AJI Posted June 16, 2003 Share Posted June 16, 2003 On the standard UK-spec T-T it has a recirculating dump valve....... I went to the Newcastle meet up on Sunday and got an idea that Michel was using. Simply chopping the pipe that recirculates the air from the dump valve so that it will vent to atmosphere. I was told that it wouldn't affect the turbo spool up time, but on a previous post I did about dump valves I was told that if the air charge wasn't recirculated then it couldn't be used by the system to pre-spool the turbo's for when they are next used. If I was to do the above would I notice a fall off in turbo response time? I should have asked more questions on Sunday but I'm not the most technically minded on certain areas of the engine. Cheers, A.J.I. Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 16, 2003 Share Posted June 16, 2003 intake air does not prespool the turbo. Quote Link to comment Share on other sites More sharing options...
Ian C Posted June 16, 2003 Share Posted June 16, 2003 First question - why would you want to vent to atmosphere? If you did want to vent to atmo for some valid reason, you would have to block off the other end of the pipe as well so that it didn't leak. The BOV stops the turbos from stalling when you lift off the throttle and thus keeps them spinning when you change gear. The recirculation of the air is to a) keep it quiet and b) not upset UK spec MAF-based systems. Quote Link to comment Share on other sites More sharing options...
400BHP Posted June 16, 2003 Share Posted June 16, 2003 I have done what you are saying before and I wouldn't reccomend it, the stock valve does not have a hight spring tension because it is a closed system. You will find when decellerating hard the car may stall, the high vacuum will open the valve and create a stall. Also you may find that when the throttle is slightly open, the vacuum will bleed off the boost. Quote Link to comment Share on other sites More sharing options...
Nathan Posted June 16, 2003 Share Posted June 16, 2003 Originally posted by 400BHP I have done what you are saying before and I wouldn't reccomend it, the stock valve does not have a hight spring tension because it is a closed system. Agreed. Venting the stock valve to atmo on a UK spec will make it run like a bag of poo. If you do want to vent to air fit a decent valve that won't open on idle or cruise, like an HKS SQV. Regards, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
AJI Posted June 16, 2003 Author Share Posted June 16, 2003 So what you are saying is that I would loose some performance in turbo spooling and also that the MAF system would get screwed. The sound increase part is the reason for why I was thinking of doing it. I think I'll stick with stock setup, I probably wouldn't have been able to hear vent to atmosphere anyways because I have a Hyper exhaust on. Quote Link to comment Share on other sites More sharing options...
400BHP Posted June 16, 2003 Share Posted June 16, 2003 you will soon get bored with the hiss, I did. it was novel to start with but soon got fed up with it. And the quicker you change gear the less hiss you get anyway! "if it aint broke, dont fix it" Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted June 16, 2003 Share Posted June 16, 2003 Originally posted by eyefi intake air does not prespool the turbo. Did you see this post AJI ? Quote Link to comment Share on other sites More sharing options...
AJI Posted June 16, 2003 Author Share Posted June 16, 2003 Yeah I saw it, is the air that is recirculated considered as intake air? And therefore this air does not go back into the system to spool turbos? As I say I'm not 100% sure how the full system works, so if I'm asking dumb questions then this is why. Going from the replies I'm just going to stick with stock setup. Thanks for your experteese. Quote Link to comment Share on other sites More sharing options...
Steve Cargill Posted June 16, 2003 Share Posted June 16, 2003 As I understand it when at WOT you have a big fast column of air being sucked into the intake turbine, being compressed and forced down the intercooler, through the throttle body and into the engine. When you back off the throttle butterfly closes and you've got this column of air that suddenly has nowhere to go. As a result the air will suddenly stop, the turbo can't compress the air and stalls. When you put the power back on the whole boost process, including spinning up the turbine has to start over again. The BOV releases the air pressure in the intake system preventing the turbo stall and leaving the turbine spinning thus allowing the boost to come back on much quicker. On rally cars (mainly, others may use it) they go one stage further and in effect squirt fuel into the exhaust manifold to keep the turbos well and truly spinning. This makes for all those pops and flames when going into a corner, but does destroy exhausts at some rate I guess. Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted June 16, 2003 Share Posted June 16, 2003 That's one of the best descriptions i have seen in a long time. The anti lag stuff is none too good for the longevity of the turbos either, especially if they were of the ceramic variety Quote Link to comment Share on other sites More sharing options...
dandan Posted June 16, 2003 Share Posted June 16, 2003 hi guys, i was just reading over the thread and thought I'd add a few lines if ya don't mind. I think one of the reasons for a BOV that vents to atmosphere is to help achieve a cooler intake charge. Air blown out of the turbo is obviously hotter than ambient, as compressing air always causes a temperature rise. (better the turbo efficiency-lower the temperature rise) If during a gear change (or similar) the BOV bypasses this air back to before the turbo then effectively the charge temperature is increased. An antilag system usually uses a large solenoid valve (or similar) to bypass air around the closed throttle. Fuel is then injected into the cylinder via the injectors. The ignition timing is then drastically retarded, igniting the charge as it's passing out of the combustion chamber. The resultant heat produced maintains the turbine speed, ready for when the throttle is depressed. I'm not trying to tell anyone to suck eggs here, I just thought I'd add my own view. Quote Link to comment Share on other sites More sharing options...
