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Less overlap more vacuum?

General engine tech -- Drag Racing to Circle Track

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rfoll
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Re: Less overlap more vacuum?

Post by rfoll » Sat Oct 05, 2013 7:25 pm

Is it safe to assume you are talking about Idle vacuum?
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SchmidtMotorWorks
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Re: Less overlap more vacuum?

Post by SchmidtMotorWorks » Sat Oct 05, 2013 7:31 pm

I think it is determined primarily by 3 dimensions.

Compression ratio
EVC determines the volume in which vacuum is created.
IVC determines how much is discarded.
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GARY C
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Re: Less overlap more vacuum?

Post by GARY C » Sat Oct 05, 2013 8:09 pm

3window wrote:Has anyone run into ptv problems running .560 lift at 226 @.050 on a 108? Right now I'm at .540 lift with 248 @ .050 on a 110 and I'm good. This is on the intake. I know valve timing events have everything to do with it. Just trying to get an idea. Thanks.
PTV clearance will have to be measured to be sure, what ci is the engine? if you give me the seat to seat overlap I can tell you what your max vacuum should be, you ignition curve can have a big impact on idle vacuum as well if you don't have enough initial advance in the engine you may want to work on your timing curve before changing cams you would be surprised how much it will change.
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BigBro74
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Re: Less overlap more vacuum?

Post by BigBro74 » Mon Oct 07, 2013 10:53 pm

justahoby wrote:
BigBro74 wrote:so you are saying the first cam (cam A) is 250 duration 30 deg. overlap 110 lsa, I am assuming @.050 because it is causing you vacuum problems and cam "B" you are contemplating is 230 duration , 108 lsa. 14 deg. overlap @ .050? are these solid or hydraulic? what engine is it in? that's the real question. this is a wide question but IDLE vacuum should increase with less overlap. the actual vacuum you see is influenced by many factors, one of the biggest of which is the engines displacement. let me know if i'm in the ballpark, then we can all look more closely at your setup. :D thanks, Jason
Wrong, cam A and B were said mild cams in the same engine.. same duration different overlaps.


The examples I gave later were of a different view( hence not within the same paragraph for those who obviously seem to write to everyone in the same paragraph), not related to cam a and b.: different durations instead.

If I was to increase duration, on the same LSA overlap WILL increase.

And yes, we refer to vacuum 99% of the time at Idle...

I could be wrong but 230@ .050 and lets say for shits 280 at the seat at 108 lsa would no way I hell be 14 degrees overlap
Often overlap is not even really considered at 0.050., but in total crank degrees... (lsa is in cam degrees)

but whatever dude,

point was at a tiny duration cam moving lobe separation wouldn't change a ding dong of vacuum at idle with a cam that has brigs and straton duration vs if you stuff a considerable larger cam overlap would be much more a consideration and fall below certain limits.

And less overlap, with a tighter lobe separation means you most likely will have to have less duration.
I was referring to the OP's cams as A and B, NOT your examples. I think what I ASKED about HIS cams was about right. Jason

justahoby
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Re: Less overlap more vacuum?

Post by justahoby » Wed Oct 09, 2013 3:54 pm

BigBro74 wrote:
justahoby wrote:
BigBro74 wrote:so you are saying the first cam (cam A) is 250 duration 30 deg. overlap 110 lsa, I am assuming @.050 because it is causing you vacuum problems and cam "B" you are contemplating is 230 duration , 108 lsa. 14 deg. overlap @ .050? are these solid or hydraulic? what engine is it in? that's the real question. this is a wide question but IDLE vacuum should increase with less overlap. the actual vacuum you see is influenced by many factors, one of the biggest of which is the engines displacement. let me know if i'm in the ballpark, then we can all look more closely at your setup. :D thanks, Jason
Wrong, cam A and B were said mild cams in the same engine.. same duration different overlaps.


The examples I gave later were of a different view( hence not within the same paragraph for those who obviously seem to write to everyone in the same paragraph), not related to cam a and b.: different durations instead.

If I was to increase duration, on the same LSA overlap WILL increase.

And yes, we refer to vacuum 99% of the time at Idle...

I could be wrong but 230@ .050 and lets say for shits 280 at the seat at 108 lsa would no way I hell be 14 degrees overlap
Often overlap is not even really considered at 0.050., but in total crank degrees... (lsa is in cam degrees)

but whatever dude,

point was at a tiny duration cam moving lobe separation wouldn't change a ding dong of vacuum at idle with a cam that has brigs and straton duration vs if you stuff a considerable larger cam overlap would be much more a consideration and fall below certain limits.

And less overlap, with a tighter lobe separation means you most likely will have to have less duration.
I was referring to the OP's cams as A and B, NOT your examples. I think what I ASKED about HIS cams was about right. Jason
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MT Jeff
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Re: Less overlap more vacuum?

Post by MT Jeff » Sat May 16, 2020 9:41 pm

Contact Mike Jones, What do you have and what do you want? You don't have a lot of compression so what do you want? Something that sounds nasty or something the drives good or something in between.
Why is the least trained, lowest paid tech working on the most important part of your car, THE BRAKES ! I know I work next to him.

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