[Hoongoon82]

So, I’ve had this idea rattling around my head all day, and was wondering if anyone could give some helpful/useful information regarding the subject.

Basically, the major downside of chevy’s 305 is the geometry. It’s got the stroke of a 350, yet a bore of like 3.736. Small bore+long stroke in a gas engine just doesnt make good power. I know there’s issues with the heads, but I’m just talking about the short block here. Basically, my idea is to take a 305, put a large journal 327 crank in it, bore it over as much as you can over bore a 305 (I’m not sure how far you can go, I don’t know a whole lot about the casting of a 305 block), and put domed pistons in it to take up for the shorter stroke because custom pistons are expensive. This would essentially make it closer to an over square motor, and the 327 crank is a little more suited to high rpm. Just a thought though.
Thanks

 

[lmsport]

350 blocks are cheep.
Build a 327.
I always intended to build a 3.25 stroke x 4.155 bore engine for oval racing using some old 18 degree heads I have.

 

[wrenchbend]

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[ericnova72]

The problem with the 305 isn't anything to do with bore vs stroke.....it is entirely bore, as in even at max overbore size the bore is too small, so small that it badly shrouds the flow of any big valve heads.

Max overbore is just .060", just like nearly any other small block....if you are lucky you may sonic check a bunch of 305 blocks and find 1 that will allow an .080" overbore, but don't count on it.
At .060" over and 3.25" stroke its just a 294" deal.....not exactly a barnstormer, especially since good heads won't work on it, you're stuck with small valve crap.

You can't bore it big enough to put a real power making head on it.....so why bother with it?? 350 blocks are still easy enough to find and will cost you less while making 30-40% more power.

There are other problems with your intended approach, but I'll let those three big ones settle in and see if this discussion actually goes anywhere.

If you want to see about the max NA power you could get from a 305 just look at the RaceSaver series 305 Sprint Car class engines....450 to maybe 475 hp max on a $10K+ engine.

 

[BogiesAnnex1]

Yep, the problem with small displacement engines is you gotta spin ‘em faster. That fakes them into thinking there are a bigger engine than they are. Power really comes down to how much CFM of combustible mixture you can run through the engine.

The problem is as always is one of breathing, with small bores there is a lot of interference with through the valve mixture flow by crowding objects like the cylinder wall. A common answer to this is to increase inlet area and at the same time get some distance between the mixture flow and the surrounding structures. There are four ways to go about this:
1. Canted valves think RAT motor valuing on an SBC.
2. Four valves in a pent shaped chamber. Buick with the Nail Head tried this with 2 valves but it resulted in excessivily tight turns in the exhaust ports that killed breathing out.
3. The hemi head with 2 really big valves, as witnesses the 4 valve pent chamber there is more space for bigger valves and the flow of both intake and exhaust is improved by the elimination of tight short side port turns and the flows take aim at or from the center of the bore instead of sling the cylinder or chamber wall.
4. Is the rotary valve where the valving is a double walled cylinder where the inner has inlet and exhaust ports similar to but positioned differently than a 2 cycle engine. Behind and concentric with the inner cylinder bore is a precision fitting outer cylinder with ports that is rocked back and forth by a gear train that opens and closes these ports to intake and exhaust passages. If this seems British, it is.

In the end power comes from the volume or weight might be a better term of combustible mixture you get through the motor in a period of time. RPM is simply a way of making the motor bigger so more mixture is consumed in that period of time. That leads to the problem of how to feed all that mixture. Well the least cost answer for an in-line valve arraigned wedge chamber is a bigger bore begets the space for bigger valves having less interference to their flow by nearby structures like chamber sides and bore walls.

So the small bore of the 305 taps out sooner than say the larger 4 inch bore of the DZ302. Now for you readers you will note the DZ was rated at 290 hp at 5000 RPM, but redline was 7000 RPM. You might consider that GM was messing a bit with your mind as to where the truth about its max power was and by how much more than admitted to.

Bogie

 

[U_Boat]

Small block parts are so plentiful and cheap that any real involved "re-engineering" only makes sense if you enjoy it. Economically, if you want a bigger small block, buy one. If messing around in the garage is your idea of heaven, the parts are cheap and you are having fun, so go for it and see what works. What's the worst that could happen?