What is safe redline for this engine?
Thread Starter
Instructor
Joined: Mar 2001
Posts: 230
Likes: 1
From: Phila. Pa.
What is safe redline for this engine?
I've got a 355 small block that I'll be drag racing. Its got a cast crank, stock rods with ARP bolts, and hyperutectic pistons (speed pro). Assuming that all the clearances are correct, what is a safe or max redline for this set-up?
Le Mans Master
Joined: Feb 1999
Posts: 5,877
Likes: 1
From: Park Ridge IL
Re: What is safe redline for this engine? (Cruz 86)
What type of valvetrain and camshaft lifters? Solid tappet and roller, especially mechanical roller, lifters will extend the rpm range, as will light weight and more rigid high-performance valvetrain components.
Assuming the bottom end is in good shape, and it has a hydraulic tappet cam with screw-in rocker studs with aluminum roller rockers and the appropriate springs, which are also in good shape, 6000rpm should be fine for brief periods, like between shifts. I'm sure it could probably go as high as 6500 rpms without immediate failure, but I'd be surprised if the valvesprings were good enough to prevent float based on the limited information you have provided.
The addition of items such as titanium valves, retainers, and keepers, along with good double springs will make the most difference in increasing your redline. Most often than not, it's the valvetrain that is the limiting factor, and that boils down to valvesprings, valvetrain weight, and valvetrain rigidity.
Otherwise, keep piston to speed to less than 4500 feet per minute. Piston speed can be found by (2 * stroke * rpm)/12
(3.48 * 2 * 6500)/12 = 3770.
[Modified by Monty, 10:07 AM 12/5/2001]
Assuming the bottom end is in good shape, and it has a hydraulic tappet cam with screw-in rocker studs with aluminum roller rockers and the appropriate springs, which are also in good shape, 6000rpm should be fine for brief periods, like between shifts. I'm sure it could probably go as high as 6500 rpms without immediate failure, but I'd be surprised if the valvesprings were good enough to prevent float based on the limited information you have provided.
The addition of items such as titanium valves, retainers, and keepers, along with good double springs will make the most difference in increasing your redline. Most often than not, it's the valvetrain that is the limiting factor, and that boils down to valvesprings, valvetrain weight, and valvetrain rigidity.
Otherwise, keep piston to speed to less than 4500 feet per minute. Piston speed can be found by (2 * stroke * rpm)/12
(3.48 * 2 * 6500)/12 = 3770.
[Modified by Monty, 10:07 AM 12/5/2001]
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
Re: What is safe redline for this engine? (Cruz 86)
I ran my stock (bottom end) 300 HP L48 to 6000 rpm for 20,000 miles during my ownership. It is cast piston/crank, stock rods/bolts, but 4 bolt block.
If the engine appears to be fresh and with good oil then I don't think you will have a problem with it even at 6500.
If the engine appears to be fresh and with good oil then I don't think you will have a problem with it even at 6500.
Drifting
Joined: Dec 1999
Posts: 1,462
Likes: 1
From: Reno nevada
Re: What is safe redline for this engine? (Cruz 86)
KB hyper pistons are good for 7000. Cast and stock rods even with good bolts are questionable. The big question. When does your cam and intake combo run out of steam. If your way down on your power curve by 6000 rpm. You get better times just shifting at lower rpm.
Racer
Joined: Jun 2000
Posts: 294
Likes: 0
From: WA
Re: What is safe redline for this engine? (Cruz 86)
Sounds like the bottom end is the weak link (assuming the heavy duty valve springs were matched to the cam by the cam manufacturer). For drag racing 6500 rpm is no problem even with the cast crank and stock rods with ARP bolts (provided the machine work and prep work is first class on the rods, crank and block). 7000 rpm is really pushing it even for drag racing. You could probably get away with a 7000 rpm shift but not many - and I wouldn't do it unless you have a trailer and some spare cash for a rebuild. I would either change to a smaller cam or upgrade the bottom end to take advantage of the cam you have.
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