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How high RPM on stock motor?

Goatman

Goatman

NAXJA Forum User
NAXJA Member
Location
Bakersfield, CA
Does anyone know what RPM the rev limiter is at on a Renix system? I've never hit it, but I assume it has one. Also, what opinions do you guys have on how high you could run a stock 4.0L motor.
 
No rev limiter AFAIK on a Renix 4.0 but the tachometer redline starts at 5000rpm. A safe limit on a stock 4.0 is 5500rpm but I'd advise only running it in very short bursts if you go that high.
 
There is an inherient balance issue that occurs at higher rpms. That is the main reason the rev limiter is there from what I understand.
 
I've seen 5500 pushing 6000 on mine a few times, and it really does sound like its going to come apart at that speed.
 
When it comes apart you've passed the limit
 
Mostly I'm concerned with max RPM for relatively short sections when in low range. I can't imagine hitting max RPM's in high range with the automatic. Thinking about punching it in open sections of canyon in low range and how far is it safe to push it.......especially if there's no rev limiter.

I've got stroker plans, but trying to work out the dough, so I'm also thinking of changing from 4.56's to 5.13's. This would work well for power in high range, but would increase the need to use max RPM's in low range occasionally. It's not a run through the gears kind of thing, it's running as fast as we can go for short sections.

How high do you guys run your strokers? Are you motors balanced? Rods reconditioned and shot peened?


Oh, BTW, I have a '98 motor with a header and 2.5" exhaust, the HO intake and Renix TB, and Renix engine controls.
 
On a stock 4.0 at 5200 rpm's your slugs are moving at about 3k feet per sec.
For a stroker 4600 rpm's is at the 3k mark. Sure you can go higher, but with a cast rotating assembly anything after that for sustained periods is sure to bring an early grave.
 
Goatman said:
How high do you guys run your strokers? Are you motors balanced? Rods reconditioned and shot peened?
Click to expand...

I've run my 4.6 stroker up to the 5200rpm rev limiter and it's smoother than my old 4.0 at that rpm. Rods and pistons weight-matched to less than 1g, rods shot-peened, and I used ARP rod bolts. I have the stock camshaft and stock valve springs with no valve float issues up to 5200rpm.
 
Dr. Dyno said:
I've run my 4.6 stroker up to the 5200rpm rev limiter and it's smoother than my old 4.0 at that rpm. Rods and pistons weight-matched to less than 1g, rods shot-peened, and I used ARP rod bolts. I have the stock camshaft and stock valve springs with no valve float issues up to 5200rpm.
Click to expand...

How do you like the stock cam?

If I can build the motor and reuse the stock cam and valve train, it will be much cheaper to build. If the quench can be brought to ideal specs, how high can you go on CR and not have a problem with the stock cam?
 
I used to have the Crane 753905 cam and, believe it or not, I like the stock cam more. It's enabled me to use the softer stock valve springs and with the Yella Terra roller rockers, the valvetrain's quiet and the engine's sweeter. Part throttle response is also better with the stock cam and WOT performance is only slightly reduced (0.18 slower to the 1/4 mile). I really don't miss the Crane cam at all.
The CR in my stroker is 9.25:1 and I don't have any pinging problems on 91 octane in 115*F mid-summer heat (I can run 89 in winter). Quench is a high 0.088". With tighter quench you'd be able to run a couple of octane lower than what I'm using.
 
Goatman said:
Does anyone know what RPM the rev limiter is at on a Renix system? I've never hit it, but ...
Click to expand...

really?

the first time I loand scrappy my junk, as he was driving away, I heard mine hit the rev limiter... 92, HO, stock engine - 5200 RPM sounds right...
Ive hit that a few times when I was trying to climb something in too low of a gear, and the judge was yelling "30 SECONDS!" and a few times on snow runs...

so much for the teralow 2500 RPM limit :gee:
 
I decided to try and find the speed limiter on my XJ...was at 5000+ for at least a minute. That's the closest thing as I can imagine to what blasting off in a space shuttle is like. Everything was wobbling and whining and sounding like it was going to come apart. It was a fun ride though...:nono:

Speed limiter hit at 119.3 mph, BTW. ;)
 
Wow said:
I decided to try and find the speed limiter on my XJ...was at 5000+ for at least a minute. That's the closest thing as I can imagine to what blasting off in a space shuttle is like. Everything was wobbling and whining and sounding like it was going to come apart. It was a fun ride though...:nono:

Speed limiter hit at 119.3 mph, BTW. ;)
Click to expand...

Auto or manual? gears? tires?

In stock form I don't think your would be redlining at 119 mph. That is where the speed limiter kicks in, maybe that is what it was.
 
Talyn said:
Auto or manual? gears? tires?

In stock form I don't think your would be redlining at 119 mph. That is where the speed limiter kicks in, maybe that is what it was.
Click to expand...

Yes, it was the speed limiter that kicked in...I don't think you CAN hit the rev limiter in a mostly stock auto Jeep in drive. I have 30" tires with stock 3.55 gearing.
 
Mine starts to sound like there is a very angry badger in the muffler around 4k, but that is with a stock muffler and 155,000 miles on it. The reason for the lower RPM limit in the stock jeep engines is partly due to the cam and as mentioned, the balance job and a little bit on the valve train too. When you have a cam that is made for torque it will have a lower max RPM vs a car that is meant to rev to 6400ish. 6400 is about the limit for hydrolic lifters, they just wont work above that range without some modifications.
When a cam has an agressive lobe, RV cams are great examples, they will produce alot of torque down low but redline lowe as well. The ramp of the cam will actually throw the lifter off at high rpm's and it will come crashing down onto the back side and all sorts of trauma will occour. If you were to use a stiffer spring and/or a lighter valve train and balance the crank to race spec (.25 inch ounces or less) then select a cam that won't run out of breath too quick you should be set to rev to 6000. :)

~Alex
 
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