Hello, i would like to know the top speed of my car. Its an 1988 Iroc-z28 no t-top whit 305 tpi , thm 700-r4 and 2.73 rear axel. The engine has flowtech hedders , k&n filter , 3 inch exhaust and no cat.

 

Probably 125 MPH. Most of these cars have a speed limiter, which was commonly set at 125.

 

First we'd need to know the rear tire size and the rpm limit on the engine.

Second with a 305 the chances are that you won't actually be able to reach the top geared speed since you won't have the HP to attain it.

 

ok but i think my car came whitout the speed limiter if you look at the rpo codes

 

I think an article on this site showed a 1990 305 manual TPI hit 142mph..

 

Yeah that could be right . My friend claims to have made 155 mph whit his camaro . Very much the same as mine. I now from experience that its good for at least 130 mph and i felt that the car had more to give. To bad that there are to many cops out during the night so i had to easy off on the right foot.

 

I got my `91 T/A 305 700r4 up to 115mph @ 2600 rpm in and out of traffic on the way home from a baseball game... who knows what the top speed is

 

I got my 88 iroc up to 120mph on the freeway without a problem(racing a mustang). It has a stock 305 with tbi.

 

Ok thank you every body. Anyone else?

 

me too 305iroc...... i had mine to like 124 and still had some to give.....i do need to change my kickdown valve soon so i can really see what she has!!!!



305auto 91rs some minor mods

 

my 87 TA with a 305 4bbl 2.73 wit 700R4 has hit at least 130 with some more coming out of it...I just need to get some more horsepower pumping, and the by pass for overdrive, and I bet the B**** will roll...they are geared to 202 mph at 5000 rpms in OD...I'd crap myself. Not too shabby for an ol' thirdgen.

 

-85 z-28 305 tpi 240km/h with 3.23 4th gear 4800rpm.

 

dang 142 is impressive....my top is 132. i got scurred and slowed down. cant wait for my T56 then i'll see whats my top speed.

 

i got my 88 firebird to 140 and at the time all she had was, headers, flowmaster muffler, K&N air filter, and the emissions were pulled off. it got up to 130 reall quick then i had to go into overdrive and it got to 140. i was scurred. car was shaking and could barely see the road. one heck of a rush though. havent taken it back up ther since i haave put a new trany in it and other mods. to many cops on the highway

 

i got mine to 135.... my friends can back me up.. it was scary as crap, but i was stupid and immature when i did that......

 

305's are mathmaticly geard for around 150 mph, and im sure i read somewhere a 149mph top speed in a mag ?

2100 rpm = 75 mph so only 4200 required for 150. (top is around 1:1 i think) 800 rpm is 32 ish, 1700 is about 60, so doubling engine speed seems to double road speed.

I was checking out a vibration in my car and backed off at 3200 rpm in top and the speedo was welded against the trip meter reset button FOREVER as i slowed down (85 mph speedo), I also was passing cars like they were in reverse! estimated speed was a good 125+

(I dont claim this behaviour is big or clever though!)

this is only what my totaly stock car appears to do, by no means take this as solid tech advise!

 

It may come out to that if you do the math, but the faster you go, the more drag your car creates, and therefore is harder to go faster. I would be extremley impressed if you could do 150. 202 is completely unbeleiveable.

 

150 sounds right with the coeffecient of drag, yeah...but if you got enough horsepower, like, 800 or something, I bet no doubt you could hit 202mph, don't you think?

 

I have an 86 T/A 305 TPI 3:27 rear P235-R15 tires and got up to 135 on the highway and this is in Colorado at mile high above sea level.

 

hehehhehe
u guys are gonna hate me :-)
the day i bought the TTA home froim joliet i hit 135 mph at 6psi just rolling into it (100mph=1psi just slowly getting into it).......this is when i about #$%# my pants cause i lost my buddy in his 87 Turbo-T Limited and then realized he was paving me in my blind spot :-)

lol after that i said #$#$#% and wussed out and went back down to 70 the rest of the way home lol

all he said when we got off the expressway was how fast were we going all i know is i hit od at full throttle and kept in it :-) (turbo regal clusters come with 85mph speedos and 3-4 comes at the 105(+ ior-) range :-)

lol and that was with 96k on it too
thats all for now
and i do believe that they will hit the 160's stock like they say
later

 

That was my point exactly. The faster you go, the more "wind resistance" you will encounter and the harder it will become to go faster, otherwise known as coeffecient of drag.

As for 800 HP, absolutely. It would easily top 202, but c'mon, were talking about near stock 305's, a far cry from 800 HP.

 

Thank you guys for all the answers . My car has 245/50zr16 tires and a 2.73 rear axel. If im not wrong you should be able to drive fast whit a 2.73 rear axel.

 

I can only add to what's been written above. I don't have data for 1988, but I do have data for something close in both year and equipment:

Stock 1991 Chevrolet Camaro B4C (special service vehicle package, essentially a Z28 for cops).
305 TPI (230 fwhp), 3.42 rear end, 5 speed, and as tested by the Michigan State Police. Top seed: 149.1 mph on the Chrysler (now Daimler Chrysler) Chelsea Proving Grounds track (banked, 4.7 mile loop). Also ran 15.84 sec in the quarter mile (with full tank of gas and driver + passenger aboard. wgt = 3393 with no passengers).

