I Think Steve Morris is WRONG and I Can Prove It!

We use In-Cylinder Combustion Pressure Analysis data to determine whether or not you have to change the amount of Spark Advance an engine needs when you add boost!

[UncleTonysGarage]

Excellent video, but i feel there is something missing from this conversation that ultimately changes all of the variables you presented, and that's the difference in fuel types.
The combustion profiles for pump gas, oxygenated gasoline, E85, ethanol and nitromethane are all going to be different, not only for their individual burn qualities but also for the optimum volume used with each fuel.
Also, just adding something to the argument, my experience with nitromethane would put me in agreement with Steve. Whether tuning for blown or N/A, the ignition lead stays constant at approximately 55 degrees for a dual plug or 65 for single plug application...this in a 426 style engine with 175cc combustion chamber. There is a difference in static compression between the two types of engines, but all else being equal (bore, stroke, cam profile) the duration of burn is the main factor and not how the chamber is pressurized.

[hankclingingsmith]

The fuel you choose changes everything with timing

[TomJ]

When I live in Japan I worked for a Japanese manufacturer's internal engine builder and parts maker for their racing programs. We also made prototype parts for future models. We had our own data from grA, GT300, GT500, Dakar rally, 24hr LeMans, Pikes Peak, etc... While I was there we started making street parts based on those programs. Our oil pumps, headgaskets, pistons, rods, cams, turbos and other parts were exactly the same as race version. But we added some cam options, oil pumps, water pumps and other parts based on racing but for street. Anyway, every single engine required less timing as we increased boost. We produced our own ecu and software too. It's not uncommon for our engine programs to have 30+ degrees at 0psi boost tapering down to 20 or even 12 degrees at 21psi and 28psi. We could add a few degrees after peak torque but didn't bother on most. That's on about 94-95 octane (USA rating) with pentroof 4 valve. If we wanted more boost then we'd remove the quench pads or use race gas. Keep in mind we could run 13:1 and extremely high egt for 30+ minutes with no damage. Of course we ran 11:1-12:1 and low egt for safety. These were 2.6 & 2.8 in line 6, 8.5:1 compression making 450-800+hp at the wheels. Oh and the pressure delta varied greatly between turbos. We even used old school clipped turbine wheels on some setups to reduce back pressure. Nonclipped would spool 1bar just before 3, 000rpm and clipped version kick in at 4, 500-5, 000rpm lol. It ruined turbine efficiency but helped VE. They would run like big displacement NA engines from 5, 000 to 8, 000 rpm. I can't imagine running the same timing at different boost.

That said if engine makes peak power at 30 degrees and 0psi. But it could also run at 40psi and 0psi without ping then theoretical maybe it can make peak power at 30 degrees and 21psi were as our engines did at 20 degree. I wanna say air-cooled Porsche make peak power NA at something crazy low like 20 degrees but don't ping till 35+ degrees. And that's like Steve is saying. The combustion shape is limiting factor not fuel. Need a "hotter" combustion design. But then again on air-cooled you probably can't keep cylinder head temperature under control if the combustion design was pushed harder

[mrctuned]

I got here from Steve's short also. Over the years I have learned so much about engines and tuning, especially after buying a dyno. I would say over 99% of the engines I have tuned are exactly what you are explaining here Ben, I have always had to retard timing with boost....

The one engine I was very surprised on though, was a turbocharged Gen 1 SBC in a drag race S10 pickup. Single turbo, low compression, conventional 23 degree head. I got involved when he made the switch to EFI, and had a local shop tune it (this was before I owned a dyno). He was disappointed with the power and resulting trap speeds when he got it to the track for the first time. He ran it like that for a while then asked me for help. I started adding timing and the trap speeds kept on getting better. I was coming from a pump gas turbocharged import background at the time and was extremely reluctant and uneasy about the numbers in the timing table. However, I knew that if it was going faster, "give it what the engine wants, not what you THINK it wants". We ended up right at what the NA engine liked all the way up to 30 psi boost pressure (we are at about 1, 000ft. above sea level). Plugs showed the timing was right in the sweet spot as well. This particular engine really opened my mind up, and I'm grateful to have created a friendship with the owner and have drag raced with him ever since.

Another thing to just mention about this particular engine that is interesting is that we went through 3 different single turbo setups, ultimately ending with a big 98mm Garrett GTX5533R. We ran it up to 54psi boost, and up there it STILL wanted a lot of timing. I later figured out why when we installed back pressure sensors... The single was choking the exhaust too much and effectively diluting the mixture and requiring more ignition lead, just as you talk about here Ben. It still went faster, but the power gain per pound of boost was really plateauing. We ended up switching to a twin 80mm turbo setup, and made the same power at only 42psi boost pressure, just because of the more open exhaust. It took less timing as well, and as an added benefit we stopped having to replace spark plugs after 4 runs.

