Flat plane crank in a SBF?

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WesS

i have a quote from a local crankshaft manufacturer here in SoCal for a flat plane crank for a small block ford for $3200.
don't have the money or time right now, but maybe in a year or two, i will. i think an alum small block ford with a flat plane crank will rev very quickly, ideal for a gt40.
wes
 
D

Doug Clark

I don't get why a flat plane crank would rev any faster? Surely thats all to do with the inertia of the rotating mass?

I've witnessed a similar effect with bike engines I remember listening to the "Big Bang" 500GP bikes which didn't sound as if they picked up revs as quick as the even firing order versions, but I'm sure they actually did, similarly the RVF750 Honda's had a 360 degree crank in them which made them sound as if they were turning slower than the normal 180 degree road version, but watching them annihilate everything else on the Mistrale straight day and night, they certainly were pulling at least as many revs as the competition.

Another small fly in the ointment is the US$15K price tag for a one of crank (thats all I've managed to find on the web in another discussion). Unless you know how to make your own?

I did see a Yamaha based 1000cc grass track sidecar outfit running in "Big Bang" mode once that might have just been done with cams and ignition though being a 4 cylinder.

If you are wondering what "Big Bang" engines are look here.
 
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J

Jac Mac

Doug68 said:
I don't get why a flat plane crank would rev any faster? Surely thats all to do with the inertia of the rotating mass.here.
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Exactly and since the flat plane crank does not have the same counterweight requirements of the conventional V8 crank ( Too put it far to simply-# 1 throw balances #2 & #3 balances #4 , whereas each end of a conventional crank has to look after itself ) then its mass is considerably less which allows it to accelerate faster.
 
D

Doug Clark

jac mac said:
Exactly and since the flat plane crank does not have the same counterweight requirements of the conventional V8 crank
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Ha ha! That shows what I know about V8's I didn't realize that the 'normal' V8 crank would be intrinsically heavier than a flat plane jobbie.
 
K

John

Hey Jac,had a feeling you might no who iwas talking about. i was talking to him at Manfeild the last time he was down , he gave me the flat shift setups for the Fraser, and he said he was going a little further, but wouldnt elaberate the big Sh#t, just gave that cheezy grin.
he will be down for whittikars in Nov so i wonder if he can better his 65"s
cheers John
 
C

colin artus

Freewheel said:
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:
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Its not quite the same with the DFV as this engine is a stressed member and is directly mounted to the tub rear bulkhead, thereby feeding every vibration right into the drivers seat (no need for revcounter!)
I've got a Stratos replica with a solidly mounted Ferrari V8 - it feels like there's a bunch of syncopated dwarves with sledgehammers in the back.
 
MikeP

Mike Pass

Supporter
On the quick to rev up idea - maybe it would be far far cheaper in the end to lighten a normal forged item and do an internal balance by removing weight (no slugs put in). Then use a really really light flywheel, light rods and pistons. This setup seems very fast accelerating (1000-5,000rpm ) to me and I'm used to 10,000rpm Imp and Cosworth MAE 1,000cc screamers. The flywheel/clutch assembly has a very strong effect on the revvyness of an engine. I remember that the further away the masses are from the centre of spin the inertia increases by the square of the distance.
Not sure whether this would have the exotic sound you want but it sounds nice to me at 7,000rpm.
Cheers
Mike
 
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Cliff Beer

Mike, you're right - a good lightening and balancing job will certainly go a long way to helping move up the rev limit but the lightening you can do on a standard crank is limited and still make the crank durable and the engine not shake itself apart. JacMac said it right earlier in the thread - the flat plan crank by its very nature reflects inherent counterbalancing without adding large counterbalance weights - this is why it can spin up fast, and rev higher.
 
C

Cliff Beer

jac mac said:
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!
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JacMac, thanks, that sounds like a winning combination - efficient and probably about as economical as possible given the unique application.

I suspect you're right about the cost. However, custom crank builds have been getting cheaper as the cost of a fully automated CNC milling machines has been coming down as these are becoming more prevalent and available. It's still not cheap - probably at least $5,000 to $10,000USD for the crank and something a little less for the cam I would guess, ballpark.

