thirtythird

Ah,if racing were about which car sounded best..

Hercules Rockefeller

Ah, but it is:

http://www.youtube.com/watch?v=hoXuoARdX74

40YRW8

The major draw back of the flat plane (or more correctly) 180 degree crank is a major increase in engine vibration harmonics. Its main benefit is it isolates the two sets of adjoining intake runners and two sets of exhaust ports that fire next to each other in sequence with the 90 degree crank instead of being evenly spaced and alternating in the 180 degree crank. A 180 degree header solves the exhaust side but not the intake side. A 60 degree V-12 (Ferrari V-12/P-51 Rolls Merlin) is naturally timed and naturally balanced and creates that silky smooth, gorgeous purr that sounds so good. A 180 degree crank is naturally timed but not naturally balanced so it sounds good but has a lot of internal stress in the crank.
Gary

SteveRiellyNZ

There's nothing like the scream of the old V12's. The engines they have now, and AFAIK what they are moving to next year, even smaller, are just dull.

SteveRiellyNZ

http://www.kingscrankshaft.com/kings...ft_llc_009.htm - They can do one for USD$2500.

I've been given the name of CHRIS PADGETT to talk to at Comp Cams to do the billett cam for it.
From memory lingefelter have comp cams make their cams for them, so I'll touch base with them to see what they can do for a tuning package.

Anyone know if the factory ECU can have its firing order modified, or do I ditch it out and put in a Link or such instead?

40YRW8

It would be easier to just lengthen the wires on the harness so you can move the coil connectors to the new firing order.
Gary

SteveRiellyNZ

Are there any figures that show flatplane to crossplane and why the torque is so much different?
I can see why the ferrari engines have less torque, as they have a very short stroke in comparison to the LS7, but theoretically I would have figured the LS7 flatplane would keep the same torque, just be able to spin up faster.

Going to have to talk to some tuners to see what comparable figures there are.

SteveRiellyNZ

Ah, good call!! Someones thinking....

Bud Meyer

As a 31 year locomotive field service mechanic...I can tell you that the crank design has nothing to do with the exhaust note...Its all about how many cylinders you have, the design of the combustion chamber and specific exhaust system you run.

SteveRiellyNZ

Very true...180 degree headers have the similar effect on this C5 here:
http://www.youtube.com/watch?v=MSZTbR6C6Lw

So far easier, if your doing this for sound, than a whole new crank, cam, exhaust, and tuning solution.
I'm looking at it for the throttle response and overall performance, but yet to see exact figures that show which was is better for my purposes.
For out and out performance I've seen that flat-plane is the way to go, but for all around purpose, cross-plane works just as well.

Hercules Rockefeller

No way... the flat plane crank makes a huge difference in how the exhaust note sounds, there's no question about that. You can tell if a motor has a flat plane crank or not just listening to it for a few seconds, no matter what exhaust system it has... even if it has just straight pipes. The firing order makes all the difference, and you can't get the same order from a cross plane.

Here's a video clip that perfectly illustrates the difference in sound I'm talking about. Both cars have V8's, but the first is clearly the sound of a flat plane crank, and the second is the sound of the cross plane crank in the LS7:

http://s1134.photobucket.com/albums/...ossPlaneV8.mp4

What I want is for my exhaust to sound like the note we hear earlier in the video. And I'm sure I'm not the only one.

SteveRiellyNZ

That vids not the best comparison, seeing as its a vette in the foreground, and we dont know what the car in the background is.
It would need to be a LS7 vette as well, at the same rev's to be able to compare.

If your just after the sound, research "180 degree headers", which will get you the sound if thats what your after. ( check my vid link above ).
I'm researching this more for the response and power capabilities than anything else. If, by what is becoming apparent, throttle response, and power curve is snappier, then thats what I want.
This matched to ITB's and the right exhaust setup to make the most of it is what I want.

foremaw

To each there own of course but it seems like a pretty big mod just for exhaust sound. I'm not so sure that many 'Vette owners want the car to sound like a Ferrari instead of the V8 muscle it is.

