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You think this is why that one set of heads from Glidden you mentioned a while ago were so big and lazy? To reduce pumping losses?
Is the velocity being too high causing reversion?
No, its instead causing increases in pumping losses
as its taking more energy to create the too high Port Velocity
it was a Nitrous Engine with supposedly a relatively short Rod Ratio ?You think this is why that one set of heads from Glidden you mentioned a while ago were so big and lazy? To reduce pumping losses?
Bret
In light of recent discussions I thought this worth reviving.maxracesoftware wrote: ↑Thu Mar 10, 2005 5:09 pmWhat "application" are you working on and what's the Engine Specs like Bore, Stroke, Rod C-C, RPM range, CR, etc. along with Cam Specs, and ET/MPH goals ??? What Dyno HP/TQ numbers so far ?What would be the cause of a port showing good results on the bench but not on the engine?Would it be because the valve eventually starts to close very quickly?Or maybe the valve timing is reduced considerably in a high rpm situation?
along with Flow Numbers and valve sizes ??
just for Research , i placed a small 1/8" buildup of Epoxy on the Short Turn and gained about 3 PerCent more Flow on a FlowBench...also did that to help make the Port legal in CC volume.....
Results=> Lost Mid to Top End HP/TQ in NHRA SS Race-Hemi
the FlowBench CFM numbers can lie to you in one respect and you must use a Pitot Probe to verify what you did does not create too much velocity at the wrong spot in a Port.
another example was a B/ED 346 cid Engine years back making
761 HP on my Dyno....removed the Cyl Heads and again tried placing Epoxy on Short Turn apex..again saw a Flow gain of approx 3.5 PerCent,
re-Dyno tested Engine and lost 17 HP to 744 HP...luckly we had 5 guys
helping that day, popped the Cyl Heads off , took apart the Heads, with a sharp Hammer strike on a long screwdriver, popped most of the Epoxy off the Short Turns and finished up with a Cartridge Roll ....assembled the Cyl Head backup and had the Engine Dyno testing a few hours later, ...made the 761 HP back like it was previously .
a "Saying" thats popular is =>
"Make it Flow the most CFM you can, at the smallest Port Volume"
Sounds good, but if taken too far, can be a Torque and HP disaster.
Example=> NHRA SS/IA #041x SBC Chevy heads 1.940/1.500 165.0 CC
One pair of #041x Heads were extensively Pitot Probed and all dead Flow areas and any area that could be built up and not show a Flow Loss were epoxied up...so what you wound up with was one pair of #041x Heads that on a FlowBench flowed just about the same exact Int flow numbers
as another baseline pair of #041x heads, both pairs had same exh port flow numbers and same chamber CCs, and used same valves swapped in each pair. About the same Flow specs as you could achieve, but very different Intake Port Shape and very high Pitot Probe velocities in the epoxied port head -VS- other pair of #041x heads.
From previous experience i knew the epoxied Heads should be a disaster because Pitot velocities were way too high at the pushrod area and all along the Floor and Short Turn apex...but the FlowBench showed almost the same exact Flow numbers between both pairs of #041x heads.
Dyno Test results @600 RPM/SEC were lost +105 HP at 7200 RPM,
and the biggest surprise was that all that very high velocity
made a little LESS peak Torque ! it was thought that atleast with all that velocity the Peak Torque numbers would be better,
but only 4000 RPM and lower were the TQ numbers slightly better, and 4500 RPM on up , TQ/HP numbers were progessively a disaster.
DragStrip test => RaceCar went from baseline 10.00's-to- teens to 10.60's ET with the very hi-velocity pair of 041x heads
heads were sold to another SS/IA racer "as is" and went 10.80's in his car
and eventually back to 10.60's with Car combination work.
Removed those Heads, completely removed all the previous epoxy work,
placed new epoxy into different port shape, reduced port velocities to acceptable levels while keeping CC legal, wound up with same Flow Numbers as before, but with acceptable port velocity.
Mostly the pushrod area velocity was the greatest problem in these heads.
DragStrip results=> 10.20's immediately, later ran 10 teens .
"Make it Flow the most CFM you can, at the smallest Port Volume"
...if taken too far , can be a disaster .
Pitot Probing the differences in Velocity between most 23 deg SBC Heads -VS- most Big Block Chevy rect port Heads...you'll notice right away that most BBC heads have much "slower" velocity , yet usually make the same amount of HP/TQ per 1 CFM of Flow , and make the correct amount of Torque per CID Ratio for Engine size and Compression Ratio as the much higher velocity SBC head engines.
i'm not saying you should slow down Port Velocities in all Heads,
but instead saying that if you make some spots in Int port have too high velocity , it will hurt you more than that same area with slightly slow velocity.
air velocity is not infinite in speed.
it requires a certain amount of cross-sectional for a given Engine cid size
and RPM operating range.
Maybe, are you testing with a manifold on it?
Not sure you could accurately probe that part of the head with the intake attached, I may get crazy and cut the intake up so I can look at it in pieces.
Right, I don't think you can draw any meaningful data about a port, especially the first half of it, without a manifold on it.GARY C wrote: ↑Sun Sep 08, 2019 5:36 amNot sure you could accurately probe that part of the head with the intake attached, I may get crazy and cut the intake up so I can look at it in pieces.
I have tried to probe with the intake on by making a probe "per say" that matches the couture of the runner, using the same probe with and without the runner for equal comparison from what I can access while keeping the probe in line with the airflow I am not seeing a big difference.SchmidtMotorWorks wrote: ↑Sun Sep 08, 2019 1:45 pmRight, I don't think you can draw any meaningful data about a port, especially the first half of it, without a manifold on it.
Bow Tie raised runner cut to fit standard 23 degree port, the clay on the floor is to mimic the epoxy in the port entry. The roof of the head has been raised some.
IIRC that manifold flows about parallel to the deck (or higher), looks like you have your work cut out for you to bring that intake port up to that angle.
It's an RHS 200cc port, its about 2 sq inch at the flange and 1.95 at the pinch, the cut away head does not have the roof raised as much as the actual head I am working on.SchmidtMotorWorks wrote: ↑Mon Sep 09, 2019 1:04 amIIRC that manifold flows about parallel to the deck (or higher), looks like you have your work cut out for you to bring that intake port up to that angle.
What head is that, it looks similar to a AFR 235 (or whatever the number is with the arched roof).
Probably to some extent but if you are comparing probe reading before and after a change then the probe is always there, the probe does not seem to have an effect on the cfm # when its in line with the air stream. The make shift probe I am using for the back of the bowl and some intake testing reads a little different the the actual J probe but I am only looking for changes due to modification and not concerned about the actual number.
