[DeTomaso] CR, Detonation, and water injection

Art Stephens artstephens at charter.net
Fri Oct 5 19:33:27 EDT 2007 

Thank you Dan,
     I just posted some updated info on the Cleveland forum about a change
in plans. Scat is going to swap my flat top pistons for dished (16cc). I am
now planning to zero deck the block and have put a hold on the head order
until I know for sure what size combustion chamber I want.  By the way,  the
combustion chambers can be viewed at www.chiheads.com

Art


----- Original Message ----- 
From: "Daniel C Jones To: detomaso at realbig.com List-Subscribe:"
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Subject: Re: [DeTomaso] CR, Detonation, and water injection


> See if you can get a picture of the 74cc chambers.  If they left a decent
> quench pad, you can zero deck the block and use the headgasket to set the
> quench distance.  That will increase your compression but will actually
> be less likely to detonate (assuming the quench pad is still there.
> I'll need to run the numbers to see what the compression difference to
> be able to make a guess at the power difference.  Alternatively, you can
> see if they will let you change the order on the heads and then have your
> pistons machined with a d-dish.
>
> Dan
>
> On 10/3/07, Art Stephens <artstephens at charter.net> wrote:
>> Dan,
>>
>>    Knowing what I think I know now,  it sounds like I should have
>> ordered,
>> my new heads with small combustion chambers,  dished pistons and a zero
>> deck
>> block?  I already have my forged Scat rotating assembly with flat top
>> pistons for the new 408 stroker.  I have ordered my CHI 3V heads with the
>> large 74cc chambers and the plan is to have the piston .035 in the hole
>> to
>> keep the CR down to 10.0:1.  How much do you think this will hurt me from
>> a
>> power and detonation resistance stand point?
>>
>> Art
>>
>>
>>
>> ----- Original Message -----
>> From: "Daniel C Jones" <daniel.c.jones2 at gmail.com>
>> To: "DeTomaso Forum" <detomaso at realbig.com>
>> Sent: Wednesday, October 03, 2007 2:34 PM
>> Subject: Re: [DeTomaso] CR, Detonation, and water injection
>>
>>
>> > Mad Dog asked me to comment on the compression discussion...
>> >
>> >> this is what I am thinking;  I go with the CHI 3V aluminum heads with
>> >> the
>> >> 74cc 4V chambers.  It looks like these heads coupled with SCAT's 408
>> >> stroker
>> >> kit including flat top pistons should give me 10.01:1 CR.  It may be a
>> >> little on the conservative side but I do have other things to do
>> >> besides
>> >> swapping engines and other things I can spend that money on :-)).
>> >
>> > It's better to have a small chamber head with a generous quench pad and
>> > a
>> > short quench distance.  That will allow you to run a higher compression
>> > ratio on the same octane fuel.
>> >
>> >> Anybody out there running this combo?  I'm guessing most of the
>> >> guys running the CHI's have the smaller chambers and more than 10:1
>> >> CR?
>> >
>> > Actually most of the guys are running the dished pistons with the
>> > smaller
>> > combustion chamber to get in the 10:1 range (or more).  A smaller
>> > chamber
>> > means a shorter distance for the flame front to travel and less time
>> > for
>> > it to detonate.  Kaase sleeved my XE block down and milled his heads
>> > down
>> > to further reduce the bore diameter and chamber volume.  He was able to
>> > run 13:1 on pump gas (and win the EMC in the process).
>> >
>> >> I've been running 10.2:1 with SVO A-3 heads, an SVO hydraulic cam &
>> >> Rhodes
>> >> lifters, a tuner Holley 700 DP and 34 degrees total ignition
>> >> advance..... since 1992. I occasionally use 89-octane but if the car
>> >> will
>> >> be flogged or for going over mountains rapidly, I use 92 octane.
>> >
>> > The SVO hydraulic cam that Jack mentions has little overlap and the
>> > Rhoads
>> > lifters bleed down further increasing cylinder pressure.  With more cam
