intake to exhaust flow ratio and cam timing

[grumpyvette]

I was recently asked if the ratio between the intake port flow and exhaust was critical to making power , for those few that have not heard the term it refers to the ratio of intake port flow in cfm to exhaust port flow measured in cfm on a flow bench, this is normally done a 28" of water weight vacuum as a semi standard.
the problem is that intake and exhaust valves open and close several dozen times a second, over most of the engines power band and intake ports see between plus 1psi to minus 30 plus psi which fluctuates rapidly and the exhaust valve sees minus 30 plus psi- a positive 600 psi at different parts of the engines repeated trip thru its 720 degree cycle its rather common to see charts like this one
(I,ll post here below)
showing the flow at each lift , measured at a set lift and constant air flow rate, at every .100, .200,.300,.400,.500,.600 etc. that also list the I/E ratio,
http://users.erols.com/srweiss/tablehdc.htm
the truth here is that larger valves have the potential to flow more gases, but the intake is generally larger because its acted upon by both outside air pressure (14.7 PSI at sea level) and inertial forces the rapidly exiting exhaust flow induces<(EXHAUST SCAVENGING),which can easily exceed the draw the outside air pressure induces by several times
A CORRECTLY TUNED SET OF HEADERS , MATCHED TO A CORRECTLY DESIGNED CAM TIMING HAS A SIGNIFICANT EFFECT ON INTAKE FLOW AND CYLINDER SCAVENGING EFFICIENCY, EXHAUST SCAVENGING CAN BE 5 TIMES STRONGER THAN THE PISTON, MOVEMENT INDUCED NEGATIVE PRESSURE (VACUUM) IN THE INTAKE RUNNERS

but keep in mind the EXHAUST gases are much higher, and once the exhaust valve opens they are PHYSICALLY forced to exit by the piston on the exhaust stroke and the inertia of the rapidly exiting exhaust , from the previous cylinder , tending to drag it out , which both greatly increase efficiency, thus the valve size can be smaller.
youll commonly see intake to exhaust ratios of about 75% on the exhaust to intake flow rates as quoted as ideal, but the truth is , from what Ive seen ,that both cam timing and exhaust primary diameter and length tuning can be used to make most engines run fairly decent at most rpm ranges, and close to ideally over a narrow rpm range.
yes I prefer as high an exhaust to intake ratio as I can get and if I can get a 70%-80% flow rate thats great, especially if your using nitrous, as a power booster, but maintaining that ratio is not critical and in most cases a longer duration on the exhaust cam timing, or changes in the header design can compensate for a less ideal exhaust ratio, if you use a low restriction exhaust behind the headers collector

Hey Grumpy, you always hear that headers give you more horsepower. How does that work and what formula can you use to determine the horsepower gain that a given set of headers may bring?

that questions a bit like asking how good a girl might be in bed based on the color of her hair brush, yes theres a mathematical formula , in fact several, but theres a whole bunch of factors that determine the results, like cam timing, compression,cylinder head flow, back pressure,engine displacement , header primary and collector length and diameter,exhaust temps,etc.
the more back pressure the exhaust system beyond the header collectors has the less effective the headers will be, but if you have a low restriction exhaust and a ram tuned intake with a matched cam timing, a tuned header can in some cases produce gains in excess of 60 hp.
as a general rule Id say your safe expecting a 25-40 hp increase in peak hp from good long tube tuned headers over stock cast iron exhaust manifolds that come on most passenger cars, but with properly matched components on a high compression engine more can be gained.

READ THESE

http://victorylibrary.com/mopar/header-tech-c.htm


http://forum.grumpysperformance.com/viewtopic.php?f=56&t=495&p=613#p613

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=1303

viewtopic.php?f=56&t=572&p=35352&hilit=rams+horn#p35352

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=185

http://www.chevydiy.com/chevy-small-block-engine-guide-exhaust-systems/

I find this graph very useful, it shows stock corvette exhaust manifolds vs headers on the same 496 BBC engine dyno test

watch the video, and like I stated many times,
its the combo of the engines,
compression,
displacement ,
cam timing
and the exhaust scavenging ,
and the intake manifold design,
NOT the intake port cross sectional area,
that are the most critical factors, in the engines lower rpm and mid rpm torque.
but for damn sure an intake runner port can be small enough to noticeably restrict upper mid range and peak power significantly,
For 5 decades I've heard endlessly about how installing larger free flowing cylinder heads would devastate the engines ability to make any low or mid rpm torque.
especially when Id suggest using a set of smaller 300cc-320cc, aluminum,rectangle port heads on a 496 BBC, or 200 cc-210cc heads on a 406 sbc, I was asked to build
yet on every engine I've ever had built or had some guy ask me to look at, to see why it ran a great deal less impressively than he expected it too,
they brought into my shop its was very obvious (at least to me) that it was the combo of low compression, too little displacement, with too much cam duration ,
a restrictive exhaust or some guy who was trying to save money and continuing to use a stock stall speed torque converter, or retain a badly mis-matched 2.87:1-3.08:1 rear gear ratio,
with an engine that he miss matched components by slapping a large carburetor , and a single plane intake on,an engine that will rarely exceed 6000 rpm, that was the major reason.
if you want an engine combo to run your first step is to logically match the list of components you,ll use to the application,
and that requires you stop, engage the brain and think things through carefully,
and the most common way to screw up the process is to over cam a low compression engine,
have a restrictive exhaust or mis-match the drive train gearing to the engines power band.

