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Well-Known Forum User
Dynamometer (or “Dyno”) testing

After reading hundreds of pages on the internet (some of which were interesting and informative and some scarily inaccurate or damn right lies) I decided to gather some facts together, “facts” I hear you say, yes facts i.e. they have been verified by reputable chassis and engine dyno owners/operators.

Before we go any further we need to understand what we are measuring as the term BHP is a number derived from two others, Torque and RPM

For years engineers, engine builders and then motor manufacturers relied on direct results to sell their products however humans like to quantify everything so there arose the need for a single number to indicate performance (James Watt was using a De-Pony brake load on his engines years before)
Torque is the engineering standard (the tendancy for "force" to rotate around and axis) but this does not give any indication of engine speed so BHP was born
And that’s all BHP is it’s the ability of an engine to deliver a specific torque at a certain rpm theres even a formula

BHP = (Torque x rpm)/5252

That’s great so now we have a single number that allows us to say that engine A is better than engine B…….NO WE DON’T

A single number gives no indication what so ever of the drivability of the car in relation to specific environments, for example.

Engine A, gives out 500hp but only between 5500 and 6000 rpm, the rest of the time it’s a flat as a pancake.
Engine B, gives out 500hp between 5500 and 6000 BUT between 4000 and 6500 it doesn’t drop below 400hp

Engine A is great to brag about
Engine B wins the race

Dyno types
1. The chassis dyno (the most common type)
This is a set of rollers (single or double) usually sunk into a concrete floor that allows a cars drive wheels to sit either on top of or in-between, the theory being that when the engine turns the wheels it in turn drives the rollers, if a known load were applied to the rollers then the “force” to turn them could be calculated.

2. Hub dynos
This is a setup whereby the drive wheels are removed and a force sensing device is connected
To each hub, these devices are then electronically linked to a central computer. Once again the theory is the same as above; if a known load is applied then the “force” to turn them can be calculated.

3. Engine dyno
This is the serious end of the market, setups 1 and 2 above are designed to measure the power with the engine in situe, the engine dyno measures the engine power with it out of the car the theory being that this removes external influences, allows the engine to be situated in a controlled environment and returns true, credible engine “power”

Each type has its own strengths and weaknesses

The Chassis and hub dynos are quick, convenient and negate the need to remove the engine from the car, they are however susceptible to a number of factors that can render the results inaccurate (these I will cover later on)

The Engine dyno is as accurate as you can get however the process is time consuming and expensive ranging from several hundreds to thousands of pounds depending on what is required

Purpose of dyno testing
To gain a measure of power output in order to ensure that build, fuelling, mechanical and electrical timing are optimum. Without dyno testing performance modification is a guessing game.

Scope of “dyno” testing
A dyno is a “comparative” measuring device, it is next to useless when used out of context in the pub or on a forum, this is due to many factors, the two most common are RWHP versus FWHP and dyno operators….I will discuss these later on.
Aside from component choice, the internal combustion engine is susceptible to a number of external factors that can influence power such as fuel, temperature, pressure, humidity and skill/integrity of the operator.
All of these should be considered when testing is commenced, a engine dyno will commonly be in an environmentally controlled room where temperature, pressure and humidity can be controlled or recorded
Chassis and hub dynos will vary, some I have been to are, and some are not, either way the operator must still record temperature and pressure for the purpose of “correcting” the final result.

General Acuracy
Outside of the motor manufacturers, there is no enforced legislation that insists that aftermarket engine testing dynos (types 1, 2 or 3) are calibrated or inspected; operator training levels range from expert to amature, accuracy relies on the professional honesty of the owner/operator. Its worthwhile reiterating that a dyno is a comparative tool and as such when considering all things, runs by the same car on different days can be several % out. Runs by the same car on different dynos can be 10% out (witnessed 1st hand)

Coast down
This is a phase (on a chassis dyno) whereby the operator will at peak power, drop the car into neutral and coast to a stop, the computer can then calculate the resistance and add a figure to the results, this coast down can be the cause of a number of errors if done wrong.

The effect of atmospherics
Atmospheric conditions can play a big role in affecting engine performance
For example
On an NA engine of 3 litre, the difference in power output between a day where pressure is low to a high pressure day can be 10 HP
The same engine will see a power drop when the humidity is high due to displaced air.
Raise the temperature by a few degrees and power will fall once again due to displaced air
Take a warm summers day just before or after rain and you may have a mixture of all three, you aint never going to break records then.

This is one reason why drag racers (amateur and professional) look at the weather
I keep records of all of my runs against weather conditions at the time, and if the weather is against me I won’t get too hung up when I run a poor time.

RWHP is “power” measured at the wheels this is a direct measurement of usable power
FWHP is “power” either derived or measured (in the case of an engine dyno) that represents direct power output from the engine prior to any drive train losses (typically 15-18% on a rwd car)
Drive train losses are made up of gearbox (gear loss and oil drag), diff (angular loss, gear loss and oil drag), driveshaft’s (angular change) and tyres (deformation and friction), most of these are frictional related with tyres being the greatest
Confusion of the two often results in accidental or deliberate miss-quoting, for example if I chassis dyno my car and it yields 200 RWHP (which is “around” 240 FWHP) and I accidentally miss-quote the later figure as RWHP then those participating in the bar stool racing game will be deluded into thinking your engine is more powerful than it is. Don’t believe me well I have actually heard it, it goes something like this

Frank “went to the dyno yesterday and we made 1000 HP” (it was a skyline of course;))
John “wow that was great, was that RWHP or FWHP?”
Frank “Err…….RWHP, yep RWHP” (it so happens it was flywheel hp)
John “Crickey that’s 1150 HP at the fly, you must be well pleased”
Frank has now dug a hole for himself and cannot get out of it easily so he agrees; this also has the convenient side effect of making him look a legend in the process.
If Franks ever asked to post up the graphs then in this instance photoshop is his best friend.

Heres a few handy rules of thumb for a RWD car to allow you to spot some dyno bullshit
Ask about the peak torque figure (where and how much)
Ask about the horsepower/torque cross over point (hint, its always at the same point)
To get a rough guess of FWHP take your RWHP, add 10hp then divide by 0.88, this will get you in the ball park.

This power differential does not exist on an engine dyno as we are directly measuring crank horsepower with a load cell and exists to a lesser degree on a hub dyno as there are no tyre losses.

Operator error or worse
All dynos can suffer from operator error or manipulation the most common on the chassis or hub dyno being the miscalculation of a coast down figure after a power run, this is a process where the car is taken to full power and at peak the clutch is dipped and the car left to “coast” down to a point that the computer can calculate the differential losses, maybe I should clarify.

Scenario 1
I take my car for a dyno run and during the coast down the operator lightly applies the brakes, computer sees larger than normal rolling resistance and hey presto your calculated flywheel figure is huge.

Scenario 2
I take my car to a dyno and during the coast down figure the operator jumps out, the computer sees a fluctuation in load and it skews the flywheel figure, I have witnessed this 1st hand.

Scenario 3
The operator does a coast down and then when the cars at a rest he ignores the figure and makes one up (30 hp) and adds it to the result. Once again, I have witnessed this 1st hand.

Scenario 4
All, any or none of the above plus the operator puts in the wrong atmospheric values…. Once again, I have witnessed this 1st hand.

Why would a dyno operator influence the figures, well it could be accidental or it could be that fact that a happy customer is likely to go straight onto and discuss till the cows come home their 500 brake horsepower 1.6 bean can exhaust shopping trolley, after which a hoard of baseball capped McDonald employees will descend upon said dyno demanding similar results and paying £75 a pop per power run.

So beware

If the dyno does not have a computer attached and is just a big dial, drive away, the results are of no use at all to anyone other than [people playing numbers games

I once went to a highly recommended dyno near Leicester, it was a dismal dark wooden shed with a great big dial, all I got was a number and no understanding of where or when power was made…….totally and utterly useless.
I also went to another dyno near Cambridge run by a well respected mini driver; once again it had a big dial with no ability to tell me where my engine was making power.....wasted trip.

Always try and get your hands dirty, some dynos (Wilcox etc) will not allow this due to (made up) health and safety issues, however many will allow you to get close and understand what is going on, after all their doing it to your car. My favourite dyno allows me to do the power runs.

Look at your results IN CONTEXT, beware of numbers that look big, get to know and talk to the operator.
Use the results to check tune not to publish in a pissing competition.

The two chassis dynos I trust emphatically are Dave Walkers ( (Dave is an engine God), and Thurston engineering near MJP eastern auto, (Pete is a highly skilled, extremely knowledgeable and all round top bloke), neither has any interest in inflated figures and will tell it like it is, both will give you power at the wheels as well as power at the fly (calc) and both will reliably correct for both serve coffee and biscuits occasionally.

