Okay, I wanted to bounce a few ideas around here and see what you guys think.

My basic idea is that a 305 should be cammed the same as a 350 (keeping in mind the lesser flow of the 305). That is to say, the rpm range of the cam will be about the same for the 305 as it is for the 350, despite the difference in cubic inches.

I say this because I think that it is the STROKE of the crankshaft that influences the rpm range of the cam, not the SIZE of the engine alone. Since a 305 and 350 have the same stroke, they should respond the same to a given cam (have similar power curves).

Sorry if I have stated something blatently obvious, but I have seen in various magazines where the tech writers say that a smaller cam must be used in a 305 vs the 350. And I think they're wrong

 

its about the volume the piston pulls in imo..

 

Actually your pretty far off.

In reality its the engine components, mainly the heads, cam, and intake that determine the amount of hp an engine produces. Meaning that if you built a 305 and a 350 with the exact same components, they would make almost exactly the same amount of hp. Or extremely close, within 5%.

But with that being said the smaller engine will make the hp at a higher rpm than the larger one. This is due to the fact that the smaller engine makes less torque and thusly has to spin faster to produce the same hp.

Stroke and bore play almost nothing in how much power an engine will produce. Neither does engine size play a huge role in the amount of hp. Engine size really only determines what rpm a specific amount of hp is made at, with a given combo.

 

I agree with you based on the stoke being the same that the cams should preform similar.

But, the extra cubes of the 350 will help eat the nasty lope and be more forgiving of being over cammed.

The 305 can not use as large of valves due to the bore restriction and will shroud the valves. Based on this I would think that a differnt cam would be needed to result in the same flow characteristis.

BUT, I think that your theory is sound.

As for a factory designed bore stroke 305 making the same power as a factory designed bore stoke 350 with the same components. Impossible.

There is no replacement for displacement.

The reason the 350 would always make more power in factory congiguration is that a 305 is a 350 with a restrictor plate being the bore size.

 

MR Leigh hit it right on the head and stated it perfectly. A 305 and 350 will never make the same power with the same cam. Sure some motors may be close due to head, induction and intake combo but they won't be the same. Even if you have two identical motors with the same parts, the 305 will make its power at a different RPM than the 350. Likewise, the 350 will make its power sooner and over a wider RPM range. The volume of the 350 is larger and thus will pull more air in than the 305 at any rpm point. Although stroke does play a role in rpm range it doesn't determine/limit power output. It is all about displacement and how you apply it. The reason whyt he 305 sucks is because of its bore shrouding. If you could run a whole different head set-up the motor wouldn't seem so bad. There are many V8's out there with similar bore/stroke ratios that make better use of their displacement. The 350 doesn't have this problem with the tradiational Gen I/Gen II head design.

 

No point in confusing the matter... keep it simple when you try to think of it.... that big cam you got will be more streetable in a 350 than a 305.

 

A Chevy 305 as engineered by Chevy does not make power higher in the RPM Band than a a chevy 350 as enginnered by chevy.

They both have the same stroke. STROKE IS VERY IMPORTANT.

You can not make a blanket statment that smaller engines make more power higher in the curve. Yes some do but when comparing the 350 vs 305 this is not the case.

All else equal a shorter stroke with the same displacement will make torque and HP higher in the curve, because of less frictional loss due to ring drag, slower piston speeds, better rod angle ratio, less reciopacating weight etc.

All else equal the short stroke should make less torque and HP at lower RPMs, due to less mechanical advantage associated with the shorter stroke at lower RPMs.

 

I dunno if what your saying is correct...or I'm reading what your saying wrong.

All things being equal, how can a smaller displacement engine make "more" than a larger displacement engine?

 

Okay, just reread it again, ( Iget so confused) but have to wonder what you're saying is:

CU. In vs Cu in . HP and torque will be the same...but at different RPM levels...

Or are you saying bore vs stroke (same displacement) can increase or decrease max power (pick one, HP or Tq.) ?

 

It can't

We seem to agree.

 

These 'static' arguments are pointless. The premise of the original question is inherently flawed. The only question that prevails is what do you want to do with the motor. All else is pointless bantering because you match the parts to the purpose of the build.

Generally speaking and keeping 'all else equal'...

The answer to the original question is no. Because of the configuration of the valves in relation to the cylinder walls, as the cam gets larger, the smaller bore motor will start to have problems handling the upper rpm potential of bigger cams whereas the 350 can still properly handle those rpm without fuel suspension problems that would arise in the 305.

Likewise in the lower rpm range logic would dictate that a cam designed more towards torque (I said generally now) should find more potential in the smaller bore motor as the velocity of the incoming column would be greater... generally.

While stroke is important, it is not, by FAR, the only part of the puzzle. Ok, next beer...

 

Isn't a short stroke engine going to have more reciprocating weight because the pistons are larger?

 

It ia all about the volume of air that the engine can mix fuel with and combust.

Smaller displacement has to turn more revolutions per minute to move the same volume of air as a larger displacement engine. So to produce the same power the RPM range of the small engine must be higher.

 

Below is a good read. I think all would enjoy all of the articles.

http://www.theoldone.com/archive/

 

Well, like I said, it was just a theory I thought about; I don't have any hard evidence to back it up, other than Desktop Dyno maybe. And from what I've seen, most people here don't seem to put much faith in that program, so I won't say any more about that.

Maybe like someone said, the question was flawed from the beginning, because it assumes too much simplification for what is in reality a very complex system.

