Sweep 6 , is using 75lbs more fuel per hour, yet with a leaner air fuel ratio according to those sheets?

Sweep 6 was with 86/90 jets. I don't have the notes with me for jetting on sweep 11. It looks to me like 6 is using more fuel when you look at bsfc and lbs but like you mentioned sometimes leaner or very little change in O2. And get this, even though he told me he was fattening it up to get egt down the cooler egt is with the leaner bsfc/lbs. Sweep 6 had some egts close to 1500, sweep 11 was cooler. I just started looking at the sheets today. He says it must be burning more efficiently even though we are putting more fuel in. Keep in mind we also saw a power loss from sweep 6 to 11. I'm at a loss.

Lol, so mis informed, as usual... don't forget, YOU bashed ME.... good luck carry on..

This is very odd. But is it ?

Below are my experiences and thinking, which is not anywhere near as some people, but more than some others. So, always take what I say with some grain of salt, but atleast think about it. LOL.

I have a semi theory - semi meaning I have seen this a few times and usually on a faster sweep rate like the OP's dyno has been using. 600rpm/sec.

What causes less fuel flow but richer fuel A/F's other than equipment not reading correctly ?

Fuel bowls !

If the needle and seats are closed (bowl is full) what happens ? Less or no fuel flow into them. Yup ! But there is still fuel coming thru boosters and into engine right ? Yes. So, of course fuel is still flowing into engine , but the fuel flow meters are measuring fuel flow into the bowls.

Furthermore, having much larger Needle and seats than what is needed causes longer time periods between 'on/off' of fuel flow into the bowls. Why ? They fill the fuel bowls faster. Note: this is effecting dyno sensor readings, not actual engine performance.

So....just something else that throws some curve balls into things, especially when total faith get's put into data without knowing everything that effects it.

Thios is yet another reason I'm a bigger advocate of slower sweep rates.

Why are their many different choices of sweep rates on dyno's ?

To better mimic the actual acceleration rate of the engine in the vehicle it's going in.

Boats obviously have a very slow acceleration rate because of 1 speed 'transmission', weight, and load.

How fast does the typical performance boat accelerate from say 3000-5500 ? A while. Definitely not 600rpm/sec, nor even close too that. 300rpm/sec (lower setting for most dynos) - nope ! But atleast this is twice as slow as 600rpm/sec. Which is twice as long for things to 'stabilize' if that's even possible at 300rpm/sec.

I discussed sweet rates with him and attempted to get him to slow the sweep rate to 200- 300. He tried to do it, I saw him turn the sweep rate control down. The sweep rate did slow down from the previous 800 but did not come down to 300. He has no idea why. He continues to challenge my faith in his abilities at every turn. When we discussed the fuel issues last night he said he places little faith in any data and based most of his tuning off plug readings.

Heres a question I have, regarding plug readings.

Lets say, you have a -6 NGK plug in the engine, and you are looking for timing . You are on the dyno doing pulls. You adjust the timing to where the heat line looks "good" to you. What happens when you stick a -8 NGK plug in it? Theoretically, you would be able to put more timing in it, to get the heat line where you want it. But does that mean the engine likes or doesnt like it? Who says what plug is correct heat range?

My thought process would be, give the engine the timing it likes, and check the plugs. Then , adjust your heat range from there.

All the fuel data I have is in the attachment on my other post. The engine made 5- 10 hp and ft lbs less on sweep 11. The egts were also cooler on sweep 11. The other engine is going on tomorrow I believe. I'll get print outs of every jet change, not just first and last. All the runs from this last engine might still be in the computer so I'll see if I can grab them. Anyone plan on being in Bflo tomorrow and want ro attend? No charge.

Sb, you mean something slower sweep rate like this? https://youtu.be/OeJ_7-hpzq0

Yup. Was that 200rpm/sec ? Appears pretty slow.

Just so people know, 600rpm/sec seems to be the standard rate as 95+% of sheets you see show 600rpm/sec. I'm just proposing here, and others agree, closer to actual engine accelration rates will of course be better. That's why OEM's and big $$$$ race outfits will dyno (huge $$$ dyno) for actual conditions. Example: road race engines will be dyno'd as it's at a certain track. Acceleration, deceleration, shifts, and etc will be done as close to exact on dyno as it's 'being driven' . Obviously not just for power/hp, but for tuning and alos component durability, and etc.

https://www.youtube.com/watch?v=J-62SiWKJzM

One last distraction , just cause I love this stuff.

