[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

16v or 8v turbo?

then why are ya using 16v's for the twin?

>From: Allyn <amalventano1@comcast.net>

>ok, now that requires a slightly different explanation.
>     BMEP is the MEAN pressure, i.e. the average pressure. for this you 
>have to picture whats going
>on during the combustion process. you cant simply consider the peak 
>pressure, you must consider the
>pressure maintained during the combustion stroke. after all, the peak 
>pressure at tdc is doing
>effectively no work at all (picture bicycle pedal at tdc). as the piston 
>moves downward, the effect
>is a pressure drop (naturally). combustion continues well beyond tdc, so 
>combustion keeps the
>pressure up, acting against the pressure drop. this results in a large 
>pressure being maintained 90
>(crank) degrees beyond tdc (pedal parallel to ground). it is that pressure 
>that is doing the work
>for you, ultimately resulting in high BMEP numbers.
>     now lets go back to the 8v vs 16v stuff. keep in mind i am talking 
>stock engines (with added
>turbos) in both cases. previously we established that we had to limit peak 
>pressure (at tdc) by
>using lower boost on the 16v. another aspect of the peak pressure to 
>consider is that spark occurs
>before tdc, so your calculated peak pressure is actually lower than the 
>actual peak that the engine
>sees. what this peak is actually accomplishing is detonation, since the 
>air/fuel has had so much
>energy (pressure) added to it that it all detonates at once. this results 
>in extreme pressure spikes
>(~1500 psi), causing ring lands to go poof and pieces of pistons to go 
>byebye.
>     oops, started getting off track there. ok. here, i'll make it simple.
>
>- 16v: higher c/r, therefore lower boost, therefore lower mass of air in 
>cylinder.
>- 8v: lower c/r => higher boost => more mass of air in cylinder => more 
>fuel to burn => more
>combustion => higher pressures maintained at/through the 90 degree mark => 
>higher BMEP numbers =>
>more torque => more hp.
>
>hope that straightens some more stuff out for ya :)
>Al
>
>Allyn Malventano, ETC(SS), USN
>87 Rieger GTO Scirocco 16v (daily driver, 180k, rocco #6)
>86 Kamei Twin 16V Turbo Scirocco GTX ('it has begun', rocco #7)
>86.5 Occo 16v Trailer (dotting 'i's across the country, rocco #8)
>87 Jetta 8v Wolfsburg 2dr (daily driver, 260k, 0 rattles, original clutch, 
>driveshafts, wheels :)
>
>
>----- Original Message -----
>From: "Larry" <rocco16v@netzero.com>
>To: "Allyn" <amalventano1@comcast.net>; "Lil B 959" <lilb959@hotmail.com>; 
><scirocco-l@scirocco.org>
>Sent: Saturday, June 22, 2002 5:47 PM
>Subject: Re: 16v or 8v turbo?
>
>
> > Al-
> >   Either you were more awake, or I was, since your second explanation 
>was
> > much clearer to me.
> >
> > However, since Brake Mean Effective Pressure (BMEP, or the 'peak 
>pressure' I
> > believe you're speaking of) is the true indicator of power (torque,
> > actually, put for simplicity's sake we'll call it just 'power'), it 
>sounds
> > like the 16v would be the engine of choice, since it will (with 5 lbs 
>boost)
> > produce the "the same peak pressure as an 8v with 15 lbs of boost."
> > Aaarrrgghh, I'm getting more conFUSED!!
> >
> > Larry
> >
> >
> >
> > > okok, heres what i mean.
> > >     by running lower c/r, you can run higher boost, meaning the engine
> > draws in more (mass) of air
> > > on each stroke. the lower c/r means lower multiplication of the 
>absolute
> > pressure coming in, so
> > > since the lower c/r engine is multiplying by a lower factor, there is 
>a
> > lower peak cylinder pressure
> > > in the lower c/r engine (with the same level of boost). the peak 
>cylinder
> > pressure is usually the
> > > limiting factor.
> > >     a (stock) 16v with ~5 lbs boost has approx the same peak pressure 
>as
> > an 8v with ~15 lbs boost.
> > > this is where the ~5 lbs limit comes from for stock 16v turbos. yes 
>the
> > 16v may be flowing better,
> > > but the 8v is still getting much more mass of air (and fuel) in the
> > cylinder per stroke (due to the
> > > much higher intake pressure).
> > >
> > > was my rambling worse or better this time? i had just woke up when i 
>wrote
> > that last one.
> > > Al
> > >
> > > Allyn Malventano, ETC(SS), USN
> > > 87 Rieger GTO Scirocco 16v (daily driver, 180k, rocco #6)
> > > 86 Kamei Twin 16V Turbo Scirocco GTX ('it has begun', rocco #7)
> > > 86.5 Occo 16v Trailer (dotting 'i's across the country, rocco #8)
> > > 87 Jetta 8v Wolfsburg 2dr (daily driver, 260k, 0 rattles, original 
>clutch,
> > driveshafts, wheels :)
> > >
> > >
> > > ----- Original Message -----
> > > From: "Larry" <rocco16v@netzero.com>
> > > To: "Allyn" <amalventano1@comcast.net>; "Lil B 959" 
><lilb959@hotmail.com>;
> > <scirocco-l@scirocco.org>
> > > Sent: Saturday, June 22, 2002 9:02 AM