YOU MIGHT WANT TO READ THIS THREAD.
viewtopic.php?f=56&t=495
the intake side of the cylinder fill efficiency, normally requires the larger valve size because its got lower pressure that the exhaust side of the equation, and the exhaust SCAVENGING helps draw in the following intake charge if its properly timed, to do so.

http://www.carcraft.com/techarticles/cc ... ewall.html

http://www.jegs.com/s/tech-articles/cyl ... Make+Power

viewtopic.php?f=55&t=58&p=36446#p36446

viewtopic.php?f=55&t=10073&p=39779#p39779

http://www.bmw-m.net/techdata/cylinder.htm

http://www.popularhotrodding.com/tech/0 ... ewall.html

viewtopic.php?f=44&t=9525&p=35027&hilit=port+flow+chart#p35027

viewtopic.php?f=52&t=8460&p=32923&hilit=port+flow+chart#p32923

viewtopic.php?f=55&t=8485&p=29767&hilit=port+flow+chart#p29767

viewtopic.php?f=55&t=624&hilit=port+flow+chart

viewtopic.php?f=38&t=1099&p=2215&hilit=+flow+bench#p2215

viewtopic.php?f=52&t=240&p=5334&hilit=cylinder+head+flow+chart#p5334

http://www.purplesagetradingpost.com/su ... eads1.html

http://www.eecis.udel.edu/~davis/z28/winter01/dyno/

http://theamcpages.com/engine-design-va ... -ports.htm

keep in mind its the total combo NOT just the port and runner size alone,
within reasonable limits ,intake port size is one of the least important factors.
your dealing with factors that are interdependent, each change effects the way the other factors respond and interact,
there are ways to predict trends or compensate for changes
change the cam LSA
,duration and lift
engines compression ratio,
intake runner length
header primary diameter and length
and you could very easily find the larger ports made significantly better power.
ID much rather, be faced with a combo where I compensate for a cylinder head with a port size that might be a bit larger than ideal for the application than one thats a bit restrictive to flow, simply because a restrictive port limits upper rpm and peak power far more than a larger port tends to loose low speed responsiveness, because that is much easier to compensate for with changes to the intake, or cam timing or compression, header design etc.

USE THE CALCULATORS, YOULL, QUICKLY FIND THE LIMITATIONS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://garage.grumpysperformance.co...ing-parts-and-a-logical-plan.7722/#post-49738

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://garage.grumpysperformance.co...-the-charts-calculators-and-basic-math.10705/

http://garage.grumpysperformance.com/index.php?threads/carb-intake-test.58/

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

http://garage.grumpysperformance.com/index.php?threads/porting-can-help.462/

http://garage.grumpysperformance.com/index.php?threads/valve-seat-angles-and-air-flow.8460/

http://garage.grumpysperformance.com/index.php?threads/is-backpressure-hurting-your-combo.495/

http://garage.grumpysperformance.co...spacers-and-related-intake-modification.1038/

http://garage.grumpysperformance.com/index.php?threads/sellecting-cylinder-heads.796/

http://garage.grumpysperformance.co...mbers-or-a-good-street-combo-your-after.5078/

 

[Grumpy]

http://www.wallaceracing.com/intake-runner-length.php

http://www.bgsoflex.com/intakeln.html

http://www.velocity-of-sound.com/velocity_of_sound/calculator3.htm

http://www.velocity-of-sound.com/velocity_of_sound/velocity_stacks.htm

http://www.swartzracingmanifolds.com/tech/index.htm

Originally Posted by howstuffworks.com

How do tuned intake runners work on your car?
you may want too mentally step back and ask yourself what the difference is in the design,s carb intakes must keep air speeds high to keep fuel droplets in the port suspended in the air flow column, turns in the port tend to restrict max potential air flow but keeping the air column moving at higher average port speeds promotes fairly even fuel distribution, as atomized fuel is held in suspension. by seperating the two plenums they effectively restrict the potential size of the area feeding that plenum so as each inlet valve connected to that plenum opens the effective rush of air trying to fill the cylinder as the piston drops and the exhaust gases, in the header primary from the previous firing cycle's , inertia trys to pull on the intake charge, is more pronounced.
and how and why one might be better or worse under different conditions,
and think through the potential of the two basic intake manifold designs.
keep in mind the reason they build dual plane (split plenum intakes)

is to promote a noticeably faster air flow rate in the intake runners,
in effect a dual plane, v8 intake manifold, intake has two 4 cylinder engines running , through it and each intake charge is desperately drawn from a smaller plenum volume , so that 750 cfm carb is effectively two 375 cfm two barrel carbs as far as the plenums sees air flow.
this is good for efficient air flow as it keeps air speeds high but tends to restrict total flow rates.
lets say you have a 383, , thats roughly 48 cubic inches of air flow volume, for each intake stroke, and, remember theres 720 degrees in the cycle and only about 240 of those degrees allow the intake runner to flow effectively, roughly 1/3rd of the time available, and at 6500 rpm thats an intake pulse every 54 times a second .

