Steve Brule for President ("Part Throttle" on Engine Masters!)

[MadBill]

Yes. This engine had been extensively dynoed, but only at WOT. Getting the part-throttle SA dialed in would be particularly problematic on an engine dyno, but a steady-state capable chassis dyno could get you very close re spark and fuel.

[adam728]

I was asking about part throttle dyno testing. What’s the point? Not to maximize torque at a given rpm, because if you want more torque you open the throttle, no?

I can see optimizing ignition, fuel, and cam timing for minimum BSFC. That would make sense on a dyno.

If dyno time is free, sure, every sort of tuning and sorting out is better done on a dyno. But for a hobbyist with limited dyno time, what’s the part throttle test that absolutely needs to be done on a dyno and can’t be done on the road driving the car with the sensors hooked up?

For a hobbyist road driving is just fine. For us emissions are uber important, and fuel economy second. A lot of thought has to go into balancing BSFC, emissions, temperatures, long term durability, etc. And often after lots of careful work and tweaks it all gets blown away by making it actually drive well on the road.

[Cougar5.0]

The last such issue I tackled (reported in S/T some time back) was a 720 HP twin Edelbrock-carbed 572" Hemi. The owner had jetted up (well, 'needled down' to be precise..) and retarded timing trying to cure a bad 1500-2500 RPM, surge, just as described. With a combination of luck, a 60 year old King exhaust analyser and experience, I leaned out the 60 MPH cruise from 11:1 to 15.5 and added 14°of vacuum advance via a Crane adjustable unit.

Not only did this cure 90+% of the surge, he reported that on his next highway trip to a regular destination, he just made it there and back on one tank when previously he had to refuel at the other end.

Interesting. I run closed loop, so adjusting AFR at light throttle (nominally 14.7 ) is difficult. There are tricks, also I might consider running open loop; it's possible the system is oscillating.

[n2xlr8n]

My .02 with the "race" engines I've assembled for street driving (with both carb and EFI) is that it is far easier to tune WOT than part throttle or "closed loop".

I spend hours and hours on the freeway at different throttle positions / rpm < WOT to get the tune right.

The difference is a far more crisp, responsive engine.

Doing anything less is a good way to get spanked by a vehicle with far less HP (off track).

[cv67]

the latest one they talk about the the 165cc vs 195cc vs 220cc AFR head ep 12 season 2

do you have a link?
Always enjoyed those shows, esp the one where dulchich ports those iron mopar heads

[burbfixer]

cuisinartvette,
Sorry, the thread went a different direction so i hadn't checked it in a while. You need to be a MTOD subscriber to see the show now, but it will show up on youtube eventually. Love the show too! There's some real eye-openers - the cooling fan shootout had surprising results. It's most interesting to me when 'small' parts do way better than they expect though - particularly heads. They do often comment on how a combo might feel in a car, but it's usually in reference to high rpm and high horsepower at wot, not part throttle responsiveness and feel.
bigjoe1,
Sir, hopefully you're still following this thread. I'm curious what surprising results you observed doing part throttle dyno testing. Care to share?

[Tuner]

I was asking about part throttle dyno testing. What’s the point? Not to maximize torque at a given rpm, because if you want more torque you open the throttle, no?

I can see optimizing ignition, fuel, and cam timing for minimum BSFC. That would make sense on a dyno.

If dyno time is free, sure, every sort of tuning and sorting out is better done on a dyno. But for a hobbyist with limited dyno time, what’s the part throttle test that absolutely needs to be done on a dyno and can’t be done on the road driving the car with the sensors hooked up?

It's difficult to simply drive my 427W to the gas station without pulverizing the drivetrain due to incessant surging at part-throttle. The engine performs well at WOT, but I haven't yet figured out how to tune out the surging at part-throttle. Cutting timing at light-throttle keeps the engine from winding up so much (like a spring), but some of it is the simple fluid mechanics (reversion) of the system. Even if I don't want a higher velocity (lower HP) port, I am curious as to how much that is affecting my ability to tune it at part throttle.

427W, AFR220, 2924 supervic, EFI, 247/250 110LS hyd roller

Cutting timing at light-throttle keeps the engine from winding up so much (like a spring),

I don't understand the phenomenon you are describing with, "winding up so much (like a spring)... etc.. What do you mean? It seems odd retarding is desirable, ordinarily an engine wants more timing and a leaner A/F for light-throttle. Retarding timing will make it run hotter, higher exhaust and water temps.

The last such issue I tackled (reported in S/T some time back) was a 720 HP twin Edelbrock-carbed 572" Hemi. The owner had jetted up (well, 'needled down' to be precise..) and retarded timing trying to cure a bad 1500-2500 RPM, surge, just as described. With a combination of luck, a 60 year old King exhaust analyser and experience, I leaned out the 60 MPH cruise from 11:1 to 15.5 and added 14°of vacuum advance via a Crane adjustable unit.

Not only did this cure 90+% of the surge, he reported that on his next highway trip to a regular destination, he just made it there and back on one tank when previously he had to refuel at the other end.

Interesting. I run closed loop, so adjusting AFR at light throttle (nominally 14.7 ) is difficult. There are tricks, also I might consider running open loop; it's possible the system is oscillating.

Good job on the Hemi MadBill..

Cogar5.0, what kind of EFI is this? I though these things were supposed to learn the ideal tuneup all by themselves. Do you have a way to monitor the system to see what it is doing in real time while you are driving? Can you tune it with a laptop or ?? How are you controlling the timing? What type of O2 sensor is it, wide-band or narrow-band?

