# weak points of the 2.5



## GLI_jetta (Jan 3, 2006)

whats up guys... I have been doing a little research as to my friend just bought a 2.5 rabbit. He wants to throw FI in but I want to find out what will have to be replaced to have a reliable 300-330whp car. How is the stock 5 speed trans, Im not sure which it exactly is. From what I have read, the head/valve train is fine and will flow well. How is the rods/pistons, what is the max that should be thrown at them. Im just looking for any area that should be taken a look at when putting power through it.
thanks guys


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## Corruptkid (Feb 19, 2007)

*Re: weak points of the 2.5 (GLI_jetta)*

um the rods and pistons should be able to handle 300whp but with a low cr kit. speak to audi4u or C2 Motorsports or even NGP Racing as they all have cars that have made 300+ whp


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## Blitzkrieg'nBunny (Feb 11, 2007)

as far as the tranny goes, it seems to be hit or miss as far as the gears and random problems, maybe the clutch can handel it but it doesnt seem like a good idea, there are aftermarket clutch adn single mass flywheel options research my friend...


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## a7xogg (Nov 25, 2008)

*Re: (Blitzkrieg'nBunny)*

you should be fine with a stage 2 clutch and flywheel kit


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## GLI_jetta (Jan 3, 2006)

*Re: (Blitzkrieg'nBunny)*


_Quote, originally posted by *Blitzkrieg’nBunny* »_as far as the tranny goes, it seems to be hit or miss as far as the gears and random problems, maybe the clutch can handel it but it doesnt seem like a good idea, there are aftermarket clutch adn single mass flywheel options research my friend... 

of course i wouldn't expect the stock clutch to hold... that would be changed obviously. I was talking about parts that arent reliable in the bottom end if any.
like with the 1.8, throw in a set of rods and skies basically your limit for power on the bottom end.. i was looking for problems like those.


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## a7xogg (Nov 25, 2008)

*Re: (GLI_jetta)*

no problems like that.


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## GLI_jetta (Jan 3, 2006)

*Re: (a7xogg)*


_Quote, originally posted by *a7xogg* »_no problems like that.

so if theres a torque spike early in the rpms... i shouldn't expect a rod out the block lol? all internals are ok for that hp?


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## jettafan[atic] (Dec 2, 2008)

*Re: (GLI_jetta)*

I was interested in the Stage 2+ kit from C2 so I called with the same questions and they strongly suggested forged internals. NGP Racing sells a couple sets on their site. Pistons for 8.5:1 CR for $899 and JE pistons with 9:1 CR for a cool grand.
http://www.ngpracing.com/store...=3520
They also have a main bearing stud kit by Raceware for $200, hope that helps!
http://www.ngpracing.com/store...=2611


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## GLI_jetta (Jan 3, 2006)

*Re: (jettafan[atic])*


_Quote, originally posted by *jettafan[atic* »_]I was interested in the Stage 2+ kit from C2 so I called with the same questions and they strongly suggested forged internals. NGP Racing sells a couple sets on their site. Pistons for 8.5:1 CR for $899 and JE pistons with 9:1 CR for a cool grand.
http://www.ngpracing.com/store...=3520
They also have a main bearing stud kit by Raceware for $200, hope that helps!
http://www.ngpracing.com/store...=2611

yeah man thats what im looking for. thank you!


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## jettafan[atic] (Dec 2, 2008)

*Re: (GLI_jetta)*

Hey not a problem man, i actually forgot to mention that they only suggested the forged internals if you want to be running over 12 lbs of boost. The stock internals will hold fine for 8-12 lbs, but who's really satisfied with that???


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## a7xogg (Nov 25, 2008)

*Re: (jettafan[atic])*

i would cause its less work.


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## Corruptkid (Feb 19, 2007)

*Re: (a7xogg)*

as long as you have the right software tune, the stock pistons and rods should hold up, however like all other things its better to do the forged internals as remember you gotta look at stuff in the long run, these stock pistons and rods could possibly fail eventually with aggresive driving


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## a7xogg (Nov 25, 2008)

*Re: (Corruptkid)*

im tryin to save aggressive driving for the track.


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## _V-Dubber_ (Jan 30, 2007)