>> > overlap, a higher compression ratio could be tolerated.  Alternatively,
>> > a lower octane fuel could be run with the same compression ratio.
>> >
>> >> So is 92 really too low for good performance at those CRs?
>> >
>> > No.  A 351C with flat top pistons and closed chamber heads will run
>> > just
>> > fine on pump gas with a bit of cam overlap and a proper quench distance
>> > (zero deck with a 0.040" gasket is fine).
>> >
>> >> Couldn't hear, feel, or otherwise detect the detonation.
>> >
>> > On a dyno, you'll notice a power drop when increasing the ignition
>> > lead.
>> >
>> >> Does anyone know if there are easy ways to detect high RPM detonation?
>> >> Seems like it would be a lot harder to detect than the obvious low RPM
>> >> "ping".
>> >
>> > Keep an eye on the spark plugs for fleck of aluminum.  Inspect under a
>> > lighted magnifying glass.
>> >
>> >> A later experiment on a chassis dyno (with new block and a Holley
>> >> carb)
>> >> demonstrated significant torque drop off at 5500rpm when I put the
>> >> timing
>> >> back in the more-advanced state.
>> >
>> > You want to use the minimum best spark timing.  If power levels off at
>> > 28
>> > degrees total and holds until 34 degrees total then drops off, you want
>> > to
>> > use 28 degrees total.  Glen's mild 408C made best power at 28 degrees
>> > total.
>> > Open chamber heads need more spark advance to make best power but also
>> > are
>> > less tolerant to higher compression ratios.  Vizard's testing showed
>> > that
>> > multi-strike CD ignitions allow the same power with a few degrees less
>> > timing on engines with open chamber heads.
>> >
>> >>    The 377 was supposed to be about 10:1 when new.  After crunching
>> >> some
>> >> numbers,  it looks like the CR could have been as high as 10.5:1 after
>> >> milling the .020 off the heads.
>> >
>> > If you were running closed chamber heads, you would need dished pistons
>> > to get that sort of compression ratio?  Was that the case?
>> >
>> >> So, if my CR was actually over 10:1, I'm guessing it was probably
>> >> going
>> >> to detonate, under the circumstances, even if I had no oil getting
>> >> into
>> >> the combustion chambers?
>> >
>> > Not necessarily.  Many people are running 10+:1 compression ratios
>> > without
>> > detonation.  I think the oil combined with an improper spark curve is
>> > what probably did you in.
>> >
>> >> While the static compression will drop if the valves stay open longer,
>> >> I don't think that implies the same happens at high RPM when VE may
>> >> exceed 1 on a well designed engine.  If high RPM detonation is the
>> >> problem (which I think Art suspected for his engine) you may be
>> >> stuffing
>> >> over 100% of the cylinder volume into the engine.
>> >
>> > Correct.  However, if you simply shift the torque curve up the RPM
>> > band,
>> > you shouldn't be any more prone to detonation (less actually).  Same
>> > cylinder pressure (torque) shifted higher into the RPM range means more
>> > power.
>> >
>> >> More advance had been making low and mid range throttle response
>> >> better.
>> >
>> > Sounds like you needed a curve which brought the advance in earlier but
>> > kept the total the same.  Curving a distributor in the car is a real
>> > pain
>> > in the posterior.  MSD and others make timing computers that allow this
>> > to be done electronically which is a bunch easier.
>> >
>> >> The point is you can make BIG power with a durable low compression
>> >> engine and pump gas.
>> >
>> > Low compression engines can be just as close to the verge of detonation
>> > as a higher compression ratio engine.  Cam design is the key.
>> >
>> >> Also, aluminum heads usually increase the liklihood of detonation.
>> >
>> > I've never heard that.  Conventional wisdom is the opposite is true.
>> > The ideal gas law (PV = gRT) implies lower temperatures result in
>> > lower cylinder pressures which means less detonation risk.  Aluminum
>> > heads are thought to run cooler, so are less likely to detonate.
