Speed Secret # 4

[jim_howard_pdx]

Speed Secret # 4

I was going to cover something else on this thread, but someone mentioned in #3 that I am recommending more duration and lift on the exhaust than on the intake.... And that would feed into the first factor of increasing cylinder pressure to generate extra horsepower.

So I am going to go into this in finer detail NOW. Because like I said, if the exhaust system does a poor job, nothing you do until you run NOS or a charged intake can overcome the mess.....

To maximize your torque and your horsepower, FOR ANY ENGINE, you have to minimize intake charge dilution. Control DILUTION better than your competitors and you will make more power than they do. This brings home trophies.....

Some of you may never have heard the term dilution EVER. So what is dilution?

As the fuel is burned during the power stroke of your 4 stroke engine event, the piston is forced down by the ignition of the air and fuel. When the compression ratio of the burning fuel charge collapses due to the pistons moving down the cylinder, you are left with burned, partially burned and unburned exhaust and fuel.

This volume of "stuff" is now your engines biggest enemy.

Your piston now reaches the bottom of the power stroke, and the enemy sits there waiting to hurt you. At the piston begins to rise, the exhaust valve is opening. This initially shows the high pressure in the cylinder a way of escape.

So the first part of the exhaust is actually physics 101. Stuff moves from from high pressure to low pressure until stuff equalizes pressure in the new volume of space.

So as the exhaust valve just begins to open, the exhaust squirts throught the valve/valve seat space at very high velocity as it seeks to equalize into the low pressure area of the exhaust valve pocket and the primaries of your headers. Some of this initial exhaust movement is improved by the scavanging effect or inertia of the other cylinders exhaust flowing down the exhaust tubes and producing a vacume for this cylinder.

Now the first negative thing happens. As the exhaust "stuff" ( burned, partially burned, and unburned fuel) moves into fresh air, it sees oxygen and the super heated exhaust fumes now explode in the valve pockets and primary tubes of the headers. This explosion or concussion front "sees" pressure in front of it, exhaust volume and mass of exhaust working its way down your exhaust pipes. So the energy converts from expanding wave fronts to ringing wave fronts. Literally, the energy slams side to side, instead of out and down the pipe. This ringing energy produces additional backpressure at the point in the exhaust system that most needs to show vacume.

Do you see the physics at work here?

Going to H or X pipes is ALWAYS in your best interests. Going to an exhaust tube size that tunes the scavanging effect to be greatest at your target torque range is extremely crucial. Going too small or too large an exhaust pipe is going to reduce your scavanging and increase your dilution levels.

But there is more really bad stuff that is about to happen.....

As the exhaust valve continues to open, the piston begins to rise and accelerate in the bore. OUCH. Pressure is now building inside the cylinder volume that increases to shrink as the piston moves up. Now the exhaust valve starts to close. D A M N, now the pressure is really up there now. So you are left with a volume of "stuff" at top dead center that is pressurized, but held back by the backpressure of ringing energy, and the backpressure of the volume and weight of the exhaust that is moving down the exhaust tubes.

So the closer your piston comes to the combustion chamber in the exhaust stroke, the slower the "stuff" moves as the pressure increases to build.

AND as RPM increases, exhaust pressure increases, and the DILUTION EFFECT INCREASES.

Now a third bad thing happens.....well both good and bad. The overlap event begins. and OUCH more bad stuff is happening to hurt your power.

Your intake valve opens to a volume of "stuff" that is very hot, pressurized, and sometimes randomly positioned in the combustion chamber.

Don't take that random position thing lightly either.......Because it effects the next ignition event and ANY MISFIRED CYLINDER will contribute to higher dillution for all your other cylinders.

So lets look at this third negative aspect of dilution and see how it effects the horsepower in great detail.

The "stuff" begins to mix with the incoming intake charge during the overlap event. It immediately heats and expands the incoming charge, increasing cylinder pressure before the piston even reaches top dead center. Worst still, the density of the overlap charge is mostly ruined by the stuff. Dilution is a big bad enemy.

Now the piston reaches top dead center of the intake stroke, the diluted overlap intake charge is now augmented by good, fresh, dense air and fuel. But the damage is already done.

