I figure you can rough guess at cfm requirements of a motor, but there should be a mathematical way of figuring when the volume of the intake plenum on an motor woudl become partly a restriction itself right?

Dont Pro Stock guys play with plenum volume itself alot, along with runner length size shapeetc

 

you can get close with equations

its best to dyno and track test plenum volumes

keeping the plenum volume to the least it can be without a significant Torque/HP Loss in the required/desired RPM range
will be a very good baseline to start with

then track test from that point on

i've seen where dragster starts to make 170+ mph
down dragstrip with a real good HoodScoop
allow you to run a little more plenum volume than the dyno would show you was correct

 

Troy Coughlin (Jegs) Pro Stocker
used my dyno for 6 weeks in 1994 July to August

we played a bunch with plenum volumes and runner lengths

its 10 years ago so i don't think it matters if i post some of data

total induction length 10 years ago was 11.68 to 11.72

average cylinder head mid-port length was = 6.680"
------------------

the plenum volumes are still relevant , so can't post this info

 

I understand Ferrari, where money is NO problem, have an engine dyno UNDER a wind tunnel so they can poke the air inlet box up into the airstream, which I assume is controllable for speed, for very accurate dyno testing. You're probably not there yet, Larry. Right?

My guess is that they use variable inlet length and plenum volume for various rpm/vehicle speed combinations.

 

I understand Ferrari, where money is NO problem, have an engine dyno UNDER a wind tunnel so they can poke the air inlet box up into the airstream, which I assume is controllable for speed, for very accurate dyno testing. You're probably not there yet, Larry. Right?
----------------------------------
i wish i was

you can easily pickup 20+ Torque with just 1.000" inch in the intake manifold runner on V8

 

Isn't that about the difference in a SBC Super Vic vs. a Vic Jr.?

 

Isn't that about the difference in a SBC Super Vic vs. a Vic Jr.?
----------------------------------------------
about 1/2" difference in runners (reg SuperVictor vs Victor Jr)
but the SuperVictor has dividers coming into plenum too far at roof and topend HP suffers until you correct this..you leave middle of runner to floor part alone for length

effect of 1.500" inch change in intake manifold runner length BBC

RPM---TQ-------HP---------TQ--------HP with 1.500"inc
6900--717.6---942.8-----775.8---1019.2
7000--732.1---975.8-----763.0---1016.9
7100--729.8---986.6-----766.3---1035.9
7200--727.4---997.2-----765.2---1049.0
7300--733.8---1019.9----754.6---1048.9
7400--724.3--1020.5-----749.6--1056.2
7500--719.3---1027.2-----757.0---1081.0
7600--720.0---1041.9-----757.1---1095.6
7700--708.5--1038.7-----734.9---1077.4
7800--705.4--1047.6----729.6---1083.6
7900--704.6---1059.9-----737.0---1108.6
8000-691.1---1052.7----722.0---1099.8
8100--686.9---1059.4----715.0---1102.7
8200--693.1--1082.1
8300--692.1--1093.8
8400--681.4--1089.8
8500--667.8--1080.8
8600--656.8---1075.5

 

Pretty strong BBC, especially if it's NA and and one 4 bbl. My guess is PS style engine. If I remember correctly, that's not far from what Maskin was getting for JC in the late 90's, especially with the extended rpm with flat hp.

 

we aborted the test early with 1.500 length increase

it wasn't where we wanted it

next test was only 1.000" increase and
1123.7 HP and 763.4 TQ

made a few more changes to compliment runner length
kept basic 760's torque but 1153.0 hp at 8500 rpm
at 600 rpm/sec accel SF-901

on a brand new Stuska dyno with Depac tech guy there helping
same exact combo 1 day later made
1220+ hp with the way Depac guy set inertia factor

i think we had to set the inertia factor to 10 or 12 to make the Stuska correlate to SF-901

Stuska/Depac/Starr read way too high numbers like it was setup initially

physics => the racecar ran down the dragstrip "correlating" to 1153.0 hp
not like it had 1220 hp (Stuska dyno)

 

Not only that but they also have a moving floor to simulate the under car aerodynamics.

