How much vac are you pulling?

[Jack's Dodge]

Quote:

Originally Posted by turbometh BFnGA--- I disagree. In theory what you are saying sounds right. In real life it is not. Ever checked vacuum on a prostock engine before? I know they dont pull good vacuum, but make 1200 hp. All the vacuum reading shows is how well the engine is IDLING. Cam lift, duration, degreeing. all change vacuum. As well as ignition timing etc. Usually the more power potential the engine has the less vacuum it will make at idle. However if you know the engine you are working on is SUPPOSE to have 18" at idle and it only has 10 then you can use vacuum as a very good diagnostic tool. It can show cam problems, ignition problems, mechanical problems. In no way can you say that because a engine only makes 10" of vacuum that it will not be efficient.

Just yesterday, my daytona was making 10" of vac. It used up a 1/4 almost a 1/4 tank of gas driving home (33 miles). My car was boosting maybe 3 psi. That is horrible. Now it is tuned to 16-17" and needless to say my fuel economy and overall performace have increased dramatically. Car spiked at 13 psi. Better hook up th i/c soon Read a few posts back. It is quite clear that the better your vac, the more boost potential your TD has. And i have a log intake. Installing my blow thru should put me close to +20"

[turbometh]

I agree that if you had 2 motors that were built exactly the same. 1 was at 12" and the other was at 18" that the 18" motor will get better fuel economy, run better. You cannot judge the effiecency of an engine based on how much vacuum it pulls at idle. You could have 2 prostock cars 1 with less vacuum at idle and have it be in better tune. Vacuum is detirmined in a big way to camshaft selection and valve timing events.
My street car is a 455 olds small cam 15" vacuum, my drag car is a 455 olds 8" vacuum. So by your explaination my street car is in "better tune" and is more effiecent.

[BFnGA]

OK I'll start slow . Apples are apples and oranges are oranges . Are your 2 455's built the same ? No . Same cam ? No . If you have two Identical motors , the one with more vaccuum is in a better state of tune EVERY time . Stop injecting your ignorant suppositions into what I'm saying and reread my post again . If you can get your "drag" olds from 8" up to 10-12" through tuning , it'll run better and faster . This is one of the most BASIC of engine tuning concepts . You are quite simply mistaken .

[turbometh]

No where in your post did you clearify yourself. You stated "more is better it indictes your engines propensity to draw air/fuel mixture into itself. It indicates the efficienty the engine is operating at." This is not true. You are saying if you have an engine that operates with low vacuum at idle that it is not an efficient engine. Most engines that pull high vacuum at idle operate in the 70-80% efficient range. A race engine with less vacuum at idle can operate at over 100% efficient.
The only thing high vacuum at idle shows is how well the engine is idling.
I understand what you are saying. If you take any given engine, no matter what it is and tune that engine to the max vacuum it will idle better. That is not to say it will run better at WOT. with that tune.
You were not specific and that is what I am saying. I do not appriciate your name calling and putdowns. Quite simply YOU are mistaken.

[turbovanman]

Settle down.

As a matter of fact, I said take two identical motors with different vacuum motors, using his concept. Quit nit picking!

[BFnGA]

A) On ANY given motor , more vaccuum is better .Always .No matter what . Fact .
B) Vaccuum is an indicator used to tune the motor at idle , However the more vaccuum it pulls at idle , the better it will run throughout it's range . Idle to redline . Fact .
C)I said that a motor with low vaccuum is less efficient than the same motor with more vaccuum . You clearly lack reading comprehension skills . Fact .
D)"The only thing high vacuum at idle shows is how well the engine is idling.
I understand what you are saying. If you take any given engine, no matter what it is and tune that engine to the max vacuum it will idle better. That is not to say it will run better at WOT. with that tune." Your words . False .
E)"You were not specific and that is what I am saying." This thread was discussing one car , and therefore one engine before you jacked it with your ignorance . No one was comparing any different motors until you started doing so . In refering to one (singular) motor , I can hardly help but be specific . Again , your words : False .
F)"Quite simply YOU are mistaken." Only factual insofar as me addressing you .
I suggest you try a Google search on "Engine Tuning" and learn the basics and buzzwords before attempting a battle of wits from such a clearly inferior position .
Good evening .

[turbometh]

I am done arguing with you. Do what you want. Tune your engine based off idle vacuum.

[Jack's Dodge]

What did I miss?

[Timmay2]

Quote:

Originally Posted by Jack's Dodge What did I miss?

Vacuum is the most important things in cars!