[Cougar5.0]

Cutting timing at light-throttle keeps the engine from winding up so much (like a spring),

I don't understand the phenomenon you are describing with, "winding up so much (like a spring)... etc.. What do you mean? It seems odd retarding is desirable, ordinarily an engine wants more timing and a leaner A/F for light-throttle. Retarding timing will make it run hotter, higher exhaust and water temps.

The last such issue I tackled (reported in S/T some time back) was a 720 HP twin Edelbrock-carbed 572" Hemi. The owner had jetted up (well, 'needled down' to be precise..) and retarded timing trying to cure a bad 1500-2500 RPM, surge, just as described. With a combination of luck, a 60 year old King exhaust analyser and experience, I leaned out the 60 MPH cruise from 11:1 to 15.5 and added 14°of vacuum advance via a Crane adjustable unit.

Not only did this cure 90+% of the surge, he reported that on his next highway trip to a regular destination, he just made it there and back on one tank when previously he had to refuel at the other end.

Interesting. I run closed loop, so adjusting AFR at light throttle (nominally 14.7 ) is difficult. There are tricks, also I might consider running open loop; it's possible the system is oscillating.

Good job on the Hemi MadBill..

Cogar5.0, what kind of EFI is this? I though these things were supposed to learn the ideal tuneup all by themselves. Do you have a way to monitor the system to see what it is doing in real time while you are driving? Can you tune it with a laptop or ?? How are you controlling the timing? What type of O2 sensor is it, wide-band or narrow-band?

The windup is the engine revs up and then bogs. The AFR isn't lean when this happens. Timing is pulled so the engine is less efficient, thus it doesn't pull hard when you're barely touching throttle and it "catches" where is manages to capture enough fuel to have a decent burn for a number of cycles in a row. The issue is due to the cam is large and dynamic compression is very low, I have no idea if fuel is reverting to intake or escaping through exhaust or both (depending on location of cylinders.) Simulation program warns that controlling air charge at these low RPMs will be difficult.

Engine control is stock Ford EEC IV. It is self learning to a degree (fuel) using feedback from the narrowband switching O2 sensors. I also have a wideband on the drivers side that I use to dial in WOT and other open loop situations (startup, lugging.) I monitor many parameters on a laptop mounted to my dash, also record for later analysis. No matter how hard I look, I can't see the chicken for the egg - I have no idea what's triggering the spin up, then bog though I know this is a common issue with EFI and medium to large cams.

When I say low timing, it's around 20 degrees at light throttle versus 30-40 for maximum light-load efficiency typical with a stock or mild cam.

[cv67]

burbfixer havnet been on a dyno in a long time, seen Steve mention on one of his shows that PT results were much different sounds like he knows
Think it was on the testing of the 410 ci ford with the tiny cam/afr head test
Have to ck into signing up I like the little details they go over even behind the scenes stuff. They have been around a long time

[Cutlassefi]

"I have no idea what's triggering the spin up, then bog though I know this is a common issue with EFI and medium to large cams".

Simply not true. A good system will allow you to tune virtually all of that out. The EEC-IV was decent for it's time but has limited capability once you start running bigger cams etc.

[Cougar5.0]

"I have no idea what's triggering the spin up, then bog though I know this is a common issue with EFI and medium to large cams".

Simply not true. A good system will allow you to tune virtually all of that out. The EEC-IV was decent for it's time but has limited capability once you start running bigger cams etc.

How does it do it? Recommended system? I'm looking at getting something like the Holley HP, which is self-learning but I'm not sure how it deals with the mechanical issue of flow reversion. A little meat on the bones would be useful since I can do most anything with the stock ECU - the only limitation it has that I know of is spinning it above 7k RPM or so. What am I missing?

Goal: Idle about 900 RPM, be able to cruise in 4th gear @ 1500 RPM, deal with load going to zero (crest of a hill) and then deal with tip in once load starts increasing again to say 10-30%.

[russxr67]

I enjoyed watching test between the three different heads but the question I had was about cam selection.
Surely each head could have used a cam to optimise the different style of head used.
Even though the duration was fairly short I'm wondering what the larger head would have done with more lift and keeping the duration short.
It may have had an entirely different outcome.

[cjperformance]

I enjoyed watching test between the three different heads but the question I had was about cam selection.
Surely each head could have used a cam to optimise the different style of head used.
Even though the duration was fairly short I'm wondering what the larger head would have done with more lift and keeping the duration short.
It may have had an entirely different outcome.

Totally agree mate, and even if they wanted to keep just 1 cam for the tests , personally I would have liked to at least use something with upper 220's@.050 on the intake and touching the .600" lift area simply to push the smallest head a little harder and to allow the biggest head at least enough lift to begin to show some potential. That said, always interesting anyhow!

[hpetew]

Cougar 5.0 are you sure that your tips is working right? Kinda sounds like it's output might be erratic.

[russxr67]

I enjoyed watching test between the three different heads but the question I had was about cam selection.
Surely each head could have used a cam to optimise the different style of head used.
Even though the duration was fairly short I'm wondering what the larger head would have done with more lift and keeping the duration short.
It may have had an entirely different outcome.

Totally agree mate, and even if they wanted to keep just 1 cam for the tests , personally I would have liked to at least use something with upper 220's@.050 on the intake and touching the .600" lift area simply to push the smallest head a little harder and to allow the biggest head at least enough lift to begin to show some potential. That said, always interesting anyhow!

Exactly mate, I thought it had way less lift than what it needed.