NA Build up Head Question E31 VS P90

[Shuyun]

I am putting together an NA motor for my 1973 Datsun.

I have a F54 Block, Turbo pistons (Dished), NA Pistons (Flat Top), L24 Crank, L28 Crank, Rod out of an L24, L26, and L28NA a Turbo, A P90 Head and an E31 Head.

My Plan is to build a stock L28 NA short Block with the F54 block L28 Crank and L28 Flat toped pistons,

I plan to use an Arizona 4 barrel intake and header in my NA setup.

Which Head the P90 or the E31 will result in the better performance in the nearly stock setup.

According to the Engine Design Utility the compression ratios for the two are as follows:

E31 = 10.15 to 1

P90 = 8.48 to 1

What if any work will result in better performance form either head as I will have the head in the machine shop to have a rebuild and 3 angle valve job.

What will get me the most for performance for my money in my proposed setup.

Thanks for your answers and I will keep searching to see if this question has been answered in an earlier post.

[Zmanco]

This has been asked and answered dozens of times - do keep searching. I think you'll find that there is no definitive answer. The P90 will be reliable and resist detonation allowing you to run full advance on pump gas. Plus it has larger valves so should flow better. The E31 has a reputation mostly left over from those who were restricted by rules (such as SCCA) as to which heads they could use. It needs some work to flow as well as a P90 (new valves and seats). It would have a higher CR, but it's doubtful you could run full advance with pump gas so would probably "give back" more than you gained.

 

Go with the P90.

 

And search!

[Shuyun]

I found this on an E31 Search which recomends hardened seats and larger valves with a simple port an polish to get the most out of the E31.

 

http://forums.hybridz.org/showthread.php?t=143162&highlight=E31

 

So no I will start looking for some more info on uping the compression on the P90.

 

Like how much can be shaved before the valves become a problem on the flat top pistons. And how much work is needed to add the height back to the cam shaft?

[Zmanco]

Like how much can be shaved before the valves become a problem on the flat top pistons. And how much work is needed to add the height back to the cam shaft?

I shaved my P90 (as well as unshrouded the valves and port matched the intake) and learned nearly everything I needed by searching.

[Shuyun]

So the solution for the P90 is the 2 mm or 80 thou off the base then shim up the came towers, springs, with longer valves.

So how about what it cost to have done what did you pay for the Shave vs. what it cost to put in hardened guides larger valves and port and polish the E31.

I have found several shop recommendations around Atlanta GA can some one give me some recommendations around Tallahassee FL and Jacksonville FL.

Thanks,

[Xnke]

The P90 is going to be what you want. The E31 will cost you much more to get to the same level of performance.

 

First, you're gonna have to have the seats and guides replaced, that's 400$ at my favorite machine shop here. (250 for the valve job, plus the seats themselves, plus 120$ of new valves, plus guides.)

 

Then, you'll have to spend for a porting, or port it yourself. (expect to spend another 300$ here, if you haven't ever ported a head before.) If you don't, well you might as well just not spend the money, the ports are going to flow even worse due to the big step in the port.

 

Then, look at the P90. Shave 2mm, at my favorite shop is 55$, including hot tanking and straightening. 2mm custom shims were 32$ at the local fab shop, and the valves are still about 120$. As long as you don't need a valve job, that's all she wrote, you're done. check the valve seats, you might get away with a simple lap to seat in the new valves.

 

Again, these prices are local to me, at my favorite shop. I trust these guys, they don't screw around. Look around in your town, check the yellow pages, go talk to the machinists. Find out who knows there stuff, and pay what they want, these guys are not in it to get rich usually.

 

p.s. I'm gay!