Tom400CFI

Oh, My bad. "rev SPEED".....I missed that. You'd get more benefits from a lighter flywheel and clutch for way less money. But you're right; flat plane would definitely be different.

DGXR

I think of a flat plane crank similar to a boxer engine: the throws are always opposing each other so the forces balance out, mostly. It doesn't mean no balancers are required, just fewer and/or smaller balancers, which means quicker revs. The old BMW motorcycle engines are boxers, they are known for smooth operation but not quick revving (they have large pistons).

Tom400CFI

While that is true, I was responding to claims of less rotating mass = faster revving. While it would contribute, that contribution to "faster revving" is very small b/c the crank is a small diameter compared to the clutch and flywheel. I've read an article where even the Ford engineers discounted rotating mass as a meaningful benefit fo the crank...specifically b/c it's a small diameter and they're still using a relatively heavy FW and clutch.

How many hp do you think any of us on this forum are losing to windage? How many hp compared to a flat plane at the same RPM that most of us are running?

cv67

Understand the concept but cant get past the sound. Wow that is real bad...
not sure what the obsession with revving in N is, big deal. To each thier own
THanks for posting OP always good to see somethign different.

Tom400CFI

I think the discussion has steered in more directions than that....but I totally agree with the part you said in bold.

Which is why I said, way back in post #3

Then Chumpvette said my post was "top 5 nuttiest post he's read on here"...which was weird.

Tom400CFI

Here is the sound of one, flat plane crank, V8...Sound a lot like a Honda, to me....


28:55, if it doesn't load there by itself. Turn up the volume and enjoy!

MatthewMiller

Whew! There's a lot to respond to in this thread! The flat crank gives no useful power advantage in this application. None. You can't make headers with long enough primaries to really take advantage of any extra scavenging benefits. The one advantage here is that even firing makes the engine less sensitive to exhaust tuning, because you don't have to worry about two cylinders on one bank firing only 90* apart. So with a cross plane V8, you have one cylinder interacting too much with the next one that fires only 90* later. This makes longer primaries advantageous by helping shield some of that. It also makes cam timing (especially overlap) more critical. With a flat plane, every cylinder on one bank fires a full 180* apart from each other, making it less sensitive to these things. You can infer that there is a benefit in terms of fuel economy and emissions with this layout for the same reason. That's it. That's your total advantage. You could get the same advantages from 180* headers, as previously noted, but those aren't practical for packaging reasons. They don't rev faster or higher, and practically speaking they don't really make more power.

The disadvantages are myriad, all related to vibration. There's a reason why the only previous flat-plane V8s (even in racing) were small-displacement, short-stroke engines: massive inherent vibration. Yes, they are even-fire engines, but they have serious second-order vibration issues. Inline four cylinders do too, but it's pretty easy and universally common nowadays to design in a balance shaft to quell them. It's not practical to do that with a V8. When you go to a long stroke with sizable (i.e. heavy) pistons, as for a production engine, things get ugly quickly. Ford had to go to heroic measures to deal with this issue in the GT350, and it's basically operating at the very edge of its envelope in stock form. If you modified that thing to go an extra, say 250rpm, you'd be well into the "Danger Will Robinson" territory. This is not the case for a cross-plane V8.

Tom400CFI

As usual, very well articulated.

qwiketz

there was that zo6 on bring a trailer last month and was on ther previously. Man, that sounded horrible through my computer. Hope it sounded better in person!!!

Didn't make much power either (530rw) considering a heads and cam package will do the same or more on a ls7

pacoW

road and track magazine liked it.

https://www.roadandtrack.com/car-cul...z06-ls7-sound/

ChumpVette

Done properly, a flat plane crank has a glorious sound. See Porsche/Ferrari and a few others.

Tom400CFI

I think that has more to do with other factors (such as the exhaust system). Because I know that YOU know...that all you're creating is even exhaust pulses and there is no magic in that. If there were, every inline 4 ever made would sound equally "glorious".

I'm not familiar with any Porsche V8's that use a flat plane crank. The 928, Cayenne, and Panamera all use a cross plane crank.

pacoW

I agree, especially the Ferrari.

confab

Okay, this is crazy.. 9K rpm.

Lingenfelter 358 CID LSx Flat Plane Crank Engine

It definitely sounds different.

cv67

Just doesnt do anything for me...guess youd expect that out of an F car or the like, to ea their own.

ChumpVette

Not surprised.
917
918

Tom400CFI

Ah yes. The 917 and 918 aren't exactly common cars

"Not surprised", huh? You love the "jab 'n run", it would seem. I'm not much of a Porsche fanatic, either -even though we own one.

FYI, the 917 had three different flat 12's...not a V8. "I'm not surprised".


.

ChumpVette

If you go to Porsche events, they are common. Head to Rennsport Reunion and see some cool stuff. Unlike the junk events GM puts on.

qwiketz

I’ll have to listen to the ls7 with the headphones on this time.

im sure a flat plane crank v8 can be made to sound good with the right selection of components. . I believe my rs7 has one and it sounds pretty exotic with the exhaust valves open and it’s only 4.0 liters. With way more displacement I’d imagine the goodness would just be amplified

auburn2

When you are going to add it back into the flywheel anyway (which you will need to do to have a driveable street car).

The flat plane crank hype for a street car is all about marketing, not performance.

The only application it is really worthwhile is in a race car where you are limited on displacement.