Idle vacum
Turbo Mini Forums

what levels of idle vacum are people seeing?

i'm seeing about 70 kpa cold and 60 kpa hot

That's a bit high for a road cam and a carb, but yours is a bit different.

What is your cam duration?

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isn't 70 kpa 0 psi as in 71 kpa would be + pressure, that doesn't seem much vacuum to me sir.
I think i'm on about 10 to 15 in.Hg

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

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Im seeing about 40KPa at 900RPM and about 30KPa at 1200RPM.

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1/4mile in 13.2sec @ 111 terminal on 15psi

its a kent 266 with 1.5's

100kpa is atmospheric ish depending on altitude.

I actually just found the bit on the megasquirt site about tuning idle and trying to achive the highest vacum, I had completly missed it somehow!

i'll go retune my idle and see if its any lower.



ah cheers matty, that gives me a good ball park. i was actually thinking that there seemed to be a lot of suck, i guess not...

Edited by Joe C on 24th Aug, 2008.

You should be seeing around 30 - 40 Kpa at idle.

Few things will cause low idle vacuum.

Idle Advnce, set this to give you a higher idle vcuum, strt with 15 degrees, if the engine speed is too high reduce the idle air, doing tht will increase the vacuum.

If you cant get the engine speed down by reducing the idle air with an idle advance of 15, then the throttle bypass is too big, or you have air leaks.

Other things that affect the manifold vcuum is the valve seal, but some how i dont think that is your problem

I see got my fig mixed up as normal lol. 100 kpa is atmospheric, i'll try and remember that.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

Hi,
Also check the settings/calibration of your MAP sensor, I got that wrong. Check with a vac gauge
Cheers,
Gavin :)

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My Mini build diary

I got it down to about 48-50 kpa with a bit of tuning, at that point i couldnt get the idle any lower, it dosent seem like there are any air leaks apart from the wastegate which i have blanked off temporarily.

currently i am not using the idle stepper so that is vertually fully shut, also there is a 4mm hole in the throttle plate that i have just blanked off. i'm guessing this was the reason the idle wouldn't go any lower.

as i went to put the TB back i noticed that one of the plug leads was off the coil, i now remember taking it off just before the MOT meaning i have been driving it around with the lead off, as its wasted spark, it must have been cutting out on 2cyls.

how the F did i not notice that!

Edited by Joe C on 24th Aug, 2008.

haha just love those moments when you strip the thing down to sort out a problem and then you see something that you left off and think "Plank!!"

48 to 50kpa isn't bad, what idle speed is that at?

I found altering the cam timing majorly effected the vacuum. (but mine was well out). Lol

Edited by matty on 24th Aug, 2008.

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1/4mile in 13.2sec @ 111 terminal on 15psi

thats at about 1000,

I think thats as low as i'm going to get it, i supos the cam is fairly warm, especially considering the rockers, also with the big ports in the 7 port it will seem even more cammy i guess,

plus i don't know where the cam is timed as the lump had a 286 and i just chucked this in instead.

it idles pretty even, so i'll leave it at that.

well,

resurecting this, as its got me curious about cam timing vs MAP...

my last two engine builds have had similar idle and fast idle MAP characteristics despite quite different cams ( 1st was a 266 on 1.5's 2nd a Ph2 on 1.5's)

my new build has a lower compression ratio 8.2 rather than 8.5, and an RE13....

now heres the interesting bit... tons more vacum, in fact it sucks like Divine Brown on an Actor... while rining the cam in at abot 2k rpm I was seeing about 35kpa, about 15kpa lower than the last 2 engines.

I,ve never been metricated but I have 15/20 inches of vacuum at idle and nearer 25 on the over -run

60-65 KPa for me at idle (ish ...).

Richard

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