8K RPM on the LT-5

[LGAFF]

Conventional wisdom says the LT-5 chains fail at 8K, however I noticed the Bonneville Racer is shifting at 8150......any know if he has custom made chains.....if so where can I get some.

[Paul Workman]

Not that this helps your quest, but I read somewhere recently that the limiting factor on the LT5 was the longer term survival of the peripheral stuff, e.g., alternators, & AC compressor bearings, etc. 8k was (author unknown) more of a limitation on the stock LT5 itself. Case in point: What rpm was Pete's LT5 turning when he hit 129.xx mph in third gear with the 3.45 rear gear??:jawdrop:

P.

[Pete]

Case in point: What rpm was Pete's LT5 turning when he hit 129.xx mph in third gear with the 3.45 rear gear??:jawdrop:

P.


7500
:-D


i would think 8k is possible with lighter valve train,maybe next project
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[tpepmeie]

At 8k, you're running way past the tuning peak of the stock 14" inlet tract. The salt racer has a sheetmetal manifold, which is tuned to much higher rpm. Of course, you can run up there with the stock design, just lose cylinder filling due to the pulse tuning.

From memory, the legend of failed chains is partly from experience on the World Challenge cars (Pirates). Sustained high rpm in those conditions did lead to broken chains. Cam sprockets are too small diameter, and thus impart stress to the chains due to the wrap angle. JVD is on here, maybe he remembers those Pirate chain failures.

Todd

[rhipsher]

Mine pulls hard all the way up to 8k if I want. I'm sure some will argue that my tack is out of calibration. And here's a vid of another guy hitting 8k in his. I'm not saying it's a good idea to do but it is what it is. With a fidanza flywheel and top end porting it raises the rpm cieling another 1000rpm'shttp://www.youtube.com/watch?v=E0Egyp4N-uA&NR=1&feature=fvwpI'm sure in short bursts it won't hurt anything but I would'nt keep it up there.

[LGAFF]

So I can hit 8K with some confidence of the motor not grenading?

[XfireZ51]

With my P&P the dyno runs showed an HP peak at 6800rpm. What's the point of 8000rpm unless your REALLY interested in making more top end power? I mean REALLY INTERESTED! As in $$$$$$$$.

[Polo-1]

I had Marc bump up the limiter to 7600 and the tach shows 8k. :rolleyes:

[Hog]

Taken from a 2005 Hemming story by Hib Halverson

"The primary timing chain links the crank to a half-speed idler where the cam sprocket is on a pushrod V-8. The idler drives a pair of duplex roller cam chains, one for each cylinder head. Cams in four-cycle engines run at half engine speed, so cam sprockets are typically twice the size of a crank sprocket. Sprockets that large would not allow the LT5 to fit through the car's frame. Using an idler for the speed change was a unique solution, which made for small cam sprockets and allowed the engine to fit.
The small sprockets put heavy load on a short length of chain. During development, there were chronic chain failures until GM switched to duplex chains. Even duplex chains have durability problems once an LT5 is modified with higher-lift cams, more valve spring pressure and a rev limit over 7,200 rpm."

Crank speeds of 8000rpm have the cams/secondary chains turning at 4000rpm.

Snakeskinner made peak power at 6800rpm in its final configuration.

I have read that slamming the rev-limiter hard at high rpm can be detrimental to the cam sprocket assemblies.

peace
Hog

[LGAFF]

Dominic, I was thinking of 8K to drop you high in the power band on the shift.

[XfireZ51]

From the dyno runs I have seen, ZR-1s have a power peak at about mid 6's. Not sure you need to shift at 8k and risk valvetrain issue. As Todd noted, you would need to go to a shorter runner length in order to push power peak up to 8k.

[Locobob]

Area under the curve is more important than when exactly you hit peak power. Mine reaches peak power at about 6800rpm but it stays at peak till at least 7400rpm - as high as I've revved it on the dyno.