Ivymike...i should have posted this

[MaxRaceSoftware]

Ivymike...i should have posted this article 1st ..but i just found it
..from SuperFlow concerning what we are discussing

Fuel Flow When Accelerating

You only have to run a few tests on an accelerating engine with your SuperFlow Dynamometer system to discover that the power output and the air-fuel ratio change with the speed of acceleration. An understanding of fuel flow within the engine can shed light on these changes. What happens to fuel delivery when the engine is accelerating? How does fuel flow differ when the engine is running at steady speed?
When an engine is running at a steady speed, fuel is mixed with air and travels down the port as spray flow. Some of the fuel is vaporized and behaves exactly as air does. Other fuel remains in droplet form. These un-vaporized fuel droplets will partially coat the walls of the ports as a result of turns and general turbulence. This will create a slow moving flow along the wall which ranges from .010" to .020", (.25 to.5mm), thick. Moving much more slowly than the spray flow, this fuel moves down the port and breaks off at the valve, where it enters the cylinder as additional spray droplets. When the engine is running at a steady speed, the wall flow and the spray flow reach a point of equilibrium, delivering the desired air-fuel ratio to the cylinder. When the engine speed changes suddenly, as during acceleration from 4,000 rpm to 5,000 rpm, the spray flow rushes to the new equilibrium point almost immediately, but the slow moving wall flow requires almost 100 engine cycles before it reaches the higher flow level.
The net result is that the engine cylinder receives insufficient fuel at the increased speed operating point for the first 100 cycles. The engine runs lean, and may stumble and miss. The traditional solution is to add an accelerator pump that delivers extra fuel during the transition. This additional fuel travels down the port primarily as spray flow and works to overcome the momentary lag in the wall flow fuel delivery.
When the engine is already running at full throttle under rapid acceleration, the accelerator pump has no effect. In this case, the normal solution is to increase the jet size so that the engine will run rich. Unfortunately, the engine then always operates rich during full throttle; a richness that is greater than necessary, if the engine was running at a constant speed. That is why the engine may stutter or blubber due to a rich air-fuel ratio.
On the dynamometer, you will generally find that the engine requires one or two steps richer to achieve maximum power under acceleration tests than during steady state tests at the same speed.
In a race car application, engines frequently accelerate at different speeds, rates, and times. First gear acceleration might exceed 2,000 rpm a second, while fifth gear acceleration may be less than 100 rpm a second as a vehicle reaches top speed. The same air-fuel ratio will not be correct in both situations. Currently, there is no mechanical carburetion system that can compensate for this problem.
If you want to determine how much enrichment is required for your particular engine, it is necessary to run a series of tests at progressively richer settings at each of the acceleration rates your engine will experience in its normal application. You will probably discover that the richest setting is required for the highest rate of acceleration and the leanest setting for the best steady speed power. You cannot determine the correct mixture by the air-fuel ratio, but only by the net power produced. For a performance application, you should select the mixture for the acceleration rate that will be used the greatest portion of the time.
Production engines experience this problem to a lesser degree, because of increased manifold heat and the higher vapor pressure of typical pump gasoline. The extra manifold heat evaporates the wall flow back into the air stream and also promotes vaporization of the droplets of fuel and the spray flow.
Unfortunately, manifold heat also increases the temperature of the air charge and reduces the volumetric efficiency at maximum power.
To determine how quickly air and fuel flow systems respond during acceleration testing, you can perform a simple test. If you have a SF-901 system, put the test select knob in the standard test position and set the auto test rate to 25. (With these settings, data is collected every .25 seconds and averaged by exponential decay over 0.8 of a second.) Run the engine at a constant speed, such as 3000 rpm at full throttle, and push the auto test button.
After 3 seconds, increase the speed rapidly by flipping the speed control knob upward approximately 500 rpm. Let the engine run another 10 seconds at this point and push stop test. If you print this set of test data, you will see the actual air and fuel flow readings: first at 3000 rpm and then at the higher test speed. By comparing the data changes over time, you can determine how long it takes to reach a stable reading.
This test should be the worst possible combination, because you are using the longest data averaging time while making the most rapid step change possible. You will probably discover that it requires 5 to 7 seconds to reach a stable data point.
Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

 

[ivymike]

Maybe I missed something, but isn't this article talking about running on the rich side of stoich (by varying degrees) to achieve peak power?

