L26 Rebuild Original E88 or P79

[Z2 D2]

Hello I just recently purchased a late 74 260z and have the engine out ready for a rebuild. My plan is to keep the matching engine block with the car and do some performance mods to cylinder head. I am having trouble deciding what to do after reading and researching.

From what I've read, the e88 head that came on the 260z is known as a emissions head and is not the greatest in terms of performance, if not the worst head that was offered on the s30. Is this head really that bad or would it be worth it to get it shaved, ported, polished, and hot cammed?

I also have a p79 head that I recevied for cheap. I've read the datsunzgarage mod for this head which is to shave, shim the towers, etc. I already have the L26 block with Flat top pistons, which I have read the P79 is better suited to. Other than notching the intake side of the bore for valve clearance, I believe this combo should work.

My thoughts are for the p79 head higher compression, better quench design, less pinging, existing steel valve seats vs brass, and better performance.

Is the juice worth the squeeze on the P79 head or should I just stick with the E88 head?

Thanks

 

 

 

 

[Captain Obvious]

I'm no engine expert, but the numbers I have here says your original E88 should result in about 8.86:1 CR, and a P79 shaved .080 should be about 9.12:1.  Not much change, and not a lot of bang for the buck.

The issue is that the P79 starts with a significantly larger chamber volume (than the E88), and I would presume they can get away with that because the P79 is designed to run with pistons that crest above the block deck height.

I'm thinking you would get a lot more CR increase by shaving your E88 head.

But remember... I'm just some guy on the internet that has a calculator and types a lot.

[Z2 D2]

Thanks for the reply. I guess I have more research to do on the e88 head. I am concerned about the possibility of pinging due the chamber design, but I'm sure the right cam can solve that issue. 

I couldn't find the actual measurements between the L26 P30 block vs F54, but from what I've read the L26 flat tops also crest above the block. There is conflicting dimensions throughout the forums.. so I might have to just pull the head and measure this one myself.

[Diseazd]

A lot of money and a lot of work to get the P79 head right. I have a 73 with the late E88 head that is a lot of fun to drive. It’s running early SU’s and has a nice toned exhaust. With the small displacement and the costs associated with the modded head, I’d go back with the E88 head. Just MHO.

[Captain Obvious]

8 hours ago, Z2 D2 said:

Thanks for the reply. I guess I have more research to do on the e88 head. I am concerned about the possibility of pinging due the chamber design, but I'm sure the right cam can solve that issue. 

I couldn't find the actual measurements between the L26 P30 block vs F54, but from what I've read the L26 flat tops also crest above the block. There is conflicting dimensions throughout the forums.. so I might have to just pull the head and measure this one myself.

Well the potential pinging concern due to the chamber design is a second order concept beyond my pay grade. I can't add anything credible to that.

But yeah, there are all kinds of numbers on the internets for the compression ratio and chamber volumes, etc. The number I'm using for E88b (late) is 47.8cc. And that came from the internets somewhere as I did not measure that myself. But... it does result in a CR close to what is listed in the 1974 FSM. The FSM says 8.8:1 and when I run the numbers, I get 8.86 (with flat top pistons that do NOT crest above the deck).

If I crest the pistons .020 above deck, I get a CR of 9.3:1. Point is... I'm skeptical about the L26 pistons cresting above the deck.

[Z2 D2]

11 hours ago, Diseazd said:

A lot of money and a lot of work to get the P79 head right. I have a 73 with the late E88 head that is a lot of fun to drive. It’s running early SU’s and has a nice toned exhaust. With the small displacement and the costs associated with the modded head, I’d go back with the E88 head. Just MHO.

Do you have anything done to the e88 head? 

[Diseazd]

Stock head……surprised at how much fun it was to drive. Won’t compete with my other Z’s, but much better performance than I was expecting.

[KenFirch]

My 73 Z had a L26 block and an E88 head when I got it.  I rebuilt it 8 some years ago, flat top pistons, but no mods to the head.  It runs great, and a blast to drive.  It will ping on regular, but not 91 gas.  

[dutchzcarguy]

On 8/27/2024 at 3:05 PM, Captain Obvious said:

I'm skeptical about the L26 pistons cresting above the deck.

I know from a official service-anouncement that the L24 from 1973-  had pistons that came above deck about a few tenth's of a mm  (about 0,2-3 mm i believe)

I'm not 99% sure.. i'm 100% sure the piston comes above deck!

[Diseazd]

1 hour ago, dutchzcarguy said:

I know from a official service-anouncement that the L24 from 1973-  had pistons that came above deck about a few tenth's of a mm  (about 0,2-3 mm i believe)

I'm not 99% sure.. i'm 100% sure the piston comes above deck!

You are correct. I remember building early L series engines using the later (73) pistons…..all that was available. The pistons would come out if I recall fifteen thousands of an inch. The books call for sixty thousands of an inch clearance. OK with the open chamber head but closer with the early E88 and E31 heads. They worked with the early heads, but it made you wonder. 🤞

[Zed Head]

On 8/26/2024 at 7:33 AM, Z2 D2 said:

keep the matching engine block with the car and do some performance mods to cylinder head.

 

On 8/26/2024 at 7:33 AM, Z2 D2 said:

late 74 260z

No offense intended, but keeping the matching block with a 260Z probably adds very little value.  It's just the way things are.  People just don't appreciate the 260's like they do the 240's and 280's.  My theory is that it's the shape of the 6 compared to a 4 or an 8.

If you really want more power then an L28 swap would probably be the best value for the money.  On the other hand, if you just want to see what you can do with an L26 then what you're talking about makes sense.  Good luck.

 

 

[dutchzcarguy]

15 hours ago, Zed Head said:

My theory is that it's the shape of the 6 compared to a 4 or an 8.

Hahaha, Zed.. Funny!!

I ones bought a 240z with a 260z engine in it.. but the real fun on it sat a E30 head of a 2 liter 6 cyl. (i guess Laurel engine?)  This can be done if the pistons are not flat tops.. as that gives to much compression (don't ask how i know haha) 

Has anyone done this before? The car ran but it was in bad shape and i never ran the engine really good so i know it ran but not how much power it had..

This L26 and (restored) head is still in my stash haha..