Full boost in 1st gear?

evolutionmovement · Post by **evolutionmovement** » Mon May 17, 2004 6:19 am

Okay. I guess I could buy that as a definition.

YES! Drunken editor wins!!

Steve

vrg3 · Post by **vrg3** » Mon May 17, 2004 6:21 am

Half wins.

vrg3 wrote:I don't think it would strain the engine more, though, since the engine is still making the same torque. It's just having a different effect in different gears due to the friction's effect being different.

evolutionmovement · Post by **evolutionmovement** » Mon May 17, 2004 6:35 am

This is actually something I'be pondered muyself and not really come to a conclusion. But if the engine was not more under strain, then why isn't acceleration the same in each gear up to maybe 70 when aero considerations would begin to have more of an effect? For that, why not just have one huge gear? The gears are there to work with the engine's power curve. That power needs to be multiplied to aw dammit, I'm don;t feel like editing this and I have no idea what the hell I was going to write now.

Steve

vrg3 · Post by **vrg3** » Mon May 17, 2004 6:45 am

Hehehehe...

Acceleration isn't the same simply because the effect of the torque isn't the same, since the gearbox reduces the final torque as gear ratio falls.

BAC5.2 · Post by **BAC5.2** » Mon May 17, 2004 7:04 am

The strain on the engine itself is the same (if it's revving at 2800RPM making 180lb-ft at the flywheel, it's making 180lb-ft at the flywheel, reguardless of gear), but it's the effective load that changes. You know how when on a dyno, you will get different numbers in different gears? Torque multiplication works both ways. 180lb-ft input is the constant, but the output is increased through the drivetrain, and decreased across the gear span.

Theoretically (pulling numbers from my ass), that 180lb-ft effectively makes 250lb-ft at the wheels in 1st gear. In 5th it makes 100lb-ft at the wheels.

This difference is load. The less power you make at the wheels, the higher the load is on the engine (to make enough torque to keep going at a constant rate).

Load isn't a number seen by the ECU that can be directly measured by a sensor. It's a condition that the engine is put under, that it reacts to.

That said, load can be defined as a quantative variable determinant solely on effective gear ratios (overall ratios at the wheels, not in the tranny or at the diff), RPM, and power. Where a baseline is set, and the variable is compared. In the situation above, you make 180lb-ft at the flywheel. In 1st you make 250lb-ft at the wheels (high yield, low load). In 5th you make 100lb-ft at the wheels (low yield, high load). Increased load requires an increase in power to compensate and accelerate. You can't spin a shaft with 180lb-ft and always have that be sufficient reguardless of the resistance set to it. That resistance is load, and to keep the shaft spinning at a certain load, more power is required. A higher demand is put on the engine. If the engine doesn't meet that demand, then acceleration does not take place and you reach the physical limits of the engine.

I suppose you could say that load is really just a term for power demand. Increased load requires more power to produce similar outputs. If you want to accelerate in 1st gear, you can do so fairly efficiently from 1000RPM to 3000 RPM. If you want to accelerate in 5th gear, doing so from 1000 RPM to 3000RPM is going to blow a rod bearing. Low demand in 1st (low load). High demand in 5th (high load).

Does that make any sense, or is it just 2am babble?

evolutionmovement · Post by **evolutionmovement** » Mon May 17, 2004 7:59 am

Waht he said. Though I can pulk from just oevr 1500 in 5th withou bad strain unless I stmop gas.(which would be dumb, of course).

Steve

vrg3 · Post by **vrg3** » Mon May 17, 2004 8:39 am

Careful with your terminology -- an increased load requires an increase in torque. Power stays the same through the gearbox. A dyno measuring horsepower directly will get the same numebr no matter which gear you're in. Increased load requires more torque to maintain the same acceleration.

But, again, I say -- this definition of "load" shouldn't be relevant to the engine, and it shouldn't affect the boost Matt can reach. Can it?

evolutionmovement · Post by **evolutionmovement** » Mon May 17, 2004 5:04 pm

Damn, what the hell was I writing last night?!

'Sippin' on gin and juice. Laid back...'

But, again, I say -- this definition of "load" shouldn't be relevant to the engine, and it shouldn't affect the boost Matt can reach. Can it?

Ah, back to the original question. I don't see why this would effect turbo spool up either unless its because the slower acceleration of the engine gives the turbo more time to catch up. If that's the case, then it makes sense that racers stage with the engine at high rpm to keep the turbo spooling. But then I wonder if that were the case, would peak boost be achieved succesively down the rpm range with each higher gear?

