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Thinking of going from a 305 to a 350......
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Posted by: 82firebird

I'm thinking about pulling the H.O. 305 in my car and replacing it with a 350 I was going to take the Heads,intake,carb (600c.f.m. carter),cam,power pully,oil pump,fuel pump,headers,e.t.c.,And put them on the 350,After haveing the bottom end rebuilt (i'm currently looking at 3 350 blocks rangeing in price from $150 to 300)I'd like to use the 305 heads because they've been ported,have a 3 angle valve job,Shaved,roller rockers,z-28 springs.How much to you think this will raise the compression ratio for the engine,And what type of problems migt i run into with this combo?

Posted by: MikeT

are the heads the 305 HO heads?

Posted by: Grape Ape

There shouldn't be an issue here, right? The heads will likely raise compression, but not that much. Going from 305 to 350 power is a no brainer. GM should've thought of it in the mid 70's (right after they 1st used the 305 in Camaros) .... That way, nobody in with the 80's models would've had your situation!

Go for it.

Posted by: Penske

Trash the heads. Or sell them and buy Vortecs. The 305 heads have tiny valves and chambers. Depending on the pistons in the 350 you get (plus the bore increase) you could get a 2 point bump in CR (maybe up to 11:1 if the block was built for 76cc heads). That much squeeze will cause detonation even on premium with those crappy chambers.

Posted by: 65fairlane

Save your money and buy a set of dart heads.

Posted by: cswrench

Go with the vortec heads! They have 62cc chambers so they will also raise compression. The 305 heads even ported is just a pathetic head!

Posted by: Giz

stay with the 305 because during winter months it makes it harder to spin the tires and ask miket how much easier on trannys thet are

Giz

Posted by: 82firebird

Hey mike,these heads are the H.O. heads,And while i can understand cs wrench and penske saying to get vortech heads,and 65 fairlane saying to get dart heads, This is going to be a budget build up,So heads like that are pretty much out of the question.Actually,I was wondering how would these heads perform with more port work and bigger valves?

Posted by: 28

you gettin a cam with this set-up?

Posted by: 82firebird

yeah,I was thinking of changeing the cam out

Posted by: 65fairlane

The guy that had my mustang before me did a cam swap. But he left the stock heads. They don't let the engine breathe enough for the cam to do too much good. You could always change the heads later. In all honesty the vortec heads probably wouldn't cost much if any more than having bigger valves put it.

Posted by: 82firebird

Ill check into the vortech heads.

Posted by: MikeT

Hey the 305 heads really do flow like shit, Penske is correct. At the very least I'd try and find some used 350 heads. If you have the tools you could clean em up a bit yourself.

I think vortec heads new are about $500 a set. You can't beat them for bang for the buck.

Posted by: Penske

The biggest problem is flattop 350 pistons with 305 heads will get you to nearly 11:1 compression. Not good. Unless you can get someone to open up the chambers some and use fat head gaskets.

They still flow like crap, though.

Posted by: Grape Ape

What's so bad about 11:1 compression?

Most 350's prior to 1993 only had about 8.5:1 and we see that 10.5:1 works quite nicely.

On another note, flow isn't everything.

Posted by: MikeT

all the L98's with iron heads had a CR between 9.3-9.5. The vette L98's w/ aluminum heads were a bit higher.

Stock iron L98 heads flow very poorly past 5,000 rpm. I imagne 305 heads would crap out before that.

Posted by: cswrench

Quote:


	Originally posted by It'llrun What's so bad about 11:1 compression? Most 350's prior to 1993 only had about 8.5:1 and we see that 10.5:1 works quite nicely. On another note, flow isn't everything.

I beg to differ! Flow is everything! I will gladly sacrifice one compression point to go from those 305 heads to the vortec heads. Flow is where you make the power. I went 12.16 on vortec heads.I would bet my paycheck that if you bolt those 305 heads on your motor and dyno it then put a vortec heads on it you will get more power from them! They are a very good product. Do not! I repeat DO NOT get wrapped up in having a high comression motor! That is my two cents!

Posted by: Grape Ape

Beg all ya want!

