Question for mechanical engineers - Chevelle Tech
2002 General Tech questions from 2002

 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 20 (permalink) Old Sep 30th, 02, 2:08 PM Thread Starter
Senior Tech Team
 
Join Date: Dec 1999
Location: Ruffin,NC
Posts: 1,236
Question for mechanical engineers

How did GM come up with the different strokes and bores when designing an engine?

Were they trying to produce engines with torque or horsepower or fuel economy or what?

Like the 427,4.250 bore and 3.76" stroke,what made them pick a 4.250 bore?

Why a 350? Did they just pick a number and ask,what stroke and bore will give me this number
supersport396_2000 is offline  
Sponsored Links
Advertisement
 
post #2 of 20 (permalink) Old Sep 30th, 02, 2:42 PM
Tech Team
 
Join Date: Jun 2002
Posts: 606
Here a few guess's.

Detroit for some God only knows reason had a 400 CID limit on intermediate cars.When the BBC was being designed it was a 427.Only the Corvettes and Full Size cars would be alowed to have that engine at that time.Since the intermediates were the target for most BBC in 1965 Chevy started with a 396..just under the 400 in rule.Since the 396 and 427 shared the same stroke it was far easier to reduce the bore to come up with the 396.In 1966 when the 427 came out they modified the water jacket cores and made the bore 4.250.

Nascar at that time had a 427 CID in limit.
That could be why Ford had a 427,Mopar a couple 426's ,Chevy a 427 ,Pontiac a 421 ect ect.

So when Chevy introduced the BBC they could have easily made it 480 plus inches but it would not be allowed to run.

The 302 came about due to politics also.The Trans Am series of road races had a 305 CID limit during those years.So they stuck a 283 stroke in a 327 block and presto 302 CID just under the 305 limit.


In 1970 Detroit dropped their opposition to 400 CID on intermediates and this allowed the
402/454/400sb into the intermediates.


The small blocks in the 50's started out as a 265 .So when they decided they needed a larger engine they found that they could make the bore larger and keep the stroke the same and the 283 was born.When the 327 came out it was a real problem as they had to redesign the block cores to allow a 4.00 in bore and the longer 3.250 stroke of the 327.

The 350 came about in 1967 when the handwriting was beginning to be on the wall that hi rpm short stroke engines for normal passenger cars was not the way to go anymore so thet simpley stroked the 327 and kept the same bore.They changed the block around again
to the large journal ect ect.

So I would guess that politics had as much to do with it as anything else.It certinally was simpler to have 3 engines useing a 4.00 bore...302,327,350 and use the same ring size
boring bar / hone stones ect ect vs another oddball size they would have to procure...

------------------
1969 El Camino
69 LS1 335 HP 427
( not the origional engine)
M21 12 Bolt 3:07's.
Daily Driver work truck.
69LS1 is offline  
post #3 of 20 (permalink) Old Sep 30th, 02, 2:47 PM
Tech Team
 
Join Date: Mar 2000
Location: nj
Posts: 64
I'm not one, but they probably design somewhat around what can be fit in the block that they're using.
They design a block based on primarily (I think) what will fit somewhat easily into an engine bay.
They have to build an engine that will be powerful, but not too powerful for the average driver.
I think when they're having the HP battle in the muscle car days that they increased the stroke on BBC's to offset the loss of low end torque when using bigger heads, cam ect.
Some are also designed around what GM says the biggest thing can be in a particular car, example: the general had a 400ci limit on camaro's until 70', so they had to design with that in mind.
Another example would be the 67-69' z28, they designed that around trans-am Racing, since the limit was 305ci, you dont want an oversquare engine for a road race car, becuase it's going to see many RPMs, so a short stroke was used to keep the piston speed low, and 4.00" bore was used probably becuase they were already using 4.00" bores for 327's and 350's.

Just my opinion on why, i could be wrong.
67Camaro is offline  
 
post #4 of 20 (permalink) Old Sep 30th, 02, 2:50 PM
Tech Team
 
Join Date: Mar 2000
Location: nj
Posts: 64
Doh, look at the times on those posts
67Camaro is offline  
post #5 of 20 (permalink) Old Sep 30th, 02, 3:54 PM Thread Starter
Senior Tech Team
 
Join Date: Dec 1999
Location: Ruffin,NC
Posts: 1,236
Woohoo,i've learned something.

They could have kept it under 427 with other configurations with bore and stroke,what made them choose 4.250 and 4"? they could have had a 4" bore and a 4.25 stroke.

