mummy.. wuts Turbo lag?  

Its the time between when you put your foot down to accelerate and the turbo come back on boost (as is my understanding, which if often wrong )

9th October 2002 - 09:06 PM  Reply  Quote

turbo engines usually run lower compression ratios then n/a engines. so when a turbo is not creating any boost ie. vacumme ,there is not alot of compression to make decent power. so when the turbo pumps up to 0psi that is where the lag stops. lag all depends on turbo size, design etc. thats the best i can really explain it, lags pretty much the feeling before you get pushed back into your seat when it starts boosting. kinda like a 2stroke with its huge powerband!!!!

9th October 2002 - 09:15 PM  Reply  Quote

most people raise their compresion on n/a to get more power. on turbo cars u lower the compresion to get more boost, (generally) the lower the compresion ration, the less power it has unless you have boost as well.



so if u have a large turbo that does not make boost until say 5500 rpm, then your car is basicly n/a untill 5500 rpm, and being low compression it will have bugger all power.



this spot under 5500 rpm is refered to as the sinful turbo lag

9th October 2002 - 10:23 PM  Reply  Quote

I thought it was the differents in speed between the exiting exhaust gases and the turbine?? Which is why u have a bov so when u cahnge gears u dont stall the turbine with the sudden back presure of inlet air. Thats what i thought anyway............... I may be a fool?????

9th October 2002 - 10:31 PM  Reply  Quote

well its not only that Twincam16, but as mentioned earlier the delay (even if u are at over 5500rpm) between wen u floor it and get any power as the turbo spools up, just coz u r in a certain rev range dosn't mean u r automatically on boost. as im sure u know



i dont really think that low end Rev range where no boost can be produced is termed as lag zone , but i could be wrong



edit: Hawk, no that situation will 'cause' lag between gears . the BOV keeps the turbine spinning at a reasonable rate so when exh pressure returns there is less time taken to spool right up again.

9th October 2002 - 10:33 PM  Reply  Quote

a bov does nothing for performance. in some instances it can increase lag. a bov is only there to take the strain off the bearings in your turbo once your throttle has snapped shut by releasing the built up presure

9th October 2002 - 10:35 PM  Reply  Quote

lol . well ill be honest and agree i dont think the performance / lag reducing effect of a typical vent to atmosphere bov is anything much. cept on a really high boosting beast.

but a stock plumback type does help cut lag , and certainly dont make it worse.. not to mention the whole bearing friendliness .

9th October 2002 - 10:41 PM  Reply  Quote

this is my understanding of turbo lag...



its the time between when u put ur foot down, and when the turbo is boosting pressure beyond normal air pressure

26th October 2002 - 10:33 AM  Reply  Quote

whoever said the BOV doesnt affect lag -IT DOES. In real life testing - I ahve found it actually helps - what used to happen before I ran a BOV (starions dont even have a stock plumbed back BOV) say i was in 2nd gear - on 10 psi boost and went to shift- the excess pressure slows the turbing down a few 1000 rpm, and as soons as im back on the throttle its back on 6-7 psi and starts to spool up to 10 again. When the BOV was fitted -same situation - 10 psi, gearchange and the boost guage snaps right up instantly to 10 PSI - VERY little loss of boost on the shift.

2nd November 2002 - 07:02 PM  Reply  Quote

[quote]If you were to run no bov at all what happens on gear changes is the turbin actually tries to spin backwards and sometimes it does and this is really bad for your turbo.

[/quote]



No it wont.

Its impossible for a turbine thats spinning in the hundreds of thousands of RPM to stop and reverse in that split second.

All that it does is put alot of "head" pressure against the front of the turbine which means that yes it slows down and yes the impeller can warp / flex (damages bearings/bushes) but no way in a pink fit will it try to spin backwards.



Also we found going from atmo vent to stock plumb back gave us more performance. This is because we have an AFM and no MAP sensor. Anyone with AFM only *NEEDS* a plumb back or else you get massive overfueling and poor performance between gear changes.



A'ight?

14th November 2002 - 05:08 PM  Reply  Quote

Yeah i wasnt to sure on that spin backwards part but i was just going on what i have read in articles. It would take a shit load of force to spin it backwards.



As for the bov thing. I just found that it felt better with the atmo bov compared to the plumback but i'm sure the performance loss or gain is only very slight.