Your intake charge density is now negatively effected, and the amount of "stuff" left over rises as your rpm continues upward.

So just when you need more and more intake volume and higher charge density, the dilution chokes off the good stuff our overlap and lift and intake velocity is designed to accomplish.

So RPM, dillution, and overlap dilution pressure build up to reduce the volume and charge density and your torque begins to fall.....
The proportion of the dilution to the fresh charge is critical to how much horspower you can make, or conversely to how much horsepower you LOSE.

Refresh this in your minds. Horsepower is calculated and not measured. We simply take the engines torque at a certain rpm, and use a formula to determine the horsepower. So torque at high rpms is critical to making horsepower.

We cannot build more torque at higher rpms because the dilution effect is increasing in your engine as the rpms rise.

It is a vicious cycle.

A split duration cam is a great way to cheat your engine into reducing the dilution volume, and to shift the dilution event into a higher rpm range. This allows me to have higher, high rpm torque and this calculates to higher horsepower.

I hope this is not getting lost on you......

Why is my short intake of .496 generating 425 horsepower on my current 358, when I had to run .540 lift on my 351 Cleveland engines to make the same horsepower in the early 70's? The intake port volume of a 351 Cleveland intake port is bigger and better flowing than the intake port of my Trick Flow PORTED heads. It should have made way higher numbers of horsepower with those free flowing heads and huge intake valves. But they could not take advantage of the engineering because back in the 70's we did not have commercially made cam shafts that reduced the dilution effect.

So dilution is your enemy always and forever. Any dilution at all is an enemy. It can never be eliminated, but it must be managed and minimized.

So lets summarize what we can do today to reduce or at least delay dilution.

First, you need excellent exhaust ports that allow easy and unhampered exhaust flow.

Second, you need large exhaust valves to minimize pressure during the overlap event. T

Third you should design an exhaust port to produce swirl to minimize the ringing horizontal energy of the exhaust event and turn it into faster exhaust flow DOWN the exhaust pipe.

Fourth, you should run dual pipes of a diameter that provide maximum scavange at your target RPM band.

Fifth you should run an H pipes or an X pipe to improve scavange and show more vacume to the cylinders.

Six, you should use a muffler design that improves the swirl of your exhaust system.

But most importantly, you should be using a dual or split duration camshaft designed to put the torque curve where you want it.

I hope this helps everyone understand power production. This topic, other than preignition and flame propogation, is the most significant thing to understand when building your next engine or improving the power on the one you race.

Your comments as always are what I am after. I do not do this for the exercise of telling you stuff, but to get a dialog going and have fun thinking the physics through.

Have fun this weekend. Now look for the areas I skimmed through, and areas I may have omitted and lets talk about dilution and the ways you eliminate it.

[Yan88gt]

I recently finish porting my GT40p heads. The CFM # are 210 int. and 178 exh. I use the crower 15511(468/486 lift and 218/224 duration) and the guy at the speed shop where they put my heads on the flowbench told me that it was not a good idea to use this split duration cam because of the high intake/exhaust ratio of my heads. The cam mfg. recommend a 5800 rpm shift point( 6000 rpm with 1.7 roller rocker) and i think that it's a good match with my professional product intake ( edelbrock performer rpm clone). I need some explenation.

[jim_howard_pdx]

They have s h i t for brains.......

Sorry, but many speed shops do not know what intake dilution is, how to minimize it, or how to build power around it. Most do not know what exhaust ringing means. Most can not explain why an X pipe flows more than an H pipe.

So you have some nicely ported heads. So I should NOT run a split duration camshaft??????

I plan to run my car only to 6,000 rpm and I should NOT run a split duration camshaft?

My engine has 8 primary header tubes bending and snaking into collectors dumping into exhaust tubes that are bent, possibly modified for H or X flow, welded to real CATS or Mufflers or BOTH, and then have tube exiting the car and I should NOT run a split duration camshaft?

You have 8 cylinders feeding high pressure exhaust into a tuned exhaust system that is overcome with backpressure as rpm increases, and you should not run a split duration camshaft?

They have s h i t for brains. And that is all I have to say about that. Decide if you are at the right shop.