> > > Subject: Re: 16v or 8v turbo?
> > >
> > >
> > > > Allyn-
> > > >   The way you've worded your reply, it sounds like you are 
>contradicting
> > > > yourself:
> > > > Less c/r ( less pressure) so you can run more boost which equals 
>more
> > > > pressure??
> > > > Please expound on your position...
> > > > ( BTW, you say less c/r lets the engine draw in more air, some 
>listers
> > say
> > > > MORE c/r lets the engine draw in more air.  I say 'don't make no
> > > > difference'.  Picture this: take a single cylinder engine of 100cc
> > > > displacement. On the intake stroke, that engine will theoretically 
>draw
> > in
> > > > 100cc of intake charge. Doesn't matter how much it compresses that
> > charge on
> > > > the next stroke, 2:1 or 10:1, it will only draw in 100cc. Because 
>the
> > > > compression stroke occures AFTER the intake, compression is 
>dependant on
> > > > intake, intake is NOT dependant on compression.  To say otherwise 
>would
> > be
> > > > like saying the position of the throttle pedal is dependant on the
> > engine
> > > > output, when it's the other way around.  Follow?)
> > > >
> > > >  Bryson-
> > > >   Regardless, the only way to make more power is to move more 
>air/fuel
> > > > through an engine. Period.
> > > > A 16v engine will move more air/fuel (all else being equal) than an 
>8v,
> > > > because it has more valve area.
> > > > Therefore, the 16v has more POTENTIAL than the 8v. In all 
>practicality,
> > for
> > > > street use the 8v would probably be the best choice when you factor 
>in
> > 'bang
> > > > for the buck'.
> > > >
> > > > Larry
> > > >
> > > > ----- Original Message -----
> > > > From: Allyn <amalventano1@comcast.net>
> > > > To: Lil B 959 <lilb959@hotmail.com>; <scirocco-l@scirocco.org>
> > > > Sent: Friday, June 21, 2002 7:01 PM
> > > > Subject: Re: 16v or 8v turbo?
> > > >
> > > >
> > > > > ok, heres the deal. the more air you can get in there, the better
> > (read:
> > > > more torque/hp). lower c/r
> > > > > means more air (mass) can come in (i.e. more boost). the reason 
>that
> > more
> > > > can come in is that the
> > > > > lower c/r engine wont try to compress it as much, so you are 
>keeping
> > > > in-cylinder peak temps within
> > > > > reasonable numbers. this lets you have more boost without doing 
>crazy
> >
> > > > stuff like water
> > > > > injection/massive intercoolers/race gas.
> > > > > ...so that leaves the best bet being the 8v. the 16v is actually
> > better
> > > > suited to the task (and
> > > > > breathes alot better), but to use it you have to drop the c/r 
>(either
> > by
> > > > spacing the head or forged
> > > > > pistons).
> > > > >
> > > > > p.s. dont forget the big injectors :)
> > > > >
> > > > > Al
> > > > >
> > > > > Allyn Malventano, ETC(SS), USN
> > > > > 87 Rieger GTO Scirocco 16v (daily driver, 180k, rocco #6)
> > > > > 86 Kamei Twin 16V Turbo Scirocco GTX ('it has begun', rocco #7)
> > > > > 86.5 Occo 16v Trailer (dotting 'i's across the country, rocco #8)
> > > > > 87 Jetta 8v Wolfsburg 2dr (daily driver, 260k, 0 rattles, original
> > clutch,
> > > > driveshafts, wheels :)
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Lil B 959" <lilb959@hotmail.com>
> > > > > To: <scirocco-l@scirocco.org>
> > > > > Sent: Friday, June 21, 2002 8:30 PM
> > > > > Subject: 16v or 8v turbo?
> > > > >
> > > > >
> > > > > >
> > > > > >
> > > > > > Hey I was wondering if I should go for a 16v or 8v turbo?  I 
>know
> > the 8v
> > > > has
> > > > > > a better compression ratio for a turbo, but if I ran less boost 
>with
> > the
> > > > 16v
> > > > > > would it be better than running more boost with the 8v?  Any
> > information
> > > > > > would be helpful.  Thanks,
> > > > > > Bryson
> > > > > >
> > > > > > 
>_________________________________________________________________
> > > > > > MSN Photos is the easiest way to share and print your photos:
> > > > > > http://photos.msn.com/support/worldwide.aspx
> > > > > >
> > > > > >
> > > > > > _______________________________________________
> > > > > > Scirocco-l mailing list
> > > > > > Scirocco-l@scirocco.org
> > > > > > http://neubayern.net/mailman/listinfo/scirocco-l
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > Scirocco-l mailing list
> > > > > Scirocco-l@scirocco.org
> > > > > http://neubayern.net/mailman/listinfo/scirocco-l
> > > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > Scirocco-l mailing list
> > > > Scirocco-l@scirocco.org
> > > > http://neubayern.net/mailman/listinfo/scirocco-l
> > >
> > >
> >
>
>
>_______________________________________________
>Scirocco-l mailing list
>Scirocco-l@scirocco.org
>http://neubayern.net/mailman/listinfo/scirocco-l


_________________________________________________________________
Join the world’s largest e-mail service with MSN Hotmail. 
http://www.hotmail.com