Slowcrash_101

My biggest worry is the increased spark knock that VTEC causes. Say your oil pressure at 4k with oil at operating temperature is 80psi - 17 psi, you're down to 63psi, that's a 15psi difference than at 6k + rpm which according to the graph is in the 70-75psi. At higher RPM you also have the added benefit of faster more turbulent air in the combustion chamber helping ignite the mixture faster reducing the tendency for spark knock. At lower RPM airflow into the engine is slower and less turbulent(hence the low cam), by opening the high cam too early you are increasing the likely hood of spark knock. Particularly since you're typically at WOT when you go into VTEC. You're practically lugging the engine at lower RPM. All the ingredients for low speed pre ignition are there, and if your car is an oil burner its even worse because oil reduces the octane of gasoline. So more spark knock pounding the rod and main bearings, and lower oil pressure reducing the hydrodynamic oil film. That's my reasoning, I could be wrong. Gernby blew a fair bit of motors IIRC.

Chuck S

I'm not worried. I'm assuming this is all handled when the engine is tuned. When my car was Gernby FlashPro tuned he worked with data from 21 "lugging" pulls (3 pulls of 7 calibrations) from about 2000 to 8000 rpm in 3d gear at WOT and adjusted fuel tables and other esoteric parameters and sent back more calibrations to run and datalog. VTEC ain't engaging from idle.

My owners manual recommends a up-shift from 2d to 3d gears at 25mph and accelerating from there. At 25mph in 3d gear the engine is turning ~2500rpm. Honda doesn't consider that rpm "lugging" the engine. And, of course, VTEC won't be engaged at that low rpm.

Modern ECUs and fuel injection can handle this much better then carburetors and mechanical spark control.

-- Chuck

Slowcrash_101

Lugging the engine means high load at low RPM which leads to increased spark knock. Yes we have knock sensors, the sensor doesn't stop knock from happening in the first place it is reactive not proactive. Honda tells you to shift and accelerate not pin the gas pedal, at low RPM you should not floor it.

Now modern oils have additives specifically for this because direct injection turbocharged engines are especially vulnerable to low speed pre-ignition, but it still happens. If you are fine with the risks and trust your tuner thumbs up from me. I had to spend $7k on a new engine + misc, I will naturally be more reserved after spending that.

Chuck S

You're really suggesting 3600rpm is "lugging" the engine?

-- Chuck

Slowcrash_101

Flooring it at that RPM yes it is lugging the engine. You don't want to WOT until at least the middle of the RPM band. Lugging implies going WOT at low RPM. If you had a way to listen to the spark knock you'd see the majority of it happens when you go WOT at low rpm and the last ~400rpm of the rev range.

windhund116

I was taught by an old-time mechanic that lugging an engine is a way to hasten bearing wear.

https://www.gregsengine.com/engine-b...ure-chart.html

Chuck S

So every time you floor it from a traffic light you're "lugging" the engine 'cuz you're not running 4000 - 4500 rpm (middle of the rpm band)? Not that anyone would ever do this but it seems like nonsense to me.

-- Chuck

windhund116

Chuck, It really depends on if the engine is responding to the throttle. Say you start off in 3rd, from a dead stop. And floor it... this loads the engine below its normal powerband. You'll noticed pressing the throttle harder or even backing off the throttle has no direct response from the engine. It's like cruising at 35 MPH in 6th and suddenly stomping down on throttle. You will get a big lag in engine response.

Lugging is loading the engine below its torque or powerband.

Slowcrash_101

Glad you want to get the specifics. Flooring it in 1st or 2nd gear won't leave you in the 3-4k rpm range for very long, the engine is pretty zippy. No much danger there. Now say you're in 4th, going around 30mph, would you floor it then? I wouldn't, I'd downshift to 2nd at the very least. Flooring it in 4th at 30mph is lugging the engine, flooring it in 3rd at 3k is lugging the engine, but maybe you get away with it because the engine accelerates out of the knock zone quickly. Now, the U.S.s2ks have lower compression ratio than JDM counter parts it's still below 12:1, imagine running 13:1, the more on the limit you are, the more careful you have to be. Or have "pro-active" methods of preventing knock. Imagine 16:1 with 42psi of boost?

RolanTHUNDER

Totally what I expected from an in depth observer such as yourself Elaborate away! That's what we need in our community