OWO Head Porting & Polishing

After about 15 mins of playing around with a dremel:





This is really not that hard or mysterious. That didn't take long, but I can see it getting difficult to reach in the deeper parts of the port.

Why are going to polish the intake ports? On turbo builds I've heard nothing but that it isn't beneficial or necessary.

Looks like you made a decent start. Here is a link to Moto IQ's OWO headwork for their project pathfinder buildhttp://www.motoiq.com/MagazineArticl…-Headwork.aspx; I will be doing my own heads as well and this is exactly how I want mine to end up. "The idea was to keep the port volume down to keep the velocity up so as to enhance low-end torque."

Another link straight to DPR site http://www.dprracing.com/snissan.html can give you good ideas what else you can do while your there.

So the claim is that polishing the intake at areas after the fuel injectors is bad. I haven't seen any data to back this up. I realize it affects the tau layer, but I can't find anything showing negative consequences. Further, fine polishing either side adds a negligible performance benefit--but I'm aiming for reduced carbon build up, especially on the exhaust side.

So, I can leave the intake ports as-is for now, until someone chimes in to let me know what's what.

I see a couple things that I'm not sure of:

• They radius the quench edge
• They Deshroud the valve

I've been reading that the valve shroud in the chamber is designed to swirl the mixture together, and that removing it is not good. I've also read that radiusing the quench edge can remove the edge hotspot, but reduce performance. Ugh. So much conflicting info.

But they do chow down on the valve guide. Guess I can try to do that…

I P&P the intake and exhaust on my 84T motor with a dremel and wrapped sanding bits.
I had no clue as to what i was doing. Smooth all the things!
Intake 1600X1200
I gasket matched things as best i could. It's been running great since 2003.

From what I've learned talking to my coworker who used to own a performance build shop, has experience porting, etc, and from my reading, you can port and polish all the way to the intake valve, but stop polishing at the valve, continue to port through to the chamber.
This promotes the fuel mixing with air once it's sucked pushed passed the intake valve. Otherwise it will pool up and cling to the polished surface, which is not what we want.
When porting you want to make the most straight and direct path in and out of the combustion chamber.
This effectively removes the oem "bumps" or velocity swirling humps in the casting.

I got schooled in what should be done by Dave rebello of rebello racing when he came and picked up my engine to have him do it up right. Things he told me (some of which is common knowledge on here):

-polish the exhaust
-for a mild build on our motors oversized valves are not worth the effort and money
-intake porting is essential but polish is useless and is better off NOT done for turbos. (N/A is different)
-w-series heads are much better than the early heads
-arp hardware isn't always the best option for mild-moderate street builds if you aren't willing to open up the motor to final retorque within a years time of the motor being put together.

I know not all applies here but I just figured I'd pass along that from an engine building master. I pick up my engine on Thursday. Interested to see his work and the dyno results when I get it back in the z.

I will correct something here, though…W-series Z31 heads are 100% identical to early Z31 heads. They're even the same castings. The *ONLY* difference is Nissan drilled steam holes in them during the machining process.

85E and OWO heads are much much better, but arent W-series technically.

I have been doing some flow testing on heads lately with an cylinder head expert, I put some info in this post.
http://z31performance.com/showthread…s-section-pics

My testing has shown that the OWO heads aren't the best totally stock.
The OWO head does have a better SSR, but no one notices that the R21V has a better bowl shape to the port.
The good thing is you can copy the bowl shape from the R21V to the OWO with a good SSR and get even better flow.

I decided to concentrate on the OWO heads, so I have done a lot of testing to see what works the best.

The stock valve and seat are where you can get the most improvement.
Porting the with the stock valve and seat really only helps the flow at .5" and above, that won't help much with the cams you can get for VG30's
I tried a 35deg. seat angle on a stock valve, that's supposed to help flow at low lift, it really didn't change the flow much.
I tried a typical multi-angle valve job on a stock valve, it helped the flow were it matters the most, at low lifts.
I tried the +1mm valve with a multi-angle valve job, and was disappointed with the increase in flow.
I added a 30 deg. backcut to the +1mm valve, it helped the low lift flow.
We tried one more thing increasing the throat. The biggest increase came from opening the throat to 90% of the valve diameter.
We got the peak flow up to 190 CFM with the velocity probe in the port at .425" lift, 28" of water, with velocity of 326 ft/sec

Here is what I finished up with for flow on the intake port.
At 28" of water
1.528" throat diameter, 30deg. backcut on +1mm valve


Lift in Flow cfm
.1 61
.2 113
.3 156
.4 186
.45 186
.5 184


For reference stock head
Lift in Flow cfm
.1 58
.2 111
.3 140
.4 160
.5 164

We are not finished working on the heads yet, still have the exhaust to go, and I still have some things to try on the test head I have.

I have also tested with the intake on.
The lower intake works fine after a little clean up, but the upper knocks off about 10% of the flow, which makes no sense, I am only flowing one cylinder through it.
I just gutted a stock intake to try it out when I get a chance.

Your right. I forgot we were talking turbo VG.

oh good lord. Did 85E castings come on anything but w-series motors?

Just curious where in the port you were 325 ft sec. with the velocity probe? Or is that the average velocity?
Also noticed that you had little gain from from the convergence to .500, that is usually caused by excessive air speed over the short turn, was wondering what kind of csa you had approaching the short turn.

That speed was in the middle of the port. I don't know the csa measurement, I will try remember to get that next trip.

On another subject, my head porting expert/mentor says, "I can make a head that will win a flow bench race, or a head that will win a real race, which do you want?"