F4i dyno tuning

[kapps]

For the past few days, we've been working on the dyno with our new intake and exhaust. We're getting some interesting numbers. Basically, the engine has nothing until just over 7k rpm where it comes alive. The same thing was felt in the car last year with a completely different setup. The dyno plots for stock f4i's seem to have a nice broad torque curve but they also have lots of air available at all times. I'm assuming that it comes alive when the engine finally gets on the cam but does anyone have any tips on how to smooth out the transition? We're literally doubling in horsepower from 6k to 7k rpm. The jump is not a product of runner length as we've varied these with no effect.

[kapps]

For the past few days, we've been working on the dyno with our new intake and exhaust. We're getting some interesting numbers. Basically, the engine has nothing until just over 7k rpm where it comes alive. The same thing was felt in the car last year with a completely different setup. The dyno plots for stock f4i's seem to have a nice broad torque curve but they also have lots of air available at all times. I'm assuming that it comes alive when the engine finally gets on the cam but does anyone have any tips on how to smooth out the transition? We're literally doubling in horsepower from 6k to 7k rpm. The jump is not a product of runner length as we've varied these with no effect.

[Mikey Antonakakis]

What is your exhaust like? Oh, and if there is a Freshman named Melvin on your team, tell him Mikey says hi!

[Mikey Antonakakis]

Also, what does your timing map look like at full throttle? And TPS or MAP load sensing?

[kapps]

4-1 exhaust, primaries currently around 29" but we're adjusting them down. We're using TPS for load. Timing at full throttle is 32/34 at 5/6k rpm and ramps linearly to 46 at 12k.

[VFR750R]

4-2-1 will have broader power band,

runner length should have made a difference, what lengths did you try?

[Mikey Antonakakis]

Maybe check your timing? The pickup wheel may be off. We noticed there was hardly any difference after more than 42 degrees advance on our F4i last year. Our timing peaked at 42 at around 7k and just stayed there, although I'm not entirely sure that was optimal. It was about 30 at 1k, as well. The timing map was screwed up, because advance increased with load, but that map worked pretty well for us at full throttle. We had a huge drop in torque at 5k, but that had little to do with our tune.

[Wesley]

Holy smokes, 2.5' feet of intake runner?

Sounds like a fueling and timing issue to me. What does your intake plenum look like?

[Mikey Antonakakis]

no no no, I think he meant 29" exhaust runners

[kapps]

Yeah 29" exhaust. We've been testing 2 different intake configurations. One with a minimal plenum (more a reverse collector) that doesn't have adjustable runner lengths (Helmholtz tuned for 7500 rpm). The other is a more standard plenum design with aluminum runners that we can cut down. We started with the overall runner length (from back of valve to plenum) of almost 20" but have been cutting them down an inch after every couple dyno pulls. Surprisingly, even with almost 2 feet of intake runner, power peak was 9500 rpm and we actually got our highest torque value yet (41.5 lb ft). When we switched from the reverse collector design to the plenum with very long runners, the bottom end got lean and the top end got rich which is exactly what I'd expect with long ass runners. As we've been cutting them down, we've been steadily richening the top end up to keep decent A/F ratios. We're also getting a little more power top end as they get shorter but there's still a huge jump in power at 7k rpm with every configuration.

[VFR750R]

Since 2 drastically different intake designs seemed to have little effect I'm going to guess then that the 29" primaries are your problem. I would try to fix that before continuing to test intake runners. You were probably going to test primary length anyways.

Do you have any exhaust you could bolt on, stock or from another car? It doesn't have to be anything good, just prove whether its the exhaust or not?

Some dyno ?'s, Is this a chassis dyno or water brake? How is the dyno handling the power jump? What rpm are you starting your pull at? Does the dyno have good repeatability in the effected area or can you effect it by your rpm start point, rate at which throttle is applied ect?

[kapps]

Ok. We still have some room to mess with exhaust primary lengths so we can work on that. I think we also have a stock exhaust laying around somewhere. We're using a Superflow SF 901 engine dyno. It hasn't been used for a while and it was previously set up for Winston Cup engines.

