How VW Chocked the Performance of the 07K 2.5 Engine

It has been said many times that VW limited the performance of the 07K 2.5 Engine, so it wouldn't pillage sales from the GTI; and Automobile Journalists comment on how lazy this engine is.

It maybe late in the game for this engine but I wanted to document some of this info.

The 2.5 in the MK5 was originally limited the HP to 150 using long Intake runners but later they increased the HP to 170 by shortening the intake runners to about 19 inches and retune the ECU. The 07K IntaKe Manifold (IM) in the Mk6 Golf is basically the same as that in the later MK5s.

I've ripped apart a few of the later 07K IMs, it's safe to say that I've never seen an intake manifold as half a$$ed backwards as the one in our lil Golf 2.5. Most IMs are designed to produce good power from low to high end and designed with some sort of bell mouth or opening that is slightly larger in diameter at the plenum, and tapering to a smaller diameter at the intake manifold connection to the head.

https://i.imgur.com/ygAWYil.jpg

Sadly in the 07K IM this is reversed, The bell mouth only measures between 1 3/8 to 1 1/5 inches in diameter; while the intake manifold port connection to the head has an equivalent diameter of 1 5/8 inches. If VW wanted this engine to perform, they would have designed a bell mouth at least 1 3/4 inches in diameter or more.

Here is a Pic of the Bell Mouth
https://i.imgur.com/GiLQmKT.jpg

Here is a pic, measuring the diameter of the intake manifold port connection to the head using a cut down plastic cable tie to get the exact dimensions.
https://i.imgur.com/P94Oiwe.jpg

Here is a pic of the cross section of the intake runner from 6 1/2 to about 8 inches from the head.
https://i.imgur.com/C9suiBj.jpg

Notice the difference in intake runner diameter and shape.
https://i.imgur.com/BGkwbZy.jpg

The large plenum volume helps Low RPM torque and flexibility, the 19 inch runners only start to take effect say at about 2800 RPM but as the revs climb the smaller diameter of the intake runners choke off the high end performance, revs climb slowly. ALL Stage1 Tunes do a lot to help the everyday drivability of this engine but can't make inroads into top end performance due to this choke point.

I've had two 2.5s (MkV Jetta and NMS Passat), and I always felt the motor had a lot of unrealized potential. I was disappointed VW gave up on it completely. It was also more reliable than anything else they've made lately.



And let's not forget that heat-soaked abomination of an intake/airbox/resonator combination engine cover!

PhthaloType said:

I've had two 2.5s (MkV Jetta and NMS Passat), and I always felt the motor had a lot of unrealized potential. I was disappointed VW gave up on it completely. It was also more reliable than anything else they've made lately.



And let's not forget that heat-soaked abomination of an intake/airbox/resonator combination engine cover!

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Agreed Heat Soak in the summer BUT it actually gives better fuel milage in the winter.

The 2.5, will continue on in some of Audi's Performance cars like the TTRS.

All blasphemy! No just kidding. Interesting. I agree VW could have done so much more with this car. I think it comes down to making a golf variant for all segments of society. The economy car vs the hot hatch, but being German have to have a diesel in the lineup, and of course an electric for mother earth. I am sure pilfering sales was a consideration when designing the 2.5L. I was thinking maybe gas mileage was also a factor in the setup but idk. I think I get better gas mileage with the intake and tune. Anyway I digress. I am curious though how many GTI owners would have gone the 2.5L route even if it was set up correctly. Don't get me wrong I think the SRI/tuned 2.5L is fun as hell and sounds freakin awesome but with no turbo it would still lose out to the GTI in appeal for many. Me I have natural aspirations so the 2.5L was ideal. People are willing to sacrifice reliability for boost all day long so no matter what the GTI still wins the sales race. That being said I still agree with you that the proper 2.5L would have swayed some potential GTI buyers for sure. Wasn't there supposed to be a Golf RS that had the TTRS 2.5L in it?

PhthaloType said:

And let's not forget that heat-soaked abomination of an intake/airbox/resonator combination engine cover!

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I am fairly sure my P-Flow has way more heat soak issues than the stock airbox. With the filter that close to the engine, rubber boot, and a joke of a heat shield it is hot as hell when I open the hood after a drive. I notice a HUGE difference in throttle response when air temps are below 60 degrees outside or the car is not fully warmed up yet. If I could get the USP intake to fit with the SRI I would do it in a heartbeat. I am currently testing the new longer catch can routing vented to atm and if that works out I should be able to build my own version of the USP for the SRI as heat soak has been a very real issue for me. I have all the parts but I need to be a few inches closer to the TB to get it to the correct angle to clear meaning I have to remove the piece that connects the catch can back to the intake.

