Unshrouding valves

[Zmanco]

I've been reading a ton lately about improving heads, and I have to say that this site has the best information, by far, that I've found. In my case I'm currently rebuilding my bottom end (N42 block, flat top pistons) and have my N42 head off the engine. A few thousand miles ago it was rebuilt and I added a mild cam with .441 lift and 260 degree duration. For intake/exhaust I have weber DGVs and MSA 6:1 header w/2.5" exhaust. Before anyone gets on me about the DGVs, I plan to switch to Megasquirt FI once the engine is broken in.

 

My question right now is about unshrouding the valves. If I understand it correctly, the idea is to remove a little material so that the valves can flow better when they are only partially open. Assuming I've got that right, I've put 2 arrows in a picture of my head. The green one is supposed to pointing to the side of the head farther in and the yellow is pointing towards the same side, only closer to the head surface (and top of the piston when it's at TDC). To unshroud this valve, is it correct that one would remove material just near where the green arrow is pointing, or would you also take material off near the yellow?

 

Although I didn't take a picture, I overlaid my head gasket and the inside edge of each cylinder is very close to the edge for each chamber in the head.

 

I hope my question makes sense, please let me know if it doesn't

 

PS. Just realized I can't attach a picture yet, maybe because this is my first post at this site? Use this link to see the picture: http://home.comcast.net/~dbailin/head1.jpg

 

Daniel

'73 240Z

[dapiper]

See my pix in Member Galleries

[Zmanco]

dapiper, I took the liberty of cropping a part of your picture and added a few arrows where I think you ground away some material. Is that correct?

 

http://home.comcast.net/~dbailin/n42_chamber.jpg

 

Also, anyone know why I can't post pictures? The posting rules box at the bottom left corner of the editing page says I may not post attachments.

[JMortensen]

 

You'd be able to see the task at hand a lot better if you cleaned that head up. I suggest you have it hot tanked then start in on it.

 

The answer to your question thought is both. You want to smooth the area from around the valve seat so that there isn't a ridge around the seat. This will allow the head to flow better at low lift. You want the max open area around the side of the valve where it comes closest to the headgasket. This is the unshrouding part. What you need to do is take the headgasket and lay it on the head, then use a scribe to mark where the headgasket sits on the head. Don't go past the line, because you don't want the top of the headgasket exposed. Then you grind away until the max amount of room is available around the side of the valve.

[JMortensen]

You're missing the image tags. Put one in front and one behind the URL like this (img)http://home.comcast.net/~dbailin/n42_chamber.jpg(/img) except use the brackets [] instead of parentheses.

[Zmanco]

Jon, thanks, that helps a lot. I'm debating whether I should attempt this. I've never done any porting or other head work myself and have read that unless you know what you're doing, you should probably leave it to someone else since you can make it worse rather than better.

 

I do have a scrap N42 head that I can practice on, so I'm kind of leaning towards trying it. It seems like I'd only be taking off at most 2 or 3 mm of material. Does that sound right?

 

I wish I had someone here in CO who could "look over my shoulder" so I don't take too much off. As good as dapiper's picture is, I would feel a lot better if I had a before and after pictures to use as a gauge. Anyone have anything that would help?

[Zmanco]

Another question: after hot tanking, could I do this without taking the head apart? Of course my concern is leaving behind any pieces of aluminum. What if I tape the valve cover on and mask off the all the manifold openings and oil and water passages?

 

Or am I playing with fire?

[dapiper]

That's my second head and don't feel scared, just take your time and you'll be fine. First one was with a drill, but much better to use die grinder with the right tool. Will try to post better pix, meanwhile send PM and I can show tool used that allows undercut of sides of chamber. You may loose some idle vacuum. I removed 3.5 cc each chamber. You may need to clean up some more after valve job, since grinder will sink seats some and create some ridges.

[madkaw]

Not to high jack this thread but I have a similiar ?? I followed the suggested unshrouding procedures in how to modify. What I had a problem with is that i used the headgasket to unshroud the head to the fire ring but when you lay the gasket on the block(l-24), the fire ring extends beyond the bore along the sides where the valves are. Are the head gasket combustion chamber cut out oblong for a reason. Or was this procedure targeted for the larger combustion chambers of the 2.8. I am using the e-88 with larger valves and notched the block.

[BRAAP]

Hmmm Looking for unshrouding info eh…

Does this help?

