ayousef

I read a couple of threads and people seem to steer away from the topic by asking useless questions like "why would you do this" etc...

So before I begin, im hoping we could discuss the real question here.

OEMs are using boost instead of RPMs to move their vehicles because its more fuel efficient, ive seen cars such as Fiats, BMW M5s, Evolutions all use boost at very low rpms and by that I mean as low as right off idle with no issues.

I used boost in my ZR1 all the time at low RPM, except that it didn't make much at low rpms, even though I had all the boost controlling from the ECU maxed out.

So now my ZL1 makes about 16psi of boost at 3000rpms, and I haven't tested how high the boost could go at lower revs. My common sense is telling me that as long as AFR and spark advance are spot on (no knock) then I should be fine, taking into consideration that torque is load and peak torque doesn't come until 4400rpms, so 1000-3000rpms have quite less torque.

The only other problem is the inability to run a decent amount of spark advance at lower rpms, without me wanting to go any richer than 11.2:1 AFR.

Anybody wanna add anything?

smokeshow

iTrader: (17)

Word on the street With your type of blower, boost should be fairly flat across the entire range. That 4.0 should hold very steady. What question are you actually asking? You should be able to make boost wherever/whenever you want as long as the tune is good.

ayousef

What i really wanted to ask is why are the "pros" saying its bad for the motor to boost from low revs even though it doesnt make any logical sense.

stevieturbo

Boost is fine from low rpm if your turbos and engine are built to do that. Which is what the OEM do with smaller engines to give the end user some sort of decent performance with that smaller engine.

But it is harder on all aspects of the engine, and drivetrain. Well, if you are seeking excessive amounts.

Torque breaks lots of things. The OEM dont simply wind as much boost as possible into the engines. They are very careful only to use as much as is needed to get the job done, and torque management is a huge issue, which is another reason why DBW is favoured. It offers yet another level of control and safety.

ayousef

Well even with all the torque I theoretically have, it doesn't "feel" like its going to break anything, my parts are made to handle much more torque so im pretty sure I wont break anything, infact I slowed down the throttle transition rate since I have dual DBW throttle bodies and throttle response is beyond snappy. Everything else is built to handle low rpm boost, I just need to verify my tune and spark advance and make sure I get no KR etc...

Thanks for the reply.

stevieturbo

Plus running in that manner, there is more risk of detonation. Chances are you'd need to run much lower timing than is optimal, simply because piston speeds are slower and combustion itself will be slower.

Really...if you need huge low rpm torque...buy a diesel lol. But you also need to look at how strong modern diesels are constructed given the torque they can produce.

ayousef

Well I don't NEED that much torque I have that much torque with my 4.0 whipple on a 427 so yes it will take much less spark advance which is why I will need to richen out the mixture as much as possible. It will take driving the car in different weathers/fuels to make sure there is no detonation.

stevieturbo

Only thing is, dropping timing far blow optimum will create higher EGT's, which again is not desirable. Simply adding more fuel isnt always a solution.

ayousef

Well that's my only option right now, I understand low timing will create high EGTs but they will only be momentary for the low rpm boost duration while cruising, however I will try to push the spark advance as high as possible without detonation. The plus is that my SCR and DCR is as low as I would ever want a street car to be.