Flat plane crank in a SBF?

[Cliff Beer]

I'm just wondering if anyone knows of anyone having tried (sucessfully or not) a flat-plane crankshaft in a small block ford engine?? Seems to me that folks who drive a GT40 are typically already putting up with a fair amount of vibration - why not employ a flat-plane crank and perhaps get another few hundred rpm, a little more power and faster throttle response?

Obviously, such an application would need a custom ground cam, revised ignition timing and probably a whole host of other adaptations but it certainly should be doable. Would be an interesting exhaust note to hear as well.

 

[John]

Cliff theres a guy down here running a VERY quick TVR with a rover engine with a flat plane crank, the sound is something you have to hear to appreciate , but designing an exhaust system to 1-fit and 2- work was the biggest dilema.
not a cheap exercise by any stretch of the imagination but, the rewards are well worth the effort if your in a position to do it.
cheers John

 

[Jac Mac]

I'm just wondering if anyone knows of anyone having tried (sucessfully or not) a flat-plane crankshaft in a small block ford engine?? Seems to me that folks who drive a GT40 are typically already putting up with a fair amount of vibration - why not employ a flat-plane crank and perhaps get another few hundred rpm, a little more power and faster throttle response?

Obviously, such an application would need a custom ground cam, revised ignition timing and probably a whole host of other adaptations but it certainly should be doable. Would be an interesting exhaust note to hear as well.

Exhaust note would be the same as a 'normal' crossover GT40 system, just that the flat plane system would not have to be crossed & therefore lighter & simpler to build.

 

[Jon Briggs]

Cliff theres a guy down here running a VERY quick TVR with a rover engine with a flat plane crank, the sound is something you have to hear to appreciate , but designing an exhaust system to 1-fit and 2- work was the biggest dilema.
not a cheap exercise by any stretch of the imagination but, the rewards are well worth the effort if your in a position to do it.
cheers John

John
Are you sure that the guy isn't running the AJP V8 engine? It was a TVR special and came with a flat plane crank as standard.

It was fitted to the Cerbera and in standard form was 4.2 and produced 420BHP with 380lbft of torque.

 

[fostereast]

Depending on what your trying to accomplish, to get any real benefits out of a flat-plane crank you would have to reconsider and match all the characterstics of the engine.

Bore & Stroke
Rod Ratio
Cam
Cylinder head specifics.

As exciting as it sounds to do something like this, I think the crank is the short piece of a long tail you would find yourself pulling on if you wanted to end up with something really exciting. But I tend to see things as pretty complicated...

As an uneducated opinion, I would shorten the stroke, use as long a rod ratio as I could, use multi valve heads and cam the engine for a high rev range, use multi-port EFI with a crank trigger.

 

[J. Salmon]

Exhaust note would be the same as a 'normal' crossover GT40 system, just that the flat plane system would not have to be crossed & therefore lighter & simpler to build.

Not sure about that, don't two pistons fire at the same time with a flat plane (two every 180 degrees, not one every 90). Flat planes tend to sound like a four cylinder. My 355 sounds like a 4 cylinder sport bike

YouTube - Ferrari 355 at VIR

 

[Mesa]

J=
I followed a 430 around the hills (well for a FEW minutes anyway) this weekend. He must have had a nice exhaust system because that thing sounded soooooo sweet. Maybe I should finish my 360 engine and stick it in SOMETHING just to hear it run....

Flat cranks sound great. If I could put a crossover system in my SLC I sure would.

 

[Jac Mac]

Not sure about that, don't two pistons fire at the same time with a flat plane (two every 180 degrees, not one every 90). Flat planes tend to sound like a four cylinder. My 355 sounds like a 4 cylinder sport bike

YouTube - Ferrari 355 at VIR

We are talking 4 strokes here? No they do not fire at the same time-they essentially turn the V8 into two 4cyl inline engines which are 90° out of phase with each other. If the Flat plane version has an exh system per bank and the normal production version has a crossover system then both sets of exhausts will have 180° intervals in each set of four primaries. The two tailpipe 'sounds' are split or 90° out of phase.

Now if its a FLAT 8 with a Flat plane crank both sets of 4cyls will be 'in phase' and two cyls will fire at same time.( A total of 4cyls @ TDC-two on o/lap-two fireing )

 

[J. Salmon]

We are talking 4 strokes here? No they do not fire at the same time-they essentially turn the V8 into two 4cyl inline engines which are 90° out of phase with each other. If the Flat plane version has an exh system per bank and the normal production version has a crossover system then both sets of exhausts will have 180° intervals in each set of four primaries. The two tailpipe 'sounds' are split or 90° out of phase.

Now if its a FLAT 8 with a Flat plane crank both sets of 4cyls will be 'in phase' and two cyls will fire at same time.( A total of 4cyls @ TDC-two on o/lap-two fireing )

Ah, you are correct. For some reason, I have always overlooked the 90 degrees between banks! But I will have to say, the flat plane engines don't sound to me anything like a crossover. Maybe I will change my mind when I have more experience, but so far nothing I have heard sounds quite the same. There is a raspy quality that is very unique.

 

[Jac Mac]

J=
I followed a 430 around the hills (well for a FEW minutes anyway) this weekend. He must have had a nice exhaust system because that thing sounded soooooo sweet. Maybe I should finish my 360 engine and stick it in SOMETHING just to hear it run....

Flat cranks sound great. If I could put a crossover system in my SLC I sure would.

That would be no fun Mesa, then you would have to get someone else to drive it while you followed on the bike to listen.

