Forced Induction ?: X-Flow versus JH head

[scirocco-al@insight.rr.com (Alan Stamper)]

So, I guess the question that has to asked is; Why are YOU turning your
engine to 8000 RPM when it has no power there?
And I guess the second question is; If a hydraulic lifter will support an
engine speed more than 1000 RPM past the power peak, how is it a detriment
to the original suggested application?

Ok, you win.  I can't see a detriment if it will handle the RPM.  As far as
the 8000 rpm question.  It's better to stay in second than shift into third
and back into second in most cases.  My car has a 4K in it and with the 13X9
wheels with 225/45 Hoosiers it would run out of RPM fast.  It would be at or
above 7000 rpm on any good slalom of semi-straight section.  I would just
put my foot in it and let it spool up.  It only makes power up to about 7200
RPM, then it tapers off.  It will still accelerate, just not very fast.

Alan

----- Original Message -----
From: "Dan Bubb" <jdbubb@ix.netcom.com>
To: "Alan Stamper" <scirocco-al@insight.rr.com>; "Scott F. Williams"
<sfwilliams@comcast.net>; "scirocco" <scirocco-l@scirocco.org>
Sent: Monday, February 17, 2003 6:10 PM
Subject: Re: Forced Induction ?: X-Flow versus JH head


> Couple thought here:
> 1). You may be spinning your engine to 8000, but that is most certainly
not
> the norm. Plus with a G cam you're spinning it way over the power peak, so
> the only reason to spin it that fast is holding a lower gear through a
> series of corners. I'd be curious what Shaun Meze would have to say about
> this kind of RPM in an autocross!
> 2). "I can't believe that the 5500 rpm limit I've felt in
> > almost every hydraulic 8V motor is going to be the best for performance
> > issues." Yep! A stock ABA cam pretty much signs off at 5500 RPM.
Changing
> the cam to a 268 let's it make power to 6500 with light mods. IT ISN'T THE
> HYDRAULIC LIFTERS LIMITING IT TO 5500!!
> 3). "I'm sure the cross flow does flow better at low RPM's but it's
> > ultimate flow numbers will limited by valve float at a lower RPM's than
> the
> > solid lifter motor."
> JH head intake flows ~130 CFM, crossflow is ~150. With a stock head
> (either!) the power peak is unlikely to be higher than 6000RPM (and I
think
> we are talking about a stock head here aren't we?). The hydraulic lifter
is
> not a limiting factor at these kind of engine speeds  (since it is the
same
> lifter as in the 16V redlined at 7200, thanks Jason!) and the crossflow
> head, with a comparable cam, will make more power everywhere.
>
> So, I guess the question that has to asked is; Why are YOU turning your
> engine to 8000 RPM when it has no power there?
> And I guess the second question is; If a hydraulic lifter will support an
> engine speed more than 1000 RPM past the power peak, how is it a detriment
> to the original suggested application?
>
> Dan
>
>
>
> ----- Original Message -----
> From: Alan Stamper <scirocco-al@insight.rr.com>
> To: Scott F. Williams <sfwilliams@comcast.net>; scirocco
> <scirocco-l@scirocco.org>
> Sent: Monday, February 17, 2003 6:23 PM
> Subject: Re: Forced Induction ?: X-Flow versus JH head
>
>
> > "This is totally true. However, how fast do you suppose you can spin
these
> > engines of ours? In stock form, our heads are capable of higher rpms
than
> > the bottom ends. Furthermore, the VW ECUs stop all the fun way before
the
> > head spins itself to death. So, again, the performance difference for
> street
> > engines is minimally effected by the lifter type."
> >
> > I think that's way off base.  My car with the stock bottom end has
140,000
> > miles on it turns 8000 all the time.  It's been an auto-x car for over
12
> > years and until recently was run 15 to 25 times a year.  It has a G in
it,
> > valve springs and a light clean up on the head.  The factory ignition is
> > gone and has a programmable unit.  It's a 84 so it had no rev limiter
from
> > the factory any way.   After years of abuse and the bottom end never
have
> > being touched it produces 168 PSI on the compression test an has less
than
> 4
> > PSI difference between any of the cylinders. Oil pressure at all rpm's
is
> > still excellent with the older style low volume oil pump.   I launch the
> > thing at 5000 RPM at every run and at on time had the rev limiter set at
> > 8750, which it would hit if I kept my foot in it long enough.  There was
> no
> > extra power there but different course layouts forced me to stay in it
> that
> > long.
> >
> > I've also never seen or heard of any competitor having any issues with
the
> > bottom half of their motors.  Ever.  I have heard several hydro cars
> tapping
> > after hard runs from their lifters deflating though.
> >
> > I'm going to stick to my assertion that the JH head would be the better
of
> > the two choices.  I can't believe that the 5500 rpm limit I've felt in
> > almost every hydraulic 8V motor is going to be the best for performance
> > issues.  I'm sure the cross flow does flow better at low RPM's but it's
