Mike
As previously expressed not much need to rev past max HP & max Torque.
But you
don't need an engine dyno you can use a Chassis Dyno. Go to
http://www.dynojet.com click on automotive section then search for one
in your
area. We are in Ft Myers, FL so probably too far away.
Best Regards
Phil 72 Elan type 45/26R Vintage Racer (car & Driver)
Mike Cobine wrote:
> ----- Original Message -----
> From: "Mark Haynes" <haynes386@netzero.net>
>
> > I have a question for those of you who have experience with testing an
> > engine's limits (hopefully I can avoid finding the upper limits for
> > mine).
> > How do you establish an upper rev limit for an engine? and what
> > factors determine where you set your rev limiter?
>
> First, it does no good to rev an engine higher than it produces horsepower,
> so you need to figure where power is made and where it falls off. Usually
> you need the engine on a dyno to find this out. The advantge of most
> aftermarket cams for small block Chevys is that the manufacturer gives a
> power range for the cam. This is a good start. I don't know if you have
> info like that.
>
> How much oil pressure and volume do you have? If you dont' have enough to
> float everything in oil, then that is your limit. Basically, you can spin
> as fast as you want if you have sufficient oil pressure to keep everything
> floating. Touch metal once and it is all over. But spinning alone is not
> all.
>
> Where do your valves float? How much spring pressure do you have? This
> determines how fast you can spin until undesireable stuff happens on top.
> The best that happens is that it just disrupts the fuel/air mixture flow and
> the bad is it lets a valve hang a bit too long and piston slaps it. The
> worse is that it lets the head of a valve snap off and you can guess the
> rest.
>
> Balance is critical. Find someone you fully understands balancing and for
> high revving engines. With the 9000 limit on the 302s, we even balanced the
> valve train, rockers, retainers, valves, etc. Don't forget timing gears.
> Anything that moves can cause a mismatch and that could create a harmonic
> that you don't want.
>
> Rod stretch happens with speed. The faster you throw that piston up, the
> harder it is to pull it back down on that intake stroke. Measure all rods
> with precision before running and on your first teardown, check to see what
> happened. If one stretches too much, a picton can slap a valve or the head
> and then it is history. Of course, downshifting to use engine braking also
> causes stretch, so don't.
>
> > Case in point is this...I have a '62 Austin XSP motor (built for
> > Formula Junior). It was the factory"cheater motor" for the 1100cc limit.
> > It's' built on the 948 base-crank has 1 3/4" journals, and 3.00"stroke,
> > it's cross-drilled and has flow restrictors in the oil passages. To
> > achieve the 1100cc's, the factory (Eddie Maher & co.) bored these motors
> > to 2.65"-giving a displacement of 1096cc. It's got the 1100
> > full-floating rods, but they're not lightened, and an AEA649 cam, and
>
> I hope I'm misreading this, but it sounds like you have oil restrictors in
> the pasages to the crank. I hope not, although I know nothing about these
> engines.
>
> With the SBC, we ran solid lifters and oil restrictors in the lifter galleys
> so that oil was concentrated on the lower end. In most SBC, we ran .0025"
> clearance and 60 psi with a high volume pump. With the 302, we were running
> 8500 and so .004" clearance with 85 psi from a high volume pump. With full
> floating rods, you need a lot of oil to float the pins and you don't do that
> by restricting crank oil.
>
> > all of the go-fast period parts. When I build it, How do I establish how
> > high to rev it?(and not blow it). I can't find anyone who used to race
> > them who remembers what they used for an upper limit. I know that the
> > 1275s have a tendancy to snap cranks,and I really don't want to do this
> > either.
> > I'm planning on putting it in my '62 Sprite, I know the 1275s will
> > eat me up,but $#%@ happens
> >
> > TIA, Mark Haynes
> > RMVR
>
> Put it together, run it 500 rpm over stock, take it apart. If anything
> shows anything bad from above, then that _IS_ your limit. If not, then go
> up another 500, run it, then take it apart. Check again for the bad stuff.
> Once you find bad stuff, back up 500 and that is the top.
>
> Don't reuse old bearings. You pull them out to check them, replace them.
>
> This is all general stuff, your mileage may vary.
--
Phil Babcock
The Dyno Shop, Inc.
Air Fuel Ratio Meters - Laser Alignment Tools - Dynojet Chassis Dyno
Race Set up - Auto Restoration
http://www.thedynoshop.net
mailto:phillipbabcock@att.net
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