Flat Plane Crank Engine

Howard Jones

Supporter
For the life of me I can't understand why people insist on stressing the hell out of small CI engines, 300-350 CI, to achieve relative high HP numbers.

The Aluminator deal is 318 CI and 580 HP and it needs nearly 8000 RPMS to do it.. That's 1.82HP/CI. If you wanted 580 HP out of a 408 stroked 351W for example it would be 1.42HP/CI And I betting it can be done UNDER 7000RPM's.

So for our purposes why not build a big as possible SBX with a aftermarket block, run a moderate compression ratio (10 -11 to 1), best available heads, hydraulic roller cam, and NASCAR style FI. I am SURE that a 430-450 CI engine like that can make 600HP and do it at a low enough RPM to last a very long time. I would also think that it could make that 400 ft/lbs of torque number 1500-2000 rpms lower than the alum. That would be killer on a road race track.

Modern cam, head , and engine internal parts design allows for a very efficient push rod engines. Hell a 400 inch 600hp SBC can be built for half and maybe even a third of that aluminator cost.

I just don't get it...……………………….maybe I'm just old and set in my ways...……………………………..
 
Did you read the attached article Howard, Stroke is 3", Bore 4.165", 5300cc or ~327cu in., I would have that even in cross plane over any long stroke option that every hot rodder in the USA seems to be in love with..........................BTW Im oldish and fairly set in my ways as well. Rod ratio looks to be around 2 to 1 or greater as well. only 30lb, Ive got a pic of the Ford Flat plane, its the ugly fat cousin by comparison. I do wonder why the car/engine is for sale though.
 

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Do you mean that the crankshaft in your photo weighs 30 lbs?
Yes, the Chev crank does, in the link provided by Les there is more info from the ebay auction. Cant remember what the Ford Crank weight was, with all the counterweights its probably close to 50lb or more at a guess.
 

Howard Jones

Supporter
Jac, I do see your point about rod ratios, however I really like the idea of relative low rpm very high torque with an ability to run through slow corners one gear higher that the high reving smaller motor would require. It's just that much less stress on the rest of the power train and a lot less monkey motion by the driver.

Without race class rules I can't see why to limit CI's and then run the engine to higher revs to make hp. I thing it's really "what you like thing" but we have established elsewhere that you are correct on the rod ratio idea.

For the record what would a 400 CI "Jac Mac" rod ratio motor look like if you were so inclined to select parts to build one. I am thinking a big block would be required to get the required bore size but I'm likely wrong about that.
 

Neil

Supporter
Jac;

Wow, a 30 lb Chevy crankshaft? That is really light- my Lunati SBC crankshaft weighs 52 lbs.
 
Jac;

Wow, a 30 lb Chevy crankshaft? That is really light- my Lunati SBC crankshaft weighs 52 lbs.
The rods & pistons must also be very light to be compatible with the crankshaft and balance factors. The ebay advert states the car had only done ~60k miles, wonder if that is also true for the engine? Need more actual user comments!!

Jac, I do see your point about rod ratios, however I really like the idea of relative low rpm very high torque with an ability to run through slow corners one gear higher that the high reving smaller motor would require. It's just that much less stress on the rest of the power train and a lot less monkey motion by the driver.

Without race class rules I can't see why to limit CI's and then run the engine to higher revs to make hp. I thing it's really "what you like thing" but we have established elsewhere that you are correct on the rod ratio idea.

For the record what would a 400 CI "Jac Mac" rod ratio motor look like if you were so inclined to select parts to build one. I am thinking a big block would be required to get the required bore size but I'm likely wrong about that.
Chev or Ford Howard??
 

Neil

Supporter
Lightweight cranks sound good but they sacrifice torsional rigidity. Driving a "flexible load" like an airplane or boat propeller is OK but not a pair of sticky tires. Frequently checking a 30 lb crankshaft for fatigue cracks would be a good idea.
 
Lightweight cranks sound good but they sacrifice torsional rigidity. Driving a "flexible load" like an airplane or boat propeller is OK but not a pair of sticky tires. Frequently checking a 30 lb crankshaft for fatigue cracks would be a good idea.
Interesting you mention the Airplane/boat prop thing, been involved with a couple of those, one was a 2.0 pinto in 3 point hydro direct drive onto 0.75" monel shaft from front pulley single keyway double row chain on two single row sprockets with only lower half of prop in water once up on plane etc. That 0.75" monel shaft developed a 3" whip at full noise ~ 7 to 8k RPM, never hurt the engine or shaft, but made a mess of every bulkhead in hull where it passed thru! All came to a halt once the shaft brg bracket tore out of transom. Lot more about that but it would take to long to type up! Lets just say we are no longer friends!!
 

Howard Jones

Supporter
Have both, but currently interested in SBC. Been reading and I'm thinking 4.0 bore with 6 inch rod and 3.5 stroke for a 1.75 RR and 351 CI. Unless a aftermarket block was used then the bore can be a 1/8 " bigger for a 377 CI. But what do you think Jac?
 
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Have both, but currently interested in SBC. Been reading and I'm thinking 4.0 bore with 6 inch rod and 3.5 stroke for a 1.75 RR and 351 CI. Unless a aftermarket block was used then the bore can be a 1/8 " bigger for a 377 CI. But what do you think Jac?
I would go with 6.250" rod & 1.025'' ch piston (1.786/1 rod ratio )to suit for those two combos.
Would go aftermarket block with 3.75 stroke, 6.125 rods, and 4.125 bore for 400 cu in. Pistons have 1.00" comp height , are available with dish, flat top or domed. That gives 1.633/1 rod ratio which is a bit shorter than I like but a fraction better than a std 350 chev only, really tricky part of build is rod to cam clearance ( Rods may need to be relieved &/or bolts shortened depending on cam choice- dont use thru bolt versions, cap screw only). Going with the 4.125 bore reduces the masking effect around valve to cyl wall clearance. Read up on methods of reducing steam pockets particularly around the center exh ports of each head plus steam vents applicable to the siamese cyl bore casting process. Torque plate hone is absolute must. supply oil presure to both ends of main gallery.
 