Wascally Wabbit said:

I am fairly sure my P-Flow has way more heat soak issues than the stock airbox. With the filter that close to the engine, rubber boot, and a joke of a heat shield it is hot as hell when I open the hood after a drive. I notice a HUGE difference in throttle response when air temps are below 60 degrees outside or the car is not fully warmed up yet. If I could get the USP intake to fit with the SRI I would do it in a heartbeat...

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I had the heat soak with the stock air box, non with the P-Flow. Your Throttle Body issues may have played a part with your experience.

I would go back to the P-Flow setup, Flow is using the P-Flow with the IE SRI, he is "power hungary' so if there was a negative issue most likely he would have said something.

The 2.5 in the TTRS is Special, especially to Audi branding; from the motorsport side VW/Audi Racing love it for the power and reliability but not the fuel economy. Two summers ago I did some data loggin and data analysis for my Buddy's Race team, they had hopes of successfully racing the TTRS, good lap times, the fuel consumption was the problem, their Tuning partner at the time couldn't Tune the engine to be fuel efficient enough. The team is now supported by VW Racing/Audo Customer Support, so it would be interesting to see what they could do BUT the focus is now solely on the New RS3 with a different engine.

I think the whole intake system gets much hotter with the aluminum SRI than with the stock plastic IM and that heat transfers to the TB and intake as it is so short. I am still using the p-flow currently but notice even with the new TB I am still having rev issues when it is hot outside, though not anywhere near as extreme as it was before. I think the heat throws off the sensors.

My concerns are not with power as I feel like I have plenty of that regardless of temp. It's with throttle response, ie what the engine is doing in response to my foot. They don't always match up. If it's below say 70 or so I never have an issue. Above that the throttle starts to act up a bit.

All this is only an issue starting from a stop. My theory is while the car is sitting it is getting hotter under the hood from lack of air flow so then you first apply the gas the air coming in is super hot and the sensors are thrown off by the sudden change in air temp coming in and they quickly try to compensate but it cannot compensate fast enough as the engine is quick to react.

Anyway I think it is the best it will ever be and when it acts up all I have to do is turn off traction control and it is fine so that's the final solution to this problem. Back to your discussion on the IM, why do they not make any SRI's out of plastic? I would think the heat transfer would be lessened significantly with plastic. You'll likely lose some of the growl and it may not last as long but performance might improve a bit.

Wascally Wabbit said:

I think the whole intake system get much hotter with the aluminum SRI than with the stock plastic IM and that heat transfers to the TB and intake as it is so short. I am still using the p-flow currently but notice even with the new TB I am still having rev issues when it is hot outside, though not anywhere near as extreme as it was before. I think the heat throws off the sensors.

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To test, try buying some thin peel and stick foam insulation with the foil outside and wrap the SRI.

EDIT: LOL maybe painting the SRI black wasn't such a good idea.

MLue1 said:

To test, try buying some thin peel and stick foam insulation with the foil outside and wrap the SRI.

EDIT: LOL maybe painting the SRI black wasn't such a good idea.

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There were many discussions on that. Some say powder coat will hold heat in, others say it will keep heat out. Personally I don't think it matters as the heat is coming from both the connection to the head and air temp so my guess it's a wash. It all came down to looks.

I have a whole role of usp heat tape that came with the CAI but it won't stick to the powder coating unfortunately to test.

Edit: Damn you know what would have been cool would be to wrap the intake in fiberglass header wrap. That probably would have looked pretty cool as well, or like crap if you couldn't wrap it well.

Wascally Wabbit said:

There were many discussions on that. Some say powder coat will hold heat in, others say it will keep heat out. Personally I don't think it matters as the heat is coming from both the connection to the head and air temp so my guess it's a wash. It all came down to looks.

I have a whole role of usp heat tape that came with the CAI but it won't stick to the powder coating unfortunately to test.

Edit: Damn you know what would have been cool would be to wrap the intake in fiberglass header wrap. That probably would have looked pretty cool as well, or like crap if you couldn't wrap it well.

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Black attracts heat, while white or silver reflects alot of it. If you shoot the surface with an infarred temp gun it will show you the difference.

