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    Thread: how much boost can stock motor handle?

    1. 12-06-2007 09:12 PM #1
      I have an 03 Tdi Jetta with 70k miles on it. i have the kermatdi powerplus 520 nozzles in it. i just ordered their q-loader chip, their "the hammer" turbo and a vr6 clutch kit. I know the turbo can handle 25+ pounds of sustained boost. but i was wondering how much the stock motor can handle without having to worry about blowing anything up. it is my daily driver . i told them to send me a tune that limited the boost to 20 psi. i plan on owning this car for a very long time and want the motor to last. is 20 pounds too much or will i be ok?


    2. 12-06-2007 09:20 PM #2
      IMHO, 20 is a lot for a stock motor... others would disagree. But you want longevity, so I would limit the boost to around 16 psi.

    3. Member QuantumSyncro's Avatar
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      12-06-2007 10:18 PM #3
      I would agree, even 20psi is a lot for this motor. It's just not designed to handle that type of boost. If you want this to last for a long time don't exceed the mfgr. spec boost by much.

      Now if it had a cast iron head and beefy bottom end that would be another story.

      My personal stance is that I don't like to do anything that would compromise the longevity of an engine. I don't mind doing maintenance or repair, but I don't like anything that encourages excessive repair since I'm the one that does it.

      my .02

      Gir - "won't the sploding hurt?" Zim - "Silence!"

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      12-06-2007 11:32 PM #4
      Quote, originally posted by TurboDieselTech »
      IMHO, 20 is a lot for a stock motor... others would disagree. But you want longevity, so I would limit the boost to around 16 psi.

      Stock is 14psi.

      These cars can handle 30psi with ease....

      I have over 270,000 miles 100,000 of those running 20psi on a stock vnt15....


    5. 12-07-2007 12:16 AM #5
      Quote, originally posted by MXTHOR3 »

      Stock is 14psi.

      These cars can handle 30psi with ease....

      I have over 270,000 miles 100,000 of those running 20psi on a stock vnt15....

      I agree they can handle 30 psi... but I think that would shorten the lifespan considerably. I would say your engine was built on a good day... I've seen a few stock engines running 20+ PSI come into our shop with blown head gaskets, bent rods, and crushed rod bearings. Not sure how long they were running with that kind of boost... or how well they were maintained for that matter. I would recommend beefing up the lower end a little first. They always seemed a little flimsy to me as compared to the IDI.


    6. 12-07-2007 12:23 PM #6
      I run 26 to 28 on mine. I wont not run more than 18 on a stock turbo. It will blow if you run to much. I would also recomend after market head studs if you plan to run over 20psi or you may have head gasket problems. I ran 24 psi with my old vnt 17 for over 100,000 miles. Engine had 283,000 on it when I installed a new one.

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      12-07-2007 01:18 PM #7
      Quote, originally posted by vw tdi guy »
      I run 26 to 28 on mine. I wont not run more than 18 on a stock turbo. It will blow if you run to much. I would also recomend after market head studs if you plan to run over 20psi or you may have head gasket problems. I ran 24 psi with my old vnt 17 for over 100,000 miles. Engine had 283,000 on it when I installed a new one.

      Headstuds for anything over 20psi? Overkill....

      There are many MANY people running in the 25psi range on stock bottom ends and stock headgaskets/studs. These engines are built like brick ****houses from the factory to withstand the insanely high cyclinder pressures. People have seen issues with the head lifting off the block at 30psi+ and coolant in the oil but not to many people run that kind of boost. The ALH comes stock with a forged crank and oil squiters... It's up to the task in stock form... (Obviously to a certain extent)

      I'd worry about adding a few more CCV's to the car before worrying about the headgasket.. All that pressure needs to go somewhere, and it's usually out the weakest link, the turbo seals...


    8. 12-07-2007 02:29 PM #8
      I have personally had head gasket problems with 24 psi. So they are not overkill. But every car is different. If you motor does not have high mileage you might be ok. I would definitely recommend them for over 20psi. Just my opinion from personal experience.

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      12-08-2007 01:01 AM #9
      Quote, originally posted by vw tdi guy »
      I have personally had head gasket problems with 24 psi. So they are not overkill. But every car is different. If you motor does not have high mileage you might be ok. I would definitely recommend them for over 20psi. Just my opinion from personal experience.

      There was definitely something wrong with your car if you had head gasket issues running 20psi... ARP doesn't even have a headstud listed specifically for the ALH.