But when they came out with the 265 how did they determine the bore and stroke.They had to start somewhere.

Rod angle? time at TDC? How could you make the perfect engine? Why have so many manufacturers stuck with the 350? is it the perfect engine with the right bore and stroke proportions.

[This message has been edited by supersport396_2000 (edited 09-30-2002).]
supersport396_2000 is offline  
post #6 of 20 (permalink) Old Sep 30th, 02, 4:04 PM
Lifetime Premium Member
 
Join Date: Jul 2000
Location: Columbia SC
Posts: 2,637
I believe a square(bore=stroke)to over square (bore>stroke)engine is considered the best mechanically. The initial decision is how many cubic inches you want and go from there.

------------------
ACES member# 5093
Elcaminos are special!
I'd rather walk around with a Chevrolet hubcap in my hand than drive a Ford

Ole Paint
Big James 4XL is offline  
post #7 of 20 (permalink) Old Sep 30th, 02, 5:30 PM Thread Starter
Senior Tech Team
 
Join Date: Dec 1999
Location: Ruffin,NC
Posts: 1,236
Build a 427 with a 4.122 bore and a 4" crank or 4.250 bore and a 3.76" crank? both equal 427ci.

So the regular 427 design would be better?

Square is better?

To me it would be like me trying to turn a 1" dia crank with my finger compared to turning a 10" dia crank with my hand and arm.The long stroke just seems to have more advantage.

What do the top fuel guys run? Bore & Stroke

Found it.They think like i do..
Bore & Stroke 4.19 X 4.50

[This message has been edited by supersport396_2000 (edited 09-30-2002).]
supersport396_2000 is offline  
post #8 of 20 (permalink) Old Sep 30th, 02, 7:56 PM
Senior Tech Team
 
Join Date: Dec 1999
Location: KC, MO
Posts: 1,859
<BLOCKQUOTE>quote:</font><HR>They could have kept it under 427 with other configurations with bore and stroke,what made them choose 4.250 and 4"? they could have had a 4" bore and a 4.25 stroke.<HR></BLOCKQUOTE>

I'll soon be an ME as I graduate next May and have had tons of dynamics classes that play into this.

I'm taking a graduate level class now called "Kinematic Synthesis of Mechanisms" in which we've had to come up with rod to stroke ratios for internal combustion engines.

Now, I don't know why the engineers at GM then picked those bores and strokes, but there is a "theory" behind rod/stroke ratios (you'd be bored to death with the amount of math you have to go through for this theory) that play into what your powerband will be (do you want this to be a high strung motor or a low rpm torque monster?), loadings on the "thrust" side of the cylinder walls (longer strokes generally give a larger "moment arm" on the crank which should produce more torque) etc etc.

You have to remember, that this is only theory and I'm sure that the engineers had to compromise somewhere as there were "other" issues at hand that could have shortened or lengthened the rod length or the stroke (i.e. is the camshaft too low in the block for the crank throws to clear? Or is the wrist pin too far into the rings due to the longer rod and short deck height?).

Engineers have to constantly make "adjustments" on their designs to satisfy many things (how much $$$ is GM willing to spend on raising the camshaft location in the block to allow a longer stroke or will the main webbing of the block be compromised if clearancing is needed due to the longer stroke or are you going to hit a water jacket if you increase the bore anymore?).

If you are really interested in the theory do a search for some engineers named "Grashof", "Chebyshev" & "Grubler". They are the fathers of modern day theory behind linkages (that's what a rod hanging on a crank really is).

Time to find some asprin

Joe

------------------
The Chevelle Page
72SSAbody is offline  
post #9 of 20 (permalink) Old Sep 30th, 02, 8:43 PM
Tech Team
 
Join Date: Sep 2001
Location: lexington, ky, usa
Posts: 224
Sorry to disappoint you, but the SBC wasn't built to be *perfect*. The key word is EVOLUTION.

VERY rarely in engineering do you start with a clean sheet of paper, and say, "What would the perfect widget look like." Usually, you take a widget that already works, and put a new twist or two on it.

Chevy developed their V8 to give more power, and less weight. But, it was an evolutionary, not a revolutionary design. It was just an extension of their existing inline sixes.

In my driveway sits a neglected 1951 Chevy Half Ton pickup, with a 1956 235cid inline six cylinder motor. The 235 has a 3 9/16" bore, and a 3 15/16" stroke. The 216 it replaced had a 3 1/2" bore, and a 3 15/16" stroke.

