Hot Rod Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
173 Posts
Discussion Starter · #1 ·
I'm planning out a build of a 532 cubic inch big block for a project, gonna be twin turbo, sequential fuel injected, coil near plug ignition, somewhat normal stuff for serious performance. The weird stuff starts here, I decided to go with a flat plane crankshaft, long aluminum rods, and short pistons so I can spin this thing higher than I could otherwise, maybe even as high as 9,000 rpm, not sure yet. For the proper quench I want, the static compression I'm eyeing, and the RPM I'm looking for I'm gonna use 6.7" aluminum rods and 1.1" tall forged aluminum pistons, netting me 0.021" quench due to the head gasket thickness. What issues will I run into? First thing that comes to mind is with that piston height the wrist pin is going to start getting into the oil control ring, would I see issues with oil consumption? If the pin is moved down towards the bottom would I have stress issues that could/would lead to cracking and breaking of pistons over time? On the crank I'm thinking an Up-Down-Down-Up rod journal arrangement so as to have a firing order closer to that of an LS, however I have no clue what the bob weight on the crank will be and in the response email I got that was one of the things they'll need, is this just the weight of the crankshaft?

Sent from my moto g power (2021) using Tapatalk
 

·
More for Less Racer
Joined
·
20,931 Posts
Bob weight is a term used in balancing....it is partly a measured amount and partly a calculated amount, the math formula is this...
100% rotating weight + 50% reciprocating weight + a small amount for oil clinging to parts(usually just 4 to 8 grams is commonly used).
Rotating is everything bolted to a rod journal, rotating with the crank...big end of both rods, 2 sets of rod bearings
Reciprocating is everything moving up the bore....small end of rod, wrist pin, piston, rings set, pin locks.
Rods are weighed by hanging one end while weighing the other end on a scale.

so, to get the bob weight that is bolted around each rod journal on the crank during the crank balancing process, we have to weigh all our parts in the rotating assembly and calculate the final result.
So..."100% rotating weight + 50% reciprocating weight + a small amount for oil "....
Big end of both rods, 2 sets of bearings + 1 small end of rod, 1 piston, pin, locks, ring set + oil = bobweight

As an example, small block-ish...
625 gram connecting rod(450 gm big end, 175 gm small end) 680 gm piston/pin/rings/locks assembly, 25 gm rod bearing.
450 big end x2, plus 25 rod bearing x2 = 950 gms Rotating
175 small end x1, plus 680 piston x1, plus 5 gms for oil = 860 gms reciprocation.
Total bobweight would be 950 + 860 = 1810 grams.

BBC stuff s a bunch heavier.
They need to know approximate bobweight so they know how big to make the crank counterweights to offset that bobweight. So you need to know what your rod and what your piston are going to weigh.
And that's just the beginning of all the things you are going to need to know to pull this off, or if it is even physically possible given the space constraints of the BBC block design, size, and shape.

So what is going to be the bore and stroke of this wonder engine?

You want the LS firing order, just get a 4-7/2-3 firing order swap camshaft for a BBC.

Flat plane crank has been tried before....it never works out well retrofitting into an engine design that never included it.
Bad idea.
 

·
Registered
Joined
·
173 Posts
Discussion Starter · #3 ·
Bob weight is a term used in balancing....it is partly a measured amount and partly a calculated amount, the math formula is this...
100% rotating weight + 50% reciprocating weight + a small amount for oil clinging to parts(usually just 4 to 8 grams is commonly used).
Rotating is everything bolted to a rod journal, rotating with the crank...big end of both rods, 2 sets of rod bearings
Reciprocating is everything moving up the bore....small end of rod, wrist pin, piston, rings set, pin locks.
Rods are weighed by hanging one end while weighing the other end on a scale.

so, to get the bob weight that is bolted around each rod journal on the crank during the crank balancing process, we have to weigh all our parts in the rotating assembly and calculate the final result.
So..."100% rotating weight + 50% reciprocating weight + a small amount for oil "....
Big end of both rods, 2 sets of bearings + 1 small end of rod, 1 piston, pin, locks, ring set + oil = bobweight

As an example, small block-ish...
625 gram connecting rod(450 gm big end, 175 gm small end) 680 gm piston/pin/rings/locks assembly, 25 gm rod bearing.
450 big end x2, plus 25 rod bearing x2 = 950 gms Rotating
175 small end x1, plus 680 piston x1, plus 5 gms for oil = 860 gms reciprocation.
Total bobweight would be 950 + 860 = 1810 grams.

