Max RPM Limit

Argess · #1 (**permalink**) 07-19-2009, 04:42 PM

What's the recommended limit for a 428? I would say 5500, but I've heard 6000 is OK with stock rods. Assume ARP rod bolts for this question.

I just did some "rough" calculations based on tire diameter, speed, etc., and it looks like I might have shifted out of 2nd at 6600 rpm. Calcs were rough, and I can't watch the tach when I'm doing this, so shift was probably lower. Sure was screaming though.....

ERA Chas · #2 (**permalink**) 07-19-2009, 05:36 PM

That is largely a function of valve springs, valve train weight and cam events. If parts are selected for elevated RPM the short block components must be selected to match the additional strain.

patrickt · #3 (**permalink**) 07-19-2009, 05:50 PM

Quote:

Originally Posted by Argess

What's the recommended limit for a 428? I would say 5500, but I've heard 6000 is OK with stock rods. Assume ARP rod bolts for this question.

I just did some "rough" calculations based on tire diameter, speed, etc., and it looks like I might have shifted out of 2nd at 6600 rpm. Calcs were rough, and I can't watch the tach when I'm doing this, so shift was probably lower. Sure was screaming though.....

You can calculate your optimum shift points and it will be based largely on your torque curve. Just because your red line might be at, say, 6500 doesn't mean that's the place to shift. Here are my shift points as calculated from a myriad of data.

ERA Chas · #4 (**permalink**) 07-19-2009, 06:14 PM

Hey Pat, you've got too much time on your hands...

PDUB · #5 (**permalink**) 07-19-2009, 10:49 PM

What program do you use, Pat?

Thanks...

RICK LAKE · #6 (**permalink**) 07-20-2009, 03:00 AM

Argess If you are looking for long term life of the motor, this is the golden rule I live by and shift by. Anything higher is just wasteing motor. This is why it is important to match all the parts to worh togeather. Carb, intake manifold, heads, compression, exhaust manifolds and most important on a cobra, sidepipes

Have to be able to get the gas out of the car. If your motor is stock, 5,200 rpms will be about the limit with max hp and torque being there. 428 motor is a torque motor, not a HP motor. If your motor puts out 400ft of torque. That's a strong running motor and very streetable. If you are looking for a little more power, the work to the heads, intake, sidepipes would be needed. This includes a carb, intake and camshaft change. I raced a stroker 452 motor with 9.2 compression for 8 years. I could run with cars that had more hp car all day. The drive train and getting the most out of the car has alot to do with this. Cobra like about 550 HP and 600ft of torque. This is about the edge of the safe limit and drivibility of a cobra. Yes we have a couple of guys on this forum running 700+HP motor. They are track cars, not saying that you can't drive them on the street but they where not built for street. If you FE motor is stock bottom end, the 2 things a would suggest is that you run a 7+ quart oil pan and HV oil pump with an 80# spring in it. This is for high spirit horse play. MSD with a 5,700 chip in it also. If the HP craze bits you, build another motor and keep this one as a spare backup just in case.

Rick L.

patrickt · #7 (**permalink**) 07-20-2009, 04:37 AM

Quote:

Originally Posted by PDUB

What program do you use, Pat?

Thanks...

Performance Trends "Transmission Gear Calculator." Free demo program here: http://performancetrends.com/programs/Trgr-w95.exe

trularin · #8 (**permalink**) 07-20-2009, 04:42 AM

I noted Pat has too much time as well.

Pat, did you retire or is work so bad that you can spend hours on CC?

patrickt · #9 (**permalink**) 07-20-2009, 04:47 AM

Quote:

Originally Posted by trularin

Pat, did you retire or is work so bad that you can spend hours on CC?

Neither. I just amass impressive results with but a modicum of my dedicated time....

Argess · #10 (**permalink**) 07-20-2009, 05:10 AM

Thanks guys. I feel better now. Although I was testing out my ignition tuning and went a bit higher than normal, it still "felt" like a good shift point. 80 mph during the 2nd to 3rd shift.....

ARP rod bolts
Crane Fireball 294 cam
Crane Solid lifters, pushrods, adj rockrs, double valve springs, retainers and locks
FPP end and center rocker arm stands
FPP rocker spacers (vs springs)
Harland Sharpe hardened single hole rocker shafts
TRW forged pistons, 9.5:1
9 qt oil Aviad pan

Oiling mods are done and it has a HV pump (which doesn't mattter up high I suppose)

So, it's fairly tough, but I think I'll keep it a little more safe. No doubt there's a weak link.....probably the rocker shaft bolts....

Darned Stewart Warner tach.....it's kind of "glitchy". I'll have to replace it. Can't get it apart to repair (probably a poor solder joint inside) as the rear housing has a lip and the front besel is swaged over it.

Besides, as I am sure most of you know, going through the gears quickly keeps your eyes on the road, not the guages.....chuckle.

ps: I have enough "stuff" to build up another 428, not counting valvetrain parts. I havn't done that (to provide me a quick spare) as I don't like seeing an assembled engine sit too long. Tons of assembly lube, plastic bag, dessicant.....maybe, but so far, I've just got parts laying around.

PANAVIA · #11 (**permalink**) 07-28-2009, 12:29 AM

IMHO: after consuming the factors involved , set it at 6200

JBCOBRA · #12 (**permalink**) 07-28-2009, 07:49 AM

These guys come out of the hole at 9000 422motorsports.com LOL
check 'em out. They tune my car.



FE Forums sponsored by Keith Craft Inc.