f54 flat top cast pistons - max rev?

[inline6]

I'm putting in a new cam and am wondering where to set the electronic stop (max rpm) on my Hi 6 ignition. The car is mainly used for track days. The cam set up is good to 7700 max. Anyone have some experience with max revs for the stock F54 bottom end? I realize that forged pistons are going to be necessary, but would like to wait a season. 7k? or can I get away with a bit more?

 

Garrett

[PapaSmurf]

That would depend on a lot of things. First the cam rotates at half the speed of the crank. The crank is internally balanced and rarely needs to be rebalanced or journaled but if it's run dry a few times it may need it. Are the rings new? Is the bore good? Can you still see the honing on it? At 7700rpms the cam is really only at 3850 rpms itself. Honestly I'd be worried about the valve train at high rpms before the bottom end though.

[Tony D]

"Honey that engine sounds like Ice Cubes in a Blender"

 

My wife after listening to an F54 flat top run to 7700-8000 during the MSA AutoX some years ago. Coming into the pits, that is exactly what the engine sounded like. Didn't sound like that when it went out.

 

Keep it to 7000 (or slightly less) if you want to live through a season (if that...)

 

Should have used a cam to optimize performance to 7K, and nothing more. They are out there. Check your dyno sheets carefully, and degree the cam you have properly and you may be able to 'cheat' the power band back down the rpm band slightly to where you gain most power under the curve and there is no reason to exceed 7000...

Edited May 3, 2010 by Tony D

[PapaSmurf]

"Honey that engine sounds like Ice Cubes in a Blender"

 

My wife after listening to an F54 flat top run to 7700-8000 during the MSA AutoX some years ago. Coming into the pits, that is exactly what the engine sounded like. Didn't sound like that when it went out.

 

Keep it to 7000 (or slightly less) if you want to live through a season (if that...)

 

Should have used a cam to optimize performance to 7K, and nothing more. They are out there. Check your dyno sheets carefully, and degree the cam you have properly and you may be able to 'cheat' the power band back down the rpm band slightly to where you gain most power under the curve and there is no reason to exceed 7000...

 

 

Haha that's what is known as a box of rocks

[Xnke]

7000RPM is a pretty good redline for the stock-internaled L motors, any higher with a non-prepped crank and you will risk crank breakage. There are some tricks you can use to go higher, but at all costs don't let it hang between 7200 and 7500, if you are gonna run through that range get through it as fast as possible. There are two wicked harmonic peaks right there, on the L24 and L28 cranks.

 

The stock cast pistons are pretty decent, and will hold up to 7000RPM without too many problems. Good quality lightened cast pistons, in an N/A engine that sees realistic piston speeds, will hold up fine with a good tune. Do the math and you will know if you've got realistic piston speeds, and check with your manufacturer to find out what is recommended for your components.

[Tony D]

7000RPM is a pretty good redline for the stock-internaled L motors, any higher with a non-prepped crank and you will risk crank breakage. There are some tricks you can use to go higher, but at all costs don't let it hang between 7200 and 7500, if you are gonna run through that range get through it as fast as possible. There are two wicked harmonic peaks right there, on the L24 and L28 cranks.

 

Bonneville engine peaked originally at 7500. Hung there at 7500 for four seasons for minutes at a time...

 

I don't know what 'prepped crank' means, but if it's cleaning it off with solvent and having it dynamically balanced before installing it, then I guess we 'prepped it'.

 

But really, my street car has more work on the internal bottom-end components than what we run at the Races.

[skib]

 

I don't know what 'prepped crank' means, but if it's cleaning it off with solvent and having it dynamically balanced before installing it, then I guess we 'prepped it'.

 

 

 

lol

[Xnke]

That's pretty cool Tony, but it was YOU who initially informed me about the crank breakages happening due to harmonics that were believed to be in that region, prompting the tests when I had access to dynamic balance and torsinal deflection measuring equipment capable of balancing objects to 20,000RPM, and showing twists on the order of fractional millimeters end-to-end The data showed the big harmonic peaks at those aforementioned points, and again in the 12,000RPM region. it also showed just how damn flexible these cranks are! I don't recall exact numbers right now, but the amount of twist end-to-end was visually apparent with the strobe.

 

That, and folks who were reportedly cutting ~6mm off the tail of the crank, and running 10-12lb flywheel+clutch assemblies in order to reliably run 9-10K RPM in the Japan scene to avoid breakage on/near the #6 rod journal

 

Maybe I'm just paranoid.

[Tony D]

Methinks not....

Methinks you are attributing to me someone elses mythology...

 

I believe Chris from BHJ also posted something very nice on how the affected nodes and peaks are effectively dampened by the use of a proper 'pulley' on the snout of the crank.

 

I guess we haven't hit the 12,000 rpm point to see what a 'prepped' stock crank will do, but as Frank280ZX can attest...we have been pretty damned close!

 

Remember the Japanese Scene is invested heavily in DRAG racing as well. The loads encountered there are seriously different from a road racer, or even a Land Speed Competition. VW Guys found running an 8# Damper on the front of the engine made their engines not pound out the case as much when drag racing... What is done to one specific application is many times not something directly applicable or even wanted in another form of application.

 

I would not talk about Crank Breakage as

1) it has NEVER personally happened to me

2) in every case I was privy to a broken crank it has been in Drag Racing, and usually attributed to bad flywheel attachment when investigated.

