Dyno testing strategy.

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Abarthnorway - Remi L
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Dyno testing strategy.

Post by Abarthnorway - Remi L »

Hi All!


Finally some fun for me:-)
I am about to order a dyno session for my engine to be used in a tarmac racing 130TC.

After calculating track speed and gearbox ratios - I am looking to maximize the torque from 4800-5000 rpm and upwards. The higher up the engine "peaks" the better.


Specs (set by class rules):
130TC GC head
Solex 40 ADDHE - tipo 37 (chokes free)
Cunningham Rods
Forged & lightened 130TC design pistons
Compression approx 10:1 (thin gasket)
130TC tubular 4-2-1 manifold
New 130 TC cams 10 mm lift (timing free)


I am planning the day along these lines:

1. Original setup: Cams 112/112 Carb chokes 32.
2. Choke size change (have 33,34,35,36)
3. Changing camtiming for more overlap 110 - 108 - 106 etc. (will drybuild to find timing limits)
4. Possible different inlet/exhaust cam timing. No experience here - suppose I could spend the whole day...
5. Tighter valve clearances. (I have looked at the cam ramps)
6. Ignition adjustment/mods.
7. Rampipe length.
8. Final rejetting.

Any suggestion regarding the order of adjustments or relevant hints appreciated. Especially regarding pt 4.

And a question - is modifying the camshaft to accept a spanner for timing adjustment OK or NOGO?
I always find changing timing to be a fiddly process..... any hints?


Best regards

Remi Lovhoiden

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WhizzMan
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Re: Dyno testing strategy.

Post by WhizzMan »

What I was taught is this sequence. It was for Fuel Injection, but most should apply for carbs just as much:

- Set timing to something conservative, so you won't be detonating for certain
- Get fueling right. Start in the middle of the throttle and rev range and work your way to the extremes. (for carbs, other rules probably apply)
- once you have fueling right, set your ignition timing.
- check fueling again, do adjustments to both if required

Once you have those done, you have a decent base line, where you can experiment with things like overlap, and individual cam timing. Those mostly will get you another rev range and possibly a better flow. They will probably not influence timing or mixture settings significantly, unless you were way out at base setting. A recent discussion on another forum suggested that most hot 2-valve engines prefer an LSA of around 108 degrees. It also suggested that going for one or two degrees less than optimal, would be better than going for too high LSE, if you're building a racing engine. You may want to start your base setup tighter than 112 degrees LSA and go up from for example 107 to 112 in steps to see where the drop-off is. Once you hit that, go back one or two degrees and leave it there.

Once you have those set, you can try and see if you can get more power with bigger chokes, ram pipe length and all that. I'd be careful with going for bigger chokes than 34 in a 40 carb. It will probably work, but velocity at lower flow rates will suffer and your engine may very well run significantly worse at lower revs as a result. I see people build an entire car and not experiment with bigger chokes until they're done trying a lot of other things, on track, setting lap times. It may be the thing for you, to go for bigger, but don't rule out the benefits of a larger rev range with more torque in the mid section. It depends on your skill, driving style and the tracks you race at which will work best for your application. Those are hard to measure at a dyno session, so I'd leave the chokes out of the equation until you have some lap time done with the car. Especially if you're not a very experienced racing driver, you're probably going to set better times with a car that is a bit more forgiving, so I'd try a 34 or maybe a 35 choke and leave it at that for now.

I personally wouldn't mess with valve clearance. Set it once at where it should be and only derive if you have clear indications you are damaging parts because your information on where it should be is wrong. When in doubt, make sure that a warm engine still has some form of clearance when the cam nose is opposite of the tappet and that the ramp is actually being used to start opening the cam. If the cam doesn't contact the tappet until the actual nose, it will wear very quickly. I'm sure Guy will be able to give you very precise instructions on how to set this up perfectly with your cam and the head he provided.

Keep in mind that fueling with carbs tends to be influenced mostly by flow rate, with the resonance and blow-back making it difficult to tune perfectly for each possibility of rpm, throttle position and engine load. If you have your basic flow rate set up correctly, you can get most other parameters determined without having to adjust fueling. That makes it beneficial to get that set up as one of the earliest stages. Changing chokes will make you have to do that all over again. Changing chokes might only work if the rest of the setup is already proper, because you won't benefit much from bigger chokes if the engine isn't pumping it's full potential yet. Therefor, I'd choose to do that as one of the last things. Once you've set all other parameters, double check your fueling to see if it's still where you want it to be and of course keep the mixture/O2 probe in during all tests for safety.

