kind of wanted everybody's opinion on this mainly the older heads of this site.i was reading the january06 issue of c.h.p about the aluminum heads vs the iron heads on the 327.the numbers that the 327 produced looked realy good i didnt think an 327 could produce # like that.i was just wandering if u could (anybody) build u a motor out of a 350 or 327 what would u prefer.i like the 350's but i like the 327 numbers also honestly i dont even know if its possible to build a 327.i think iread in a past c.h.p issue that u can build an 327 out of an 350 by usin a 350 block 327 pistons and a 307 crank how true this is i dont know but it sounds about right.would this be an inexpesive build im not.i dont even know if u can even get an 307 crank.all i know is itl probaly be less expensive and easier to build an 350.now i know the 350 well im guessing that the 350 has the 327 beat as far as t.q numbers but i also heard that the 327 has the 350 ford 302's and 281's and any dodge motors beat as far as h.p and rev! numbers are concerned the only thing that will come close is probaly the imports and thats because theyre throwing 4 less pistons/ rods/ and crank journals.and also actual block weight so of course the import h.p numbers are going to be close or higher.i guess it depends on what u like h.p or t.q.kind of wanted everybodys opinion as far as a daily driven motor.maybe an every blue moon "street race"ooops!!!! probaly shouldnt of said that but just give me your opinion thanks!!!!!!!!!!!!!!!  

a 350 and 327 share the same 4 inch bore, the 350 uses a 3.48" stroke, whereas the 327 uses a 3.25" stroke. The 307 also shares this stroke, but all 307 cranks are iron and are large journal. So the 307 crank will not fit into a pre '68 327. The 327 and 350 share the same deck height and rod length, so the piston compression height differs: 1.675" for the 327 pistons, and 1.56" for the 350.

There's nothing special about the bore or stroke relationships of a 327 versus a 350. Physics tells us that for two engines of identical displacement and all other things being equal except one with a longer stroke than the other; the work each is capable of is the same. In an engineering sense all that happens is that the maximum power values will occur at different revolutions for a bunch of reasons. But what physics looks at is the cumulative area under the power curve and they would be identical.

Using the work efficiently becomes an engineering exercise to optimize the characteristics of the power curves. For example two identical cars one with the long stroke engine, the other with the short stroke engine would need different gearing to achieve identical performance. Generally the short stroke engined car would want low gears to move the engine up into its higher RPM power peak than the car with the long stroke engine.

Physics also tell us that engines of different displacement, all other things being equal, develop power in proportion to their size. From an engineering standpoint we know that the RPM where peak power occurs also has an inverse relationship to size. That's to say a small displacement engine develops peak power at higher RPMs than a large displacement engine. There’s a hole bunch of reasons for this, some relate to physics other design choices. So there’s a range of events where any engines of roughly similar displacement overlap each other in terms of performance characteristics. The difference between a 327's 3.25 inch stroke and a 350's 3.48 inch stroke is largely in this zone of inconsequential differences.

The heads used in the Jan 06 issue "Head to Head" article would behave the same way attached to most any displacement small block. The smaller displacement engines might see more top end improvement than the 327 because the port and valve sizes will allow deeper breaths in the higher rev ranges, but this would come at a loss of torque and horsepower in the lower revs. The 327 and 350 family would show changes pretty much the same as the article suggests. These heads strapped on a 383, 400, or 406 might well show a power gain in the lower rev range since the port velocity will pick up at an earlier RPM, but power will fall off in the higher rev range since these ports and valves will max out earlier. Of course all these things change if you can move port and valve size around with changes in displacement.

What this story really tells us isn't much beyond a modern aluminum head will produce a little more top end over a ported pre smog cast iron head where compression ratios were held constant. The output of the article presses harder on the issue of whether a cast iron head produces greater power compared to a comparable aluminum one because of cast irons slower heat transfer rate to the cooling system but doesn’t really answer the issue.