 

[evelrod]

Larry and Mike, I have stayed out of all this up to now, but I must inject a bit of the real world into this trully facinating and entertaining thread , or threads as it be. This article addresses the problems I had with the gentleman doing the porting on my first overhead valve engine ( '55 Olds, Rootes, Hydro, '47 Ford). I was a 3rd year engineering student bent on reinventing the wheel and he was me now, today. The argument was wheather to polish the ports to a fine sheen or leave them with a rough pattern. I wanted to leave them rough to improve boundry flow and had to prove it. I used the drop of water on a piece of glass v drop on sandpaper and compressed air. It convinced him, and I still do not polish my ports.
What I mean to say here is that , as Larry said, nothing is new in the auto game. It's pretty much been done before, but due to technical limitations, not implemented until now.
There has NEVER been an engine taken from the dyno to the track that did not require jetting and timing changes to perform at it's max potential, NEVER. However, in deference to Superslow, the new dynos have made the job MUCH, MUCH simpler.
As to the mixture strength, Mike, it has meen my experience that on engines set up on steady state (old fashioned) dynos, the jetting usually was a bit ritcher at the track. With the newer Superflow systems whereby acceleration rates can be varied, the jetting has sometimes been a bit leaner. Altitude, humidity, track temp. ,track configuration, gear ratios, etc. all effect the ultimate setup. RPM range in road race engines usually stay within 1000 to 1500 rpm ideally. In practice it is closer to 2000 to 2500 rpm because of driver, traffic, errors in judgement(???).
What I am inferring here is that the dyno room is a sterile environment, devoid of wind, weather, track anomolies and, " stupid driver tricks". It is the normal practice to run the fastest setup possible, and in the real world, at the track, this tends to "read" a bit on the lean side as seen by the plugs. I still use Weber type carburation (class restrictions in my case) and it has been my practice to use the e-tube -main jet- air corrector jet combo to keep the mix at leaner levels during acceleration and then use bleed from the pump jets to richen things a bit at the top end of the rev range. The overall "read" is lean, but the fact is that at a steady 8000 to 8500 it is a bit richer. Stoich is a derived number that does not always translate to the real world.
Sorry to butt in, just had a "hair".


Rod

 

[MaxRaceSoftware]

Maybe I missed something, but isn't this article talking about running on the rich side of stoich (by varying degrees) to achieve peak power?
--Mike
-------------------------------------
Yes, i know the SuperFlow article states basically the "opposite" of what i was saying, but i thought it was interesting to post ...however, in the realworld results in racing..just about 100.0+% percent engines that really go fast down the track will correlate towards the "lean-side"
14 to 15:1 A/F

in dyno testing SuperStock engines, they have to run the exact carb that came on the engine from the factory...
so i mostly windup testing engines like GM that run QuadraJet 's ..and Chrysler engines that run ThermoQuads..both of these two carb types have very large secondary bores to very small primary bores ...
cause uneven fuel distribution problems ..so we sometimes epoxy dams in plenum floors and also use an carb-adapter
spacer and change its shape to even fuel-distribution out ..
sometimes 15 to 27 HP can be gained in intake manifold fuel-distribution mods with these two type carbs ..
anyways,...when dyno testing these SS engines , we find the best jetting..but at the track, with no ram-air hood scoop on these cars, and enhaling underhood hotter air, they seem to take less jet than dyno sometimes........in contrast the Comp Eliminator or bracket race engines with hoodscoops
seem to run the fastest with the same exact jetting the dyno says..as long as weather conditions are the same
and there are no weird problems from incorrect hoodscoop dimiensions or placement in airstream Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

 

[evelrod]

There has never been an engine-IN MY EXPERIENCE- taken from the dyno to the track---------------------------etc.
I am pretty good, hands on. It's verbalizing my ideas that I seem to stumble over.

Sorry for the error.


Rod

 

[MaxRaceSoftware]

I used the drop of water on a piece of glass v drop on sandpaper and compressed air. It convinced him, and I still do not polish my ports.
--evelrod

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

Rod,..i used a small cup of varsol ( mineral spirits)
and poured on 180 grit sandpaper to show a racer once exactly what you did.....another cup on a piece of glass
..i even let hime direct and blow the shop air gun
at both ...was amazed that the varsol on the 180 grit sandpaper immediately disappeared ...and on the glass it just slid along . pretty good visual aid ??

i need to nail this down more thouroughly in future dyno tests that i will do on my own engines (dyno test mule)
where i can control all the variables closely !!
..so far, i haven't seen a lot of difference either way ,
but everything i dyno is mostly 5000 rpms on up
Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

 

[evelrod]

A short question, Larry.

What finish do you use on your in. valves. I have had a couple of wierd finishes show up lately.