Ignition timing is primarily set by determining the "load" of the engine and the RPM. As soon as you know how much mixture is in the engine, you can determine what ignition timing is giving the optimal power without detonation at the rpm it's running. You will only need to readjust your timing if your fill rate changes significantly. By staying on the conservative side of timing while doing other adjustments, you can judge the fill rate improvements without having to tinker with your ignition timing and having more than one factor to consider. Setting ignition timing proper for partial load on race cars is only done when people have spare time on the dyno, or if fuel economy is a factor in the race. Just setting advance proper for full throttle and not advancing more at partial loads is a common practice. You can gain "throttle response at part throttle" and "fuel economy" by setting those too, but it will be expensive to do so if you're not done experimenting with other parameters.

If you have the option to do rampipe length tuning, I'd do that as one of the very last things. Usually, you can calculate more or less what the optimal pipe would be from the alternatives you have available. Don't expect big horsepower changes if you change that length by only a few centimeters. Things like these, when prepared and calculated correctly, are details that will help you gain horsepower, but should not be perfected until you have the basics worked out. A "ballpark figure" is probably going to give you a very close to optimal result from the start. If you have to choose what tests to do on the dyno, I wouldn't put my priority on these.

Once you're happy, make sure you do a final check for mixture and detonation (ignition timing). Things tend to creep in without you noticing because you're focusing on other areas. Don't leave the dyno place without actual proof your mixture and timing are "safe" for the engine.

Don't overestimate the time you have at the dyno. Things go wrong, tinkering takes time, you get tired. Establish a list of things you want to do with the order in which to do them. Do not take shortcuts you haven't planned in before. For example, set yourself rules before you go to the dyno like "If I run out of time, I'll only do 3 LSA angles and no individual cam angle advance tests" or "I'll only do idle and full throttle rev range timing setup, I'll disable vacuum advance". If you make on the fly decisions to skip things, you may oversee consequences your decision may have. If you make them in advance, you can make rational decisions and think them over for a while, without wasting valuable dyno time or breaking your engine. You seem to have this part already figured out. You asked others about their opinion here, so you'd learn from their mistakes and experience as well.
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Guy Croft
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Re: Dyno testing strategy.

Post by Guy Croft »

will look in on this, bit busy at present,

G
Abarthnorway - Remi L
Posts: 207
Joined: June 24th, 2006, 1:39 pm
Location: Oslo, Norway
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Re: Dyno testing strategy.

Post by Abarthnorway - Remi L »

Hi!

@ Guy
Nice to hear You are busy at the "office"

@WhizzMan
Thanks for the input:-)
WhizzMan wrote:- Set timing to something conservative, so you won't be detonating for certain
- Get fueling right. Start in the middle of the throttle and rev range and work your way to the extremes. (for carbs, other rules probably apply)
- once you have fueling right, set your ignition timing.
- check fueling again, do adjustments to both if required
This is covered by setting up the engine according to standard specs for the 130 TC in point 1. Jetting might be a bit off as the head is flowed by the expert, and compression slightly higher. But as a baseline it hopefully works fine.
WhizzMan wrote:Once you have those done, you have a decent base line, where you can experiment with things like overlap, and individual cam timing. Those mostly will get you another rev range and possibly a better flow. They will probably not influence timing or mixture settings significantly, unless you were way out at base setting. A recent discussion on another forum suggested that most hot 2-valve engines prefer an LSA of around 108 degrees. It also suggested that going for one or two degrees less than optimal, would be better than going for too high LSE, if you're building a racing engine. You may want to start your base setup tighter than 112 degrees LSA and go up from for example 107 to 112 in steps to see where the drop-off is. Once you hit that, go back one or two degrees and leave it there.
Regarding cam timing I do not think there is a specific degree thats perfect for a hot 2V engine. Its all about engine setup, cam type and wanted powerband. I have run race cams up to 10 degrees off their recommended setting and it still ran beautifully. This time I will go from a known standard towards the unknown = more overlap. I and decide from the dynofigures when I get to the "limit", and decide the timing from there. My guess is that the ideal timing for me will be less than 107....
WhizzMan wrote:Once you have those set, you can try and see if you can get more power with bigger chokes, ram pipe length and all that. I'd be careful with going for bigger chokes than 34 in a 40 carb. It will probably work, but velocity at lower flow rates will suffer and your engine may very well run significantly worse at lower revs as a result. I see people build an entire car and not experiment with bigger chokes until they're done trying a lot of other things, on track, setting lap times. It may be the thing for you, to go for bigger, but don't rule out the benefits of a larger rev range with more torque in the mid section. It depends on your skill, driving style and the tracks you race at which will work best for your application. Those are hard to measure at a dyno session, so I'd leave the chokes out of the equation until you have some lap time done with the car. Especially if you're not a very experienced racing driver, you're probably going to set better times with a car that is a bit more forgiving, so I'd try a 34 or maybe a 35 choke and leave it at that for now.
Regarding changing the choke sizes first or last, I am pretty sure is that the engine will respond to fitting a larger choke - especially considering my goal of a "highrevving" engine. When considering the various adjustments to be done on the dyno this is the one I am most confident on. If that theory is a right - better do it right away, and do the more uncertain adjustments later..... thats my thinking anyhow.
If setting up the cams for maximum power using 32 chokes, I am not sure the cam timing would be optimal with - let`s say - 35 mm chokes..... on that subject I have no experience.