>> > The flipside is you need a bit more static compression to make the
>> > same power.
>> >
>> > I like to run all the compression I can safely get away with.
>> > Compression
>> > lifts the torque curve across the RPM range.  10 ft-lbs of torque
>> > increase
>> > across the RPM band is worth a bunch more acceleration than a 10 HP
>> > increase
>> > at the top end of the RPM band.  Compression also allows you to offset
>> > the
>> > loss of low end torque when running a larger overlap cam.  Compression
>> > also
>> > increases fuel efficiency.  I know of people running 12:1 compression
>> > on
>> > pump gas but it takes a carefully coordinated engine package.  Also,
>> > there
>> > is a point of diminishing return.  Going from 11:1 to 12:1 compression
>> > ratio
>> > is worth a lot less than going from 8:1 to 9:1.  Mad Dog runs 11.4:1
>> > with
>> > his aluminum headed stroker.  I went with 10.75:1 on mine for a bit
>> > more
>> > margin with bad gas or hot weather on my street car.
>> >
>> > Vizard has published a couple of good articles on compression.  A
>> > summary
>> > of
>> > things to do to run high compression on pump gas is listed below:
>> >
>> > 1. Feed cold air to the induction
>> > 2. Keep water as cool as possible (170-180 degF)
>> > 3. Keep the air cool in the intake ports
>> > 4. Put a heat-reflective shine on the outside of the intake manifold
>> > 5. Polish the chamber side of the intake valve to reflect heat or coat
>> >   the valve with a thermal barrier
>> > 6. Minimize heat transfer through the common exhaust/intake port wall
>> > 7. Keep fuel temperatures down (cool can)
>> > 8. Run with plugs a little colder than the minimum required
>> > 9. Use an ignition system that is gross overkill
>> > 10. Utilize as large a spark plug gap as possible
>> > 11. Use no more ignition advance than is necessary
>> > 12. Maximize quench action
>> > 13. Minimize head chamber volume
>> > 14. Use flat-top or dished pistons if possible
>> > 15. Minimize under-hood exhaust heat--use coated headers
>> > 16. Do not ram in but vent out hot air through hood vents
>> > 17. Run knock sensing ignition retard
>> > 18. Inject water and alcohol mix under high loads
>> >
>> > Compression is good but detonation is bad (MMkay).  Too much timing
>> > always
>> > feels best seat-of-the pants but what you want is the least amount of
>> > timing
>> > that doesn't cause a power drop-off.  This is known as MBST (minimum
>> > best
>> > spark timing).  If you are detonating, it will hammer the rod bearings.
>> > If the bearings show distress the crank, rods, and pistons will all
>> > need
>> > to
>> > be checked.  Detonation is death on bearings.  They'll lose their crush
>> > and
>> > can spin.  If this happens at speed, you lose a rod out the cylinder
>> > wall
>> > and generally destroy the engine, not to mention the coolant and oil
>> > that
>> > finds its way under the tires.  If the clearance has opened up enough,
>> > there
>> > may be an oil pressure loss but this can be masked by the pressure
>> > relief
>> > spring.  You should be able to see detonation on the spark plugs.  They
>> > make
>> > a lighted magnifying glass to check spark plugs for the little flecks
>> > of
>> > aluminum (from the piston tops) that get transfered to the plugs under
>> > detonation.
>> >
>> >>    I had the same Spearco system on my 70 MACH1 and had the same
>> >> durability
>> >> issues as you did.  The aluminum jet disintegrated and the motor gave
>> >> up.
>> >> The system did as claimed though in preventing pinging.
>> >
>> > Noted 351C racer Animal Jim is a big fan of that system.  My dad used
>> > one
>> > on a 12.5:1 427 side-oiler stroker.  He had no durability issues but he
>> > used distilled water and alcohol.  We had a still in the basement and
>> > it
>> > did require periodic cleaning to remove the deposits.
>> >
>> > Dan Jones
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