Thanks for the message. I really needed to vent, my wife is giving me a pain in my a s s.

Better yet, go to your town's best dyno shop. They will have kept every dyno run on every engine they ever worked on IF THEY ARE WORTH A D A M N. Then give them your engine specs and have them show you the horsepower and torque curve of an engine similar to yours with small primary tube full length headers, then with large primary tube full length headers.

The split cam will provide the horsepower of the large primary tube header, but with the broader and more useable torque curve of the small primary tube header. This is my most simplified explanation of what reducing intake dilution reads like when you test ANY engine on a dyno.....

The split duration just holds off the intake dilution volume and ratio to a higher rpm point which will improve the ets on your car. If you don't believe me, and you don't believe them, then buy both and run each for one month. Then keep the one that produces the best times with the best overall usable torque curve for the driving you do. I am betting that cam will be a split duration cam EVERY TIME.

You just cannot take a flow bench result, and say this is what the engine flows at high rpm with an engine running.

Even a wet flow bench, where they use water and a carb to simulate gasoline CANNOT show you dilution effect because there is still NO BACKPRESSURE, NO EXHAUST RINGING, and No PREIGNITION or FLAME PROPOGATION that might be ruined by the contamination caused by the dilution.

Do you see where I am coming from? YOU TEST AN ENGINE AT A TRACK not on the dyno. The dyno helps you get to the best combinations so the track testing gives you meaningful ways to improve your combination.

Hope this helps explain some of your questions.

By the way I LOVE Crane hi lift, low duration, with split duration camshafts. Other than the racing cam profiles I use from Comp Cams, Crane does the best on the street cam profiles. I will probably catch some grief on this, but if you pick a well engineered brand like crane or comp cams, and test their series of cam steps on a given combo it makes development time much faster than trying 8 brands of cam. So YES there are a lot of really great cams out there. I have just picked the poison that tastes best in my opinion.

And by the way, I have not run a standard grind camshaft since split duration camshafts were first made available on a custom grind basis.

And finally, When you are running 9,000 to 15,000 rpm engines, this is where split duration cams show the least effect. This is because even the spit duration cannot overcome the exhaust pressure and ringing. So dillution must be overcome with more and more intake event. That means more and more overlap. You cannot increase overlap without increasing dilution.

Hope you see the light now. Your shop has things back a s s ward.

[jim_howard_pdx]

Similar ported trick flows like the one I am running flow 298 cfm and 240 cfm on a wet bench. I would rather stick a needle in my eye, than run a standard grind cam in this engine.

[jim_howard_pdx]

Your times and top mph look pretty good in your signature. But I would be temped to run the 225 intake duration with 525 to 540 lift. I hope the pistons are forged and fly cut for your heads. The exhaust should be 550 to 560 lift. This should put the 302 near 385 hp, about 300 at the rear tires.

This might put you in the high 11's with slicks and a 4.10 gear ratio.

SUCH FUN.

Make sure you gasket port everything to keep flow smooth through the transition between intake and heads.

[95mustanggt]

Is the TFS Stage 1 cam any good? It has split lifts too.

Also why is there bumps on the exhaust ports of the stock heads. Removing these would likely net some gain, right?

[Kevin Price]

Assume large exhaust valves and large, unhampered flow through exhaust ports through porting. By your description it would appear to be an ideal (well, close to ideal) situation with regards to minimizing dilution.

So as the exhaust valve just begins to open, the exhaust squirts throught the valve/valve seat space at very high velocity as it seeks to equalize into the low pressure area of the exhaust valve pocket and the primaries of your headers. Some of this initial exhaust movement is improved by the scavanging effect or inertia of the other cylinders exhaust flowing down the exhaust tubes and producing a vacume for this cylinder.

What about the velocity with which the exhaust exits through the exhaust itself? It would appear that you would need some resistance, in some cases that is, to increase the velocity and flow efficiency.

In short, by running an exhaust valve to large and/ or increasing the exhaust port to extensively thus decreasing the initial velocity that is created when the exhaust valve first begins to open might loss of torque be a result?

