Chevy 305 Heads and Engines De-mystified A little more truth a lot less fiction There’s a lot of talk on various web forms about the Chevy 305 and its cylinder heads. Most of what I’ve read is negative; a lot sounds to me like second-hand regurgitated opinion and just a little first hand knowledge. I’ve owned a few 305s pre and post 1987 engines, carbed and tune port injected, stock as well as modified. I have also owned a flow bench for some 20 years or so, a number of computer engine dyno programs as well as an interest in developing engine technology. The 305 is interesting to me. The pre 87 motors did what they were designed to do they made just enough power to get by and they got reasonable gas mileage The post 87 motors were a little better with roller cams, different heads and fuel injection. So why not hop this thing up that’s what most people who own one want to do, it’s what’s in the car or truck right.... what can we do with it? are the heads any good? Good question, the first and most immediate response is “replace it with a 350” or “the heads are crap”. So what about the heads ? The pre 87s are somewhere comparable to the old 283 power packs but with a better spark plug location, not really designed to flow a lot of air, just get the job done on a small motor. After 87 the motor came in TPI & TBI configurations which included swirl port heads. People say the swirl ports are no dame good the design is restrictive, But is it really ? I’ve read numerous articles on various heads being flowed but never any definitive testing on swirl ports themselves; I wonder how so many people can say these heads flow poorly when there’s no hard data to back up these statements. I’ve flowed all kinds of Chevy heads and the day came when I flowed a set of swirl ports I wasn’t expecting much cause I like everyone else heard they weren’t great, the only thing I did to them was a 4 angle seat grind and back cut the valves, I guess I would have to say I was pretty dame impressed, Chevy swirlport heads flow !!! they will easily outflow the Vortec, in fact they kick the Vortecs butt particularly at high lift, the swirl port heads short coming is far from being its intake port, Its the exhaust port that is stunningly bad, the good news is this ports bad short side radius can be easily modified by anyone with a dye grinder and the improvement is huge. The other significant short coming of the 305 as I see it, is the pistons, they all have some varying degree of dish with a tiny ineffectual quench ring, not conducive to better combustion and making power. D-dish flat tops are the best piston for this motor imo. Not everybody has access to a milling machine like I do so that they can make there own d-dishs from a flattop but I think this motor will run nicely with flattops if mid-grade gas is used. Camshafts in these motors are pretty mild to say the least; I found the LT-1 cam worked really well in my TPI motor. I like how the roller motor cams can be re-ground, You can have your cam re-ground to a whole host of different profiles or even a close copy of a big name grind. I’m always amused when I read people saying 305 swirlport heads don’t flow, How did the swirlports get loped in with the old heads of yesterday ? I think the person or persons who designed the swirlport intake port were darn smart, maybe a little smarter than there detractors ? People who poo poo these heads quit simply do not know what they are talking about. I wonder how many perfectly good sets of modifiable heads have been replaced (with older style poorer heads even, in some cases) or discarded because of the ill-informed advice given in various forms ? What motor is going to make any kind of power if it can’t pump its exhaust, that’s the 305 swirlports crippling handi-cap. The 305 swirlport with a little exhaust port work and a hi-lift cam with some duration isn’t a half bad little motor and That’s the truth ! As a side note; 305 heads can be modified for 0.500 plus lift by using a set of Vortec take out valves purchased cheaply on e-bay, the intakes need to be cut down to somewhere around 1.84” to 1,88” or so and re-faced, what ever diameter you think you’d like to try. Vortec valves are just single grove (hence the ability to go high lift) so you have to use positive type valve guide seals. Also I’ve tried porting the intakes and found little gain, the port as it stands is that good.

http://www.thirdgen.org/techboard/tb...ted-193-s.html (Garage Ported "193"s (Flow #s))

Looks like an old member re-registered and posted up more of his drivel.

Whats the flow numbers? Power numbers? ANYTHING numbers? All I see is a lot of and no factual data and a glaring error of SBC history.

Gee thanks for registering here and posting this. So helpful.

lol

It's all relative though? Maybe to some one with a 305, it IS all that?

I remember when I thought my stock car was the shiznit, until I rode around in a 12 second car.

I'm not getting into none of you guys' cars anymore, not no way but nohow! I can't afford it. Especially not one with nitrous or a turbo. Never.

Here's your numbers...
http://www.thirdgen.org/techboard/tb...ted-193-s.html (Garage Ported "193"s (Flow #s)) (Garage Ported "193"s (Flow #s))

Hey petetinga,
Thanks for sharing your thoughts! In the spirit of "hot-rodding" and "turning a wrench" - I'll work on a set of heads that I have from a 1993 or 1994 5.7 - 4 bolt main engine. The last set of heads that I blueprinted were on a "30-over" 429 Cobra Jet engine... now that was FUN!!

Yea, thanks. The OP did not post any results to back up any of his banter. Waste of internet space.

But it's on the internet; it MUST be true !

There's a reason why Vortecs are popular.

Vortec are good but nobody ever talks about how air flow becomes unstable @ .500 and up lift, with porting they'll flow 250 cfm at .450 lift but it falls off after that piont because of instablaty.

vortec is the perfect street head because of it's low peak #s...... compare it to any afr head or whatever you consider the best and it's power under the curve for a factory power band is unmatched... It's all about most flow under the curve with the highest velocity. Just remember the smaller runner the higher velocity (yes this is an oversimplified view ,but tends to hold water to a point).....

No btw i'm not saying a vortec is the best head btw...... i'm just saying as a bolt on head especially for this era f-body it's pretty much your best pick.... Good swirl, high velocity, smaller runner. Works perfect with crappy gear ratios and stock converters as well as a 2 bolt main cast engine like most of us are running, also is a good addition to tpi/tbi combos in the instance that they aren't designed for massive camshaft combos.

it doesn't matter how great your heads are at peak flow, it's flow under the curve, unless your building a motor as a straight up race car or circle track so on (wider power curve thats higher under the curve will always win).

how often are your heads running over .500 lift....... on a stock application never since you are maxed out around .460.
anything over .500 is starting to get in to a little wilder territory.... Now when you are considering highly modified race cars, the peak #s maybe the most important depending on the rpm range you run in and what kind of gear ratios....

i'm just saying people shouldn't concentrate on peak flow #s so much..... It's the same thing with camshaft bigger is usually not better especially for the street.

also i do beleive your intake flow #s to be a little on the low side for a vortec btw.....

Ya ive read that about peak flow and under the curve info, If peak flow is .460 than ya you should run .510 lift or more so the valve spends some more time open at or around that optium ive wondered what that unstability dose above peak flow, i suspect in that short time frame its not that much of a problem.

My flowbeach isnt setup right now cause i moved (devorce eh) my datas in a box somewhere so i just go by memery for now,
one thing ive always wanted to do is build a rig to open and close the valve while im flowing the head, a variable speed motor, cut the lobes off some old cams that i have. im sure somebodys allready done this but ive never seen any info on the net.
I think it would be interesting to see what is happening in a more dynamic state.
I built a plexy glass carb adpter about 6" tall once it had 4 tubes i stuck it on a engine and fired it up to have a look at what was happening, basicly all you see is a fog, what i wasnt expecting is that the adaptor nearly shattered it formed cracks like mad, you see the vapor froze the plexy glass, vapor pulls a lot of heat. well anyway thats just some more of what did someone responding to this thread call it......Blah, blah, blah.