When talking about lack of mid range torque, I do not consider this a problem when using std camshafts, and most races have rolling starts. From a calculation of gear ratios and track speeds, 4800-5000 and upward is the powerband that will be used 99% of the time. I am not worried about performance at lower revs.
WhizzMan wrote:I personally wouldn't mess with valve clearance. Set it once at where it should be and only derive if you have clear indications you are damaging parts because your information on where it should be is wrong. When in doubt, make sure that a warm engine still has some form of clearance when the cam nose is opposite of the tappet and that the ramp is actually being used to start opening the cam. If the cam doesn't contact the tappet until the actual nose, it will wear very quickly. I'm sure Guy will be able to give you very precise instructions on how to set this up perfectly with your cam and the head he provided.
Setting standard clearances is a safe bet for engine longlivety - and nothing wrong will happen from that. I have studied the ramp of various Fiat cams, and found that they differ quite a lot. When comparing the ramps, it seems to me that the 130 TC profile might get away with a tighter clearance, and I have had no issues even in real life. I do not feel that the factory stated clearances neccesarily applies to a race engine. I suppose that recommended clearance has a lot to do with the fact that factory engines are supposed to run for 50.000 miles or so without any adjustment.
(Warning: Running tighter clearances is not OK with all Fiat cams!!!!)
WhizzMan wrote:Keep in mind that fueling with carbs tends to be influenced mostly by flow rate, with the resonance and blow-back making it difficult to tune perfectly for each possibility of rpm, throttle position and engine load. If you have your basic flow rate set up correctly, you can get most other parameters determined without having to adjust fueling. That makes it beneficial to get that set up as one of the earliest stages. Changing chokes will make you have to do that all over again. Changing chokes might only work if the rest of the setup is already proper, because you won't benefit much from bigger chokes if the engine isn't pumping it's full potential yet. Therefor, I'd choose to do that as one of the last things. Once you've set all other parameters, double check your fueling to see if it's still where you want it to be and of course keep the mixture/O2 probe in during all tests for safety.
I do not really understand what You mean by "Your basic flowrate set up correctly"
What do I have to do all over again when changing chokes?
The mixture will be monitored all the way....
WhizzMan wrote:Ignition timing is primarily set by determining the "load" of the engine and the RPM. As soon as you know how much mixture is in the engine, you can determine what ignition timing is giving the optimal power without detonation at the rpm it's running. You will only need to readjust your timing if your fill rate changes significantly. By staying on the conservative side of timing while doing other adjustments, you can judge the fill rate improvements without having to tinker with your ignition timing and having more than one factor to consider. Setting ignition timing proper for partial load on race cars is only done when people have spare time on the dyno, or if fuel economy is a factor in the race. Just setting advance proper for full throttle and not advancing more at partial loads is a common practice. You can gain "throttle response at part throttle" and "fuel economy" by setting those too, but it will be expensive to do so if you're not done experimenting with other parameters.
I run the standard ignition system Marelli DigiPlex. This is preset in many ways, but changes can be made by moving the crank sensor and a few other tricks. This is set as one of the last points when "everything else" is optimised. Fuel economy is not a factor in the race series.
WhizzMan wrote:If you have the option to do rampipe length tuning, I'd do that as one of the very last things. Usually, you can calculate more or less what the optimal pipe would be from the alternatives you have available. Don't expect big horsepower changes if you change that length by only a few centimeters. Things like these, when prepared and calculated correctly, are details that will help you gain horsepower, but should not be perfected until you have the basics worked out. A "ballpark figure" is probably going to give you a very close to optimal result from the start. If you have to choose what tests to do on the dyno, I wouldn't put my priority on these.
I have absolutely no idea how to calculate ram pipe length - Do You have a calculation for my setup for maximum torque from 4800 and up?
This point is set as the last thing before final rejetting of the carbs, and will be left out if time is limited.
WhizzMan wrote:Once you're happy, make sure you do a final check for mixture and detonation (ignition timing). Things tend to creep in without you noticing because you're focusing on other areas. Don't leave the dyno place without actual proof your mixture and timing are "safe" for the engine.
Point 8 is final rejetting
WhizzMan wrote:Don't overestimate the time you have at the dyno. Things go wrong, tinkering takes time, you get tired. Establish a list of things you want to do with the order in which to do them. Do not take shortcuts you haven't planned in before. For example, set yourself rules before you go to the dyno like "If I run out of time, I'll only do 3 LSA angles and no individual cam angle advance tests" or "I'll only do idle and full throttle rev range timing setup, I'll disable vacuum advance". If you make on the fly decisions to skip things, you may oversee consequences your decision may have. If you make them in advance, you can make rational decisions and think them over for a while, without wasting valuable dyno time or breaking your engine. You seem to have this part already figured out. You asked others about their opinion here, so you'd learn from their mistakes and experience as well.
Thank You! Good advice.