    10. 12-08-2007 01:19 AM #10
      Speaking of overkill... if the engine is built that well, but the factory is only running 14 PSI, then the whole engine is overkill for it's intended use. The fact is, the engines are designed to run as they come from the factory. There is a built-in margin of stress that allows for longevity... over build the engine and it will last longer. The european way of thinking. Unlike GM and other American companies who build engines with very little stress margin... thus the reason we drive VW's right?

      My whole point wasn't to get into a heated discussion about what the engine can or can't handle. The original poster was looking for some added performance without sacrificing longevity. I gave my opinion, based on my experience and on his request for longevity. I've know certain high stress parts to fail at 20 PSI. Not that all will, but some will. Since there's no way of knowing which will fail and which will not, I gave a very conservative opinion. I'd hate to tell someone, yeah go for 20 PSI and have a rod fail a week later.


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      12-08-2007 09:40 AM #11
      I would have to agree with TurboDieselTech on this issue. No one overbuilds anything anymore, except maybe for HD trucks...and that's even a maybe, it isn't cost effective.
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      12-08-2007 10:10 AM #12
      I hope this isn't a heated discussion There are many cars running 20psi and over on stock bottom ends.. Now 20psi on a stock vnt15? Yeah, you are really reducing the life of that turbo, but it's a trade off. But for someone who is looking for a decent upgrade (nozzles, chip) they shouldn't be worried if the bottom end is going to hold together, there are hundreds of TDI's(maybe 1000's? ) that have zero issues.

      I think there are far more parts in that engine that will fail long before a connecting rod running mild upgrades.. But hey, I am sure you have pulled apart more engines then I ever will If someone is looking for some serious boost, I would definitely tell them to start off with a PD150 bottom end and build it from there. You gotta pay to play


    13. 12-09-2007 12:01 PM #13

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      12-09-2007 03:42 PM #14
      i've run 23-25psi plus water/meth for 50000 miles and no problems, just blown FMIC boots
      Quote Originally Posted by ..Derek.. View Post
      Clearly you aren't familiar with the "Golden Corrado". It's so clinically clean that in the event that you must urinate it must be done at least one zip code away in fear that it may catch a staph infection.

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      12-10-2007 10:51 AM #15
      Quote, originally posted by TurboDieselTech »
      Speaking of overkill... if the engine is built that well, but the factory is only running 14 PSI, then the whole engine is overkill for it's intended use. The fact is, the engines are designed to run as they come from the factory. There is a built-in margin of stress that allows for longevity... over build the engine and it will last longer. The european way of thinking. Unlike GM and other American companies who build engines with very little stress margin... thus the reason we drive VW's right?

      I would have to disagree with you. German manufacturers build their cars to run on the Autobahn. but have to detune them to run in America so the same basic engine is in several models depending on the amount of power you paid for. it is cheaper to make a lot of the same parts, than it is to build different parts for different engines, (another example is the Vortec V6 and the Vortec Chevy 350, they same engine internals, just the 4.3 L V6 uses two less cylinders.)
      VW makes the same engine for the older ALH that is in the 90 HP American version, 110 HP, 130HP European versions. there is no reason the software and injectors would not cause the same power in America.

      Quote, originally posted by TurboDieselTech »
      My whole point wasn't to get into a heated discussion about what the engine can or can't handle. The original poster was looking for some added performance without sacrificing longevity. I gave my opinion, based on my experience and on his request for longevity. I've know certain high stress parts to fail at 20 PSI. Not that all will, but some will. Since there's no way of knowing which will fail and which will not, I gave a very conservative opinion. I'd hate to tell someone, yeah go for 20 PSI and have a rod fail a week later.

      keep in mind that every one's experience is different, with a stock VNT-15, 15-16 PSI sustained boost is safe for an extended period (granted some will always spike to 20 PSI +). Although 18+ PSI sustained boost for the stock turbo will typically cause turbo failure before engine internals fail. more than likely the stock turbo will overspeed and snap, because it can't spin fast enough to make 20+ PSI sustained boost.

      Also most modded TDI's have excessive blow-by and oil burning before they have broken parts. you are more likely to blow a head gasket, damage the rings, before a structural component will fail on a diesel running high boost.

      This heated argument is mute, getting more boost, and not adding more fuel, (i.e. turning the manual boost controller up without adding more fuel) will make some more power, but bigger injectors are needed because the TDI engines run so lean to begin with. adding more air to a fire will make it burn a little hotter, but if you don't have enough fuel what's the point.


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