Please do fit a crossover or 8 into 1 on your SLC- the tractor version does nothing for me.

 

[BruceA]

My understanding is that the only reason you would be using a flat plane crank is to get the benefits of even exaust pulses, eg scavaging effect from one side of the engine, instead of crossing over the pipes ah la GT40 etc.
Also I believe a flat plane crank is not as balanced as a 'normal' crankshaft and will introduce more viabration than the normal crank.
But of course feel free to point me in the right direction ......

 

[J. Salmon]

Here's some video of the flat plane in all its glory. Possibly the best example I have heard. The video is worthless, but the sound....

YouTube - Ferrari 360 Challenge Stradale São Paulo (SOUND!!)

 

[Jac Mac]

J- if you listen to the sound on the vid by 'babylon 355' in the 'butetown tunnels-cardiff' it sounds very similar to a couple of Ford rally escort twin cams with webers ( circa 1970 ) which it essentially is in ferrari clothing.

Bruce L- right on both counts, '3rd' good reason behind flat plane is reduction in rotating mass.

 

[fostereast]

My understanding is that the only reason you would be using a flat plane crank is to get the benefits of even exaust pulses, eg scavaging effect from one side of the engine, instead of crossing over the pipes ah la GT40 etc.
Also I believe a flat plane crank is not as balanced as a 'normal' crankshaft and will introduce more viabration than the normal crank.
But of course feel free to point me in the right direction ......

I think it is more used because it is a little smaller in diameter, lighter and lets the engine rev faster and it does introduce more vibrations. Some flat plane crank engines use a balance shaft which can be a detriment if your packaging size and weight is critical.

 

[Ross Nicol]

Personally I hate the sound of a Ferrari because when and if I hear it, the b......y things passing me. For some strange reason I never hear any exhaust note when I pass them.

Ross:laugh:

 

[Cliff Beer]

Some very interesting points being made.

I do think this would be a very interesting project - where I'm basically at is deciding to do two engines in parallel - an upgraded 347 (ideally alum) for the near term installation and a flat-plane SBF derivative to engineer and work on over the next couple of years.

I hear what JacMac is saying about the orientation and firing of the cylinders, but somehow every flat-plane V8 I've heard or worked with in some detail has a distinctly different sound that is unique and appealing.

There are some distinct benefits of the flat-plane configuration - generally, the flat-plane crank utilizes smaller counterweights. As I understand it this is because counterweights are less effective/capable of balancing the rotating mass. So, yes, there's generally more lateral vibration. My GT40 is pretty rumble tumble going down the road anyway so I doubt this will make that much difference. The lower rotating mass allows for faster spin up and a somewhat higher upper rpm limit (if not limited otherwise by the valve train).

Agree with fostereast - to extract maximum advantage then it has to be a total engineered package including bore/stroke, rod length, cam profile valve configuration/breathing, compression, etc. And, yes, tuning for top end would optimize, so a valvetrain that doesn't impose a lowish rpm limit is an essential element (multi-valve works well for this).

Thank you for the feedback, good stuff.

 

[Jac Mac]

Cliff, might I be so bold as to suggest a way in which you can do these projects so that results will give some excellent feedback for comparison purposes.

1. By all means use the Alloy Block, preferably with 4.125" bore.
2. Use a 289 crankshaft- 2.870" stroke- std cast or steel, wont really matter.
3. Chev SB rods 5.700" long- preferably aftermarket & a light version if possible.
4. Pistons with 1.070" pin height ( These are originally designed/intended for the 3.400" stroker versions of the SBF and are available in the 4.125" bore size ).

Now when you build your flat plane crank ( with the same 2.870" stroke ) & camshaft ( with the same lobe spec's as the original build ) to suit that is all you will require and be able to fit the new crank & cam to your existing block. Have specimen weights for the rods/pistons made up at the time of building/balancing the first engine. I have a feeling that crank & cam will cost more than the whole initial engine build, thats why I suggest the shorter stroke, less machine work/metal removal involved.

With the 4.125" bore & 2.870" stroke you will have 306 cu in and both motors will love to rev!

 

[John]

John
Are you sure that the guy isn't running the AJP V8 engine? It was a TVR special and came with a flat plane crank as standard.

It was fitted to the Cerbera and in standard form was 4.2 and produced 420BHP with 380lbft of torque.

hi JON no its not the orig TVR engine, it started life as a 4.2 rover, but lots of money and a flat plane crank later, its now a 5ltr 6oohp rocket ,
and i agree with Jac, if you wernt looking you'd think it was a couple of twin cams idling away and when it revs, its instant.
cheers John

 

[Jac Mac]

hi JON no its not the orig TVR engine, it started life as a 4.2 rover, but lots of money and a flat plane crank later, its now a 5ltr 6oohp rocket ,
and i agree with Jac, if you wernt looking you'd think it was a couple of twin cams idling away and when it revs, its instant.
cheers John

And going by a phone conversation I had from the other side of the planet recently Carl has a few tricks up his sleeve yet!!

 

[Price Walton]

It is my understanding that if you wish to install a flat crank engine, several items must be completed first (based on the DFV, but nonetheless has also applied to SBCs I imagine will be a factor in a SBF);


1. Any fillings must first be removed in a convenient place.

2. All chassis joints should be double welded and have additional bracing fitted.

3. Place one's eyes on an independent suspension system.

4. Flexi-mount any fixed windows.

With these and other items done, some regularly, everything should be :thumbsup: