Secondary Throttle - Who needs them?

[Paul.P]

Bloody hell, there's some clever buggers on here !, words i can't read, never mind understand, still it makes for interesting reading .

[Doc Fizzix]

Just found this, sounds interesting:

Could you route the vac solenoid (the actual part that connects to the secondary butterfly) directly to the manifold? that way, you'd have vacuum holding them closed in the low end, and boost holding them open top end? Just wondering... that way, the secondaries would always open immediately when boost hits, not necessarily at 4700rpm...

This sounds very "do-able" to me Would this work, I guess I could just try it. Could it be this easy

[ESM]

I can't see how you think it'll do any good when the ECU will not know you've opened the secondaries early and so won't adjust the fueling. If you improve the VE (that's questionable) you'll simply push it leaner.

[Aurora40]

FWIW, and this is nowhere close to a solution for the Elan. But here's one solution for the LT5:
http://forums.corvetteforum.com/showpos ... tcount=196

One key difference is that on my car, the port throttles will open at any rpm once the throttle hits 100%. This means that lookup tables for throttle already exist across the rpm range, though presumably not across the throttle% range. Though apparently they do and are well sorted.

It may or may not be that simply lowering the rpm the secondaries open would be all that's needed on the Elan.

Another difference is that folks who do this on the LT5 actually remove the secondary throttles completely. The point is that even when open, the blades still restrict flow to a degree. It's a way to get some extra power out once everything else is done, especially on big-cube motors.

I can only guess, but I'd guess that if the Elan doesn't open them at WOT at lower rpms, then perhaps it's because someone did some studying and found it didn't help? One reason, at least on the LT5, for the secondary system, is for emissions and fuel economy concerns. There is no WOT testing of those, so there's no regulation-related reason to wait until a higher rpm to open them, at least not that I'm aware of. Which would leave the reason to be because they don't help below a certain rpm.

Again, all just guesses. And maybe on non-stock cars it makes more sense. Just two cents, if that...

[Doc Fizzix]

I can't see how you think it'll do any good when the ECU will not know you've opened the secondaries early and so won't adjust the fueling. If you improve the VE (that's questionable) you'll simply push it leaner.

Well, I only posted for discussion

My thought was this:

I was thinking that the flow through the intakes would be improved on boost at low RPMs so there would be less pressure and resistance against the turbo so it will spool-up a bit quicker, then the rpms would quickly go up and the computer will then be back on track. Remember, with this "trick" the secondaries would only open sooner and only on boost. I also thought that the fuel needs would be measured by the mass air temp sensor, MAP sensor, and then the exhaust by the O2 sensor so the coumputer might be able to make any ajustments. After all, we are only talking about opening the secondaries a bit quicker and only to get better spool-up. Maybe this is what the computer already does.

I know I am most likley way off but I would just like to learn more about this concept and how the computer in our car does work. From my years studing Bosch injection systems I think the Bosch computer would have been able to measure the increased air flow and adjusted the gas.

[Sy V]

Just to complicate matters, Doc.

Don't forget that only the Fed, S2 and some Euro Elans (French Spec for sure) have a O2 sensor.

[Doc Fizzix]

Just to complicate matters, Doc.

Don't forget that only the Fed, S2 and some Euro Elans (French Spec for sure) have a O2 sensor.

I wonder why not all had the O2 sensor?

[Sy V]

I imagine it was all down to national emission rules. In '89 there weren't any in the UK (where most SEs were destined to go).

[ESM]

Even on the catalyst equipped cars the ECU runs open-loop when on boost. Its a narrow band oxygen sensor and so when the fuel enrichment kicks in it saturates at rich.

[Aurora40]

I know I am most likley way off but I would just like to learn more about this concept and how the computer in our car does work. From my years studing Bosch injection systems I think the Bosch computer would have been able to measure the increased air flow and adjusted the gas.

I could be way off here, but I believe your car has an Intake Air Temp sensor (not a mass air temp sensor) and a Manifold Absolute Pressure sensor. Together, these can compute how much air is flowing, but that requires having some model of the intake system ahead of time. As ESM said, one place this is modelled is the VE tables. If you change the parameters of the intake, then this model isn't acurrate. So you'd need to adjust it to get proper fuel control. This is often referred to as a speed-density system.

I suspect the Bosch FI systems you dealt with had a Mass Airflow Sensor. In this case, the sensor can determine exactly how much air is flowing through, regardless of the intake size or design. So it can be much more flexible to a changing model of the intake. This is often referred to as a mass-airflow system.

In the 80's, I believe Bosch was it for mass-airflow FI systems. The first Corvettes to use this in 1985 had Bosch MAFs. Back then MAFs were a restriction after a point. That plus probably cost is why some cars in the 80's and 90's went the speed density route. After OBD-II in 1996 took effect, it seems most fuel control systems have both a MAF as well as an IAT and a MAP sensor. I suspect due to the need to diagnose troubled components to meet with the OBD-II's predictive failure requirements. Though I don't know that for fact.

MAF systems have definitely improved though, and there are 500-1000hp cars that run the air through a MAF without problem or restriction.

I'm no expert, but I would say generally speaking, if you have a computer-controlled engine, it's not a good thing to misinform the computer as to what is going on in an attempt to improve performance. That's just a good way to either have the car run poorly or dangerously. If you want to change something, change the programming too so the computer can still adequately control it.

[Doc Fizzix]

I'm no expert, but I would say generally speaking, if you have a computer-controlled engine, it's not a good thing to misinform the computer as to what is going on in an attempt to improve performance. That's just a good way to either have the car run poorly or dangerously. If you want to change something, change the programming too so the computer can still adequately control it.

I am sure that if this would have worked (opening the secondaries on boost) they would have done this from the begining

Oh well, its fun to day dream

[isuzuimark]

opening the secondaries sooner wont help with the performance using the stock turbo. It will actually hurt it by decreasing the intake velocity as well and increasing turbo lag by having extra runners to fill.
Using a better turbo(Ball bearing, bigger...) one soultion is,(kind of haggard tho), is to simply twist tie them open.
Another is to use the intake manifold from a 4XF1-W. it has 4 shorter, fatter runners with no secondaries. but you will lose low rpm, read off idle, torque (like there is any to begin with) on the shorter stroked 1.6 .

[Doc Fizzix]

opening the secondaries sooner wont help with the performance using the stock turbo. It will actually hurt it by decreasing the intake velocity as well and increasing turbo lag by having extra runners to fill.

Very strange, when my secondaries were stuck open my turbo seamed to spool up quicker.

[isuzuimark]

very strange indeed