 

 

Maxima N-47 roughed in…

 

Custom polished exterior N-42 in the rough in stage…

 

These next few are of a custom Welded chamber N42 at various stages..

 

 

 

 

 

 

And a P-90 that we just shipped out this week.

 

 

 

 

Does that help?

[Zmanco]

Thanks Paul, the first 2 of the roughed in views are really great, that's the first time I've been able to really see where the grinding was done. It's a lot harder to see in a picture AFTER it's all polished.

 

I do have a question: on the N42 head, why did you take material off the bottom half (as viewed in the picture) of the chamber? Seems like it would just lower the compression without having much impact on flow. Or does it impact flow?

 

Also, what did you use to do the rough in work? Was it a stone, or perhaps one of the sandpaper tubes (don't know the proper term for it)?

 

I'm building up my confidence to attack this:)

[BRAAP]

I’m assuming you are talking about the N-42 chamber that wasn’t welded. The sanding wrap marks are just for removing the “as cast” finish during the process of polishing, going to finer and finer sanding wraps to a polished finish for that head. We had no intention of removing material other than to get a polished surface.

As for what tools we use, For Aluminum heads like the L-series, We use cutters for non ferrous metal in a die grinder, (no Dremel tools here. I ported my very first head for myself using a Dremel and will NEVER do that EVER AGAIN! Dremels are for modeling, not porting.) These non ferrous cutters are more aggressive than ferrous metal bits and don’t clog as easily when carving on metals such as Aluminum because of the angles ground into and on the flutes of the cutters themselves. For porting Iron heads, such as OE Chevy heads, we use the ferrous cutters. We only use the sanding wraps to remove the high spot of the divots left behind from the cutters.

The picture below represents only a small portion of all the porting tools we use to port heads. The cheapo fat die grinder on the right is for hogging and the long skinny Dotco grinder is for finish work. The cutters along the top left are for aluminum, (non ferrous), and the cutters in the middle are for porting Iron heads. The dead valve on the top are my sacrificial L-series valves. They are nothing more than a pair of sacrificial valves which will help protect the valve seats from runaway die grinding efforts, and trust me, it WILL happen no matter if you have only 30 minutes experience or 2000 hours behind a die grinder, it still happens once in great while and those sacrificial valves will protect the seats from having to replace them because of an uh-oh. Speaking of run away cutters, “when” that cutter does grab and takes off across the head, if you position yourself and the cutter in such as way that “when” the cutter does take off across the head, it will do as little damage as possible, i.e. divot tracks across the deck surface, big gouges in the spark plug threaded hole, removal of to much material causing the head gasket fire ring to over hang the chamber requiring rewelding, etc. The more damage you cause, the more machining and material removal needed to clean up those uh-ohs. Tricks like positioning the cutter in such way that “when” it does grab and take off across the head, it only goes across the open chamber and not the deck surface. This requires repositioning yourself and the head in several positions for each and every chamber. Porting is very time consuming, patience demanding, job that requires experience to get it right.

If you have never done this before and are dead set on trying it yourself, try using a scrap head for practice. I don’t mean just doing one chamber and then moving on to your good head, I mean complete the head to its entirety, as mistakes will be made, and a scrap head is the best place to make the biggee mistakes. Making these mistakes on scrap head will help point out where your weak points are in regards to keeping the cutter from getting away from you. Using a scrap head in this manner allows you to mess up as much as needed so that you can establish little tricks that help you and your technique in keeping those inevitable uh-ohs to a minimum.

Hope that helps.

 

[phantaz]

You need your own forum on here Paul =).

links to pictures, guides, and general help. its not like you dont ramble enough once you get going LOL

 

love your posts though.

 

ok question.. in the first pic of the maxima head the areaaround the spark plug hole was still humped up.. was that removed later or left ? and for what reason was it left if it was? maybe a stupid question but an honest one.

 

thnx

 

Paul

[BRAAP]

Ok. Due to the secrecy of the PINKS project up to the day the race aired, the custom P-90 cylinder head that we built for that project had to be kept on the down low, which was at the time I posted those pics. Now that the race is over, I can let the cat out of the bag. The head that we shipped that week was actually indeed the P-90 head for the PINKS project…

 

Here it is, the PINKS P-90, just prior to assembly…

 

BTW, Garret, (The PINKS driver), informed me that the car ran 124+ MPH trap speed… YEE HAAA…

 

 

 

 

Hmmm Looking for unshrouding info eh…

Does this help?

