intake port short turn radius 2

[NeilRoshier]

It would seem that (given single In valve per cyl, round ports, carb fed, semi-hemi CC engine) that the short turn radius prior to the valve should be as generous as possible to avoid shrouding. However is the a recognised minimum radii in such as circumstance or are there too many variables (in addition the small number I have mentioned)?
Secondly does the shrouding that occurs from too tight a short turn radius create more problems with wet flow (ie fuel in suspension with its associated mass and inertia) vs that of a dry flow as per flow bench testing.

 

[Marquis]

When I evaluate ports, quickly by inspection, I usually look at things such as the port throat area as a ratio to the bore area –as there is a good correlation of BORE shoruding relating to this number- I compare this to my emipirical database I have (classified!)-the biggest valves possible in the shallowest chamber ( for good efficient combustion from favourable surface to volume ratios)-isn’t always the way to go!
Secondly , as you correctly say, I look at the angle of attack of the ports- a nice profile diagramwith combustion chamber is usually helpful. Again, as you corectly say, the more generous the short side radius the better. The guidelines I use are to use 15 –20 mm radius as a minimum starting point for the normal range of SI cylinders/port sizes but in reality every case is individual and depends on its size and the local gas velocity- there can also be 3 D effects due to the shape . When you talk about “shrouding” I assume you’re refering to the flow breakaway due to a sharp short side radius turn and the shouding this might cause. This is easy to confuse with the BORE shoruding I just refered to originally. I’m about to undertake a porting job on a two valve shallow hemi.
I imagine you’re undertaking your work on your Fiat Abarth twin cam engine…Best of luck!

I’m not sure what to recommend for fuel suspension effects-for carb engines. I know that there were guidelines for SIZING of ports that had to consider fuel suspention in the old carb days along with all the other aspects we still have to consider today! I can only extrapolate that intake charge seeded with a suspention of fuel will be even more sensitive to too high a velocity and sharp bends,- as you want to avoid wall wetting and fuel droplets falling out of the main body of the charge.

 

[MaxRaceSoftware]

Secondly does the shrouding that occurs from too tight a short turn radius create more problems with wet flow (ie fuel in suspension with its associated mass and inertia) vs that of a dry flow as per flow bench testing.
========================================================

its not only possible but also Factual, that you can modify intake port short turn radius ..and see healthy increase in dry flow numbers ...but in live running engine
on dyno see HP/Torque decrease



Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[NeilRoshier]

Marquis thank you for the reply. You guessed correctly re the model/brand.I was considering modifying a series of ports and recording/comparing the results to a std port. This head was chosen as I have some knowledge of them, they are cheap and I would benefit from the results, and they have a poor (ie small in dia) short turn radius which leads to the turbulence that you described, particularly when a larger than std valve is used e.g. 46mm.
Mod 1 was to do a 'std' porting job of cleaning up the port, reshape the valve and 3 angle seats.
Mod 2 was to build up the floor of the port approx 15mm prior to the short turn radius (and approx 4-6mm of material added to the port floor) to increase the diameter of the radius and then to restore the port volume by removing the required material from the port sides.
Mod 3 was to raise the whole of the port roof approx 3mm and then fill in the floor the same amount
Mod 4 was to machine away a section of the port roof and the associated cam box and then insert a new ali tube port at an approx 18deg steeper angle or more if possible (the spring seat may be the foil for a greater angle).
Re the fuel in suspension, I was curious and wondered if the turbulent shrouding of the valves was more significant (in the disruption of) with the 'wet' flow vs that usually recorded with a dry flow on a flow bench. I shall ponder on your reply some more.
Larry it is a quandry that's for sure! Even though such port comparison was done long ago (and published) by D Vizard I thought that it might be worthwhile following it up and republishing the results. Certainly the broad concept is applicable to other engines and such old workhorses are still often used in 'club' level motorsport around the world.

 

[MaxRaceSoftware]

Mod 2 was to build up the floor of the port approx 15mm prior to the short turn radius (and approx 4-6mm of material added to the port floor) to increase the diameter of the radius and then to restore the port volume by removing the required material from the port sides.
======================================================

becareful..if you make air velocity too high
at Short Turn's apex , it can show you flow gains on FlowBench ..but TQ/HP Losses on Dyno or RaceTrack



Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[NeilRoshier]

Larry, thanks for that information, I shall keep it in mind. Do you feel that there is a potential avenue of modification unexplored?

 

[MaxRaceSoftware]

NeilRoshier,

5 angle intake seats
radius exhaust seats

purchase "J" type Pitot velocity probe for intake ports

http://www.maxracesoftware.com/Flow_Max_Intake_1.jpg

Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

 

[MaxRaceSoftware]

Peak_HP = Flow_CFM * .257 * Number_of_Cylinders

is estimated potential Peak HP to expect
you multiply .87 percent times cam's theoretical max lift , round off to nearest .050" in Flow Test, then see what CFM is at 28 inches

example=> .700" Lift cam
.700 Lift times .87 percent = .609" Lift
Flow head at .600" Lift , then take CFM at 28 inches and calculate HP potential with above formula

.257 Factor = for beginning engine builders

.285 Factor = would be for Professional engine builders with wet sump pans, lightweight rotating assemblies, low tension great sealing rings, deep oil pans, etc.

.300 to .310 Factor = Current ProStock Technology with dry sump, unlimited carburetion, Hi Comp Ratio, ultra lightweight rotating assembly, etc, max use of inertia/wave tuning, etc
(usually no better than .2980 efficiency)

all factors are just baselines
and "ALL" HP estimations are baselined for Engine Dyno acceleration test rate of 600 Rpm/Sec

major errors will be from no 2 FlowBenches or Dynos read the same, or if Dyno tests were Steady-State or Step-Test

and there are people with bogus FlowBenches and bogus Dynos out there ..that makes above Factors appear to be incorrect

but if dyno or flowbench is honest,
those Factors will be very close to reality

but its still bench racing
just gives you a ballpark guesstimate of what to expect.

---------------------------------------------------------

Darrin Morgan of Reher-Morrison
has SpreadSheet online at his website

in that SpreadSheet, Darrin's HP prediction is
1324 HorsePower which is 165.5 HP per Cylinder

which is about .2982 Factor

pretty close to .3000 Factor i came up with for Pro Stock technology

Reher-Morrison
1.025 " max approx Lift range times .87 percent
equals = .892" lift, rounded to .900" Lift

at .900" lift heads flow 555.0 CFM at 28 inches

.2982 Factor




Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3