While we're on the subject, there's a side note I'd like to mention. This really messes with my head:

Okay, most people say the 305 sucks because of its small bore size. But, looking at many modern cars, their engines use a relatively small bore in relation to the stroke. Some even have as small or smaller bores than the 305! The catch is, in most cases these engines use multiple valves, which must solve the airflow limitation problems. So it looks like that the bore size itself isn't the limiting factor, it depends on how much air you can flow past the valve(s). I don't know why these engines are designed with a small bore; perhaps an emissions advantage?

 

Bingo, you got it. The 305 sucks because the design of Gen I heads shrouds the valves. I mentioned this same thing a few posts back.

 

Hmm, I am provoked to speak here.

Air flow, or restrictions thereof such as is posed by a 305 head, is not any huge problem that can't be overcome. Follow the link at the end of my sig for a good how-to on making excellent flow with various 305 heads.

Most people don't like 305s, (if I have EVER understood the question), simply because they can get more power from a 350 for the same or less money.

PS Desktop Dyno is fairly accurate as long as you give it the right data. Much of the time I've seen it come within 10 hp of actual dyno-proven hp.

 

Come on, Todd. 305s suck and all the positive thinking in the world won't change it.

Your link is a great resource for turning 305 heads into 350 heads though.

 

Yeah, they "suck" in less air than a 350 and thus don't make as much power. Funny thing though ... 350s suck less air than 400s and thus make less power, all other things being equal.

It must be those 350 heads that "suck" so badly compared to 400 heads, eh?

 

How about we put a bone stock 400 in your car, that would really suck.

 

Yeah, it would twist the old 86 Sport Coupe into a pretzel

Or are you maybe hinting that you want to give me that 400 you have stashed away back in Kamloops???

 

Oh, but if I gave you one of my 400s the others would get lonely.

 

Rub it in why don't ya???

 

BOT....

The reason it's generally said a 305 should use a smaller cam than a 350 is for when it's used more on the street. The 45 cubic inch advantage of the 350 causes a lot more low RPM torque to be produced.

Because a 305 doesn't have as much low RPM torque, a smaller cam will cause it to produce torque at a lower RPM, therefore making it seem more powerful off the line. That's what the SOTP meter feels, and what most people want.

Just to remind some of you how bad the low RPM torque of a 305 is, it's the whole reason TPI came to exist.

 

Actually, a 305's low rpm torque is not bad. The stroke is the same as a 350's. Of course a tpi unit on top of it will produce even more.

 

The stroke is the same as the 350, but the piston area is smaller so that there's less area to convert cylinder pressure into force.

Power comes from burning gas. The TPI system and the 350 both accomplish the same thing compared to an ordinary 305, they get more air and fuel in to be burned on each stroke.

 

Fine don't believe me.

 

Notice how max hp is within 2%

 

350 and 400 make the exact same max hp.

 

In your simulation, yes.

 

Well in theory, engine size has no role in max hp. But in reality it has a slight effect, so does bore and stroke.

But theoretically...

 

I'm not in the habit of building theoretical engines.

 

As stated somewhere in this little dialogue, power is about burning fuel. Burning fuel is about getting air and fuel into the cylinder to be compressed and burned (and getting the burned stuff out, of course). The more you pump into the engine and burn, the more power you will make. The larger the displacement of the engine, the more you will pump in and burn - generally speaking.

Of course, reality has a habit of putting its ugly head in the middle of our dreams. The same cam in different displacement engines will act differently in each engine. In general, the smaller the engine, the higher the power band will be for a given engine. That means that a small engine will be lower on torque in the lower RPMs and the peak torque and horsepower will be at a higher RPM than the same cam would be in a larger engine. HOWEVER, that does not mean the peak torque and power will be nearly the same in the smaller engine than in the larger engine.

And, of course, this reality thing also means that the same components on difference sized engines will work best on one particular engine size, and not so well on another engine size. The 305 heads on a 400 will keep the 400 from working as well as it could with the cam that works best in the 400 for instance. Etc., etc., etc.

There is a reason cam manufacturers spend a lot of money on R&D, and why they have tech help lines. You might not get the brightest bulb when you call said tech lines, but if you call each one at least 3 times on different days, you're bound to get two that are close to each other - that's the cam to go with. I've also gotten better advice via tech email than tech phone call. The key is to provide all possible information about your car, including engine size & type. And keep the salt shaker handy.

 

The 80ish truck and van 305 and 350 were rated at the same 165 hp in trucks. In vans they were 175 due to different manifolds, carb tuning, and distributer advacne curves. The 350 made peak power at 3,800 rpm and the 305 at 4,400.

 

I appoligize to anyone who wishes to have a 305 vs a 350.

I was certainly wrong and now know that a 305 makes just as much power as a 350 when equally ill equiped.

I am now confused as to why chevy ever made any 350s at all; much less big blocks. Think of all the money they could have saved by using a briggs and stratton.

Like Forest Gump,"That all I have to say about that."

 

I almost pee'd myself laughing at this post You're a funny man SDIF

 

Using the same cam in a 305 might move the powerband up compared to a 350 when all else is equal, but intended RPM range of operation is an important (maybe the most important?) part of cam selection for an intended application.

Would it be preferrable to say that when cammed for similar RPM ranges, the larger displacement engine will always have a higher peak than the smaller one?

 

Bah! Forget the Briggs and Stratton. Use a model airplane engine! Alcohol burning, 20,000 rpm of 1cc fury!! Yeah!

 

No, No gm should use one of these motors I bet it would save money in gas and its faster than a LS1 T/A


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