I have my motor torn apart currently and have the perfect opportunity to notch my block to help unshroud the valves a little. The head gasket and fire ring left perfect stencils for what material I need to remove. Now as I understand it you are supposed to measure 1/16" of an inch up from where the fire ring stops in the cylinder bore and taper back to where the head gasket outline stops on the block deck....does this sound accurate? I am a little worried about bore integrity (my block is .060" over). How much material is safe to remove?

I was also wondering about off set dowel pins. Can they be used in conjunction with the block notching? If so, wouldn't that change the notching locations? Thanks!

 

I have never heard of block notching; just the idea makes me nervous. Combustion chamber work, on the CYLINDER HEADS, yes... opening up combustion chambers to relieve area around the valves, and using the head gasket as a guide... followed by machining of the mating surface to get your CC's back in line. I have had blocks relieved in the crank area for rod/throw clearance on a stroker motor.

Relieving the tops of the cylinders in the block would accomplish absolutely nothing to help airflow... or are you using gigantic valves? The cylinders are already huge holes as it is. I am intrigued - who might have given you this advice? Maybe I've been living in the dark.

 

 

what size valves are you using that you feel a benefit could be achieved by block notching? It is usually done when much larger valves than stock are used.

 

Dumb question: Doesn't his block being 0.060" over mean that all of his cylinders already have "valve deshrouding" done on the cylinder side?


Adam

 

JoeMinnesota:
I can definitely see how it would increase flow and horsepower. I need to take a picture of my deck surface and maybe it will better demonstrate the cylinder shrouding that is occurring. Where my head gasket was there is a clear moon shape where flow is impeded by the deck surface. Rounding off that ledge allows a more direct/smooth transition into the bore. I'm just not sure what the limits are with modifications like this. People have done it with .100" over 454s. It is supposed to be good for 5-10 horsepower depending on how shrouded things are. I am curious if anyone here has done this?

MelWff:
2.25/1.88s with a 4.31" bore. 2.25s from what I've heard, in a 454 size bore, causes some shrouding from the cylinder walls due to their diameter. Notching the tops of the cylinder walls with a taper is supposed to help smooth out the travel of the air/fuel charge into the cylinder and also with the exhaust's exit from the cylinder. Without the block notching you can clearly see that the block deck creates a ledge for the intake and exhaust.

NewbVetteGuy:
Yes you are correct, boring out a motor does help some with shrouding. Offset head dowels will also help with it, I'm just curious about the two being used together. It may seem like small potatoes (5-10hp) but a lot of little things eventually add up to a big thing.

 

I have notched every high performance BBC build. Have yet to experience a problem. I Have never used offset dowel pins though.

 

396 and 402 had notched bores. Some 427 and 454 also.

 

I in the distant past I owned two notched bore 396 HO motors. You have to remember that the notch is near the top of the bore not down on the thinner cylinder bores

I would try and find some bbc blue print diagrams to see what the factory motors were

the offset dowl is also the rage to shift the heads to the front of the block. 030. Getting the intakes out into the bores. Especially when using 2.30 intakes

the notch wasn't tapered and it was right down to the cylinder ware Ridge right at the top of the first ring.

 

When a couple of drag racing Corvette people built my '64 for the street ~30+ years ago, they notched the block.

Engine was done right and makes great power for what it is and has been stone reliable all this time even after throwing the belt and overheating once.

331 CI, pump-friendly 9.5:1 CR
K&N 14"x4" air filter, Corvette drop base and lid
Holley 600 dp, choke horn milled and blended, Primary - 69, Secondary – 74, Squirters - 21
1/2" Aluminum open spacer port matched to manifold, exterior polished
Edelbrock Performer RPM intake manifold, port matched, exterior polished with all extraneous castings and lettering removed
Homemade lifter valley splash shield to keep hot oil off manifold bottom
Manifold heat riser crossover blocked
Camel hump 1.94/1.50 heads hogged out to 2.02/1.60, pocket ported, port matched, pump-friendly hardened seats, 3-angle valve job
All porting and port matching performed by Juan Mendoza of Flow Technology
Cylinder bores clearanced to unshroud the valves
Comp Cams 1.52:1 roller-tip rockers
Crane Cam Vintage Muscle 327/350 hp cam, 222 degrees @ 0.05, 0.447" lift (with 1.50 rockers)
Doug Thorley headers, dechromed and ceramic-coated
2.5" mandral-bent exhaust (including tips), 2" cross-over just before rear axle
DynoMax stainless Ultra Flow mufflers
Millerspeed 1-1/2” Gilmer under drive belt drive system
Mallory Hyfire IV CD ignition box triggered off Accel points
Mallory high voltage chrome coil
Mallory spiral-wound coil wire
Mallory solid copper plug wires, ends soldered to wires
Champion plugs
37 degrees total ignition advance
Carter high volume fuel pump
Melling high volume oil pump
Open breathers
Polished aluminum high flow water pump
160-degree thermostat
Flex fan with polished aluminum spacer
Polished aluminum one-wire 100 amp alternator
Header Power Bracket
Keisler TKO600 5-Speed
Hurst shifter
3.70:1 positraction with Big Block yokes
225/60/15 Firestone Firehawk SZ50s on 7”-wide Western 30-spoke Turbine Wheels

