blue82_z28

i've got a late 70's 4 bolt main 350. i'm looking to make at least 300 horse. the engine is going to have hypereutectic flat top pistons with 4 valve reliefs, a stock crank, 600 holley (for now), and stock ported heads, i forget what the casting numbers are. but since the cam was missing an entire lobe, it needs to be replaced, so i want something that's a little lopey and can bring me into the 300 horsepower range.

five7kid

iTrader: (14)

Need to know that before we can say much more.

Assuming they aren't 882's (but they probably are), something like a Comp XE268 would easily get you to 300 gross flywheel horsepower with decent 64cc heads.

Orr89RocZ

iTrader: (20)

since you say late 70s block i'm assuming its flat tappet. that XE268 or similar will work great.

even stock L98 motors with just an HSR or miniram is close to 300 on motor. it dont take much, just a mild cam will net 300 hp

blue82_z28

the heads are 624's

Sonix

iTrader: (1)

That's the same as the 882's, very light weight smog casting. Excellent paperweights for high wind areas, and pesky paper... Or a good boat anchor.
Notoriously bad high performance cylinder heads though.
With flat tops, you should be around 9.3:1 CR or so? Maybe less if the block wasn't decked. Those heads are 76cc's.

A compxe262 would work ok. If the port job is good, you might be knocking on the door of 300FWHP, but don't expect miracles. It'll be decently torquey and fairly fun to drive, but don't expect any more out of it then the cash you put into it

blue82_z28

well what are some good/better heads?? i kinda don't feel like payin an arm and a leg for a pair either, so used for me is obviously better.

Orr89RocZ

iTrader: (20)

vortec heads from SDPC setup for .500+ lift. they can be bought for 500-600 a pair complete. very good heads.

need a vortec manifold tho.

and i think summit sells some nice aluminum heads now for 650 or so complete.

Sonix

iTrader: (1)

You can also port and polish the 305 heads from the carbed 3rd gens, or TPI 3rd gens. ie, the heads off the 305 you're removing from the car right now.
Port those up, and you'll be light years ahead of ported 624 heads.

blue82_z28

how much compression do you think i'd be running if i were to use my 305 heads?? safe enough for pump gas?

sofakingdom

iTrader: (1)

Assuming:

9.025" deck height (stock, undecked)
1.54" compression height (stock -.020")
.039" head gasket (1014 etc.)
76cc chambers
6cc valve reliefs

I get approx. 8.3:1 compression.

Assuming everything else the same except 58cc heads, I get 9.9:1 CR.

If the 305 heads are properly worked up to go on a 350, meaning, 1.94" intakes and the correct chamber unshrouding, they'll end up around 62-63cc. That will put the CR at about 9.4:1. A Comp XE262 or Lunati Voodoo 262 is about right for that combo.

You're not going to make 300 HP with some 8¼:1 350 with 70s smogger heads, so I'm not going to recommend anything for that. Throw those heads in the trash and forget about them.

blue82_z28

how does having those heads on the motor effect my top end?

sofakingdom

iTrader: (1)

Which ones?

blue82_z28

the 305 heads, lol.

Sonix

iTrader: (1)

Effect it compared to what?
Compared to the 624 heads? Better.

blue82_z28

so if i just take my 305 heads off the motor that's in the car and replace the 624's it would be safe enough to run on pump gas and actually give me more power?

Orr89RocZ

iTrader: (20)

the increase in compression will definately help power. i'm not sure about the flow of those 624's compare to 305 heads. if 305'sflow more, then it also will help make more power

blue82_z28

well if anyone here knows which flow better, the 305 heads or the 624's??

Fast355

iTrader: (2)

HO 305 heads flow better, have better port velocity, and burn better than the open chamber 350 smog turds.

blue82_z28

well unfortunately i don't have h.o. heads, but which heads would make more power and flow better on my 350, my 305 heads off my motor now, or the 624 350 heads?

Fast355

iTrader: (2)

The 624s ARE turds. I bet your current 305 heads are 416s, 416s are > 624 heads. Some 305s came with 601 heads. 601s(Truck/Crossfire) > 416s(LG4/L69/early TPI) = 081s(TPI) > 624s = 882 = 993.

416 heads are 305 HO heads. The LG4 came with the SAME heads as he L69 305 HO, same valve size, etc.

blue82_z28

well thanks, then i guess it's settled, i will use my 305 heads for the 350 until i can afford better flowing 350 heads.

Sonix

iTrader: (1)

Port them as well. If you ported the 624's you can port the 416's you've got.

blue82_z28

will do, and again, i appreciate everyone's input, thanks again.