Cobra289

Hi,

Perhaps you can guide me to find out what is the safe maximum RPM from my engine combo.

I did build it my self so I don't have any consulting shop that can help me.

- It is a 350 / L31 4-Bolt Main GM Performance Parts Short Block Engine Assembly GM # 12556121.
- I have the AFR 180 Eliminator heads that was angle milled till 58 cc combustion chamber. All the parts are AFR.
- The rocker roller are Scorpion with 1.6 ratio (As advised by AFR)
- The Hydraulic roller are standard GM
- The push rods are Trick Flow, Chromemoly, Heat Treated, 5/16 in. Diameter, L= 7.100”
- The CAM is a ISKY # ISKY 257_265-HYD
ISKYRIDIAN 211257/265 0,496 IN 0,517 OUT with the 1.6 rockers it is a 257/265 Adv. @0,050" 209/217
I did install the CAM with 2 degrees retarded at the chain.

- Compression ratio is 10:1 Dynamic Compression Ratio = 8.26
- Estimated power at the flywheel = 419 HP at 5500 rpm, Torque 496 ft-lbs at 4000 rpm
The numbers where found with "Engine Analyzer Pro v3.5" trial version and the approximate the same came out from DD2000.

The induction is an HSR with a T/B of them with 1000 cfm flow and I will use the 24# injectors (for the moment)

So the question is:
What is the endurance RPM limit of this engine?
Witch component do originate the RPM limiting factor of the combo?

Let me know if you need more information.

Thanks!
Regards,
Cobra289

327???

Shift it a couple hundred rpms after the power starts to fall off, so somewhere around 5800-6000.

The cam determines the rpm range for the most part, spinning it higher than you need to make power is silly, you go slower and put more wear and tear on your engine.

Cobra289

Thanks!
I use to drive at the circuit and there we need to have the best RPM shift possible so that we don't drop to much the RPM outside the power band.
According a simulation software (See picture) it advice to shift at 6000 rpm to keep the engine above the 4000 rpm (max. torque) but this software don't take in account the RPM capabilities of the engine.
I was thinking to at the safe side and shift at 5800 rpm but 6000 would be better according the software.

Do you think that I take a risk if I put at the EPROM a max. of 6000 rpm?
Will this combo capable to hold the shifts at 6000 rpm in the long therm?

Regards,
Cobra289
Cobra

Regards,
Cobra

Cobra289

?????

Sonix

iTrader: (1)

Yea, 5800-6000RPM shift points are fine, that's pretty close there so I wouldn't sweat the difference.
That's a very well done motor, if you can actually get close to 500ft/lbs torque i'd be very impressed.

Hydraulic roller lifters are heavy, the heavy lifters and fact that it's hydraulic is going to limit your RPM (and the intake duration of the cam, it's rather small). You can get a higher max RPM by using solid lifters, a rev kit, bigger valve springs, stud girdle, and a bigger cam obviously.
I'd just leave it as is though, and shift at around 5800RPM.
Your best bet is a dyno however, if you get valve float at 5500RPM then you know something is amiss, and you should shift sooner.

327???

No, then you should get better valve springs.

Sonix

iTrader: (1)

haha, well yea, but in the meantime then you just don't rev it as high

Cobra289

Thanks!
Like I say the figures mentioned are from the "Engine Analyzer Pro v3.5" trial version check here the attachment, please if you have the time, let me know if I make mistakes with the input values.

The torque output with DD2000 is much lower than the 496 ft lb. DD2000 calculates with 432 ft lb at 4500 rpm I don't know why?
Some one told here that "Engine Analyzer" was better but probably I make some mistakes with the input.

It is a huge difference but I will be happy with something in between.

At a road track course the engine power band is very important because we need to put the torque on the asphalt and the limiting factor become the tires, to much torque an bas selected differential ratio and you need to learn again how to take the turns, a bit to early with the right foot and you are gone.

So I am not looking for a top end drag race car with lots of torque, but just a smooth working, with very fast rev. engine.
I did estimate a working area of 3200 till 5800 rpm and I hope that the parts selected will fit the purposes.

When I put at the EPROM a maximum rpm of 5800 it will cut off the injectors but I need to put the value when it should resume, would be 5600 rpm a good point?
Or is it better to put there a max. of 6000 and start resume at 5800 rpm.

Sorry if I ask to much.

Regards,
Cobra289