*Re:*

The weak point of this engine, of any VW engine, are the rods. Our pistons, straight off the old 1.8T are already forged 9.5:1 units, the block is iron, and our crank is cast iron. Pretty stout stuff. The rods are just basic hardware and not forged. Many people on here will tell you your friend would be fine with stage 2 with stock internals and an upgraded clutch and they're right. However, thats nowhere near the power levels you're talking about. Stage 2s vary in power output but a typical install nets you maybe *250whp* on 8-10psi. You're asking for another 50-80whp _above_ that. 
To do this, you'll need more than just off the shelf parts. So I'll help you. Necessities include a much larger than stock exhaust, maybe a stage II spec clutch, and at least 14-15psi to reach your power goals (if nothing else on the engine changes besides boost level and exhaust size). Those things alone will get you close to 300whp. Obviously, your friend wants more. You'll need to visit a machine shop or an experienced Volkswagen tuning shop to make some custom stuff for you. In any case, your friend should do more research to figure out what a realistic power goal is for this engine and not just throw numbers out there. I would love to have ridiculous 500 horsepower from my 2.5, but thats just not reality. The costs to reach certain power levels would be so financially intensive and require so much down time to build that it just wouldnt be worth it. After all, these cars cost under 20 grand. I mean, you wouldnt buy a Geo Metro and spend 100 grand on engine mods to get it to make 1100whp would you? Of course not.
But I'll stop that omnicient, thinks-he-always-knows-better rant and try and help you a little more before I decide to call it quits. Anyways, you're now making twice what the engine typically puts down in stock form. Your engine internals were not designed to cope with this much power. So unless you're planning on always keep the revs below 3 grand and never applying more than 25% throttle for the rest of the life of your vehicle which I know your friend wont then you must upgrade your internals. If you're going to run 15psi of boost you need the 8.5:1 pistons. You could maybe squeak by with the 9.0:1s but you'd really be pushing it big time. And of course, you'll need those rods. Of couse these are all off the shelf, open-a-catalog parts. But they're a start. Idk if the Pauter rods are just drop-ins. If not, you'll need to tear apart the head and do a complete engine teardown and rebuild. And I do not know if the bore of those new pistons is exactly the same as stock. If they're even a little bit over, your cylinders will need to be bored out to accomodate them. You will need to find a machine shop to do this for you. This means the block will have to be pulled out and then reinstalled in the car after this is done. Dont forget the lengthy downtime and immense costs associated with this. 
Maybe you'd be happier with just a basic C2 stage2 kit and stock internals and be happy with ~235-255whp. If you really have your heart set on 300whp and above and won't settle for anything less, creative thinking is needed. Dont rely on off the shelf stuff. You might need custom work done. Finding a local machine shop or nearby VW-specialized tuning shop will help you tremendously. Visit with them or have another conference with C2 about the logistics of getting all this done and learn from people who have been there. Read up more on the C2 kit literature, search this forum's archives to see what else is available for your machine, and definitely do your own research. This is a huge investment and you shouldnt base it off of what a couple people on the internet that you've never met in your life say. Do your homework and make a good decision and settle upon a setup that fits within your budget (there's nothing worse than running out of $$$ mid build, and spending every last penny you have on your car is irresponsible and an irrational use of your finances) and can safely/reliably put down a power level you can live with.


_Modified by _V-Dubber_ at 4:56 AM 2-2-2009_


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## Audi4u (Jun 29, 2002)

IMO the stock engine is good for 300whp. 
If I had to chage anything, then the weak parts for these motors would be.
the pistons.
But if your going to try and change piston the you might as well do the rods.
*engine*
coated pistons $1k
Rods $650
*tranny*
differential $900
Clutch&flywheel upgrade $500+
*chassis*
suspension 500-1200
brakes $??
IMO if the 2.0t fsi can make 300w hp safely then we should be able to make 20% more power. That would be 360whp. 
I won't give you a safe number for 300whp, all I can say is I made 370whp+ on stock engine and I am comfortable doing 300-325whp again.
Thats my goal for the mk4 with the gt3071.


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## GLI_jetta (Jan 3, 2006)

