max cfm / horsepower thru stock valve diameter (35 x 32mm)?

[Jim Ratto]

With all the talk about the small cc powerhouses, what about cfm / hp possible with stock diameter valves (dual port head, of course)

Reading some of the info in the old Bill Fisher book, some of the simple mods made to stock dual port heads gave some pretty impressive increases in flow. Unfortunately, they never published any results as far as these heads on a motor, on a dyno.

Does anybody have any hard facts? Engine specifics?

My friend ran a 1679cc, stock valved (ported by Roger Crawford/Heads Up), Web Cam 110 (think Engle 120), 1.25 rockers, 40IDF Webers (32mm vents), 8.4:1, 1-5/8 header. With this motor, and muffler, radials, bumpers, interior....etc, the car went 14.71 @ Sacramento. Doing some rough math, that's what....128hp or so?

[John Maher]

In theory, an engine fitted with 35.5mm inlet valves could flow enough air to make well over 160 bhp normally aspirated but in the real world you might make 140 bhp with an optimised port.

How the theory works....

Max possible airflow at 28" test depression is 147cfm per square inch (sharp edge orifice)

Due to port shape, valve angle, chamber design etc, true absolute maximum for an optimised port and chamber design will not exceed 133cfm/sqin (most heads get nowhere near this figure)

Smallest area of the port (max flow limiter) is likely to be seat ID, which would be no bigger than 92% of valve diameter

Some maths....

35.5mm = 1.286 inches

1.286" x 92% = 1.183"

1.183" diam has an area of 1.099 square inches (pi x radius^2)

Subtract the area occupied by an 8mm valve stem: .0764 sqin....

Flow area available = 1.0226 sqin

Max theoretical flow for the port: 1.0226 x 147 = 150.3cfm @ 28" test depression

Using the 133cfm/sqin calculation instead: 1.0226 x 133 = 136cfm @ 28"

Superflow's formula for converting port flow @ 28" into bhp...

CFM @ 28" x 0.257 x number of cylinders

gives us...

136 x 0.257 x 4 = 140 bhp

Tuning the intake and exhaust lengths to boost volumetric efficiency above 100% (possibly as much as 120% at peak torque) could result in bigger numbers.

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

As useful as the theories and formulas are, they only count if you put them into practice   

PS,  the Bill Fisher book doesn't state what test depression was used for the published flow numbers. Also, I assume the flow bench they used wasn't calibrated against a known standard because the figures are so high, meaning the results are only useful for comparison with tests carried out on the same bench

[Udo]

140 hp is the same as my thought's , i had a 1776 in the mid 80's with 130 hp with 35,5 x 32 valves , but this was in the begining of building engines . 

Udo

[Jim Ratto]

Thanks John and Udo. I was thinking 120hp tops. There is an interesting formula to compute air-speed vs. cam profile and its effects on engine powerband in AG Bell's book "4-Stroke Performance Tuning" and it came up with sorely conservative figures for stock valve diam and larger cc motors.

[Bewitched666]

My first 1679 engine with
69 c/w crank
stock ported and polished heads
40 dells
w120 cam
1:25 rockers
made 100 hp on a dyno back in the mid 80's
 

[dirk zeyen]

hello,

that is a perfect question!!!
my engine is a 78x90.5, w120, dellorto 45 drla, 35.5/32 valves and 1.5/8 merged header, and i hope to run in the low 14 or maybe high 13, so what do you think?!?
i am thinking about thining the valve stem on the inlet valve from 8mm to 7 or 6.5 mm under the valve guide to increase flow?!?
i run a stock 4.375 r/p gearbox with 195/65-15 tires.
what do you think? any tips?

dirk zeyen ( friend of power and stock size valves)

ps: sorry about my english

[Torben Alstrup]

Yes, real life (street)engines typically have a max around 130 hp. with stock valved heads. 120 hp out of 35/32 mm valves is relatively easy. From thereon up, its getting more difficult. Race is another story.
T

[Udo]

run in the low 14 or maybe high 13

Dirk

For this you need something about 150 hp i think . Depends on the car and gear ratios .

Udo

[Tom G.]

run in the low 14 or maybe high 13

Dirk

For this you need something about 150 hp i think . Depends on the car and gear ratios .

Udo

yes i have also done so far tests with my 1955ccm engine with 35x32 valves, 324° german cam, 9,3:1, 205/70, 4,375 transmission, and 40 dells...My best run was 15,5s in a 63 bug w/o bumpers, rear seats, only one driver seat...if you done more compression, better valve job, better porting, bigger carbs,  i think low 14s are possible....but only with a lightweight car....
This season i will take the compression higher, 1.25 rockers and change to fuel injection, 205/60 tires.. i hope this could be the step to high 14s...Maybe:-))

Bye
Tom

[dirk zeyen]

hello,

i think an important thing is lightweight!!! 1ps/5kg means 160ps/800kg or 180ps/900kg and 140ps/700kg!!!
so if i can´t spent much money for the engine - lighten your car!!!
with a stock valve engine my car pulls hard from 2500-6000rpm so i don´t need a close ratio gearbox, i will use my 4.375 gearbox with small diameter tires on the 1/4 mile.
hey tom i say it again, you use the wrong tires, put some 195/50-15 in the rear and you think you have won 20ponys
ok they look ugly but it will work on the quarter with your engine and gearbox!!!
hey udo you said i need 150ps but what about the weight of this car you mean, thanks for info?

dirk zeyen

[Bewitched666]

There is this guy running stock heads and stock valves with some work on them on a 1835.
Think he runs in the 12's,saw it on you tube or some thread here or the other forum

[dirk zeyen]

hello,

12´s with stock valves? more infos!!!
that´s what i want

dirk zeyen

[Tom G.]

There is this guy running stock heads and stock valves with some work on them on a 1835.
Think he runs in the 12's,saw it on you tube or some thread here or the other forum

there is the thread for the 13,??s 1835ccm car with stock heads...
http://cal-look.no/lounge/index.php/topic,188.0.html
But the car weight nearly 650kg or so....

Marcus nwe project is now a WBX turbo concept in a Type 3 fastback...

Bye
Tom

[dirk zeyen]

hello,

now i think we should ask johannes persson how much stock valve heads can flow
he take them to a new lewel!!!

dirk zeyen

[Tom G.]

Hi,
Johannes has talked to me, that 170 HP with a 2,3l with stock heads (35,5x32) are realistic....with right cam (W120 with 1,25 rockers) and 40 Dells (34 vents) or Fuel injection....

Bye
Tom

[dirk zeyen]

hey tom

that's music to my ears

if you are interrested i can give you different tires for some test at DDD. i'll be there with two cars so i can give you 195/50, 195/60 and 195/65 alll with 130/5 porsche pattern.

dirk zeyen