some of what you posted is true ,Scotthatch wrote: ↑Fri May 04, 2018 11:37 amIf there is a big difference in dyno HP and track then need to look at the car setup ... gear ..converter..... question becomes where is it not right at the track to where it should be ... also loading can change tune ... dyno does not load the same as in the car do may have to adjust the tune
however , what MELWAY posted is referring to is like this scenerio :
the Race Car's ET and MPH is slower than it is calculated to Run
or in reverse-engineered = the ET Slip Data Feet incrementals / MPHs do not matchup to the Dyno numbers
its not a Race Car parts combination problem ,
instead its an Intake Port FPS Problem showing up ,
and there's nothing you can change or fix on the RaceCar to make it correlate properly !
the ONLY Fix is to correct the Intake Port CSA FPS speed problem
this CSA FPS Speed problem will show up more in 3-Speed Auto/Converter Cars than 2-Speed Powerglides
and in 4 or 5 Speed Manual/Clutch Race Cars even more !
the Intake Port FPS down the Dragstrip is changing drastically faster than in a 300 or 600 RPM/SEC Dyno Pull ,
especially in 1st Gear , so there's greater "Intake Port Pumping Choke" TQ and HP losses happening down the Dragstrip .
So MELWAY sees AFR245npp Heads make 750hp at 7400 RPM on his Dyno
but it does not accelerate down the Dragstrip or correlate back to 750 HP
the Intake Port CSA is too fast ... its only going to match the Dyno in high-gear towards the end of the Dragstrip
where its way too late in time and distance to correlate back to 750 Dyno HP
... that 434SBC engine is probably off by 20-30+ HP or more from the Dyno , in 1st Gear and early parts of high gear Feet distances
another similar scenerio :
Chrysler 360cid NHRA SuperStocker (371cid Legal cid ) with a maximum Intake Port Volume CC's = 162.0 CC
so you maxout the Intake Port and make it hold about 161.0 cc to make sure it checks out under 162.0 Legal max CC's
at 161.0 CC Int Port CC ( Intake Port CenterLine Length in SS form = 4.94800 inches length )
1.880 Intake Valve OD = can and will Flow 285 CFM @ 28" inches on my Flowbench
or i can make it Flow using another Shape = 255 CFM or 265 CFM with still another Port Shape
all 3 Shapes still hold 161.0 CC Int Port Volume , but Flow test different CFM and have very different local CSA FPS velocities
the 285 CFM Ports on the Dyno or down the Dragstrip does not make any TQ or HP or ET or MPH differences
-vs- the 265 CFM Ports
and a 255 CFM is within a few HP and TQ of the 265 CFM Port shapes
the 285 CFM in 161.0 CCs and thru 4.9480" length is just way too fast to make anymore TQ or HP
and its a "Miracle" it does not actually loose Peak HP and higher RPM HP
... very luckily that Chrysler Chamber and Intake Port shape combo can handle very lean Air Fuel Ratios
whereas the SBC Chevy SS Ports cannot !
255 to 265 CFM Chrysler #308 or #576 casting at 161.0 CC 1.880/1.660 valves can make 561 Peak HP at 6900-7100 RPM
485-487 Peak TQ with 9.459:1 CR + ThermoQuad and run as fast as
9.69 ET 137+ MPH in GT/CA and 9.72 ET in GT/DA
thru the years i've had the very same SuperStock Chrysler Customers back-to-back same Day
Dyno test same 162.0 CC Ports 1.880/1.600 #576 castings from other Head Porters
on the Flowbench ... CFMs were very close to identical on Int and Exh Ports
but Pitot Probe FPS in certain areas were very different !
on the Dyno , the other #576 castings that were too fast , yet Flow tested the same CFMs, were down -20 HP or more at other RPMs ,
yet , down the Dragstrip it runs the ET and MPH like its down -40 HP or more
so that down the Dragstrip with a 3-Speed Auto/Converter in a NHRA Record GT/CA setting Race Car its 2 Tenths and almost 4 MPH slower
( it should have only slowed down maybe 1 Tenth ET and maybe 1.5 MPH , but it slowed down more than the Dyno showed )
and theres nothing you can do to that Race Car to improve its performance any further ,,
the Head's Intake Port too fast FPS making it not correlate back to the Dyno 600 RPM/SEC Tests properly .
its exactly what MELWAY is describing in his Post .
the Intake Port CSA FPS velocity is drastically changing way too fast in an actual Dragstrip Run
causing Flow separation + Air-Fuel separation + Pumping Choke HP loss
that does not show up at 600 or 300 RPM/SEC Dyno Test Rate .