? A87 vs U67 ?

[Apollo77]

im looking at possibly building a Frankenstein motor and was wondering if i could get some advice on heads? Ive heard good things on both but other opinions would be great! so lets hear what ya got!

DV

[MicroMachinery]

You're gonna have to be a little more specific than just saying "frankenstein motor" if you want the best answer; there are so many different combinations, and it really will depend on what you're trying to do.

 

A87 closed(peanut) chamber heads have smaller combustion chambers(higher compression), and smaller valves.

U67 heads have larger combustion chambers(lower compression) and larger valves.

[metalmonkey47]

It would seem that the U67 is a better head for forced induction, but thats just my opinion.

[DISLEXICDIME]

It would seem that the U67 is a better head for forced induction, but thats just my opinion.

 

open chamber such as u67 are more prone to detonation

[Braden]

open chamber such as u67 are more prone to detonation

how did you figure that one???? its called pre detonation and it happens with higher compression heads, not lower like the u67 open chamber

[Apollo77]

well what id like to do is a z22 block with flat top pistons and an unknown head as of yet, with a race cam and a z trans. thats all ive got so far. any thoughts on what else i should do? Datdoug said turbo, but i wanna see what i can do before i get there.

DV

[banzai510(hainz)]

open chamber such as u67 are more prone to detonation

 

True statment!!!!!!!!!!

 

I had a L16 with stock pistons the motor would ping and have run on proplems.

Put same head on block with flattops. same thing detonate and run on proplems.

Thats why L20s had anti desieling selinoids on the carbs. or alater OPEN CHAMBER A87s

 

My L18 with this same head still pings up hill with load and diesels(run on). It alot less run on with SUPER and Does NOT ping with SUPER. In Washington Super is 92. other states they might have 94

 

But nothing too much wrong with a U67 head if run stock pistons. Just puy SUPER or time it for daily driver.

[DISLEXICDIME]

how did you figure that one???? its called pre detonation and it happens with higher compression heads, not lower like the u67 open chamber

 

have you ever ran closed and open chamber head on the same block ?I have that's how i know.

have you had a built l series? I have that's how i know .

have ever read any of the literature on building a L series ? obviously not

 

I like the medium chamber w53 on a z20 block .

[banzai510(hainz)]

have you ever ran closed and open chamber head on the same block ?

YES

my521 truck 87octane gas

L16 block with 7cc dish pistons .

stock L16 210 head NO pinging no run on

 

same L16 block U67 head Pinging on HOt days and RUN ON.

rebuilt L16 block with same U67 head pinging ,run on

 

moved U67 head to L18 4cc dished pistons,still pinging,run on

 

yes this U67 head has been on 3 blocks

 

my yellow car ,87 octane

L18 flattop pistons A87 closed chamber head no pining NO run on

 

My Banzai car ,87 octane

L16 block with L18 4cc pistons with W53 head. No ping No run on.

 

http://olddatsuns.com/html/tech/head_ID_2.htm

 

For some reason the U67 head is prefered when doing a LZ motormaybe using stock pistons. I however do not know about adding flattops as youll need real good Gas.Dave on here with the help of Jeff Hino (Icehouse). Daves car would just detonate like a mofo. But when he ran Avgas/race gas it was fine but he was going broke paying 8$ agal. It was a LZ with flattops.

 

this is my opinion but for a daily driver this is my recommnedation and only that.

L20s stock block and prefered a closed chamber head

L16 /L18 flatops and closed chamber head.

 

where there is 94 octane

MAYBE a l20 with L18 4cc dished pistons and a closed chamber head. Seen a kid in my neiboohood that had alot of detonation proplem with this set up on 92 octance

 

LZ

stock Z block/pistons and U67 head

[ppeters914]

this is my opinion but for a daily driver this is my recommnedation and only that.

L20s stock block and prefered a closed chamber head

L16 /L18 flatops and closed chamber head.

 

where there is 94 octane

MAYBE a l20 with L18 4cc dished pistons and a closed chamber head. Seen a kid in my neiboohood that had alot of detonation proplem with this set up on 92 octance

 

LZ

stock Z block/pistons and U67 head

Sounds like excellent advice that many folks will ignore. "I ain't got a pot to p!$$ in, but I want a 300HP 3MPG fire breathin' L-motor cuz it's kewl!"

