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Automotive Small block Chev (classic) exhaust notes/tuning physics etc

  1. Apr 13, 2012 #1
    Somewhere in a dark corner of the "internet" lies a video of somebody that somehow crossed the leads from the header pipes so instead of all the primaries going into one collector some go into the other side collector........that produced a very exotic sound.

    Can someone tell me a little more about his process?

    180 degree headers are NOT going to fit in my car so I am starting to try and find other options that will make a higher pitched more exotic (Ferrari like etc) sound (not rice...).

    Working with a 327 Chevrolet. I love the sound of muscle, the car is not muscle and should not sound that way, or to the best of my ability to capture it. The complete setup of the engine.
    4.040 bore (3.25 stroke) inches (we are going to magnaflux the block to see if it is capable to go to a 4.060 bore)
    team g intake single plane manifold
    jegs 195cc intake port, 64cc chamber heads aluminum strait plug(these heads are getting worked and will be put on the flow bench soon)
    the cam will be setup for the intake/heads/headers that are selected in the end result. The cam will put the engine in the 3000rpm-7000rpm range and a redline of 7500, albeit will be designed around the intake/heads/headers flow etc.
    The compression will be at 10.5:1, so as to utilize pump gas.
    Forged crankshaft (small journal block, two bolt) cross plane style crank shaft I am not going to swap in a 180 crank (flat plane) as per Ferrari spec much too much work and $$ to do such a thing.
    I have yet to decide if I should pony up for 6" rods or just stay 5.7" rods
    the rockers are at a 1.6 ratio.

    The engine is designed around the fact that I wanted a specific rpm range, the car is very light and tires are very limited. The max tread width I could find in the max rim size available was 8.5 inches. The section width of the tires are 245mm. The rim itself when measured end to end was 240mm. The car will weigh in at about 2800lbs. The donor car is a 1978 Datsun 280z five speed which is going through a sbc v8 conversion. The drivetrain (axles, transmission, and differential) that are available can hold to the hp (which I realize is tq(rpm)/5252). So the rpm of the motor has been raised to the 7000rpm mark to best match the transmission ratios and differential ratio as well as to produce more peak hp than low end tq. Too much tq will just cause the tires to spin and cause premature part failure.

    ratios
    1st gear 3.06:1
    2nd gear 1.63:1
    3rd gear 1:1
    4th gear .7:1 (more of an overdrive)
    Differential 3.545:1

    The tires are 245/50r16 at a speed rating of 97w. The speed rating limits the tires to 168mph.

    One issue that I have found is header clearance. So I need to know what header type is going to best suit this as well. From my understanding "shorty" tubes with a larger diameter (about 1 and 3/4 of an inch) would be beneficial to the rpm I am going for rather than long tube headers. The kit (jags that run) comes with sanderson block hugger headers to avoid the steering shaft that is in a inconvenient location.

    I found this on the Ferrari forums.

    "An American V8 with a cross-plane crank doesn't fire alternate banks consistently. The firing order means that you sometimes get successive exhaust pulses into the same manifold. In a dual exhaust, this means inconsistent pressure pulses in the two sides.

    Look up "beat frequency". When you have two frequencies that are almost -- but not quite -- the same, the difference causes a low frequency pulsation (beat frequency) that gives the American muscle car its distinctive low frequency rumble.

    The same thing happens in twin engine aircraft when you don't "synchronize" your props -- the rpm difference between the two props makes for a low frequency throb you can feel as an intermittent vibration.

    With pure alternate bank firing, the Ferrari engines have identical pressure pulse rates into both exhaust manifolds, so the exhausts are "synchronized". After that, it's just a matter of tuning the exhaust paths.

    So, no, a Ferrari type exhaust on a cross-crank engine will not replicate the Ferrari exhaust note.

    Some newer GM V8 engines have cross-connections between the exhaust sides to reduce the exhaust "rumble"."

    I would like to know more about the cross-connections that are done on newer cars if you guys know anything about that?

    Also from my understanding (this may or may not be true) a "x-pipe" exhaust with chambered mufflers will help create the more European sound that I am looking for as well as help with the exhaust pulses. Any thoughts there?

    Are there any other options I may consider? Lets please stay on topic and factual please.

    Any educated answers would be greatly appreciated.

    An example of the sound (which btw I have heard corvettes (cross plane cranks) as well as the larger v8 bmws (cross plane cranks) create, I just don't know enough about exhaust to know what is done to create this as well as keep performance as well. Hence the posting.