A real test would be of identical heads except for material. Cast iron compared to aluminum with the same valve and port size; identical port shapes and angles; identical combustion chamber shape and size results in what power characteristics? Then what happens as you start to modify each using tried and trusted hot rod techniques. We'll guess the cast iron head will accept larger valves than the aluminum head because of the need to use space in the aluminum head to accommodate seat inserts; therefore it can't get to as large a valve as cast iron, so what’s the effect of valve size? Another useful test would be heat transfer power loss against compression gains. It has been theorized that aluminum's faster heat transfer rate reduces combustion chamber temps thus power, compared to cast iron. But it's also been assumed that because of aluminum's faster heat transfer rate, it will tolerate higher compression before the onset of detonation. Now here's a useful hot rodder test. Test this assumed thermodynamic theory. For otherwise identical engines with otherwise identical heads, does cast iron really produce more power because of heat transfer rates? If so, then can you really increase the compression ratio of an aluminum head further ahead of a cast iron head before detonation becomes a problem, and can you push the compression to a point where it overcomes aluminum's (assumed) higher heat transfer rate, potentially producing more power than that obtainable from cast iron. Another test would be if you hold compression constant, can you run an aluminum headed engine hotter than a cast iron headed engine to overcome any heat losses versus a cast iron head. Again the limiting factor will probably be the onset of detonation. Or is this all just smoke and mirrors based on faulty assumptions, or are the differences so slight they're inside the noise limits of the data? But tests like these would provide really use full and definitive information we can all use.

There have been lots of tests of things that are sort of but not quite similar.  However, most published tests are of things that are mostly dissimilar, and this one rather borders on the latter. But what it tells you is what it tells you, without connecting this information to the larger body of data; it really doesn't do a lot for us by itself. Some recommended reading which helps put this stuff into perspective is at the end of these URLs:

http://www.chevyhiperformance.com/techarticles/46320/index.html

http://www.chevyhiperformance.com/techarticles/46326/index.html

http://www.chevyhiperformance.com/techarticles/46359/index.html

http://www.chevyhiperformance.com/techarticles/46364/index.html

http://www.chevyhiperformance.com/techarticles/46370/index.html

http://www.chevyhiperformance.com/techarticles/46438/index.html

http://www.chevyhiperformance.com/techarticles/46461/index.html

http://www.chevyhiperformance.com/techarticles/46467/index.html

These don't provide 1 to 1 comparisons but they do take you down a road that tells a pretty good story about cylinder head technology.

Bogie

MAN !! Now thats why when I ask a question I'm really hoping you will give me the low down on what really works, and not some of these miths that have been around and forever and that have been passed on and added to for years (like the dubble humped head being the holy grail)

David 

Bogie, I thought a longer stroke would be able to produce more power because of greater mechanical advantage, like using 4.11 gears versus 3.08. Isn't a longer stroke like using a big breaker bar versus a little stubby ratchet?

Brian

u see i was thinking the same thing i thought that a bigger size motor would produce more power.but i guess it all depends on what u/r using the motor for or what kind of racing u/r doing me personaly i think that the 327 would be a better motor as far as weight and street racing.depending on cam/compression/carb and heads set up.i just didnt think that a 327 could produce #'s like that by being a smaller displ. motor.i guess it all depends also on who's building the motor for u because when u go to the race track you'll a big block that will jump all over a small block and you'll have some small blocks that will jump all over some big blocks so realy i dont know i just like the idea of a small displ. motor that has alot of power.just as much power or even more power as a big engine. it'l probaly be cheaper to build im still not sure if u can use a 307 crank in a 350.or can u even get an 307 crank anymore!!                         (P.S whats the max rev limit on an 327)  

At the end of the day, a 350 can walk all over a 327.  It's all about displacement.  But... cube for cube, the 327 can walk all over a 350.  Does that make sense?

IMO, pound for pound (read, cid for cid) the 327 was the finest small-block Chevy ever produced.  It had it all - 4" bore, short stroke, optimal rod/stroke ratio, etc.  They were only limited by their relatively small displacement.

A well built 327 (w/ a forged 327 crank, not an imposter cast 307 crank) will buzz to the moon.

I try to deal with the rocket science going on behind the scene so that people can assemble the information that helps them make informed choices and to understand that there is no perfect solution. There are lots of people, myself included, who have made expensive mistakes from following articles, assumed theory, follow the leader, and just plain baloney that gets into the either.

The article confirms that a modern aluminum head with CNC ports is a little better in top end performance than a reworked/ported pre smog/camel hump/cast iron head. Is anyone surprised by this answer? The surprise I had was how much the aluminum head gave up on the bottom end compared to cast iron and how little it gained on the top end. I'm not discounting 10 horsepower, but it isn't nearly as much as advertiser's claims would lead you to believe.

