JBL Big Block Poll

[Tom T.]

How about a poll choice that says: "A nice alternative to a small block. Build them both ways!"

TT

[cobrashoch]

Richard - As am sure you know this but beware. All big blocks do not weigh the same. For example that boss aluminum block you mentioned is most likely heavier than a production 460/429 iron block. (depends on the casting dates/codes) All things being equal a iron FE will weigh about 40 to 50 lbs less than most 385's, with a Shelby block even lighter yet. Fact is, a Shelby alloy engine will be lighter than a all iron 351 windsor. If you do this, all I can say is "IT'S ABOUT TIME!"
cobrashock

[Edley Rondinone]

Richard, if you can sell more cars by having a "Big Block" option, and you can make back your investment, then, by all means offer it to the public! It's the American Way!! lol !!

[Richard Hudgins]

OK,

I will try to answer the questions in order.

Grumpy.

There is no angle. JBL Dave is a Freak for Boss 429 engines. He has a couple of alloy 460 blocks and a bunch of cylinder heads, injection systems and dry sump stuff laying around and he just wants to do one. Also, a large number of inquiries are about BB fitment. (I designed the chassis for a SB only on purpose, it gives the best weight balance and lowest polar moment.) Of course the Modular motor seems to be a pretty good piece and it is bigger than just about anything, but the weight is OK.

Rick,

A "harmonic period". This is a point (or natural frequency) at which a structure will vibrate at the greatest amplitude for a given input. It is important that the harmonic period of the engine be different then the harmonic period of the chassis. If they are the same, then you will have a vehicle that is unbearable to drive. I have driven some FA cars (Swift in particular) that had this problem. You would end up seeing a number of horizons going down long straights as you would be in this period for extended time.

Your description is also correct.

Tom T.

I cannot change the poll. But the chassis would fit all the engines as listed. Also, The original design would still be available.

Ron Shockley,

Yes, I understand. The various engine weights and CG's will create some setup issues and handleing variations. As all of the engines will sit in the same chassis location (relative to the rear face of the block and chassis) there will certainly be some polar moment and F/R weight differences. You see, this is why I keep telling JBL Dave to leave well enough alone.

Edley,

It is not JBL's intention to sell more cars. They have a hard enough time getting the current stuff done. But rather a matter of building a car that fulfills the market demand.

That is why I posted this poll. If the customer base really wishes a BB capable chassis, then I will design one.

Believe me, I would prefer to leave the car alone, it works very well just as it is and I do have other things to do with my spare time.

Looking the poll at this point, it seems that it is close to a tie between BB and SB.

But the way I read it, SB's are ahead.

[darteaus]

It does seem kind of like overkill when you can get a crate SBC from www.amerspeed.com w/500hp for $7K w/warranty. OTH, it's tough to say no to more hp & torque. Richard, I've heard that some muscle cars will get "bent" if the driver dumps too much torque at one time. Is that true, or just another rumor?

Keep up the good work.

Regards,
Dart

[Ant]

Richard,

Making engine mounts solid, I like the idea but have reservations, as my last Cobra was solid and I could not notice any harshness or whatever.

How does one know on whether the harmonics periods are different, or is it trial and error?
Solid mounting might not be great on some engine blocks and contribute to cracking, unless alloy engine plates are used, and having said that I would assume that alloy plates could well go the distance in giving a small amount of soak or compliance!

[rdorman]

I think I experienced your version of harmonic period in our old Reynard. You could hear the car buzz as every panel on the chassis vibrated.

In general, those who scream loudest for a big block in a 427 chassis/body style are those who are most concerned about originality. Since this does not appear to be one of the design goals of the JBL, why bother?

Rick

[decooney]

My engine builder who built my FE Big-Block just built a very nice full roller, fully ported, 331 Small-Block stroker for my friend's Unique Cobra. After driving in multiple 450 to 550HP FEs in Cobras, I must say , I was extra impressed with this 435HP small-block. This builder does the same witih Windsors too, but it sure proved to me once again that a (well built) small block can sure hold it's own, without question. Pulled and sounded like a big block too once he opened it up. Verrrrrry impressive to say the least.

[Woodz428]

Every Cobra made should have room for a BB( Bodacious Babe), I don't understand the poll results. Let the SB's (Stuck-up B**ches) walk.

[Richard Hudgins]

Dart,

I would think that you could certainly twist a chassis too hard with torque. (If you could hook up the tires) We bent a couple of T300's monocoques this way. But they were so weak you probably could of bent them just by jacking them up wrong.

Ant,

Using the engine as a stressed member has been done for many years in racing chassis. You have to do it correctly in order to not introduce loads in the wrong places on the block.

Harmonics et al.

The basic high amplitude frequencies of the engine are fairly easy to calculate. (The engine harmonics are quite difficult due to the many factors involved, However, one is only concerned with the major amplitude events as they relate to harmonic periods of the engine and chassis.)

In a standard layout V8 engine, one cylinder fires every 90° of crankshaft rotation. This is a "fourth order" excitation, (Four power pulses per revolution) which at an 1000 RPM idle, produces 66 pulses per second (Hz), and at 5000 RPM, produces 333 pulses per second (Hz).

Therefore, If your chassis has a natural frequency of 66Hz, it will be in "harmony" with the engine frequency at 1000 rpm. If it had a natural frequency of 333Hz it would be in "harmony" at 5000 rpm. In other words, if the engine and the chassis had the same natural frequencies, the amplitude of the instantaneous torque peaks would excite the chassis to the greatest extent as you are dividing by 1.

The JBL chassis has a natural frequency of 22.3Khz. (This was found by sonic testing, FEMA studies of the design are really beyond my capabilities.) Therefore, at 1000 rpm you have a result (JBL chassis) of 337. This number reduces the transfer amplitude by 337. As the revs go to 5000, you now have a result of 66.9.

It appears (from SAE papers and other NVH studies) that anything below a 20-1 ratio becomes quite evident to the occupants of the vehicle and very annoying. Conversely, anything in the 700>5K range is also considered quite bad as this is the range of human hearing that is the most sensitive to amplitude. (The buzzing that you hear in some econoboxes is due to this ratio.)

Now, this subject is very complex and there are all manner of papers relative to even and odd frequency divisors, second and third order harmonics, and relative fatigue points, etc. etc. You will have to speak to someone smarter than me to get the true story.

Jeez guys, how asking me some easy stuff that I can understand?

[rdorman]

Seems you go that one down! But is it shorter to walk to school or carry your lunch?
Rick

[Tom T.]

Geez Richard, I don't think JBLs should've been big blocks from the start (small blocks are great too), and I don't think SB guys are wimps, but I still think the BB is a good thing to provide as an option. What the heck, I'll just push a button.

TT

[decooney]

Originally posted by Mr.Fixit


The one time I played with a Viper, and blew his doors off, he followed me a few miles untill I pulled into a gas station where he had to know "what I had under the hood?"
"Just a small block." I tell him, he didn't believe me, I opened the hood and to his amazement there was a single carbed 351W.

there are just as many fast small blocks as there are slow big blocks

Hey, have you guys ever had the opportunity to race along side a FAST, modified Viper? I have. There are a few 700-850HP versions on the street near me. A few supercharged/nitrous ones at that. With those big/wide sticky tires they run, they can suprise even the best of the 512ci Cobras in the straights, and the small block FIA/351 Cobras on those twisty mountain roads. I compared some of the track times at Willow Springs between the Cobras and the Vipers, and it might suprise a few. I still wouldn't own one though... I like my manual steering, manual brakes, and no stereo options.