Forced Induction ?: X-Flow versus JH head

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

"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."
> -
>
>
>