And finally horsepower figures never ever won a race, you can troll all day long, giving it "HP this" and "Torque that" but at the end of the day pink slips talk and bullsh1t walks.
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Well-Known Forum User
Power sanity check
Another “bullshit O meter” is to look at engine potential, this rule of thumb will allow you to determine if the engine figure that is being mentioned is a mile out (only works on NA engines)

Potential engine power is directly related to number and size of inlet valves (note I say potential)
The rule of thumb being total inlet valve size (all inlet valves added) / 30 = engine potential

So here’s an example for our L-Gata engines

E88 head
42x42/4 x 3.14 = 1385mm (sq) x 6 (inlet valves) = 8308mm (sq) /30 =277 hp

N42 head
44x44/4x3.14x6/30 =304 hp

Big valve head
46x46/4x3.14x6/30 = 332 hp

Hold on a second, there’s more, before we all start professing silly hp figures we must make some deduction for it being a non cross flow head, this can be as much as 10% so your big valve head could be down to 300hp and remember this is “potential” for these figures to be realised then all other components must be contributory, cam, chamber, compression, inlet runners, exhaust system etc etc

There is a caveat to the above, most 4 stroke engines can be tweaked above and beyond these figures by clever manipulation of cam timing, inlet tuning and general design, the above is only a guide to help you smell a rat, and you will notice I make no mention of engine capacity as in this context it is irrelevant (ie even if we had an unlimited engine size it would still be governed by the inlet valve size)

For a more accurate “bullshit O meter” use the BMEP calculation, more on that later
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Thanks SKiddell!
That has to be one the most comprehensive and helpful posts on dyno's ever written. I even learned a few things myself. (and I'm a poor student).


Well-Known Forum User
Your welcome
I just thought I would write a general guide as often people are too fixated on a number rather than the actual performance...I guess some people think "If I have a number i won't have to prove it in the actual car"

No one needs to prove anything, we all know (or at least should know) what each of the Z variants is capable of given its state of tune


Well-Known Forum User
Nice wright up Skid, I've had a lot of dealings with dyno operators over the years with my last car and have seen a lot of what you said about the figures being manipulated to keep the neds happy, I think you're only cheating yourself if you don't get accurate data, You need accurate data to gauge how well each mod works or doesn't as the case me be, Otherwise you're just pissing up the wall.

I was speaking to one operator who said he could make me a better print out if I wanted, My car had just made 399.7 bhp and he asked me if I'd like a 400 bhp print out, I kindly refussed his offer.

With my last set up my car made 497 bhp and then on a different colder day 519 bhp so you must take these things with a pinch of salt, And use the data as a whole to see where things work and where they don't.

I enjoyed your valve post as well and feel happy that my spare engine is an N42.



Well-Known Forum User
Ports valves and stuff

Port and valve size.

OK so we now have some information correlating engine potential and inlet valve size (bigger the valve, the more air/fuel you can get in right)

So let’s talk about some specifics.

The biggest stock inlet valve in a Nissan head (in the UK anyway) is the 44mm found on several later heads with an accompanying exhaust of 35mm

Why are ports and valves specific sizes?
Once again it’s a matter of synergy, items complementing each other with the single aim to allow enough flow of air and fuel at a high enough speed/volume to fill a cylinder in a given amount of time.
If the port to valve ratio is wrong then airflow will be either to great or too low resulting in partial cylinder fill or a massive efficiency drop off.

Each engine size (and use) will have its own air/fuel flow requirements, what’s right for a shopping trolley 2.4 won’t necessarily be right for a race spec’d HSCC 2.4 or 2.8 or 3.1, the cylinder volume is greater/smaller and hence the flow requirements are different. (The same applies to camshafts with valve lift and duration, what fills the cylinder on a 2.4, might not be enough on a 3.1)
Imagine I have a pint pot and I have 1 second to fill it, then image I have a gallon bucket and only .5 of a second to fill it….the hose/tap/pipe requirements for each is different.

Valve/port size guide
General rule of thumb (again) for a given inlet port diameter the valve should be 125% bigger and the exhaust valve about the same (or 80% of the inlet valve) this does vary depending on state of tune but not by much.

