Hercules Rockefeller

Would it be possible, when rebuilding an LS7, to build up the motor with a flat plane crank as opposed to the standard cross plane crank that comes with the stock motor? As far as I know, no matter what exhaust, headers, etc you use, the cross plane crank is the primary reason we can never get that wild sound you expect from a high end exotic or a real racing motors. Most high end motors, and practically all racing motors (except NASCAR of course), use flat plane cranks while cheaper less exotic engines (i.e. everything from trucks to vettes) use cross plane.

glenB

Simply put, you will need to find room for a balance shaft

Instead of trying to re-engineer the engine, just make a recording of your engine of choice and play it continuously while driving, far cheaper.

And I wouldn't call the LS7 less exotic than other high end engines, but certainly less cumbersome and easier to work it.

What other manufacture produces a 427 CI engine for street use..... ?

Hercules Rockefeller

Well, it's true, no other high end manufacturer produces a 427 for street use, but maybe that's because companies like Ferrari are already getting 550 HP out of a smaller 274 CI engine. Of course, in that context you might still try to claim that the LS7 is not less exotic, whatever floats your boat I guess.

Here's a link to someone trying to do something similar:
http://www.eng-tips.com/viewthread.c...179471&page=25

Looks like it's just a lot easier to buy a proper flat plane crank engine in the first place. Or I could just get the recording

glenB

That was 4 years ago, any follow up?

jgaches

550hp with far less torque. The F car is an exotic piece but judged by size and weight vs output, the LS7 holds its own against much more "exotic" pumps out there.

Hercules Rockefeller

Seems not, so I'm guessing somebody else already figured out this isn't going to happen.

True enough, however in the context of horsepower, torque is irrelevant to performance. Through the magic of gearing, a 510 HP engine with 100 lb-ft of torque will outperform a a 500 HP engine with 1000 lb-ft of torque.

I'd rather have a Z06 for $60k than the latest F-car for $260k, especially since I've never gone up against a Ferrari and lost at the track. That being said, the Ferrari 458 is a hell of a car and beats the Z06 in every way imaginable, but I don't think it's worth 4X the price. Damn the engine on that thing sounds good though, especially when it's hooked up to headers and straight pipes!

AirBusPilot

You forgot to add that it takes RPM, very high RPM, to be able to use the short gearing needed to get the at the wheels torque up. That high rpm comes at a price.

Hercules Rockefeller

Oh I didn't forget; you are right, it does take a lot of RPM to get that wheel torque up at speed, in the case of the 458 it means we get a 9k (!) RPM redline. But then there's the sticker price and maintenance price of the 458. I guess you get what you pay for. But that spectacular sound of a 9k RPM flat crank V8, well that's something special and well worth the price of entry

dstiger

My LS7 makes awesome music on the throttle running to redline!

MitchAlsup

Is it possible: yes--albeit very expensive a custom forged steel billet crank would be the ticket--and you also have to get a cam shaft manufactured for the flat-palned-ness. After machining, you may find that the crank only weighs in at 60% the weight of the cross plane crank due to the way the balance weights are distributed.

Sound: There is another stumbling block in the LS engine architecture. The ports are not shaped to give great sound (like FORD Coyote engines) either. Then there is that little thing about valve opening and closing rates with pushrods that gets in the way.

Vibration: You will not need a balance shaft as the engine vibartions are only 4X more energy (2X transverse movements) than the cross plane crank. Those liking the smooth ride of the CPC need not apply.

SteveRiellyNZ

I was just doing some research into this myself. Sound was part of it, but from what I'm reading here and other places, a flat plane crank would give me a higher redline?
Yes, I would have to use stronger push-rods, probably rockers etc, but in the end would I actually benefit from it?

The only reason I could think of increasing the redline is if the cams etc where matched to give me a wider power curve, and maybe spinning up even faster.

OnPoint

IMO the sound of a flat plane crank is inferior.

To each their own, tho.

40YRW8

If you are really interested in the sound, the easiest thing to do is carve a hole in your passenger floorboard and inner fender well and build a 180 degree header. Of course, you would also need 50-55 inch primary pipes. I used to race against a guy that had a 180 degree header on his 283 cu in 57 Chevy Super Stocker. It sounded like a gazillion rpm but I don't think it was worth the effort as far as horsepower goes.
Gary

ZAKsPop

As a non mechanic, I had no idea what this thread was about so I did what I usually do, I googled it. Looking at the difference between the 2 it looks like the cross plane would be better as a cylinder would fire every 90 degrees and the flat plane would have the cylinders firing 2 at a time every 180 degrees. Would that not cause a loss in torque. The crank would have to travel twice as far on the power stroke than the cross plane crank, granted it would be doing so from the power of 2 cylinders. Oh, did I make it clear that I am "NOT" a mechanic in any form so don't beat me up if any of what I typed is completely wrong.

PaintballaXX

Idk how much more rpm you would get, that might be a valve train limitation. You might gain power from the weight savings of the crank alone (depending on how a power measurement is done). The real advantage would be the increase in exhaust scavenging (and therefor power). Same with the intake if it was redesigned to take advantage of the new firing order.

ZAKsPop

This $#!+ is making me . What is exhaust scavenging?

glass slipper

Google or Yahoo search "exhaust gas 1/2 wave and 1/4 wave tuning"...you'll get more reading than you ever thought possible.

glass slipper

Both crankshafts have a cylinder firing every 90° with the flat plane firing alternating banks LRLRLRLR while the cross plane has two pairs of cylinders on each bank firing in succession in the firing order LRLLRLRR. That's what makes exhaust tuning so difficult on a cross plane V8 and so easy on the flat plane V8.

Hercules Rockefeller

It's also, I believe, the main reason you can hear that smooth, race-engine-like sound of a flat plane crank coming from a mile away. I've got a good video i'll try to post later tonight that exactly illustrates what I'm talking about.

jsilvz

Great explanation