Justin Posted May 26, 2002 Share Posted May 26, 2002 I have just fitted my digital guage. I'm not very impressed with my high score:mad: (13.5 psi). I thought that with my straight Nur spec, HKS de-cat etc I would be at least around 17 psi. Question 1. Does this sound right? My guage indicates that the pressure is around minus (-7.0) at idle and only goes above 0.0 when I accelerate to over 2500 rpm. The display can go down to -11.0 during driving. It gets to 13.5 when I'm red lining it. Question 2. Should the psi start at zero when idling (ie my guage is not reading right) or are the above readings correctish? Please educate me. Quote Link to comment Share on other sites More sharing options...
Adam W Posted May 26, 2002 Share Posted May 26, 2002 It's normal to show a vacuum when idling - the turbo is not spinning as there is not much exhaust flow, so the engine is relying on the suction of the pistons to vacuum the air into the cylinders. Your boost pressure does sound a little low if you have lost both cats. Also, you should hit max boost at about 5k rpm after the 2nd turbo has come online, and then possibly a slight creep upwards as you head towards the redline Quote Link to comment Share on other sites More sharing options...
Barry Posted May 26, 2002 Share Posted May 26, 2002 Justin - Your boost guage is plumbed into to read the boost at the manifold, or what the engine is actually getting as apposed to what the turbo's are producing. When you start your engine it will show a negative pressure, then, when you drive off the guage will still read negative untill the turbo does come on-line and start to force air into the engine instead of suck it in. Nothing wrong with it. Have you had boths cats removed or just the one.? If its just one then thats probably why its only reaching about .9 bar. Quote Link to comment Share on other sites More sharing options...
Barry Posted May 26, 2002 Share Posted May 26, 2002 Adam - The turbo is always spinning, even on tickover, just not enough to produce any real pressure. Remember these turbo spin at upto and over 150,000 rpm. Quote Link to comment Share on other sites More sharing options...
Adam W Posted May 26, 2002 Share Posted May 26, 2002 I know, I know, I just didn't want to confuse the issue! My new turbo arrived last week, it was balanced at 180,000 rpm apparently! Mmmmm . . . boost Quote Link to comment Share on other sites More sharing options...
Keith C Posted May 26, 2002 Share Posted May 26, 2002 Eh? That can't be right - mine has the lardier steel internals and I get positive boost from as little as 1000rpm, and that's near-identical mods to yourself. Have you checked for a boost leak? Stu - where's my boost guage plumbed into? Is it at the turbos or the manifold? Quote Link to comment Share on other sites More sharing options...
Terminator Posted May 26, 2002 Share Posted May 26, 2002 13.5 psi is 0.93 bar stock limit is about 0.8, so that does sound a little low. If you can get some connectors I have enough hose to connect up to my gauge hose and compare idle and static boost at various revs. Doing it on the move may be a bit tricky. Quote Link to comment Share on other sites More sharing options...
Justin Posted May 26, 2002 Author Share Posted May 26, 2002 Phil, sorry to call upon you again but I feel I might have to take you up on that. The situation is rather distressing for me after all the flippin money I spent on exhausts and de-cat pipes etc. MUST HAVE MORE BOOST! I am hoping that the t-piece is not tight enough or something. Would that cause low readings? Let me know if/when I can pop round if only for you to cast your experienced eye over what I have done. I don't want to have to buy a boost controller just yet! Quote Link to comment Share on other sites More sharing options...
Rich J Posted May 26, 2002 Share Posted May 26, 2002 When I had both my cats removed with the standard exhaust still in place I got just over stock boost on my j-spec. Quote Link to comment Share on other sites More sharing options...
