[DeTomaso] Dynomation as a Dyno Lie Detector

Mon May 17 12:28:29 EDT 2010

Will,
I remember when I first learned about the very minimal gain in horsepower by 
increasing the compression ratio,  I was amazed!  It does seem that the risk 
of detonation would not normally be worth the small performance advantage 
for many of us.

Art

----- Original Message ----- 
From: "Will Demelo" <wdemelo at cogeco.ca>
To: "Daniel C Jones" <daniel.c.jones2 at gmail.com>; "Pantera REALBIG forum" 
<detomaso at realbig.com>
Sent: Saturday, May 15, 2010 5:15 PM
Subject: Re: [DeTomaso] Dynomation as a Dyno Lie Detector

> Increasing the compression from 9.8:1 to 11:1 only made 6 or 7 more
> horsepower? I would have thought that more compression would have made 
> more
> power. Why would someone take the chance on detonation for only 7 more hp?
> Will
> ----- Original Message ----- 
> From: "Daniel C Jones" <daniel.c.jones2 at gmail.com>
> To: "Pantera REALBIG forum" <detomaso at realbig.com>
> Sent: Saturday, May 15, 2010 6:37 PM
> Subject: [DeTomaso] Dynomation as a Dyno Lie Detector
>
>
>> That suspicious Powerblock 351C buildup has re-surfaced in March 2010
>> issue of
>> Muscle Car Review magazine in an article entitled "Cleveland Hall of
>> Fame".  The
>> article has a picture of the "finished beast" without distributor, water
>> pump,
>> balancer, thermostat housing, etc. and claims it was dyno'd at 466 HP and
>> 471
>> ft-lbs of torque but no RPM values are provided.  It also claims a
>> compression
>> ratio of 9.8:1, though the Edelbrock Performer RPM 351C-2V cylinder heads
>> are
>> nominally 60 cc's and Keith Black KB177 flat top hypereutectic pistons
>> are used.
>> Those pistons have a 1.67" compression height and valve notches of 2 cc's
>> and
>> are listed by Keith Black as providing 11.07:1 compression ratio with
>> 62 cc heads.
>> I ran it through a compression calculator that I wrote, assuming 60 cc
>> chambers
>> and a Fel Pro headgasket of 0.041" compressed thickness and got an 11.1:1
>> compression ratio.  Not even close to 9.8:1.
>>
>> The article states the camshaft was a Comp Cams part number 32-000-5 
>> which
>> is
>> a generic core part number.  I believe that to be a typo and the part
>> number is
>> actually 32-600-5 which is the smallest 351C Thumpr cam:
>>
>> http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=1477&sb=2
>> Grind Number 279TH7
>> Thumpr Series hydraulic flat tappet, high performance street, stock
>> converter ok,
>> best with 2000+ converter and gears, choppy/thumping idle, 2000-5800 RPM
>> range
>> 278/296 degrees advertised duration
>> 226/241 degree @ 0.050"
>> 107 degrees LSA, installed on an intake centerline of 102 degrees
>> 0.506"/0.493" valve lift
>> 0.300"/0.291" lobe lift (appears to be a typo on the lobe lift or
>> assuming short
>> than 1.7 rocker ratio)
>>
>> 0.006" valve timing is given as:
>>  int open  39 BTDC
>>  int close 67 ABDC
>>  exh open  80 BBDC
>>  exh close 45 ATDC
>>
>> The specs listed in the article are hydraulic flat tappet with:
>>
>> 278/296 degrees adv. dur., 0.491"/0.476", 107 LSA
>>
>> but the lift assumes the 1.7:1 rocker ratio of the Comp Cams Magnum
>> roller rockers
>> used in the build.  Still, the lift numbers don't quite match up to
>> either the lobe
>> or valve lifts from the Comp Cams card.  If you assume the valve lift
>> in the Comp
>> card is with 1.73:1 rocker ratio, the lift with 1.7:1 would be
>> 0.497"/0.484".  If
>> the lobe lift is correct on the Comp cam card, the lift would be
>> 0.510"/0.495".
>> Let's be generous and use the largest lift and assume cam specs of:
>>
>> 278/296 degrees adv. dur., 0.510"/0.495", 107 LSA
>>
>> Edelbrock cylinder heads 2.05" 1.60"
>>
>> http://www.edelbrock.com/automotive_new/mc/cylheads/ford/cle_perf_rpm.shtml
>>
>> Lift     Int    Exh
>> 0.100  058 054
>> 0.200  120 105
>> 0.300  180 138
>> 0.400  227 151
>> 0.500  260 161
>> 0.600  265 165
>>
>> Flow numbers as tested on Edelbrock's SuperFlo SF-1020 flow bench.
>>
>> Inputting everything optimistically and using Edelbrock claimed flow data
>> with open headers and 9.8:1 compression ratio:
>>
>> 422 HP @ 5000
>> 470 HP @ 4000
>>
>> Increasing compression to 11:1:
>>
>> 429 HP @ 5000
>> 476 ft-lbs @ 4000
>>
>> With TMeyer independent flow bench data on Edelbrock 2V heads and 9.8:1:
>> 416 HP @ 5000
>> 472 ft-lbs @ 4000
>>
>> With cylinder head flow from Cleveland Confidential magazine article:
>> 419 HP @ 5000
>> 471 ft-lbs @ 4000
>>
>> In my experience, when fed accurate data (actual cam timing specs, flow
>> bench
>> data from Dave's conservative bench, minimum/maximum port areas, etc.),
>> Dynomation has been close on the HP but optimistic by 20 to 30 ft-lbs
>> on torque.
>> The above simulation is likely optimistic since the minimum port sizes 
>> are
>> assumed to be the same as an unported iron 2V head.  The simulation is
>> quite
>> sensitive to the minimum intake port area.  A slight increase in that can
>> drop
>> the HP prediction by 10 HP.  The simulation is less sensitive to larger
>> minimum
>> exhaust areas (at least for a relatively large port engine like a
>> 351C).  In any
>> case, I'll buy the Power Block engine made over 400 HP (assuming it was
>> ever
>> dyno'd which I see no evidence of) but not the claimed 466 HP.
>>
>> As a point of reference, Edelbrock claims:
>>
>> 456 HP @ 6000 RPM
>> 445 ft-lbs @ 4500 RPM
>>
>> for a 4.04" bore by 3.7" stroke, 9.75:1, Cleveland with RPM Air Gap 
>> intake
>> and flat tappet cam with specs:
>>
>> 312/322 degrees advertised duration
>> 234/244 degree @ 0.050"
>> 112 degrees LSA, installed on an intake centerline of 107 degrees
>> 0.571"/0.589" valve lift
>> 93 degrees overlap (seat)
>> 0.050" valve timing is given as:
>>  int open  10 BTDC
>>  int close 44 ABDC
>>  exh open  59 BBDC
>>  exh close 5 ATDC
>>
>> With the above entered into Dynomation, along with Edelbrock's claimed
>> flow bench data and 750 CFM of carb flow, the predicition is:
>>
>> 434 HP @ 5000 RPM
>> 460 ft-lbs @ 4600 RPM
>>
>> With 800 CFM of carb flow, that increases to:
>>
>> 444 HP @ 5600 RPM
>> 463 ft-lbs @ 4600 RPM
>>
>> for the headers assumed.  The Edelbrock numbers are much more believable.
>> The Power Block build reads like fiction.
>>
>> Dan Jones
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