I HAVE A 1989 iroc 305 TPI. I JUST RACED A 1996 MUSTANG GT .I WAS PASSING HIM AT ABOUT 118 AND MY CAR STARTED TO SPEED UP AND SLOW DOWN LIKE I WAS LETTING OF THE GAS AND BACK ON. I WAS AT ABOUT 4100 RPM.I HAVE INSTALLED A SUPERRAM INTAKE AND RUNNERS,CORVETTE ALUMINIUM HEADS ,PORTED PLENUM,EDELBROCK HEADERS ,FLOWMASTER 3 INCH EXHAUST ,GUTTED CONVERTOR,ADJUSTABLE FUEL PRESSURE REGULATOR,THE FUEL PSI IS SET AT 49 PSI.I HAVE THE STOCK CHIP IN COMPUTER,I BOUGHT A JET STAGE 2 CHIP ,BUT WHEN I PUT IT IN I GET A CODE FOR THE KNOCK SENSOR.ALSO IF I RUN AT HIGH RPM FOR LONG PERIOD OF TIME ,THE CAR BACKFIRES.I THOUGHT MAYBE MY FUEL PUMP IS THE PROBLEM FOR EVERYTHING BUT CHIP PROBLEM PLEASE GIVE ME SOME IDEAS THANKS

[This message has been edited by bdiroc (edited December 26, 2000).]

 

Congratulations! You have just experienced the speed limiter in your stock chip. Your IROC probably came with tires that weren't V or Z-rated, so you get to stop accelerating at 120 mph. It can be bypassed by burning your own chip and using TunerCat or GMEPro, although I think most aftermarket chips get rid of it too.

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Greg Westphal
'87 IROC 305TPI/A4

 

this could be true becuase my iroc came standerd with 15 inch iroc rims not 16 inch.do you think it is the computer program causing the motor to run lean at high rpm or the fuel pump cant keep up? also does anybody burn chips in columbus ohio,i figure jegs hot rod shop might,this is not there mail order business ,they are located local,i was just wondering if you took your car to the track and have any 1/4 times?thanks

 

ALL 80's model computerized F-bodies had speed limiters in the stock chip....and they are ALL set to about 118-120 MPH.....mine's an '86 and it's got it too!! You can bypass the speed limiter without changing the chip or anything else....find the VSS (Vehicle Speed Sensor) and splice into the wire and hook up a switch.....the computer uses the VSS to determine how fast the car is going and therefore LIMIT the speed.....when you flip the switch, the VSS goes off and the computer can't tell how fast you're going and presto!, it CAN'T limit your speed!! Keep in mind tho' when you flip the VSS off the check engine light will come on because the computer thinks it's not working....so during everyday driving just keep the VSS on and when you're in a race flip the VSS off!! And please don't send me a reply saying that this won't work because I have my car hooked up like this and it DOES work!! (Check out the article here on thirdgen about disabling the lock-up on your 700-R4 transmission, this will improve race time also)

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1986 Trans AM
305 TPI
Completely Stock
Soon to upgrade to a 327 TPI with pocket ported 64CC heads, comp cam, TPI air foil, Adjustable Fuel Pressure Regulator, possibly bigger injectors!
Current project: Installing an Accel Inline Fuel Pump since I've been through 3 Fuel Pumps in 2 Years! :-(

 

no not all had speed limiters. I can name about 5 off hand that don't mine included. my 305 had no limiter and my 350 also using a stock gm 350 chip has no limiter as well I can just watch it go past 140mph and keep on going.

 

will all aftermarket chips bypass this limiter?? does my 89GTA have one? with 5.7TPI?

 

The computer cuts the injectors off to limit the speed, just like the rev limiter that's also there but not used. Most aftermarket chips get rid of the speed limiter; I know the Hypertech chip that was in my '87 IROC did since I saw 125 mph a few times (ran out of straight road) and 131 mph on a chassis dyno.

Yeah, I've been to the track a few times. I guess I have about 180 timeslips from the past 5 years. My best is a 14.86 @ 90.95 mph in 75-degree weather, running too rich and not enough spark advance. I know I could knock off a couple tenths and add 1-2 mph to that, but I never got a chance to get back to the tracks before they closed for the winter. Oh well, they'll be opening back up in a few months.

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Greg Westphal
'87 IROC 305TPI/A4

 

My 92Z28 convt has a limiter, cuts in at 110mph. Came stock with Eagle GA tires (not speed rated V or Z).


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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

Wrong.

 

GregWestphal has the right answer. The TPI cars were speed-limited if they didn't come with the speed rated rubber.


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Mike

'90 IROC-Z , 5-speed, ZZ4, G1 Trick Flows
Moderator SEThirdgen

[This message has been edited by Lounge Lizard 6 (edited December 27, 2000).]

 

My car doesn't have the speed limiter and it does have the stock chip. I have seen the far side of 125 in mine.

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TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

well i take it i need to change my chip to get rid of this problem.but does anybody have an idea about the backfire problem in original question ?. heres another ?.has anybody put on the fiberglass front end they sell at year one parts.and how much weight did it take off of the car.

 

If your car doesn't have the 145mph speedo then you most likely have the fuel cutoff. If you are continually bouncing off of it at high speed then that could make the car backfire. It's not good on the engine to keep running up against it over and over.

did you put a superram & 'vette heads on a 305?

if it's not backfiring b/c you're hitting the rev limiter, get a fp guage from hypertech or somewhere for $35 and tape it to your windshield. Take it for a run and see what the pressure does when it starts acting up.



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87 IROC-Z, 5.7, auto, 3.27, leather, !cat, Holley fpr, K&N'S, SLP 1-3/4" Jet-Hot coated headers, SLP .218/.224 .495/.502 cam, Comp 1.5 roller tip rockers, $uperPITAram, Edelbrock lower intake, Holley 52mm tb, Dynomax\Flowmaster catback. Coming Soon(?)- Fasttrack/Accell DFI

1989 Pontiac 20th Anniversary Turbo Trans Am - 161,000 miles, !cat, 9" K&N

 

Whether or not you have the 145 speedometer has nothing to do with the speed limiter. I have the 120 speedometer and I have been well over 120... I'd say 130-135. The car was still pulling when I let off. It all comes down to which tires your car had originally: Those with V or Z rated tires have no limiter.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

yes i put the superram intake and runners and vette heads on my 305 ,I looked up parts # on heads and the book said they were 58cc heads .so i thought they would work great .i am happy with the power right now .but i know there has to be a lot of hidden horsepower since i have stock chip.i still need to change the rearend gear.plus i figure i will put underdrive pullley's on and accel 300 ignition ,after that i want to lighten the car thats why i asked about the fiberglass front end earlier.