# vacuum to low possible causes



## DrGtr (Jul 18, 2009)

270 in/out procams 10.8 lift, i have around -19 vacuum to the map sensor and fpr, the cams are dialed in properly, i have rechecked the TB today, and gave 2* advance to the intake so from 2*retard i have put it to 0 on the pulleys and still the same. i suspect that some valves are not sitting properly and i will make tomorrow a compression test , leak test and then remove the top of the head and filler the shims .

any suggestions for the cause ??


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## Marky_GTSt (Dec 31, 2005)

-19 what ? it can't be psi...

Are you suggesting the vacuum in the inlet is not low enough or too low ? bearing in mind it's physically impossible to go below -14.7 psi vacuum. If you have a device measuring below 15psi vacuum then its wrong and might be worth finding some other device to measure with.

Does the engine idle at a normal speed ?

Let us know the test results please.

Also, What engine is it ? You say shims so guessing RB26. Might be worth checking valve clearance if its running shims.


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## infamous_t (Jul 9, 2007)

Marky_GTSt said:


> -19 what ? it can't be psi...


I'd guess mmHg, as that's what the stock gauges read...

I'd work out how much overlap it has at the moment, as I reckon the large cams are the likely cause, otherwise I'd put it down to a small air leak somewhere on your cold side


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## geoffree (May 16, 2010)

Inches of Hg.


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## Marky_GTSt (Dec 31, 2005)

infamous_t said:


> I'd guess mmHg, as that's what the stock gauges read...


I did wonder that, Knowing the unit of measure would help understand the severity as -19mmHg is a tiny vacuum.


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## David (Apr 25, 2003)

infamous_t said:


> I'd guess mmHg, as that's what the stock gauges read...
> 
> I'd work out how much overlap it has at the moment, as I reckon the large cams are the likely cause, otherwise I'd put it down to a small air leak somewhere on your cold side


An air leak would loose vacuum in the manifold not increase it.

If you have to much vacuum simply move the throttle stop position. I don't understand why you think it's a problem


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## infamous_t (Jul 9, 2007)

David said:


> An air leak would loose vacuum in the manifold not increase it.


Correct. Which is his problem, as noted in the title, 'Vacuum to low'.


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## David (Apr 25, 2003)

infamous_t said:


> Correct. Which is his problem, as noted in the title, 'Vacuum to low'.


Not correct

I think you have your definition of low confused. 

Say normal vacuum = -5

Too low = -7

To high = -3

Which is it?

An air leak will will make the vaccum reading higher, i.e more positive.


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## DrGtr (Jul 18, 2009)

its in mmhg i should have -65 normally, i can understand with this cams it could go low to -45 but in my case is almost not existence . when i was checking with oil the cc of the head when i was taking the oil off i have noticed in few inlets that the oil was coming from the valves but then i thought it could be cause i have dropped it by mistake there,now i believe that the job that machinist did to the head was like the worst ever , i really want to brake his face and probably i will after i check the shim clearance because the last time i spoke to him after i discovered from a friend who did his head there he had some issues with some valves knocking and i have called him and ask him with the nicest way to be 2 times careful with my head , i am going to check the clearances and get some pic to show you, i hope to be the shims clearance and not something with the seats, cause i cant be bothered to get the engine out again. i am also scared if thats the case if i have already burn some valves cause i did already 200 miles on the engine.


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## DrGtr (Jul 18, 2009)

David said:


> Not correct
> 
> I think you have your definition of low confused.
> 
> ...


then is higher than normal.


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## infamous_t (Jul 9, 2007)

David said:


> I think you have your definition of low confused.


Your thinking is in terms of numbers, not in terms of how they relate to the real world.

The higher the number the lower the vacuum ie.
-7 = low number, higher than normal vacuum
-5 = normal vacuum
-3 = higher number, lower than normal vacuum

Back on topic


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## jimmy1234 (Nov 16, 2011)

Just for reference my stockish car idles at around -500mmhg

Which is around -20 inHG


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## David (Apr 25, 2003)

infamous_t said:


> Your thinking is in terms of numbers, not in terms of how they relate to the real world.
> 
> The higher the number the lower the vacuum ie.
> -7 = low number, higher than normal vacuum
> ...


I am an engineer who work in numbers relating to development engines for many OEM's every day. You can't make a statement that isn't mathematically correct or it will be mis understood.

As proven by this thread


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## David (Apr 25, 2003)

Getting back to the original question now I understand it.

Did you try closing the throttles further?
Did you check your cam timing especially overlap using lift at TDC to check the timing is actually correct? I.e not just checking the cam marks

I would start with a compression test on a warm engine as this will show if the valve clearances are correct, only if there is an issue would I dissmantle the engine to check/ change the clearances.