[bigred90gt]

I know not much about cams and such, but would really like to understand exactly what this post is telling me. Please explain what a split duration cam, and a dual duration cam are. Thanks.
Caymon

[HotRoddin]

Originally posted by bigred90gt
Please explain what a split duration cam, and a dual duration cam are. Thanks.
Caymon

The exhaust lobe has a different duration than the intake lobe
For instance a cam listed as 230/230 @ .050 is a straight duration camshaft (same duration on the intake as the exhaust) A split duration camshaft would be for instance 230/238 @ .050 ....
230 degrees duration intake and 238 degrees duration exhaust

[bigred90gt]

Thanks for the info. That sheds new light on the post.
Caymon

[jim_howard_pdx]

Kevin,

Your point is well considered. Let's review some basics. The engine cannot build more horsepower than the amount of air and fuel it can pack into the combustion chamber relative to the compression (either static or dynamic).

As a result of this principle, Yeats built an Intake valve size to dominate the NASCAR field. He sized the intake valve to build the power he needed, then ran the best possible exhaust valve given the geometry of the cylinder, valves, push rods, spark plug, and so forth.

Also you may know that the port pocket of any valve cannot be larger than 80% of the valve size. We need this much meat around the valve seat, or it will collapse and this is really an ugly sight.

The feeling is that the exhaust is easier to move than the intake charge. And this is basically correct until rpm goes up, the exhaust backpressure rises, the valves are now moving faster than the intake charge moves!

Ha, I shared a secret with you Kevin that I was not going to mention just to see if anyone out here has built top end power engines like those used at Bonneville.

The valve opening and closing at 9,000 RPM is so fast, and the fuel charge is so dense and thick that it is somewhat like pouring molasses into a jar. I am oversimplifying, but I know the point is not lost on you. The air fuel mixture is a liquid, the valve event becomes faster and faster and less air and fuel can be packed in. It is just simple physics.

That is why most all high rpm engines are supercharged or turbo charged, not because they by themselves push more air and fuel into the engine, but because the provide a positive pressure behind the air and fuel at the intake pocket that with the proper overlap will generate good cylinder pressure that atmospheric pressure could not accomplish.

So enlarging the exhaust valve to the optimum flow is really not possible. To solve this, several european manufacturers explored 3 valve per cylinder heads in the 60's and 70's.

The first 3 valve cylinder configuration I saw tried to rectify this by using one large intake valve and two small exhaust valves that yielded much better exhaust flow figures. A 2V race engine with maximum porting typically delivers 80% of the intake's flow at the exhaust end. But this three valve design delivered nearly 95% flow and the engine built great power.

Within one year 4V engines became the norm. The crossflow of the 4V over-comes any slight benefit the 3V engine might have. It drags an amazing amount of intake charge at very nominal dilution. This is why my Honda VTEC engine makes 90 horsepower per liter and the typical early 351 Lightening engines make 66.37 horsepower per liter. 4V is simply a superior valve design to enhance cylinder filling and cylinder evacuation.

Going back to your point, you mention that too large an exhaust valve and port or too large an exhaust system would reduce exhaust flow and create lower torque and more dilution.

Yes it is possible to have too large a primary tube, and have overly large exhaust pipes. Large is not necessarily good in exhaust systems. But in your engine Kevin, your primaries, collectors and exhaust pipes seem PERFECT for the power band you are working to achieve.

Just see if you can build an insert to spin the exhaust in your collector, and run a spin tech muffler. Don't be concerned if your peak horsepower goes down 2 to 4 horsepower, because you are after the spin throughout the entire rpm range and your ets should go down just a little bit from the extra scavanging, even with slightly lower peak horsepower. The torque under the curve will expand, and this will be worth the trade-off.

Kevin did hear about exhaust "ringing" before my speed secret. This is fascinating physics I did not learn until I hear a 427 SC Competition Cobra. I was shocked by how loud the exhaust was. The owner explained that the side pipes spun the exhaust but did not muffle it. I asked why spin it, and he filled me in on spin tech's work.