So lets look at our late Nissan head (N42 for example)

Inlet port 35mm, inlet valve 44mm and exhaust and surprise surprise the ratios are spot on, was it luck…….no these ratios have been around ever since Mr Mercedes said to his wife “lets ride”

Port Mach number
There is a point at which port/valve will no longer flow efficiently, in fact once past a certain velocity it can drop like a stone, this is the Mach number and it reinforces the statement that everything must work in unison, general consensus is that the velocity should not reach 0.5-06 of the speed of sound.

Velocity versus volume…discuss
Which is more important, well both, but either can get to a point where efficiency drops off,

Imagine a diameter of pipe and a given amount of water going through it, make the pipe really small and you will have a jet 10 feet long but it will take an age to fill a bucket, make it really big and it should fill the bucket really quick but because the bucket is 10 feet away it cant reach.

Too much velocity and we hit the Mach number, efficiency drops and the power curves falls of the edge of a cliff.
Too much volume (large ports, valves etc.) and we can completely lose the lower end of our power, because velocity has slowed to a crawl, fuel drops out of suspension, car coughs and splutters, fuel drips on the exhaust, car catches fire everyone has a bad day (Not uncommon on over carb’d and over cam’d cars, several well known Z’s suffer from it). It’s a fine balancing act. This balancing act is not one of guess work it begins with a flow bench to measure flow and velocity at specific lift profiles, however few people have access to one so we go down the DIY route and guess.

The trouble is humans get stuck in the “big is always better” trap and with engines that doesn’t always work.
The real trick is to use the well known numbers to calculate the correct sizes for the engine type and use.

By using port/valve ratios and Mach numbers, valve lift, rod length, displacement, static and dynamic compression ratio (plus many more) we can calculate how our engine will perform for instance when we built my three litre, the numbers said the cam didn’t have enough lift and had too much duration for a long rod large capacity engine.

The calculations predicted that at a certain rpm the engine would choke up because of too much duration on the exhaust allowing over scavenging, too much duration on the inlet bleeding off dynamic compression and the lift too small falling foul of the Mach number and not allowing enough air/fuel into the engine to sustain higher power and rpm figures.

Day of dyno run guess what, it produced within 2% of the predicted HP value at exactly the rpm predicted and fell off a tree at exactly the rpm predicted……lucky guess or what.
(BTW the recent 12.78 ¼ mile also supports the dyno value within a couple of % as well)

Shortly we will be fitting a custom cam better suited to the engine characteristics….I am not too bothered about the results because we already know them……within a % or two.

Anyway to sum up, no matter what your wife says, bigger is not always better

Hogged out inlet ports on their own yield little gains, possibly lose power
Too large inlet and exhaust valves the same
Large ports and valves are no good without a large cam and large carb setup

Large everything is no use unless you’re racing it or driving a nail in with it.


Well-Known Forum User
Very nice write up again and very interesting, I actually learned something which is always a bonus lol.

It confirmed somethings I've been thinking about for my spare engine build.

Thanks very much.



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Christ there are some clever sods on here!
But it seems to make sense after about 10 reads!
An old bloke who built engines for some of the plaky cars we made when asked about bhp used to smile and say 'as far as your concerned sunshine there is no such thing as bhp that's just maths, all you care about is what you feel when getting shoved back into your seat and that's torque'
Simple but mostly true.
The difference in air temperature and the relative oxygen content per volume does make a big difference,
I have an old jap gt4, now I live nearly 2000ft above sea level but my factory is at sea level.
I can go full bore at sea level but on a winters day at home if I floor it hard the car senses an overboost coming on and puts it in limp mode.
Boring but true.


Well-Known Forum User
Cylinder filling (inlet stroke)

OK so now we have some insight into power, ports, valves etc.
Some swotty swotts out there will have looked at BMEP, Mach numbers, VE and so on then said “right OK so how come some engine builders get more power than you recon smarty pants”
Well the answer is simple….some lie and some are really smart.

To help explain
Lets look at cylinder filling….

Easy right. Piston goes down, sucks stuff in, dead cert, easy peasy, nothing to see here, move along sir
Well sorry but you’re wrong, there’s a lot to be seen and had here.

Let’s slow things down and look in a little more detail because there’s a real trick hidden in here.

The action of the piston going down (at varying speeds) creates a pressure differential between atmospheric and cylinder, with the inlet open, air will rush in through the carbs or throttle body(s) collecting metered fuel as it goes, this air/fuel mixture has mass and therefore inertia.