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## DrGtr (Jul 18, 2009)

ok i have check the valves with a filler today and i did a compression test 

it seems that i will have to cut the 1,2,12 shim a bit to have more clearance just for the piece of mind. the compression test was performed with cold engine just to compare the cylinders and not to find the actual pressures, due to the modified head(lowered compression) and cp pistons which have big clearances and mineral 15w40 oil i was expecting low numbers , the result was 

1)145psi
2)150
3)150
4)150
5)150
6)145 
which i believe is very good but i will make a leak test tomorrow as well.
according to the tb was checked and corrected yesterday, it was quite open and running 1500rpm but now its 950rpm with the same vacuum.










these where the results of the clearance 










now the only thing left is to play with the cams i have left the ex to 2*retard and advanced the in cam 2* with no change so i will try tomorrow to add an other 2*intake.


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## DrGtr (Jul 18, 2009)

David said:


> Getting back to the original question now I understand it.
> 
> Did you try closing the throttles further? i did no improvement
> Did you check your cam timing especially overlap using lift at TDC to check the timing is actually correct? i did with a micrometer as tomei advice ,i got both of the cams 2* retard
> ...


any other advice ?


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## R32 Combat (Jan 29, 2004)

My vacuum went from ~550mmHg to ~450mmHg when I fitted 272 10.8 jun cams.

It's due to a change in overlap.


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## DrGtr (Jul 18, 2009)

What settings did you have on the pulleys?


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## David (Apr 25, 2003)

In my experiance you need to measure actual timing not the pulley value as some times the profiles are ground offset to the key way by as much as 10 degrees relative to the original key way (engine other than rb)

What is the problem not enough vacuum giving you?


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## DrGtr (Jul 18, 2009)

David said:


> In my experiance you need to measure actual timing not the pulley value as some times the profiles are ground offset to the key way by as much as 10 degrees relative to the original key way (engine other than rb)
> 
> What is the problem not enough vacuum giving you?


nothing much is just that i got used to hear the engine running soo smooth before now it seems to run much more rough.
and i dont know if its healthy to run like this. 
boost is running -190 at idle. 
i will run a leakage test and measure again the timing, but first i have to cut a bit the 1,2,12th shim about 7 hundreds of mm to go from 381mm to 450mm


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## R32 Combat (Jan 29, 2004)

DrGtr said:


> What settings did you have on the pulleys?


0 on the inlet and 4 degrees advance on the exhaust.


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## DrGtr (Jul 18, 2009)

is it any way that after i have installed the link g4 the acc valve doesnt work and the vacuum is low ? or i just worry too much. how can i test if the acc valve is working? 
compression is good, i just brought the dial guide to check again the timing tomorrow and i have corrected the 3 shims which where 381mm to 457mm which is the recommendation from tomei. do you think it can be from too much overlap? but how is it possible if the cams are dial properly. any thoughts??


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## DrGtr (Jul 18, 2009)

did all the shims to 45mm of intake and dialed the cams again intake is set to 0 and exhaust is advanced 5* started the car the vacuum is a bit better but still -250 
the comp test was good for cold test, but didnt do a leak test. 
is this normal??


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## DrGtr (Jul 18, 2009)

Did a new engine with 87.5mm wiseco same cams tomei 270 in/ex 10.80 lift 
Fixed the head dialed in the cams as tomei recomends had 0deg on intake and 2deg retard on exhaust skimed the head to 0.40 and used 1.5mm tomei hg so its like I am running 1.1mm hg cylinder head volume is 72.5cc in each cylinder and still huving low vaccum -200 is this normal? Car runs fine though just a bit rough, will this affect the low down and have more hp at high rpm?


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## RonniNielsen (Jan 14, 2011)

DrGtr is this your new engine after the other one with the awefull headwork blew?

ive got around -0.50 - -0.55 bar on my engine,

Ron


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## DrGtr (Jul 18, 2009)

Yes thats with the new engine , I will have to contact tomei to see what they say I am almost sure that is from the cam shafts too much overlap


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## mark_30_30 (Dec 29, 2005)

i was reading this the other day, it could be relevant to you:

moto iq Degree Cams


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## peckhs (Jul 20, 2013)

Bump an old thread...
So i just installed my Tomei Genesis onto my 32, with Tomei Procam 270 10.25.
My vacuum is low, and it seems to be affecting my brakes?
Is the R32 GTR running vacuum assisted brakes?
If yes, what can i do to rectify this problem?
Thanks.

Sent from my SM-N910G using Tapatalk


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## R32 Combat (Jan 29, 2004)

The brakes are vacuum assisted. With big cams they change to fear assisted. Lol


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## peckhs (Jul 20, 2013)

R32 Combat said:


> The brakes are vacuum assisted. With big cams they change to fear assisted. Lol


Lol...

I was told it might help if i dropped a gear before i brake. ...
Gonna try if that will help

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