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C900 Performance, Mods & Tuning Covers Tuning & Performance modifications for the Classic 900 (C900)

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  #1  
Old 14th December 2003
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Default Boost issues...

Bit of a strange one this...

Fitted a boost gauge yesterday and replaced most of the vacuum hoses with silicon ones. I had to plug my new boost gauge into the system somewhere so i temporarily used the hole for the original boost gauge, where it goes into the inlet manifold, just until i could get a tee piece. Boost has been improved, showing base boost of around 4psi. Maximum boost was 14psi knocking back to 9-10psi after 4krpm. Car felt much quicker than recently until today. I got hold of a tee piece and plugged the original gauge back in so i now have 2 gauges. However, maximum boost is now only 10psi all the time. Vacuum hose leading to original gauge split :-?? Admitedly i haven`t been outside to make sure none have fell off. Any ideas other than that?

What should my base boost be? 4psi seems a little low. The saab board at my ex workplace showed 0.43 bar for base boost on a B202 with performance kit. Not sure how many psi that is? And what should max boost be? If the base boost is not right i am getting a price for a new actuator on monday cos mine is too corroded to adjust.
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  #2  
Old 14th December 2003
tandino tandino is offline
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base boost should be 5.5 - 6 psi,
Aim for the high end of tolerance if poss..

Pete.
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  #3  
Old 14th December 2003
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Cheers for the quick response Pete. Do you think 14psi is too high though for max boost? This is with my apc plugged back in, not the MBC

I can appreciate this will vary from car to car. I mean you have 17psi ( i think) but thats with a lot of mods.
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  #4  
Old 14th December 2003
Johann F Johann F is offline
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Did you disconnect the hose altogether that goes into the bulkhead? - this is needed by the APC to measure boost and if you unplug it you will get strange boost behavior as teh APC is not seeing boost. Actuators are pretty expensive new - have you tried removing it from the turbo and working it free in a vice? As Pete says base boost should be the upper limit - if your base boost is low it will have a direct effect on the maximum boost your APC will allow. As for maximum boost you can run - what mods do you have so far?
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Old 14th December 2003
tandino tandino is offline
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14 psi tapering to 10psi or so sounds about right - cold weather right now will help - an uprated actuator will help with spool up/reducing wastegate creep and top end boost by preventing the wastegate from being forced open at high rpms,
Im only running 17-18 psi for a combination of reasons - my Td04 flows alot more air and hence you dont need as much boost to develop power and i want the car to be drivable.
Higher boost is only a tweak of the apc for me but then reliablity (gearbox) and the fact that my big end bearings are starting to complain doesnt help :!

Pete.
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  #6  
Old 14th December 2003
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Quote:
Originally Posted by Johann F
Did you disconnect the hose altogether that goes into the bulkhead? - this is needed by the APC to measure boost and if you unplug it you will get strange boost behavior as teh APC is not seeing boost.
I disconnected the hose going into the inlet manifold for the original gauge, and put my new one in place of that. Straight swop temporarily. Are you saying the original dash gauge must be working in order for the apc to work properly?

My actuator has been off in a vice but would have sheared off its that bad. Did get my hands on a 9000 one but they are different types.
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  #7  
Old 14th December 2003
Johann F Johann F is offline
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Yes - the hose that actuates the dash gauge also supplies the pressure transducer and overpressure switch.
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  #8  
Old 14th December 2003
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I see. Best leave that plugged in then. Shame, it was going quite nicely too... Thanks for that Johann, you learn something new every day. Looks like i will get an actuator and start from scratch then. If only i new what i was doing with the red box
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Old 14th December 2003
Taylor Taylor is offline
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No no no ( :

Just by a vacuum tee that has three fittings on it. Run the hose to your new gauge, then one to the stock one. It's a 20 cent and 2 minute fix.