Then I read Carroll Shellby's recount of the SC Cobras, and he mentioned it in greater detail. The SC Cobras had basically the same engine. same cam, same carbs, same intake, but produced nearly 500 flywheel horsepower. Most of this due to the spin techs and extra balancing, blueprinting, and equalization of the carburation. They were using either twin holleys, or down draft webbers. The webbers were tuned for maximum midrange torque for twisty courses. The twin holleys worked better on long straightaway tracks.

It is fascinating that the exhaust slams side to side inside the primaries, collectors, and exhaust tubes with greater horizontal velocity than its linear velocity. Chevy picked up nearly 25 horsepower in its 454 Rat Race Heads when they brought out the D port design. They saw what Valley Heads did with the Boss 302 heads and 351 4V heads with their ultra cool raised D port plates and they pretty much copied this into their race head. Most racers used the old rectangular ports because the better oval ports had really aweful low rpm torque (just like the Cleveland 4V engine.) Now the new heads flowed like the ovals with torque like the rectangular heads.

We discovered that the D ports actually spin the exhaust as it comes into the primaries. We used clear plastic tubes, and colored smoke with strobe lights to see the effect. The spin was present in almost every rpm range, but highest at the cam's maximum torque peak which we were counting upon.

In fact, you did not want a d port shaped primary tube on the header, because it would kill the spin created by the D port. So the exhaust port shape made alot of the ringing energy diminish and their exhaust velocity was increased. This netted the extra 25 horsepower!!!!

Within the last 20 years, it is correctly assumed that there is a high end for the cam overlap which should not be exceeded. The higher the overlap, the worse the dilution.

That is why Kaase, the guy that created the 429 Aluminum Cobra Jet Head rarely uses a cam with over 290 degress duration at .050 lift. He would rather run .780 lift to get the dynamic compression up with minimum overlap, than dilute the intake charge and waste the potential torque.

But the 429 allows very large valves, very high lift, incredible cfm flow, and great valve geometry. So he can run less overlap to generate 800 horsepower on gasoline. If we small block guys want 800 hp on gasoline, we have to build in more overlap to get the cylinder pressuse we need.

Good job Kevin. I think you have done the best in terms of digesting all this detail.

Let me know if you experiment with spinning the exhaust in your collectors. I think you will be surprised with the results.

[Kevin Price]

A couple of months ago I purchased Moroso's 'Spiral Flow" mufflers. Without seeing the spin techs I wonder if it may not be the same concept. Could you send me in the right direction for getting a bit more info on these?

Back to the Moroso's, I installed them approx 6 inches from the rear of the collector. I simply don't have much room under there. I didn't try them at the track as I could see some additional tuning would be required and the race was the next day.

Car ran fat and just would not idle. Seemed way too restricted at higher rpms. Don't know, I may put them back on this week and o a little playing to see what I might come up with.

As far as a spiraling modification in the collector. I'm interested to hear a bit more. I'm assuming somewhat of an angled fin? What angle and how high? How many?

Hey, I'm always willing to try new things here.

[jim_howard_pdx]

Kevin,

You know for a guy like me that knows a little bit about a bunch of stuff, I really must tell you that I know nothing about the Moroso spin muffler.

We built an exhaust system for the cobra jet alot along the lines of your exhaust. Similar but different.

The exhaust port on a 428 SS class must remain the same dimensions as stock, so to get 9's we reshaped the bowl to be 80% the valve dimension, smoothed the runner and made sure the rectangle had a 3% twist effect. We had to go through alot of castings to find ones we could modify to hit this mark. Then we shot peened it so that it appeared "as cast".

Some will say we cheated, but the dimension to the stock port was exactly the same, the ports pocket and bowl smoothing and widening was really to prevent the flow from bumping and bruising. In other words, CFM increases were not the goal, just smooth, regular, flow.

EVERY CHEVY AND CHRYSER HEMI I FACED WAS DOING THE SAME THING.

So to get more swirl, and better scavanging we needed to increase the velocity of the exhaust. We ran 1 7/8 inch primary tubes off the head, the pipe was neither round nor rectangular, we shaped it to create swirl. I will not describe it further, because I do not want the Chevy crowd to know how to do this.

