Building a P90 head for supercharger service

[Xnke]

Since my lightly worked N42 cylinder head developed a crack in the deck, which I found out last friday, I have been working on getting the P90 head casting I picked up cheap ready to go.

 

This is the beginning of what I would consider a full effort street port, since working the chambers much harder than this results in limited life. I have not started on the ports yet, just worked on the chambers and the water jackets.

Valve unshrouding:







Water jacket modifications...AKA "Why the hell are you drilling holes in that cylinder head?!?"



Because down inside here, the exhaust port and intake port are connected with a web of casting flash. It shouldn't be there...I got in with a small drill bit and drilled and chipped out all the casting flash between the ports.



Marking out for the port sizing.



Intake valves will remain 44mm diameter, and exhaust valves will be cut down from LS1 exhaust valves, to 36mm diameter. The LS1 valves need to have the diameter reduced, margin thinned, 25* back-cut applied, the stems cut down by 8.3mm, and the keeper groove re-cut lower on the stem. Even with all that work, it's cheaper to buy a set of Manley LS1 exhaust valves, cut them down and re-groove, than it is for a set of Ferrea standard alloy +1mm L28 valves.

The circled bolt holes will get drilled and helicoiled, as they often pull out in normal service and the threads gall up occasionally too. I use 2D series helicoils for this as they are twice as long as the normal ones.

Edited June 8, 2013 by Xnke

[Xnke]

Port work has commenced, one exhaust port is near-finished, the others are in various stages of finished. I work them round-robin till I get all six to the state I want them to end in...five more exhausts to go.

[motomanmike]

Looks good man. 

[Xnke]

Been working on this some. Crossposting from another forum.

Stock port:



Little better detail:



About halfway done, smoothed out to judge contours and stuff:



Another port, also about halfway done:



I'll be taking some more shots of ports much closer to finished tonight. Yes, the ridges giant cliffs under the seats are now gone.

Edited June 8, 2013 by Xnke

[col]

I took a look at your build pictures, Heaps of hours there, Nice work.

[Xnke]

Porting updates:

Exhaust ports are finished, will get a final 120 grit finish before the flowbench and will get polished after. I have one intake port roughed in at 37mm, finished port will be 38mm.

Progression of an exhaust port:










Good shot of a finished port:





I swear this port isn't as wonky as it looks...the port floor is level with the deck surface. I went and checked twice after taking this photo.

Edited June 8, 2013 by Xnke

[redzedturbo]

Looking very tidy jake good job man!

[Tony D]

I will be interested to see flow bench numbers for improvement over stock. Should prove interesting.

Big runner size..38mm!

[Xnke]

The exhaust ports I worked from a template I obtained a few years back...the port that the exhaust template was made from flowed 145CFM at 0.500" lift. Last time I managed 134 at 0.480", hopefully this time I did at least as good.

 

The intake ports are eyeballed based on ports I've found in photos, descriptions, and comments on this and other forums. I don't have a stock P90 head to flow, and while I am trying to find a local flowbench to measure on the one I used before isn't around anymore...so far the closest I can find is a 12 hour drive plus 200$ for the work. The money, I don't care about...it costs what it costs. The shipping time is what gets to me.

 

38mm runners are still 4mm smaller than the largest ports I've seen...which was a 42mm port on an N42 head, on an engine turning out 370HP, naturally aspirated, at 7700RPM. The engine was run up to 8200RPM in service, but I don't know much more about it...I don't read japanese. Most port jobs I see have port sizes about 40mm...but that may be by convention more than anything. Those ports inbetween stock and 40mm seem to be clustered around 38mm as well.

 

I picked 38mm because it should provide the flow numbers I need, without sacrificing port velocity. This port, if I can get the flare and the bowl sized properly, should provide as much as 220CFM at 0.500" valve lift. It should do this while providing port flow rates not exceeding 300ft/s until higher than 7000RPM, but still keeping flow rate above 200ft/s from 2000RPM. I would like to see 210-220ft/s at 5300RPM, up to about 240ft/s at 6300RPM or so.

[Gollum]

So refreshing to see someone actually doing something and actually know what they're doing. As opposed to the millions of "how do I xxxx" threads.

 

Thank you for making my day a little brighter.

[Xnke]

Who says I know what I'm doing?

 

I'm just goofing around with this thing before I install it. Hopefully it works out well.

 

I am fixing to go ask some questions though...gotta get edjamacated on oil coolers.

[Gollum]

You've at least READ the head cooling thread, which is more than I can say for many people...

