Cross Plane crankshaft ?

In reply to Streetwiseguy :

I had that thought too..

It's not an unnecessary word. It's used to emphasize that it's the same 5.2 but without the flat-plane crank. 

As for why, Ford people said it was because they wanted over 500hp without forced induction.

rustybugkiller said:

I'm confused. If a flat plane crank is hard to balance, why would they allow such high revs?  Doesn't a smooth balanced engine allow for higher revs?

I meant harder to balance with off-the-shelf parts.  Once you get it balanced, it's balanced like any other engine.  You just can't stab in a flat crank without changing rods and pistons with expensive specialty pieces.

Knurled. said:

rustybugkiller said:

I'm confused. If a flat plane crank is hard to balance, why would they allow such high revs?  Doesn't a smooth balanced engine allow for higher revs?

It's not that they "allow" high revs.  It's that they tend to be fairly small, and motorsport-biased, which means they require high revs.

 

The rest of it is exhaust tuning - crossplane crank V8s have uneven firing order per bank, which screws things up with the headers unless you can run a bundle of snakes exhaust that crosses two cylinders' exhaust from one bank over to the other.

 

Don't confuse crank balance with the issues with being a flat plane.  You can make a flat plane crankshaft perfectly balanced but it will still shake your eyeballs out of their sockets because of the piston weight effects, which happen at a frequency that you can't fix with crank balance.

Agree with all of the above except "allow" high revs.  The lightweight of the crank and the associated parts in the rotating assembly certainly do allow for higher revs.

Maybe poor choice of words.

In the case of the Ford v8 (gt350) if you are going to build a high power NA engine why do you chose a flat plane crank that has balance issues and then spin it to 8200 rpm. Wouldn't a design that is more balanced spin at higher rpm and be more reliable?

rustybugkiller said:

Maybe poor choice of words.

In the case of the Ford v8 (gt350) if you are going to build a high power NA engine why do you chose a flat plane crank that has balance issues and then spin it to 8200 rpm. Wouldn't a design that is more balanced spin at higher rpm and be more reliable?

THE SOUND

Worth it.

It's not a road racing homologation special like a real GT350.  It serves no purpose to exist any higher than "make upper middle class people giggle".  (Rich people don't drive Mustangs, unless they are nuveaux rich, in which case their opinion dosn't matter)  To that end, the power numbers merely are a statistic for 14 year old R&T readers to argue over. 

But they sound incredible.

Mind you, I'm hoping they depreciate a little harder, because I want one myself, but I ain't nuveaux rich, I ain't even upper middle class, I'm just some guy who likes engines that scream.

At this point, Ford really has the engine choices covered for the Mustang.  Pretty much anything you want is an option.  Turbo 4, V6, V8, insane sounding high revving flat crank V8, more HP than a Hellcat supercharged V8. 

The sound can be pretty spectacular.  One of the GT350-based turn-key race cars (Mustang GT4) showed up at a track day I attended recently, he later posted a video of it and wow.

rustybugkiller said:

Maybe poor choice of words.

In the case of the Ford v8 (gt350) if you are going to build a high power NA engine why do you chose a flat plane crank that has balance issues and then spin it to 8200 rpm. Wouldn't a design that is more balanced spin at higher rpm and be more reliable?

Very much so.  Flat plane cranks in V8s typically are a race-type thing because they get torn apart frequently.  I'm wondering how Ford keeps theirs bolted together for the duration of a warranty.

It's not that it can't be balanced, it's that no matter how well you balance it, the even firing has all kinds of harmonics and vibes that tend to rattle things apart.

In reply to codrus :

If you can hear the engine over the transmission!

Jeez straight cut gears like to make themselves heard.