SteveRiellyNZ

I'm not doing this for the exhaust sound, a 180 degree header would achieve this.

There's potential throttle response, and power-band benefits with moving to a flat plane crank that I'm researching.
It's possible this will be with a minor loss of torque at low-rpm, but over-come with a wider more progressive torque curve....thats the part that I'm confirming.
And to be honest, USD$2500 for a crank, a bit more than normal for cams, is a lot less that what some people will spend on pretty rims.

I dont do normal, and frankly the vette V8 sounds the way it does because the design is in-efficient. If it was the way to go, most exotic high performance cars would use it, but they dont, they use flat plane. Same if not more horsepower with smaller engines.
So, if I go flat plane, with larger capacity ( LS7 ), I should theoretically have a faster responding, high horsepower engine, and this is before I get to work on ITB's and more down the track.

SteveRiellyNZ

One of the better descriptions on the difference....its regarding bikes, but I'm thinking the overall theory applies:

http://darkriderindia.blogspot.com/2...rankshaft.html

Hercules Rockefeller

Here's a question. If you had a 90 degree flat plane crank V8, would the crankshaft essentially be the same configuration as a cross plane straight 8?

Also, while the 180 degree header does sound interesting, it still doesn't have that flat plane sound (but then again, it's hard to tell what something sounds like in real life until you hear it in person).

4GS7

So what is the goal for this build? Do it for the sake of having done it? Do you want to make X amount of power?

OKsweetrides

The primary reason is crankshaft acceleration. No counterweights=lower inertia to overcome but you need to build enough space for balance shafts to cancel the nasty harmonics. A secondary reason is that since most race engineers have an affinity for mid engine, it's a bit easier on the packaging of exhaust routes with the flat plane. That's really about it... Nothing in engineering is free; everything has a trade-off. If I'm not mistaken, weren't flat plane cranks thought of and built first and then the cross-plane branch evolved out of them?

Speaking of free! If you get a .25M minimum order of flat plane cranks, you'd likely see a $2500 per unit rate... else it's gonna be mad expensive.

I'd be curious how one would even go about slapping balance shafts into the mix.

edit: IIRC, NASCAR experimented with flat-planes and well, there's a reason that "low brow non-exotic" engine still outclasses a heck of a lot of Euro engines.

SteveRiellyNZ

Yes, flat plane came first, and it was two american car companies (Cadillac and peerless ) that came up with cross plane. They tried to patent it each, and ended up agreeing to share.
Due to the firing order a balancing shaft isn't needed, hence cheaper development costs, but does require the heavy counter weights.

http://en.wikipedia.org/wiki/Crossplane

It also does say that most racing teams use flat plane ( they're not to fussed about balancing really ), and from what research I've done, with the right associated forged, light weight components, the extra vibration would be minimal.
What I would lose in a bit of low end torque ( and I do mean just a little bit ), I would potentially gain in a wider, faster responding, more usable powerband.
Its that faster responding part that really interests me. I would have overall about the same torque, but faster access to it.

In track work I "think" this would mean when two comparable cars are powering out of a corner, the cross plane would have slightly more torque, which would equate to extra power, but its going to be accelerating slower that the flatplane, which has slightly less torque, but is climbing up in revs' faster.

That's the theory anyway, and what I'm trying to find actual provable figures that show exactly that, or that its not the case.
There's a lot of "this is how it works", but from people that are just stating what they think, not what they've actually tested and know for fact.

Hercules Rockefeller

You're kidding me, right? NASCAR doesn't use a cross-plane crank because it works better, they use it because their I'm-so-drunk-I-can't-fish target audience wanted a 'racecar' that sounded like the low-revving, big block V8 their grandpa used to run moonshine in backwoods Arkansas. Every decision NASCAR makes is done in the interest of maintaining their low brow, beer swillin', tabaccy-chewin', trailer trash image.