Speed Secret # 3

[jim_howard_pdx]

I think we have picqued some interest out there in learning speed secrets.

So far we have talked about SQUISH and quench factors in ignition events, and reducing parasitic power losses to improve et times.

I have had just a couple of you who seem incredulous at first, then someone with experience chimes in and they see the light.

No single approach to speed is ever the best or only way. It is only important to know these secrets and apply them as the rules of the class allow you.

But you had better know these, and learn how they can be applied to your engine. I guarantee that the winners taking home the trophies know it and apply it.

Now on to speed secret number three.

Why did one pass net a decent time slip and next week we shaved almost 4 tenths off the ET? More Cam you say, Intake change, different Carb, NOS.....

Just one change..... the Compression Ratio.

We were running a wild Pinto with a full space frame, FMX automatic, 4.88 rear end, and the tallest slicks we could buy at the time. Times were ultra sweet unless we blew the launch. The engine had all the good stuff, a stroked 351 Cleveland with $2,000 of custom head work to raise the exhaust port, reduced and lightened valves, and run some really light rods and pistons.

We spent hundreds of hours on the bench to develope hurricane like swirl, which the cantelevered heads made possible. Ultra cool titanium rods that were so beautiful it was a shame to hide them in the block. Custom pistons with all the tricks I outlined in speed secret one.

A custom forged steel crank rated for 10,000 RPM that we knife edged and filled with mallory metal inserts to maintain balance.

But the thing that the engine responded to most was small changes in compression ratio.

So what is my speed secret???? After all every engine builder worth a d a m n knows that compression ratio effects horsepower. So what is so secret about this? Well how do you increase your compression ratio while keeping the static compression constant?

This will be the subject of today's secret.

First, you really have to build the engineering around the bracket you plan to race. Ours dictated we had to run a static compression ratio not to exceed 12 to 1. The class we ran at required all winners to subject to complete engine disassembly. And at the time, coatings were not allowed in this bracket. So guys we could not cheat. Measurements are measurements. But cheat we did, in a legal fashion.

Our engine ran at 14.5 to 1 compression ratio......wanna know how?

Engineering.

An engine is really nothing more than an air pump. You have to do everything you can to make it inhale and exhale properly at the rpm you run to win your races. So what I am alluding to is you need to compute your rpm from 1/8 mile to the speed trap and figure how to build maximum torque during this period. On our engine, RPM at third gear started at 5,700 RPM (the stall of the converter and we crossed the finish line at 8,600 RPM.

So the goal was to increase the compression ratio between 5,700 RPM and 8,600 RPM. See why we were using a Cleveland Head. This is the RPM range where this engine sings and dances.

Now how did we get 14.5 compression out of a 11-1 static ratio?

Well lets go back to physics 101. I take 50 cubic inches of stroked area, and compress it into 5 cubic inches of combustion chamber, we get 55 cubic inches of area divided by the 5 cubic inches of combustion chamber and voila....we get 11 to 1 static compression ratio. Now measure the actual cylinder pressure obtained at the rpm you want with the cam you are using. Now bump up the static compression to 14 to 1 and look at the cylinder pressure. If you want your 11-1 engine to run like a 14-1 compression engine you simply need to produce the same cylinder pressures at the proper rpm range of the 14.5 to 1 engine. This is what we call dynamic compression ratio.

Understanding how to build maximum dynamic compression at the rpm you need to win, is why 100 guys go out to race and 1 guy wins. 1 guy figures out how to do this best with his 12 to 1 bracket class engine.

Now there are 5 ways I will tell you about right now to build dynamic compression ratio. But there are alot more.

Please comment to this thread by remembering what things you did to improve ET's without adding stuff like blowers, Nitrous, nitrogylerine and the like.

First way to improve cylinder pressure. You have got to get all the exhaust out, or flowing at a pace that allows the air fuel mixture to pack the cylinder at the rpms where you want to build power.

Unless you really scavange well, you might as well forget this whole speed secret. The whole thing starts with the exhaust flow.

What we did is run 3 inch primary exhaust tubes out the raised D port heads for about 6 inches. The D ports were specially shaped to create swirl out of the exhaust port as it entered the round primary tube. Then we stepped the primary to 3.5 inch tubes for the next stretch to the collector. Then we ran 4 inch collectors for 22 inches with vanes to keep the exhaust spinning instead of ringing. The vanes were an insert we built and placed into the collector. We ran 3.5 inch H tubes to the spin tech mufflers, and 4 inch pipes from the mufflers on out.