> > ultimate flow numbers will limited by valve float at a lower RPM's than
> the
> > solid lifter motor.  I will also give you the fact that you can get a
> turbo
> > to fit those characteristics and make more torque and HP at lower RPMs
> than
> > the solid lifter set up, but I still say the high RPM motor with the
> correct
> > turbo will smoke the hydro motor in the long run.
> >
> > Alan
> > ----- Original Message -----
> > From: "Scott F. Williams" <sfwilliams@comcast.net>
> > To: "scirocco" <scirocco-al@insight.rr.com>; "scirocco"
> > <scirocco-l@scirocco.org>
> > Sent: Monday, February 17, 2003 4:43 PM
> > Subject: RE: Forced Induction ?: X-Flow versus JH head
> >
> >
> > > >  Yes, but less RPM = less exhaust gas velocity and less efficiency.
> > >
> > > First of all, says who? Since when does higher rpms automatically =
> > exhaust
> > > gas velocity or more efficiency? And, what type of efficiency are you
> > > referring to, anyway? Frictional losses increase with the rpms, for
> > > instance. That certainly ain't going to help with a blanket term
called
> > > "efficiency". If the head or exhaust can't flow at 5k rpms, they
> certainly
> > > aren't going to make more power at 10k rpms.
> > >
> > > Practically speaking, a street-driven engine with solid lifters has
> hardly
> > > any rpm advantage over one with hydraulic lifters. Now, if we're
talking
> > > about race engines, that's different. But, there's much more to making
> > power
> > > at sky high rpms than just the lifters.
> > >
> > > >  Also expecting the turbo to produce power over a shorter RPM band
> would
> > > > probably increase turbo lag.
> > >
> > > Um... no! Getting a *properly-sized* turbo to produce power over a
more
> > > narrow RPM band will DEcrease so-called turbo lag. All turbos start
> > spinning
> > > from zero rpms. However, a turbo that is expected to perform at very
> high
> > > rpms will be bigger (or bigger A/R ratio) and will take that much
longer
> > to
> > > spool.
> > >
> > > So, throw in a teeny scroll and that thing will boost *very* quickly.
It
> > > will also run out of steam (into the compressor surge zone) more
rapidly
> > > than the big unit. But, if you're only interested in sub-6k rpms, who
> > cares?
> > > Okay, consider the boost-generating characteristics of a 1.8T engine
> with
> > > K03 versus K04 turbo. Or, take a Garret T3 from a Saab 900 and then
> > compare
> > > it with a T3 from a 1st gen 300ZX. See what I'm saying?
> > >
> > > >  Having a larger RPM band to work with the and the correct gears in
> the
> > > > tranny will give you more of a window to drive the motor in rather
> than
> > > > just a window from around 2500 to 5500 RPM that
> > > > will be partially consumed by getting the turbo up to speed.
> > >
> > > This is totally true. However, how fast do you suppose you can spin
> these
> > > engines of ours? In stock form, our heads are capable of higher rpms
> than
> > > the bottom ends. Furthermore, the VW ECUs stop all the fun way before
> the
> > > head spins itself to death. So, again, the performance difference for
> > street
> > > engines is minimally effected by the lifter type.
> > >
> > > >  My .02 cents.
> > >
> > > We'll need a heftier deposit than that to open an account with this
bank
> > of
> > > knowledge. ;^)
> > > --
> > > Scott F. Williams
> > > NJ Scirocco nut
> > > '99 Subaru Impreza 2.5 RS
> > > Mazda 323 GTX turbo "assaulted" vehicle
> > > Golf GTI 16v "rollycar"
> > > ClubVAC: "Roads found. Drivers wanted."
> > >
> > > ----- Original Message -----
> > > From: Scott F. Williams
> > > To: scirocco
> > > Sent: Monday, February 17, 2003 11:14 AM
> > > Subject: RE: Forced Induction ?: X-Flow versus JH head
> > >
> > >
> > > "Scirocco" wrote:
> > > > I'd stick with the JH head.  What you would gain from the cross flow
> > > design you would more
> > > > than loose from the hydraulic lifters.
> > >
> > > The  hydraulic lifters are only a liability at very high rpms.
Spinning
> > the
> > > motor that fast isn't a requirement for a turbo motor. What's the
point
> of
> > > revving higher when increased volumetrica efficiency can be had by
> turning
> > > up the boost? The cross flow head is superior for turbo use because
of:
> > >
> > > a) flow reasons
> > > b) turbo fitment
> > > c) *much* less heat transfered to the intake manifold from the blazing
> hot
> > > turbo and manifold
> > >
> > > With all these factors considered, it is fairly evident that the cross
> > flow
> > > design provides far more benefits than whatever minor penalty the
> > hydraulic
> > > lifters impose.
> > > --
> > > Scott F. Williams
> > > NJ Scirocco nut
> > > '99 Subaru Impreza 2.5 RS
> > > Mazda 323 GTX turbo "assaulted" vehicle
> > > Golf GTI 16v "rollycar"
> > > ClubVAC: "Roads found. Drivers wanted."
> > > -
> > >
> > >
> > >
> >
> >
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>
>
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