 

In PS type run, lower gears must accelerate engine maybe 2-3000 rpm/sec or more. Top gear (5th) seems to be about 3 secs max from incar cameras, and if that's 600 rpm/sec it's only 1800 rpm. If you use 9000 as shift point (probably low), that's a 7200-9000 band, so I guess a 6900 and up dyno pull makes sense. That's about 3 seconds/pull from 6900. I'm sure nobody could miss that engine running in anger, even for 3 seconds!

You have any experience with DTS dynos?

 

That would be for full vehicle testing, which I believe is not full scale cars. Maybe by now Ferrari has a full-scale tunnel.

Yes, especially with open wheel cars, a moving ground plane is critical. The kicker is that the downforce being produced sucks the "belt" away from the floor of the tunnel. Keeping it down is a major challenge, especially for a full-scale tunnel. Imagine what it takes to keep the belt down with 4000 lbs. "sucking" on it! A 40% tunnel would reduce that by many times.

The tunnel above the engine dyno probably only has the air box and top of the car with exhausts sticking up thru the floor. I'd truly like to see that run!

 

In PS type run, lower gears must accelerate engine maybe 2-3000 rpm/sec or more. Top gear (5th) seems to be about 3 secs max from incar cameras, and if that's 600 rpm/sec it's only 1800 rpm. If you use 9000 as shift point (probably low), that's a 7200-9000 band, so I guess a 6900 and up dyno pull makes sense. That's about 3 seconds/pull from 6900. I'm sure nobody could miss that engine running in anger, even for 3 seconds!

You have any experience with DTS dynos?
-------------------------------------------------------------------------------

yes, in PS , i'd have to use my program to be sure/exact, but from memory its definetly around 3000 + Rpm/Sec in 1st gear
2.56 1st / 4.86 gears

so what happens is in 1st gear and the next gears
if actual dragstrip engine Rpm/Sec accel rate is "FASTER" than the SF-901 600 RPM/SEC test rate the engine is actually making less
than dyno shows

when dragstrip engine Rpm/Sec is slower ..the engine is putting out "MORE" HP than showed on SF901

my program displays engine Rpm/Sec rates each foot distance

with onboard data recorder , you can easily calculate Rpm/Sec accel rates, work backwards thru rest of data, and determine Torque/HP data


and the DTS dyno

theres 1 30+ miles North of me
it was Sportsman model setup ??
the inlet hose to absorber was way too small
and readings were inconsistent (cavitation and spikes)
but was later corrected with hose dia increase fix

then another DTS Pro version 100 miles east of me
works very well ...reads approx 30 to 40 HP higher than mine
but test runs mirror otherwise

 

Yah, this has been one of the "big ticket" items that the smaller teams have been complaining about. All the top team have there own private full scale tunnels. If my memory serves, all the movable floors were "scale" tunnels. God knows, what they have now though. It's all a big secret. Just can't imagine trying to do "aero." on an F1 car.

 

Another dyno that seems to work very well is the Land & Sea Dynometer

i have a good friend that has one for Jr Dragsters and GoCart racing

some people say you can't measure down to 1 or so HP accurately on engines, but the Land & Sea model he has
seems to be able to accurately measure 1/4 to 1/2 HP accuracy

i've plugged in his data into my program and it correlates very well
even correlates very well with Comet Torque-A-Verter claims of 3.25:1 Torque Multiplication
the range i come up with is 3.00:1 to 3.70:1 TQMLT
from plugging his data

he got the Jr Dragster to go 7.80's at 74.5 mph 660 Feet
with 24.0 HP @ 8200 325.0 Lbs 6.13 gear ratio 18.5*8 to 19.0*8 tires

has SF FlowBench also, but abandoned Jr Dragster efforts when officials put a LIMIT on how fast you could run with Jr Dragster

now running Go Carts at Dirt Tracks