ITB's on a 24v project, Dyno results Post 136!!!

[The Dark Side of Will]

Well, seeing the maps are calibrated to a plenum that has limited available air, I would gather it's a lean spike. Lean spikes are common, even with stock configurations, just as rich is when the throttle is snapped on way or other, but the ECU isn't compensating for this much air fast enough. All the values will have to be moves closer to the bottom left of the tables.

I'm not sure how to evaluate the accel enrichment curve in a purely MAF engine management.

In a MAP based engine management, the manifold starts off at low pressure behind a close throttle. The throttle snaps open and air starts to flow before pressure builds in the manifold. So the AE curve needs to add fuel over a particular time interval until pressure in the plenum comes up to the point at which the MAP sensor registers the increased load on the engine. At that point, AE fuel tapers out while fuel calculated from engine load calculated from MAP reading tapers in.

So with a TPC system, the volume is smaller and the throttle area is larger, so the pressure behind the throttles comes up more rapidly. This means that the AE from the plenum manifold results in a rich spike when used on a TPC system, as the AE fuel hasn't tapered out before the MAP reading comes up and adds more fuel.

Without high end analytical tools, the only way to tune AE is empirically... dyno or street time.

[ForcedFirebird]

Using the stock IAC plumbed into the vacuum block.

[Wanganstyle]

Well, seeing the maps are calibrated to a plenum that has limited available air, I would gather it's a lean spike. Lean spikes are common, even with stock configurations, just as rich is when the throttle is snapped on way or other, but the ECU isn't compensating for this much air fast enough. All the values will have to be moves closer to the bottom left of the tables.

Trying to work on this project in between other things going on around the shop. Might have time to get a WB installed today, was hoping the stock maps were close enough to go directly to the dyno, but don't want to waste rental time tuning diveability and part throttle on the rollers. Only have it running and moving under it's own power as of yet. The problem was less amplified prior to the IAC and vacuum block being installed, seems the IAC response is too slow with abrupt throttle changes.

IAC mapping+itb is a pain in the ass to program; are you using the standard 3 wire IAC unit or a 2 wire one?

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[LJ851]

Individual throttles on a performance engine are wonderful, hands down.

[digger]

Right, and on the flip side, peak gains is often all people look at. ;)

Just like a comment on a before/after dyno from a chip we wrote. Comments were of the like "only three WHP?!?!?", but they weren't looking at the places we gain 15+ WHP.

I know the response can be misleading. That's why we test everything we do.

ive done a fair bit of testing on my m20 of late with 42 itb and im still sorting things out and will do a write up oneday in a suitable thread

you can also have no extra peak torque or peak power but have a faster car if the power curve does not fall off the cliff as fast allowing more useable rpms but this is lost among alot of people

[ForcedFirebird]

Right, and on the flip side, peak gains is often all people look at. ;)

Just like a comment on a before/after dyno from a chip we wrote. Comments were of the like "only three WHP?!?!?", but they weren't looking at the places we gain 15+ WHP.

I know the response can be misleading. That's why we test everything we do.

[digger]

Right, but useable power under the curve should always be the target. If peak power is similar in two engines, the one with more area under the graph will always outperform.

As Rama has shown us, peak power still can be gained in a proper design, but unless it's an engine operating in a very narrow band of engine speed, peak gains is not always the best.

yeah i didnt mean they cant provide peak gains at all, merely that seat of the pants is not a good judge. the number of times ive been proven wrong by the dyno is alot and usually in a bad way ;)

[ForcedFirebird]

Right, but useable power under the curve should always be the target. If peak power is similar in two engines, the one with more area under the graph will always outperform.

As Rama has shown us, peak power still can be gained in a proper design, but unless it's an engine operating in a very narrow band of engine speed, peak gains is not always the best.

[digger]

its deceptive to gauge improvements with ITB as you get so much response when you crack the throttle that it is often perceived as a big improvement when infact it can often be a little gain, small gain or no gain at WOT it just depends. in addition to this the part throttle will be better because the cross talking is almost completely eliminated and in some cases the engine will make highest torque at low rpm with less that 100% throttle particularity with big throttles, camshafts and exhaust tuning that isn't complementary to low rpm.

the dyno and only the will tell the story if there is a proper comparable baseline with which to compare to.

one thing for sure is the tunability and driveability of an ITB is far superior to a single common plenum on a inline 6 and IMO worth it alone.

[ForcedFirebird]

Are you seeing a rich spike or a lean spike?

Well, seeing the maps are calibrated to a plenum that has limited available air, I would gather it's a lean spike. Lean spikes are common, even with stock configurations, just as rich is when the throttle is snapped on way or other, but the ECU isn't compensating for this much air fast enough. All the values will have to be moves closer to the bottom left of the tables.

Trying to work on this project in between other things going on around the shop. Might have time to get a WB installed today, was hoping the stock maps were close enough to go directly to the dyno, but don't want to waste rental time tuning diveability and part throttle on the rollers. Only have it running and moving under it's own power as of yet. The problem was less amplified prior to the IAC and vacuum block being installed, seems the IAC response is too slow with abrupt throttle changes.

[The Dark Side of Will]

A supra mk4 has a 60 mm throttle; it's ok for a 600rwhp.

That's with boost and is not relevant to a discussion of N/A engines.

How can one cylinder alone pull more than 36mm worth of throttle?

Because the intake valve is only open ~1/3 of the cycle time. With 33% duty cycle, the peak flow while the intake valve is open is MORE THAN THREE TIMES the average flow.

The throttle on a plenum manifold only sees average flow.

850-1000 CFM worth of carbeuration on a 350 Chevy is decent for a single 4 barrel. However, if you run Webers, you'll need a total of more than 3000 CFM on top of the same engine.

[The Dark Side of Will]

Have the whole thing bolted back on the car. Idles like a rock, but off idle and stabbing throttle bogs pretty bad. Was hoping to go to the dyno tomorrow, but will need to re-write all the maps to add fuel sooner. Rolling on the throttle, or once the fueling catches up, this thing is a rocket.

Are you seeing a rich spike or a lean spike?

[ForcedFirebird]

in my experience, unless your using a wideband in the collector at the end of your header then your readings will be delayed if you are using the dyno's wideband shoved in at the end of the tailpipe. additionally, road tuning on the street/track using datalogs gives a more accurate picture of load put on the motor vs the normally 500 lb wheel on a mustang dyno or hydraulic load from a dyno jet.

obviously, tuning with the dyno will get your A/F to a point where you will not be running too lean or too rich on track and is needed to get the timing advance where it needs to be for usable power. however, IMO there are some benefits to be hand to dialing in the motor, A/F wise, with road tuning.

just my 2 cents.

Understand completely. We use the road, track, flow bench, engine sims, dyno and even driver feedback. No sense in wasting time on a dyno to get a vehicle moving, no sense in tracking something that will blow up getting logs etc.

EDIT: Typically tune with a local WB, not the dyno tailpipe unit. Have with the tailpipe ones, just takes longer since the RPM based AFR is laggy and inaccurate.

[jrockbk]

Def subscribed looking forward to see e30 Swap setup! Love how you guys argue over the numbers too it's funny

[digger]

Either way, 45mm will serve a wide range of engines.

yes, make them smaller and the modded guys will complain