400BHP Posted June 16, 2003 Share Posted June 16, 2003 I dont know about that, from what I learned in college and what I have learned by reading manuals etc, when the throttle is released, the injectors go into what is termed as "over run" which means they close off and do not open until idle speed is once again reached. The engine had no way of knowing wether you are decellerating to stop or merely taking time to change gear, thereby it cannot retard the timing, if it did do this then when you re-accellerated if you caught it at the right time the spark would catch itself, ie.try and fire twice at the same time. Also, firing when the exhaust valve is open, which is what would happen if the timing was massively retarded would cause backfiring, and more than likely destroy the valve and the turbo, as combustion is not designed to take place there. Am i right? Quote Link to comment Share on other sites More sharing options...
dandan Posted June 16, 2003 Share Posted June 16, 2003 what i descibed is what happens when the antilag is engaged. I'm in the process of building a 599cc Yamaha engine, turbocharged, antilag, dta engine management, aquamist 2s water inj, dry sump lubed etc. This is exactly how the antilag in the dta system works not good for exhaust valves, turbines or exhaust manifolds hence mega expensive inconel s.steel exh manifolds on wrc cars Quote Link to comment Share on other sites More sharing options...
dandan Posted June 16, 2003 Share Posted June 16, 2003 on a normal car the injectors would normally cut till around a few hundred rpm above idle speed, then fire again. This is definately not the case when the anti lag is switched on. This is an advanced feature, only really available in good aftermarket ecu's... Quote Link to comment Share on other sites More sharing options...
400BHP Posted June 16, 2003 Share Posted June 16, 2003 I see, I didn't think it was an OE feature... Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted June 16, 2003 Share Posted June 16, 2003 Nope anti-lag is only available on aftermarket ECU's. Toyota were a bit worried about warranty costs to include it as standard.. I'd never thought about the cooler charge air aspect of a vent to atmosphere BOV before. It's a good point, but i wonder scientifically what the difference in charge air temps would be between a recirculating one and a vent to atmosphere one. Quote Link to comment Share on other sites More sharing options...
Steve Cargill Posted June 16, 2003 Share Posted June 16, 2003 Originally posted by Martin F I'd never thought about the cooler charge air aspect of a vent to atmosphere BOV before. It's a good point, but i wonder scientifically what the difference in charge air temps would be between a recirculating one and a vent to atmosphere one. Mmmm, intersting one that. I guess it's hot as the BOV has triggered due to the high pressure, so to atmosphere is probably a good thing. Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 16, 2003 Share Posted June 16, 2003 a little extra fuel can b injected in low pressure situations (very low or closed throttle) to help cool the cyls, this will also produce the exhaust bangs, pops and flames. i think the main reason the stock mkiv recirculates is for refinement (obviously on uk's cos of the MAF). it wasnt designed as a £40k ricer i think the charge temp is a reasonable issue when venting to atmosphere but its all down to how good yr charge cooling is in the first place. dan, why r u building that engine? Quote Link to comment Share on other sites More sharing options...
dandan Posted June 16, 2003 Share Posted June 16, 2003 yeh i'm not sure of any specific temps, but the air has been compressed and heated and then literally dumped back in behind compressor to be heated again!! Obviously this is only a transient thing and not happening constantly so effect MAY be small. Perhaps someone should try to get a thermocouple in there and get some temps?!? Quote Link to comment Share on other sites More sharing options...
dandan Posted June 16, 2003 Share Posted June 16, 2003 is bov after intercooler....cant place it off the top off my head! Quote Link to comment Share on other sites More sharing options...
Alex Posted June 16, 2003 Share Posted June 16, 2003 Originally posted by Steve Cargill Mmmm, intersting one that. I guess it's hot as the BOV has triggered due to the high pressure, so to atmosphere is probably a good thing. Air that has just come out of the turbo will be very hot...which is why I think the vent to atmosphere BOV's mounted away from the intake are best. This way the hot air is expelled and not re-injested....thinking about it it would make sense in my mind to be post turbo, just before the IC...out of the engine bay as such. However - Vent to Atmos BOV's are only really any good - as hinted at earlier - on Jap spec MAP Supra's. Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted June 16, 2003 Share Posted June 16, 2003 Stock one is before intercooler. Aftermarket ones can be either, depends on how they are fitted. Quote Link to comment Share on other sites More sharing options...
Alex Posted June 16, 2003 Share Posted June 16, 2003 Originally posted by dandan is bov after intercooler....cant place it off the top off my head! Nigh on, on top of the first turbo as you look at all the pipework. Quote Link to comment Share on other sites More sharing options...
dandan Posted June 16, 2003 Share Posted June 16, 2003 thought so.....so the "dumped air" is pretty hot, it hasn't had the pleasure of a cool down thru the intercooler! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.