that allows that combination to work, you'll share the secret.

 

 

Ok, I wont argue this anymore, I've said all I have to say on this topic, you guys build what you want and I encourage you to report your results whether it worked as expected or not.

[xonix_digital]

Will do.

 

Thanks.

[NewZed]

BRAAP and z-ya, thanks for spending the time on this.

 

xonix_digital, thanks for the loan of your thread, I hope your Maxima N47 head works well for you. Going back to your other post - "My $200 L28 Surprise" - there's some data not really discussed. The Maxima head was already showing detonation on a dished piston N42 block. Too bad you can't go back and find out how the guy who owned it was running it.

 

It will be interesting to see if there is any ring land damage, just to get a clue on of how bad the detonation was.

[Tony D]

What's wrong with 'dynamometer'? I know when I'm on the dynamometer, I often have a mate stand near the back to watch the colour of the exhaust smoke, and to track tyre growth and movement. Always good to have a second set of eyes...

 

But always remind them to stand clear of the engine, chuck a gudgeon pin and it's lights out like a dead torch!

[Gollum]

Forget all the compression and timing arguments. Just run the MN47 with flat tops, then put E85 in the tank. Done!!!

 

I've seen E85 allow guys to see where optimum timing actually lies at the TOP of the power band, mean that they gave it more timing and there was no knock AND less power!!! Whoa! You of course need to run a lot more fuel than 87-93 octane petrol, and you have to run it rich when feeling the waters of timing, but once you get it dialed in it makes TONS of power EVERYWHERE. And I'd be a lot less scared of knock on a 11:1 L series on E85 than a 9.5:1 L series on california 91.

 

I personally want to run a mildly shaved P90 with flat tops with the "A" cam, turbocharged non-intercooled w/E85 targeting around 350 whp. That'll blow some minds, ya think?

[NewZed]

"Done!!!" meaning done driving your car for a while after you fill the tank with E85, unless you make some substantial modifications. Wrong?

 

It takes a lot of work to get an old car to run dependably on E85, doesn't it?

Edited November 15, 2010 by NewZed

[Gollum]

Define "a lot of work", as you're rebuilding your motor. Seems like you're already past what most car guys consider "a lot of work".

 

It just take a fuel system that won't be corroded by the alcohol content (new hard lines possibly, new soft lines definitely). Then you just need carbs and jets that are alcohol safe and capable of running the 30% extra fuel you'll need compared to the same petrol setup. Might also be wise to swap out the stock tank for a fuel cell, something any race should be doing anyways though.

 

And also define "dependably". Your current setup with dish pistons and MN47 could hardly be considered "dependable" on certain, other forums.

 

But I do agree with the large consensus here, that if you're going to run this as a street engine (NOT a race engine) and just want to run 91 octane on a stock, crappy distributor then take the MN47 and put it to the side, or sell it. Put a N42/47 on and call it a day. Or swap out for some flat tops and put on a P90/79.

 

But E85 does offer the ability to get "the best of both worlds" so to speak. There's guys (not L engines) that have run 13:1 comp with boost pushing over 200hp per liter. I would call that "timing limited". In NA application there's guys (again, not L engines) running up over 15:1 on E85 that costs less than $3 a gallon pretty much anywhere in the country and as low as $2 a gallon in some places. That's some cheap race gas.

 

Even with the MN47 and flat tops, you could run two different timings for petrol and E85. Having carbs would make the swap a pita, but IF you were staying EFI and running megasquirt which was also controlling spark with just a simple map flash you could switch to petrol for casual cruises and road trips, where the loss in power from the retarded timing wouldn't be a big deal.

 

I'm actually wanting to get some documentation together and write up a thread talking about the benefits of E85, as I think it's the best bang for the buck mod most people could do, and it's costs are sometimes less than what many spend on meth kits.

[xonix_digital]

And also define "dependably". Your current setup with dish pistons and MN47 could hardly be considered "dependable" on certain, other forums.

 

But I do agree with the large consensus here, that if you're going to run this as a street engine (NOT a race engine) and just want to run 91 octane on a stock, crappy distributor then take the MN47 and put it to the side, or sell it. Put a N42/47 on and call it a day. Or swap out for some flat tops and put on a P90/79.

 

What are you grounds for referring to this configuration as being not dependable?

Why on earth would I swap my MN47 for an N47? To lower my compression ratio from a conservative 9.2?

 

I am very curious to understand why everyone thinks I should be running a compression ratio in the mid 8s. (which is where I would be with your P79/90 suggestion)

 

I'm just looking for some sort of supporting data that the MN47 has some sort of flaw besides the higher compression capabilities that would justify selling it and swapping for a Z car N47.

Edited November 16, 2010 by xonix_digital

[Gollum]

It depends on what you're looking for. Do you want a track engine that runs on race gas, or do you want a reliable street engine that will go 100k without even blinking?