Howard Jones

Supporter
Wow, that's pretty interesting. A 400CI SB with a pretty good rod ratio. Would the 377 with the shorter stroke (3.5) be a better combination as far as being closer to ideal RR and still a fairly large CI engine?
 
Wow, that's pretty interesting. A 400CI SB with a pretty good rod ratio. Would the 377 with the shorter stroke (3.5) be a better combination as far as being closer to ideal RR and still a fairly large CI engine?
In your case with SLC it might,
IIRC correctly your averse to high RPM and the $$$$ it costs to build with suitable valve train and the extra work that entails. There is another factor that creeps in with bigger cu in- torque monster engines and that is drive train related. Lets say we have the above 400 combo & by some fluke we have a hi RPM ~350 that both make say 700hp. The 400 will break the driveline sooner than the 350 as its like a big hammer hitting 10 times whereas the 350 might take 15 smaller hammer hits to achieve the same result. everything is a trade off.
 

Neil

Supporter
Howard;

It is very common to bore SBC cylinders 0.030" to 4.030" and use 6" rods and a 3.75" stroke aftermarket crank to achieve 383 CID. Since it is a common mod, the parts to do this are readily available and relatively inexpensive. An aluminum block and heads would save quite a bit of weight, equivalent to more horsepower.
 

Howard Jones

Supporter
Neil, Thanks I have waved that one off already and stayed with a 350 for a variety of reasons at the time. I have my 350 apart right now to clean up and inspect for debris damage having loss a distributor gear. If I find other bad parts, now the time for a change depending what I find is not reusable. At this point I do not think I will find any real damage its more of a clean it out thoroughly exercise. But if I do I find the need to redo the rotating assembly pieces I was just wondering...……………

Jac, Ya I like hyd roller cams and valve train systems that last pretty much as long as the rest of the motor and those two factors pretty much limit revs to about 6500. I guess what I am saying is I would like to take out the number of gear changes by making the same torque but lower on the curve. My engine pulls real hard once it gets to about 3500-6K but if it did the same thing down at around 2800 I could stay out of 2nd quite a lot and run the center of the corners in 3rd. I was thinking that the reduction in the number of gear changes would really improve power train life and not upset the car from the center of the corner to the exit making gear changes. I wrote down the 377 & 400 info Jac, thanks again

I think I have drifted the flat plane crank thread far enough for now thanks guys.
 
Neil, Thanks I have waved that one off already and stayed with a 350 for a variety of reasons at the time. I have my 350 apart right now to clean up and inspect for debris damage having loss a distributor gear. If I find other bad parts, now the time for a change depending what I find is not reusable. At this point I do not think I will find any real damage its more of a clean it out thoroughly exercise. But if I do I find the need to redo the rotating assembly pieces I was just wondering...……………

Jac, Ya I like hyd roller cams and valve train systems that last pretty much as long as the rest of the motor and those two factors pretty much limit revs to about 6500. I guess what I am saying is I would like to take out the number of gear changes by making the same torque but lower on the curve. My engine pulls real hard once it gets to about 3500-6K but if it did the same thing down at around 2800 I could stay out of 2nd quite a lot and run the center of the corners in 3rd. I was thinking that the reduction in the number of gear changes would really improve power train life and not upset the car from the center of the corner to the exit making gear changes. I wrote down the 377 & 400 info Jac, thanks again

I think I have drifted the flat plane crank thread far enough for now thanks guys.
Starting to think you need an auto transaxle Howard:cool: Was just thinkin, the reason the hyd roller works so well is the residual oil pressure in lifter maintains roller contact with cam lobe, fit a rev kit with the solid roller & most of your problems will dissappear.
 
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Howard Jones

Supporter
Ya...…...one of those variable belt things. Also the oil is getting worse all the time with the exception of some aftermarket oils with added ZDDP so hyd rollers have become the norm. They are heavier than flat tappets however where in lies the rev limitation. At least that seam to be the common wisdom.

I was under the impression that solid rollers were difficult to keep alive but maybe recent advancements have overcome their finicky oil requirements.

But back to flat cranks. Given everything else being equal with lets say a 5 liter, 2 valve, push rod V8. Is there any REAL advantage to the flat plane layout? Or is there something about multi valve overhead cams heads that make a flat plane crank a performance advantage?

After watching this video I think the Voodoo kept all the disadvantages of both. Same size block that does not take advantage of the theoretical reduced crank size being the one that jumps off the page.

 
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Neil

Supporter
As I've mentioned before, John Horsman, in his book "Racing In The Rain", says that the first time JWAE ran a Cosworth DFV (180 degree crank), the vibration was so bad that it vibrated the needles off the instruments in the dash.
 
The Hyd Roller can have its upper RPM limit extended by using a rev kit to keep roller in contact with lobe and using minimal lifter pre load when setting valve lash so recovery time is reduced when the lifter pumps up. That has a side benefit as when you set lifter preload at say 0.005" any valve train wear/ damage will become evident with increased noise.

IIRC the DFV Cosworth that Neil mentions was the longer stroke version & vibration increased in proportion to longer stroke.
I do not remember mention of vibration being a major issue in the early 3 liter F1 Cosworth engines, probably still there, but lower in magnitude.
 
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