Decisions Decisions

[EZDUZIT]

Whats happen guys, lets look at the pros and cons and see if you guys can help me make a decision. Alright working on my brothers 1974 260Z stock motor with dual Webbers. My delima, we are going to put a cam set, Header, 3-angle valve job, resurface the head, new seals, mabey a little blending on the intake and exhaust ports, The only problem What Head? We can use the stock E-31 that is currently on it, or we have a N-42 and a N-47. I know we are not going to use the N-47 due to the exhaust liners so the battle is between the E-31 and the N-42. The E-31 is supposed to have alittle more compression but I think the N-42 has a larger exhaust valves. Another determning factor is he can still drive his car(daily driver) if we use the N-42 head. I don't know which one flows better nor do I know all of the pro's and con's. I do have a P-79 head but I just don't think we won't to do that much machine work, not a full race application here if you know what I mean. Any feedback would be appreciated. thanks Josh

OHH YEA: I will be putting 280Zvalves and seats in either head so they will be up to date 8)

[JMortensen]

Shave the P79 .080 and install the N42 valves and shim the cam towers .080 and the cam geometry and all that should stay correct. Your machinist should be able to get cam tower shims for you. Don't worry about the exhaust liners, they're not much if any hindrance until you really start porting the head a lot.

 

The N42 can just be slapped on, but some have experienced pinging with that combo. Both the E31 and the N42 have lots of sharp edges in the chambers which can cause pinging, where the P90 uses a much better casting AND has a much larger quench area which should provide a significant advantage. Neither the E31 nor the N42 is the best head from the factory IMO, and you'll spend probably 3x more in machine work to install larger seats in the E31 then you will to shave the P79.

 

That P79 should theoretically get you to ~9.6:1 with a bone stock flat top L28 bottom end. The N42 gets 9.8, and the E31 gets 10.2. These numbers assume that the head hasn't been shaved before you got ahold of it.

 

We just had a LONG and surprisingly bitter argument about this, search the 6 cylinder archives for a post that started with Newbie. Should still be on the first page of the 6 cyl forum.

 

Look here for more info on shaving the head: http://www.geocities.com/zgarage2001/head.html

[Dan Baldwin]

On a 260Z L26 bottom end, any of those head options will have your compression ratio very low (E31=>8.6:1, N42/N47=>8.3:1, shaved P79=>8.1:1). You might consider getting a 1981(?)+ 280ZX non-turbo bottom end (aka F54 NA) with flat-tops if you want a good base to build performance with. Here's what the New England ZCar club got with that bottom end with a stock N47 head and stock cam:

http://www.zccne.org/events-2004/dyno-2004/bad-dog.jpg

Thats 164rwhp at 9.8:1 CR on pump gas, not too shabby.

 

The N47 and presumably the P79 linered heads reportedly flow as well as square-ported heads stock, only drawback is you can't port 'em.

 

Me, I'd go the flat-top L28 route with the N42. If the chambers have sharp edges (never recall seeing anything particularly nasty in my N42), it shouldn't be any big deal to sand/grind 'em down. Otherwise, no mods whatsoever required, but of course you can shave a bit and/or use the 1mm gasket to get over 10:1 CR.

 

If you get a warm fuzzy from the heart-shaped P79 chambers, or are dissuaded by reports of detonation with the N-heads (never a prob for me) go ahead and shave that head, shim the cam towers, and use the longer N-head valves. If you shave .080" and use the 1mm head gasket, that puts you at 9.8:1, on a flat-top L28 bottom end.

 

Either way, I don't think I'd bother with a stock L26 bottom end.

 

Go here for all the bitterness regarding L-series cylinder heads :

 

http://hybridz.org/nuke/index.php?name=PNphpBB2&file=viewtopic&t=36702

[JMortensen]

Either way, I don't think I'd bother with a stock L26 bottom end.

 

I just assumed he'd be going to an L28 bottom end. Dan's right, there isn't really any point to working on an L26, unless it's just to keep it running while you source an L28.

[EZDUZIT]

Thanks for the replies guys, I hate for him to tear down that engine anyway it runs great and performs very well. We just got finished building our cousins 88 300ZX with full race cams, shaved heads, new pistons ect. and he waxed my brothers a$$. Which has caused an uprising I do agree with you guys to build the L-28 and have researched this pretty well. But for right now we could buy the cam, header, 4 barrell carb and intake, and put on the L-26 untill we have a L-28 built. Then we just swap over all of the performance parts. Again thanks alot guys, this is for my brother to see more than myself Josh

[Dan Baldwin]

I'd leave it the frick alone and spend ALL efforts on the L28 build. You might get some sidedraft SU carbs to replace the downdraft Webers, but I don't think the 4bbl is a good idea. 4bbl = GREAT for a V8, less than ideal on an I6. I think the cam you'd want for the low-comp L26 and what you'd want for a built up L28 might be different anyway. I really think I'd leave the L26 alone except maybe SU carbs. Wet nitrous setup, maybe

[EZDUZIT]

Dan I get where you are coming from, However ive heard mixed feelings about the Holley 390cfm 4barrell. We are getting it for next to nothing from a friend who is runnung triple mukunis and he said that it pulled like a mule. The Webbers run like scalded dogs when the weather and tune up are right but thats not very often. We are hopeing to use the Holley for more predictablity. Thanks again for the info we really do appreciate it!