All -

Does anyone make a "Flat" (i.e. - 180 degree) crankshaft for LT1/4 engines?

FYI - Italian V-8s use flat / 180 degree crankshafts vs most other V-8 makers, which use 90 degree crankshafts; and this helps (NOTE: I did not say this was the ONLY factor) those engines rev higher than other engines of the same displacement.

So, that being said, and my desire for a higher redline exposed, does anyone know if a Flat LT crankshaft is available?

(Yes, I do indeed know a new cam and a revised tune is also required)

 

In a SBC, there is arguably no performance difference especially for the work involved. There are also inherent vibration issues that many folks haven't been able to work out. There's a reason you don't see any of them around anymore, especially in SBCs. Waste of money, IMO.

Although if you still wanted to do it, any flat crank for a SBC with a one-piece RMS will work (or convert to a 2-piece).

 

Forgive my ignorance; what is an "RMS"?

FYI - I was told by my brother that a few (non-factory sponsored) Vette / LS-engine based road racing teams have sucessfully used flat crankshafts and gained 500 to 700 extra top end RPMs; hense my curiosity about doing this on an LT-based engine...

 

Rear main seal.

I can't confirm your brother's claim, but to be honest I HIGHLY doubt it.

There's no reason a high quality well-assembled conventional rotating assembly can't spin to whatever RPM you want, as long as you have the valvetrain to support it.

 

do a search for the 500rwhp N/A LT1 on here. it had an 8000 rpm redline. had a solid roller cam

 

I remeber reading about a 10K plus rpm LSx.

A flat plane crank in theory may be optimal, but that doesnt mean you would gain anything in the real world. There have been SBCs that have revved higher than Im sure your looking for, Id just do research on high revving SBCs, im not talking street motors, Im talking motorsport engines, and base your build on some of their ideals.

If your stuck on a flat plane crank their was someone on here looking to do it and found a manufacturer that would do it in sweden I think with a decent turnaround time. (not the engine, a one off crank)

 

Thanks! Brain Fart.

Not arguing that point at all; there are several ways to skin a cat / get to 8k.

As for your doubt, it's really just simple physics - "Flat" crankshaft have no counterweights, therefore the reciprocating mass is greatly reduced. With lower mass comes lower inertia, with lower inertia comes greater RPMs - sorta like a lightweight flywheel impacts the speed at which an engine achieves a particular RPM.

BTW, it's not his claim - he just stumbled on it and then asked me about it - he's a machinist, I'm a Mechanical Engineer; a google search (that's what I did) will confirm that some Vette teams have indeed used flat cranks on their LS engines.



I do not want to argue opinions - too many folks do this here - I just want to find out if a flat crankshaft for my engine exists.

So, given that, thanks for the info (really! ) stating if I found a standard SBC flat crankshaft, then I could use that unit in my LT. I'm a baby blue Pontiac guy, so I thought that the orange Gen I engines were too different from the black Gen II (i.e. - LT engines) to allow for crankshaft interchangability.

 

Thanks for the info; this may be a case where it can be done, but it's just too cost prohibitive... (New Crank, Cam, Tune, etc...)

 

A flat plane crank LT1 would sound so good. OHHHHH

 

I got a light weight 385c.i. LTx that peaks at 7400 and makes flat power to 7700 and sees 8000. Heres a video of me forgetting to shift and bouncing off the limiter at 8200. Good rotating assembly and good valvetrain will rev, of course theres no reason for it unless you can make the power up there.
http://www.youtube.com/watch?v=E_rTT9PcZ2Y

 

This is an interesting subject. I was always under the impression that the advantage of a "flat crank" was that intake manifold and exhaust tuning worked better since the firing was L-R-L-R-L-R-L-R rather than L-R-R-L-R-L-L-R. The back to back R's and L's cause a large pulse, followed by a smaller one, followed by a space, which confuses any tuning that gets done in the collector and plenum.

Also, rotating mass doesn't limit the peak rpm as long as it's balanced. Otherwise, a local engine builder told me a while back that it's very difficult to balance a flat crank because there isn't material to manipulate in the area needing manipulation.

 

completely off topic but what field of engineering are you in, mechanical I would assume? I saw your name engineermike; my name is mike and I'm an electrical engineer....just found it kind of cool.

 

Yep, Mechanical from La Tech in '99!

 

damn. Im guessing there are a few engineers here. I also do mechanical engineering and as well as industrial focused engineering.

 

Normally the limiting factor is the valvetrain, not the rotating assembly.

 

Just a few of us lurking around, BSME here.

 

nice to know theres alot of us on here....this thread is covered BSME's to BSEE's...and I didn't mean to hijack this thread at all I was just curious

 

haha it seems like a lot of threads end up this way. Well im sure some one will get it back on topic soon

 

ok I'll try to clean it up lol......Back to the flat plane crank thing....
I understand how people like to rev cars alot, hell we all do it. However, how fast do you really want to spin it? Like I said earlier the only reason to spin higher rpm's is to make more power, the issue is you need to be able to make power that high in the rpm range. You are going to need a serious set of cylinder heads, some really serious valvetrain and an absolutly ballastic cam to make it rev that much.

Look at my motor for instance:
Lightweight billet/forged rotating assembly, one of the best LT1 cylinder head offerings out there (AI TFS 215CNC) and a really big AI solid roller (25x/26x .7xx near a 106LSA) and I'm peaking at 7400 with usable power to 7700-7800.

The motor is perfectly durable to those rpms with a strong and lightweight standard geometry crank. Like engineermike said, as long as your balanced the weight almost wont matter. The light weight parts just put less of a load on the mains and rods and will allow the motor to generate rpm quicker. In my engine we actually went with a 51% over balance to reduce high rpm (7,8,9K) vibrations. In case your not familliar with it what you do is split the bob/counter weight 49/51 instead of 50/50. Racers have been doing this for years on longer stroke high rpm motors, the slightly heavier counterweight helps to pull the rod/piston assembly back down the bore at high rpms.
The problem with alot of rpm is even with the best of everything you still stand a much higher chance of breaking things than you do with a lower rpm motor. RPM kills alot more engines than horsepower does. If you do some math you will see that up at very high rpms the force on the rotating assembly increases dramatically per every rpm. Not to mention the speed that the valvetrain must remain stable at.
I'm not trying to rain on the "flat plane crank" parade but I'm just trying to understand the need.

 

Imagine this: Dart's SHP LT1 4.125" bore block with a 3.25" stroke and some 6.2" connecting rods to build a 370" or 377" high rpm (8000 - maybe 9000 rpm) LT1. Now all you need is a really good flowing set of heads and a sr cam and corresponding valvetrain.