Added note: the 350 L98 version (245 fwhp) of the B4C, during the same tests and equipped with the MD8 trans (700R4) and the 3.23 rear end, ran 150.0 mph and 15.05 sec quarter. wgt = 3463 lbs with no passengers).

I don't know what the weather conditions were during the tests, but they usually conduct the tests in later summer, so the acceleration data is watered down by both hot weather, and by the extra weight they carry (driver + passenger + full tank).

Further note: the L98 version of the B4C got 15 more hp than the LB9 car, but the L98 car got a lossier trans (automatic) and a numerically smaller rear end, so the LB9 car was able to keep up with slightly less drivetrain loss and probably a trans/rear-end total ratio that allowed the engine to run at peak hp rpm AND max speed simultaneously.

Since both cars had the same exact drag coefficient, and reached essentially the same top speed, then the power to the road was a wash (equal). That's not true for the acceleration data, where the bigger L98 did much better than the LB9 did. The larger difference in the avg timeslips (15.05 vs 15.84) is due to the better torque on the L98 car. Driver + passenger weight does very little to the top speeds of any car, because it only increases the mechanical rolling resistance slightly, and the aerodynamic drag is MUCH greater. So the results make sense.

Your car is modified beyond a stock Z28, so I would expect that you have slightly better-than-stock power (if the engne is running well, and if you have it well tuned for the added mods). The 2.73 ratio might be better for top speed given that you have a TPI engine that peaks in power in the mid-4000s, so you could easily have the same, or better, top speed as the 1991 LB9 cars (149 mph) especially if you made the run while in D (3rd).

I will add that the sticker on the driver's door jamb will tell you what tires the car was equipped with from the factory, and that the speed limiter within the ECM is likely to be the same, or less, than the factory tire speed rating.

So if the car came with H-rated tires, for example, and you still have the stock programming, then your top speed will be 130 mph via programmed limiter, and regardless of the potential top speed based on the engine, mods, gearing, and tire radius.

 

I used to hit the speed limiter in my 88 vert ALL the time, back before my tranny woes, (thinks to self "hmmm wonder if there's a connection") and it's a 305 TBI.

My buddy and I just drove to Laughlin, NV in his 92 RS (305 TBI) and we would hit the speed limiter with his cruise control, back it off one and cruised most of the way there at an estimated 120 He had a LOT of RPM and a lot of pedal left on it too. He has the open element mod and that's it. It's the 2:73 gears, man you can wind them up. Try doing that with a 4.10! It isn't going to happen. But off the line the 4.10 will have you every time. I like high highway speeds, so the smaller gears for me are just right.

As far as top speed back than I could of done 135 no problem, but I do have some High RPM mods like the all of the ignition upgrades. My buddy could of gotten there too, with less trouble than my 700lbs heavier vert.

James

 

well the tires are 245 zr from the factory if im not wrong

 

Mine are kumho 245/50 16 ZR rated... 150mph plus! woohoo Down side is only estimated life of 20k miles on em.

 

yeah you are lucky if you get 20k from your tires. Its a shame the are expencive.
Does anybody know how you can see if your car has a speed limiter or not. I belive i dont have one

 

the easiest and the funest way to see if you have a speed limiter is to take onto the highway and just let her rip. but there is always a possibility of being caught by the wonderful cops.

 

As far as actually looking around your car I do not know, but go out and hit 125mph, if nothing happens your good. If the car does a "mini" die on you than you have the governor.

James

 

20K, you poor dear! there there there!

(summit radial trac's destroyed (less than legal limit of 1.6mm) in 10,500 miles!) v. poor traction too!

still cant complain, I once destroyed a tyre on a Yamaha RD350LC in 2000 miles, 2 stroke powerband to blame for that!

 

philoldsmobile...

I am still trying to decide whether you were being mean, or actually feeling sorry for me lol

But hey 20k miles on a 305 TBI is not a lot. Maybe on a firebreathing Ram jet 502 it is great, but not for my daily driver.

 

Just yankin' yer chain!

I think the terrible milage I got was due to slime coverd (Y)UK roads meaning wheelspin everywhere!

I kid u not, my bog basic 305 4bbl has broken traction at nearly 60 before when changing lanes to overtake, eeeeeeeeeeeek!

new pirellis seem 100,000% better. maybee with them not spinning so much they might last? diesel coverd wet roundabouts seem worst, as soon as you edge carefully out a huge truck seems to pop out of nowhere and try to kill you, u panic, try more right foot and end up goin' nowhere!

 

So then i guess i dont have one since i made 130 mph and it still had more to give. Well thats nice to know , you never know when you need to go fast maybe when the highway patrol shows up.

