Is this the MN47 head?

[Mycarispurty]

 

A guy is wanting my Weber DGVs and intake manifolds but doesn't have quite enough cash so he offered this head to help make up the difference. He said it isn't stamped MN47, just N47 but was told the difference can be told by the combustion chambers.

[Mycarispurty]

Nevermind, saw where the combustion chamber dictates the M or regular N.

[roger280zx]

And thats definitely an M.

[Mack]

that is an MN47 for sure!  that will be good for around 11:1 on a stock L28 flat top block with a felpro head gasket. 

[rayaapp2]

I just tossed a set of those DGV's in the recycle bin yesterday and hauled it with about 2400lbs of other Z car related recyclables to A&S metals.

 

Take the head if you can use it.

[Gollum]

I just tossed a set of those DGV's in the recycle bin yesterday and hauled it with about 2400lbs of other Z car related recyclables to A&S metals.

 

Take the head if you can use it.

 Most def. Those DGV's will probably never raise in value much other than inflation, while here in the states people are probably going to start importing those MN47s from places like Australia where they're still semi-common. Getting to be slim pickings here in the state, and even still, welding chambers can be more work/more expensive than sourcing that lovely head.

[KillerBjt]

I have one of the MN47, glad i picked it up when i saw it. Getting real hard to find and it does seem to have the best combustion chamber of the L series heads.

[Heroez]

Even on a dished piston motor you get a nice bump in compession. My question has always been about the valves. Keep them or go larger? Everyone seems to disagree.

[Gollum]

I think a large part of that debate is that it can really depend on the build. If you're going for 300+ NA HP then larger valves never hurt. If you're building a street motor that will see mostly sub 4k rpm 95% of the time then maybe the smaller valves are fine and will actually help down low.

 

It can also depend on the displacement. Is it going a on 2.4 bottom, or a 3.1 stroker? Changes the topic entirely.

 

There is no best, no magic bullet. That makes it hard to definitely say which valve size is better.

[Leon]

IMO, there is a "best" and that would be to put in as large of a valve as possible without shrouding (unshrouding the chamber helps). This is what an engine designer attempts to maximize. I struggle to believe that just going to larger valves will inherently hurt low end torque. The thing is, smaller engines don't need as large of a valve to breathe. This is the main reason why you see the larger valves on the 2.8 heads and smaller on the 2.4.

Edited January 16, 2013 by Leon

[Gollum]

If runner size can be RPM power specific, and if exhaust manifold primary size can be RPM specific, why can't valve size?

 

I can certainly agree if the statement is made that the larger valves won't hurt low end enough to matter to most people. And I agree that valve unshrouding is far more important than actual valve size. But at the end of the day nissan used smaller valves in certain combos for a reason. You see the same thing in the V8 realm to an even greater degree. You can find two SBC motors from the 60's, one from a truck, and one from a muscle car, and they'll have radically different valve sizes. They were designed around two totally different power bands from the ground up.

 

At the end of the day, I say arguing about valve size is never a reason to not "get it done". Don't have much cash? Reuse the valves you got. Going all out? Spend the time to put in larger valves and unshroud as much as you can with them. But never flip flop back and forth if it's delaying your project.

[Heroez]

Im going to have to replace a head gasket in my stock/no mod 80 zx. So it has dished pistons, and n47 head. I have a complete mn47 head. I figure why not toss in the mn47 since the head has to come off? Then we come to the cam, and valves. I was kinda thinking along the lines of Leon/Gollum. Use L28 valves and cam, leaving the 2.4 designed cam and valves behind.

[Xnke]

Cams for engines of larger displacements are often times smaller profiles than the same engine of lesser displacement....the L is not an exception...

 

That said, check the cam stamps. the K stamp cam is ~.400" lift, 218 degrees duration, and the A stamp cam is about .410" lift, 248* duration.

[JMortensen]

 

I think a large part of that debate is that it can really depend on the build. If you're going for 300+ NA HP then larger valves never hurt. If you're building a street motor that will see mostly sub 4k rpm 95% of the time then maybe the smaller valves are fine and will actually help down low.

If you're not going for massive power than 11:1 compression isn't necessary either. I wouldn't use this head unless I was planning on running race gas. We went through this maybe 5 years ago ad nauseum, Mycarispurty can look it up if he cares to. It's a good trade for a set of DGV's though, that's for sure. 

[Gollum]

If you're not going for massive power than 11:1 compression isn't necessary either. I wouldn't use this head unless I was planning on running race gas. We went through this maybe 5 years ago ad nauseum, Mycarispurty can look it up if he cares to. It's a good trade for a set of DGV's though, that's for sure. 

Or you can run E85 which is now commonly available in much of the country, and really I would understand completely doing a "mild" street L motor with 11:1 with that head if E85 is the intended fuel. If the head can be found for cheap, that's a pretty darn cheap way to make a decent little motor for not much coin. You'll spend more money converting your fuel system than you will on the longblock rebuild/assembly costs.