BBC stuff s a bunch heavier.
They need to know approximate bobweight so they know how big to make the crank counterweights to offset that bobweight. So you need to know what you rod and what you piston are going to weigh.
And that's just the beginning of all the things you are going to need to know to pull this off, or if it is even physically possible given the space constraints of the BBC block design, size, and shape.

So what is going to be the bore and stroke of this wonder engine?

You want the LS firing order, just get a 4-7/2-3 firing order swap camshaft for a BBC.

Flat plane crank has been tried before....it never works out well retrofitting into an engine design that never included it.
Bad idea.
Bore and stroke will be 4.6" and 4" respectively

Sent from my moto g power (2021) using Tapatalk
 

·
More for Less Racer
Joined
·
20,931 Posts
Quench height has almost nothing to do with piston-to-valve clearance.....you don't decide on a quench clearance using valve clearance as a criteria.

Seems from your questions so far that this level of build is well beyond your abilities and understanding of basic relationships between parts??
 

·
Registered
Joined
·
173 Posts
Discussion Starter · #6 ·
Quench height has almost nothing to do with piston-to-valve clearance.....you don't decide on a quench clearance using valve clearance as a criteria.

Seems from your questions so far that this level of build is well beyond your abilities and understanding of basic relationships between parts??
I made a mistake on which thread of this I posted that comment on. I understand that valve to piston clearance is separate from quench distance.

Sent from my moto g power (2021) using Tapatalk
 

·
Registered
Joined
·
4,426 Posts
Quench height has almost nothing to do with piston-to-valve clearance.....you don't decide on a quench clearance using valve clearance as a criteria.

Seems from your questions so far that this level of build is well beyond your abilities and understanding of basic relationships between parts??
Scared him off Eric, would be a neat build, but has a lot of ideas rooted in the wrong spots I believe.

Quench distance on a 9000 rpm boosted build is extremely dependent on the rod and rod material. But being below .060" is 100% unnecessary IMO. Depending on the rod material it might need to exceed .080" if my memory serves me correctly.

What are your thoughts?
 

·
More for Less Racer
Joined
·
20,931 Posts
He might have looked at the price of that custom flat plane crank and had second thoughts.....

The 1.1" tall piston that can withstand dual turbo and 9000 rpm might have been another.....

Seemed like an outside the box build plan made just to be the guy "outside the box" rather than rooted in any power target.

Yeah, I agree, tight quench with super/turbo charging is not the best idea.

You doing Drag Week this year?
 

·
True Hotrodder
Joined
·
1,955 Posts
Just from a interested observer I don't think he had any "real" idea of the cost involved. Currently a RMS 540 Super Series engine is just over $18k and that's a conventional engine as far as most of the parts and machining involved. It's also very close parts wise to my 555 (I did use theirs as a guide) and I know what mine cost. Just a guess but I would think he would be in the $25k - $30k area if he did it right now and could find a machine shop to work with him.
 

·
Registered
Joined
·
4,426 Posts
You doing Drag Week this year?
I paid my entry last night, so barring hell, high water, or a blown up tranny in the 2 weeks prior - yes. I was 130ish on the waitlist, but got in fortunately.

I'm really hating the weather presently. I haven't ran the car yet this year on the track because of rain cancelling every test-n-tune within 2.5 hours of me since the season opened. SMH.

I'm really pulling to run it a couple of weekends to get the CO2 dialed in to run a respectable time, then I'm going to try to get it painted and the last couple of items needed for 8.5 cert.
 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top