Steve

91White-T · Post by **91White-T** » Mon May 17, 2004 7:23 pm

With the hose pulled off the wastegate, my car made 17psi in 1-3 gears and 22+ in 4th. There is a lot more load on the engine in top gear with the TC locked than the other gears.

vrg3 · Post by **vrg3** » Mon May 17, 2004 7:37 pm

You got those figures when accelerating at WOT with the wastegate actuator disconnected?

I get well over 20 psi even in first gear if I disconnect the wastegate actuator.

91White-T · Post by **91White-T** » Mon May 17, 2004 9:00 pm

vrg3 wrote: I get well over 20 psi even in first gear if I disconnect the wastegate actuator.

Hmmm... strange, I can't get more than 17 in 1st-3rd...

rsstiboy · Post by **rsstiboy** » Mon May 17, 2004 11:17 pm

evolutionmovement wrote:Damn, what the hell was I writing last night?! 'Sippin' on gin and juice. Laid back...'

But, again, I say -- this definition of "load" shouldn't be relevant to the engine, and it shouldn't affect the boost Matt can reach. Can it?
Ah, back to the original question. I don't see why this would effect turbo spool up either unless its because the slower acceleration of the engine gives the turbo more time to catch up. If that's the case, then it makes sense that racers stage with the engine at high rpm to keep the turbo spooling. But then I wonder if that were the case, would peak boost be achieved succesively down the rpm range with each higher gear?

Steve

basically because the more load you put on the motor, the more fuel and the more heat, which makes the air expand which in turn spins the exhaust wheel faster which in turn spins the comp wheel faster, hence creating more boost.

vrg3 · Post by **vrg3** » Mon May 17, 2004 11:59 pm

Why does slower crankshaft acceleration translate to more fuel and heat?

THAWA · Post by **THAWA** » Tue May 18, 2004 12:36 am

have we come to a conclusion yet? I stoped paying attention a while back

vrg3 · Post by **vrg3** » Tue May 18, 2004 12:49 am

No, I don't think we have, yet...

legacy92ej22t · Post by **legacy92ej22t** » Sun Jun 20, 2004 4:55 am

I forgot to keep this going.

I think my case is the turbo running out of blow at higher rpm's. And the high load ( like 5th going uphill) causing me to get slightly higher boost levels, I believe to be mild boost creep. Here's what I was getting on recent pulls.

1st- quickly spools to 10-11 psi and holds to redline.

2nd- quickly spools to 13 psi then drops to 10-11 psi to redline.

3rd- quickly spools to 14 psi then drops to 10-11 psi at about 4800-5200 rpm and holds to redline.

4th- the same as 3rd pretty much with maybe a .25 psi of creep on a good, steep grade.

5th- I believe I would get the same drop in boost here but frankly I didn't push the car past the 4800 rpm mark because I would be doing about 100-110 mph.

On a steep grade I would get .5 - 1 psi of creep.

So, that's what I've been seeing lately but it's still hard to say if it always reacts this way or not because I can't just stare at my boost gauge while driving. But I believe the above to be the best average of what I'm seeing at the manifold. Atmosphereic conditions seem to affect my Joe-p MBC a bit too.

charlierh2 · Post by **charlierh2** » Tue Jun 22, 2004 1:38 pm

ok if i understand your question correctly you wanna know if the amout of "strain" on the engine has an affect on how much boost is created.
if thats rite it is very simple, load you car up with sandbags, people, whatever you want then run your tests again.
i understand that this will allow more time for spool up due to slower acceleration so there may be poor results in maybe first and possibly second but it should tell you if they are related.

free5ty1e · Post by **free5ty1e** » Tue Jul 06, 2004 10:10 pm

Just have to add my experiences to the discussions on 'load' here... with my stock boost control, I could hit the 8.7psi mark in each gear with no problems. With the MBC in place though (pre-FCD), 1st wouldn't give more than 9psi, 2nd and 3rd to 11psi, 4th to 12psi, and 5th resulted in a fuel cut every time I tried. After the FCD I could turn the boost up a bit more, it just seems to hold with this theory of engine load vs turbo boost... 1st gear = 11psi, 3rd gear = 14psi... (no 5th gear pulls yet)

How the hell are other cars making equal boost in all gears? Seems a bit easier to tune that way...

legacycentral bbs

A forum for 89-94 BC-BF(BJ) Legacy Owners and Fans

Full boost in 1st gear?