Anyways, that's already too much info in a YouTube comment, but thank you for the great video Ben!

[Justme-jtef]

I love data as well. I don’t care who right or wrong I’m excited I found all this knowledge your willing to share.

[themotoroilgeek]

Great lesson! Combustion analysis for the win. Science, Not Speculation!

[BrickNewton]

Just saw Steves short about this so had to check it out

[mikebates]

When you talk about 426 hemi. When Dodge wanted the old men to run the new hemi instead of the 392 that everyone else was using. Gar couldn't get it run hard like the old one, in frustration he cranked the timing up, way up, said Gar, well that was what was missing way more than they ran in the 392. Ask him

[racerd]

The wrong cam will also act like EGR, I have guys come up to me at car shows and tell me about overheating problems that they just cannot fix. My first question I always ask, have you looked into the intake manifold for your problem. Never thinking the engine is eating it own exhaust, so the intake is black all the way back to the base plate of the carb.

[nhra]

Excellent video Ben. I admire you for being at the top echelon top be able to get in cylinder pressure data - it so interesting to us engineering nerds!

[ts]

Great video Ben! What is your opinion on mixture motion inside the combustion chamber prior to ignition. High swirl /tumble heads & tight quench-high mixture motion, vs low swirl/ tumble & chamber softening-less mixture motion. Thank you.

[cliffords.]

I'm a retired motorcycle technician and machinist and it took me 18 months to completely restore a 1980 GS1000ET Suzuki and completed it in August 1997. 1100 Wiseco 10:25-1 forged piston kit. Vance & Hines drop in camshafts (Not), HD valve springs. .030" milled off the cylinder head, .005" off the cylinder, intake and exhaust port clean up only (Intake port completely done wrong from the factory), five angle full radius valve job, aftermarket V&H exhaust, stock air box and stock carburetors (Jetted), degreed in cams, Dyna Jet 35, 000 volt coils with Taylor 8mm plug wires, crankshaft blue printed, trued, indexed, balanced and welded, HD clutch basket backing plate and springs and balanced, undercut transmission. It had a Hemisphererical combustion chamber which I should have dual spark plug each cylinder, but I didn't. I don't remember what I set the full advance to, but I had to run 4 gallons 93 octane pump gas and 1 gallon VP 100 low led gas to keep the engine from detonating with the ignition timing It needed. I started trying octane boosters like PJ1 and 104 plus, but neither worked. I found Lucas raised the octane by points rather than points of a point which prevented drtonation. I ran 5 gallons 93 pump gas and 4 ounces Lucas octane booster which prevented detonation. Stock it probably did 125 - 130mph and this engine was doing 151 and still pulling hard at 10, 000rpns, but ran out if gear. Stock gear ratio, but I went from 630 to 530 chain & sprockets to lighten it up and it would pull to 10, 000rpms in 5th gear when redline was 8, 500rpms. Most of the time the tachometer didn't work because the cable would break.
So basically you need the correct fuel type and octane, ignition timing etc., to make peak hp & torque and each engine may require different amounts.

[shannonstebbens]

Flame front propagation across a large piston we find that alive and well in the 1939 technology of your aircraft engine. Another great video!

[bainracing]

We need a temperature overlay. As there's a density shift and the speed of sound changes. Would love to see this. 👍

[uberdang]

Greg's Airplanes just did a similar video. Its rather interesting that NACA did studys on this to improve aviation engine efficiency back in the 40s. It would be cool to see your burn time data with just changing air fuel ratios and fuel types.

[davidciesielski]

Thanks, I'm 65 and learned a lot from this....

[MattZadarnowski]

You should make an episode with the following tests, preferably on an LS v8 using the same fuel throughout the test:

-Show how the wideband o2 sensor reading becomes compromised as back pressure goes up in an exhaust system.

-On a turbo setup, show what situations lead to the setup prematurely not gaining any more power through increased ignition advance.
Also show, what situations on the same turbo engine, would give an increase in power with timing despite the timing value seeming high, yet still gaining.

In all these tests, having a way to artificially increase back pressure for demonstration purposes, would be a visual bonus to the viewers.

Some say a very efficient setup won't want much timing, others say you're hitting a restriction somewhere if timing isn't helping.

Some say if it keeps wanting timing, the setup is so inefficient that you are fighting pumping losses, encountering EGR, thus advancing timing to compensate.

I'm sure multiple situations may show the same symptom, so I'm curious to see you demonstrate the theory live.

[ValiRossi]

Steve can be right and wrong. He can also divide by zero. Chuck Norris is the only other person to do this. Good job tho.

[Timbuck]

Newly Subbed from SM. Have you got any data on port water/meth injection and its effect on cylinder pressure, detonation and timing ? Love to see a video on that.

[kcgym]

That is one of the best explanations of why some heads need more timing than others that I have heard.
The power is in the heads, regardless.