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  #1 (permalink)  
Old 05-06-2003, 04:51 PM
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Default "427 engine sound you can feel"

This is NOT a discussion about big blocks vs. small blocks! But during a recent such argument, one of our Cobra buddies made the comment that he liked the 427 because of the sound . . . that he could feel it as well as hear it. He reasoned that it was because of the uneven firing. So that got me to wondering. . . what is the comparison of firing sequences for the popular engines, and could this lead to a difference in perceived sounds? Assuming we have true dual exhaust like in the Cobra sidepipe arrangement, the sound we perceive will depend (in part) on the left-right sequence of firings, not the sequence of cylinder firings. The left sidepipe does not care if it was the number 5 (front) cylinder or the number 8 (rear) cylinder that fired, it will sound the same in that sidepipe, but the relative sequence of other firings in that same sidepipe COULD make a difference. The results are clear, we will need to find another reason to like one engine over the next. Here are the firing orders of the popular engines plus the left-right sequence of pulses:

Ford 302 (early) 15426378 RLRRLRLL
Ford 351, 400 13726548 RRLRLLRL
Ford 427 15426378 RLRRLRLL
Ford 429, 460 15426378 RLRRLRLL
Ford 292 15486372 RLRLLRLR (I threw that one in just for fun!)
All Chevy V8’s 18436572 LRRLRLLR

These would all appear to be different, but if you repeat the sequences indefinitely, as in an engine that is running, you will see that they all follow the same pattern. You can start it anywhere you wish, the pattern is the same for all the engines . . . RLRRLRLLRLRRLRLLRLRRLRLL . . . etc. The firing pattern of these engines cannot be responsible for any perceived difference. So what is it? Exhaust system? Seems likely to be a big factor. But my 351 has a free flowing exhaust and is very loud, but it doesn’t pound me in the chest. Cubic inches? Big c.i. would seem to relate to more “feel” in the chest cavity. But the old 460 Lincolns would purr like a kitty, not pound you in the chest. So c.i. alone can’t be it. Radical cam? Possibly, but again I submit my 351 SVO with its fairly radical cam profile. That funny car at the drag strip just about knocks the wind out of me, so what does that have that all these other scenarios don’t ? Plain old horsepower! I submit that is the real source of the “feel it as well as hear it” effect that we gear heads love so much. If true, any of these engines with equally high levels of horsepower should produce the same effect.
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Old 05-06-2003, 05:09 PM
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I vote for big bore and short stroke.
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Old 05-06-2003, 05:29 PM
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Glad to see you're thinking along those lines. I wondered about that too. Here are the bore to stroke figures:

302 4.0x3.0 ratio = 1.33
351 4.0x3.5 ratio = 1.14
427 4.23x3.78 ratio = 1.12
429 4.36x3.59 ratio = 1.21
460 4.362x3.85 ratio = 1.13

chevy 350 4.0x3.48 ratio = 1.15

The 427 actually comes in with the least oversquare bore (guess that's why it revs so well). Still, that could be part of it. But some of the others are soooo close it is a hard sell. I'll stick to horsepower as the cause (or effect).
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Old 05-06-2003, 06:58 PM
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I heard that about you stumpy. I mean Bill.

All kidding aside I think it is a matter of power, displacement, port design, exhaust system and compression.
A 500 HP 351 does not sound like a 500 HP 460.

A 460 does not sound like Bill's Tunnel Port.
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Old 05-06-2003, 07:47 PM
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Thats much to complicated for me.

You don't need to know the firing order. Just listen. There is no mistaking a 427 for a 351. No way.
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Old 05-06-2003, 09:24 PM
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Scott, you're a rather amusing fellow.
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Old 05-06-2003, 11:05 PM
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Good stuff!

It looks to me like the 302 is the LEAST square of the motors, with the 427 being closer to "square" than the others.

A "square" motor would be like the old Chevy 283, bore and stroke being identical. Some say this makes for the most reliable configuration.

For a motor that "builds rpm quickly" the application generally recognized as "best" has been larger bore relative to stroke. Porshce and many other "race" bred type engines employ this principle. THIS ratio is often WHY a "small block" will generally beat a "big block" in the 1/8th mile, or even 1/4 mile. Or,,,,coming out of a corner on "road course".........

Watch out on the straight away when the big block starts to build some serious horse power and just KEEPS pulling strong!

Based SOLEY on the bore/stroke ratio numbers on the motors I would expect the 429 to "build" rpm faster than the 427.

Now the stroke length on that 460 is downright scary! Theres a motor I would NOT want to spin higher than 6,000 rpm, IF that much!

Ernie
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Old 05-06-2003, 11:12 PM
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I am sure it is the firing order....

WHOMP, WHOMP WHOMP

Weeeeeeeeeee!