Almost everyone in our class ran Hooker Competition headers, 4 or 5 inch open exhaust (no mufflers). They laughed when they saw mufflers on our car. Ugly and square looking ones too. They laughed when they saw the primaries snaking all over the place so we could phase their exhaust pulses into the collectors. They laughed until we wiped them up.

Second way to increase cylinder pressure: Takes some time to understand what is happening to the intake charge at the rpm you need to make maximum torque.

Ever wonder why your street cam runs so good at 4,000 to 5,000 rpm and then falls on its a s s at 6,000+???? Simply, as your RPM increases, exhaust pressure increases. The valve event is insufficient to maintain the earlier flow it produced at the lower rpm. Air and fuel are actually a LIQUID in engineering terms, and as your RPM climbs, they cannot keep up with the faster and faster valve events.

Sorry to oversimplify here. Someone will probably address this in a response. I just want to get you thinking here.

So cylinder pressure drops as your rpm increases.

In the 60's and 70's, we would correct this drop in cylinder pressure at high rpms by increasing valve overlap. Your average modern street rod cams open the intake valve about 24-36 degrees before the exhaust stroke reaches TDC. On a 7,000 RPM cam, that is increased to about 40-60 degrees of overlap. On my 8,500 RPM big block, I was running 110 degrees of overlap.

Understand what the overlap does. Literally, as the exhaust valve is closing and the piston is chasing it back into the head, your intake valve begins to open up. You might incorrectly think that the piston coming up would push the fuel back into the intake, but the opposite actually happens at high rpm. The exhaust rushing out the exhaust port creates a vacume that pulls the air fuel mixture into the cylinder as the piston comes to top dead center. The amount of air and fuel we actually squeeze into this overlap area determines how much extra cylinder pressure we build at a given RPM.

Lets look at the problem with too much overlap. As the intake and exhaust valve remain open longer and longer, unburned fuel moves into the exhaust port and exhaust pulse energy remains in the combustion chamber. If the exhaust flow is hampered by any event like a couple of cylinders misfiring, the exhaust flow collapses and now the easiest way for it to flow is through the open intake valve, into the intake manifold and BOOM. This is why we see blown fuel engines launch their intake and blowers up in the air. In the 60's they could fly as high as 15 or 20 ft in the air and sometimes killed the driver or spectators. Now we use engine straps to contain the parts.

So knowing we need a proper amount of overlap, we can just measure what we need and get the cam made to our specifications. Right? Well... YES AND NO. You also have to understand intake velocity.

The third point is that intake velocity is just as important as overlap to increase the cylinder pressure. As intake ports are widened and as the valve diameters increase, your intake velocity decreases. The vacume of the exhaust flow during overlap pulls fuel in, but this is really a small fraction of time during the crank rotation. As the intake valve opens larger and larger and the piston now begins moving down, the intake charge begins to slow down.

In flat head days we found that by tuning the intake ports to specific volume, we could get more fuel into the cylinder at given rpm. Your typical intake is a single plane or dual plane and it does not individually tune the cylinder very well. But look at your high rpm, low ET race cars and you will see individual intake runners going to the cylinders. Then we can use a tunnel ram set up to make huge volumes of dense air fuel mixture that as they move from the top of the intake, compress and force the air fuel below into the cylinders that are a foot or more below it. This is the power of inertia. Once we get that heavy air and fuel moving, it wants to STAY MOVING.

So in whatever bracket you race, don't overport, don't over cam, don't over carburate, don't over intake. You need to run the package that moves the most air and fuel the very fastest speed possible in your target RPM range.

Fourth point, air fuel density.....

Ever wonder why the race car that beat you was exactly like yours in every way. Your car has the proper 600 cfm rating for the 306 engine you built. His has a 750 which should be way too big......

Smokey Yunich worked with Chevy for many years to develop maximum rpm on their race engines. As he built more and more record producting power plants, he found one thing to be true. You need about 2 cfm of carb for every horsepower you plan to build.

This flys in the face of carb selection formulas that say a 289 should run best with 500 cfm of flow. So why was Shelby running a 715 on the Cobra R? Because he was producing 350 hp from a good portion of these engines and you need two cfm to build one horsepower.