Best regards

Remi Lovhoiden
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Guy Croft
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Re: Dyno testing strategy.

Post by Guy Croft »

Good posts both, well done!

Re your original post Remi I will give the answers succintly - though I would say how kind it is of Homme to write at length, something I don't have time to do so often these days:

MY REPLIES IN CAPITALS FOR BREVITY..

1. Original setup: Cams 112/112
2. Choke size change (have 33,34,35,36) GO 34MM
3. Changing camtiming for more overlap 110 - 108 - 106 etc. (will dry-build to find timing limits) EVERYTHING I HAVE SEEN INDICATES THAT REDUCING THE LOBE SEPARATION ANGLE INCREASES THE TOP END POWER. THE STANDARD CAMS ON STD TIMING WILL DEVELOP PEAK TORQUE AT ABOUT 3800 WHATEVER YOU DO. YOU CAN CHANGE THE INLET TIMING TO 108/106/104 EVEN 102 BUT I SUGGEST OPTIMUM EX FL WILL BE SOMEWHERE BETW 106/108 DEG BTDC. I RECKON YOU WILL GET BEST POSSIBLE RESULTS WITH 104 INLET 108 EX. ASSUME YOU HAVE ADJ PULLEYS OR YOU CAN'T DO IT.
4. Possible different inlet/exhaust cam timing. No experience here - suppose I could spend the whole day... COVERED ABOVE.
5. Tighter valve clearances. (I have looked at the cam ramps) DON'T ATTEMPT THIS IT WILL NOT GIVE MORE POWER
6. Ignition adjustment/mods. BEYOND WHAT YOU KNOW HOMME HAS COVERED THIS ONE SUFFICIENTLY WELL ALREADY BUT ABOVE ALL MAKE SURE SHE HAS 34-35 DEG TOTAL ADVANCE AT FULLTHROTTLE ANYWHERE BETW 3500-5500 RPM.
7. Rampipe length. YOU CANNOT PREDICT RAMPIPE CHANGES EXCEPT TO SAY THAT LONGER WILL GIVE MORE BOTTOM-END AND VICE VERSA
8. Final rejetting.


And a question - is modifying the camshaft to accept a spanner for timing adjustment OK or NOGO? BEST WAY IS SLACKEN THE ADJUSTABLE PULLEYS AND TURN THE CRANK.

G
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