 

I never said the MN with dish pistons wasn't reliable, I just said that some people might consider it just that. The MN47 is BEST suited to race applications with HIGH compression. As people have already touched on, you're rebuilding this engine for a reason, and finding that reason is kind of paramount, don't you think? As it's been said, the L engine is VERY prone to detonation. IF you want a race engine and run race gas then run as high as you want! Anything is possible. But just slapping together a combo and saying "well it's in the 9's it'll be fine" is just being ignorant. Yes, there ARE street driven L engines over 10:1, and they're mostly built by very experienced builders that understand the short comings of the L engine and know them pretty well.

 

What I was getting at, is that if you just want to throw together a street engine, pushing conservative numbers, then you're better off with one of the more common combos.

 

And also, quench REALLY DOES make a big difference, and you're sacrificing nearly all of it with your setup. A P90 with flat tops is less detonation prone than a P90 with dish pistons. We've seen this with turbo L series, that the P90 with flat tops can make quite a bit more power with less timing. Sure, it detonates easier timing for timing, but it'll make more power overall. This isn't because of the compression really. It's that the engine doesn't NEED as much timing to make a good complete burn. There's a big difference between your timing detonation limit, and your timing power goal. Some engines, like the EVO, don't make much extra power with extra timing. Putting flat tops on the P90, or even the MN47 makes the engine need LESS timing for power potential, but as BRAAP was getting to is that on pump gas you still can't always reach the timing power potential of this combo (flat tops with the MN47). But you CAN reach the timing potential of the P90 with flat tops, and N42/47 with dish pistons, on pump gas.

 

So again, it all just depends on your goals, which I haven't seen stated here in this thread.

[xonix_digital]

My goals are maximum fun per dollar spent.

 

Not to sound "ignorant" but Im slapping this motor together to see how it does.

 

Its in the nines it'll be fine.

 

But in all seriousness sacrificing a quench effect is less of a concern than whether or not this motor will make good power (optimal timing or not) on 93.

 

As stated previously when I get it together, if I have to start pulling back the timing due to detonation I will consider using another head.

 

Until then let's just call it an experiment.

Edited November 16, 2010 by xonix_digital

[NewZed]

xonix, I think the conversation went off on a tangent with the E85 comment.

 

Probably the worst case in your situation is that you find that you can't optimize your timing without running high octane, or at all. If so, you'll have a freshly rebuilt head that you can probably sell to someone who wants what the Maxima N47 offers, and you can go from there in getting the head you want. But you might be fine with how the Maxima N47 head ends up running.

 

If you do stick with the Maxima head, I'm sure it will of interest to some out here how things turn out for you when it's done.

 

Modifying for E85 is a whole separate topic from what your original question was.

[Tony D]

I'm going to dig up some old Sony Mavica photos I have of when I pulled the N47 head off my 260Z. This this will not run on premium unleaded (California) without ping-fest at midrange RPMS and at partial throttle. I don't recall if it was open or closed chamber, and I do know that with enough octane it goes away, but that seems to be in the 95 range if ratios of mix are correct. I did the head gasket in 1999 or 2000. When they go to oxygenated gas during the winter here, and we get a 70+ degree day the car is almost undriveable with premium and additives must be used to keep it rattle free. Terrible combination, and stock distributor/curve shouldn't do this---I assumed it was a lower-compression L28 N47 but this talk has convinced me to dig in my archive to see what we have in there... I may be putting the E88 stocker, or another stock L26 head on there to rectify this issue. Annoying to say the least. I couldn't imagine what it would do with another 200cc's of compression to deal with (mine is cranking at 150psig on all six, totally different than my L28 with 185 psi and not a rattle/ping/knock to be heard at any time!)

[Gollum]

Tony, our gas here in CA sux big huge spaceballs!

 

From looking at dynos, and looking at tune files for various setups across the USA, you can SEE that people aren't getting as much power and timing from our 91 octane than other people get from 91 octane in other states.

[Tony D]

I've found my photos and damned if it's not an open-chamber N47 with flat-tops in there... DAMN!

Taken in 2000 "How to Change the Head In-Car"

 

Step 1) Have a Head and a Car

 

 

Step 2) Have a clean block surface.

 

 

Step 3) Install Head onto Block.

 

 

 

 

Step 4) Tighten and Test, and Inspect.

 

 

Yes, that is actually how it came out and went in, BTW... And remember my 8 year old was taking the photos so there was a lot of 'freeze' and 'reshoot' time involved as he learned to work the camera and to 'direct' me on the best pose to have for the moment...

 

Closer shot of the rattle-prone head:

 

 

This should probably be a 'Sticky' for the FAQ section for when someone asks how to replace a head. It would be most instructful in that regard...

Edited November 17, 2010 by Tony D