good luck,
Taylor
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Old 14th December 2003
Johann F Johann F is offline
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Taylor is right - you can run both guages with a T piece - Halfords do em in the windscreen washer accesory dept. Have you got a red box or are you trying to mod a black box? If you are going to buy a new actuator it would be good idea to get an adjustable one - that is one where you can set the spring tension. Fixed actuators are not really adjustable as you are just adjusting the preload rather than the spring force. If you are planning on running more boost -a higher rated actuator will be very useful.
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  #11  
Old 14th December 2003
Phate Phate is offline
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Default 87 Turbo with major underboosting

I have an 87 Turbo that hasn't been boosting right for a while, even with this cold weather it wont boost right. The current unit is the stock Garrett M14 turbo, and has recently been replaced with another M14. Haven't tuned it yet but even with the previous one it wouldnt boost quite right the whole time, and that one had been tuned. Was curious if it could be my APC messing things up, or a bad intercooler or something of that sort.
Been looking into an 85 SPG and since we're discussing boost I'm looking for ways to increase HP and boost pressure without installing a new turbo.
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  #12  
Old 15th December 2003
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Quote:
Originally Posted by Taylor
No no no ( :

Just by a vacuum tee that has three fittings on it. Run the hose to your new gauge, then one to the stock one. It's a 20 cent and 2 minute fix.

good luck,
Taylor
Thats what i have done, i had only disconnected the stock gauge temporarily to get the new one up and running. I have 2 gauges running now with a tee piece i bought from halfords yesterday afternoon strangely enough

I have a red box which i will be trying to adjust sometime in the near future. Is this actuator recommended?--> http://www.forgemotorsport.co.uk/pro...roduct=FMAC900 Or is there anything else you would recommend?
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  #13  
Old 15th December 2003
tandino tandino is offline
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The forge actuator is a nice piece of kit however mounting is a pain in the backside,
You have to cut the old actuator off its mounting plate and this proves rather tedious as its all one piece - after the actuator is removed and the remains of the mounting plate is tidied up from sharp edges you will have to drill two holes for the new actuator bolts - only problem is the hole left by removing the old actuator from the plate coincides where one of the holes wants to go - you will have to make up a plate to clamp the new actuator to the mounting plate.
Ask DaveB as i fitted his at Kodak - what should have been a 10 minute job turned into an hour one involving driving round trying to find a something to clamp it all together

Pete.
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  #14  
Old 16th December 2003
Johann F Johann F is offline
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My mod on the red box was to max out F to get the maximum boost setting of about 1/2 in the red and then play with the P to get the right rate of boost rise - the P setting is the important one as too much and you get boost overshoot and high torque loading ( bad for gearbox) and too little and the boost does not rise quickly enough to keep up with the revs( limits the total boost to less than set by F). Get the actuator sorted first though and make sure you have enough fueling - stock lucas will handle about 1bar of boost without mods but Bosch LH may need some help from a higher rated pressure regulator.
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  #15  
Old 16th December 2003
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Thanks for the advice guys. Mine has a 3bar fpr, that should be fine i hope. Which actuator are you guys running, seems the forge one is a pain to fit. Any recommendations or are they all the same to fit?

With regards to red box mods, i have heard you can check ohms with a multimeter. Do i go on the back of the pots themselves or is it on a couple of pins? Electrics never really were my thing Also, engine running or ignition on?
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  #16  
Old 16th December 2003
Johann F Johann F is offline
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There is no need if it's already a proper red box to measure anything- turn the F as far as it will go clockwise. Drill a couple of holes in the case above the F and P and you can adjust them on the car ( obviously requires a bit of dismantling in the first place to work out where to drill) Remember to seal the holes as well once you have set it.
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  #17  
Old 17th December 2003
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I used to remove the top of the APC case, when adjusting the pots. Needs a very short screwdriver though to go between the inner wing panel and the APC.
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  #18  
Old 17th December 2003
Johann F Johann F is offline
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For the ultimate control - remove the P and F pots and run wires from the pin mounts through to the dash and fit adjustable pots with rotary knobs that you can set as you drive!
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  #19  
Old 17th December 2003
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Isn't that the setup Keith uses?
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  #20  
Old 17th December 2003
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It is. His F pot is a 1kohm unit which allows the sustained boost to be raised
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