Poll: Who has ever hit the rev limiter?

[Paul Workman]

Just following along here...

Seems to be a lot of pushrod SBC experience being projected onto a DOHC platform; a platform that was tested by alternating it from max rpm to max torque continuously for over a week before being torn down for inspection. It was deemed ready to go again!

I believe it was in the book "Heart of the Beast" where it was mentioned that the motor was good to about 8000 rpm, and above that oiling was the problem and lubrication-related failures of varous kinds, e.g., cams seizing, chains breaking ensued, as I recall. (However, Fastlane was running his LT5 to the mid 9000s in the quarter, but I never saw anything written about what all mods were done to that motor to address the rpm issue - if any.)

The (approx) 7200 factory limiter setting was chosen as a practical limit because 1) the power curve had peaked around 6400 (stock motor) and was tailing off past practical use, but 2) the main concern was the periphery components - alternator, PS pump, etc. (The AC compressor is shut off by the ECM above 4xxx rpm)

Serious performance is in the offing after porting and especially porting with cams, and cutting it off at 7200 is apparently premature for most properly modded LT5 motors (or certainly the case with the "FBI" modded motors at least).

Cases in point:

Y'all have seen Pete's video where he hits 129.x mph in 3rd gear. (The video done at Great Lakes Dragway showing a couple burnouts and 3 runs) Considering 120 mph is achieved at 7200 in third gear for stock tire sizes, Pete would have to set his limiter north of 7700 rpm to hit 129 mph.

Then there's the 10.x second big inch LT5s running way north of 7200+++ at WOT

After porting my LT5, it was still pulling hard when the danged limiter would cut me off; I hit the limiter many times. I, as well as Dom and others had to bump the limiters to at least 7600 to accomodate (in my case) a 7200 shift point, AND allow some headroom as I hit the 7200 rpm mark way short of the finish line.

Something else...

Some have questioned if their rev limiter was working at all because they had observed the tach sweeping up to or past 8000 without hitting a limiter. I can tell you that before I recalibrated my tach the needle would sweep off the end of the scale before hitting 7200 rpm! It is apparently quite common for these tachs to go out of calibration over time - mine was reading 20% high, in fact (resulting in running off the scale before hitting 7200 actual rpm).

So, I suspect there are some that have been cutting their LT5s waay short of their potential because of a combo of unwarranted concern for reving too the stock limiter setting, and because they're looking at a tach that may be reading significantly higher than the actual rpm. That is too bad, because it is robbing them of the biggest gift the DOHC LT5 has to offer...RPM! (I observed this very phenomenon when I let a friend of mine drive my Z while I rode shotgun. He was short-shifting it at about 5800 rpm! I asked him why he wasn't riding it out, and his response was he was going by the sound and what he knew from "regular" V8s. So, I wonder how many Z drivers there are out there that are instinctively shifting their Zs according to patterns long etched into their minds by experience with pushrod putters!? AND, here is a classic comparison between a pushrod LS1 and a stock LT5. Notice what happens to the gap every time the C5 driver has to shift. You'll get a really good view of the beauty of the LT5's reving)

Fuel cut-off is the method used by the limiter. The result of hitting the limiter is the engine will pop and sputter until the rpm is reduced. I don't know why anyone would attempt to hold the rpm against the limiter intentionally - that can't be a good idea (on so many levels). But, bumping into the limiter occasionally is apparently not going to hurt anything: after all, the limit of the stock motor itself is somewhere more like 8000 rpm. (excluding belt-driven accessories - I'd be more concerned about that Chinese-made replacement alternator than anything.)

A shift light, e.g, the Raptor that can be hidden behind the vent grill, would be "thee" way to know when to shift without bumping the limiter - AND the lights are much more accurate than the tach, due to the tach's inertia lagging (especially in lower gears).

Uz guys afraid of going above 6500 rpm either have lace on your panties, or have "pushrod characteristics" embedded in your brains, I recon! Let that LT5 stretch it's legs and show ya what she'll really do!


P.

[sammy]

where can one get the raptor shift light .?????and how does it get wired to the car ???

