Very interesting! I like Jettas, my dad has a TDI and it's pretty torquey. After researching modding it I found it not to be very practical ...but this is the 4-cyl diesel with the tiny turbo I'm talking about. What you're saying is the GAS VR-6 engine was originally designed as a diesel ....and that it's built like a tank. I'll tell you what, I'd love to have something like that for a daily driver ...have to keep that in mind for the future. I wouldn't want to go crazy like 420 whp on a damn fwd but I'd like to boost it up to 250-300 whp. I wonder how stout the transaxle is? (only way I'd have a Jetta would be in a 5 sp) ...is it a LSD?

 

Yup.
And I got that DIRECTLY from an inside saurce at VW.

Do a google search for pictures. It's a really fascinating engine. It's the only "V" engine I know of that has only one cylinder head.

It also has SEVEN main bearings.

Follow this link and scroll down, you can see a pick of the crank and of a W12 shortblock, which is two VR6 engines mated at the crank:

Link 1


Here's a pic of the VR6 head:

Link 2

 

Awesome! Mere 15* separation allows the head to use all six cylinders ...pretty cool. So is it all forged and really strong all around? How sturdy is the transaxle and can you get LSD stock? I bet turbo setups are expensive and hard to tune just as in our case. What about the C.R. ...is it boost friendly or do you need race gas? I don't even know the stock TQ/HP number of the VR6. What about the turbo gas 4-cyl is it stout too? Would be easier to get one of those and just crank up the boost I would think.

 

You would be far better off asking these questions at VWVortex.Com, which has a VR6 forum. (Or did the last time I looked.)

Just to briefly hit your questions, I believe that the stock transaxle is good past 400hp, but I don't know how far past. You can get a Quaiffe limited slip unit, which IIRC is a Torsen type of differential.

I also know that you can get a VR6 passat into the low 13's with bolt-ons.

As I said though, you will get a lot more info at the website I mentioned.

 

Thanks, I will have to consider one of those for a daily driver at some point.

 

http://www.full-race.com/articles/Bs...st_writeup.pdf

food for thought on the log vs tubular question.

As far as turbo vs supercharged power, thats just silly. You are comparing apples to oranges there. If the same volume of air was pushed by both the turbo on the VR6 and the supercharger on the Cobra, then I could see arguing that, however, they aren't. All parasitic loss aside, you are going to make X amount of power when Y volume of air is combined with Z volume of gas at whatever RPM. I don't know the exact formula, however, there is no way to give a blanket statement that X PSI on the turbo is relative to X PSI on a supercharger. It doesn't work that way. Your friend is moron.

 

Thanks for backing me up.

 

PSI is just the amount of pressure running through the engine whether it's coming from a turbo or s/c. It's still going to be the same number.

CFM is a different story. A turbo will tend to more CFM at the same boost setting as the s/c. Of course theres a lot more to it than that. Take in count the trim of turbine/impeller of the turbo, A/R.

Comes down to this:

900CFM @ 25psi < 1400CFM @ 17psi

I know that seems logical but ricers are idiots and think BOOOOST is all that matters, when in reality you want more CFM.

 

SantaCruz163, "boost" comes from airflow. Excess airflow in the intake system is what causes the higher pressure over the n/a setup. Given the same engine and intake temperatures (post compression) 15 psi from an exhaust driven supercharger would be the same inlet airflow as 15 psi from a belt driven supercharger. There would be less intake charge contamination from the belt driven supercharger providing a more ideal cylinder fill.

 

Everyone likes to state that boost is a measure of restriction. That is true to an extent, but not totally.

If you have a supercharger running 15 psi in the plenum, then you port the intake runner, then the boost will reduce down to. . . say. . . 13 psi. Of course, it will make more power. . . blah blah blah. . . we've all heard it before.

What most people miss, though, is that the cylinder during the intake stroke is a dead-end path. There is no exit during that time. The idea is to get as much pressure as possible in the cylinder at BDC of the intake stroke. Let's just say that you had an intake port with zero restriction. Well you should have zero boost, right? Nope, just full boost pressure actually in the cylinder at BDC.

 

....the jetta is at least 500 lbs lighter than the Cobra.

I don't know squat about VW's but I own an '03 Cobra. It's a very heavy car. With a 200 pound driver, it weighs in at slightly over 3900 pounds. The convertible variant is 4000+ pounds.


....9.5 lbs on the Cobra would be around 500 hp.

Not exactly. The stock Eaton puts out 8.5 psig boost. The engine is rated by Ford at 390 hp. Dyno runs on stock '03s have shown a range of 365 to 384 rwhp. It would take much more boost to reach the 500hp mark.


The VR6 was originally designed as a Diesel engine so it'll stand boost that would send the mains out the bottom of the pan on the Cobra.

Actually, the '03-'04 Cobra engine uses all forged internals. You'll see guys running up to 600-650 hp on the stock bottom end with no catastrophic failures. This power level usually takes a Kenne Bell or Whipple supercharger running up to 23-psig boost -- again, on the stock bottom end.

 

Diesel engines are built to withstand static compressions of well over 20:1 and are designed to put out 2 to 4 times as much torque as a gas engines.

It's more than just "forged internals"

It's the metullurgy and design of both the internals and the block itself.


By way of reasonably well known example, I offer the Oldsmobile DX block as compared to the Gas block.

I know a guy who took a naturally aspirates 350DX block to 9.01/149mph in a 3200lb car, revving to (IIRC), over 8,000rpm; which gives you an idea of the stresses a diesel block will tolerate.