We built a stand for our engine and are using a short driveshaft to attach to the brake. We are having some issues with the dyno. In the 5-7k rpm range, it 'searches' for the right load to apply. Instead of being linear, it allows the engine to run up a couple thousand rpm and then drags it back down. It does this 3 or 4 times until the engine gets to around 7k (where the plots show it starts making power) and then smoothes out. Most of the pulls started at 5k rpm but we did try some lower. On the lower pulls, it starts out smooth but then begins hunting when it hits 5k and smoothes out at 7k. We've tried pulls in 3rd, 4th, and 6th gears and they are all the same. We've also adjusted the water control valves on the brake with minimal affect on the hunting. Because of this, I can't be sure if the horsepower it's giving in this range is correct. The only reason I tend to agree with it is from experience in last years car. At 7k rpm, it came on like a light switch (with a completely different intake/exhaust). That setup was never dyno'd.

Since it's hunting in all three gears, I'm really not sure what the problem is. It's not the clutch as the dyno rpm rises and falls with the engine. The professor who used the dyno previously was here for the first couple pulls and he thought we might be overloading it since it's not expecting to see so much load at so little rpm. 3rd gear multiplies torque by 3 and divides engine speed by 3. This is why we then tried 6th gear. One of our guys is going to call Superflow tomorrow and see if they have any ideas. Once everything stabilizes, I trust the dyno plots to be correct. Our first pulls topped out at 68-70hp and we're up to 77 today.

[AndrewUofL]

Im not sure what anybody else runs for ignition but we are running about 5 degrees less of timing than what you stated of our F4i. I know that the ignition map doesn't change much from F4I to F4I or at all with runner length so this difference is surprising. I would see if there is a problem with the dyno first but it may be acting the way it is because of a tuning issue. Our torque curve is pretty broad and mostly flat which sounds like what you are looking for.

[Marshall.Hagen]

Shaun,

We are also using a Superflow SF-901 and an F4i.

We had the same problems using 250 or 500rpm steps where the dyno would hunt for the correct load.

Our solution was changing the test type to 'acceleration' with a test rate of '200' or '300'. We were seeing very smooth power plots with variance of ~0.5% between pulls.

Once you fix the dynamometer problem, then start validating your intake and exhaust.

Our dyno cell:
http://www.itrspec.com/FSAE/FSAE022.jpg

[kapps]

Interesting. That made me think, what would happen if we're getting slight detonation...not enough to hurt anything but enough for the dyno to sense a loss of power. Maybe it drops load for a split second, the engine would then stop knocking because of the drop in load, then rev up, where the dyno then applies additional load to drag it back down to the correct rpm where it starts knocking again. Any of this sound plausible?

[Wesley]

What I would give for a dyno cell like that. Almost anything...

[kapps]

I'll post a pic of ours soon. Looks similar (obviously). The professor who used it previously did lot of stuff with 350 chevies. He stopped using it when it started having problems with the tach pickup. Apparently, the last time he used it, it was on a blown 350 making over 900 hp. It was at 7k rpm at full load when it lost tach signal. Tach controls load. He said he was milliseconds from blowing that motor. For our project, he got the cards upgraded as well as replaced the bad dog bone that holds the strain gauge...not cheap.

[Erich Ohlde]

speaking from experience. almost all of you problem is the exhaust. switch to a 4-2-1 and the engine will get a lot better.

I'll try to find some dyno plots on the network drive and post them.

[kapps]

Did some more runs today. We re-adjusted the control valve on the back of the brake so that it just was strong enough to hold the engine at full throttle. It still allowed the engine to run up a little bit but it was much better. We also continued testing with shorter intake and exhaust runners. Our final (shortest) setup proved to be the best looking plot. 78hp, 45 lb ft torque. We're over 70 hp from 8k to over 12k rpm.

Also, we messed around with different test types. We had been using 'accel' on a 50 or 100 auto test rate. On our final setup, we tested accel at 100, 200, 300, as well as step tests of 250 and 500 one after the other. Our best looking graphs came from the step 250 test. It allowed the engine to surge like it was previously but the graph showed power coming on more gradually compared to the other tests. Also, the accel tests at 200 and 300 gave very different looking dyno plots than the rest. They jump up to around 70hp at under 6k rpm and pretty much stay up there for the duration of the run. With the engine ramping up quickly on those tests, the surging was very minimal.

