350 vs 327 revisited

[Guest Anonymous]

How is the thermal effeciency better on the 327? Not being a wise guy here, just wondering how it could be thermally better when the blocks are for the most part the same? Are your refering to combustion chamber heat or what? (keep it in english please, I'm not a mathamatician or engineer and speak neither language very well.. )

 

I like 327's just fine, they are one of my more favorite engines back in the day, these days, I like the 350-355 just for the added low-mid range grunt which unless your drag racing the car is where your going to spend most of your time on the street.

 

I was at Zdreamer's house today, he was showing me the DD2 charts on the long rod (6.25) 350 and I was more than impressed. 11-1 compression on pump premium is pretty cool. That motor put out over 500 hp, and had a really flat torque curve.

We were playing with turbo's and blowers on that motor and were getting just sick HP out of it and most of that was all by 6000 rpms.. Pretty cool.

 

Oh well, my .02, either engine in a Z hauls ass, and unless you are counting every last tenth on et's, I can't see either being a bad way to go, particularly when the original question was talking in terms of a budget build.

 

Regards,

 

Lone

[Guest Anonymous]

There are two definitions for thermal efficiency, indicated thermal efficiency, and brake thermal efficiency (which I will refer to from now on as just thermal efficiency) , which is indicated thermal efficiency x mechanical efficiency (which is how much of the actual work gets transmitted to the crank and is of the order of 90-95%) With that out of the way, the reason the 327 has a higher thermal efficiency is because of its higher rod/stroke ratio and smaller rod and journal bearings... Smaller bearing speeds and rod angularity/sideloads = less friction = more power and greater mechanical efficiency. The greater dwell time also allows more time for the mixture to burn completely and push down on the piston earlier down its stroke while it is still compressed, providing more useful power and torque. And like I said, higher rod/stroke ratio means you can use a higher compression ratio without detonation, providing additional increases in thermal efficiency, especially at part-throttle. There is a formula linking maximum theoretical thermal efficiency and compression ratio... I will look it up and post it later.

[Brad-ManQ45]

Chevrolet first used fuel injection (in production) on the '57 Chevy and Corvettes.

 

Volkswagon had fuel injection on the TypeIII engines (Squareback and Fastbacks) in 1970 for sure - I had one.

 

Fuel injection has been around a LONG time and Chevrolet wasn't the one to develop it.

[grumpyvette]

the 350 is the better choice as several of the other guys pointed out.just a new cam and a set of top quality cylinder heads with a new intake and 750 cfm carb(after you rebuild the short block of course) will get you over 400 hp(if you want part numbers from a proven combo just say so)

 

oh why wait, this combo is worth about 450hp 450 ft lbs AT THE FLYWHEEL

AFR 195CC HEADS (#1037)

EDELBROCK VICTOR JR INTAKE

750 HOLLEY CARB

LUNATI 30114 HYDROLIC FLAT TAPPET CAM

350 SHORT BLOCK AT AT LEAST 9.8 TO 1 COMPRESSION RATIO (CHEVY FLAT TOPS WITH THOSE HEADS GIVE YOU 10.1 CPR)

[Guest Anonymous]

Thanks for the explaination, good job, I actually got that...

 

Regards,

 

Lone

[grumpyvette]

Omar

while you are correct on all the points you brought up(with in limited parameters)(and yes it is possible to make more power PER CUBIC INCH with a shorter stroke engine) this disscussion is a little like argueing over which playboy playmate is the prettiest (alot depends on whats important to who) now while all your points are valid your overlooking the fact that the extra 23 cid MORE than makes up for the theoretical pumping/thermal losses if that were not true building a 383 with its even greater stroke and even worse rod angles would not be as popular a combo as it is! and no one in his right mind would think that a 327 will produce more total hp than a 350 or a 383 with the correctly matching parts installed,and in any racing class where there is a set minimum car weight the largest engine displacement available is normally used even though as you point out the shorter stroke with a set displacement would be used if the car weight was based on weight per cubic inch, look here:

http://www.ryanscarpage.50megs.com/combos.html

 