Then after a few inches we ran it into 2 1/4 inch primaries, and then stepped it to the 2 1/2 inch primaries, then it dumped to the collectors. The idea was to get each section of the exhaust to "SEE" low pressure in front of it, so it would be tugged along to move faster. The reshaping of the tube was to generate some areas of the tube that would impede the exhaust speed, and some that would allow the exhaust to scoot right along. The impeded area would get suctioned by the faster moving exhaust.

We tried a second design that started out with Primaries that were rectangular to match the port and continue the twist to encourage spin, then bumped the primary up by 1/4 inch steps to the collectors and maintained the rectangular shape all the way to the collector. This design showed NOTHING on the dyno, and showed NOTHING on the track, but the seat of the pants feel was very torquey.

So we ran the first design all during season one. Then I saw my first Chaparrel car, and Smokey Yunich had built this snaky exhaust system that took the out of phase cylinder exhaust from one bank and added it to the correct in phase ports of the other bank. It was like any regular header but with one of the four primarys welded to the other banks collectors.

What a mess of tubing. He aluminized the header so it also looked like Medussa's head of snakes.......

I cannot remember who I spoke to, but he told me the mess was good for almost 20% better scavanging, almost twice what you get from an H pipe system.

So we decided to build a third header. My muffler champ, Chuck, ran the three in phase primaries as we had with header number one. But the out of phase primary was made LONGER and we ran the tube inside the collector about 6 inches, but cut on a 45 degree angle.

The out of phase pulse was then dumped into an area of very fast exhaust flow to get equal scavanging form the cylinder bank. This worked well, so we ran it the next two years. It showed big horsepower gains with no loss or shift of the torque range. We liked this!

This is so similar in principle and function to Flow Tech's muffler that I wish we had applied for patents...... They dump the out of phase exhaust pulse past the collector to do the exact same thing, but without the extra welding and fabrication.

Now for the spin insert....We had to make a larger and longer collector than normal.

What I will tell you about the inserts is this. We tried one with vanes similar to the impellers of a centrifugal super charger. Wide space on the outside, thinner and tighter on the inside, with additional shaping to enhance fluid movement of the gas so it would not create a dam of exaust that slowed everything else down.

We tried a second design with spiralled tubes of different lengths and 45 degree entrance and exits. This was like putting a hundred straws into a big hole, and twisting them so the exhaust had to spin through them.

The third design was to take a wide mouth split it into two pipes and then back into one wide mouth. So the exhaust would have to split, and generally speed up then dump back together which created swirl.

To understand the physics here, watch TOP GUN the movie. When Tom Cruise is gunning for JESTER in the first training session, he puts the TomCat into afterburn (extra fuel is dumped into the jets exhaust to provide momentary thrust increases). You will see two plumes of dark exhaust that counter spiral away from the air craft. Taking a wide pipe to two narrow pipes and back to one wide pipe creates this same effect inside the exhaust tube.

Chuck was running just your standard Hooker Competition headers on his 400 ci smallblock. He ran the collectors to 4" side dumps just past his front wheels. He had a bypass switch to 3" exhaust and hemi mufflers for driving around. This was also a 9.2 bracket car, but he ran downdraft webbers and direct port NOS injection. He found that with NOS, an insert wasted top end torque and slowed his ET's.

This seems to be the effect of those MOROSO mufflers on your car. So be carefull not to waste 20 hours of time trying a trick that works on a super stock class engine, when you are headed to the 8's.

There is a universe of difference between these engines, and you need unrestricted flow even more than you need exhaust spin. I would like to see a Yates head again. I cannot remember the exhaust port shape. But I think it is rectangular. Try making the port roof round. So rectangular on the bottom and sides, and round on the roof edge. This should generate some extra swirl in those big primaries you are running.

[Yan88gt]

The speed shop owner is a moron. He have a beaumont that he invested 70 000$ on it and he only run 10 flat. I don't want( and i will not) to change my cam cause it work well on my stock speed density computer and i can't go bigger ( i also have 24# injectors and it make the cam selection harder). I'm on a budget and i had the entire motor out of a wreked explorer for 75$( the intake was missing and the motor need new rings and bearings due to bad storage) I recently put 1 5/8 longtube on my car with h-pipe and i'm waiting for my aluminium flywheel.