    Link of a Ferrari 348 engine sound
    http://www.youtube.com/watch?v=g2Cx...PL3320E3F23893E064&lf=results_main&playnext=2

    If there is more information needed about the car I will do my best to provide the information.

    Fayt~
     
  2. jcsd
  3. Apr 14, 2012 #2
    Short of a flat plane crank or 180 degree headers, no, you will not get the even exhaust pulsing you are after. An X-pipe will be the best you can do.

    Since you have only a 3.25 stroke, the 5.7s are fine; a redline of 7500 means better rods anyways and I usually put in 6.0s when upgrading.

    Have you considered using a Supra turbo motor/drivetrain? That would give you the smoother sound and have more than enough power.
     
  4. Apr 14, 2012 #3
    It is extremely more expensive to work with import motors than a sbc. The sbc is the least expensive motor to build. I also already have about 2300 into the motor. I am looking for a 500 plus hp engine that could produce and even tq curve through the entire range so I needed the proper amount of displacement as well. I was going to do a 283, but the piston availability was very small and expensive compared to 4 inches or more.

    It was less expensive to build a 327 than the l28 that the car came with. I was going to supercharge the 2.8 L6 the car came with but mega squirt is not my friend. I like to try and keep the fuel delivery process simpler with a carb.
    --------------
    Could I take shorty headers and connect the primaries necessary? One big problem people have found with 180* headers is that the length necessary before the collector limits the usable rpm range.
     
  5. Apr 15, 2012 #4
    Better set your sights a little lower, a very good street 327 will be doing well to top 400 hp.

    The long tubes are needed to cross over to the other side of the engine to produce the even pulsing and there aren't any shortcuts.
     
  6. Apr 15, 2012 #5

    You are incorrect about the 327s maxing out at 400hp.

    As just an example.
    http://www.chevyhiperformance.com/t...7_small_block_chevy_engine_build/viewall.html

    The heads I have are knock-off afr 195cc comp heads.
     
  7. Apr 15, 2012 #6
    Last edited by a moderator: Sep 25, 2014
  8. Apr 15, 2012 #7
  9. Apr 15, 2012 #8
    Any chance that you can get a camshaft ground so that the firing order changes to cause alternating banks of cylinders firing?

    ...Looked into this further and it appears not to be possible due to the dual-plane crank. Never mind
     
    Last edited: Apr 15, 2012
  10. Apr 15, 2012 #9
    I never said they maxed out at 400 hp, I said a good street 327 would be doing well to top 400 hp.

    The most recent SBC in that displacement range that I built was a 343 that made 664 hp at 7200 rpm; quite civilized in behavior considering, and some people might be tempted to put that on the street but it was built for a local GT-1 racer.

    I'm building him a 422 for his street car that should make close to 600 hp but be much nicer to deal with. Still will be on what I would consider to be the ragged edge of being streetable though.

    As per the article, a 254/260 cam hardly qualifies as a street cam for most but it depends what you're willing to live with.
     
    Last edited: Apr 15, 2012
  11. Apr 15, 2012 #10
    No; the crank dictates the movement of the pistons, not the camshaft. Unless equipped with a 180 degree crank ("flat" crank) or 180 degree headers, the exhaust will have the distinctive V-8 sound.

    ETA: seems you already found that out.
     
    Last edited: Apr 15, 2012
  12. Apr 15, 2012 #11

    turbo

    User Avatar
    Gold Member

    What is wrong with the sound of a Chevy small-block? Spend a day at the strip and watch those 283 wheel-standers run and listen to them. Who needs $$$$$$$$ foreign cars?
     
  13. Apr 15, 2012 #12
    Some people like the smooth sound of equally spaced pulses:


    I'm one of them.:smile:
     
    Last edited by a moderator: Sep 25, 2014
  14. Apr 16, 2012 #13
    "To replicate the Ferrari exhaust note exactly will take 1) Single plane crank with shorty equal length headers and a short overall length exhaust system, (shorter length is higher pitch). 2) 180 degree headers of equal length, as short as possible with the primaries to retain as much high pitch as possible along with as short of overall length. This will get you 90% there. 3) 8 into 1 headers all primaries being equal length, again as short as possible. 4) Some mufflers such as Spintech have a unique of absorbing the tones that give the domestic V8 that old boat drumble giving a more distinct crisp smoother "raaaaaaaap" to the exhaust note with a hint of off beat rumble. Listen to youtube sound clips of c-5 &C6 Vettes with spintechs for an example.

