displacement

[txchevy]

why does everyone dog 305s. everyone talkes about how fast the old 302 camaros were and the had only 3 cubes smaller. is it the fact that the motor has been destroked so the powerband moves up in the rpm range? just wondering. i have a 305 to rebuild to put in my car but wondering why every one hates them. can i destroke a 350 to 302 or would it cost too much?

[89IROC&RS]

The reason the 305 gets dogged is its poor bore to stroke ratio. The 350 and 302 had large 4in bores which allowed large valves and increased port flow. The 305 has rather small 3.736in bores that shroud the valves and decrease port flow. This means that the 305 with the small bore and long stroke makes good low end power but gets weak in the upper rpms.

The reason the 302 was such a terror was that it was the opposite, down low it didnt make alot of power, but once you wound it up it had low piston speeds, great port flow, and could rev to 8000rpms.

As far as making a modern day 302, the main problem youll run into is finding a crankshaft. To my knowledge there are three possible methods.

one, find an old (pre 1987) block with a 4in bore, then find an old 302 (good luck) or 283 crankshaft and then get the nessesary connecting rods and pistons to fit.

Two, get a post 87 block with a 4in bore, and the crankshaft out of a 4.3L LT1 engine that can be found in 94-96 B-body sedans and wagons.

Three, call up scat or another name brand manufacturer and have a custom crankshaft made for your application and use whatever block you have laying around.

[txchevy]

good thing i didnt waste my money building the 305

[89IROC&RS]

well dont get me wrong, you can definatly mod up the 305, and to be honest, it will probly be a very strong daily driver, just dont expect to be banging 5000rpm shift points and running at top speeds on the highway. Remember that any mods you do to the 305 short of pistons will transferr directly to a 350 or other small block. this includes intake, headers, and so on and so forth. So if you dont have the money right now for a 350, you can mod the 305, and transferr everything to a 350 later. Also, check out chevrolet high performance magazines web page, they built a project 305 with vortec heads and TBI that made over 330hp, so there is hope for your 305. Its just that its going to be at a lower rpm range than would be possible with the more performance related brethren.

[CamarosRsweet94]

What about the Chevy 327? Wasn't that a pretty strong motor? How does it compare to the 305 and 350 bore and stroke wise?

[89IROC&RS]

cid = bore x stroke
283 = 3.736(?) x 3.00
302 = 4.00 x 3.00
305 = 3.736 x 3.48
327 = 4.00 x 3.25
350 = 4.00 x 3.48
383 = 4.030 x 3.75
400 = 4.125 x 3.75

that pretty much covers the most popular displacements. The only one im not entirely sure of is the bore on the 283, if im wrong someone call me on it. i dont really have time to check it myself.

[Link85x]

Originally Posted by 89IROC&RS

cid = bore x stroke
283 = 3.736(?) x 3.00
302 = 4.00 x 3.00
305 = 3.736 x 3.48
327 = 4.00 x 3.25
350 = 4.00 x 3.48
383 = 4.030 x 3.75
400 = 4.125 x 3.75

that pretty much covers the most popular displacements. The only one im not entirely sure of is the bore on the 283, if im wrong someone call me on it. i dont really have time to check it myself.

it's crazy how the little bit of percentage in the bore can make so much of a difference. 89 any idea how much it would cost to get the 305 bored to a 350?

[89IROC&RS]

cant do it, the 305 although very similar to the 350 block, has different water passages. If you were to bore a 305 out to a 4.00 inch bore you would hit water jackets in the block and ruin it. If you want the 4.00 bore, you have to get a 350 block.

[CamarosRsweet94]

What determines the RPMs at which the engine will produce the most power? And what determines piston speed and how high the engine can rev without damage?

[89IROC&RS]

wow, complicated question, there are alot of variables, head design, cam profile, journal sizes, bore to stroke ratio, displacement, naturally asperated vs forced induction, exhaust design, intake runner length. so without giving a class on engine design lets do a simplified version based on what weve been talking about.

With the 305, its small bore, long stroke ratio will give it very high piston speeds for a given displacement, this will create high port velocities in the heads with small valves dictated by the small bore. At low rpms this works to better pack and evacuate the cylenders, however as speed increases, there is less and less time to fill and evacuate the cylenders and those small valves, with those high piston speeds will choke the engine, and it wont be able to fill the cylenders proporly meaning less power at higher rpms. Youll also notice the cam in the 305 engines are rather on the small side, which further aids in creating a cork in the airflow into the engine. Creating very high low rpm port velocities, but cutting off airflow at high speeds.

Now the 302 was a rev happy motor, with its large bore and short stroke the piston speeds were very low, the piston didnt move much from tdc to bdc, the larger bore alows larger valves which remove the cork in the system we are plagued with in the 305. The combination of larger freer flowing ports and low piston speeds allow the 302 to rev up to 8000rpms and still make power. The cam for these engines has generous lift and durration to allow the cylenders to fill. However what youll notice is that due to low rpm port velosities and bad turbulance, you will suffer some low end power losses, not unlike the blackbird these engines were designed to be running fast, and didnt like running slow.

[CamarosRsweet94]

Ok, thanks for the in depth description. I probably sound like a Noob asking a question like that but I was curious. This is why our mods ROCK around here, cause they know their shit.

[txchevy]

i wonder what the ideal bore/stroke and bottem end would be for 500hp and to pull most of the torque around 2000 to 6000 rpms. i want to spank ls1s easily in my thirdgen. i can put money into the car as is i dont drive it much. i weighted it yesterday at the scales at the junkyard. it cost me 5.00 my car weights 2,978 pounds. how much lighter is it than a 4th gen

[Link85x]

89, you were right about how the 305 pretty much falls flat around 90, but i was wondering if work is put into the motor can it accelerate to speeds over 90 decently(bad choice of words). It still has pull, just you don't feel it as much. Say when people run the 1/4mile and get trap speeds over 100, can the 305 be made capable of doing so? Also, since you said it will have great low end power, does that mean excellent 0-60 times?

[CamarosRsweet94]

So how did GM work up the LS2 and the LS7? Those engines are hugedisplacement but are still SB. I know the stoke on them is crazy long but how did they bore the 6.0L LS2 out to 7.0L for the LS7?

[95LT5]

TX Chevy, '89 IROC made a good point of why the 305 motor is lack
luster. Another point is the milder cam lift and more restrictive heads as compared to L98 heads. At my shop, we only have a few 305's come through every blue moon. What we like to do with them is increase bore,
put compression around 10.65:1, run Wiseco forged pistons, little better heads, and a custom cam w/ 1.6 rockers, last but not least a N.O.S nitrous kit in which we convert to wet system and allows a 75-150 horsepower boost, great for high rpms. The destroke to 302 crap is just impractical and too expensive.