Why a 306?

[Bens95cobra8594]

All -

I have searched but never really found an answer to this question.

I am trying to decide what to do to the engine this winter and wondered why people would bore out a 302 (5.0L) to a 306 (5.1L?)? ? ? I must be missing something because all the work of yanking an engine and boring it for 4 cubes seems counterproductive.

From what I know of strokers, they use bore and a different crank to achieve a higher total cube amnt. So why would someone only want to bore the thing to a 306? Not knocking anyone's work here but just trying to find out some information...

Thanks all.

 

[95Vert]

Well, when I've heard of people doing this is when they break their motor and need to repair it. They take the opportunity and bore it out. Hey 20hp/tq is 20hp/tq. You're right though, I wouldn't pull mine out and go through all the trouble just to do this, but I would consider if I need to reapair it.

 

[Jackie Chan]

generally it is when the internals are freshened up. i would personally just go ahead and go to a 331/347 if i were doing that though

 

[Therian]

generally 306s come about due to a budget rebuild because of an engine failure or heavy blow-by.

sometimes you must bore the engine slightly to accomodate piston clearances.

also it's quite a bit cheaper than buying a new crank for a 331/347

306s also have better potential to spin higher than 331/347 setups

 

[AznStanger3v]

i made mine a 306 shearly because of money issues and time constraints. I was in college at the time and i needed my car back. No more worry of p/v clearance. I wish it gained 20 hp/tq with it. more like 10 at most, and i might be overshooting it. It was also a chance to get forged internals as well.

 

[HISSIN50]

Right-on. It's not done as a means of displacement increasing, but just to get things tight again if a hone won't cover it.

A fresh 306 vs an old 302 (with same parts, like HCI) can be kinda disappointing timeslip wise if someone was expecting times to drop.

 

[Guero]

yeah i only went with the 306, cuz it was the same price as a 302

 

[Bens95cobra8594]

Okay, cool. Thanks for the answers!

 

[Pokageek]

I went 306 because I had 150k on my engine and wanted a new one but I really like the awesome sound of 5.0's.

I didn't know whether a 331/347 would sound the same as that 302 and they were a lot more money than I wanted to spend. So I went 306 with a better cam and upgraded arp rod bolts and some extras..then I added more and more to it until it runs so well n/a that I don't even want the nitrous anymore. It's fast enough at 290rwhp and that is even with cats on the car.

 

[SeventyMach1]

If the walls get gouged or scratched up .... you have to bore it. And leave it at that if you're on a budget.



Since you're doing research .... I made this a year or so ago. Just a chart showing the displacement of different bores/strokes.


STROKE x BORE = C.I.

3.000 x 4.000 = 302 *

3.000 x 4.030 = 306 *

3.000 x 4.040 = 307

3.000 x 4.060 = 311

3.250 x 4.000 = 327 *

3.250 x 4.030 = 331 *

3.250 x 4.040 = 333

3.250 x 4.060 = 336

3.400 x 4.000 = 342 *

3.400 x 4.030 = 347 *

3.400 x 4.040 = 348

3.400 x 4.060 = 352

3.450 x 4.060 = 357


* = common or fairly common.


There is also a way to get a 363 c.i. out of a 302 SBF ..... but I don't know what the exact bore x stroke combo is for that.

 

[AznStanger3v]

If the walls get gouged or scratched up .... you have to bore it. And leave it at that if you're on a budget.



Since you're doing research .... I made this a year or so ago. Just a chart showing the displacement of different bores/strokes.


STROKE x BORE = C.I.

3.000 x 4.000 = 302 *

3.000 x 4.030 = 306 *

3.000 x 4.040 = 307

3.000 x 4.060 = 311

3.250 x 4.000 = 327 *

3.250 x 4.030 = 331 *

3.250 x 4.040 = 333

3.250 x 4.060 = 336

3.400 x 4.000 = 342 *

3.400 x 4.030 = 347 *

3.400 x 4.040 = 348

3.400 x 4.060 = 352

3.450 x 4.060 = 357


* = common or fairly common.


There is also a way to get a 363 c.i. out of a 302 SBF ..... but I don't know what the exact bore x stroke combo is for that.

i *think* its something like:

Bore x Bore x Stroke x .7582(?) x 8

so find the mystery number and youll get the 363. im not in my math mode right now, but it shouldnt take you more than a couple minutes

 

[SeventyMach1]

Pi (3.1416) x Bore x Stroke x # of Cylinders = C.I.


You can't really do it that way. For example, there are 2 different 327's. One uses a different stroke and is very uncommon, IIRC. So you really have more than one variable.

 

[HISSIN50]

i *think* its something like:

Bore x Bore x Stroke x .7582(?) x 8

so find the mystery number and youll get the 363. im not in my math mode right now, but it shouldnt take you more than a couple minutes

That's racers math (I think it's .78XX though. The true value is pi/4).

Justin's conventional math: Pi(R^2) * H * number of cylinders, gets the same thing.

 

[The Green GT]

BIGGER IS ALWAYS BETTER