[rhipsher]

I've never seen a shift light in mine and have reved as high as 8k. But at 8k I do notice the drop in torque. The engine revs faster than my tac needle can keep up with in first gear. I don't make hitting 8k a habit either. 2500rpm drag strip launches may be fine with the dual mass flywheel but not with a Fidanza. If you launch at 2500 with the Fidanza you'll drop like a rock and bog for a second before the rpm's come back up. I've launched mine with the Fidanza at 4500rpm's with Mickey Thompson s. Thats the sweet spot for me. Having a stroked LT5 with a Fidanza may not cause you to bog off the line because of the massive torque and hp they produce.

[WB9MCW]

On the Dunlop street tires I do a 3500 rpm clutch dump.

Having a nice ceramic stage II from CC helps a lot as well on the launch plus my secret tuner chip all have worked well to give extra spunk to the Z.

I really do like the Fidanza a lot.

I shift at 7K on the needle and have only hit the rev limiter once - so I know it works!!

[bdw18_123]

I hit the rev limiter once, I was in 4th gear. Put the hammer down and didn't let up until the needle was right at 7K and that is when the engine hit the fuel cutoff limiter. I don't remember exactly what my speed was I think it was a bit north of 140MPH.

So I think my tach is actually fairly accurate still, being that the limiter is set at 7200, that would mean it was reading only 200 RPM low at that point.

Nearly every time I drive my Z, I do at least one short run through the gears to at least 6K to make sure the secondaries stays clean and working. And every time it amazes me how it just keeps pulling and pulling! Not to mention the awesomeness of the scream of the LT5 at those higher rpms. Love it!!

[Kevin]

top of 4th is probably closer to north of 160

[A26B]

Originally Posted by sammy

where can one get the raptor shift light .?????and how does it get wired to the car ???

http://raptorperformance.com/products/Shift_light.htm

[Paul Workman]

(I thought I posted this earlier, but now can't find it here. Anywayz..)

Thanks Jerry for the detailed info re the A pillar mount.

The shift light is ever so much more accurate than the analog tach, and when drag racing, ya don't have to be looking directly at it to see it in your peripheral vision - and keep ya from bouncing off not only the rev limiter, but the guard walls too!

I really like the clean cockpit look, so the hidden approach apeals to me. Your mileage may vary. AND, the popular AC vent installation looks like this...

(Note: there are acutally six (or so) leds and on start-up the light says "hello" by turning them on and off in a circular pattern for a second or so. The camera only caught a couple, but when the time comes, all come on, and even in daylight you will not miss it. In fact, I have mine intentionally aimed toward my right eye. As you can see, ya miss it!)

The Raptor is only 3/4" in diameter, and can easily be inserted through a hole drilled in the plastic. Plastic tape is wrapped around the barrel of the lite to generate the desired fit.

Referring to the FSM, the C100 connector is where the white tack wire can be intercepted. You'll have to remove the hush panel to see the connector, located about 2" from your big (left) toe (while driving).

To fische the wires down there, after disconnecting the negative terminal of the battery...very important...you can use a coat hanger wire to snake down to where you can grab it, and tape the Rapor wires to the other end, you can them pull the wiring down to the footwell area and splice them.

[tomtom72]

the only time I hit the limiter on a consistent basis is in 2nd gear. I usually watch the tach like a hawk with my left eye in 1st as I find by not watching closely it is too easy to hit the limiter in 1st. If I shift by "ear & feel" of the motor in 2nd I will always hit the limiter, but then my only other vette was a C3 LT-1 car. So seeing 6 to 7 k rpms on a tach is "normal" for me! Even my DD, Cobalt Sport 2.4 DOHC/4V has a 6.5 k rpm limit on the tach!



JMHO, but 1st gear ratio is too big ( isn't it like a 2.63 gear? ) for the power available and the stock rear gear ratio. If I had money to waste I would like to see the Z's box with a 2.20 1st gear like the M22's used? That set up in my 72 LT-1, an M22 box with a 3.55 rear gear & 15" wheels, yielded 10 mph per 1k rpm in 1st gear. So 0 to 60 mph was done in 1st without even being close to the factory red line of 6800 rpms. To a road work person, having a "useable" 1st gear is a God send! Those pesky hairpin turns & all ya know.


Tom

[mlotruglio]

I have never hit the limiter in mine but Im almost 100% sure I have cams in it, the higher you run it up the harder it pulls all the way to 8k. My close uncle has a 90 Z and his " dies" at 6700-6800 ish