Somewhere I have an early ad celebrating the Chevy V8 -- weight was the chief advantage touted. Other manufacturers tried Inline 8s to get the power of more cylinders. The V8 thrived while the Straight 8 died; due to weight, and life of the l-o-n-g crankshaft needed for the Straight 8.

And don't forget ease of manufacture. V8 engine blocks are cast from iron -- they needed to be relatively cheap and reliable to pour, for mass production.

But, evolution is pretty efficient, after all. If you were to start from scratch, you probably wouldn't end up too far off of where the SBC ended up. Cylinder size (bore) is limited by several factors. Speed of flame travel is one -- with too large a bore, you can't get full combustion. Stroke is also limited by several things, including what's already been mentioned here -- rod speed being one of the bigger ones. So with roughly a 4" bore, and roughly a 4" stroke, you've got a pretty good picture of what the "ideal" V8 would look like. (Maybe NOT ideal to a TC gearhead, but ideal for mass production.)

Want more power? The best (easiest, cheapest, etc.) way to do it is more cubic inches. Already got a ~4" bore and a ~4" stroke? Add cylinders. That's how we went from the inline six to the V8, and have you seen the Dodge V10?

Cheers,
mark.
BSME Washington University St. Louis MO, 1992
'71 Fodor
"Soon to be... 383"
hd99fxst is offline  
post #10 of 20 (permalink) Old Sep 30th, 02, 9:07 PM
Tech Team
 
Join Date: Jun 2002
Posts: 606
The origional idea of the SBC was quite an accomplishment at the time.No one was doing thinwall precision castings.Ed Cole wanted this engine to be light in weight, Hi reving ,inexpensive to produce ect ect.They came up with a way to use 9 major and 3 minor casting cores...others used over 20 cores.By haveing
fewer cores you had less problems with core shift.It was origionally designed to be only 245 CID...useing a 3.750 bore.They soon realized that they could easily get 260 CID with the cores they had.This would require a 2.930 stroke.But Ed Cole was intrested in Hydroplane racing and the class he ran had a 266 CID limit...So they increased the stroke to an even 3.00 in and that made it a 265 CID
just under the 266 limit.

Ya have to remember that back then these overhead valve V8's were still new.The flathead days had just ended.Airflow testing and dyno's were no where near as good as todays stuff.Look at some of the early V8 designs...Ever seen a Y block Ford V8 .. 272,
,292 , 312 type engine with it's intake ports sitting one over the other... not side by side.... Or they old Nailhead Buick engines that had rectangualar intake ports sitting sideways not up...or the polysphere Mopar V8's.... I doubt that they really knew what worked airflow wise.

I think they did have an idea about the bore and stroke combinations as the larger bore short stroke hi reving engines completely took over the small bore long stroke low reving flatheads.Back then this concept was pretty darn new.

They could have easily made a longer stroke
427 but it was designed as much for speed as it was for the street and the high reving type engines of the day were still the direction to go.One of the major reasons for the longer stroke 454 was that it turned out to be a cleaner engine emmissions wise... But when the 427 came out emmissions was just barely starting to be a concern and racing was a larger concern and for what they were doing at the time (1963) when they first developed the 427 (mystery motors) that later became the Mark 4 BBC .. the large bore short stroke was the way to make the power.

------------------
1969 El Camino
69 LS1 335 HP 427
( not the origional engine)
M21 12 Bolt 3:07's.
Daily Driver work truck.
69LS1 is offline  
post #11 of 20 (permalink) Old Sep 30th, 02, 9:59 PM
Lifetime Premium Member
 
Join Date: Jul 2000
Location: Columbia SC
Posts: 2,637




------------------
ACES member# 5093
Elcaminos are special!
I'd rather walk around with a Chevrolet hubcap in my hand than drive a Ford

Ole Paint

[This message has been edited by Big James 4XL (edited 09-30-2002).]
Big James 4XL is offline  
post #12 of 20 (permalink) Old Sep 30th, 02, 10:51 PM
pdq67
Guest
 
Posts: n/a
GM tested a whole bunch of different engine design theories at the same time under the gise of the Chevy, B.O.P. Cad. and Gimmy labels...

Chevy 454 = 4.25" x 4.0".
Buick 455 = 4.32" x 3.9". (??)
Olds 455 = 4.125" x 4.25".
Poncho 455 = 4.155" x 4.21".
Cad. 472 = 4.3" x 4.06".
Cad. 500 = 4.30" x 4.305".


And from an outright engineering standpoint the Big 500 Cad. was about the best from a brute power standpoint but NOT stock-wise from a hi-po standpoint!!!

AND the Buick 455 was NEXT!!!!!

