Firebird 305

I have a 305 bored .40 with flat top pistons just wanted to no if anyone nos how much hp and torque gain I could get

sofakingdom

iTrader: (1)

Probably not .40; probably more like .040. (40 thousandths)

HP "gain" is negligible from that one factor alone, all else being equal. (assuming replacement flat-top pistons vs stock flat-top pistons) Which of course it never is. Wouldn't be surprised if it was a HP LOSS, new engine compared to other new engine. The list of reasons is long, too long to type out.

I'll stick with "negligible" for the time being.

Firebird 305

It Is completely built had v pistons in it factory has a 2102 elderbrock cam 650 elderbrock carb performedr high rise in take intake ne valve job

ASE doc

An overbore can improve cylinder filling and evacuation by unshrouding the valves. Any improvement is small at best and to capitalize on it you would need higher flowing cylinder heads. In the case of your apparently stock heads, the improvement would be negligible. You do pickup about 4 cu in, so there is that. Your stock 305 makes about 145hp, which works out to about 1.4hp per cu in. If you do the math, you may have gained 6hp from the added cubes. Don't mean to burst your bubble, just giving an honest answer. The cam and intake manifold change may be worth something in added torque, which is what you'll feel when driving. HP from a small motor comes from sustaining torque at higher revs, which you're not going to do very well with stock heads regardless what else you do.

To ask anyone to guess at what the increase might be is a stretch. Try an online HP calculator. They are usually not too accurate but better than a guess based on some part numbers.

Edit: WTF was I thinking. I meant 1.4 cu in per HP, or a little less than .5 hp per cu in. That's assuming this is an LG4.

Tootie Pang

iTrader: (2)

Stock Bore is 3.74"

Stock bore at .040 over is .080 on the diameter for a new bore size of 3.82" bore which is 3.82/3.74 = 2.14% more cubic inches which probably gives you a 2.14% power gain.

However if your compression is lower due to the bigger bore, you would lose more power than the 2.14% gain.

nhgator

But,that Elderbrock stuff tho...........

WildCard600

All the whorespower.

Orr89RocZ

iTrader: (20)

Could be decent if the old bore was worn and ring seal wasnt as good. Nice fresh round honed hole with new tight rings, especially if a smaller ring package than stock could free up a decent amount from improved sealing, reduced friction. Depends on what was in there and what was replaced with

but few more cubes could be worth 1 hp per cube since these motors produce slghtly less than that

Orr89RocZ

iTrader: (20)

.040 over is just .040”. Its not doubled. Stock is 3.736. .040 is 3.776. More bore increases compression all else being the same

BadSS

There’s a lot of bad math in this thread.

.040 overbore is just that – an increase of .040” on the DIAMETER over stock. A stock 305’s bore is 3.736”. If it’s 0.040” over the bore will be 3.776”.

Stroke is 3.48” – actual cubes (rounded to the tenth) for 3.736” bore is 305.2 cid. A 3.776” bore calculates to 311.8 cid. The increase in cubes is 6.6cid or a 2.15% increase in overall CID. All else the same, compression will go up slightly with the larger bore.

The 2102 cam (204/214 – 112) is a much better cam than the LG4 305’s cam and a little bump over the L69 HO cam. The 650cfm carb is slightly more flow over the stock 585cfm of an unmodified Q-jet, but less than the 750cfm you can get out of the Q-jet with a few modifications. The Performer intake will give a little bump over a stock L69’s. Depending on the year, the 305 could have the 1.84/1.50 heads that were on the L69. Assuming you have the 1.84/1.50 heads you’re looking at a 305 making a little more power than a stock L69 (rated at 180-190hp) - my guess would be about 25HP more.

So, the 305 with your mods could be making around 205 - 215HP. Assuming a slight increase in compression and cubes bumped to 312 you could be making around 210 – 220HP. Headers would bump that up a bit.