14th November 2002 - 10:42 PM  Reply  Quote

*ahem*



From an engineering perspective, Turbos are a great idea, since it uses wasted energy to create even more energy. When that extra power isn't needed, you simply bleed it off. To do this, the majority of turbochargers feature a wastegate - which is a valve that allows some of the exhaust gas to be directed around the turbo's impeller instead of through it. This allows the turbo's shaft to spin at a reduced speed and therefore increases turbo life (among other things). Since the turbo isn't needed during relaxed driving anyway, this effect is harmless...

...until you suddenly want to accelerate. Let's say that you are loafing along, engine spinning at about 2000rpm or so. You instantly floor the throttle. The exhaust gas flows through the turbo and cause it to spool (spin up to speed and create boost). However, at this engine speed there isn't very much exhaust gas coming out. Worse still, the turbo needs to really get spinning to create a lot of boost. (Some turbos will spin at 150,000rpm and beyond!) So you, the driver, need to wait for engine revs to raise and create enough exhaust gas for the turbo to spool. This wait time - the period between hitting the throttle and the creation of appreciable boost - is what is known as turbo lag.



There are two aspects to consider when trying to reduce lag: engine factors and driver factors. As far as engine factors go, there are many things which affect turbo lag. The amount of air ducting between the turbo and the intake manifold, for example - the more there is, the greater the lag. Intercoolers will tend to cause a pressure drop. Finally, the design of the turbo itself has a big influence as well; turbos can be designed to minimize lag but this usually comes at the expense of top-end flow.



Driver factors are another matter. You basically need to understand how a turbo works and modify your driving style accordingly. To sum it up, don't get caught with your pants down! If you feel that there may soon be a sudden need for serious thrust, downshift until your engine speed is at least 3000rpm. This way there will be noticable boost almost as soon as you hit WOT. If you are going up a hill at WOT around, say 1800rpm and your speed is dropping, you'll need to downshift just like any other car in the same situation. Remember: turbos need exhaust gas in order to spin. Let them have some when they need it.

15th November 2002 - 09:09 AM  Reply  Quote

turbo lag is why god invented nos



can someone now explain to me how an anti lag setup works

15th November 2002 - 11:20 AM  Reply  Quote

*ahem*



Simple explaination:

A Turbo anti-lag system works by allowing fuel and air into the engine, when the throttle is not depressed. This passes through the chamber, but explodes on contact with the hot exhaust manifold. This explosion then drives the turbo impeller, maintaining a very high rate of spin.



Detailed explaination:

Current technology gives engineers the chance to minimize turbo lag through the use of electronic wizardry and stronger mechanical parts. When the driver backs off the throttle the engine management computer advances the ignition timing by around 40 degrees and continues to feed fuel into the combustion chambers. By moving the ignition point like this most of the fuel remains unburned as the exhaust valves open and the mixture is flows into the exhaust manifold. Obviously the manifold is extremely hot and the unburned mixture explodes creating a huge force, driving the gas through the turbo and hence keeping it at a usable revolution speed. Once the driver pushes the throttle down again the computer changes the ignition and fuel settings back to normal and the boost is available for maximum power.



The turbo generally works a lot harder in cars using anti-lag and the temperatures are a lot higher as the turbo is spinning constantly at high rpm. This requires additional maintenance on the turbo making it uneconomical for anything other than competitive events. Most WRC teams use anti-lag systems of this sort which are driver adjustable. The explosive force of the detonation in the exhaust manifold near the turbo is enough to damage the already abused components in a rally car. So when the drivers are moving between special stages they turn it off or to a minimum. This sort of system in a road car would destroy the turbo and exhaust manifold in a matter of minutes.

15th November 2002 - 11:48 AM  Reply  Quote

Anit lag is BAD, very very bad.

15th November 2002 - 11:52 AM  Reply  Quote

Basically...yep.

15th November 2002 - 11:59 AM  Reply  Quote

wicked thanks, i never knew how it works. i was only thinking about drag cars n shit. i mean to get a motec ecu or sumfn is gunna set u back a good 5k or so, so its not as if its really a viable solution for your average driver

15th November 2002 - 01:39 PM  Reply  Quote

lag isnt that bad. infact i may go out on a limb here and say it is your friend.



Because once lag is over something good is gonna happen. (either that or something will blow up)

18th November 2002 - 03:36 PM  Reply  Quote

looks like ive started.. sumthing interesting..

2nd December 2002 - 06:19 PM  Reply  Quote

Lag is cool, I wouldnt say good but its like fun just getting smashed back in your seat. But the anti-lag system is not cool for your turbo, or at least the few I have read about, they baiscally send a flame through the turbo to keep it spinning.

2nd December 2002 - 06:30 PM  Reply  Quote