Especially since every darned vac gauge reads differently!!

[Jckrieger]

Why the heck are you guys letting Jack's Dodge mess with his cam timing just to get more vacuum at idle? Has anyone told him to put the cam straight up? I'm not sure he should be changing his cam timing by 14-19 degrees from stock without knowing exactly what he's doing. If our cars were more efficient OVERALL with our cams significantly advanced or retarded, why wouldn't the factory have installed them that way? Also, why would most adjustable sprockets only have 10 degrees of adjustment in each direction, including the DC sprocket? I agree that more vacuum is good, but the engine should be tuned by adjusting ignition timing advance and fuel, not by moving the cam around in tooth increments! If your cam is 1 whole tooth off from the stock location, you WILL NOT make as much power at the same boost level as stock with a stock cam and sprocket.

[Jack's Dodge]

Quote:

Originally Posted by Jckrieger Why the heck are you guys letting Jack's Dodge mess with his cam timing just to get more vacuum at idle? Has anyone told him to put the cam straight up? I'm not sure he should be changing his cam timing by 14-19 degrees from stock without knowing exactly what he's doing. If our cars were more efficient OVERALL with our cams significantly advanced or retarded, why wouldn't the factory have installed them that way? Also, why would most adjustable sprockets only have 10 degrees of adjustment in each direction, including the DC sprocket? I agree that more vacuum is good, but the engine should be tuned by adjusting ignition timing advance and fuel, not by moving the cam around in tooth increments! If your cam is 1 whole tooth off from the stock location, you WILL NOT make as much power at the same boost level as stock with a stock cam and sprocket.

Certainly an interesting point. I had to reset my overall timing to TDC 3 times during this adjustment, and it runs OK at this setting. See for yourself. Set your timing to TDC, set your ignition timing to 12*, then turn your cam 3 teeth towards the front of the car, and then set your ignition timing again. Those three steps sent my vac from 10/13 to 19/20. Went off without a hitch, and runs better this way than it ever has. Granted, the TDC location of the timing gets it started, but is not the most power & fuel efficient setting for my car at least. In fact, my ignition timing is now set at 14* advance to balance ou the advancement of the cam timing. This made a positive effect on my milage, and gave another 2" of vac. Drive my car with everything at TDC, and again with the adjustments perviously mentioned; then try to tell me there was no power increase

[Jckrieger]

Are you sure *3 teeth advanced* isn't really straight up? How to you make sure the crank is at TDC when you set the cam? Do you use a mirror to get a straight view at the cam sprocket when you set its position? There's an aweful lot to setting the cam timing correctly. I've run the cam off a tooth or 2 both directions from the correct TDC, and I promise it does not give a performance increase. Ask Gary D how much he ran his reliant from the stock position, or anyone else who goes fast.

[turbovanman]

Quote:

Originally Posted by Jckrieger Are you sure *3 teeth advanced* isn't really straight up? How to you make sure the crank is at TDC when you set the cam? Do you use a mirror to get a straight view at the cam sprocket when you set its position? There's an aweful lot to setting the cam timing correctly. I've run the cam off a tooth or 2 both directions from the correct TDC, and I promise it does not give a performance increase. Ask Gary D how much he ran his reliant from the stock position, or anyone else who goes fast.

I agree with you, 2 teeth runs like crap but he seems to be happy so let it be. He also mentioned in another thread his key way got messed up????

[Jckrieger]

Hmm, sounds like he ought to get a new cam and sprocket so he doesn't have to readjust the sprocket every weekend! At least the cam only experiences load in one direction, so the sprocket shouldn't move around too much as long as it's good and tight.

[Jack's Dodge]

Quote:

Originally Posted by Jckrieger Hmm, sounds like he ought to get a new cam and sprocket so he doesn't have to readjust the sprocket every weekend! At least the cam only experiences load in one direction, so the sprocket shouldn't move around too much as long as it's good and tight.

You are not listening. My car is running fine. It makes the proper amount of vaccum, and milage is about 25mpg. Why do I need a new cam and or sprocket? I spent about 3 days tinkering with my timing, and now it's every weekend And I never mentioned anything about a damaged key way. Are you in the wrong thread?

Maybe you guys are right. My car is running like crap. It is pulling 17" to 18" of vacuum. How can I fix that? When not in boost, I am making around +25mpg. What should be adjusted so I am making whatever milage you two say I should make? Oh, and the car fires right up when I turn the key. Is that right? Since I have no clue what the **** is going on, please show me the way!