Rod

 

[MaxRaceSoftware]

The argument was wheather to polish the ports to a fine sheen or leave them with a rough pattern. I wanted to leave them rough to improve boundry flow and had to prove it. --evelrod

Rod, when i'm doing a set of SuperStock heads, it just about always involves using epoxy in intake ports ....
sometimes if the racer decks his block excessively
or for other reasons has manifold fit problems,
the combined effects of hot engine oil and race gas
in intake ports will sometimes loosen up epoxy...
so over the years , i've found some high quality epoxy
with a lot of adhesion..after this dries..i come back with a very thin film of Devcon 2-Ton clear epoxy to seal the other epoxy from gas and oil to prevent lifting .
.....so i've personally seen heads where epoxy was "rough"
surface finish and dyno then track test and then
compared it back to after i smooth out the epoxy a little and put a lite coat of the clear ontop ...now the port's finish is definetly smoother ,..but redyno testing it still
the same numbers basically and at the track you can't see any difference in times...so far, but i plan to do more personal testing later in next year.
.........as to valve texture ?? i mostly use the valves like they are out of the box..except i always lightly resurface the seat and usually also backcut the valves
..sometimes profiling or changing shapes of valve head or margin once in awhile...but half the valves i use are titanium which come with pretty smooth finish Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

 

[MaxRaceSoftware]

Rod, i can apply a swirl or polish finish to backs of valves
but i don't have hard evidence either way which makes HP
..if thats the finishes you are talking about ???????

i do have very accurate data on differences between
a tulip shaped 1.880 dia intake valve in
a Chrysler #308 casting -VS- a nailhead shaped 1.880
valve in the same heads ....i have dyno , flowbench,
track times either way !
Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

 

[evelrod]

I tried several valve combinations on Lotus, not all of which were all that great, despite the "NAME" brand.

Vegantune (UK)---VERY thin head, little margin, extreme back cut (flick it with your finger and it would RING)NO tulip---STATE OF THE ART for Vegantune engines ???, poor flow and performance at anything but max lift.

Tilton---Nice looking, swirl polished, 8mm stems, professional looking, flowed well at all lifts, VALVE HEADS PULLED OFF CONSISTANTLY after low engine time and low revs.
Bad batch???? Tilton said I overrevved it! This was on a 10,000 rpm rated engine and the rev limiter was set at 8500 rpm. All that saved the engine is the fact that it was a DOHC and when the heads broke we lost all the lash and pulled the head to see what was wrong.

Manely---Top notch in SS expensive in titanium. Good performance overall. Would use them again.

Dave Bean---SS worked well, flow was very good at all lifts and durability was good. Cost, a bit pricey.

"Bad Attitude Racing" specials---(mine) Re-shaped and cut down Jaguar SS, swirl polished with back cut and a "good" margin---Best flow rate on bench, especially at low lifts, good durability, good availibility, cheap to build.
Nissan L-20 1.625 swirl polished and back cut, multi angle etc.---Almost as good as the Jag, and just as cheap to buy, but less work involved in making the fit. 8mm stems , too. This is what I tended to use most of the time.

Lotus (UK)---Flow and performance was equivelent to the Bean or Manely, but the cost was EXTREME and sometimes difficult to find, or always on backorder.

Ford (UK)---Cheap junk, poor metalurgy, failed often, burned up.

Ford (US)---Good quality, but required a lot of work to make them fit in the Lotus DOHC engine. Otherwise they were OK.

TRD (Toyota Racing)---Top notch for the money, I guess, in a Toyota. Come in oversize for my application, and must be rather radically cut to fit, but performance about the same as the Nissan L-20's just cost more.

On the exhaust side I tried several different types, but found that a stock L-18 1.375 flowed better than the "high priced spread"!!!!!! What is that all about? I could have used anything, but we tried the stockers by chance and they worked very well! Added a back cut later, but it didnt seem to improve except at very low opening.

Bottom line to all this, is a moderately tuliped and swirl polished valve with a good back cut and multi angle along with an undercut (venturi shaped) port(34mm min. dia and 14 inches from valve to air horn) was best for my application and combined with In. cam timing of 276 @ .050, 302 @ .020 set at 106 ATDC and Ex. cam timing of 280 @ .050, 310 @ .020 set at 111 BTDC ,(very high acceleration rates on both cams) produced as much as 205 hp at 8500 rpm with power band in the 2500 rpm area. Not bad for a 95 cubic inch, 16 valve engine good for at least 50 hours of racing, eh?


Aww, shucks---this turned out to be an editorial, sorry Larry. All I wanted to know was if you had run into valves with a "radial" polish to them. I have a set laying around and was wondering what they were all about. Never seen them before. These particular valves were out of a used head I got somewhere, but I never did anything with them, they look good and I guess I could swirl polish them if need be.


Rod