Forced Induction ?: X-Flow versus JH head

[jdbubb@ix.netcom.com (Dan Bubb)]

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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