*Re: (Audi4u)*


_Quote, originally posted by *_V-Dubber_* »_The weak point of this engine, of any VW engine, are the rods. Our pistons, straight off the old 1.8T are already forged 9.5:1 units, the block is iron, and our crank is cast iron. Pretty stout stuff. The rods are just basic hardware and not forged. Many people on here will tell you your friend would be fine with stage 2 with stock internals and an upgraded clutch and they're right. However, thats nowhere near the power levels you're talking about. Stage 2s vary in power output but a typical install nets you maybe *250whp* on 8-10psi. You're asking for another 50-80whp _above_ that. 
To do this, you'll need more than just off the shelf parts. So I'll help you. Necessities include a much larger than stock exhaust, maybe a stage II spec clutch, and at least 14-15psi to reach your power goals (if nothing else on the engine changes besides boost level and exhaust size). Those things alone will get you close to 300whp. Obviously, your friend wants more. You'll need to visit a machine shop or an experienced Volkswagen tuning shop to make some custom stuff for you. In any case, your friend should do more research to figure out what a realistic power goal is for this engine and not just throw numbers out there. I would love to have ridiculous 500 horsepower from my 2.5, but thats just not reality. The costs to reach certain power levels would be so financially intensive and require so much down time to build that it just wouldnt be worth it. After all, these cars cost under 20 grand. I mean, you wouldnt buy a Geo Metro and spend 100 grand on engine mods to get it to make 1100whp would you? Of course not.
But I'll stop that omnicient, thinks-he-always-knows-better rant and try and help you a little more before I decide to call it quits. Anyways, you're now making twice what the engine typically puts down in stock form. Your engine internals were not designed to cope with this much power. So unless you're planning on always keep the revs below 3 grand and never applying more than 25% throttle for the rest of the life of your vehicle which I know your friend wont then you must upgrade your internals. If you're going to run 15psi of boost you need the 8.5:1 pistons. You could maybe squeak by with the 9.0:1s but you'd really be pushing it big time. And of course, you'll need those rods. Of couse these are all off the shelf, open-a-catalog parts. But they're a start. Idk if the Pauter rods are just drop-ins. If not, you'll need to tear apart the head and do a complete engine teardown and rebuild. And I do not know if the bore of those new pistons is exactly the same as stock. If they're even a little bit over, your cylinders will need to be bored out to accomodate them. You will need to find a machine shop to do this for you. This means the block will have to be pulled out and then reinstalled in the car after this is done. Dont forget the lengthy downtime and immense costs associated with this. 
Maybe you'd be happier with just a basic C2 stage2 kit and stock internals and be happy with ~235-255whp. If you really have your heart set on 300whp and above and won't settle for anything less, creative thinking is needed. Dont rely on off the shelf stuff. You might need custom work done. Finding a local machine shop or nearby VW-specialized tuning shop will help you tremendously. Visit with them or have another conference with C2 about the logistics of getting all this done and learn from people who have been there. Read up more on the C2 kit literature, search this forum's archives to see what else is available for your machine, and definitely do your own research. This is a huge investment and you shouldnt base it off of what a couple people on the internet that you've never met in your life say. Do your homework and make a good decision and settle upon a setup that fits within your budget (there's nothing worse than running out of $$$ mid build, and spending every last penny you have on your car is irresponsible and an irrational use of your finances) and can safely/reliably put down a power level you can live with.

_Modified by _V-Dubber_ at 4:56 AM 2-2-2009_

now running the low boost your talkig about.... does that include the head spacer or is that on stock c/r? we have a t61 on my brothers vrt that throws over 400whp and I have a 3076 on my 1.8 and i built that bottom end bullet proof and thats also over 400whp so I'm familiar with whats needed to flow and all that... vw pistons seem to be strong, theres guys on my end thats throwing over 600wheel at them and they just smile... but i figured as much that rods were garbage... thanks for the info...

_Quote, originally posted by *Audi4u* »_IMO the stock engine is good for 300whp. 
If I had to chage anything, then the weak parts for these motors would be.
the pistons.
But if your going to try and change piston the you might as well do the rods.
*engine*
coated pistons $1k
Rods $650
*tranny*
differential $900
Clutch&flywheel upgrade $500+
*chassis*
suspension 500-1200
brakes $??
IMO if the 2.0t fsi can make 300w hp safely then we should be able to make 20% more power. That would be 360whp. 
I won't give you a safe number for 300whp, all I can say is I made 370whp+ on stock engine and I am comfortable doing 300-325whp again.
Thats my goal for the mk4 with the gt3071.


so the pistons and rods seem to both be the weak point and is highly suggested to be changed for a reliable 300-330whp then? I was thinking about a 50 trim .63ar would be sufficient for his power goal.. that will kick his full spool to around the 3.5kmark so Im a little nervous on the tq spike blowing a rod.. the power is a on a little early for me... but anything bigger would be over kill and spool later...



_Modified by GLI_jetta at 12:44 PM 2-2-2009_


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## _V-Dubber_ (Jan 30, 2007)

*Re: (GLI_jetta)*

Both the regular stage2 and stage2 low C/R kit both use head spacers. However if you mean to say is this with the stock CR or with the stage2 lowered CR kit with the larger head spacer, the answer is neither. You wont need the stage2 lowered CR kit since you are already lowering the CR by throwing in 9.0:1 or 8.5:1 pistons. The lowered CR kit doesnt mean more power if you have lowered your CR, what it does is lower the CR for you so you wont have to throw in pistons but still allow you to run more boost as if you had. The 300-330whp I was talking about you may be able to squeak by with the bottom end but at least for myself I always try to err on the side of safety. There's no point in having the fastest 2.5 on Vortex for a week and then blowing it up. Thats why I'm going for forged pistons with a lower CR and rods when I do my install.


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## Corruptkid (Feb 19, 2007)

*Re: (_V-Dubber_)*


_Quote, originally posted by *_V-Dubber_* »_ There's no point in having the fastest 2.5 on Vortex for a week and then blowing it up. Thats why I'm going for forged pistons with a lower CR and rods when I do my install.

lol try two days if that even, i blew my car up twice within a week and a half


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## _V-Dubber_ (Jan 30, 2007)

*Re: (Corruptkid)*

lol Dayyyyummmm! Something I wish to avoid...


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