Most extreme I have seen is Porsche's oil sump dyno testing. It simulates running the Nurburgring (sp?) track Yikes !

https://www.youtube.com/watch?v=fv53RbvgfGc

As joe did, we did mine slow rate also in marine trim, that was as accurate as we could get, still changed a lot putting them in the boat mid summer I see low 11 air fuels sonetines a high 10, I am rejetting This week glad I have widebands to keep eye on that, I recommend that on any HP boat.

http://youtu.be/F5sQmgFHOf4

How many of you see a huge change in boat over dyno o2?

Most dyno shops dont simulate part throttle loads. They simply do a full throttle pull, and call it a day. That does nothing for part throttle fuel tuning.

Ryan Retter allowed us to bring the engine up to certain rpms, and partially load the engine and monitor the air fuel ratios, etc. For example, 3000rpm and 0" , 3500rpm, and 2psi boost, etc

From what Ive been learning over the past couple years, is that , a dyno tune on your engine, is only as good as the operator,tuner, and equipment they have. Slapping an enginr on a dyno for unrealistic sweep rates, questionable data acquisition, and 30 year old tuning techniques, is pretty much a waste of time. And in the wrong hands, can do more damage to the engine than its worth.

That was 150 per second starting around 2800rpm to 6500rpm. . We ended up going to 300 rpm per second i wanna say on the next engine. I felt the 150 per second was a bit extreme. My boat would never accelerate THAT slow.

We held mine at peak TQ for how long to monitor A/F? Like 3 minutes just held it there.. That was good to see stable A/F throughout.

Thats why i am so happy to have a dyno in.my own shop now. Mine has manual brake control, i can mimic the way it accelerates in the boat real easy and the 550 hp 502 mpi i just built and dynoed i did numerous part throttle pulls hitting map tables from 40 to 100. By doing this i didnt have to spend 10 hrs driving around in the boat tuning w the laptop. I did all my tuning at 50 psi of fuel pressure, when installed in the boat the tune was a little richer than i wanted almost everwhere so i was able to lower fuel pressure about 5 psi this making "global changes" to get afrs where i wanted with just some small tweaks here and there, Smitty

I may have missed it somewhere in your other post however are do you have wideband o2 installed in your boat? With where your currently running AFR's I believe your engine will like the cooler temps without a concern. I'm probably old school but along with wideband I still like to do plug checks from time to time on hottest cylinder due to equipment failure or possibly inaccurate?

I mentioned earlier regarding seeing extremely high EGT's while jetting was overkill. It was one of my learning days many years ago on BBC with a 420 mb. In a nutshell the the EGT's were so high from way to much fuel/jetting. Fire was blowing out of the hole (exh port) so to speak. Had to bring jetting way down to get numbers where they needed to be. Initially it was a real head scratcher with seeing such outrageous EGT's yet the plugs showed extremely rich. Would have been caught much quicker if the wideband would have not malfunctioned via day one.

What did your engine builder say about your AFR's currently vs when in the boat?

I had egts in my lightning headers years ago in my supercharged Baja and when you got the afrs into the mid 11's the egt temps were past aluminum meltdown (1600+), seen that again since then on dyno when making blown pulls too so to me I dont even bother running them on dyno as they give false results, Smitty

I do have O2 in the boat so I will be able to check/ compare. We haven't discussed changes to be made after installation. I'll probably have to start another thread...

If EGT`s are too high with a rich mixture I`d say it doesn`t need less fuel but may need more timing to burn the fuel off.
I saw lower egts with more fuel. Pulled 4 jet sizes EGTs went up.

I can't speak to how it affected egt but we did advance it as far as 36. Power peaked at 34. I'll check the old sheets for the egt

The best thing about a dyno, is using it whats its for, and thats watching what changes the power numbers. Many times, you will see when richening the mixture, the torque numbers INCREASE. Theres a reason this happens, and it kind of applies to what Icdedppl just said.

The richer fuel mixture, simply takes longer to burn. Why would this make the torque output increase? Because now the peak cylinder pressure inside the cylinder, is happening at a later time, where there is more leverage on the crankshaft. You slowed the burn down with more fuel. When in reality, you may have simply had, too much spark advance in the first place.

