Got a 95 z28 6 speed v-8 engine that wont go over 90, anyone know why?

 

what is it doing? lacking fuel or air or electrical issues? What are some symptoms drive-ability issues?

 

does it run strong up until then? If so might be speed regulated somehow(might be able to in the tune) I know all the rentals ive had thats been regulated at the 90-100 mark


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So where did you find this out?

 

So broad a question without any details is impossible to answer.

 

There were LT1 cars that had a speed limiter. The ones that didn't come with Z rated tires. They also got a 120MPH speedo instead of the 155.

 

it doesn't have any issues other than that, i found out on a track out where i live and it runs super strong up until then, it still is only at 2 or less rpms then it just wont go any higher, it was really weird.

 

There could be 100 reasons why the car won't go past 90mph......BUT.....the most likely culprits are:

1. Your valve springs are weak and your valves are floating;

......or, and most likely......

2. Your PCM has been programmed by a previous owner to limit the speed at 90mph.

KW

 

is there a way to bypass or get the limit raised? or completely removed?

 

Exactly what happens when you reach 90 MPH? Does it just shut off, like the fuel got shut off? Or does it start to misfire, stumble, etc?

You indicate you are "only at 2 or less rpms".... do you actually mean 2,000 RPM (the numbers on the face of the tach get multiplied X 1000). To be at 2,000 RPM with a T56 and the stock 3.42 rear axle ratio, you would have to be in 6th gear. That's not the way to get it over 90 MPH, and I can't conceive of any reason you would use 6th gear at the track.

Shift out of each gear at about 5,500 RPM.... shift to 2nd at 45 MPH, shift to 3rd at 67 MPH, shift to 4th at 92 MPH, shift to 5th at 120 MPH. Did that allow you to get past 90 MPH? A healthy LT1 with stock gears and a T56 should top out at about 155 MPH in 5th gear, assuming your car had the previously mentioned Z-rated tire option.

 

Yes. IF the PCM has been reprogramed to top out at 90mph, then have the PCM recalibrated to remove any speed limiters and have it set to rev-limit at 6000+ RPMs.


Also.....do what Injuneer suggested......get to a relatively secluded spot (maybe the same track?) and rev to approximately 5500+ RPMs in 4th and 5th gears to see what that does for getting past the 90mph mark.

If you hit that 90mph wall in BOTH those gears, I'd look into having the PCM checked for a speed limiter.

KW

 

I received this PM from vhtony:
You have to answer the questions. There is no way anyone can help you with the limited info in that sentence.

Were you trying in 6th gear?

Did you try exceeding 90MPH in the sequence of gear shifts I suggested?

How does it "refuse".....

-engine shuts down like it hit a rev limiter or a speed limiter?

-engine loses power, like it is misfiring or running out of fuel?

 

I hit 90 mph and I'm in 5th usually, then the rpm's will not go any higher than 3500 so i though hmm, maybe try shifting to 6th and push the gas, that didn't help either rpm's still under 2000 and they wont go higher, but in any other gear i can get them up above 3500 easy

 

I think i may of caught the problem, i took it to my dad's mechanic and it turns out i need a new clutch and work on my transmission because they both are shot right now

 

my speedometer is the lower of the two you have stated, but I have buried the needle and kept going faster.

did all cars with the 120mph speedo come with this speed limiter?

the only reason I ask is because Im curious if my pcm has already been tuned.