Mn-47 Vs. E-88

[Xnke]

I have a '72 L24 that is going to be rebuilt as soon as I can decide what to do with it. I will eventually be swapping in a VG30, in the mid-distant future, so going to an L28 just for the larger displacement is just an unneeded expense.

 

Now, given that the MN-47 doesn't need eyebrowing the block, and the E88 will need a valve job, plus suboptimal chamber shape Which would you choose as a starting point? I have a stock L24, with a worn out 83mm bore. Probably going to bore to a convenient size, as I have access to the machine tools to do it.

 

I'll have to run 89 octane or less, as the 93 octane around here is hit-and-miss....lots of water, and the occasional 900lbs of sugar in the tanks...lots of greenies who think that all high-performance vehicles need to be banned. I think that this means a static compression ratio of 9.5 or so.

 

With the E88, Assuming that you have the large valves installed and eyebrow the block, can it be welded to reshape the chamber, without closing it up so much that the compression ratio exceeds 9.5:1 with stock flat-top pistons? If it would, then would moving to L26 dished pistons be of any gain, or would it negate the reshaping? Would starting with a MN-47 head work better? Remember, this is a SU carbed L24. It will be built nicely, but not extensively. I'll move to TBI when I get the thing running. Most of the machine work will be done in a university setting, as I can get free tooling time up there.

[OlderThanMe]

"MN-47 doesn't need eyebrowing the block"

 

This is not correct for a stock 83mm bore.

If you look at an L24E engine block it has eyebrows in the bores. They are smaller than the ones in an L26 block but they ARE THERE!!

I don't know why the eyebrows are smaller on the L24E block because it has the same size valves as a 260Z E88 head (I have a set of maxima MN-47 valves in my 260Z E88...)

[steveosupremeo]

i have an MN47 laying around that i smoothed the ports on. i'll put it on something one day. it seems to be a good design and great for a street car. if it were me, i'd use it, even if you go with an 84 mm bore.

[Xnke]

Ok, this is good feedback, but no one has answered the real question: Is the MN47 head a better performing head than the E88?

 

BTW, does the MN47 head have steel intake valve seats? the E88 doesn't, and to run unleaded gas, needs them. That kind of work would make or break my decision, as if I've gotta have new seats either way, the question of budget goes out the window.

[OlderThanMe]

The MN-47 will reaise your compression ratio a good bit.

It is a closed chamber design as opposed to the open chamber E88.

I'm pretty sure guys with E88 heads are still running stock seats and using unleaded gas. Mine has the stock seats still in it.

[ProjectSR20]

I might be going out on a limb, but I know topics like this has been covered for years on this sight so that might be why no one is jumping in and making conclusions as to what one is better "for you". Just do a little searching and you will come up with enough information to make your head hurt. It all comes down to what your final application is going to be and how much money you want invested. Here are some good links that might help shed some light on what you are looking for, sorry I can't offer much more help...

 

http://forums.hybridz.org/showthread.php?t=104420

http://forums.hybridz.org/showthread.php?t=105653

http://forums.hybridz.org/showthread.php?t=116680

 

Check out some of the link provided in those posts, they will provide you with more information. Pay attention to BRAAP, he knows a thing or two about building a good head.

[steveosupremeo]

yes the MN47 has steel seats. it is a couple of CCs smaller than an E31 so it would be ok on an L24 and probably an L26 on pump gas. the E88 is several CCs more than an MN47. i don't know the exacts though. i think the MN47 is around 38.5-39CC and the E31 is like 41ish.

[OlderThanMe]

The MN-47 is around 38.5-39.5 CCs...I have heard all of those numbers.

The E88 is 44.7 supposedly.

 

With the engine design program at:

http://ozdat.com/ozdatonline/enginedesign/

 

A stock L24 with an MN-47 head(39cc) will get bumped from 9.17:1 to 9.79:1

An L26 with L24 pistons and an MN-47 will be at 10.2:1 CR and will have more torque thanks to the bigger stroke crankshaft...FWIW

[Xnke]

Thanks guys, for the info. Yes, I did search, but no one here uses the 83mm bore, all our really excellent information is on the L28/stroker. Especially compression ratio numbers, and cylinder head reccommendations.

 

The steel seat is, IMHO, MANDATORY for unleaded gas, because without it you are chewing little bits of the bronze valve seat up and running them through the engine. It's like leaving that ultrafine aluminum dust from polishing your intake runners to be blown through the engine...only the bronze seat is harder. As minimal an issue as some may think it is, I wouldn't trust it.

[OlderThanMe]

I put 15k miles on my L26 with bronze seats and when I went through it to put in new bearings and gasets I didn't notice any appreciable damage to the seats...and my motor has been flogged with more than its fair share of time at 7000+ RPMs. I highly doubt that an engine is "chewing" away at the bronze valve seats if run on unleaded.

[X64v]

I, too, have run original E88 'leaded only' seats for 25,000mi (5,000 of them under boost) on unleaded gas with no problems. That's all it's run in my lifetime, but it's got tens of thousands of miles more on it running on unleaded since the 80's.

[datsun 1/2 dozen SD]

the maxima n-47 head works great i use one on my 240z that has a l26 flat top pistons my compression ratio is almost 11-1 i run it at 15 degrees without no pinging

[OlderThanMe]

the maxima n-47 head works great i use one on my 240z that has a l26 flat top pistons my compression ratio is almost 11-1 i run it at 15 degrees without no pinging

 

An L26 with 83mm L24 flat-top pistons and an MN-47 should be 10.2:1 unless the head is milled down or you have aftermarket pistons and maybe an overbore.

[datsun 1/2 dozen SD]

An L26 with 83mm L24 flat-top pistons and an MN-47 should be 10.2:1 unless the head is milled down or you have aftermarket pistons and maybe an overbore.

 

its actually 10:7:1 the maxima n-47 head comes in differnt size chamber stock like mine is 38cc my brother has a 40 cc plus using a 1mm head gasket