I'll try to post some plots from the dyno when we're done. Due to the gear reduction, we have to export the data to Excel and correct torque and rpm. The dyno software has the capabilities of handling a built in gear reduction but the auto-test only goes up to 10 rpm so if we tell it that there is a gear reduction, it won't let us rev past 10k.

[VFR750R]

[QUOTE]Originally posted by kapps:
Did some more runs today. We re-adjusted the control valve on the back of the brake so that it just was strong enough to hold the engine at full throttle. It still allowed the engine to run up a little bit but it was much better. QUOTE]

i'm not sure if your talking about the water in or water out with this brake, just make sure you have enough water flow to not burn up the brake. water out temp should be measured somewhere and shouldn't go above ~150deg. If you run the brake hotter then this, you can experience cavitation of the rotor.

also, if changing the non-pid looped valve (either in or out depending on the brake) helped, then you might be able to adjust the pid's instead to get the response/stability without being way off the page in water flow. typically they say the best response is when the pid control valve is around 50% in its range. With brakes that have the pid control on the outlet more water will result in faster holding response, but it tends to be less stable. less water has the opposite effect, with more overshoot, but more steady state stability. I tend to get the best results by putting in more water and using the pids to get back the stability, sideeffect is the brake is happier temp wise. With a brake that big running an engine that small, this might not be possible or the best route.

step tests really are the best for looking at part swaps. they give you the most data for each data point, and eliminate inertia. Superflows have inertia correction built in that trys to predict steady state hp based on inertia and your sweep rate. When it works correctly you'll make the same hp at any sweep rate. But, it's probably set for a 350 v8 so at 200-300rpm/s its greatly amplifying your power thinking you have to accelerate all that extra inertia. There is a way to turn off the inertia correction (i think), and you should do that. I think it will be alot more consistent for a small engine, but you'll want to do all your testing at one sweep rate or better yet, keep doing the step tests. Use transients to help with your transient fuel mapping only, keep step tests for hard part swaps.

[kapps]

We were adjusting the small valve that controls water into the brake. We spoke to a guy from Superchips who explained how to calibrate it (his explanation was different than what the manual says). With this calibration, the brake could hold the engine at 10k rpm but did not have enough water to hold the engine at 4-5k rpm. I assume this is because of our gear ratio. The dyno is only spinning at 1500 rpm when we start the tests. It's not expecting to see power at such a low rpm. We ran a couple tests, unscrewing the valve until the brake seemed happy. This minimized the oscillation and allowed the dyno to apply more steady load.
It's not optimal but considering how the dyno was used previously, it's pretty good.

[kapps]

Just wanted to give an update with our dyno figures. Here's a plot for our final configuration.
http://gallery.me.com/kapps/100024/Picture-202/web.jpg

[Kirk Feldkamp]

Unless it's a byproduct of how you made that dyno pull, your drivers are going to be hating that rapid of a rise (2.25 times!) in torque between 5000 and 7000. Most drivers at this level (newbs/amateur drivers) are unable to keep the engine between 7000 and 12000 consistently, which will tend to catch them out when there is the big surge through that rpm band. What I've seen from all our road racing data is that if the driver is unable to deal with the torque surge, they tend to keep the engine just below it, and in turn go *really* slow. If you can smooth out that area, the driver's confidence will increase, and the predictability of the car will increase. As a result your amateur drivers will tend to run faster, more consistent lap times.

Lookin' good so far, keep it up. Just need to work on some fine tuning from here, and you'll be ready for comp! Don't forget part throttle driveability too!

-Kirk

[kapps]

Yeah, this whole thing was a senior design project. The idea was to maximize the area under the torque curve. Now we're finally done with it, we can take our time and go back and fill in the gaps where we just didn't have time to test. I want to put the stock exhaust back on and see what that does, and of course, tune the partial throttle.

On the plus side, we are lucky to have two good drivers this year. One races Formula Ford and the other races karts. They did a very good job last year in the endurance with a car that was hardly tested and the suspension setup was average at best. My main concern is now with the drivetrain. We're making more peak torque than the stock bike and those halfshafts are going to take a beating.