Bore Notching

[RLander]

I have another 390 that I would like to build up. Due to the obvious smaller bore I have been looking at notching the area around the intake valve. I have seen this done on some brand x engines on both sides. Would I gain any flow with the notches? Would it be worth while doing both intake and exhaust sides? Or is this a mod only reserved for Engine masters.
Thanks and Best Regards
RLander

[jayb]

Do you need to notch for valve clearance, or just for flow?  I've notched 390 bores to fit big valves in the past, but never to improve flow characteristics.  That actually sounds like a great flow study subject, because I'll bet you would pick up some substantial flow if you did that.

The biggest thing to consider when notching the bores is where the top ring on the piston will end up at top dead center.  You don't want to notch into this area, of course, and I'd probably recommend a .100" safety margin between the top of the top ring and the bottom of the notch.  Also, you don't want to notch the bores so far that the head gasket hangs over the notch.  Get the head gasket you want to use installed, and mark the top of the bore so that you don't undercut where the head gasket will be located.

Offhand I can't think of any other major issues.  The block deck is thick up at the top of the bores, of course, so you should be able to notch the cylinders as much as you want within the previously stated constraints.

[RLander]

I found the article from engine masters in my mag collection. Its from Dec/08. Its for one of their entries (350 chev) and a (318 mopar) & on the front at the top it says Bore Relieving for flow and power. Searched the internet and there is not much out there (including the article) . Mostly chev stuff with 350 heads on 305's. I plan on investigating this on the 390 I'm going to build up once I get my hands on a set of Edelbrock heads. Seems to be simple and may be worth 10-30hp depending on where you get the information.
Best Regards,
RLander

[Qikbbstang]

Rebel George studied one of my side-oilers to copy the relief prior to running big valve High Riser Heads on his marine based 427. I think he made up a template to get the placement.

[TorinoBP88]

My machinist will do a little of this as a matter of practice, he will clearance the intake and exhaust area of the cylinder bore a touch, claims it helps the flow somewhat.  No direct testing to prove it.  We just finished a Boss 302 (342 CID) type engine with Cleveland heads, had to (or chose to) notch the cylinders for that as well. He does manage to build 600 + SBC and SBF's and other stout engines by the seat of the pants, so ill give him that.

He also un-shrouds the chamber to match the chamber work to help the swirl (if that is possible in the old wedge FE's, as they don't swirl too well... according to carbon tracks on the pistons and such.)

[rcodecj]

I have another 390 that I would like to build up. Due to the obvious smaller bore I have been looking at notching the area around the intake valve. I have seen this done on some brand x engines on both sides. Would I gain any flow with the notches? Would it be worth while doing both intake and exhaust sides? Or is this a mod only reserved for Engine masters.
Thanks and Best Regards
RLander

I remember years ago I put cj exhaust valves on my .030 over 390, mounted the heads on the bare block, and look from underneath. Man there wasn't a lot of room, and it did seem like notching the area would have helped flow. I now am running a 2.2 intake and 1.66 exhaust on a stock bore 390.  If I remember correctly the exhaust is more critical room wise than the intake, but hopefully someone will chime in if that's incorrect. I would love to see a dyno before and after on notching the cylinders, I am sure it would help, especially on a 445 stroker.

[jayb]

I remember years ago I put cj exhaust valves on my .030 over 390, mounted the heads on the bare block, and look from underneath. Man there wasn't a lot of room, and it did seem like notching the area would have helped flow. I now am running a 2.2 intake and 1.66 exhaust on a stock bore 390.  If I remember correctly the exhaust is more critical room wise than the intake, but hopefully someone will chime in if that's incorrect. I would love to see a dyno before and after on notching the cylinders, I am sure it would help, especially on a 445 stroker.

Was that a hint?    I agree, that would be an interesting dyno test.  I will keep that one in mind...

[rcodecj]

I remember years ago I put cj exhaust valves on my .030 over 390, mounted the heads on the bare block, and look from underneath. Man there wasn't a lot of room, and it did seem like notching the area would have helped flow. I now am running a 2.2 intake and 1.66 exhaust on a stock bore 390.  If I remember correctly the exhaust is more critical room wise than the intake, but hopefully someone will chime in if that's incorrect. I would love to see a dyno before and after on notching the cylinders, I am sure it would help, especially on a 445 stroker.

Was that a hint?    I agree, that would be an interesting dyno test.  I will keep that one in mind...

No, not a hint, just thinking that I might be changing head gaskets on my 390 and I've got big valves in it and it's standard bore. It might be worth the effort to notch the top of the bores when I have it apart. My 390 may not see much improvement, but a stroker, I can't see how it wouldn't help. And I would love to see a dyno test on......

[billballinger]

The exhaust side is tight, but .060-.065 of clearance is really all that is needed, the important side is the intake, .225 at least clearance is needed according to Darin Morgan formerly of Rehrer-Morrison.  A small relief would not hurt anything, except that it is only leading the flow into a dead spot in the port on the outside.  In other words it won't accomplish much either.  The main concern is that the valve never hits the bore.  Loose or knurled guides really makes .060-.065 a minimum.