So we have a mass of air/fuel rushing in at a fair lick, this mixture slug will lag the piston so when the piston is at a dead stop (BDC) the air is still moving, smart tuners use this inertia to fill the cylinder MORE that its static capacity….a little like forced induction…..naturally forced induction if you like, now you can see why atmospheric pressure plays such a big part. The more air and fuel you can get into the cylinder the more power you can generate.

This slight overfilling is how top engine tuners get more than 100% VE (volumetric efficiency) out of some engines, but it requires a number of things, well tuned port flow characteristics, ideal valve sizing and precise valve lift and timing as the inlet valve must close at exactly the moment that peak cylinder fill has occurred otherwise the opportunity is lost, a bit like a genie in a bottle.


Well-Known Forum User
Compression stroke
OK so we have filled our cylinder hopefully a little bit more than the static capacity, the inlet valve is closed and we are now quiet a few degrees past BDC and ready to squish our nicely measured mixture into the smallest space possible.

As the piston rises, the molecules of fuel and air are forced closer and closer together, piston gets to the top, spark goes Zzzst and the thing goes bang right…….well once again if your watching Iggle Piggle then yes however were not so lets look at things in more detail.

As the piston gets ever closer to the chamber, it is advantageous to create a swirling motion, this promotes a faster burn (not a bang, bangs are bad) which delivers more power, this is done by the shape of the chamber and or the piston crown, the most common is the closed chamber design on the E31, N47, N79 and P90 type heads they all have a flat surface directly opposing the piston, this surface does two things.
1. Promotes swirl as the air/fuel are squished between this and the rising piston the air/fuel tries to get out of the way and rushes into the larger chamber area
2. Creates a quench area to dampen uncontrolled burn and help prevent detonation.
It is advantageous to design your engine so that the piston runs very close to this “squish” area however here’s a rule of thumb, never ever run closer than 36 thou (0.9mm) other wise you run the risk of the piston clipping the head, Very bad thing tm
“why, 36 thou is loads” no its not, a rod alone can stretch 15 thou at full beans, add to that crank flex, piston stretch, pin flex and 36 thou can get eaten up quickly.

Other head designs (open chamber such as the E88, N42 etc) are more targeted at emissions and economy rather than outright performance and if they are to be used in highly tuned engines will need modifying as much above 11:1 compression they are detonation prone. This is generally done by welding up the existing “ramp” or slopped area and re machining to make it flat, this will result in the 2 valve tuners dream of a kidney shaped chamber. An alternative is to have some intruded crown pistons made that mate to the combustion chamber.

OK so we have compressed and swirled our mixture into a nice tight corner of the head and its time to set it on fire, however as always things are not what they seem, the timing of this is critical, to early and you risk engine damage and lose power, (image how your engine would feel if you try and ignite the mixture whilst the piston is only half way up its stroke), too late and you lose power as the piston is well on its way down and the burn energy is chasing it, ok got it I will trigger the spark at exactly TDC right….wrong.

Like all things, particularly in a high speed process like this, there is a lag between action and reaction, it might be only a few milliseconds but in an engine rotating at thousands of times a second, a millisecond is a long time, so we trigger the spark several degrees before TDC to ensure that the “burn” happens at the right moment and delivers peak power precisely when needed. Its worth while looking at what happens when this spark varies ie spark scatter.

Spark scatter
This is a symptom of a mechanically driven system such as a distributor, that have gears and bearings, even new, their not perfect “But I have an electronic one from a 280ZX” don’t care its mechanical and will still suffer from scatter.
Lets imagine an L6 on full chat and every spark is perfect, happening at exactly the right time, governed by the “perfect” distributor with a “perfect vacuum advance system, burn is predictable and therefore cylinder pressure is stable, now lets drop back to the real world where the gear play, bearing float, cap gap etc all randomly affect the spark so that it happens 2 or 3 degrees either side of where it should, the burn becomes unpredictable, the cylinder pressures vary and power drops, worse still we have set up a vibration source in the engine that no amount of balancing will remove…..even worserer, if we are running very high compression on a borderline engine we can induce pre-ignition (pinking) or worserer still, detonation Very bad thing tm


Club Member
Superb Steve. Absolutely brilliant comprehensive write-ups. As knowledge is power, is that how come your car is the fastest class 1 S30 in Britain? :D


Well-Known Forum User
Superb Steve. Absolutely brilliant comprehensive write-ups. As knowledge is power, is that how come your car is the fastest class 1 S30 in Britain? :D

