isr85-T/A

i was told you can put the heads of the 305 onto a 350 block and it will increase hp on the engine. and if it is true would that combination be able to pass smog in california?

zraffz

Search it, I know it has been asked many times.

Yes you can do it. Will it increase power? Yes, it depends on the heads and chamber size but mainly it will increase low end power. I did it, car had descent low end grunt and nothing after like 5 grand. Running with 2nd gear grinding badly and without 3rd gear in a T5, 3.73's, two burnt wires, open dif, and a vacuum leak between carb and intake manifold I put down a mid 14 second pass. Running right we figured a mid to high 13. It was also my first time ever running a manual trans at the track (my experience driving a manual is also very limited). All I was running was a mild cam and a set of hand ported 58cc heads.

I think you are better off porting the heads you have and camming it. The only reason they run 305 heads is some of the heads have smaller chambers, increasing compression. Most 305 heads flow terribly though. I wouldn't do it again unless I was putting the motor into a truck.

whitedevilTA

iTrader: (8)

It's not worth it IMO. The 305 heads will SLIGHTLY increase your compression ratio, but they flow horribly and will kill any top end. A freind of mine put some on his carbed, cammed 350 and my TPI 305 with a small cam ran circles around his car. You are basically choking out the motor. If you're doing all the work to pull the old heads off, at least throw something good on there.....or have the stock ones ported. Plus 305 heads have smaller intake valves than 350 heads.

iroc-z_23

iTrader: (1)

would not recommend this, it causes hot spots on your pistons from the cylinder heads. will it raise compression yes, but flow, no.

Apeiron

Lots of misinformation here.

The only difference between a 305 head and an equivalent 350 head is the chamber size, and the size of the intake valve they come with from the factory. The ports are the same. Put a larger intake valve in, and it'll have just the same flow as the 350 head, with higher compression. They don't kill flow, and they don't cause hot spots on pistons. It's possible to do some dumb things, like replace 350 L98 heads for 305 LO3 heads, but the power loss there isn't due to any 305/350 distinction.

Technically by the letter of the law, putting 305 heads on a 350 would not be emissions legal in California. Then again, neither is the 350 block in an 85 to begin with.

Kyle86

iTrader: (1)

We put 305 heads (601 castings) on my buddy's 350. We were both surprised how well it pulls down low with the performer eps intake, and a mildish 224/235 480/488 113lsa cam. It will scoot up a hill no problem and put you in the seat on the way up if you do it right. Just my experience with the swap.

Doom86

If you over come the only draw back of a 305 head by putting bigger valves in you will have a far better head then it's 350 equivalent because of the valve job and 55cc chambers.

If you took it a bit further with stainless back cut valves and the bowls blended you would have a much better head then any cast GM or it's era.

zraffz

Yeah I dont remember the casting I ran but they were ported on a comparable cam. It moved but it didn't have much top end. It was putting down 14 second passes at like 72 or 74 MPH... it wasn't running right as previously stated though.

iroc-z_23

iTrader: (1)

Well I've seen the hot spots on the pistons from a 305 head. I've also heard that from multiple machinist. Chance it if you want but really I don't think it's worth it to put them on.

iroc-z_23

iTrader: (1)

Maybe after you changed valves it would eliminate that problem I guess, rather thann just sticking a bone stock head on.

Apeiron

I'm sure you believe you have. Find some better machinists, though.

Doom86

It looks like a dump truck from the times. Somethings wrong though, my LG4 305 with headers was +18mph faster.

As pointed out before the casting you start with would change results considerably though. L03 heads would not be a good choice unless ported by a pro. But I think in general when people are talking about "305 heads" they usually mean 416, 601, 081 castings.

Air_Adam

I used a set of 601 castings on my 350, which replaced a set of 882s. The 601s had 1.94/1.60 valves in it, along with screw-in studs and guideplates. No port work, only a little unshrouding of the intake valve in the chambers. The top end power was a little better, but the low and mid-range power increase was HUGE! The mid-range punch was awesome, and the throttle response bordered on ESP lol. The heads were milled a little bit just to get them flat, but my calculated CR went from 9:1 to a little over 11:1.

It was a VERY good upgrade - highly recommend it... and I've actually done it, so I actually have a 'before/after' unlike alot of the speculators in this thread (no offence intended).

You could pass california smog with them, as long as you have the right valve cover bolt pattern ('86-earlier perimiter bolts, use casting 601 or 416, '87+ centerbolts use casting 081) because they look the same as a 350 head externally, and the casting number is hidden under the valve cover.

zraffz

Yeah well I previously stated when I pulled the motor I realized it had 2 burnt wires and a vacuum leak between the manifold and carb... not sure if the wires were burnt at the time of running it but it had a very bad vacuum leak. It took off very, very hard for the little bit of money into the motor. I talked to a local shop, I replicated a motor the motor from one of his low dollar builds and I think I recall he said it put a Nova into the mid-high 13's.

crazyman

There is a difference between centerbolt and perimeter bolt heads.. If you're talking the perimeter to perimeter style, do it. Centerbolt? Nightmarish ramps in the intake port either way that slow flow.

I had an 82 GMC 3/4 ton 2wd 350 that had nothing more than perimeter 305 heads, a 204/214 cam, th350, 3.73's, performer intake, quadrajet, and 31 inch tires that was the terror of my highschool and averaged 19mpg.... Cast ex. manifolds too.

One thing that most people neglect to realize when putting 305 heads on a 350 is that you gain an 1/8" wide squish band around 80% of the chamber, which is beneficial to power, mileage, and efficiency...

Not to mention, that combo spun up to 7,600 RPM during one burnout.... Sounded nascar like, but died three weeks later due to rod clatter. It wasn't the combo that killed it, just rpm and being a junkyard engine that had 1/8" play between the piston and bore, every cylinder. Too tired for 7,600 RPM..

Really, just the heads is like going from a stock cam to a 204/214 cam. Your butt will feel it. So will your gas gauge.

Too many people will say no, because there are expensive bolt-on go fast parts available to make huge power, but if you're on a budget, and you have them, do it. You'll learn, and have fun in the process....

Apeiron

That ramp has nothing to do with whether it's center or perimeter bolt. It's a feature of the swirl-port TBI heads. Other centerbolt heads don't have it.

crazyman

I did not know that. Thank you. I've only messed with one set of centerbolt heads.

Air_Adam

All SBC heads from '87-on are centerbolt heads, including Vortecs and LT1/LT4 heads.

Grumbles

What are the stats on the "Vortec 5000" 5.0L cylinder heads? I bet a set of those on a 350 would be murderous.

EDIT: Did some searching, came up with this:

http://www.hotrodders.com/forum/vort...ine+305+vortec

zraffz

The chambers are the same size as the 5.7 Vortec heads.

Grumbles

It actually says in that article that they are 55-58cc

Doom86

Aren't those the same heads Fast355 used to build the 356rwhp 305?

Never used them my self but people who have say they are 55cc chambers.

five7kid

iTrader: (14)

I thought he used 601's.

Doom86

I had to dig it up to check (since he's got a motor a month habit, hard to keep track of )and it's the 059 Vortec 305 heads he used.