What is the conclusion here.?I have a stock 2.5L. Should I get a SRI or not? How do I know if my engine has MAF Sensor?

https://www.aemintakes.com/21-733c-aem-cold-air-intake-system or https://neuspeed.com/products/neuspeed-p-flo-air-intake-kit-651080?variant=31583314182278

ivanbcanada said:

What is the conclusion here.?I have a stock 2.5L. Should I get a SRI or not? How do I know if my engine has MAF Sensor?

https://www.aemintakes.com/21-733c-aem-cold-air-intake-system or https://neuspeed.com/products/neuspeed-p-flo-air-intake-kit-651080?variant=31583314182278

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Mk5 or MK6? MAF went to MAP in 2010 I believe with the MK6. As far as CAI I am a neuspeed fan. SRI depends on your wallet and what your goals are in the end. I had the SRI on my car for a couple years with IE stage 2 but decided to remove it and go back to Stage 1.

Wascally Wabbit1 said:

Mk5 or MK6? MAF went to MAP in 2010 I believe with the MK6. As far as CAI I am a neuspeed fan. SRI depends on your wallet and what your goals are in the end. I had the SRI on my car for a couple years with IE stage 2 but decided to remove it and go back to Stage 1.

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My car is 2011 Golf Sportline. The goal is to eliminate the heat soak due to our horribly designed intake....My car is bone stock so any improvement is good.

https://www.aemintakes.com/21-733c-aem-cold-air-intake-system or https://neuspeed.com/products/neuspeed-p-flo-air-intake-kit-651080?variant=31583314182278

Also, is it worth getting a 91 tune to go with this? Thanks!

ivanbcanada said:

My car is 2011 Golf Sportline. The goal is to eliminate the heat soak due to our horribly designed intake....My car is bone stock so any improvement is good.

https://www.aemintakes.com/21-733c-aem-cold-air-intake-system or https://neuspeed.com/products/neuspeed-p-flo-air-intake-kit-651080?variant=31583314182278

Also, is it worth getting a 91 tune to go with this? Thanks!

Click to expand...

To answer in general, the best upgrade you can do on the 2.5L is an air intake with stage 1 tune. It won't even feel like the same car.

For me the Neuspeed P-Flo is the best intake. I would not worry about heat soak too much as this is a naturally aspirated car so it's not a huge deal compared to a turbo. Any intake under the hood will be taking in warm air. Those little heat shields don't do squat except hold the filter in place.

If you want an actual cold air intake USP Motorworks is the way to go but there are downsides to this as there is the possibility of pulling water through the intake if you drove through a really deep puddle. Also because of the location the filter get dirty faster and is not as easy to service but when I had it I loved it. I only got rid of it when I installed the SRI.

I use the P-Flow because it is California C.A.R.B legal and with stage 1 I don't have to change anything for my semi anual smog checks that just came due.

I've experimented a lot on this car and put a lot of money into it and for me the best all around daily driver has been with IE stage 1 and the P-Flow. If you don't live in California and you have the $2k to spend the SRI with Stage 2 is pretty damn fun and the car sounds like a beast.

Wascally Wabbit1 said:

To answer in general, the best upgrade you can do on the 2.5L is an air intake with stage 1 tune. It won't even feel like the same car.

For me the Neuspeed P-Flo is the best intake. I would not worry about heat soak too much as this is a naturally aspirated car so it's not a huge deal compared to a turbo. Any intake uder the hood will be taking in warm air. Those little heat shields don't do squat except hold the filter in place.

If you want an actual cold air intake USP Motorworks is the way to go but there are downsides to this as there is the possibility of pulling water through the intake if you drove through a really deep puddle. Also because of the location the filter get dirty faster and is not as easy to service but when I had it I loved it. I only got rid of it when I installed the SRI.

I use the P-Flow because it is California C.A.R.B legal and with stage 1 I don't have to change anything for my semi anual smog checks that just came due.

I've experimented a lot on this car and put a lot of money into it and for me the best all around daily driver has been with IE stage 1 and the P-Flow. If you don't live in California and you have the $2k to spend the SRI with Stage 2 is pretty damn fun and the car sounds like a beast.

Click to expand...

Sad I never got to experience what a tuned 2.5 feels like with Sri. My rabbit got totaled right before I was going to do that. Ended up replacing it with a 2.0t fsi Jetta, debating taking the k04 off my Gti and putting that on the Jetta then going bigger with the gti. I also really want to pick up a mk1 project to which I've always said I'd throw a 2.5 in. Maybe my time with the 5 cyl isn't over