[DISLEXICDIME]

Sounds like excellent advice that many folks will ignore. "I ain't got a pot to p!$$ in, but I want a 300HP 3MPG fire breathin' L-motor cuz it's kewl!"

 

and it will be na and have 32/36

 

Hainz i was not saying that to you. I know you have had plenty of l series i was talking to ghettobraiden.

[datzenmike]

how did you figure that one???? its called pre detonation and it happens with higher compression heads, not lower like the u67 open chamber

 

Yes to a point, higher compression will ping more than a lower compression.... more on this later as there is an exception.*

 

If you run an L head on a Z22 or Z24 engine block you are cramming .2 or .4 liter more engine into the same head so you are going to increase the compression. (Z heads have much larger combustion chambers than the L series)

 

Open chamber L head on:

Z22 = 9.84

Z24 = 9.47

 

Closed chamber L head on:

Z22 = 10.48

Z24 = 10.10

 

Now the closed chamber head was designed for use with a compression of around 9.48 on the L16 with flattops and 9.68 on the L18 with flattops I believe. As you can see from the above chart running a p-nut on either Z motors puts the compression well above 10.00 so it's way above it's intended design and will likely ping anyway. Hell even the open chambers are above 9.5!

 

*Compression alone is not the determining factor if an engine will ping, heat is. True compression concentrates heat into a smaller space raising it, and if enough, it will auto detonate causing ping. Other causes are over heating, too hot a plug range, running lean, carbon build up and over advanced timing. Generally though all things equal a higher compression will ping more or easier.

 

So how does the closed chamber reduce ping even though it has higher compression? The fuel and air in the combustion chambers is never evenly mixed some areas are richer or leaner. Richer areas will be cooled by the evaporated fuel which soaks up heat. Lean areas are hot and get hotter. All it needs is compression to push it over the edge and it pings.

 

Open chamber heads have an open space above the piston when at TDC. The p-nut head's combustion chamber does not extend fully to the top edge of the cylinder walls. There is an area where the piston comes within the head gasket thickness of touching the head surface. This is known as the quench or pinch area and is very important. When the piston approaches TDC on compression the air trapped between piston and head surface in the quench areas is violently pinched out into the open area and turbulence or swirl is produced. What this does is it further mixes the fuel and air as it burns reducing rich and lean areas which reduces hot spots and generally improving efficiency/economy.

 

Which would ping A87 closed chamber or U67 on a Frankenmotor??? Good question. I think they both would ping. The p-nut perhaps slightly less.

[HRH]

Ah hah, says the Datsun enthusiast with flat top Z20 pistons in his 20B (completely flat save valve reliefs), with a U60 head (identical to U67). Yes, there is a detonation issue, but it's not horrible. Granted, my carbs have been running super rich, which helps, but also hurts. Hence the EFI thread going on now.

 

I'm pretty sure the general consensus is with factory dished pistons, the peanut head is a much better way to raise compression and the chamber style is less prone to detonation. However, sticking the peanut head with what, 45cc volume on a Z22 or Z24 is going to require 92 octane and probably methanol or water injection. With race gas it will be happy.

 

So far I have been able to get away with 14-16 degrees advanced at idle with dual SUs with flat tops, .030 off the head, and the U60. I only have bad detonation problems when it gets pretty hot out. Had I done a Z22 or Z24, I still would have used this head. Looking back, if I had a peanut head laying around, I might well have built it instead. And it's funny, I just had one and sold it to my buddy for his chump car because I figured I'm not going to build another L anytime soon. If anything I'll be playing with the KAs.

[datsunfish]

Both of those heads are good but a87 requires alot of port work to meet the U67. The airflow attributes to alot of the power on an L motor. BTW for the record the U67 and A87 have the same valve sizes so that is not an issue. Bolt and go a U67 would be the appropriate choice in my opinion but the A87 has more potential.

[mr68gts]

My 76 620 is running the same setup as HRH. Z20 pistons (flat top instead of dish) and dual (factory datsun competition package) SU's on a U67 head. Been that way since 76 and the only 2 problems I have are I HAVE to use super unleaded and it diesels when shut off. I always just pop the clutch when I turn the key off and that takes care of it. Never had a noticeable detonation problem as long as I don't cheap out on the fuel though. I also run a reground Web Cam. Motor has been that way since the truck was new and it's been the most reliable engine. Even has over 100,000 miles on it!

Paul