An interesting test against the base cast iron head used in the test would be a Vortec head. Here's cast iron against cast iron old tight chamber against new tight heart shaped chamber; old port ideas with porting against what are essentially LT-4 ports. If you read the content of the URLs I included, one of the things about the Vortec that sticks out of the data is that the Vortec like the AFRs in the January article give up some bottom end for top end. I find that an interesting trend, even though the numbers aren't all that big and you probably can't really feel them in the seat of your pants when you step on the go pedal.

You see this trend a lot where the power curve doesn't get fatter so much as it diagonally pivots, trading bottom end power for top end power or vice versa.

The URLs I sighted are also an article in a book these good people publish; "Small Block Chevy Engine Build-Ups". This is a might good read, you have to do some interpolation of the data like anything else the tests are frequently not exactly against equals. Another terrific read is "Maximum Performance Chevy Small Blocks" by David Vizard.

I don't know the details of your engine nor the vehicle it's mounted to or how you want to use the combination so I can't get too specific on recommendations. But I can say that the late model heads whether cast iron or aluminum with the (Ricardo) carotid or kidney shaped combustion chambers are the way to go. I can't say for sure who's the best based on personal experience as I can't afford to experiment with everybody's heads, and there's a lot of choices. But there's a lot of published data out there that one can pull together. I've run GMPP 23/18/15, ProComp, and Trick Flow's Twisted Wedge. They're all good. Does one stand head and shoulders above the rest in terms of performance? Not in my experience. All require living with them over an extended period of time to work out their best attributes. But while I’m massaging the best they can deliver; generally this work doesn't make amazing differences from how they ran out of the box. It's a process of incremental and often small improvements. Frequently after a dyno run, the improvement you see (or want to see) isn't outside the range of test equipment error or test to test natural variance. One has to be wary of the “placebo effect” where after all that work, you just know it's gotta be better so your brain makes it so. This is especially true of untimed midnight burnouts, yeah oh yeah what a difference. The next day on the track you run slower, what the heck is that? It’s the placebo effect at work on your brain!

One effect of the article is the recognition that the old camel hump head ain't all that bad. Another is that given the thermo properties of aluminum, there still was a gain against cast iron at the same compression. Yikes! this isn't what anyone expected. Is that a function of better porting, better combustion chamber shape? Are our assumptions about thermo effects of heat transfer between iron and aluminum exaggerated? My own experiments between cast iron and aluminum can't find the differences that many people claim are there and certainly the thermo formulas say should be there. Though I prefer aluminum heads because they can be welded on, you can run at least another point of compression on a given octane fuel, they're lighter by almost half to cast iron. The down side of them is front end cost, I have more rocker stud thread pull out failures, and you're valve size limited because of the space the press in seats need.  

Most any modern head (that includes the L-98 and the truck swirl port) is an improvement over the open chamber smog heads. Fast burns/Vortecs etc. are better still. But if you've got a decent set of 040, 041, 186, 187, 291, 292, 414, 460, 461, 462, 492, 742 castings use 'em, especially for a hot street engine. They’re not all that bad. Hot rodders that strap small chamber 305 heads with bigger valves and ported passages pick up considerable performance on 327s and 350s. Sometimes I think that if GM made this head with extra material in the chambers and ports so we could carve to our heart’s content, that most of these other heads would be pushed off the market because even currently with its structural limitations a reworked 305 head delivers a lot for where it starts from.

Bogie

well your first comment realy didnt make sense and second i didnt think it realy matter.i see what u are saying as far as cast vs forged but i thought a 327 is a 327 wouldnt both of them buzzz!!!!! if properly put together.im not saying that gm never made bad parts or should i say not worthy of high r.p.m parts.but still a well built 327 with a cast crank or what ever should do the same thing as a forged crank 327 dont ya think? i know forged products has the better material.but i also think it depends on the better builder.by the way nobody told me the max r.p.m of an 327 that anybody has experienced?

Yes, a longer stroke brings the torque peak to a lower RPM. This bottom end grunt works well on the street for the average person because the manufacturer can bring the axle ratio up to trun the engine slower and still have customer acceptable performance. For a racer this combined with 4.11 gears might get into a wheel spin problem off the line, sticking in a set 3.90s might solve the spin problem, but bog the engine up on the top end.

