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Stock Twins King
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Discussion Starter #1
I have read 3 years of post on the famous "spring mod", but no one seems to prove how it works and why it works. I have been in discussions with friends on this subject. I know the main reason why it is done is because people can't get decent boost, or can't hold boost, Mostly due to maybe higher mileage cars.

So if you think about it, if it is because of weak turbos, then you would think that they are not flowing as much. If this is the case, then why would you put resistance on the wastegate so it is harder to open. Can't be because of higher flowing turbos, or too much pressure on the internal wastegate flapper??

My thought is that it has nothing to do with the turbos or the exhaust pressure on the flapper, maybe it is because the wastegate actuator itself has weakened and can't hold the flapper closed, hence loss of boost. Or........there is a small leak in a hose and at a certain pressure it leaks causing the same symtom.

I ask because I am trying to see how high of boost I can achieve. What are the drawbacks as to why a stock twin car can't get above 25psi if you were so inclined to do so. Another example would be to actually weld the flapper closed and see how high of boost you could hit.

(PS) this isnt so I can blow my turbos, but to test a set of hybrid turbos that are currently on my car that are rated at 28psi. More details later on these.
 

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well... i did the spring mod in order to hold higher boost, and not fall off at higher rpms... i was able to achieve roughly 27psi peak off to about 23psi... these turbos begin to blow hot/inneficient air at that high level so hp per PSI is drastically reduced, but still an increase in power is there

it works by using the spring to hold the wastegate shut because our wastegate is soo small and crappy that it tends to get "blown open" even if you have your boost controller set all the way to 100%

why weld it shut? just disconnect the little arm
 

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were can i get info on doing the spring mod. i can's find it here or on mkiv.com. BTW, how is the upgraded twins project going?
 

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supralover93 said:
were can i get info on doing the spring mod. i can's find it here or on mkiv.com. BTW, how is the upgraded twins project going?
search for "secret sauce mod"... its basically putting a holley carb spring between the wastegate and a hole in the alternator
 

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thanks for the help. is there anywhere i can see how exactly to do the spring mod? like what actuator it goes on. how it goes on....
 

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It was my understanding that the spring mod puts resistance on the wastegate actuator arm to keep it CLOSED longer to help hold boost.

When I did the mod, it definetly worked. Infact I think it also helped make controlling the boost more consistant.
 

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supralover93 said:
thanks for the help. is there anywhere i can see how exactly to do the spring mod? like what actuator it goes on. how it goes on....
i wish there were pics of it, but the wastegate is tucked under the turbos so its not like ud see it in a photo anyway

i will try to explain this as best i can...
-go purchase a semi-stiff carb spring from napa
-position yourself in front of the car, where the alternator is
-remove intake
-look on the top of the alternator and you will see an empty hole
-place one side of spring into empty hole
-now pull the spring back towards the firewall, you will see a large canister (that is the wastegate)
-there is a rod going to a arm (lever whatever you want to call it) that you want to connect the other side of the spring to

when finished the spring will be streteched about 7 inches, from the back of the wastegate lever to the front where the alternator hole is

stiffer spring = higher baseline boost
weaker spring = same baseline boost, but doesnt fall of on the top end

sorry to thread hijak, but i didnt want to start a new thread about this
 

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Stock Twins King
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Discussion Starter #9
I have 4 sets of turbos on a bench at home. I have one set that is totally assembled with VSV's and actuators that I use as a "mock" for viewing/anylising. I can take pictures of this and post where to install stuff. I have some on my webpage, but not this specifically since I have never had boost problems. I did a "test" install last night and it took me like 1 minute.

I have made an adustable one with a wing nut. I used the existing water pump hole to bolt a plate. Then I have the spring mounted on the plate with a threaded rod extending out with a wing nut to turn and loosen or tighten.

I find it odd that an OEM wastegate is spec'd at 17.5 psi before it even starts to open. I think that when the car is running in boost, the exhaust pressures "aid" in allowing the wastegate flapper to open at a lessor resistance. I have so many air flowing mods that I am seeing a boost limit problem. I can hold boost probably past 7000 with still room to go, so it isnt "holding" that I am having a problem with.

It would be intersting if there was away to have the flapper totally closed to see the limits. I will first try with a very "taught" spring so the flapper has high resistance to even open and see what happens.

