Eyebrowing a block

[MONZTER]

I know eyebrowing an L-24 block is necessary when running l-28 valves in the head, but what about eyebrowing a L-28 block that will be turbocharged? Will this improve the flow by helping to un-shroud the valves? My biggest concern is that it will expose the top ring more, will this cause the top ring to be overexposed. Does anybody have an opinion on this?

Thanks

[G.I.jonas]

Do it anyway,whats the worst that could happen? pistons flying into your face and possibly killing nearby babies as well.Stop being a sally.

[Daeron]

Do it anyway,whats the worst that could happen? pistons flying into your face and possibly killing nearby babies as well.Stop being a sally.

 

and then the sig, "the most successful people are the ones who are good at plan B."

 

PRICELESS!!!

 

Well, it wouldnt be a wise idea if you are running a P-series head, because that "unshrouding" would be defeating the high-quench design of the head, and may lead to a tendency towards predetonation. I am kinda parroting a little, here, so I hope someone comes along and backs me up, heh...

 

but otherwise, if its actually a scenario where you would be unshrouding the valves and improving the shape of the combustion chamber, I suppose it could help.. its not just a simple question of "should I do it or not," its an issue of combustion chamber design; do you want to alter that? are you comfortable designing your own, thumbing your nose to the engineers at Nissan, and the folks at various machine shops? I don't.. (at least not until this thread develops quite a bit and we all learn something, like a quality epsiode of your favorite family sitcom. )

 

I'm trying to be funny, and it may be taken as offensive, so advance apologies if needed, but I am making a point, too...

[MONZTER]

My plans are to use a welded N-42 head, I will weld it up to generate the quench. This will make the volume too small for a Turbo application. So what I will do is unshroud the valves back to the 91mm head gasket. The bore will be 88 or 89 (havnt decided yet) so the head will be wider than the bore causing a step. Eyebrowing the bore will smooth this out and again help to lower the compression ratio down, along with custom dished pistons.

 

[JMortensen]

If you eyebrow the same area where you unshroud the valves on the head, you'll have a relatively smooth contour around the valve which will help flow. The valve will actually open into the chamber, so there will be a nice smooth curve around the valve head, then the cylinder wall will be right in the way if it hasn't been eyebrowed.

 

Do the same thing you did on the head, lay the gasket on the dowels and mark the area to be eyebrowed, then break out the die grinder and get to it. Especially on an L28 there isn't much metal that can be removed, so it's not a very time intensive procedure.

 

You need to be careful that you don't go too deep into the cylinder, but it would take a lot of effort to screw that one up I think. I think the recommendation is that you eyebrow no closer than .070 above the top piston ring, should be in the How to Modify book. That still means you're getting in there quite a ways.

 

Be careful taking either the head or the block all the way out to 91mm. Do some searching and you may find it, but there was a thread maybe 3 years ago where that was discussed and it seems to me that there was some negative consequence on the flowbench from taking too much metal from around the valves.

[MONZTER]

Thanks for advice. I did hear about hurting flow by taking out too much out around the valves. I am running OS valves 46 intake 38 exhaust, so I wonder how this would apply. I wonder if the flow was cut down due to the head being so much wider than the bore, or if it was because of the redirection of the flow, due to the fact of more room all the way around the valve. I will have to do some hard searching.

 

Thanks Jeff