Bonneville America Forums Forums Technical Forums Performance Mods Air/fuel setting.

I think AFAIK I have the same set-up as Grump. Have my new mercury carb sync. tuner. A/F mixture screws: I don't have the knurled ends ,mine are the (D) stock type.I know what the AFR is supposed to be for the bike 12:1-14:1 (outer limits)with the Ideal mixture of 13:1. My question is I'm setting at 3T,what if I turned 3.25T,3.50,3.75,4.0T How do you know what is sufficiently adequate,spark-plug glance,Exaust end deposits,overall RPM ? How do you determine, However Uneducated or Experienced is it still a guess? Would a Dyno be in order? ....I just would like to know what is the correct way, so I can dial in my bike.Edited;I went on line and found a bunch of dyno-testing facilities in my area. bike shops , dealerships. curious what I should exactly ask for when I go with one...exactly what types of tests should I ask. Speed. Anybody?

get the a/f ratio across the rev range, and find out what its doing steady-state, say 4000 rpm in 4th. It 'll give you a hp and torque reading but thats just for bragging rights. the a/f is the most important reading
G

Hey G,on hold right now on the phone with river city harley trying to schedule an appointment $69.00 hour...[Dyno]still have to sync the carbs...a little apprehensive about that part but will get it done have to take off my dunce cap. will ask what you said A/F ratio across the rev range and find out what it is doing steady-state..4000rpm in 4th is an example..correct?...... I need to check in tommorrow [9:00a-3:00p]with the dealer(Wild Bill) they say because it's not a Harley...need to be "approved" there are not as many as I thought around here. Doesn't look good but I'll try.

A dyno is a dyno, but some shops are wifty that way. Tell them you dont want them to tune it, just run the dyno and hand you the results...that may work
G

Actually, not to start a bunch of hooey, but there are more than one type, and it is somewhat relevant. Dyno come in Inertial or Braked.

Advantages and disadvantages of a modern computerised braked dynamometer system:

* They / the operator can vary the load so that the engine can be held at constant speeds while such things as ignition and fuelling can be adjusted to optimum values at different steady state throttle openings and rpm's - extremely useful! Easier to fully set up a new engine management or carb system quickly and accurately. For this reason alone these types of Dynamometers are preferable for setting up and tuning road cars and moderately tuned vehicles where you are not just looking for "ultimate" power.

* Unfortunately most braked dynamometers seem to use dual rollers on each wheel. These "trap" the tyre, cause slippage, heat, HP losses that vary, and can cause tyre problems. A single drum per wheel of 16 inch diameter or greater is far superior.

* Can be dangerous to certain very high performance, boosted, nitrous injected, or tuned two stroke type engines as they are already on the edge of detonation and heat damage. This mostly depends on the experience of the operator. Trying to hold a 450bhp turbocharged nitrous injected bike at steady full power is a recipe for an engine meltdown! In the real world its not a problem because they would be going at say 170mph in 8 seconds and then shut off! The correct ignition timing and fuel mixture for these types of vehicles is generally not suitable for continuous steady state non accelerating conditions.

* Because of the fact that they CAN be calibrated, and in fact need to be calibrated from time to time, means that they can never be totally accurate. And that an owner or operator can "ahem" re-calibrate it themselves! Never trust a tuner to give you reliable figures! Most are honest but some are not! Its only too easy to make the results "look good" if you see what I mean...

* Because of the fact that, the rollers are "wrong" in layout, and size on most of these, and because they use a dc voltage signal from a load cell connected to the "brake" to determine roller torque (torque x rpm or speed gives them the BHP) which in itself has a level of Hysterisis, and because this low level DC output is subject to electrical noise & variable resistance due to temperatures, errors from the analogue to digital conversion process etc, they can NEVER be completely accurate. Or in fact very repeatable.

Advantages and disadvantages of a modern computerised inertial or inertia dynamometer system:

* 1st a word of warning... Because the principal of an inertia dyno is so simple there are rather a lot of really badly designed systems out there. Its hard to know which ones are good well designed systems, and which are practically useless.