I am going to leave this sketched out like this now, because carb technology should be the subject of its own speed secret, and many of you are using tuned port, sequential fuel injection systems that eliminate the carb sizing all together. However for you fuel injection guys, on our 214 mph Pantera engine, we sqirted the closed intake valve during the opening of the exhaust valve, and then again when the intake openned. This got us the fuel density we needed to make over 900 horsepower.

Fifth point, ignition timing.

So now our stroked 351 Cleveland with excellent quench of .039 at the piston edges, and .085 at the wedge and .18 at the spark kernal is built with a cam that has proper overlap, really fast intake velocity from a custom tunnel ram intake with tuned runners, great fuel density charge from proper carburetor size, venturis, and ciruit tuning, and an awesome exhaust that literally sucks the intake charge into the cylinder.

Now in order to use all that great cylinder pressure created by the intake stroke we need to properly fire it. This is where a lot of dyno time and track testing are required to find the right ignition curve to properly ignite the mixture from 5,500 rpm to 8,500 rpm.

The difficulty is that a great many things change during the acceleration process. These include changes in the exhaust flow and back pressure, the reveberant energy due to overlap, misfiring in cylinders and a lot more. It may be necessary to run 36 degrees at 6,500 rpm, but 26 degrees at 7,000 rpm and 34 degrees at 7,500 rpm, and 32 degrees at 8,000 rpm.

See what I mean. We are after the best burn cycle and the best breathing possible and ignition timing effects this in really significant ways. Your air fuel mixture does not remain constant at any rpm. It is constantly variable. So you need to find out what works for your engine, then remember that it is effected by bariometric pressure (weather), air temperature, air density, altitude, track temperature, engine temperature, and even more than I want to think about.....

This too needs to be properly discussed later, so I will not go into all my ways to vary ignition timing.

I hope the whole point I am making does not get lost on you as you read my NOVELS.

Compression ratio is more than static compression. In fact in my mind, static compression is a worthless figure to me except as the rule book definition of what parts I put into the engine block.

In every race engine I build, I am looking for the dynamic compression of the engine at the rpms that are meaningful to win. PERIOD. End of story.

Now I want to hear your comments GOOD and BAD. I have drastically oversimplified alot of this just to keep this short and sweet and to test those of you out there that really know your stuff about engines and making power.

So please comment on this third speed secret, and help fill in the blanks so we can keep FORD "FIRST ON RACE DAY!"

[HotRoddin]

Originally posted by jim_howard_pdx
We were running a wild Pinto with a full space frame

We spent hundreds of hours on the bench w.

What we did is run 3 inch primary exhaust tubes

They laughed when they saw mufflers on our car.

In the 60's and 70's, we

I have a question Jim and i mean no disrespect by it ... who are you ?? and who is "we" You sound like you were in on every major race that took place and outsmarted most of the competition, and around here in the late 60's early 70's you are talking about the best of the best ... Don Prudome, Tom Macewin, Roland Leong, John Mazmanian, Gas Ronda, Dyno Don ... every major name in drag racing spent alot of time here ? I've heard you say you were in So Cal in the early days .... I almost lived at Lions and Irwindale and Orange County and Ontario and Riverside between 65 and 75 ... what team or business were you part of that gave you such an opportunity to be in on that much ?

[Dark_5.0]

Yeah I was wondering too especially since in 1970 you were 13 years old according to your profile.

No disrespect intended.

[ultraflo]

Originally posted by HotRoddin
I have a question Jim and i mean no disrespect by it ... who are you ??

LOL, you guys are killin me...

I think there's more than just one speed secret in there, btw

[Eric4Nitrous]

I wonder what magazine he gets his info from? Ryan is he your new "hero"? lmao If he was 13 and turning wrenches for the big boys then he's my hero.lol

[ultraflo]

Originally posted by Eric4Nitrous
I wonder what magazine he gets his info from? Ryan is he your new "hero"? lmao If he was 13 and turning wrenches for the big boys then he's my hero.lol

I just finished reading Jim's post in its entirety. Sounds like he has done and knows it all... but you're still my hero Eric, don't worry, LOL

Hey Jim, I dropped .2 in the 1/4 through tuning the fuel delivery alone... no parts changes. I dropped .1 off my 60' with a swap from Goodyear to M/T slicks... and .2 in the 1/4mi. Those are the only speed secrets I can share, however

[jim_howard_pdx]

Ultraflow gets the first award for thinking today.