 

I notch every one. Or to be more accurate, I pay my machine shop $50 to do it for me. If they screw one up, it's on them.
All you need to do to see how much it helps is to bolt a head onto a block with a couple of head bolts, get 'em snug. Flip the block over and reach up through the bore and feel the huge obstruction that the deck has where the chamber hangs out past it.
Cool thing is that once it's done, you reap the benefits from that point on, every rebuild.

 

it is worth 30 hp on a 454 or smaller i have heard. less on a 502. i have a pair of late MK4 350 hp 454 in my 34 hatteras. peanut heads 2.06 valves and they were notched at the factory. OP sounds like a small block guy. don't know about notching a small block. you can really do yourself with a small drum sander. just stay inboard of head gasket ring and above top ring.

 

 

Every 4-bolt main short deck block I've had my hands on had notches from the factory.

My guys use a Serdi machine to open the chambers to very close to the gasket line. They use the same gasket to trace the outline on the deck and use that plus a depth mark to do this.

If it hasn't been developed yet, there has to be a way to get a CNC block machine to do this safely and quickly.

 

on the street,you don't need every last HP,you need a reliable eng,,that last 20 HP you can wring out ,wont make a difference ,you want to make more HP make the eng bigger,throw a 1/4-1/2'' stroker crank in it,,

heck ive got 2 fresh 588''BBC engs that make 750hp on pump gas,,put one in and be done with this HP stuff

 

Milan454:
Thanks for the confirmation, it eases my worry quite a bit. I haven't decided on the offset dowel pins for sure yet. I wanted to make sure the block notching was safe for a street motor and probably start with that.

gkull:
I also worry because my block has a "0" deck, whereas the pistons used to be .020" down the bore, they are now at .000". Is this something I should worry about or do you feel there is enough material there?

L88Plus:
That was kind of my thought as well. I pulled the heads and the carbon left a perfect stencil for me to let me know where the obstruction is and where to remove the material from. It is pretty easy to see how it would increase air flow across the board.

derekderek:
That is the plan, to use a dremel tool and remove the material myself. From what I have read you are supposed to stay at least 1/16" above the fire ring and stay within the head gasket.

JoeMinnesota:
I don't think it is limited to just big blocks. When I was talking to my machine shop I thought they mentioned doing it to a number of small blocks but I could be wrong.

dmaxx3500:
I almost always need every last horsepower, that usually helps cancel out mistakes in my motor that are costing me horsepower lol. I want to stay with a factory size motor and see what I can get out of it on my own but I see what you are getting at.

 

I'll see if I can dig up a pic of one that's finished.
The shop actually uses a cylindrical cartridge roll rather than a cutter, it's easier to control and has less chance of skating across the deck. Stand the block on end and raise it to a good working height, keep the roll flat. Start in the center and work your way back and forth, sneak up on it. I'd try to find a way to lock an old junk flat top piston in place to act as a guide.
Make sure to have the shop unshroud the intake valve to a point close to the gasket line which will help even more. I'm kinda **** about it, I use an old gasket and bolt the head to the block with a couple of snugged bolts, then feel inside each one and mark and tweak it until it's a smooth transition. I look at it and treat it like an intake manifold gasket match.

 

L88Plus:
That is some great information. I was planning on using a sanding roll, it will likely take much longer but like you pointed out it should be a little easier to control and gradually remove material with. I actually have some old flat top pistons laying around so that isn't a problem. The heads are already at the machine shop having the valves unshrouded (I didn't feel comfortable doing that task). I just need to wait for them to get back from the shop and I can start notching. I like your process of bolting the heads on with a head gasket and using that as a guide, I hadn't thought of that. Thanks for the information.

 

Bolt the head gasket to the block. If you dont touch the gasket, you didnt touch the deck there. When moving gasket from block to head for this, you have to move the dowel pins too.

 

You/they are correct, and it is more important if using, or going to, 2.02" or 2.05" intake valves.