You can imagine which one is which.
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Old 05-07-2003, 05:17 AM
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I'm not suggesting that a 351 sounds like a 427. All I am saying is that it can't be because of the firing order. And that you can get that pressure pulse in your chest from many engines, not just a 427. A quick visit to the NHRA nationals will convince you of that. There is something else that causes these effects. Actually, xlr8or is probably on the right track, that it is the unique combination of ALL the engine variables like port size, displacement, exhaust system, etc. that produces the sound, but I think it is the horsepower level that produces the shock waves we feel.
So if someone will donate their 427 engine to me for scientific study, I will get to the bottom of this mystery!
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Old 05-07-2003, 06:57 AM
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I just fired up 351W and my son-in-law says it's sounds better than his 596 cu.in. Chevy I don't know about that but it sures sounds "nasty"
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Old 05-07-2003, 07:34 AM
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Last month we pulled a friends BB Chev in the shop and the only thing we changed was the heads drop the compression 1 1/4 point it went in sound like a tiger came out sounding like a kitty cat ????
Ken
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Old 05-07-2003, 08:33 AM
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A lot of research has been done on the noise created by an internal combustion engine.

A quick search on google reveals all kinds of research.

A quick glance at several projects seem to imply the biggest factors affecting exhaust noise is in-cylinder pressure, intake and exhaust valve interaction (i.e. valve sizes and timing), block, head, and piston design, and -- of course -- the exhaust system.

Apparently it's a very complex problem. Automakers are interested in this and spend a lot of time and money on research and computer models to design engines that make as little noise as possible or at least tailoring the sound to be pleasing to the buying public.

Of course, this doesn't explain the horrific sound some of those modded import cars make...

Due to the economic benefits, the internal combustion engine is probably the most researched and tested piece of technology in existance. Someone somewhere has to know the answer.

I sure if we could find an engineer in this field he could give as a quick concise answer on why a small-block Ford doesn't sound like a 427 even if they are of similar power and compression.

Now finding that person is another matter.

Interesting question.
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Old 05-07-2003, 09:16 AM
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No doubt about one thing. Compression in the combustion chamber, wether forced or naturally aspirated has a HUGE impact on sound.

A high compression race type engine decellerates MUCH quicker when you lift the loud pedal because of the high compression more than any other factor. Revs up the same way too.

Ernie
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Old 05-07-2003, 09:19 AM
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Mike,
I think you may have hit upon it! Cylinder pressure must be it. It seems so obvious now that you have said it. The funny cars on their nitro-methane must be producing cylinder pressures that go off the charts and that is why they knock the breath out of you when you stand at the starting line. Ken made the comment about lowering the compression on the Chevy BB and the punch in the sound went away. Again, directly related to cylinder pressure. The old 427 engines have high compression by todays standards, so they have that punch as well. A long rod-to-stroke ratio will park the piston at TDC longer and get that higher pressure peak. The stroke is shorter on the 427, so its rod-to-stroke ratio must be higher than the 428. Anybody know if the connecting rod on a 427 is longer than the rod on a 428? That would make it even more pronounced. I'll check my books when I get home. Of course this would mean that the 427 is not unique in its ability to produce this effect, but it may be well suited by virtue of its bore-to-stroke ratio.
Charlie
(still waiting for someone to donate the 427 to start the comparison studies . . . in the name of science, of course).
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Old 05-07-2003, 09:50 AM
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Charlie, slow day at work today, huh.....

BTW Mike Sisk, I'm surprised you couldn't tell, Charlie is an engineer....these are the kind of things that keep him up at night....

Mike
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Old 05-07-2003, 09:52 AM
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I believe it would be a combination of cylinder pressure and cam overlap. I had a 510 lift 310 duration cam in one of my cars (400 CID) without changing the heads or pistons and it changed the sound dramatically. I also lost all low end torque and the idle was at about 1500+ RPM at idle.

I loved that cam.
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Old 05-07-2003, 09:52 AM
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I run 9.6:1 in my 427 and I think you will find many owners are in that same range or just a tad higher--a far cry from the 11.x:1 from the factory.

Mine still sounds good--even at idle.
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Old 05-07-2003, 10:10 AM
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assuming the engines in question all have good headers and similar exhaust systems, do not have siamese exhaust ports, and have 90 degree crankshafts (not 180) three things influence the sould. Compression, valve over lap and duration via the camshaft, and ignition timing. A radical 300 ci engine will make more noise than a mild 600 ci engine.
HTH,
Mike
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Old 05-07-2003, 10:30 AM
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I'm the newbie who made the comment about the "odd firing order of the FE series engines" being the source of their distinct thumpety-thump. I have read all the posts in this thread, and I have no mechanical facts or figures to support my comments.

All I can say is that REAL 1 summed it all up: There is no mistaking an FE engine when you hear it (and feel it). Even the more "docile" FE's that I have heard with 9.5:1 compression, a mild cam, a dual plane intake, and a smaller carb still have that very recognizable "FE" sound.

Sorry that I don't have any mathmatical equations to solve this mystery (I flunked College Algebra). You'll just have to trust me...

Russ
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Old 05-07-2003, 10:46 AM
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Hey Mike, thanks for chiming in--as usual you get down to the facts.

While making my last post it occured to me that since I run relatively low compression, yet the motor still sounds good at idle--I would have to attribute that to cam duration (for which FE's are know to like long duration) as well as cam lift (about .579 for me), and finally valve overlap--a product of the cam.
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