In last months issue of Super Chevy they did an article on a 396 build up. Apparantly, the 396 shrouds valves in comparison to a 454 the way a 305 does compared to a 350.
On the 396 they flycut the top of the cylinder wall on each side to unshroud the valves. They were careful not to cut down as far as the top ring would come up at tdc, and they didn't cut out far enough to cause head gasket seating problems. I was wondering if a similar modification would work on a 305.

 

Russ,

That sounds like an idea worth investigating. Any little bit of extra space around the intake would help, and as long as the chamber volume wasn't increased significantly, compression ratio loss would be minimal and could easily be compensated by head milling.

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Later,
Vader
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"I'm gonna talk about some freaky sheet now..."
Adobe Acrobat Reader 4.0
KaleCo Auto Parts

 

Gee, sounds oddly like something Ford did in 1970 to a stupid little engine called the 351C.
I think the best way to unshroud the valves on a 305 is to replace the problem area with 4" bores, aka 350

 

Mad Max, you are right about the ultimate solution being a 350. Actually the ultimate solution would be an aluminum "Rocket Block"
punched out to about 440+ cubic inches, but I'm looking at a budget. I don't race my car. I'm just looking at some free horse power. 305's are cheap because everybody wants the 350. I just want a high performance touring car, I don't care about having the fastest car on the planet. This looked like free horse power, and to my way of thinking, free horse power is the best kind.

 

I seem to recall doing that to a number of 396s over the years... don't know for sure if it helped or not (I am dyno challenged), but it was good for a warm fuzzy feeling anyway. I do know that at least it didn't make them run any worse.

Still, if I was going to all that trouble and expense of tearing one of those motors down far enough to do all that, I believe I'd also install the virtually free at that point missing 45 cubic inches while I was at it.

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"So many Mustangs, so little time..."
ICON Motorsports

 

The additional cost could go toward a 350. If you want to keep the 305, and just maximize it's potential, go for it. You can improve on the stock engine quite a bit. Do a good rebuild and match all the parts to a powerband from idle to 4500-5000rpm. The higer you rev it, the more of an effect the shrouding has on performance. I would ask around and see what it would cost to modify the cylinders.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

 

Use the 305 - Three Zero Five - head gasket as a template.

First use Dykem blue or a magic marker (which'll work in a pinch) and color the area around each cylinder bore.

The lay the gasket in place and with a sharp pointer, scribe a line in the marker coloration to indicate the ID of the gasket.

Now you'll visually be able to see how much, if any metal can be ground away to unshroud the valves.

You can use the same procedure on each cylinder head to unshroud the valves near the combustion chamber walls. Working on the heads will lower compression ratio a tad, but not enough to be noticed unless you really get carried away.

I used to do this on 396 and 427 BB Chevys all the time. On the BB the head gasket was not completely round in shape where it fits around the cylinder bore and the areas where it juts outward is where I did most of my grinding. About a 45 degree angle is what you should shoot for.

BE SURE NOT TO ALLOW YOUR GRINDING TO EXTEND INTO THE CYLINDER AREA TO A POINT WHERE THE TOP COMPRESSION RING WILL MAKE CONTACT WITH THE AREA YOU'VE GROUND. YOU'LL LOSE RING SEAL IF YOU DO.

Hope this helps.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

 

Thanks Jake that was pretty much what I had in mind to do if I ever do a 305. I figured I would also slide in a crank, rod, piston
assy and measure where the piston came at tdc
then take it apart and measure down to the top of the top ring groove. This should give me a good measurement down to the lowest point I could grind without interfering with the ring seat.

 

Isn't that the same thing as chamfering the mating edge of the cylinder and deck before installing the pistons? I'm trying to learn all about this stuff so sorry if it's a stupid question...lol.

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Base: 89 Iroc-Z LB9 auto 2.73 posi
Exh: 3" Dynomax muffler, 3" Pipe in place of cat
Ign: Accel 300+ wires, cap&rotor
Fuel: Cleaned and flow-matched injectors, afpr, !air pump&diverter valve
Sound: Clarion deck, Kicker speakers and amps
Suspension: KYB Shocks, BMR Strut Tower Brace
Misc: TB Bypass, Synthetic Oil, Flexlite Transmission cooler,
free mods, hopefully engine swap and 4th gen seats in the works...

 

Not really. Chamfering is just a slight bevel that allows the rings to enter the bore on build up without catching and perhaps chipping on the sharp edge of the block deck.

What I tried to describe is a method that will cause you to end up with a bore that isn't perfectly round at the deck. It involves the removal of more metal than a simple chamfer.

The area to be ground corresponds to the location of the OD of the valves at a point closest to the bore walls. This unshrouds the valve(s) as a result of the metal being removed from the cylinder bore wall at the deck.

Another trick, when assembling an engine is to bolt on the heads without the crank, rods, etc. installed. A couple of bolts on each head will suffice.

Then turn the engine upside down and look to see how the combustion chamber corresponds to the cylinder bore.

You can do the Magic marker trick here too, and scribe a line indicating how much and where metal can be removed from the combustion chamber. It will also indicate if the head dowel pins are properly positioned. On an occasional BB Chevy, I had to use offset dowel pins to better center the heads.

Hope this helps.

Jake



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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

 

If you can find a copy of the Feb. issue of
Super Chevy magazine, it has a nice picture of what we're talking about in the article on the 396 build up. They called it a "budget build up," but when they put Brodix
Aluminum heads on it, it went out of the realm that I would classify as "budget."