SOHC Head Porting Experience and Data...

eeastment · Post by **eeastment** » Sun Feb 13, 2011 12:21 pm

Just found this forum, I had posted the information below on Neons.org, thought I'd share it here...

Hello. I thought I'd share some of my experience with porting my 2001 SOHC head. I'm an electrical engineer, mechanically inclined, have built several motors before, but never touched a Neon until now. I am by no means an experienced head porting guy but I did some research that I thought you all might find interesting.

As I'm sure many of you are aware the exhaust ports just behind the valve heads are INCREDIBLY restricted by the "bump-outs" on three sides that jut into the port. The intake side looked fantastic.

The work I did consisted of the following:
INTAKE - These ports looked really good to me, all I did was gently blend the port floor from the valve seat to the rest of the port, very minimal work, performed with 120 grit Dremmel sanding drums. Other than that I made the manifold port openings more uniform and matched, very little work here. Probably spent 8 hours working slowly, taking small amounts of material at a time.

EXHAUST - These ports were a chore. I probably spent 30 hours on the exhaust side (sanding drums and carbide cutters w/Dremmel). The goal was only to remove the "bump-outs" behind the exhaust valve heads, blend around the valve guides lightly, and raise the port roof slightly while knife-edging the center divider between ports of the same cylinder.

After removing the bump-outs I ran across a graphic in the FSM showing why the bump outs exist, there is an odd-shaped coolant passage that impinges through the center of the head and makes a bit of a bump in the exhaust port.

"CRAP" I said to my stupid self, I know I didn't hit the coolant passage, but I now had to answer the following questions:
1.) How thin did I make the port wall by removing the bumps?
2.) How thin is too thin?
3.) Would the supposed thin walls be OK for use in a daily driver application?

Well,... I was able to get answers for each of these questions!

#1 - How thin did I make the port walls by removing the bumps? I asked a buddy of mine at work if we could use his ultrasonic crack and wall thickness detection system (used for determining the wall thickness of various pipes or cracks in bolts, parts, etc.). We were able to calibrate the detector to the cast aluminum by measuring an external flange with calipers then calibrating his instrument until it read the measured thickness. Thus it was calibrated and accurate to within 0.001". We proceeded to measure/map the wall thickness of the eight ports after my porting job. The thinnest single spot we found was 0.093" in one very small area, most areas were between 0.100" and 0.120". Awesome! Now I have real port wall thickness data,... but, how thin is too thin? My gut said 0.100" was getting a bit thin. So I asked my head guy (SCH Cylinder Head - racing head porting, machining, and normal valve job shop).

#2 - How thin is too thin? I asked SCH, they (really he) indicated 0.080" port wall thickness on the exhaust side was an acceptable, but thin, minimum thickness for a daily driver application. He indicated that for "pushing the limit racing applications" he has reduced wall thickness to as little as 0.030", of course he wouldn't advise this for anything but certain purpose-specific applications. Daily driver applications, for reliability and longevity, require more port wall thickness. Please don't hog out your ports until the walls are 0.030", have them fail, and flame me and/or SCH for it. I'm not saying 0.030" is OK, I am saying 0.080" should be a min. thick guideline (not a rule)! I'd prefer 0.100" but one spot with 0.093" will probably be OK for the next 200k mi. FYI - At this time the motor is not even together yet...

#3 - Would the supposed thin walls be OK for use in a daily driver application? As explained in the above paragraph my minimum thickness of 0.093" will probably be just fine.

Note: If anyone see a silver 2001 Neon on I-25 billowing white smoke disregard the above information!

tkstoysrt · Post by **tkstoysrt** » Sun Feb 20, 2011 10:15 pm

did you happen to take any pics of your work. I am currently in the process of tearing down my engine for a rebuild and thinking of attempting to do some port work also.

eeastment · Post by **eeastment** » Sun Feb 20, 2011 11:16 pm

tkstoysrt wrote:did you happen to take any pics of your work. I am currently in the process of tearing down my engine for a rebuild and thinking of attempting to do some port work also.

I will post some pictures tomorrow.

Mat · Post by **Mat** » Mon Feb 21, 2011 4:27 pm

I've never heard of anyone doing what you did (the mapping), however if you're talking about the "hump" at the bottom of the exhaust port and saying you ground it away, you may see reversion issues.

Post by **occasional demons** » Mon Feb 21, 2011 7:25 pm

The Magnum exhaust ports don't have that huge hump, so I wouldn't think it would have a huge effect. Since Magnum valves are the same size, and you aren't making the ports as huge as the Magnum's, I doubt velocity will be hurt too much either. If you are worried about reversion, run the Magnum header. The step in size will act as an anti-reversion step.

NickKo · Post by **NickKo** » Mon Feb 21, 2011 10:00 pm

Well, Magnums do have a 'hump' in the exhaust port..... but it's nowhere near as big, as on a standard SOHC head.

- Nick

Post by **occasional demons** » Tue Feb 22, 2011 8:36 am

True, I guess I should have been more specific, as the Magnum's is more of a way to direct the flow, more than just a huge obstruction.

eeastment · Post by **eeastment** » Sat Mar 05, 2011 9:57 am

I've never heard of anyone doing what you did (the mapping), however if you're talking about the "hump" at the bottom of the exhaust port and saying you ground it away, you may see reversion issues..

No, I didn't remove the large hump in the exhaust floor, that would be a mistake. I'm talking about the bump-outs immediately behind the exhaust valve head. These are visible if you're looking into the exhaust port from the combustion chamber side.

I've seen threads where people have removed the hump (which is visible if you look into the exhaust port from the manifold side). I don't believe removing the hump is a good idea because it makes the port so large that I believe it will reduce port velocity too much.

I will try to post pics today, I'm still working on the motor...

esteinmaier · Post by **esteinmaier** » Sat Mar 05, 2011 11:40 am

I think I have a couple extra broken heads I can take over to my machinist and have him cut some cross sections to visually see where to port if someone is curious enough to pay for the machinist's time.