Race car: P79 + flat tops for turbo engine? (Moderate boost)

[turbogrill]

Hi

Is it possible to build a turbo engine using the flat top pistons with any head/gasket combo?

Or will compression be too high? Would be looking at <300hp.

According to the calculator the P79 and flat tops gives 1:8.63 with Fel pro gasket.

My NA N47+flattop build has everything that I need for turbo except turbo parts. (fresh rebuild, ARP head+rod bolts, megasquirt, pallnet w/ supra injector, large pump, loud exhuast)

 When I get tired of this engine I might try the turbo route, would be nice if all I needed is a P79 head and the turbo gizmos....

 

This would be in an enduro race car in Texas, so plenty of heat and abuse.

Edited November 9, 2017 by turbogrill

[Chickenman]

As long as you can get decent fuel ( 93 to 94 Octane ) , 8.6 CR is not too high IMHO. Done all the time.  Race fuel would be a piece of cake  Nissan went really conservative on the L28ET CR, because of no intercooler and archaic ECU controls.  You can push the envelope much further with some upgrades and a decent Standalone ECU. manufacturers in the 80's through 90's were very, very conservative on most Turbo motors. Now you have EcoBost 2.3L  4 bangers pumping out 350HP... stock!! ( Focus RS ) 

Add a couple of VW Bosch WB Knock sensors to the block would be a smart idea on a race engine. Not too hard to do. I'm sure Tony D knows how. 

[turbogrill]

14 hours ago, Chickenman said:

As long as you can get decent fuel ( 93 to 94 Octane ) , 8.6 CR is not too high IMHO. Done all the time.  Race fuel would be a piece of cake  Nissan went really conservative on the L28ET CR, because of no intercooler and archaic ECU controls.  You can push the envelope much further with some upgrades and a decent Standalone ECU. manufacturers in the 80's through 90's were very, very conservative on most Turbo motors. Now you have EcoBost 2.3L  4 bangers pumping out 350HP... stock!! ( Focus RS ) 

Add a couple of VW Bosch WB Knock sensors to the block would be a smart idea on a race engine. Not too hard to do. I'm sure Tony D knows how. 

That is a very good point, while I am sure the EFI was spectacular in the 70s it's very ancient.

So intercooler will reduce the temps and therefor reduce the possibility of knocking. I terms of engine management what is important from a knocking perspective, is it make sure that AFR is what it's supposed to be and timing is being where it so supposed to be?

 

 

[Chickenman]

A correctly sized  ( and low pressure loss ) intercooler will dramatically reduce charge temps which will also reduce the knock threshold.. It will also reduce the boost necessary to produce the same horsepower. Cooler air is denser.  Same HP with  Less boost =  better efficiency = lower cylinder pressures = less chance of detonation. A Win/Win situation.  

The ability  of a Modern ECU ( or standalone ) to precisely control the AFR and Timing at any RPM and Load allows you to maximize the Torque and HP potential of the engine. It's very hard to improve modern EFI efficiency because of the feedback controls. Modern  Dual WB Knock sensors really allow the manufacturers to push the efficiency and power envelopes.

Also,  car manufacturers have to make things conservative in case low Octane fuel is used by mistake. Race cars don't have that issue. The ZXT did have a factory Knock sensor... but it was a dinosaur compared to what is available today. 

You can also make Timing digressive at Peak Torque with programmable ECU's.  Ramp timing up aggressively at low RPM's to generate maximum Torque, then back off a couple of degrees at Peak Torque ( Peak Torque is usually where detonation will occur ) then ramp it up again ( if necessary ) after Peak Torque. Cylinder heads that are prone to detonation ( N42/N47 for example ) respond well to this Timing strategy. You can also use some extra fuel to control detonation. Kind of a " Band'Aid " fix... but it will work. This should all be done on a Load Cell dyno of course.  

You can also do individual fuel and timing trims with most stand alone  ECU's. #5 and #6 are known to run a bit hot on the L-6. So you can pull a small amount of timing from those cylinders. Or add a bit of fuel. Run multiple O2 sensors ( or EGT probes ) and you can dial in the ideal AFR for each cylinder.. Most Intake manifolds, especially stock manifold, never have equal air distribution from cylinder to cylinder. 

 
 

[rossman]

Run a newer, efficient turbo & intercooler, good ecu, do the head cooling mod, smooth out the combustion chambers and deshroud the valves and I bet you'll be pushing 300 hp no problem.

[turbogrill]

43 minutes ago, rossman said:

Run a newer, efficient turbo & intercooler, good ecu, do the head cooling mod, smooth out the combustion chambers and deshroud the valves and I bet you'll be pushing 300 hp no problem.

What is this head cooling mod? 

[rossman]

Look for the thread in the L-series FAQs.  Basically, cylinders #5 & 6 tend to be prone to detonation due to poor coolant circulation in that area of the head.  The mod is to drill/tap holes on the driver's side of the head just above #5 & 6 exhaust ports then plumb those ports directly to the thermostat housing.