kallark

iTrader: (1)

I have a 1990 RS with 305 TBI. I put in the Xstream filter , new distributer with cap... However I seem to be hitting 90mph right before Redlining my engine in 4th gear. I am afraid to go any further. The speedo says it can do 110mph. I wander could it be the tranny? Any suggestions? Car feels very underpowered. I can't imagine that 90mph is the top speed for this car. Pls help...

//<86TA>\\

iTrader: (15)

first off, the 305 tbi is not a powerhouse, so dont expect it to feel very powerful.

The tac could be off,
the car should be able to do 100+ with no issues, unless somebody swapped in really tall rear axle gears, that could explain why the car redlines so quickly.

for what reason do you really need to drive that fast?

If it blows up, it only means time to build something better.

kallark

iTrader: (1)

Thanks for your reply. I think that tac is on, because every other time its pretty solid, car idles at 900. If I pull off the rear axle seal, how do I tell if the gears have been switched? I don't think it will even do 95 before it blows. Could it be anything else?

//<86TA>\\

iTrader: (15)

how do you figure? is the car screaming at 90 mph? if it is, then the gears are swapped.

if you pull the cover, you can count the teeth on the ring and the pinion gear, then divide them, or most of the time, the ration or tooth count is etched into the gear, if you can find that, your all set

kallark

iTrader: (1)

thanks a lot i'll do that this weekend. yes, the car is screaming like hell around 90mph. do you think it could be anything else? could it be the tranny?

JamesC

iTrader: (5)

Here's how to determine what ratio the rear is (jerk the diff cover and look): numbers are stamped on the ring and pinion:

41 : 15 = 2.73
41 : 14 = 2.93
40 : 13 = 3.08
42 : 13 = 3.23
41 : 12 = 3.42
41 : 11 = 3.73

JamesC

atc3434

iTrader: (4)

This is an automatic car, right? The 700R4 didn't come from the factory with the ability to upshift to, or hold, 4th gear at full throttle unless you had a police duty vehicle. So, your probably in third. Till, you should be able to go over 90mph if you've got a stock 2.73, 3.23, or even 3.42 rear.

I don't know what your redline is, but with 3.73's and a stall converter I'm at about 5000rpm in third at aprx 95 - my speedo gets funny between 65mph and 100mph, so that an approximation. I can go on to about 105mph at 5500rpm in third, then let it upshift with about 1/2 throttle and go up to about 120mph. I can't throttle it enough in 4th to go any faster without it trying to shift back down.

Saber

iTrader: (2)

I had 3.45"s behind my old 305 and i could go over 100, never pushed it past 110mph though but it had a few more mph i could squeeze out of it, my 350 is the same way though, not that there would be any difference. Chances are your tach is off, it could read idle at 900 but when the rpms rise that is whrer the inaccuracies arise. Its a proven fact on these boards that the tachs after 20 something years become innacurate. I know mine is off but i just havent gotten around to buying a new one.

kennn

Don't trust the speedo. Use either a GPS speedometer or a radar gun to determine your actual speed.

subroc

iTrader: (2)

I was able to get my tuned port 305 to 110 with 3.42s. You shouldnt have any problems going 100. You sure that tranny is shifting to overdrive?

atc3434

iTrader: (4)

The tranny shouldn't be shifting into over-drive - and if it was upshifting into 4th he would have way more top speed potential, even a 3.73 rear end still can do 150mph in overdrive at stock redline rpms - provided the power was there to overcome the drag.

kallark

iTrader: (1)

T^hanks to all of you for your replies! I did check my speedo with a GPS, it confirms I am around 90mph near redline. I am not sure about the tach... Also I thought that there is a possibility I am not shifting into 4th gear. So I put the car into Drive (not overdrive) to check how fast it will get me, because from my understanding this will keep me in 3rd. I redlined around 60mph. I am really puzzled with this one. I haven't had a chance to look at the gear ratios yet, but from the replies I get, this should not be an issue. As for the tach, it seems to be ok, because the car shifts when tach is in yellow if I accelerate from stop. Again thanks for all the input.

kallark

iTrader: (1)

Also I noticed about inability to upshift at full throttle, thanks for explaining it. It is when I do half throttle upshift I can get to 90 at about 5500 rpms, before this upshift I an near redline at 85mph. Am I confusing things here?

atc3434

iTrader: (4)

You got bad instrumentation or really crazy gear ratio's - if the speedometer is right, my money is that tach is way off - very common with these cars. What are the RPM's reading when the car full throttle upshifts?

kallark

iTrader: (1)

I dont remember the exact numbers but its right in the yellow, before red.
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How would I check if my tach is off? Or better question yet, how would I fix it if it is off?

notguilty_25

where does the car shift at part throttle?. it shouldnt be near the yellow unless at wot. like the other guys said, ur tach is probably way off or u have like 4.56 gears. but i think u said it was a dog... if it had those gears it would feel like a torque monster off the line. u might be able to have a shop hook it up to there diagnostics and check ur rpms that way. i think their scanners have that capability.

ATX-Iroc

Are you sure the transmission is shifting to third. with 2.73s my instruments will read 90 at a little over 5k in 2nd gear (I know its not accurate but proves this does happen) check your tv cable it might be too tight causing it to downshift out of third at ridiculous speeds ( u think its coming out of 4th but really its coming out of third) One last question, what are your cruising highway RPM's ( going 60-65 under light throttle) If its under 2k your not getting into third when youre redlining.

91z 2 8

with 2:73s and a 305 ive had my speedo needle resting on the trip reset button (110 mph speedo) wich im thinking is 120-25 idk you should be able to do way more then 90 unless you got like something like 5:13 gears lol

kallark

iTrader: (1)

No the car does not feel like a torque monster , unfortunatelly :-( I'll try to find a shop that can check my tach. I think they need the computer for that. THANK YOU!
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60-65 is definitelly above 2K... Wait did you mean to say "if its above 2k" I am not in third? Also, how do I check my TV cable? It seems you had a similar problem, how did you remedy it? THANKS!!!

ATX-Iroc

to get a ballpark setting for your tv cable make sure the cable is at full extension when the throttle body is open all the way. If you cant open the throttle body all the way without the cable maxing out that could be the problem. there is a tech article on this in the technical section. earlier you said that you were redlining at 85 then shifted and redlined at 90. your gear ratios wouldnt be that close with 4.11s in the rear. Maybe your trans is slipping does it feel like the car is reving but not going anywhere. what MPH is your 1-2 and 2-3 shift under regular driving around town driving

kallark

iTrader: (1)

Yes, after 85mph it does feel that car is reving more, but stays at the same speed. 1-2 shift is very early may be around 10-15mph, 2-3 seems to be around 30mph. Can you pls give me the URL of the tech article for TV cable? THANKS!

ATX-Iroc

On the home page TGO click on technical articles below the message boards button and then scroll down to the transmission section, its there. I think you have some serious gears man. go ahead and pop off that diff cover and count the teeth on your ring and pinion gears like mentioned above. if you dont want to do that. put the rear on jackstands, trans in neutral and rotate the wheel one revolution, see how many times your driveshaft spins. That will give you a very rough idea and if you see 4 or more revolutions of the DS youve got big gears and thats it.

kallark

iTrader: (1)

I'll have to wait till the end of the week to do that. Job and all :-) THANK YOU VERY MUCH!!! for all your help. I guess now that I have some ideas, I'll have to work on it. I'll report back to let you know! Thanks again!

a1990camarors

my 90 rs V6 car could get to 115 your 305 shouldnt be done at 90 lol. Only reason i know the v6 could get there was bc i was trying to blow it up on purpose lmao.

vette9190

iTrader: (2)

did it have this problem before you put in the new dizzy?
Are you sure that your timing is set right?
if its way of it could act like this. Lack of power.

atc3434

iTrader: (4)

The car upshifts to second at 15mph crusing (that would be pretty normal), or even at WOT? (That would be very, very wrong.) I'd like you to do an experiment. Put the car into first gear, and bring the revs up to 5000rpm and note your speed. Then upshift into second gear, and again bring the revs up to 5000rpm and note your speed. That info my help figure out whats really going on here. Please be careful doing this, don't get caught with your head down reading the rpms or mph and run into someone, be safe!

kallark

iTrader: (1)

The timing is set to 8. I got the light and everything. Its not the problem.
Thanks , I'll try shifting it manually tomorrow!

kallark

iTrader: (1)

Also, it seems that car feels even weaker after I installed the Xstream filter. Not sure why. Could it be because the vacuum tube is not completely plugged (i put a screw into the vacuum hose)...?

Saber

iTrader: (2)

It would be really helpfull to note the gears in your diff. If you know outright that nothing has been changed than just post up some of your RPO's, and if not, you need to pop that cover and count some gears, if you are red lining at that speed, you either have a serious drag car, or something is wrong with your tranny, or your tach is like 1500 rpm off, im betting a tranny problem at this point.

kallark

iTrader: (1)

Got 4 inches of snow today...Car stays in the driveway for now, not a good time to be experimenting if I can do 90mph without redlining it :-) Hopefully better weather on the weekend. Thanks for you reply!!!!

kallark

iTrader: (1)

Ok, I did a few stupid small things and this is what I got.
1 Gear 5k = 18mph
2 gear 5k = 40mph
D gear 5k= 65mph
Overdrive 4400 = 90mph
Now this time I didn't redline at 90. But does 4400 sound right?
Things that I did: poured in a bottle of carb cleaner, resealed my vacuume tube, put in higher octane gas.
I know 4400 leaves some room to play to redline (600 rpms). I just want to make sure that 4400 90mph is about right. THANKS!!!

atc3434

iTrader: (4)

You would need a 6 to1 rear gear reduction for that to be accurate - I've not seen a ratio like that in a stock rear end. So you have bad instrumentation, probably a bad tach.

Time to get that fixed - you're leaving a lot on the table. At what RPM and MPH does the car upshift into second gear when you just put it to the floor from a stop?

kallark

iTrader: (1)

Ok, I tried a few times and this is what I got, from stop it is
5500-5700rpm 23-25mph
Does this sound right?
Its above 5000 redline, but it is a little wet outside.

atc3434

iTrader: (4)

Sounds like a cluster! Sounds like both your tach and speedometer are significantly off. A stock TBI car should be shifting around 4700-5000rpm, and even with a 3.73 rear gear that would happen at over 30mph. The tach is clearly ready high, maybe by as much as a 1000rpm when the rev's are up. If it was the tranny shifting late, the mph would be a lot higher, even with short gear - my 3.73's shift at about 36mph at 5300rpm. It also sounds like the speedo reads awfully low.

Play with the tool below, it'll help you get a better handle on what speeds happen at what rpms and what gear on your car. Bare in mind its a ballpark, torque converters will skew those figures some, but it will get you close. The 700R4 gears are 3.06 for 1st, 1.60 for 2nd, 1.00 for 3rd, and 0.70 for 4th. Plug in your tire size and a rear-end gear and you'll get a chart that plots mph and rpm. A stock rear for that car is probably a 2.73, but its possible you got a 3.23 or a 3.42 as a fluke.

http://www.f-body.org/gears/

kallark

iTrader: (1)

Thanks for the link , yeah it looks like something is not right in the car. Funny thing is ; the speedo , I checked against my GPs, its on the money. But it sounds like my tach is definitelly off.
Just found a link with an amazing tech article, where?! HERE of course!
https://www.thirdgen.org/forums/elec...meter-fix.html