 

 

And a P-90 that we just shipped out this week.

 

 

 

 

Does that help?

[hughdogz]

Hey everyone, you guys wanted to see some more "roughed-in" pictures?

 

Paul was generous enough to show me how to do this today...I had the same questions and luckily I don't live too far from Rusch Motorsports!

 

He did all the grinding work for cylinder #1 (although he saved the finer abrasives work for me). We didn't mess with the intake, since the ROI is negligible compared to the exhaust and combustion chamber. I'll do my best to duplicate his work for the rest of the cylinders.

 

This is a P90 head...

 

Shrouded and bulge in the bowl (notice the hump of material around the depressed valve guide):

 

 

Unshrouded & smooth bowl:

 

 

There is also some work in blending the floor transition, but I'd have to cut my head apart to show you that.

 

I can start a new thread documenting the steps, etc.

 

Also, I would like to thank Paul again for his generosity, he is a great guy!

 

Here I go, there's no turning back now!

[Daeron]

Hugh:

 

Thanks for the pic post!!! that much more knowledge and confidence to go at it myself, when the time comes.

[jgkurz]

Hey Hugh, I was at my machinist today picking up my new downpipe I had welded up and guess what I saw....

 

A very nice P90 head just waiting to be ported.

 

He said he was just cleaning it up for you. Do you have big plans for the head? I'd enjoy seeing how a ported head helps your L28 turbo.

[MONZTER]

Can someone explain to me the difference and advantages between "flow" and "velocity" It seems to be you can make a port flow by opening it up, way up, but then people talk about loosing the velocity if you go too big. It seems for a NA motor you need the flow for High RPM and the velocity for low RPM (we always want it all)?? But what about a turbo motor? Is velocity less important because of the turbo? how does all this affect off boost vs. on boost? The American car guys quote port volume, and I believe it relates to the size of the engine being built, a bigger motor needs more air, but will it also tolerate the bigger port volume due to the fact that the bigger engine also increases the velocity? Am I getting this correct?

[MONZTER]

Can someone explain to me the difference and advantages between "flow" and "velocity" It seems to be you can make a port flow by opening it up, way up, but then people talk about loosing the velocity if you go too big. It seems for a NA motor you need the flow for High RPM and the velocity for low RPM (we always want it all)?? But what about a turbo motor? Is velocity less important because of the turbo? how does all this affect off boost vs. on boost? The American car guys quote port volume, and I believe it relates to the size of the engine being built, a bigger motor needs more air, but will it also tolerate the bigger port volume due to the fact that the bigger engine also increases the velocity? Am I getting this correct?

 

I just found the answer to my questions

 

http://www.highperformancepontiac.com/tech/0211hpp_cylinder_head_flow_testing_ii/

[hughdogz]

Hey Hugh, I was at my machinist today picking up my new downpipe I had welded up and guess what I saw....

 

A very nice P90 head just waiting to be ported.

 

He said he was just cleaning it up for you. Do you have big plans for the head? I'd enjoy seeing how a ported head helps your L28 turbo.

 

Yes indeed. I'm gonna port it. Well, I may port this one...

 

The head you saw is actually a small part of the "big plan" which I won't bore you guys with at this time...plus it is top secret j/k. It will get relatively mild unshrouding and exhaust runner work...really just smoothing out the stock restrictions.

 

I hope you were able to check out cyl#1 that Paul did the die grinding demonstration on. Just this mild work should help it breathe a lot easier. I'm going small now so I can get experience...and if I mess up, not as much material will have to be re-added...hopefully not any.

 

It will then go back to Rusch Motorsports to get the seats cut, 5-angle valve job, my work inspected and cam installed...But, with just this mild amount of work, I'm kind of reluctant to use the head with the OEM EFI...even with a stock cam because of the VE change. I won't be able to tell the before / after effects of the head work alone due to my plan unfortunately (I'd really like to know via dyno numbers too!! Hmm...I know where there is a flowbench )

 

I have to get the Wolf3D system ready to go before I can even think about installing the head...this whole upgrade thing is proving to be a challenge for me.

 

Turbo downpipe huh? I really need to get me one of those soon too...probably better to do the DP first before the head porting like the route you've chosen.

 

Whoo hoo!! I'm getting the head back tomorrow!