Byron - Sunday, October 26th

[DarkSS]

There's really no reason to bring the rpm's up to launch. The converter will flash to the same rpm either way. Stab it off of or slightly higher than idle. No need to stall it all the way to 2500 or whatever the converter will hold. Sounds like you need a vacuum accumulator though, raising idle won't do anything if you're seeing this happen at 2K.

[SYCK SS]

There's really no reason to bring the rpm's up to launch. The converter will flash to the same rpm either way. Stab it off of or slightly higher than idle. No need to stall it all the way to 2500 or whatever the converter will hold. Sounds like you need a vacuum accumulator though, raising idle won't do anything if you're seeing this happen at 2K.

Not all torque converters will flash the same. Plus stabbing it off idle could shock the tires too much. We see this with the jeeps I build big time. Pending converter style and setup, it's better to get the fluids flowing on a taller stall then to leave it empty. Sure on a stock stall or lower one I'd agree. But in Jims case it would benefit him to be able to bring RPM up at launch

And the reason you raise idle is because that's when the brake is applied. The reason he's pulling through the brakes is because of no vacuum down low then revving up to even less vaccuum. On cammed cars sometimes if you bump idle up it will produce more vaccum.

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[Pro Stock John]

I just bring mine up about 500-600 RPMs, but I'll write down what I do the next time I go out just to make sure.

[SCOTCH MAN]

Before the cam and after we installed the stall, I was getting my best times at 2200 or above. Tried launching at an idle and the times were not as good by tenths. I now creep forward at about 1800.


Jim
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[Hoosierguy]

I launch at 1500. Any higher and I was worried about doing a burnout because of the street tires.

[DarkSS]

Not all torque converters will flash the same. Plus stabbing it off idle could shock the tires too much. We see this with the jeeps I build big time. Pending converter style and setup, it's better to get the fluids flowing on a taller stall then to leave it empty. Sure on a stock stall or lower one I'd agree. But in Jims case it would benefit him to be able to bring RPM up at launch

And the reason you raise idle is because that's when the brake is applied. The reason he's pulling through the brakes is because of no vacuum down low then revving up to even less vaccuum. On cammed cars sometimes if you bump idle up it will produce more vaccum.

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Just reading his mod list as a "Yank 3400" I am assuming it's an SS model like John runs and what I had. These are tighter converters made to be more street friendly. At his power level I would assume the shock to the tires wouldn't be that extreme.

Before the cam and after we installed the stall, I was getting my best times at 2200 or above. Tried launching at an idle and the times were not as good by tenths. I now creep forward at about 1800.


Jim
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If the vacuum is bleeding off at 2K, raising the idle won't do much. Like it was previously stated, a vac canister is the best bet. I would first look for a vacuum leak anywhere. I have seen a lot of LS' run some huge cams like the Trex and MS3 and never have a vacuum issues since the vac is pulled from the back of the intake.

[SCOTCH MAN]

The Yank is a 3400 Poweradder not an SS


Jim
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[Pro Stock John]

I'm running a Circle D 3200.

[SYCK SS]

Just reading his mod list as a "Yank 3400" I am assuming it's an SS model like John runs and what I had. These are tighter converters made to be more street friendly. At his power level I would assume the shock to the tires wouldn't be that extreme.


If the vacuum is bleeding off at 2K, raising the idle won't do much. Like it was previously stated, a vac canister is the best bet. I would first look for a vacuum leak anywhere. I have seen a lot of LS' run some huge cams like the Trex and MS3 and never have a vacuum issues since the vac is pulled from the back of the intake.

as stated he is not running a SS. The power adder benefits from torqueing up at the line.

And his vacuum isn't bleeding off at 2000rpm. He doesn't have vacuum at the time when the pedal is depressed. Naturally when opening the throttle plate more the vacuum drops regardless of cam.

The issue again is jim is depressing the pedal at IDLE. Where vacuum is reduced.

Raising idle on a lopey cam and playing with timing adjustments can increase vacuum. If you only add 100 - 150rpm and reduce the "lope" vacuum is produced easier. But as jim says he's like the lope as does anyone else.

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[DarkSS]

That's a nice concept expect that the vacuum is taken from the back of the intake on a LS, not a the TB.

Scotchman, just look for a vacuum leak. It's not going to hurt anything and it won't cost you a penny.

[SYCK SS]

That's a nice concept expect that the vacuum is taken from the back of the intake on a LS, not a the TB.

Scotchman, just look for a vacuum leak. It's not going to hurt anything and it won't cost you a penny.

That makes no sense? Doesn't matter if it's close to the TB or the back of the manifold. Vacuum is the same throughout the manifold itself. But when the throttle body starts to open vacuum is reduced. Ever see a boost gauge?

Plus the MAP sensor is just behind the throttle body and I have the logs from the track. His vacuum is reading "normal" for a low idle, cammed car.

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[DarkSS]

Arguing with you is like pissing in wind. LS1tech would benefit greatly from your knowledge.

I'm suggesting looking for a vacuum leak first because countless of LS cars have installed donkey dick cams and never had a vacuum issue. Up the idle then get back to me. I guarantee you it won't do a damn thing.

[SYCK SS]

Arguing with you is like pissing in wind. LS1tech would benefit greatly from your knowledge.

I'm suggesting looking for a vacuum leak first because countless of LS cars have installed donkey dick cams and never had a vacuum issue. Up the idle then get back to me. I guarantee you it won't do a damn thing.

There is no vacuum leak. It's been looked over by a shop on here.

So the fact your information is based purely on "forums" says alot.

His vacuum at idle is between 13-16inhg. Pending operating temp, ambient temp, etc.

His idle is very low which amplifies the "lope" that Jim likes. Not having a smooth idle with a cam like Jims will produce low vacuum.

It was much more pronounced on old school small blocks and big blocks because too. Vacuum pumps were very common back in the day to compensate for weak vacuum due to these issues.

If you read back I said raise idle and adjust tune. It's not just bring the RPM, but play with timing to reduce the lope. That will increase vacuum.

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[SCOTCH MAN]

There is no vacuum leak. It's been looked over by a shop on here.

So the fact your information is based purely on "forums" says alot.

His vacuum at idle is between 13-16inhg. Pending operating temp, ambient temp, etc.

His idle is very low which amplifies the "lope" that Jim likes. Not having a smooth idle with a cam like Jims will produce low vacuum.

It was much more pronounced on old school small blocks and big blocks because too. Vacuum pumps were very common back in the day to compensate for weak vacuum due to these issues.

If you read back I said raise idle and adjust tune. It's not just bring the RPM, but play with timing to reduce the lope. That will increase vacuum.

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Jeremy

I did a quick test. Stopped the car, put it in neutral, ran the RPMs up, put the brake on to the floor, put it in drive , ran the RPMs up to 3000 and NO MOVEMENT. I want to do this a couple of more times but this is progress.

Proves your thinking on idle and vacuum.