Flat Plane Crank
- Thread starter any_key
- Start date
There are lots of notable examples of flat crank V-8 without the use of balance shafts. There certainly is some marginal amount of added vibration but this doesn't necessarily have to be significant - more minorly unpleasant to the seat than destructive to the engine. And, the sound of a flat crank V-8 is quite different - more like tearing a phone book in half than a melodious rumble. The delta in power output is typically impressive - can be up to 15% more with the same displacement.
any_key said:
Yes you will need a Flat Plane Specific cam, Dist is just a matter of moving leads around in the cap for 15374826 firing order. This gives 1342 on each bank. Balance shaft not rqd on race type setup or practical on SBF. I believe Crower & other manufacturers will build you one. I would not consider one unless I was in a class where light weight & acceleration were paramount and had exhausted all other avenues. If you only want the exhaust note then it is simple to arrange the primary pipes in the correct sequence to obtain this.
Jac Mac
I know that a 180 exhaust setup would give close to the sound of a flat plane, my question started out as more of a "has this been done".
Now I'm going over it as an engineering problem... something I should probably wait on until I finish my degree and get a few ASE certifications under my belt.
Now I'm going over it as an engineering problem... something I should probably wait on until I finish my degree and get a few ASE certifications under my belt.
Lynn Larsen
Lynn Larsen
AnyKey,
Do some searches as well. There have been some extensive discussions of this topic in the past.
Lynn
Do some searches as well. There have been some extensive discussions of this topic in the past.
Lynn
I seem to remember there was a TVR Griffith racing in UK Historics with a flat plane crank some ten or fifteen years ago. The car made the Shepherd bros Cobras look slow which is saying something. The car didnt appear very often as it wasn't very popular with other competitors and was probably bending the rules a bit too much.
You should check with Crower or another before you drop it. What the heck, a phone call will answer a lot of questions, and maybe they have done it before.
I think you get better exhaust scavenging, but there are other benefits too, aren't there? Spin up is faster, but I can't remember why... off to the google...
I think you get better exhaust scavenging, but there are other benefits too, aren't there? Spin up is faster, but I can't remember why... off to the google...
i got quotes from Crower for both the crankshaft and the cams to go with it for a 4.6 mod ford DOHC. also, Valesco quoted me on the flat plane crank. Scat told me they were too busy the first time, but when i was there in person, they said they could build one.
just have to be persistent. of course, you will need special cams. and EVERYONE advises me about the vibration. haven't found a balance shaft yet, but i am considering a damper by ATI. should help some, i hope.
just have to be persistent. of course, you will need special cams. and EVERYONE advises me about the vibration. haven't found a balance shaft yet, but i am considering a damper by ATI. should help some, i hope.
As I recall, vibration problems became less evident with shorter stroke crankshafts. For a SBF block, if I remember right the recommendation was that a flat plane crank for a 289, with it's shorter stroke, could work and have limited vibration.
Someone recommended I consider a flat plane crank in a previous thread and Jac Mac diplomatically suggested that unless I wanted to spend my reitrement tightening everything connected to the motor I might not want to try a flat crank. Most every other flat crank motor I've seen mentioned on this forum (I've only been active in the forum for a limited time, though) have been short stroke motors.
Doug
Someone recommended I consider a flat plane crank in a previous thread and Jac Mac diplomatically suggested that unless I wanted to spend my reitrement tightening everything connected to the motor I might not want to try a flat crank. Most every other flat crank motor I've seen mentioned on this forum (I've only been active in the forum for a limited time, though) have been short stroke motors.
Doug
My 76 308 had a flat crank, it was a very short stroke and had good torque for a small engine. It did have a buzz around 3000 rpm and used cams that had about 99 degree lobe centers. Crower has a 308 that he developed some cams for so I think that he knows what is required to make that work.
After reading the website about the V8 layout i recalled about my amazement when I first got the Ferrari, it truly was 2 four cylinder engines stuck together. 2 separate ignition systems, when one failed the engine would still run very smoothly, it just would not make power.
It also sounded like a Yugo when it was idling but when it hit 7000 RPM it sounded lijke an F1 !
It also sounded like a Yugo when it was idling but when it hit 7000 RPM it sounded lijke an F1 !