I say this "tongue-in-cheek" b/c if you look at the LS1 you will see Cad. influence all over it's heads!!!

And GM even did it with the small 350 engines b/c of all of them that floated around through the years!!!

And there were even two Olds 400's! A 4.0" x 4.0" and a 3.875" x 4.25". Go figure???

pdq67

Best Car Insurance | Auto Protection Today | FREE Trade-In Quote
post #13 of 20 (permalink) Old Sep 30th, 02, 10:54 PM
pdq67
Guest
 
Posts: n/a
69LS1,

I have been looking for pic's of the old MOPAR "poly" heads for years but haven't found anything yet. Do you know where I can see what they look like???

I say this b/c they were SOTA when they came out but fell by the wayside and I'm just wondering why??? pdq67

Best Car Insurance | Auto Protection Today | FREE Trade-In Quote
post #14 of 20 (permalink) Old Sep 30th, 02, 11:35 PM
Tech Team
 
Join Date: Jun 2002
Posts: 606
pdq67,

Yes actually I do have a couple of pics.I once had a friend who had an old 64 or 65 Dodge that had one of them and I adjusted his valves for him.This was the only one I ever worked on.The pics are from an old Peterson Pub book.One is a cutaway of the engine.And the other pic is a pic of the head but from a top view...you cant see the chambers.The book
is at work.I'll bring it home and scan it and see if I can E mail if you like.

It's a weird looking piece.It's part wedge and part Hemi.The intake valves are inclined
tho not as much as a Hemi.They have the rockers facing in opposite directions like a Hemi. The Ex valves are nearly in the center of the chamber along the bore axis.The Spark plug is slanted but in near the center of the chamber.No real flat area for squish in the chamber.I have no idea how many CC's they were.But my guess is that the Hemi made so much more power and since they were small engines I guess Mopar decided to concentrate on the Hemi and B/RB engines.One of the sales reps who used to call on us had a 57 Ply with a 2x4 bbl 318 poly engine.Ran well but hardly inspiring in that 4500 pound barge.

------------------
1969 El Camino
69 LS1 335 HP 427
( not the origional engine)
M21 12 Bolt 3:07's.
Daily Driver work truck.
69LS1 is offline  
post #15 of 20 (permalink) Old Oct 1st, 02, 9:33 AM
Senior Tech Team
Bill R
 
Join Date: Aug 2002
Location: Gold Canyon, AZ
Posts: 2,807
HS99fxdt (?) post was right on, evolution is the name of the game in engine design. Next to evolution would be "copy what works for the competition". The 265" Chevrolet is possibly the most unique engines ever designed from a standpoint of new ideas. The first overhead V-8's made by Olds and Cadillac in 1949 were close, but they did use a lot of parts and design features from earlier model 6 cylinder and straight 8 engines. Good example of evolution is the 427 Mark series engine. This basic engine was introduced in 1958 as a medium duty (2 ton) 348 cubic inch TRUCK engine. Corporate hot rodders (aka "engineers") experimented with 3 X 2 carbs, free flowing exhaust, then aluminum intake manifolds, put it all into a '58 Bel Air or 210 sedan and had a winner on the dragstrip. This engine evolved into the 409 and the 409 evolved into the 427 "Mystery" engine. The 427 Mystery engine gave birth to the 396, then 454, 502, etc.
One of the most successful engines(agruably !!??) is the 225 Buick V-6. This basic engine was designed around 1964 or so and is still, and has been, used in just about every GM car on the road, and was used by Jeep at one time. This engine is now the 3.8l (3800) V-6 engine. This engine was copied almost to the last bolt by Ford when they designed their own 3.8l V-6.
Anyway, the engineers design the engines with focus on flame travel, emissions, fuel economy, bore/stroke and rod ratios, etc. The commanality of parts is also kept in mind. That is why you see 4.000" bore size used by GM, Ford and Chrysler.

------------------
Bill (MI)
64 Chevelle Malibu Sport Coupe (original owner) car now has 427" BB, Chrysler HEMI 4-spd. trans., 12 bolt 5.57 w/spool & axles.
"HOT RODDER is NOT a dirty word"
"Too much horsepower is just enough"

[This message has been edited by engineguy (edited 10-01-2002).]

[This message has been edited by engineguy (edited 10-01-2002).]
engineguy is offline  
Sponsored Links
Advertisement
 
 

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.

Email Address:
OR

Log-in









Old Thread Warning
This Thread is more than 919 days old. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
If you still feel it is necessary to make a new reply, you can still do so though.

Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome