[turbo_lover]

tyres stock - 175/70 13''..

thats a huge speedo error ..damn !
in 5th @6600 rpm will it touch 219 ks ?

[Shan2nu]

in 5th @6600 rpm will it touch 219 ks ?

Yes, provided your car produces enuf power to get there.

thats a huge speedo error ..damn !

So, at 5600 in 4th, whats the speedo read?

Shan2nu

[Shan2nu]

4th - shoud fly all the way to 150 ,car takes a while till it crosses 160s @ 5000rpm i think ...

U mean to say your speedo shows 160kmph when it's actually doing around 133kmph? Daaaamn!!!

Shan2nu

[turbo_lover]

1st 3.73/6.8 -44.8
2nd 1.96/12.9 -85.14
3rd 1.31/19.3 -127.38

the above speeds match my personal readings ...i am almost hitting 130 while i shift to 4th ..

i think i should try another run and read the tacho /speedo again properly ..cause at that time i am focussing far ahead in the road ..

..30ks is a huge error..

So, at 5600 in 4th, whats the speedo read?

173-174

[turbo_lover]

shan2nu - why did you ask for the Final Drive ratio ?

i went to the GM showroom ..the guys checked the wiring and checked for "gear skip" found everything was fine ..

how can i correct the caliberation ?

he also said running a car at 170 k's in 4th can cause back compression (resulting in sucking the air back in from the exhaust into the engine) ...
is it the same thing as lack of back pressure ?
even then how can the air be sucked in from the exhaust when its a naturally aspirated engine ..
i found it very weird when he tried to explain it to me with such confidence ..

[adya33]

even then how can the air be sucked in from the exhaust when its a naturally aspirated engine ..

wierd but true.
even my astra has that

if you open your air filter box you will see something like a "VALVE" type system there
just check where those two pipes go.
i don't think all exaust might be used but in some ratio

[Shan2nu]

shan2nu - why did you ask for the Final Drive ratio ?

Thats bcoz the final drive is a part of the drivetrain. It's the diff in rotational speed between the input pinion gear and the ring gear of the differential.

Just think about it, if your car only had one reduction, then at 5600rpm in 4th gear (which has a ratio of 0.95:1) the rpm of the wheels would have been 5894.73 rpm (which is 638.73 kmph).

But, your car doesn't do 638.73 kmph at 5600 in 4th, why? This is where the final reduction comes in. Your car's final drive ratio is 4.19:1, so 638.73 divided by 4.19 = 152.44 kmph (which is what your car actually does at 5600 rpm in 4th).

The final reduction helps you increase or decrease the revolutionary diff between the engine rpm and the wheel rpm without changing the gear ratios.

This site will give a better idea - Howstuffworks - gear ratios and final drive

Shan2nu

[Shan2nu]

he also said running a car at 170 k's in 4th can cause back compression (resulting in sucking the air back in from the exhaust into the engine) ...
is it the same thing as lack of back pressure ?

Well, if back compression (what ever he meant by that) is the same as lack of back pressure, shouldn't it be making the engine's work easier?

I think he meant that doing 170kmph in 4th causes more back pressure. Maybe Psycho can help varify that.

Shan2nu

[turbo_lover]

thanx for the info on final drive ...

think he meant that doing 170kmph in 4th caused more back pressure. Maybe Psycho can varify that

meaning there will be too much back pressure since it has a stock muffler with a higher restriction air flow causing the exhaust air to fill back into the chamber?

..so a free flow would help.avoid something like thst from happening.

ahh waiting for Psycho to verify...

[Shan2nu]

Well, i don't think back pressure results in exhaust gasses re-entering the combustion chamber. It only slows the movement of the next batch of exhaust gasses that are let out by the engine.

so a free flow would help.avoid something like thst from happening.

Yup, but everything from the headers to the exhaust tip will have to work as a unit to make things work efficiently. A badly done exhaust job can even reduce power output and slow down the car.

Shan2nu

[turbo_lover]

It only slows the movement of the next batch of exhaust gasses that are let out by the engine.

thats what am hinting at..if say the back pressure is very high the intially slowing exhaust gases may stop venting out and might rebound back ..

if lack of back pressure can pull air back in the chambers (why we dont fit free flows in deisels).. same thing can happen with excessive back pressure cant it?...

say like .we have water hose connected to a tap with those rubber thingies ..the tap is running water at a high pressure ....squeeze the end of the hose (restrict the flow)and try and stop the water from flowing out ..what we see is the water flowing out of the mouth of the tap due to high pressure which builds up as the water cant flow out from the end of the hose .. now because air and water have similar characteristics ..wouldnt that explain how exc essive back pressure can send air back into the engine?

or am i sounding really stupid?heh

[Shan2nu]

But the water isn't going back into the tap. It just stops the flow of water.

I don't think an exhaust can create enuf back pressure to send gasses back into the engine. If that happens then the engine will stall.

I still don't get what the GM guy was trying to tell you. Is he trying to say that the exhaust system in their cars is in efficient?

Shan2nu

[turbo_lover]

But the water isn't going back into the tap. It just stops the flow of water

water oozes out from the mouth of the tap to where the hose is attached ...

GM guy said-

at 170 in 4th gear ,engine is producing max power ..which causes back compression ..he mentioned the engine sucking back air from the exhaust ..which we still dont think makes sense...

he said -speeed zyaada hai but gear chota hai so it'll move too fast.. i thought he was referring to engine over revving and blowing..but he said no...

i really got lost in that convo..
as long as i am shifting up before hitting the limiter i am not damaging the engine...thats what i know

[Shan2nu]

at 170 in 4th gear ,engine is producing max power ..which causes back compression ..he mentioned the engine sucking back air from the exhaust ..which we still dont think makes sense...

The engine produces max power in every gear, so how come you don't feel it there?

he said -speeed zyaada hai but gear chota hai so it'll move too fast..

No idea what he's talking about. Vehicle speed is relative to it's gear ratios.

BTW, you never told us why he mentioned that in the first place. What has that got to do with speedo caliberation?

Shan2nu

[nikibusa]

Luckily got to do a max upto 140 kmph in my friends customised Ford Ikon on the western express highway and doing 110 on my Pulsar 150 is just becoming common.