Flat top pistons--->P90 or N42?

[JelmerPatrol]

I have a set of flat top pistons that I plan on putting in a L28 JDM block that I have. I have a Megasquirt that I will be using for this engine.

I've read a lot about the flat tops and a N42 head and this combo will detonate easy. Backing of timing will "solve" this but at a cost: less HP and torque. Compression will be around 9.8 with this combo.

 

Now If I get a P90/P79 head compression will drop to 8.5 but this will not detonate due to the better shaped chambers.

But what combo would be better for Hp and torque?

 

I planned on putting a cam in it.

 

 

Second thing, I original planned on putting a turbo on my Patrol L28E (4000Lb truck) but now that I bought a Datsun Laurel (roughly the same size as a 910 Maxima) I want to put the turbo stuff on a spare L28 that i have and put it in the Laurel.

 

So the flat top engine goes into the Patrol and needs torque rather than lots of Hp. As a cam I need more lift but not a lot of duration so I was thinking of a Racer Brown 325r cam.

What do you guys think of this?

[BluDestiny]

I ran a 10:1 compression F54 with an E88 (same chamber design as the N42) and It was great. I had the Schneider stage 3 cam and triple Weber 40's. I never tore the motor apart, but 10k miles were trouble free before I sold the car. 

[JelmerPatrol]

What timing did you run?

[zdizeeze]

I have talked to to experienced builders. One said a N42 that has had a lot taken off will detinate

[NewZed]

Interesting unexplored topic.  Share what you learn, nobody has really discussed this before.

[Chickenman]

Running an F54 block and Flat Tops with N47 head. 10.3 to 1 CR calculated. 34 Degrees total Mechanical Timing ( 14 degrees static and 20 in the Dizzy ) . Vacuum advance modified to 15 degrees total.

 

Edit: Unknown if head has been shaved or how much. PO build... and his specs are suspect.

 

OK on Shell 91 or 92 Nitro. Had an issue recently where engine detonated under high load with Chevron 94 ( BC Canada ) . Never had that happen before. But Turbo guys have been complaining on and off about Chevron 94 in BC for 2-3 years now.

 

1: Gasoline quality plays a big part in ignition timing. Golden rule: When in doubt... take it out. Better to be a couple of degrees under perfect timing than a couple of degrees over. Modern knock sensors allow Manufacturers to maximize Ignition timing ( aggressive timing curves ) and that increase HP and Fuel mileage. Of course we don't have knock sensors ( stock )

 

2: Ambient temp plays a big part. What works in the PNW may not work in California, Florida or other Southern states. YMMV

 

3: Cooling. You must have a PERFECT cooling system. L series engines don't like to run hot or even hottish. In Southern states a 160 degrees ( Tropical Nissan Thermostat ) seems to be the ticket. Tony D reported that the actual cylinder head temperate at #6 cylinder runs about 20 F higher than what is seen at the Thermostat housing. AC puts a big Toll on cooling system... but I can't drive without it.

 

Strangely enough. The annual summer Temps in the PNW are regularity in the 90's for the last few years ( Lower Mainland BC ) . Supposed to hit 35C ( 95 F ) in Metro Vancouver today.

 

32 degrees mechanical total may be a safer bet in really hot climates or with iffy fuel..

Edited August 17, 2016 by Chickenman

[JelmerPatrol]

@Chickenman: Thanks!

 

We have 95 ron (91 in US) available as the lowest quality.

I plan on running it with coil on plug ignition.

Cooling is not an issue either, my Patrol radiator is twice as big as a 280zx radiator and 3 core thick.