OK, so I got into an argument with a friend of mine a while back about some stupid video he showed me of a volkswagen jetta with a turbo VR6 beating a 03-04 Cobra. The VW was using 19 psi which is over twice that of the Cobra. My argument was that if the Cobra had even close to that much boost then it would have been a different story. He counters this by arguing that 19psi from a turbo is the equivalent of 9.5 psi from a supercharger (or in other words, it takes twice the psi from a turbo to make the same amount of power as a supercharger). I then said that 19 psi is 19 psi, I dont care where it comes from be it a supercharger or a turbo. Now, I was hoping that some of you guys more knowledgeable of the subject could prove one of us wrong. Thanks guys.

 

4 words "your friends an idiot"

hahah good luck im sure someone else has more informational post than me

 

Just real briefly, the jetta is at least 500 lbs lighter than the Cobra. 19 psi on the Jetta would be around 420-430 hp or so. 9.5 lbs on the Cobra would be around 500 hp. Boost pressure is relevant to the airflow of the engine. The VR-6 is around 170 cubic inches. The Cobra is 281 cubic inches. With their respective boost levels the Cobra flows roughly 18% more air than the Jetta and makes more power, but the car is heavier.

 

He showed me another video of the VW on a dyno and it had 420 FWHP I believe, so good calculation, guess or whatever method you used.

But what my buddy was suggesting was that on a motor, any motor, it would take twice the amount of boost that a supercharger was running for a turbo to achieve the same amount of horsepower as the supercharger(sorry, I couldn't think of a better way to word that). So a VR6, turbo, 20psi puts down the same power as a VR6 supercharged 10psi. And as I stated before, I argued that X psi equals X psi and it doesn't matter where it comes from. I hardly know anything about forced induction, but his argument seemed rediculous to me. So who is wrong me, him, or both of us?

 

ill second that.

he dosnt know what hes talkign about

brook

 

He is wrong, it would actually be the other way around. Given the exact same engine and the exact same boost level the turbo would make slightly more power because of the parasitic loss of the supercharger. It takes a lot of power to spin a supercharger, probably somewhere around 50 HP at that boost level.

 

A compressor, no matter how it is driven, will take roughly the same amount of hp to spin when compressing the same flowrate at the same pressure ratio. The turbochager is simply more efficiently driven. I read about an interesting test where a motor made 1000 hp when run on compressed inlet air. The same motor made 800 hp when it had a supercharger at the same pressure and 950 hp with a turbocharger at the same pressure. Therefore, the supercharger takes 200 fwhp to drive and the turbo soaks up 50 fwhp at that power level.

Also, my own testing revealed that a turbo on an LT1 will make ~30 more rwhp than a supercharger at the same boost level, all other things being equal. That's at the ~550 rwhp range.

 

Ok, I'll take all of this as meaning that I'm "more" right and "less" wrong than him. And the wierd thing is that this guy is not clueless when it comes to cars so I don't know where he got this idea from. And he's not one of those ricer fools, although he is into VWs which only puts him a slight step higher than the ricers.

 

Mike, is that difference with the log-style header? How much of of a difference do you think a set of 4-1's would make at that level?

 

Also, have no doubt that peak lb for lb the turbo is going to produce a lot more low rpm torque. In other words, if they both make a peak of 10 PSI at say 6,000 rpm ......the turbo is going to make more like 8 PSI at 3,000 rpm and the blower is going to make more like 3 PSI at that rpm. The supercharger's impellor rpm is limited by pullies, whereas the turbo impellor isn't directly connected to anything to produce it's rpm, so at very low rpm if there is a lot of load the turbo impellor can spool up to a much faster rpm, producing a lot more torque than a comparable centrifugal blower.

As others have stated, he has it backwards. The supercharger is at quite a disadvantage pound for pound since it requires more power to be driven and can't spool up as quickly.

 

Yes, the turbo made 30 more rwhp than the T-trim Vortech at the same boost level with a supposedly crappy log-style header and a supposedly all-wrong blower cam.

From the reading that I've done, I think the log header may cause a 10 - 20 rwhp debit at the 580 rwhp/13 psi level, probably up to 40 rwhp at higher boost/power levels. Keep in mind that the turbo Buicks have log headers on the turbo side and they don't bother changing over to 4-1's until they get in the 9's on 231 cid.

 

Very true, one key difference is that the primary tubes are angled towards the direction of the turbine before attaching to the log header. http://www.gnttype.org/techarea/pict...stockhdrs.html It should help flow to a certain extent.

 

I actually was able to do mine the same way, except for #1. The tubes for my #3, 5, and 7 are angled to merge into the log. I simply didn't have enough room on #1, so it Tee's in at a 90 deg angle.

 

Sounds good Mike, keep us updated on her progress.

 

On a side note, and talking about stock engines here; I don't think the cobra has a chance against the VR6 in a turbocharged application. Probably not a supercharged one either.

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. Plus, the combustion chambers are essentially zero cc's. The head is completely flat. All the combustion takes place in the piston; so it's basically a perfect engine for boost.

One of these days I'd like to build a motorcycle around one of those engine, but that's WAY off topic.