I just installed a set of hybrid turbos with T3-60 trim cartridges. I will definately post all my results after the dyno session. As it stands now, it feels stronger, still having a very good transition, and hold HP with 0 drop-off at redline. They run considerably more efficient than OEM. Not moving "hot air" now. They appear to be running about 15-20,000rpms less in the compressor sweet spot.
 

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Supra Owner Since 1996
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Yes Stu you are going to you the Fatty. The smaller springs have little to no effect at all. You have to stretch that sucker 4-6" IIRC. It will slip out of your pliers about 3 times and you might scuff a knuckle, but it's the fatty at 8" unstretched.
 

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As the RPMS rise and load increases, the flapper begins to be pulled open by the action of the ever increasing velocity of exhaust gases. This leak typically leads to the ability to only hold about 16-18psi at redline on most stock twins, regardless of what peak boost is set at. This "leak" occurs even if the wastegate hose is pulled. The addition of the spring to the wastegate lever provides resistance in the opposite direction, thereby keeping the flapper closed longer and preventing "leaking" of boost. This allows for the ability to both generate greater peak boost and hold more boost to redline. I have been able to hold 20psi to redline with a slightly taught srping. With a stiffer one, I'm certain I could generate and hold about 2psi more. I don't have any times with the higher spring setting, yet, but I can tell you it certainly feels stronger. If you were to go one step further and wire the lever so as to prevent the flapper from opening, I would guess you could easily build at least 25psi on a good set of stock twins. Though I would advise against doing this.

Also, I wouldn't recommend the spring mod to those who are looking to rejuvenate weak turbos. Because the spring mod will likely just mask the real underlying problem and lead to the quicker demise of your turbos.
 

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A zone of danger.
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Stu,
I've heard several times that the stock exhaust manifold is very restrictive. Have you done anything with the stock exhaust manifold, or strictly the turbo internals? I'm only curious as to when you believe the hotside will run out of flow.
Well done, by the way. I'll be watching for the results. Oh, and seeing as to how you're the BPU guru, YGPM. :)
 

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Stock Twins King
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Discussion Starter #14
Unfortunately and or fortunately, I have ported my exhaust manifold, all 4 turbo pipes, and all of the internal "flappers" inside the exhaust housings. I also have an enlarged Bypass tube that was ported on the In and Out side where it connects. I also have a stage 1 head.
So basically, if I slapped a single turbo on, I could safely run some high numbers. But.............as the twins nutcase that I am, its all about the twins.

A stock 2JZ flows about 57 CFM at 6800 @20psi. Im my case, I am probalby at 68 CFM. With all of my supporting mods, I am at least 20% greater in flow. Hence the reason why I am considering this spring so I can use this extra flow and power that I can safely run. I would have to actually go to 28+psi in my configuration to = 20PSI in the stock configuration. So I am assuming my OEM wastegate actuator is not able to handle this, so I think it needs an assist.~!
 

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uhhh sorry if this is a dumb question but if you do this mod you can still control your boost with your boost controller right....
 

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Yes you can control boost. It basically adds more tension to the entire system, so its similar to increasing the spring rate inside the actuator. PLus, it allows to keep boost from falling off as much on the stock turbos.
 

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You can control boost but your entire range of boost settings is shifted upwards. In other words, let's say you can normally control your boost between 15-20psi with a boost controller. Afterwards with a spring attached, you'll be able to control it only in a range of say 18-23psi. By forcing the flapper closed longer it basically shifts the boost range upwards. So be careful, you can very easily pull timing and induce knock at these higher levels. Honestly, I wouldn't recommend this mod to most, unless you are religiously monitoring boost and A/F carefully and know what the F you are doing.
 

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Stock Twins King
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Discussion Starter #19
earl3 said:
Lbs/min ?
Sorry, my bad, I meant Lbs/min------ I also checked the # and it is actually 48 lbs/min @20psi-6800 on a stock engine. Mine is probably 58.




PS I do agree with crossways, running much above 20psi on a regular basis will surely kill the twins.
 

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Boost4fun
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I have also tried one thing out and it works also flawless: The wastegateactuator underneath the no.1 turbo is screwed to the turbo with two 12mm screws. I placed a thick shim at the right screw under the bracket (towards the actuator) what will "adjust" also the spring force on the wastegate and assist it to prevent a too soon opening of it due to the increased prestressing on the gate. It is an easy 20minutes job and with my AVC-R and the "usual" settings (73% duty cycle etc.) I see a steady 1,2 bar (around 18psi) up to 7k rpm. :)
I think this is a cleaner thing than using an external carb spring there;)

Gerd
 
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