[Xnke]

Here are a few preliminary intake port shots. These ports are still about 1mm undersize.

 

Stock port:

 

 

After working the port to the first intermediate stage:

 

 

Getting pretty close to the desired profile now:

 

 

Four more intakes to go...Then the balancing.

[Tony D]

Slover's, Rebello, and BCG all managed 200+ CFM at a 35-36mm nominal diameter at manifold flange.

 

The old Carburetted ports on big HP engines resulted in a reasonably constrained taper from 55, 50, or at least 40mm ports at the flange of the Cannon/NISMO manifolds.

 

Big ports are slow down low. You have a supercharger to correct that, but I think it's been shown you bon't need huge ports to get the flow...it's almost all in the Bowl!

 

Also, cheat your port higher, do not lower the port floor by simply making it symmetrically larger. Yes, you will have to do the same to the manifold...but...

Edited June 9, 2013 by Tony D

[PMC raceengines]

If you port to engine size and rpm you need to make the hp  , a L 28 with a 88.5 mm bore that makes max power at  7500 it needs a 39mm port with 225cfm @500 will make 310hp with all the right gear on it , 

On my 3.3 + motors we did a test with port size , from stock all the way to a welded 41mm port , flow did not change much and it was all about x section and port volume , what we found was the engine just keeped making power in the top and torque moved up with it .

 

TORQUE was at its best at 5500 with a 40.5 mm port ,  cam was the same 310d 550 lift , 260 @ 50 .

this was on a 3.35 engine

 

same test on  L28 with 89mm bore  same spec engine same cam and carbs 

Torque was best with 39mm port and was at the same 5500 rpm ,  

 

so you need to port to engine size , and yes it has to be the right size for what you are doing , if you want power at 3500 you need a cam and head that work there and you need a primery pipe lenth that work there as well ,

 

AS for big ports being slow thats crap,,, there is only bad ports , if you port it right the L head is more than up for it at any size it will go , mach your port to the engine you are building , ....

[PMC raceengines]

BTW  Xnke  the ports are looking good ,  you could take more from the cheeks off the short turn , this will help in the top end from 300 to 500 lift , and wont hurt the bottom to much , 

keep up the good work should be a top engine

[Xnke]

Tony, the port is all lifted...the port floor hasn't moved at all. I need to blend the sides, (I guess what PMC is calling the cheeks?) into the floor more, and clean up the surface...it's a smidge lumpy yet.

The port diameter is set by the 38MM runner diameter, and the desire to get 200CFM at only 0.400" lift. It can be done, I've seen it done, and I'm trying to emulate the port job that I've seen it done with. The cam is only 0.480" lift, so no need to aim for flow higher than that. I need the port to be all in by 0.450" lift or so, and I want as much flow as I can get there.

[Tony D]

I've got a head with 50mm holes in it... I'm sorry, but even The way I drive, that's a damn slow port unless I'm running 20" tall tyres and a 5.62 gearset!

 

This goes hand in hand with the "small port engine build" Oz Connection was doing. A 30mm port on a stock L28 isn't necessarily a bad thing.

 

But if you can get 218 out of a raised floor, FIA-Legal 35mm nominal port diameter hole... What benefit do you get going bigger? How does that not simply raise the RPM you need to twist the engine to get optimum performance?

 

The desire to get X/CFM@0.400" lift IS a valid design consideration, and being supercharged it will mask the normal tendency of a larger port to sog below a given RPM.

 

The photo looked like your proposed enlargement was simply a symmetrical enlargement of he existing hole (which I see people do all the time!) It looked bad, glad to hear you were uplifted!

 

I'm getting the itch for my supercharged car... Who knows when I'll get back to it? I didn't even get a chance to sit in it before I pushed it into the container for Hoardification!

Edited June 9, 2013 by Tony D

[dexter72]

Nice work Xnke.

 

PMC engines, Nice to see you back. I always look forward to reading your posts.

[Xnke]

The only material removed from the floor of the port was to remove the casting texture and blend the sides in.

 

The old head, with this cam, manifold, and shortblock, made 8.5lbs of boost at 2000RPM and had 6lbs of boost at 1400, on throttle.

 

Swapping out only the cylinder head, I hope to see boost drop some...this gives me a good estimate of the change in VE, since the blower VE is relatively fixed.

 

The difference is port velocity, Tony. I can't claim to be an expert in it, but I've got my ideas. We'll see how it turns out, I'm still scrambling to find a local flowbench.