 

I only bring this up because E85 wasn't nearly as common just 5 years ago, let alone almost 10 years ago when I joined HBZ. In today's world, a budget E85 street motor might make sense, while 10 years ago I'd say you were a bit strange for doing such a thing.

Edited January 17, 2013 by Gollum

[JMortensen]

That's a good point. We don't have E85 here, so never crossed my mind. Without getting too political, I'd say that E85 only exists because of subsidies and there are growing arguments against it, so there is really no way of knowing when the money spigot will be turned off and then your fuel becomes unavailable almost overnight.

[Leon]

That's a good point. We don't have E85 here, so never crossed my mind. Without getting too political, I'd say that E85 only exists because of subsidies and there are growing arguments against it, so there is really no way of knowing when the money spigot will be turned off and then your fuel becomes unavailable almost overnight.

 

My thoughts exactly. I'm not a fan of E85 and would not build a performance engine based on that fuel, especially considering its existance is relatively unstable comparted to "normal" gasoline. I hope E85 gets killed off, personally. Get rid of E10, too.

 

I'm not too up on the MN47, but if it puts comp at 11:1 I'd avoid it for anything besides a pure race engine. I assume on dished pistons, the compression ratio would be more within the realm of possibilities. With that said, I see people putting a single spec like comp ratio (or any other given single parameter) on a pedestal all the time. Valve size, header size, R/S ratio, rod length, blah blah blah. It's a system, so it must be treated that way. Frankly, make "enough" compression (>8:1) while minimizing chances of knock and you'll be fine. This is not an all out race engine where we're sqeezing every last 0.1hp that we're talking about here.

 

As for small valves vs. big valves, I'll stand by my statement of "big as possible with minimal shrouding". The only reason for having smaller valves is if your engine is designed for just low-end torque (narrower intake and port runners, low-rpm cam profile) therefore not needing larger valves. That's the case with your SBC truck engines. Valve size is the effect, rather than the cause. It's the classic causation =/= correlation... situation.

 

From this, I hope that one can deduce that just installing bigger valves won't gain you a ton without changing the system. To accompany larger valves, it is beneficial to work the ports, intake and exhaust runners, cam profile, etc.

[Heroez]

Thanks for the tip on checking the cam. On my dished piston motor it will be mid 9 compression. It will be the only mod on the car and not that big of a deal as far as results either. Just an availability kind of thing. I expect it will be something similar to a flat top p79 type motor. Im not an expert in this area but it seems in my student theory that using the mn47 with flat top pistons at 11 : 1 you could run a medium+ /long duration cam on 93 octane with overlap and be on the ragged edge. The head is a good design to be able to pull something like that off. Maybe back initial timing off a hair. I dunno. Kinda makes me wonder what the maxima head can do with triple carbs or itbs, opened up. Mine will be in the mid 9 CR so the theory is just out of interest. What would you do with one?

[Xnke]

Overlap is a red herring....intake valve closing point is the cam event you were looking for in order to make a 11:1 compression more detonation resistant.

 

Run a flat-top L28, MN47 head, cam with a normal exhaust lobe and a long duration intake lobe (think 330+ degree duration intake lobe with a normal 230 degree exhaust lobe) and bolt on a twinscrew supercharger.

 

BAM! Instant miller cycle engine!

[Gollum]

That's a good point. We don't have E85 here, so never crossed my mind. Without getting too political, I'd say that E85 only exists because of subsidies and there are growing arguments against it, so there is really no way of knowing when the money spigot will be turned off and then your fuel becomes unavailable almost overnight.

 

I won't deny that's a possibility, and I'd rather not get into the politics of it either. But it SHOULD be noted so that people understand, there were more Ford Model T's sold as alcohol cars than gasoline cars. That's how prevalent alcohol was back then as a motor fuel. Alcohol was made by most farmers at the end of a crop cycle with the excess that couldn't be sold or stored, especially if it was rotting. Thus alcohol was easier and cheaper to find than petroleum fuels. When oil became big oil alcohol disappeared almost overnight with the lower cost. As the oil barrel price is high, alcohol becomes viable again as long as agencies "stay out of the way". If I chose to get the required permits I could make alcohol as a fuel for under $1.50/Gallon. Standard 100% markup and I'd be right near gasoline price per BTU.

 

Thus, I personally feel that for some, this will always be a viable fuel, and we all know there's been an alcohol class in NHRA for a LONG time, and it ISN'T going anywhere anytime soon.

 

My thoughts exactly. I'm not a fan of E85 and would not build a performance engine based on that fuel, especially considering its existance is relatively unstable comparted to "normal" gasoline. I hope E85 gets killed off, personally. Get rid of E10, too.

 

As stated before, it's history in the automobile industry and racing industry is actually very deep with a lot of heritage. The whole "green fuel" thing is more of a political move. There's nothing "new" about it. Other than corrosion obstacles (which ARE able to be overcome with relative cost effectiveness) there's not a single "bad" thing about it. I personally hope E85 gets killed off in favor of an alcohol fuel that DOESN'T contain gasoline, but that would require manufactures to design engines with enough compression to not be gasoline compatible.