Flow is NOT everything.... Several other factors come into play, such as velocity, when it comes to making an engine perform.

We all want decent flow volume, but at what cost? I know a guy who ran in the 11's with ported 305 heads on a 350, and that was in an 86 Camaro, not exactly the best choice for a street rod. The same guy ran 12's when it was just a 305. Now that's rare.

If the carb, intake and exhaust can't keep up with the flow rate of the heads, it's almost useless to the engine. It can even hurt performance, mostly due to velocity related problems, which can cause trouble with the flow, even if the heads flow outrageous numbers.

11:1 compression is no big deal. Commonly, engines today have 10:1 or more when stock, like the LS1, for instance.

The advantage of having high flowing heads shows up when you also have good carb, intake(manifold) and exhaust numbers, coupled with the right camshaft AND good compression, or at least a power adder.

Large valves aren't exactly a requirement either.

There are many things to consider... Headflow is close to the bottom of the list though, when veiwed seperately. Most V8's can be built to pull a 3000 lb car into the 10's while using heads that don't even hit 250int. and 220exh. flow numbers. It's all in the combo, not just the flow numbers.

Posted by: Penske

There's a BIG difference between 10:1 in an LS1 engine and 11:1 in a mid-80s engine with the little 305 heads. The newer engines have better swirl characteristics to help prevent detonation, as well as more accurate air/fuel computer systems to get the mix and set the timing on the fly. They also use aluminum heads, which also resist detonation better than iron.

Velocity is all well and good, but you HAVE to have a certain level of volume. The stock 305 heads with 1.84 intakes only flows about 180 cfm STOCK on the intake, 127 exhaust at .500 lift. A mild port job pops it to 190/170 at best.

A STOCK Vortec 1.94 head will flow 240/160 at the same lift, as well as giving a better chamber design for detonation resistance. The dime-a-dozen 882 heads from the mid-70s with 76cc chambers flow 205/145 stock with 1.94s.

Sallee Chevrolet has Vortec heads complete for $465 a pair.

Posted by: cswrench

11to1 Compression is great But if you can not get the air into the cylinder then 11to1 will no get you shit!

Posted by: Penske

Eh, It'llRust just likes to argue, regardless. Chevy guys KNOW.

Posted by: Grape Ape

I do like to argue, no doubt!

The point is, he doesn't need more flow than those heads allow, for this budget engine.

He's not planning to swap heads. It's a budget build, which tells us he's not looking to run 11's or 10's. The heads he has should do fine for his goals. If this was to be a race car, I too, would say scrap those heads in favor of the inexpensive aftermarket's. But it's not.

Posted by: Penske

You're missing the point. He's going to a 350, that'll need more air. OK, it's still a 600 carb, but that can still supply more than the heads will take. Plus the fact the CR will be too high, especially with the cam which I'll bet does not have a lot of duration to drop the dynamic CR. Without some good overlap, the cylinder pressure will be way high even at low RPM, and he'll have to dial back the advance so much that any gains will get wiped out.

Best thing is to get some 76cc 1.94 heads ($150 TOPS) and put the goodies from the 305 heads on there. They'll flow at least as well as the ported 305s, with a more reasonable 9:1 CR, and more potential down the line. You don't want to "budget" yourself into a corner.

Posted by: MikeT

Quote:


	It's a budget build, which tells us he's not looking to run 11's or 10's. The heads he has should do fine for his goals

Ya sure, if his goal was to run a 15.00 1/4

Posted by: Grape Ape

He's already said what his plans are... He's gotten some input. I ain't gonna argue with those who haven't, over what can or cannot be done.

Posted by: 82firebird

I can understand everyon'es point of view,But i know there are some members of thirdgen.org running 383's with 305 heads.Does anyone know how they get away with that?

Posted by: Penske

Well, if going from 305 to 350 raises CR to 11:1, going on to a 383 would probably be 12:1. So that's racing gas or a lot of 104+, or running dished pistons to get the static CR down.