that tends to keep a higher percentage of the atomized fuel droplets in suspension
have you ever wondered why EFI intake designs tend to be single plane

while carburetors use dual plane designs for lower average engine speeds but carbs prefer single plane intake manifold designs for higher average engine speeds, or why a single plane intake design may work ok on an oval port BBC for average street strip high performance , use while a 302 -327 SBC with a high rise dual plane , may still perform rather well, even at high engine rpms compared to a single plane.
it helps if you understand that most INDIVIDUAL PORT INJECTION EFI intakes are single plane because a single plane intake design is the least restrictive and allows the most direct route for the air flow to enter the cylinders, and they don,t have to be concerned with fuel droplets falling out of the air flow as the injectors mist fuel in a cloud directly behind the inlet valve.

the tunnel ram is the most efficient single plane design for higher engine speeds as it allows a direct strait line path from carb base to the back of the inlet valve, but remember its properly timed EXHAUST SCAVENGING, displacement, cam timing and compression ratio and port cross sectional area, that has the most effect on intake runner flow rates

USE THE CALCULATORS, YOULL, QUICKLY FIND THE LIMITATIONS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php

http://garage.grumpysperformance.com/index.php?threads/carb-intake-test.58/

http://garage.grumpysperformance.com/index.php?threads/mechanical-constant-flow-injection.4502/

single stack injection with an individual injector per cylinder is the best potential intake design as it ,
if properly designed and correctly matched to the engine size,
cam timing and exhaust scavenging can provide over 100% cylinder fill efficiency ,over a narrow rpm band through inertial ram tuning.

The intake system on a four-stroke car engine has one main goal, to get as much air-fuel mixture into the cylinder as possible. One way to help the intake is by tuning the lengths of the pipes.
When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder. When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner.

If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively acting like a turbocharger.

The problem with this technique is that it only provides a benefit in a fairly narrow speed range. The pressure wave travels at the speed of sound (which depends on the density of the air) down the intake runner. The speed will vary a little bit depending on the temperature of the air and the speed it is moving, but a good guess for the speed of sound would be 1,300 feet per second (fps). Let's try to get an idea how long the intake runner would have to be to take advantage of this effect.

Let's say the engine is running at 5,000 rpm. The intake valve opens once every two revolutions (720 degrees), but let's say they stay open for 250 degrees. That means that there are 470 degrees between when the intake valve closes and when it opens again. At 5,000 rpm it will take the engine 0.012 seconds to turn one revolution, and 470 degrees is about 1.31 revolutions, so it takes 0.0156 seconds between when the valve closes and when it opens again. At 1,300 fps multiplied by 0.0156 seconds, the pressure wave would travel about 20 feet. But, since must go up the intake runner and then come back, the intake runner would only have to be half this length or about 10 feet.

Two things become apparent after doing this calculation:

The tuning of the intake runner will only have an effect in a fairly narrow RPM range. If we redo the calculation at 3,000 rpm, the length calculated would be completely different.
Ten feet is too long. You can't fit pipes that long under the hood of a car very easily.
There is not too much that can be done about the first problem. A tuned intake has its main benefit in a very narrow speed range. But there is a way to shorten the intake runners and still get some benefit from the pressure wave. If we shorten the intake runner length by a factor of four, making it 2.5 feet, the pressure wave will travel up and down the pipe four times before the intake valve opens again. But it still arrives at the valve at the right time.

There are a lot of intricacies and tricks to intake systems. For instance, it is beneficial to have the intake air moving as fast as possible into the cylinders. This increases the turbulence and mixes the fuel with the air better. One way to increase the air velocity is to use a smaller diameter intake runner. Since roughly the same volume of air enters the cylinder each cycle, if you pump that air through a smaller diameter pipe it will have to go faster.

The downside to using smaller diameter intake runners is that at high engine speeds when lots of air is going through the pipes, the restriction from the smaller diameter may inhibit airflow. So for the large airflows at higher speeds it is better to have large diameter pipes. Some carmakers attempt to get the best of both worlds by using dual intake runners for each cylinder -- one with a small diameter and one with a large diameter. They use a butterfly valve to close off the large diameter runner at lower engine speeds where the narrow runner can help performance. Then the valve opens up at higher engine speeds to reduce the intake restriction, increasing the top end power output.

 

[87vette81big]

Bringing this thread back to Life Today Grumpy .
Race School is back in Secession for Spring 2016 with Mike...Loves 302.

 

[Loves302Chevy]

Race School is back in Secession for Spring 2016 with Mike...Loves 302.

I'm gonna try to get it on the road before winter. It won't be DONE DONE, but maybe it can move under its own power.

Yeah, I read the links.