chosing between E88 and P79 heads

[hagdog]

Z newbie disclaimer: While I have moderate knowledge on performance topics, I don't have mega performance or Z-specific knowledge. Folks here seem to have mad Z knowledge and I'm looking for a handout...

My recently acquired 260Z came with an E88 head and P30 block. It seems to be bone stock, i.e. flat-top, boat anchor SU's and a slushbox. Via craigslist, I got a P79 head and a P30 block. This setup came with 3-screw SU's, simplified balance tube, 5spd, and headers. With these parts I would like to figure out the best head/block combo for autocross performance. I will run with 93 octane.

Most of the time I am in 2nd gear for the autocross courses that I run. I need good torque at low RPM for pulling out of tight corners and smooth response at 1/2 to full throttle for rest of the course.

The following points seem to be the consensus in the Z community.

P79 Head

• 53.5cc chamber
  
• 1.74" intake and the 1.38" exhaust
  
• 9+:1 compression ratio with an F54 block
  
• lined exhaust ports are restrictive
  
• excellent quench
  

E88 Head

• 47.8cc chamber
  
• 1.65" intake and the 1.38" exhaust
  
• mid 10's compression ratio with an F54 block
  
• likely to result in detonation unless a "hot" cam is used and vacuum advance is disabled.
  
• square exhaust ports have good flow
  
• good quench
  

Considering cost and performance, I am thinking that I should use the E88 head with the F54 block for good power through high compression. I am looking at a #155 grind on a cam which is .488/.488 lift and 230/230 duration. Will this cam be hot enough to avoid detonation and perform well in autocross?

Should I look at a different approach? The .080 shaved P79 is also interesting but more pricey. I am hoping to get away with minimal machining charges in order to save up for other mods.

[LeonV]

A stock P79 head on a flat-top L28 will not yield over 9:1 compression. It should be about 8.7:1 if I remember correctly. The exhaust ports are not restrictive as some like to proclaim, and will flow better than an E88.

The 260Z E88 is not as desirable as the earlier E88 (yes, there are different castings of E88 heads) because the 260Z E88 is an open-chamber (poor squish) head. Also, if you do the math, the compression will not be over 10:1 but in the mid-9s.

There are tons of threads on building up L-series engines, search around, especially on HybridZ. Spend the time to read the countless threads on the topic and you'll be rewarded with having that knowledge within yourself. Take a month or two to read and soak in information.

Take a look at datsunzgarage.com. While some of the information is not 100% accurate, it's a good resource for basic Z-car modifications.

[Zed Head]

Some of your "consensus" comments are questionable. The liners in the P79 exhaust have been shown to be of little to no restriction. They just look that way. "Square exhaust posts have good flow" - no supporting data. They just look that way.

Quench is more complicated than it seems. Just because the pad is there, does not necessarily mean that there will be effective quench.

You said that you had two P30 blocks but your examples are F54 blocks. If you're autocrossing, predominantly in one gear, then a torquey engine with a flat torque curve is probably best. The best option there is probably the F54/P79 combination. Also the cheapest, machining-wise, since none is required.

The comparison between higher compression and bigger valves (E88 vs. P79) would seem to favor the bigger valves, on the L28 block. More flow for more displacement. But, if you wanted higher compression and bigger valves, then the N42 or N47 head on the F54 flat-top long block would be the way to go. No machining required and meets all of your desires. Most people recommend a "bigger" cam with that setup though to keep the detonation problem in check.

Edit - Full disclosure - I just picked all of this up on the internet, probably just like you did. But I've been hanging out on the Hybridz site for a while and they have some good information over there. BUT - I may not know what I'm talking about.

Edited March 2, 2012 by Zed Head

[Diseazd]

http://www.classiczcars.com/forums/showthread.php?34448-New-l-28-for-my-72&highlight=. This thread may help ............

[hagdog]

Thanks for the info!

Although I have hunted around quite a bit, I was confused by the varying opinions, e.g. P79 does/does not have restrictive flow. The last thread was really useful as it showed real data and actual results. Nice work, Guy!

This has me leaning towards the F54/P79 combo--assuming the parts are solid once I tear them down and inspect them.