I would guess they went to 1.94 valves to get some extra flow, otherwise a 383 would starve pretty quick. There's two things 305 heads would do for you on that big an engine: get a lot of compression from the small chamber and high port velocities from the small ports. As long as you can keep it from detonating, that combo makes great torque down low, like for a Jeep or a tow rig. It will probably run out of breath before 5000 RPM, though.

It would be cheaper to find some heads that are 1.94 to begin with than to rework the 305s.

Posted by: 65fairlane

Quote:


	It would be cheaper to find some heads that are 1.94 to begin with than to rework the 305s.

Definitely. MY friend had a set of 289 heads cut for bigger valves and milled for compression to put them on a 302. He might have got them matched to a gasket I don't remember. He ended up having about $475 in them I believe; and he didn't even get screw in studs put in them like he wanted. He could have picked up a set of used aftermarket heads at a swap meet for about the same price.

Posted by: Grape Ape

BTW, 1.94 valves should fit into the 305HO heads without cutting. The design is all but identical to that of the L98 Corvette head. I still say that flow isn't everything and in this case, it isn't anything at all to be concerned with. Even with the 55cc cumbustion chamber version, compression probably won't be above 10.5:1 and I don't think it will even approach that. Of course, it depends on the 350 shortblock underneath it, but most of those were low compression, even in the Corvette. If the idea didn't work, nobody would copy it. Good luck.

Posted by: skeezix

82, a thing you might wanna take note;

If the 305 heads you have are H.O. heads, I'd KEEP them. 305 H.O. heads have the 1.94 intake valves just like the 350, so there won't really be a necessity to change them unless you wanna run a set of 2.02 heads.

Posted by: 82firebird

Thanks for the info skeezix.

Posted by: DODGE_MAIN

Yeah the 305 heads are good cheap way to bump up compression and get some bottom end velocity for a truck or any other low rpm application, and unless you know how to port the bill is gonna be about the same or more for the vortecs anyways. flow is important obviously when you increase swept volume (305 to 350) then there is more demand for air to fill the cylinders at all rpms.

Posted by: 82firebird

....I've decided to keep the 305,And pull the heads and do some more port work.they have a mild port job now,But i think I'm going to pull them and have them pocket ported,Besides,I did the math and i really can't afford to do a complete engine build-up,Don't have the funds,Besides that,I'd like to get a motorcycle next year.

Thanks for all the replys.

Posted by: skeezix

Well man, you can never really go wrong with having a SBchev under yer hood that's for sure.

Besides you can tweak some good street power out of a 305, it just won't be as easy as a 350.

What do you have for engine mods right now 82?

Posted by: 82firebird

the 305 i have has been bored 30 over,I'm running keith black flat top pistons,reconditioned rods,Turned crank (10 under),The heads have been ported,With a 3-angle valve job,They've been shaved,and they have z-28 springs and comp cams roller tip rockers,Edelbrock performer r.p.m. intake that's been ported,I'm running a clevite cam,the specs are 224int,224ex @.50duration,Valve lift is 450int and 460ex,and a carter 600c.f.m. carb,A.S.P. power pulley,And Accell cap and rotor and spark plugs,and 8.5 spark plug wires from crane.

Posted by: skeezix

Cool.

I'd say your next step would be to install headers with a hi-po exhaust, then your pretty much done.

Posted by: 82firebird

actually,I have flow tech headers and a flowmaster exaust on already.I'm really thinking about doing some more port work to the heads.

Posted by: MikeT

turbo

Posted by: 82firebird

Quote:


	Originally posted by MikeT turbo

Well,Actually,I think the compression ratio is to high for a turbo (10 to 1,Probably a little higher since the heads have been shaved)And I've read that getting a turbo to work on a engine with a carb instead of some type of fuel injection can be a nightmare

Posted by: Grape Ape

It's probably not much fun making a turbo work well with a carburetor, but with compression that high, it would be a real problem with any amount of boost to speak of.

Posted by: LS1JAY

Just drop an LS1 in there! problem solved!

Posted by: 82firebird

Quote:


	Originally posted by LS1JAY Just drop an LS1 in there! problem solved!

Sounds like a good idea,LS1JAY,As soon as you send the $$$$$ or a donor LS1 engine,i'll start right on it.

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