Thanks Monsieur Ruby, :thumbs:
No its just luck;) and its not as difficult as going round and round and round a circuit:rolleyes:

I am hoping that we will see some other quick NA cars out this year, Tel240 was going really well, Mr Johnny Mason has been a little quiet but is one of the quickest 1/4 milers out there, Rob Huge will have a nice good looking, quick car but has forgoten how to drive, Glen Stone pops up from time to time sometimes bringing Dean Bottriel with him:bow:
Ian Patmore has a lovely setup that will run a good time, Charlie Boy has a great pedigree engine under the hood of a really nice car.
I would pay good money to see Bens car on a good surface as that thing will pull low 12's
I also have more than a slight suspicion that we might see a new (old) familiar face pop up for a shot at the title....who knows but he'd better get real good, real quick:devil:

But...Watch this space, more serious mods to come for the 2011 season, the target is a 12.6xx....road legal NA L6 which will be about it without slicks or.........Gas;)

Of course the RB and JZ turbo boys are in a different league and if Darren thinks he's got it all to himself then he had better watch out;)....Johnny Palmer and Dave Porter might have something else to say on the long as
1. JP stops thinking that Santa Pod is for drifting.
2. DP remembers where it is.

And lastly don't underestimate Mark Raynors twin turbo L6, thats no slouch or a certain V6 powered S30 in white and red.

Can one of them be the UK's 1st road legal Z in the 11's :eek:

Oh nearly forgot, wheres Phil "big hair" Ellicot got too.


Well-Known Forum User
Thank you steve

Thank you Steve for your efforts , very impressed , so much to take in . It has come at the correct time for me , as I am going to see a prospective rolling road in Crawley on Friday. Hoping to take my car to them next month , Will have to read your post a few times to even get some of the info to stay in Thanks again



Well-Known Forum User

Seve , There are a few of us taking our cars to a rolling road in the future , As I have said I am going to check out a company in Crawley that have spoken to on the phone to see if they have the equipment and knowledge to tune my new set up , the last time I had it tuned I have fitted a stehl header a complete exhaust system Weber45s and a cold air induction system , so things have changed a lot , the company I used last did not have the jets and chokes etc in stock enough to change if required . the company in Crawley say they have a full selection ,
So it would be very helpful if you could tell us your top six or twelve questions and thing to look for when visiting a rolling road for the fist time without the car to see if at approx £95 an hour the company is suitable to tune our very precious Zs . Your thoughts would be much appreciated .In laymen terms .

Phil . :driving:


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Thanks for putting the time and effort in Steve, All your posts have been very interesting if not heavy going for the first couple of reads lol, And thanks for writing them in English and not gobbly gook!



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Your more than welcome
I sometimes get some flack for being to technical so I tried to put some humour in there

Phil if its ok I will spend an hour or two writing up a crib sheet for you

I will post it up later on this evening, if thats OK


Well-Known Forum User
Thank you Steve

Thank you Steve , That is just what I need and I hope will be of use to others as well . Look forward to your reply .

Phil :driving:


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Remember its your money and your car so we need to determine if they are worthy no particular order

Ask about other customer’s cars on carbs any regulars, what set ups have they seen
It’s not critical but have they tuned an L series before (more conversation than anything)?
OK so they have a supply of jets but what about chokes ?
How extensive are their spares, mains, idle, pump, emulsion tubes ?
Test THEIR knowledge pretend you don't know anything and ask about, RWHP and FWHP
Ask to look at a sample of their print outs, look to see several successive runs of HP, torque and also AFR (Air Fuel Ratio) with improvements on a graph with date time and preferably temp and pressure
Ask how temperature and pressure could affects things
Ask about ignition timing, triples and vacuum advance.
Ask about cam timing a good dyno will discuss cam timing and offer to swing the cam on request (assuming you have an adjustable sprocket.... you should if you have triples and a cam)
You have heard people mention about "coast down" ask them to explain.
Ask them what you should do to prepare for a visit, a good dyno operator will say check oil, water, tyre pressure, fuel etc.
Ask if you can watch what they are doing or do they require you to be out of the room.

The aim of the day is to tune your set-up so that it makes optimum power (not always maximum) coupled with drivablity so when they have finished ask to take it for a quick spin before you pay, the last thing you want is to shell out, get 2 miles up the road and hate it.

Maybe you could do a write up after the session and give your views, there aren’t many carb tuners around these days they have all gone to the dark side of fuel injection and ECU’s.