The issue you get into if you hold displacement the same but change the bore stroke relationships is that you tip the torque and horsepower peaks. If you think of the power curves as a diagonal line on a chart, all your doing is changing their steepness angle. The area under the line which is "work" doesn't change. A longer stroke increases the area under the curve in the lower rev ranges and reduces the area under the curve in the higher RPM range. A shorter stroke changes the angle of the line where the area under the line becomes smaller at low revs and larger at high.

Make no mistake, this does have a seat of the pants feel. For equal vehicles with equal gearing the long stroke engine will come off the line harder than the short stroke engine. As the revs increase, the long stroke engine will start to slow toward the top end. The short stroke engine will come out of the hole with less intensity but will gain intensity as the revs go up. When you talk about "work" in a physics sense. Both of these cars should have the same quarter mile times. The long stroke engined car will have a faster 60 foot and perhaps eigth-mile time than the short stroke car. The short stroke car will have a shorter time from the eigth-mile marker to the finish line and have a higher top speed through the traps.

This is the kind of thinking that's hiding under class rules. So within a class, it's the engineering of the physics that leads to winning or losing combinations. The headache is that there's so many variables going on at once, people tend to get lost in the details and forget what the problem is. Sucessful racers develop a method to solve these problems. Don't loose sight of the fact that Bill "Grumpy" Jenkins started his racing career with an engineering degree for Cornell. This doesn't mean you can't be competitive without having an engineering degree, what it does say is that you have to develop a sensitivity to the techncial issues and acquire an engineering approach to problem solving. Otherwise you end up following the crowd or going down the wrong path, neither of which can make a consistent winner.

Bogie

"...but still a well built 327 with a cast crank or what ever should do the same thing as a forged crank 327 dont ya think?..." 

Yes, up to a point (such as 6,500rpm).  Above that, you'll want a forged crank.  And with higher rpm capability of the forged piece...you can build the 327 (w/ forged crank) to operate at stratospheric rpm levels.  Personally, I wouldn't risk taking a cast crank above 6,500rpm.  Ever seen what happens when a crank lets go?  Not much is left of the engine. 

Back in the 70s, we use to hop up 327s.  They were a dime a dozen.  We'd stud the 2-bolt caps, run forged internals, bolt on a pair of healthy 2.02 heads with screw in studs, and a nice mechanical stick - and spin those things +8,000rpm all day long.

327s are somewhat outdated today, having been replaced by big cube small-blocks.  But, pound for pound (read: cid for cid) - I'd still lay bank on a 327.

ok so let me ask u  this. would the 327 be a simpler build than the 350 as far as cost on special parts ect?or would it be about the same? also would it be worth it to try to build the 327?the reason why im asking is because i have an torn down 350 block with an ok 350 crank ect.i was thinking that it would be cool to have an uncommon these days 327 sittin in my car.not sayin that there so uncommon its just that right along now if u go to the parts store or just so happen to pop open a hood u wouldnt hardly see one.maybe every now and then you'll probaly see one sittin in a hotrod at the track maybe. but not in your average car thats runnin around.now adays its all about fuel injection commin off the lot or an import or what ever like an t.b.i/ lt1or just your average fuel inject and most of the time their mounted to a 350/305/or the newer motors like the 325/348/thanks for your response!!!!!!!!!!!!!

A 327 will be just as easy to build as a 350...provided you have a 3.25" crank.  If you do go the 327 route, ensure you get pistons designed for a 327 and not a 350 (you might pay a little more for 327 pistons - because their demand is much less today).  The pistons are the same width, yet the wrist pin is located differently.

Another option is to build a 350, and just tell everyone that it's a 327.  They'll be impressed by how hot that little '327' is.

thanks for the info but that last option i take as a kind of an insult to the little 327/if ima have a 327 under the hood i am going to fly the 327 sticker.if ima have a 350 under the hood then thats what kind of sticker im going to have on the car.why say i have a 327 under the hood when i realy dont?i realy dont think its about the size of the motor but who's the builder.maybe im wrong but i took that comment as though you're saying that the 350 is the better motor.(maybe im wrong forgive me if thats what your not saying but it sure sounds like thats what your saying!!)  

Would a 305 kick a 302's butt? I always hear the 305 is a crappy motor, but the 302 is a legend. But physics say the 305  should come out on top. Is that so?