    Not positive about diameter and it's effect on exhaust note/tone. Pretty sure smaller equates to higher pitch due to higher velocities, if that is indeed the case, finding that balance of small but so small it is restricting.

    Spintech is a chambered design, I dont recall if they offer a Stainless version, if so Stainless will last much longer than mild steel, 15+ yrs. Not sure how long the mild steel versions would last, 5 years?

    So shorty equal length headers that as soon as possible go into one collector, an x pipe, and then to a chambered designed muffler. Do muffler lengths and tips change the pitch? Im not sure, I would suspect it would, but only slightly. Most likely would the tone coming from the shell of the muffler/exhaust as it rings from the sound traveling within, most likely noticeable only standing right next to the muffler if..."
     
  15. Apr 16, 2012 #14
    Faytmorgan, I know a couple people with Dat-conversions (Mopar and BBC powered) and they can be a lot of fun. First off, you need the flat crank or 180 headers for the sound. There is no short cut. You can try some fart-cans, but it will probably sound like a school bus instead of a Ferrari. 8) X-pipes will change the sound, but not transform it. They are good for the torque curve though. What is your plan for this car? Is it a street car, a part-time strip car, strip only? Given your desire for pump gas, I'd guess a street-strip car, so I'd have to lean toward Mender's comment that 500hp is a bit optomistic. Not at all impossible, but you may have overlooked that the engine in your noted article had 11.5:1 compression and used a pretty aggressive (pass the gas-can please) solid-roller cam. You can't even come close to the opening rates of that cam if you're thinking hydraulic; it will pass everything but a gas station if you go to the big solid cam. Is that a 4-speed stick or auto trans?

    I don't understand why you want it to sound like something it's not, but that's your decision. Good luck to you!

    Tongue-in-cheek....there is a device my sister bought me that keys on your alternator frequency and plays Ferrari-like rpm sounds through the radio in tune with the engine rpms. How about that? 8)
     
  16. Apr 16, 2012 #15
    The gear ratios he listed are for a 700-R4 (automatic) and unless he has a 3500 rpm stall convertor or higher it'll be pretty doggy off the line with the combo he's been indicating.
     
  17. Apr 16, 2012 #16
    Yes, that's why I asked. A high-stall, lock-up converter isn't cheap either. There are a few challenges here, but it could be a very nice car.
     
  18. Apr 16, 2012 #17
    I don't need off the line power, nor want it. The car doesn't weigh that much. I am limited on tire, and the rear axles won't hold to tq, they will hp but not tq. Hp is a function of rpm and tq, if the tq comes in later and more gradual they will be fine. Also 700r4s are not known for strength, this one has been built, albeit all the same.

    As for the rest of it. Do you guys have any thoughts on diameter sizing before I will be choking the motor?
     
  19. Apr 17, 2012 #18
    If you want something different, read Smokey Yunick's Best Damn Garage in Town particularly the exhaust section with a race car he built and holes he drilled in the header. More labor intensive with what he did, but you won't hear anything else like it. Not sure it will work the same with a street car application though.

    Your exhaust note is made during the blowdown phase, if you want to attempt to manipulate that area.
     
  20. Apr 18, 2012 #19
  21. Apr 18, 2012 #20
    Faytmorgan, your links will get you in the ballpark. If you're buying off the shelf headers, and that's a pretty small shelf for a conversion kit, you'll have to go with the best compromise. Use your calculations to pick the best size for your application and needs. If you're thinking custom built headers, then your wallet is your guide. The person flowing your heads should have adequate software that will not only tell you the ideal cam specs for your heads/engine combo, but it should also define the header range for your engine to breathe most efficiently. I say range because it depends on where you are targeting the power curve. Ideally, the primary tubes would be constantly expanding (megaphone-like, to a degree), but that's a pain to package, build and even calculate. Second best would be stepped headers that have 2 or 3 primary pipe sizes before the collector. They are expensive and tough to package, but very adaptable to slip-on construction. Thirdly is the header you see every day with one primary size. Honestly, you're not building a highly-tuned engine looking for every lb-ft of torque it can make. It's a compromised design for general use. And that's fine, since most engines are. The headers simply provide a path of lower resistance for the gases...you're not tuning your power curve with them by more than a few hundred rpm. If anything, I'd keep an eye on the future, when you decide to add more power, and go with the pipes that are at the very top of your results from your calculations. You may need the flow later, and the worst case is that they move your torque peak up the rpm band a little bit now...which is what you want anyway given your traction concerns.

    Fahlin, are you talking about the temp probe holes for the dyno that Smokey put in the pipes?
     
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