That would be an amazing engine - alloy block will save a bunch of weight, and, the crank should be a few pounds lighter as well. With excellent valvetrain componentry I suspect that turning to 7,500 rpm shouldn't be too big a stretch. Would you think that peak hp would be around 6,500? Peak torque around 5,000?
 
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Jac Mac

Your typings too fast Cliff- Those RPM would be 'very safe' on that combo, camshaft would decide where the max hp/tq would be.
Cliff, while the counterbalance factor is there-do not forget the secondary imbalance factor of the flat plane. That is why I suggested in post #17 that you do a comparative test with the 289 (2.870") stroke etc to minimise the balance factors.
Most conventional cranks can have an enormous amount of weight pruned off them without affecting reliability- its just the cost of removing that weight that makes it uneconomic to most. Have a look on some of the manufacturer sites for pics of the ultralite speedway type , scalloped counterweights -centerdrilled mains/throws- not a lot of metal left in some cases.

All this metal removal is great for racing/acceleration etc, but in a road car it can be a pain at lower RPM, every time you climb a slight rise a downshift is reqd and if you push the clutch in the rpm drop away real fast.

Mike, used to play with Imps/Anglias myself back in the sixties, & my son just bought a couple of Imps recently that he has grand plans for! I told him he should not feel obliged to copy all of his fathers mistakes! Have to admit that an Imp motor @ 7000+ was a bit different to all other cars back then.
 
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MikeP

Mike Pass

Supporter
The main problems with the Imp engines was that we had used to use lightened and polished standard rods with a larger little end bush at 10,000rpm but they were on the limit and when things went wrong the little end came off and the rod then punched a neat slot right through the engine from top to bottom. Also bigger motors ie 1220cc had a longer stroke crank would only brev to 8,500rpm. The wise folks now use custom H section rods and the engines are much more reliable as a result.
Jacmac - Glad to see the young people getting into Imps and Anglias. We had 4 Imps at the recent Oulton Park Gold Cup meeting. All finished well in the race. Took me back a bit!
Cheers
Mike
 
J

Jac Mac

Russ Noble said:
Yeah, thats true. They used to destroy themselves spectacularly !!! :lipsrsealed:
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I knew I could rely on Russ to remember 'that'- just goes to show his memory can work at times:). Actually that was a fairly special 'Lotus' ford block in the car at the time Russ, & had it not punched a dirty great hole in the side would now probably be worth more than the whole car was worth at that time. Never actually 'destroyed' an Imp motor....was not for lack of trying either.
 
F

Price Walton

sfm6s said:
Its not quite the same with the DFV as this engine is a stressed member and is directly mounted to the tub rear bulkhead, thereby feeding every vibration right into the drivers seat (no need for revcounter!)
I've got a Stratos replica with a solidly mounted Ferrari V8 - it feels like there's a bunch of syncopated dwarves with sledgehammers in the back.
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Colin,

Quite right, thanks for the reminder - didn't Derek Bell win his first Le Mans in a Mirage that was pretty much broken in half due to the DFV?

I seem to recall some F5000's having similar issues in the late 70's, but I don't remember whether they used their engines as stressed members.

Interesting description of your Stratos - I looked long and hard at the HF Stratos before deciding I wasn't likely to find all the bits I needed.
 
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Jac Mac

Paul, interesting thread on that site, I note that your concern about the sound difference between the Ferrari with flat plane crank & the GT40 with 180° headers.
While there are many differences between both motors like capacity- valve layout etc , probably the main reason is the larger mass of the ford crank/rods/pistons which slows throttle response time compared to the lighter Ferrari combo.
 
p thompson

Paul Thompson 'Hooligan'

Admin
:laugh::laugh::laugh: LOL!!! :laugh::laugh::laugh:

Un-Bloody-Believable....

Just when I thought I'd seen it all - along comes a gizmo that'll turn a Fiat 500 into a Barracuda... yeah right..:laugh:

Mind you, I can see this being VERY popular at numerous Halfords Car Park weekend meetings across the country where just about every Citroen Saxo must have 500BHP judging by the size and sound of their tailpipes.:thumbsup:
 
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