I think you will find that as the displacement gets larger so do the hp and torque numbers and that even though the rod angles and thermal effiecency may fall the total power goes UP as the displacement and stroke gets larger and factors like cylinder head flow and cam timeing have a far greater effect on total power output than small stroke changes.and did you notice there are very few small(265-327cid engines)thats because in every case the money spent will produce more hp on a 350cid or larger engine and if the cash outlay is the same getting more hp through the use of more cubic inches is the way to go! not limiting yourself to a theoretical effeciency level!and while were talking big cube sbc engines, check this too;(and yes the rod angles/thermal effiecency really suck on this )

 

http://www.carcraft.com/editorial/article.jsp?viewtype=text&id=1004

 

and this;

 

http://forums.chevytalk.com/forums/Forum64/HTML/004971.html

 

btw that thread address is;

 

http://forums.chevytalk.com/forums/Forum64/HTML/004400.html[/url]

 

(you left on the url crap so its not a direct link)

and since IM the moderator on that performance forum you might as well be able to get there and you will also notice the 350 consistantly has slightly higher hp/ft lb #s over the 327

[Guest Anonymous]

Guys, I know that there is no replacement for displacement. A 383 will always make more power and torque than an equivalent 327 or even 350... This is just about the 327 vs. the 350.

 

Now according to Grumpy's computer simulations, the two were within 5bhp of each other, and the 327 was 15lb/ft down on torque. This was with identical setups. If we were to optimize the compression ratio on the 327 to take advantage of its increased rod/stroke and detonation resistance that would make up for the (admittedly marginal) difference in power AND get better mileage to boot.

 

Let's recap... The 350 would have a (slightly) fatter torque curve, mostly at the low end, and a 327 wouldn't give up anything to the 350 at the high end. Will a 350 net you better 1/4 mi times? Probably... But a 327 would likely have an edge around a racetrack or autocross...

 

Nobody here has mentioned anything about accelerative horsepower (I forget the exact term) yet... Remember, dynos runs are usually made at a leisurely 300rpm/sec so as to minimize the hp losses that stem from accelerating a rotating assembly. When you're flooring a car in 2nd or 3rd you're accelerating a lot faster than 300 rpms/sec. Rotational inertia is related to the square of piston stroke, giving the 327 a clear advantage, even though a 327 piston is slightly heavier. So any reduction in rotational and reciprocating inertia serves to increase performance. That is why things like lightened flywheels and vibration dampers make the car accelerate faster without actually increasing power output.

 

The bottom line is, the 327 will be more willing to rev, and more responsive, in addition to offering more traction off the line and being (slightly) less hard on the driveline. To quote the JTR manual... (albeit in different context) we're building a car here, not an engine... And it is my belief that the 327 suits the characteristics of our cars better. Remember, we're building a Datsun Z, not a '64 Impala Hope I haven't bored you guys with all this

[pparaska]

Great discussion guys.

 

BTW, Grumpy Jenkins wrote in his book on the SBC that the 327 SJ crank was the heaviest forged crank among them all, if I recall correctly. Also, the 327 piston will have a taller compression height (if the same rod length is used). These things MIGHT take away that seemingly lighter rotating/reciprocating assembly.

 

Me, I'd go with the 350 to save money. If I were starting all over, it'd be a 406 or 415 for me! For the time being, it's a 327 (331).

[DavyZ]

Grumpy,

 

The "law of diminishing marginal returns" totally supports what you just said (paraphrase): even though the efficiency goes down, the overall horsepower goes up with the larger motors like the 350 or 383. This, of course, jives completely with what David Vizard explains in some of his books.

 

Taking nothing away from Omar or anyone else, this discussion is very enlightening!!!

 

Davy

[Kevin Shasteen]

Just my .02 worth, in Joe Mondello writings (sounds like I'm quoting some Philospher or something) he mentions that theory is always relative; but w/a large cubic inch engine (big bore & stroke) that sometimes the rod/angularity theory goes straight out the window.

 

I guess on a pure dedicated drag engine...rod/angularity isnt that important; but for efficiency on a street car that needs durability...then efficiency may be more important. Everything effects power/efficiency. The questions is where do you give up efficiency for power or power for efficiency? again it boils down to intent of use of that engine.

 

Definately a good discussion/I'm sill learning.

 

Kevin,

(Yea,Still an Inliner)