Converting a Cross-Plane V8 to Flat-Plane 1

[theonlynamenottaken]

I'm looking in to converting a cross-plane V8 to a flat-plane. Specifically, the Toyota/Lexus 1UZ. I understand the basics of difference between the two configurations but was looking for recommendations on engineering the balance shaft(s).

I have the CAD/CAM, engineering and machining/welding capabilities but need to figure out those balance shafts. Anyone know of any texts that cover the secondary vibration characteristics of flat-plane V8's? Or perhaps someone knows the specs on the bottom end of Lotus' Espirit, Ferrari's Modena or the TVRs?

I've got a couple of friends that can handle the ECU, ignition and fuel injection but would cherish any advice you folks may have....

 

[MikeHalloran]

I'm surprised that anyone would bother putting balance shafts in a V8, and given that they apparently did, I wonder what imbalance they were trying to offset.



Mike Halloran
Pembroke Pines, FL, USA

 

[Fabrico]

Are you sure the existing system is robust enough for the increased duty?

 

[Tmoose]

Flat crank v-8 has big secondary imbalance like a pair of inline 4s. The vibration is one of the things for whichg the NOVI V-8 engine was famous

Since the secondary imabalance is along the cylinder axis you >>might<< need a pair of 2x encrank speed counter-rotating balance shafts for each bank. Serious complication to simplify exhaust manifolding

 

[theonlynamenottaken]

MikeHalloran -- Flat-plane V8s are essentially like two inline 4's mated together, on a crank with no counterbalance weights. Therefore there is a secondary vibration similar to an I4, although the components of the imbalance from each bank negate each other....

Fabrico -- based on the Toyota Supra's block being capable of +1000 HP I'm GUESSING this block should handle it. Do you think perhaps the crank bearings won't have the area necessary to resist the unbalanced forces?

Tmoose -- I'm not really after the simplified exhaust... more along the lines of the decreased rotational mass (throttle response), the oh-so-beautiful sound and for sheer uniqueness...

 

[MikeHalloran]

I understand what a flat-crank V8 is. Did I understand correctly that the Toyota/Lexus V8, presumably not a flat-crank design, has balance shafts anyway?



Mike Halloran
Pembroke Pines, FL, USA

 

[theonlynamenottaken]

No, it has no balance shafts. I'm planning on welding in what I need, re-heat treating the block and then machining. My two business partners are ex-race machinists. I'll be doing a good bit to this block anyway - replacing the head gasket with compression rings, mating a 6-speed Porsche tranny, etc. - so I thought I might try the flat-plane conversion. I've got the time and tools; just need the theory.

 

[MikeHalloran]

It seems like a lot of work, weight, complexity and power loss just to reduce vibration. How about some soft motor mounts instead?





Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

I wouldn't bother either. There's a million flat plane cranks out there and I have never seen balancer shafts used. Since they don't reduce the bearing loads they can't improve reliability much.

First you need to work out your effective forcing function. Then you need to design eccentric masses to give the same forcing function.

All the equations are in Theory of Machines and Mechanisms by Shigley and Ucker, or you can do it from first principles.

Then you need to figure out where to put them.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[PackardV8]

Greetings,theonlynamenottaken,

You should have used, "theonlyroadnottaken." Your project, your money; however, of all the possible modifications one could make to that engine, a 180-degree crankshaft with balance shafts is the greatest investment of time and effort for the least return I can imagine. It will be unique.

Keep us posted as you work through the project.

thnx, jv.

 

[franzh]

On a technical note, the V-8 engine use shared rod journals on the crank. A flat plane crank would change the camshaft valve sequencing and firing intervals too.

If you were to take a four position standard V-8 crankshaft and change it to a 180 degree two position crank, you would introduce uneven firing impulses (instead of one every 90 degrees). Hmm, it seems to me you would be introducing more vibration than you are trying to eliminate.

Somewhere, there would be 4 cylinders with 180 degrees firing impulses, followed by 4 others. I visualize a master/slave cylinder relationship.

I can think of better ways to spend a couple of hundred grand, and you would get more power and a better sounding exhaust with exhuast tuning.

Franz

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[amorrison]

There are some cross vs. flat references on this Wiki article

http://en.wikipedia.org/wiki/V8

 

[bigpaul]

got to ask the question why do you wish to change to flat plan crank

 

[EHudson]

My understanding was that the principle advantage of a flat plane V8 crank was the ease of forging compared to a cruciform design. Racing engines design requiring a forged material rather than a cast crank then tended to be flat crank engines.

The racing engines were not as constrained by 1)the need for better balance and 2) the better fuel distribution that a dual plane intake manifold provides with a central carburetor mount.

The availability of independant fuel injectors solved the latter problem and your no holds barred approach to cost should permit you to whittle a strong crank from a big chunk of sturdy steel.

Sound? You want sound? Take the savings and make a downpayment on a P51.

 

[patprimmer]

If anyone cares to follow the link posted by amorrison4, that kind of says it all.

Flat plane crank is lighter, so more performance while accelerating as there is less inertia to overcome, and it changes the firing order so that each bank fires like a normal 4 cylinder at 180 degree increments, instead of a pair at 90 degree like a cuneiform crank.

This allows for an exhaust system that is more efficient without a need to cross pipes from one side of the engine to the other.

It also means that a dual plane manifold will have a left and right hand plane rather than a top and bottom plane.

Regards

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[Fabrico]

My understanding was that the principle advantage of a flat plane V8 crank was the ease of forging compared to a cruciform design. Racing engines design requiring a forged material rather than a cast crank then tended to be flat crank engines.

Things have been taken the other way too. There have been sucessful racers that stretched rules to the max by making flat plane cranks out of qualifying standard OEM cranks. New wording ended the practice.

 

[thruthefence]

Seems like there was a drag racer back in the old 70's A/FX days that ran 180 cranks in his cars ( Dick Landy?? Dodge Hemi??) The benefit was efficent exaust scavanging and intake tuning. As I recall it Literally shook pieces off the car on every run. The increased power was offset by much increased maintenance bettween runs.

regards, Steve

 

[gt40pinhd]

theonlynamenottaken,
i am going to put a flat plane crank in a 3uz.
i am going to use a balancer from a company in san diego. it is not a secondary balance shaft but a balancer to put onto the crank out front. looked for a balance shaft, couldn't find one for this engine or one to adapt to this engine. ferrari uses one. i'll look up the company, can't remember the name. would love to have a balancer shaft though.
wes

 

[GregLocock]

That's a harmonic damper (or TV damper). It won't really help much with the roughness of a flat plane crank, but I don't think you got to a flat plane crank if you want refinement. The thing will live, that is your primary concern.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tmoose]

If a carbureted motor shakes enough it won't run very well, even if the crank and block don't care.

A well respected balance shop balanced a race shop's enlarged by stroking 4 cylinder Opel motor. It shook so violently the intake manifold would not stay on. Settled out of court. Really the balance shop was blameless. Vibration analysis would almost certainly have revealed the heavy vibration was at 2X rotation, not 1X (where "balancing" can help).
The secondary vibration was made worse if the cranks was "stroked" and original length rods were used. Heavy pistons aggavate secondary imbalance too.