 

ok i will be the one to put this one to rest, so to speak....i have ofically reached the top speed in my car...91 gta lb9 t-5.....the road was strait and level for 15 miles or so....i got into 5th at 120 and kep her matted..about 30 seconds later (damn .74 5th gear) i got to 140 and i kept goin.....from about 135 or so its slow gainin speed..but like i said the road was long and falt so i kept my foot in it....i saw 140 and the speedo kept goin past the 140 mark...by the time i let off. it was at 143 and the rpms were at 4400 (wear it makes peak hp)...i must of coverd 10 miles in 5 mins or so.....and at that speed the car felt very stable, no wondering lifting or any thing like that....it felt as stable at 143 as it does at 80.....ohh just for comparison the l98 cars will do 145...my buddy and i did it in his....i think were gonna go to that road and i will follow him and well do some draftin....i bet ill pass him lol

and yes its a helluva rush....and if n e of you question this your welcome to pm me and i will call you and will put my g/f on the phone and she will tell exactly what i did...hell she was cheerin me on lol....

she does the same thing when we street race stangs... lol

 

Ohh wery nice 143mph but how fast will you go if you have a thm700-r4 gearbox, since you have the five speed manual i dont know if its the same top speed.

 

well, I've had mine up to about 4800 rpm in 5th, with 3.42 gears out back and the mods in my sig. calculator says 160 something, I believe it but kinda doubt it too.


--oh, and it was still climbing, but I was running out of road VERY fast

 

yea no doubt...that stop sign or w/e a mile ahead comes up real fast lol....and when u get on the binders and u start gettin brake fade..nad have to let off the pedal for a few seconds to let the rotors and pads cool then do it again...it does get a little hot under the collar..

 

oh hell yeah it does. atleast the road I did it on is pretty much perfectly straight with just a slight curve at the end of it. but its gradual enough that you can take it at over 100 and have no problem staying in the lane, I mean this road is perfect. its funny how you never know how bad the stock brakes suck until you try to slow down from extremely fast speeds. oh well, just something else to upgrade I guess!

 

anyone else who want to share??
Come on and tell me how fast are your thirdgens??

 

Ive coaxed my bird to around 4500rpm in OD with the old 305 and B&M upshift valve. Mine has 215 60 R14' tires and 3.42 gears "75MPH=2900RPM no tc lockup" so if I had the larger tires most of you guys have I'm sure that would be impressive since when it kicked out of OD @4600 it slammed the tach past 6K in 3rd. I havent bothered to take the 357 to top speed since its only got a couple hundred on the engine. Ive gotta get some larger wheels.

 

My 1992 RS B4C 5.7L, Auto, 3.23 hit 142, slow going from 135 to 142, was taching out.

 

Aaahhh sounds very nice to do 142 mph. I wounder when a thirdgen hits over 200 mph.
I also want a 4-wheel drive thirdgen but i dont know if i have enough time to build one. Would be kinda nice to have.

 

Maybe all wheel drive based on Syclone/Typhoon parts. This would require much fabrication and very expensive.$$$

 

Yeah maybe but your thirdgen would be a real killer on the street. I hope somebody will do this that would be really nice.

 

i hit 155 with mods below and not spraying....

 

with just a bum basic 305 and TH400R4 i did 90 + while rushing to an appointment today without breaking ANY sweat (1/4 throtle) and was keen to do more, my S/C went from 70 to 90 faster than most euro cars go 40 to 60, mathmatic top speed is 150+ , would it do it? dunno, would it crack 135, i'd be very suprised if it wouldn't, 145 on a hill.

Verdict, fast enough. in the UK at least, a MAJOR motorway tool for the money!

(show me another car that can do this for the money, i dont like to push my car like this, but it's good to know it's there if i need it)

BTW, my comfortable motorway (freeway) cruising speed is 65

 

Damn it My 91 Camaro RS 305(LO3) top speed is 110 and I have no idea of what is wrong with my car

 

108 MPH speed limiter, 305, TBI, 700R4 that wont shift into OD at WOT, etc, etc...

my STOCK 92 Z28 top speed is 125@5500RPM, 5.7L TPI 700R4 3.42's, but thats in D, it wont shift into OD, because if i let off, it goes into OD, but stomp it, back to D it goes...stupid 700R4, and the B4C kit deal i tried it the reason my Z is getting parked this year with a mega slipping transmission...

 

B&M sells that kickdown valve for about $40 that will eliminate that. Does your Z28 have the 4 wheel disc brakes, oil cooler , etc.

My old 1992 Z28 5.7L would cruise up to 142 with no kickdown of the tranny. I had G92, J65, KC4 all of that. I bought the car new so I knew it wasn't tinkered with. Some of the Z28's that came with the non "Z" rated tires and no 4 wheel disc brakes would only go to 125 in drive and wouldn't shift to OD at full throttle.

 

I have a 92 Z28 350 TPI G92 oil cooler, 4 wheel disc, i tried the B4C kit from GM, it ended up ****ing my tranny up, now its slipping hard, even though we put hte stock peices back in, so this winter i get to leave the car sit with a ****ty tranny, and get it rebuilt and a shift kit put in...