Forget about balance shafts in a SBF, unless you want to design and fabricate your own system. Short stroke and a light reciprocating assembly is what would be used to mitigate vibration in a flat-plane-crank V8. When I talked to Crower about it they said that there were some very lightweight options for the cranks, pistons and rods. I think the ideal flat-plane SBF would be a Dart aluminum block with the bores maxed out to 4.125" and a 3.00" stroke for 321 ci. AFR 185 heads and 8-stack EFI. Tri-y exhaust. Cam it to make power up through 8,000 rpm. That would be a sweet motor.
Come on, somebody has to do it!!!
Come on, somebody has to do it!!!
Still trying to get my head around the big reason for the v8 flat crank, is it predominitly for the lighter reciprociating weight and thus faster acceleration (Like tossing out the 30lb flywheel and runing a 15lb)?
Sounds like a very interesting package. Racing, might be interesting, but it had better twist well past 8k rpm to be compelling, as the longer 3.25" stroke motors are running well into that with good reliablility. I still like the regular 289 stroke Crank in the 4.125 Bore Dart block as the next motor as my interesting but simple combo.
It would be very interesting to find the weight of a equiv flat plane crank vs a nice lightned billet of equiv stroke (crower might have the info), and if you went to really light weight components (i.e. Ti Rods, pins) how much can you reduce the counter weights, and thus rotating mass on a regular crank?
Very interesting stuff again!
Sandy
Sounds like a very interesting package. Racing, might be interesting, but it had better twist well past 8k rpm to be compelling, as the longer 3.25" stroke motors are running well into that with good reliablility. I still like the regular 289 stroke Crank in the 4.125 Bore Dart block as the next motor as my interesting but simple combo.
It would be very interesting to find the weight of a equiv flat plane crank vs a nice lightned billet of equiv stroke (crower might have the info), and if you went to really light weight components (i.e. Ti Rods, pins) how much can you reduce the counter weights, and thus rotating mass on a regular crank?
Very interesting stuff again!
Sandy
salmjo1 said:Whoohoo, through an aluminum block in there, just for funIf I am reading correctly, you get to dump the counter weights all together, as the crank itself is balanced. Adding Ti rods... you really will be spending the kid's college fund, and then some.
Only if its a Lysaurus( Lycoming), You still have counterweights ,only not as much weight required. I think Sandy meant to say that the rotating weight would be considerably reduced.
Jac Mac
Hmmm, Just remembered, have a stick of 5"dia 4340 in the shop, Now lets see, 2.700" stroke, 2.000" journals, 5.700" rod, 4.155 bore, pistons from 3.25 stroker with 0.015 of the top,= 292+ ci. Might go out and buy some new hacksaw blades and make a start. Any blank cheque books in the USA still or did RL get them all?
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Yes, I was trying to say really how light of a counter weight can we get on a non-flat plane crank, and can we get closer to the rotating mass that a flat plane that crank style might have. On the 3.25" stroke SBF going together now, I had the crank work done to minimze the weight of the crank to the point that the builder is nervous about getting it balanced. I don't know what he got the weight down to but I'll ask.
I wouldn't waste any of this short stroke light crank in an iron block, as the 100+ lbs saved is likey the easiest weight to get out of a car
Some one calculate the math and on all this as well 
: Something like 100lbs out of the static weight of the car == ?? lbs of rotating mass. I have seen the calcs on one of the books (might have been Herb Adams chassis book...)
Jac Mac - Get to work, I'll give the crank a spin (so to speak), I like that combination. If you need any help with the hacksaw blades let me know...
My wife also has a load of Nail Files that might help with the final finish
I also found a discussion on how that the fellow that did the damBest carbs (another thread) mentioned the smaller rod ratio is better. I'll follow up and post to the other older rod length thread when I get a chance to read his theory!
Sandy
I wouldn't waste any of this short stroke light crank in an iron block, as the 100+ lbs saved is likey the easiest weight to get out of a car
Some one calculate the math and on all this as well : Something like 100lbs out of the static weight of the car == ?? lbs of rotating mass. I have seen the calcs on one of the books (might have been Herb Adams chassis book...)Jac Mac - Get to work, I'll give the crank a spin (so to speak), I like that combination. If you need any help with the hacksaw blades let me know...
My wife also has a load of Nail Files that might help with the final finish
I also found a discussion on how that the fellow that did the damBest carbs (another thread) mentioned the smaller rod ratio is better. I'll follow up and post to the other older rod length thread when I get a chance to read his theory!
Sandy