THOR Racing Posted May 27, 2002 Share Posted May 27, 2002 When I had both CATs removed I didn't get any extra boost only a descrease in the turbo lag. It spooled up far quicker. It was only when I went for a complete new exhaust system that things made a big jump. I believe it was a collapsed or damaged rear end of my exhaust. If you have a complete straight through system then it may still only be indicating that your car can maintain stock boost control, which in a way is good. The boost only normally rises due to a failure of the car to maintain stock boost levels due to boost creep, wastegate problems etc etc. Getting boost up is a piece of p*ss! controlling it is another matter. If all you want is cheap boost increase do the following..... Buy a "T" piece and insert in to the pipe from the top of the wastegate actuator to the turbo bleed nipple. Simply cut the pipe and insert the "T" piece. Now to control boost you need to control how much of the boost is bled away to atmosphere from the "T" and how much is allowed to flow as normal. For this you will need a small valve, opening the valve 100% will give MASSIVE boost and will probabaly kill the turbos. SO!!!! Start with the valve CLOSED. Now start to gradually open the valve and keep trial running the car. You'll notice the boost should be increasing a little at a time. Don't go mad, just a 1/4 turn at a time will do. You don't need much air bled off to increase boost. You can get a combined "T" piece and valve and I think Chris Wilson or others will be able to source you this for about £30-£40. (Guess!) SUMMARY. There's probably nothing wrong with you car. Make sure all pipes are on and air tight, as even small leaks can cause boost drop. Check that you get an increase in boost between single and twin transition. If all the above are fine then fitting a cheap bleeder valve will get you as much boost as you can handle. BUT!!!!!!! BE WARNED. The bleeder route is potentially dangerous as you have no way of controlling boost dependant on ambient conditions. So if it's raining be careful (too much BHP) and if it's really hot be careful (to high EGT temps) etc etc Regards Pete Quote Link to comment Share on other sites More sharing options...
Barry Posted May 27, 2002 Share Posted May 27, 2002 When I got my car off JB, its could quite easily hit 1.5 bar (@ manifold) and that was on stock j-spec turbo's. Probably why my turbo decided to spit its dummy! I've now had a restrictor plate put in the exhaust to limit it to .9 bar untill I sort out the fueling. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted May 27, 2002 Share Posted May 27, 2002 In standard form with both cats in place but with a free-flow exhaust I was getting around .85-.90. I can have boost coming in just over 1200rpm if I floor it or 0.00 if cruising at 3000rpm. I hardly got any boost whilst parked... It seems to only go up properly when the engines under load. Get a boost controller. that way you can dial in how much boost you want from inside the car at any time. Mine, (Blitz DSBC), has a warning function that you can set to whatever you want and when you hit that point, it automatically reduces boost to save your engine/turbos. Quote Link to comment Share on other sites More sharing options...
badtoy Posted May 27, 2002 Share Posted May 27, 2002 did you install a greddy bcc and adjust it right? if yes, try a bleeder-t like descripted in the mkiv.com/tech articles good luck markus Quote Link to comment Share on other sites More sharing options...
Doughie Posted May 27, 2002 Share Posted May 27, 2002 Originally posted by Keith C Eh? That can't be right - mine has the lardier steel internals and I get positive boost from as little as 1000rpm, and that's near-identical mods to yourself. Have you checked for a boost leak? Stu - where's my boost guage plumbed into? Is it at the turbos or the manifold? Not 100% sure but think it's the manifold. Leon fitted that guage so he will know for sure. Quote Link to comment Share on other sites More sharing options...
Justin Posted May 27, 2002 Author Share Posted May 27, 2002 Thanks a lot Pete and everybody else too. I'll check for leaks but it's looking like I 'll need a flippin boost controller next Could I do the following with a boost controller fitted: a) Keep it at 14 psi when raining b) Put it up to say 18 when I need/want to hammer it. Is 18psi a safe limit with stock cooling system? Cheers: Quote Link to comment Share on other sites More sharing options...