3) I have several engines running well over 7500 on what I would call a stock unprepped crank, without ever having any problem (other than one incident where the overly-thin snout washer induced a loosening of the bolt and trashing of the snout...and that happens stock.

4) I have consistently said the issue with 'harmonics' is way overblown, especially the "7500 rpm limit" of the VO7 Crank, and have consistently posited that this is a legendary hold-over from the first generation L24 Cranks which were not counterweighted properly. Same as saying engines need an overhaul at 100K miles because that was the standard on a 1956 Chevrolet V-8. "Tain't True, sez I! Tain't True!"

 

<EDIT>15# Flywheel/Clutch assembly 10,500+ rpms at the Dyno Facility used by another person on this board with another rusty old Datsun. No shortening done at all. Hell, the crankshaft holes still have burrs in the balancing hole. TRUST ME when I say, my personally assembled street engine has more crank and block prep done to it than the engines we run in competition. It drives me nuts to see that, but the rationale is 'we have spares' and if something blows having the ability to go to a local junk yard to harvest major component assemblies and install them has GREAT appeal when you don't have a full race trailer to stock prepped shiny spares in!<EDIT>

Edited May 5, 2010 by Tony D

[sbooth]

Personally, I feel if you're running a stock bottom end to 7800 rpm and something on the bottom end lets go you don't have much invested in the grand scheme of things and shouldn't worry too much as you can buy a new bottom end core for 200. Go get a core and start building the bottom end or buy a 3.0 assy from rebello and get it ready as time and money allows. In the meantime, let us know how the stocker holds.

[Tony D]

Other than ARP Bolts and standard Electronic Balance of the crank, it's how we got it from the junkyard.

My thoughts on the stock rod bolts are known already.

 

But this really wasn't the point of the OP. The cast pistons will not handle what the bottom end is capable of doing, so that it 'can' rev to 8000, it's likely not recommended on those cast pistons.

 

If one of them comes apart, it can be 'spectacular'...

[Xnke]

Hey, if i'm wrong i'm wrong, But I did truly think that it was you who had said that Tony. Either way, without a damper or flywheel mounted, the harmonics are at those points mentioned.

 

Tony is correct, the point has been made that the pistons are the limiting factor for speed and power in a stock bottom end, anyway.

[inline6]

So, I'll set it at 7,000 for this "season" and look to go forged pistons over the winter, if I like the cam. My season consists of a about 2 track weekends (usually VIR and Summit Point) a year at this point. So, I think I'll be ok. A couple of you mentioned dampners. I am running a euro single pully unit. Issues?

 

The flywheel is stock, which is what, 23 lbs? The clutch is a 225mm Centerforce unit with probably 40k street miles, a pile of autocrosses, and a few track events. Again, is this a problem for 7k or for 7.7k for that matter?

 

Garrett

[Mayolives]

I'm putting in a new cam and am wondering where to set the electronic stop (max rpm) on my Hi 6 ignition. The car is mainly used for track days. The cam set up is good to 7700 max. Anyone have some experience with max revs for the stock F54 bottom end? I realize that forged pistons are going to be necessary, but would like to wait a season. 7k? or can I get away with a bit more?

 

Garrett,

Lots of sound advice here, and as usual, Tony has the real life experience and solid technical expertise to back it up. Keep in mind that you will probably run out of hp and torque long before you reach those high RPM numbers and you ultimately may be faster by short shifting and catching another gear wherever you are running out of power and at a lower rpm number.

[inline6]

I definitely appreciate the advice anyone is willing to provide. I was spoiled when I was a teen, as Dave Weber of Malvern racing was local. And Tom Howen, his long time friend, driver, machinist, is here as well - but no longer doing car work. So, I find myself without the readily available L-series expertise that I used to enjoy.

 

Regarding the cam, it is not run of the mill, though perhaps as Tony said, I should have gone with something more common - a more typical off the shelf cam. It is from Sunbelt - same cam grind as Dan Baldwin I believe. Here are the specs:

 

Intake

Seat duration 320 degrees

.050" duration 290 degrees

Valve lift with zero lash .565"

Hot valve lash .015"

Net valve lift .550"

 

Exhaust

Seat duration 315 degrees

.050" duration 274.8 degrees

Valve lift with zero lash = .565"

Hot lash = .015"

Net valve lift =.550"

 

I am not sure of the power band, but since I was told by Sunbelt not to exceed 7700 RPM, I'm guessing the power band goes somewhat north of 7k. Perhaps that is not the case. When I degree it and jet the Mikuni 44's, I'll know. Still looking for input on the euro dampner and the stock flywheel. I cam across a post that mentioned lightening the stock flywheel (done correctly) to 17 lbs is a good way to go. All other things equal, will a correctly lightened flywheel help with any crank harmonic issues?

 

Garrett

[Tony D]

Lighter flywheel helps in drag racing style starts, but in drag racing you want the extra mass for inertia to keep from bogging. Catch-22 Yossarian.

 

If you are road racing, light flywheel is better. Tomei makes a nice 9# unit which gives wicked-quick response compared to the similar weighted CrMoly HKS unit long since out of production.

 

9# is a misnomer, really, as that damn pressure plate will add another 24# on top of that!

[280zbeeT]

How do you adjust your engine to reach 7k rpm?? I have a NA cam, can you do it with any cam or you need to upgrade to a performance cam? sorry if this was already answered, I read this thread twice but dont exactly understand.

[1 fast z]

Yea that was some years ago Tony. Too good of a head and intake, and not a good enough Bottom End!