On most fuel injected cars, the computer controls how long the fuel injector is on. The computer bases this on some pretty complex algorhythems but it requires one constant. FUEL PRESSURE.

It is important to carbs too but in different and interesting ways.

So if the algorythem is set for 45 psi, and your fuel rail delivers 41 psi at WOT you are way short of the power you can produce.

I like to use really big rails, feed them with way more pressure and fuel volume they would ever need and use the gorgeous Vortec fuel pressure regulator. It is specifically designed for high volume fuel consumption and maintains the pressure expertly well for natural aspirated, turbo, and supercharged engines.

Yes slicks make a big difference. I always liked MT slicks, and have used a variety of hard wall, soft wall, and crinkle wall models. I knew a couple of brothers that owned a Goodyear shop, but their slicks were too slick and not enough stick.

I never said I competed directly against any top fuel team, because I never raced that bracket. I raced primarily in the 9 and 10 second brackets.

"We" refers to me and my racing buds. I wrenched alot of engines from about the age of 12 on. Did my first carb rebuild at 14. Did my first dyno session at 15. Did my first capacitive discharge ignition system at 16. Ran 10 seconds at 18 and so on and so on and so on......

I have never driven a quarter mile in under 8 seconds. So when I see Ron and Eric talk about their competition licenses I must admit I salivate like Pavlov's dog.

I have been beat a zillion times. There isn't an engine in the world I could not break, or a transmission, transaxle, rear end, or chassis. You name it and I have broken it or bent it.

Good job Ultraflow.
Love the car!

[Old Guy with 87 GT]

yet another great post jim .........

your discussion on exaust kinda reminded me of a two stroke engine and how much of a difference the exaust pipe makes .......agian i'm not an expert but if you've ever torn down a two strock engine it would seem that the exaust flow actually creats a vacuum that premotes air flow through the engine
........the guy whos gonna build my engine has curruntly been experimenting with the same concept ........him and a friend of mine are curruntly building a sort of experiment ....using the concept of a smalle exaust port +valve with a large intake port+valve to premote a higher velocity of exaust flow ........i don't know all the logistics ......but there basicly planning on a high rpm, high compression set up , the same concept your talking about will come into play with the engine build

i'm not building my engine with plans for high rpms (planing on high gearing and stock ignition).......my plans are to aim for power at 3000 to 6200 rpms .....if all goes well i'll be crossing the 1320 at the top of third at redline ( using 3.27s and 235-15 tires).....my underlying plans are really to make the car into a nice highway car that will double as a fun car to play with at the track........

as for speed secrets ,i'm far from an expert ....my only insight would be to plan on what you want the car to do and what times you want to aim for, before spending any money ......there's like a million different combos that *all work together* to give you the result you want .....make plans , find a combo then ,then build the combo rather then miss matching a combo and bolting on whatever you hear works that week.

ps. jim....i don't care how old you are or if you started building cars in diapers ,you seem to know what your talking about and thats all that matters to me .....your novals are eppriciated and make for interesting reading .......now i'm thinking about different ways to premote higher velocity of ex discharge,a more centered flow of intake air and less obstructions in my cylinders causing turbulance ........all this info will com in handy as i build my moter ...........even if its a mild combo any tricks are helpfull

[jim_howard_pdx]

Good point on learning to apply secrets that help you with getting free power with whatever combo you decide to try.

NOW I HAVE GOT TO CHASTISE EVERYONE A LITTLE BIT. 112 people have read the thread, and no one has called me on an omission I made JUST TO SEE IF ANYONE KNOWS THEIR STUFF.

HERE IS THE OMISSION. On any engine, there will be a maximum safe overlap. and a maximum safe lift for the valves. Max valve travel is more dictated by the spring height and the compressed spring height than any other factor. So you rarely see an engine with more than .790 lift, because it takes custom length valves and custom length springs, and custom geometry rocker arms, and custom length push rods, and jeeze guys THESE CUSTOM THINGS COST BIG BUCKS.

That is why I decided to stay at the 9 second bracket. MONEY!