Alex Posted May 27, 2002 Share Posted May 27, 2002 Most boost controllers hold multiple presets...so preset one runs at 14psi, 2 at 16psi and 3 at 18psi... The Blitz DSBC has 4 "channels" The Blitz SBC-id has 4 but it can be mapped to the speed your travelling at through the powermeter-id. So it ups the boost on the fly taking advantage of the extra cooling you get when traveling at high speed. It also means you don't have to take your hands off the wheel. For quick boost most boost controllers have a scramble mode. This is thumb operated on the Greddy Profec B Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted May 27, 2002 Share Posted May 27, 2002 That's pretty much what I do. I run with the boost controller off untill I need it. If you turn it on to 18psi in mid WOT it feels like a 3rd turbo coming in:D Quote Link to comment Share on other sites More sharing options...
Keith C Posted May 27, 2002 Share Posted May 27, 2002 Ooh - triple sequential turbos - now there's an idea! :D /runs off to get a spare turbo and some sticky-tape Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted May 27, 2002 Share Posted May 27, 2002 Originally posted by Keith C /runs off to get a spare turbo and some sticky-tape Left over from his last Supra!!!! Sorry Keith, just couldn't resist. Quote Link to comment Share on other sites More sharing options...
eyefi Posted May 27, 2002 Share Posted May 27, 2002 the triple turbo supra has been done in the states. i cant remember where ive seen it, but ill try and dig it out. Quote Link to comment Share on other sites More sharing options...
THOR Racing Posted May 28, 2002 Share Posted May 28, 2002 Could I do the following with a boost controller fitted: a) Keep it at 14 psi when raining b) Put it up to say 18 when I need/want to hammer it. Is 18psi a safe limit with stock cooling system? a) This will be what ever the MINIMUM is now! So If after changing the mechanicals like exhaust and intake etc you get a maximum boost of 17psi then this is your new minimum without boost control. You cannot control below the minimum mechanical boost levels of the car. Well you can try and a lot of effort can get you to something reasonable. In summary your LOW boost controller setting cannot go any lower than what you would get if you had it turned off. b) Yes this could be your hammer mode and yes 18psi would be about your limit without any further cooling mods. You could have OFF = 14psi (or whatever your minimum is) ON setting A=16psi and setting B=18psi if the boost controller has two settings. Again the power of a simple bleeder valve should not be forgotten, it's just a fiddle getting under the bonnet each time you want to adjust something. I only run 18psi knowing I have my water injection system as well. Be careful on very hot summer days. You'll soon tell as the power will drop off dramatically. Don't be tempted to just up the boost without first thinking of the consequences of doing so. Regards Pete Quote Link to comment Share on other sites More sharing options...
Justin Posted May 28, 2002 Author Share Posted May 28, 2002 Perfect info Pete thanks a million. Do you think my stock air box is preventing me from getting an extra psi or 2? I was thinking of the Blitz SUS induction kit with dust sheild plate. Would this be a good idea better than the standard system or not worth bothering with? All the best Quote Link to comment Share on other sites More sharing options...
Adam W Posted May 28, 2002 Share Posted May 28, 2002 I have the Blitz SUS (with a homemade cold air intake) and it looks and sounds lovely. Filtration is only average though - the best cone filter out there is currently the Apexi one, available from Paul Whiffin, this seem to have the best flow AND the best filtration. It doesn't look as good though . . . . Quote Link to comment Share on other sites More sharing options...
THOR Racing Posted May 28, 2002 Share Posted May 28, 2002 The stock air filter is more than enough to get you to 18psi. That's all I use and I have no problem boosting my turbos to bits. I'd look else where. (Mind you check the air filter isn't clogged up, I change my every two engine oil changes roughly) Pete Quote Link to comment Share on other sites More sharing options...
Adam Kindness Posted June 23, 2002 Share Posted June 23, 2002 Im toying with the idea of fitting a bleed valve! I've searched the tech forum and found a few articles on the subject... BUT could someone just explain the process again I know the more air you 'bleed' off increases the boost, i also know its not the easiest way to control boost! Where do i put the T - piece? any pics? Quote Link to comment Share on other sites More sharing options...
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