* There is NO calibration ever required or possible on a good properly designed (not all are!) inertial dynamometer system. My own systems for example used a free running solid steel turned drum of 402mm in diameter x 562mm wide. All of the dynos I produced used this exact same drum. The inertial values were calculated mathematically from the density of the steel and the technical drawings, and integrated directly into the software. There are simply no external user parameters that could be changed to alter the "calibration". There simply is no need. So there can be no errors, or calibration requirements. If a healthy car / bike reads 56bhp on one dyno, then it will read this exact same figure on all of the others! Its just maths. Unlike braked systems there is no no DC voltages, nothing can change, no variations due to Hysterisis etc. Companies such as DynoJet do the same thing. In fact I took my own motorcycle to ten different DynoJet dynamometers in the UK over a period of a couple of weeks, and it / they read between 135 and 136 BHP on all of them, as well as on my own dynamometer systems. Nice to know your maths is the same as theres is! You simply cannot do this with any normal braked dynamometer systems, as they vary quite wildly due to the above and one or two other minor things like they all require Calibrating!

* They are dynamic testing dynamometers only! This means that when you open the throttle the drum always accelerates. It is not possible to hold a steady "under load" rpm. So making changes to fuel and ignition maps is much more difficult. It is less good at this kind of thing than a braked dynamometer is. If your main job is to set up fuel systems across the range, for e.g., rather than absolute accuracy and repeatability you are better off using a braked dynamometer.

* For deadly accurate back to back power runs when testing things like different lubricants, plug gap changes, different ignition coils, tiny jetting or fuelling changes, then they are superb! Its even possible to easily and repeatable see the effect of turning the lights on during a run! Try that on a braked dyno and the small difference is lost in the "noise" of the system. So for ultimate performance tuning, bikes, drag racing, etc they are preferable.

For example...

On this bike below! It was mine, but it does not like braked dynos (or rather having its rpm held at a constant speed) due to the sheer amount of nitrous being used in two stages. It detonates a little after being held at a constant 6,000 rpm for a short period. We were trying to get a fix on the mixture at this point, but this takes a good few seconds to stabilize. In real life it does not see 6000rpm for more than a second on the strip. So the heat build up on plugs / valves etc does not get time to start it detonating! After 6000rpm - no problem. We know this because a knock sensor and a data logger tells me so... Retarding ignition more at this point, or adding a touch more fuel stops this happening. But the bike is then measurably slower! So for some situations a dynamic run climbing through the RPM's is very important. Whilst some braked dynos can also do rpm "climbing" runs, it defeats the object of using one because then you may as well use a nominally more accurate inertial dyno as you can't check the mixture at any given RPM any more!

shamelessly coppied from:

http://www.dynamometer-info.co.uk/advantages-of-each-type-of-dynamometer.htm

OK now I'm trippin" Inertial dyno or braked dyno? Which will work the best in = my application Brake? Inertial is for drag bikes etc.,nitrous and so forth for pinpoint accuracy or is it the other way around also I've also heard they are not real world(Dynos),Bring in Real world elements,Heat,Humidity,cold,dry,dust,etc.and that brings on other complications

If your main job is to set up fuel systems across the range, for e.g., rather than absolute accuracy and repeatability you are better off using a braked dyno with a single 16" or larger roller.

For deadly accurate back to back power runs when testing things like different lubricants, plug gap changes, different ignition coils, tiny jetting or fuelling changes, then Inertial dynos are the ticket! Its even possible to easily and repeatable see the effect of turning the lights on during a run! On a braked dyno and the small difference is lost in the "noise" of the system.


The real world component is also true. All the things you mention are individually valid to some degree, and more so when compounded, but not really significant unless the real world environment is extreme. However, the biggest variance seems to be with air flow. It's hard to duplicate the flow rate and volume of fresh air with the bike not moving. They will set up fans to keep the bike cool, but your not going to get the ram effect (or - vacuum effect). You would almost need a wind tunnel to replicate the bike at speed with a rider aboard.

All that said, it is the best tool that we have, so be excited, use it with zeal, tune that baby up and let her rip! Be sure to post the results with your mods.

Thanks man,I appreciate it.Now it will be a challenge to find one in the surrounding area as the HARLEY shops look down on us. You know thats ironic though I haven't met one harley owner/rider that wasn't in some kind of awe about the black Speedmaster. It's a corporate thing. Speed. Keep the rubber on the ground.