So to get the best cylinder pressure at the rpm range you need to run to win the race, I tune the best overlap first, then vary the valve lift until I get maximum TORQUE at the mid-line rpm zone. So for the 5700 to 8500 rpm zone I run between 1/8 and 1/4 mile, midway would be 7,100 rpm.

SEE WHAT I AM DOING. Establish your zone, build the engine, set the proper overlap to best fill the engine at 7,100 rpm, then play with the valve lift until you hit the best torque you can make.

Just one word of warning. You know I own and love trick flow heads. The twisted wedge drops the intake valve down d a m n near the center of the cylinder, giving you the absolute best opportunity to generate swirl you can. It is so close to the Yates head it is SCARRY. But a cam that works best on a inline valve AFR head will not perform the best on the Trick Flow Head, because the AFR will not make the excellent swirl, nor will it dump the charge in the center of the cylinder, where the air fuel has longer to travel before it bumps the cylinder walls.

SEE WHAT I AM GETTING AT. What will work for one head and valve arrangement will not work on a different design. So there is a bit of work to get to the finish line.

I wish I didn't have to offer you this tid bit, I wanted YOU TO POINT THIS OUT TO ME!

NOW I HAVE LEFT OUT A SECOND B I G OMISSION, so lets see who can find it. Common guys you are really doing some great things. Think this all through...... Here is a BIG hint....Just what is the biggest danger in developing a cam to produce the highest possible torque at a given rpm????

Now get to work building that awesome power.

[95mustanggt]

Originally posted by jim_howard_pdx
NOW I HAVE LEFT OUT A SECOND B I G OMISSION, so lets see who can find it. Common guys you are really doing some great things. Think this all through...... Here is a BIG hint....Just what is the biggest danger in developing a cam to produce the highest possible torque at a given rpm????

I'm grasping at straws here...lifter speed?


Question: What cam or cam specs do you think works best with the Trick flow heads and track heat intake? T-5, street tires, not daily driven.

[jim_howard_pdx]

Old guy with an 87,

I don't care what people think of me from what I write. Anyone who has raced with me knows I do this because I love engines. I love everything about making power. It is my addiction.

My friends do not all go as slow as I do, and some go WAY faster. I took 15 years off racing to raise my two kids, and now they beg to go to the race track and drive the car. It is great family time for me.

Now my 17 year old daughters teachers know she has drag raced! My wife doesn't know what to do with me? She wouldn't drag race if her life depended on it......

So thanks for the kind words. And I hope those that want to know who I am, get to know who I am, cause they will become friends too. I will never mislead them in the quest for power and trophies.

So exhaust is the cornerstone that every other piece of the engine survives on. One guy wrote in a thread one time that backpressure was a bad thing and you should do everything you can to eliminate it all together.

Well run the engine without a header or any tubes. Just let it fire into the air.

The engine will have no torque, or little torque over any rpm range. Then it might create ok horsepower readings at wide open throttle, but I doubt that too.

What I can tell that guy, is that exhaust back pressure, and exhaust flow are his friends. They allow him to build a long and wide torque curve to keep the car clipping right along.

That is why tuning an exhaust system is so frustratingly painful for me. My street rod engine was making 350 hp, and I knew it could make 375 even with the old street cam (since changed) so I went from 2 1/4 inch exhaust to 2 1/2 inch exhaust. Well my horsepower jumped right up to 383 hp, but my torque from 2,000 to 4,000 rpm went down. So my low end throttle response went down. So I am faster, and more powerful, but I really MISSED the low torque I was making with the smaller pipe.

My hope is that someone comes up with a variable backpressure exhaust system where a computer could tune the backpressure to the throttle position, vacume level, and rpm of the engine to maximize both horsepower and torque.

It could be done. the fact no one has done it is more a factor of putting profit over performance.

One friend I respect alot, just put a MAC 3 inch exhaust system on his 4.6 twin overhead cam Cobra. He hates it. He misses the low torque much more than he enjoys the extra 5-8 hp at top rpm where he rarely drives.

So perhaps exhaust system factors can be the subject of speed secret number 10 or so. We have more to cover before we should talk about that......

By the way, my current thinking is to use the flow tech headers with the off-pulse cylinder primary dumping past the three on pulse cylinder's collector point. The idea is to use the excellent flow pattern of the three on pulse cylinders to scavange off the off pulse cylinder and getting more even horsepower from the entire cylinder bank.