There is an area, in which we want peak cylinder pressure to be. Controlling that , is spark timing, and fuel mixture. If you make peak cyl pressure happen too early in the cycle, you lose leverage forcing the piston down the bore. Same goes if you make it happen too late.

This misconception, that spark timing is some sort of adjustable power adder, or power reducer, is just that a misconception. The entire goal, is to fire the plug at the right time. The dyno will tell you alot, about whether you are firing it too early, too late, etc, by watching the torque output, as that is what dyno's measure.

So, lets say, you have a air fuel ratio of 11.5, and you are making, say 600ft lbs at 4500rpm, and you have, 32 degrees of timing there. You then change the timing, to say, 29 degrees at 4500RPM, and do another pull. Now the engine maybe makes, 610ft lbs. What happened was that you simply moved where peak cyl pressure is taking place in the cycle, for the BETTER. The engine is not fighting itself as much now. Lets say, you do another pull, this time with 34 degrees of timing at 4500RPM, and the torque reading is 590FT lbs. What happened? You moved peak cyl pressure to early in the cycle, and the crankshaft lost that leverage.

Now, that example was with 11.5 air fuel ratio. The magical timing advance was 29 degrees. What happens if the air fuel ratio was say, 12.5? The leaner mixture will now burn even faster, and in order to find that sweet spot of peak cylinder pressure to piston position, you may now find that lighting the spark off at 27 degrees, is the magical number for best torque output.

In a marine engine, I would rather have the richer fuel mixture, WITH the extra spark timing, because the extra fuel, does cool things. But it all goes hand in hand. Some people FREAK about igntion timing, under the impression that it creates super high cylinder pressures. While it certainly can if the engine KNOCKS, but aside from that, the cylinders pressures aren't necessarily higher with more timing, they just might be at the wrong "time". Which equates to power loss, both with over advanced, or overly retarded spark timing.

Personally, I think most custom high perf engines, even naturally aspirated, run overly advanced timing in the lower rpm range, and overly retarded timing, in the upper rpm ranges. The problem with a typical old distributor setup, is they are RPM based timing. What the engine wants at 3k rpm cruise for timing, might be 34 degrees. What it wants at 3k rpm wide open acceleration, might be 22 degrees. Hence the modern map sensor. Why is that? Again, its about the max cylinder pressure, relative to the pistons position on the stroke. At light load, the intake charge is not very volitle. its a slow burn. So, you need to fire the plug sooner to get that peak psi at the right spot. At wide open, a very fast burning volitle mixture is entering the cylinder, and that requires the spark to be ignited later, to again, put the peak cyl pressure at the right spot.

Everyone has heard of "boost retard" devices. Boost retard devices, were not invented on the premise to save the engine so much. They were invented, because forced induction setups pack a very fast burning charge into the cylinder, which requires retarded spark timing, and doing so, increases the power output. I personally have pulled out 8,9,10+ degrees on a boosted engine with the daytona box, and saw an INCREASE in torque output. So, what does that tell you? If you are firing the plug 10 degrees to soon relative to what the engine "likes", you are simply putting yourself that much closer to spark knocking it. In this scenerio, Going from 34 degrees at 4000rpm, to 25 degrees at 4000, resulted in a power increase, is really no difference, than say at 6000rpm, going from 34 degrees, to 44 degrees. If someone said "i have 43 degrees in my blown BBC" they would get laughed out of the room. But, that really wouldn't be any worse, than having 34 degrees in an engine at 4000, that wants say 25 degrees.

Guys that dummy down there engines on the dyno, whether its retarding timing, adding tons of fuel, thinking they are doing a "safe" tune, are many times, doing just the opposite of their intention.

Well I will tell you first hand it does and can happen however only when way over jetted.

Merc Racing dyno; 30 minute pull. 30 seconds at each data point.

http://www.mercuryracing.com/dyno-mighty/

Oh sure, now I feel better. Killing me here.

That is pretty friggin AWESOME. Man have things changed since the old 600/800sc days.

i guess that partially justify,s the cost of the merc 1350 engines.i can,t imagine what it cost to build that caliber of a dyno cell.

Ya and then even go back a little further. Unreal... Remember when 70 seemed fast? Lol

I know its crazy! I see 73 now lol