This is awesome thinking. I would use this and an X pipe system with Edelbrock or Spin Tech mufflers and Hi Flow Cats. Just delete the cats with by pass tubes until you go for smog testing.

This should give you great exhaust velocity as long as you do not go HOG wild with the size of the X pipe. It should be only as large it takes to provide the maximum horsepower you intend to build. So without a CAT a 400-500 hp engine runs best on 2.5 inch tubes, but the 2.25 tubes would improve low torque. A 500+ Hp engine needs 3 inch tubes. Why not 2.75? I do not know all the physics, but the 3 inch produce dramatically higher torque bands than the 2.75 tubes. So there is a hint of what is to come later.....

Thanks for the encouragement. I am really happy there are some people out there that want to learn some stuff.

Again, I am not purporting these secrets to be the only ones, or the best ones, or the ones to follow. NO. I am just after getting you guys thinking and commenting and looking at a bunch of options that allow you to build the best platform you can to run consistent times. Because in bracket racing the fastest car NEVER wins. The car most CONSISTENT TO THE DIAL IN WINS!

Have fun this weekend. I am still recurving my street rod's distributor. It is getting closer and closer to excellent. AND THANK YOU Denny Aldridge for helping me with that project.

[jim_howard_pdx]

95MustangGT

At least you are willing to think.....

What typically happens in engine development, is that the engineering group builds the hard parts, bolts them together and then plays with cams until they get the performance, or lack thereof, that they desire.

So when they built the 351 Cleveland, it was designed very much like the Tunnel Port 427 that they never could win a race with. The Tunnel Port 427 was a beast, with horsepower even higher than the 427 SOHC engine.

So going for highest peak torque (horsepower) at the target rpm, they ended up with a cam that sucked across the entire power band, until they get to the rpm sweet spot, then the power was awesome.

So there is a big balance act to build the cam with a broad torque curve in the desired band, and one that can generate adequate horsepower to hold a lead or pass during the straight aways.

On my 400 HP engine I was running a lift of .472 on the intake and exhaust, 214 degrees at .050 and advertised at 278 degrees. It was an ok cam, good for a daily driver.

On the rebuild we did three weekends ago we used a .496 intake and .520 exhaust, 224 duration at .050 lift and 234 for the exhaust. This is the Edelbrock RPM cam that gave them 401 HP with the RPM heads, intake and EdelBOG 750 carb.

I have ported heads, a little more compression, and a better carb, so I am guestimating 425 hp until I can afford some dyno time.

Trick flow sells 3 roller cams for their heads that should work really well to build substantial torque with their ports, valves, and valve angles.

For daily drivers they recommend a 221/225 duration @.050 lift at .499/510 lift. (A little less powerful than my Edelbrock 351 rpm cam) On my engine, my computer says it will build 410 HP +/- 5 HP.

For Strip/Highway 224/232 .542/563. Looks awesome to me. The computer says 445 HP +/- 10 HP for this delicious little tasty treat. ( A little nice step up from my daily driver street rod cam)

For Racers, 236/248 .574/.595. This would put my engine very near 500 hp +/- 15 hp. (This is one serious mama, and would be ideal for NOS as well.)

The 236 cam would work on the street, but be prepared to run at least 102 octane, and it will overheat in traffic without a high flow water pump and aluminum radiator. In the long run, curtin number two would be best if you like to get in and drive the highways and biways of America, but want to dominate Z-28s on the street or strip.

Hope this helps.

Build a 351 block and slip it in your car. You will not believe the awesome torque curve it produces, but your fuel mileage WILL SUFFER.

I am doing 0-60 in 5.5 seconds, even with my grand-daddy highway lovin 3.25 gears and the C4 with 2.47 first gear. Imagine what I would cut with 4.30 gears!. My computer says 3100 lbs would generate 11.95 to 2.20 Slicks or street tires at 112 mph

[95mustanggt]

Thanks, I noticed will all your recommended cams, you go with one that has more lift on exhaust. This is to help with your speed tip, I assume (removing more exhaust is better).

I would LOVE to build a 351W. But I'm not even going to think about it until I move back to the US. Parts here in Canada are insane.

[jim_howard_pdx]

Please read speed secret number 4 and we will examine split duration camshafts in detail. This will explain alot about intake dilution.